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5631 articles

L0015 – Thermal analysis of coal minerals, ash and slag

J.D. Saxby, S.P. Chatfield, AIE 8th Australian Coal Science Conference (1998) 57-63

L0004 – Preparation of dense tetragonal zirconia ceramics from ZrO2 micropowders

A. Smith, B. Cales and J.F. Baumard, Journal de Physique, Colloque C1, supplément au n°2, Tome 47 (1986) 237-241

L0025 – Experimental assessment of thermophysical properties of (Pu,Zr)N

The thermophysical properties of plutonium-zirconium nitride (0-25 at.% Pu), namely heat capacity, thermal conductivity and thermal expansion were measured on pellets produced thanks to the well established pellet pressing route. The experimental results obtained on ZrN were consistent with the existing literature data. The thermal properties measurements reported for (Pu0.25Zr0.75)N were in rather good agreement with predictive values calculated from ZrN and PuN available data.
V. Basini, J.P. Ottaviani, J.C. Richaud, M. Streit, F. Ingold, Journal of Nuclear Materials 344 (2005) 186-190

L0014 – Thermal properties and structural aspects of PbO-SiO2-B2O3 glasses

V.K. Shrikhande, V. Sudarsan, G.P. Kothiyal, S.K. Kulshreshtha, Thermans (2002) 213-215

L0003 – The formation and characterization of a ceramic-ceramic interface between stabilized zirconia and lanthanum chromite

D. Smith, M. Sayer and P. Odier, Journal de physique, Colloque C1, supplément au n°2, Tome 47 (1986) 153-157

L0024 – Synthesis of CaAl2O4 from powders: Particle size effect

Starting from high energetic attrition milled mixtures of either alpha-Al2O3 or amorphous (Al(OH)3) with CaCO3 the binary compound calcium monoaluminate (CaAl2O4) was synthesized with high purity. The processes were carried out on samples with the nominal CaAl2O4 stoichiometry. High energetic attrition milling of the reactants does not eliminate the starting carbonate, both batches showed a high degree of homogeneity and they behaved similarly on heating, forming CaAl2O4 at temperatures lower than 1300°C. These temperatures are lower than that required for the traditional solid state reaction process. The CaAl2O4 synthesis path implies the formation of cryptocrystalline and crystalline Al2O3, CaO, Ca12Al14O33 and CaAl4O7 as transitory phases. The nucleation and growth of CaAl2O4 took place at 1300°C and shows a porous structure and small grain size (-1.5 m).
J.M. Rivas Mercury, A.H. De Aza, P. Pena, Journal of the European Ceramic Society 25 (2005) 3269-3279

L0013 – Thermal expansion properties of some sealing and related glasses and glass ceramics

G.P. Kothiyal, V.K. Shrikhande, M. Goswani, Thermans (2002) 22-27

L0002 – Phase equilibrium and martensitic transformation in lanthana doped zirconia

The system ZrO2-La2O3 has been studied in the 0 to 15 mol% La2O3 range using X-ray diffraction and thermal analysis. Two kinds of diagrams were elaborated: First is a phase equilibrium diagram where the eutectoid decomposition of ZrO2,ss(T) => ZrO2,ss(M) + Pyss occurs at 1100°C and 0.75 mol% La2O3 (Py is the pyrochlore compound Zr2La2O7). The maximum solubility of La2O3 in ZrO2,ss(M) is 0.5 mol% at room temperature. Second, a nonequilibrium diagram is determined showing the correlations between grain size, La2O3 content, and the martensitic transformation temperature start (Ms).
B. Bastide, P. Odier and J.P. Coutures, Journal of the American Ceramic Society 71 (1988) 449-453

L0023 – Colloidal processing and sintering of nanosized transition aluminas

The dispersion of nanosized gamma aluminas with high specific surfaces areas (100 m2/g) and primary particle sizes around 20 nm, using polyacrylic acid, has been investigated. The effect of pH and polymer concentration showed that the highest density green bodies were produced using high polymer concentrations (6 wt.%) and pH of 6. Interparticle potential calculations have been made and help explain the underlying dispersion mechanism at least on a qualitative level. The dispersions were then used to slip cast green bodies followed by drying and sintering. The types of gamma alumina powder have been investigated, the pure gamma alumina, doped with MgO and also with the addition of alpha alumina seeds. The high degree of agglomeration of the gamma alumina powders led to very low densities (60%) even the alpha seeded alumina reached only 85% theoretical density. Attrition milling with zirconia media improves both green density and sintered densities significantly with all powders showing sintered densities >97%. Microstructural analysis on polished and etched surfaces show, however, that the grain sizes are well above 1 Am over 50 times greater than the initial gamma alumina primary particles. A two-step sintering cycle was investigated with the Mg doped powder and average grain sizes around 580 nm were achieved.
P. Bowen, C. Carry, D. Luxembourg, H. Hofmann, Powder Technology 157 (2005) 100 - 107

L0012 – Sintering of a transition alumina : Effects of phase transformation, powder characteristics and thermal cycle.

The effects of several parameters on the pressureless sintering of a commercially available transition alumina has been investigated. The capacity of the particles to re-arrange during the phase transformation into the alpha-alumina phase has been shown to be a key feature in the densification mechanism. The degree to which the particle re-arrangement can lead to an enhanced densification over and above the change in density due to the phase transformation from y to alpha phase depends on several parameters: compact density, heating rate and the amount of alpha-alumina present in the as-supplied raw powder. The parameters influencing the degree of particle re-arrangement and what directions to take to improve on the above densities and grain sizes are discussed.
C. Legros, C. Carry, P. Bowen and H. Hofmann, Journal of European Ceramic Society 19 (1999) 1967-1978

L0001 – Sintering behaviour of Y(u)Ba(v)Cu(w)O(7-d) (u ? 1; v ? 2; w ? 3)

B. Dubois, A. Douy, M. Gervais, F. Cabannes et P. Odier, International Conference on High Temperature Superconductors and Materials and Mechanisms of Superconductivity, Interlaken (Suisse) (1988)

L0022 – Evolution of the coefficient of thermal expansion of a thermosetting polymer during cure reaction

The evolution of the coefficient of thermal expansion (CTE) of a thermosetting polymer during cure reaction is an important parameter for industrial applications such as composite processing since it influences the development of internal stresses in the material. The CTE being almost impossible to measure on a reacting thermoset, we propose to use an indirect method based on the modelling of ionic conductivity by a modified WLF equation, allowing to calculate the evolution of CTE from dielectric spectroscopy measurements. This method is applied to a dicyanate ester thermosetting polymer, leading to encouraging results both qualitatively and quantitatively.
E. Leroy, J. Dupuy, A. Maazouz, G. Seytre, Polymer 46 (2005) 9919-9927

L0011 – Pre-eutectic densification of calcium carbonate doped with lithium carbonate.

Pressureless sintering of CaCO3 was carried out, with Li2CO3 (from 0.5 to 8 wt%) as an additive, under different pressures of CO2. Densification occurs between 600 and 700°C. Sintering above the eutectic temperature (T>662°C) leads to the decomposition of calcium carbonate and the materials become expanded. At 620° under 1 kPa of CO2, a relative density of 96% is reached. Li2CO3 enhances the densification process and grain growth of calcium carbonate. CO2 pressure slows down densification and grain growth kinetics. These results are explained by the influence of carbonate and calcium ion vacancies on the sintering mechanisms.
F. Tétard, D. Bernache-Assollant and E. Champion, Journal of Thermal Analysis and Calorimetry 56 (1999) 1461-1473

HE0086 – Volumetric hydrogen sorption measurements e Uncertainty error analysis and the importance of thermal equilibration time

The design of a volumetric measurement apparatus is studied by means of an uncertainty analysis to provide guidelines for optimum hydrogen sorption measurements. The reservoir volume should be as small as possible (i.e., 10 cc) to minimize the uncertainty. In addition, the sample mass loading has a profound effect on the uncertainty and the optimum loading is a function of the sample's intrinsic storage capacity. In general, the higher the sample mass loading the lower the uncertainty, regardless of any other parameter. In cases where the material to be tested is not available in gram quantities, the use of high accuracy pressure and temperature transducers significantly mitigates the uncertainty in the sample's hydrogen uptake. Above all, the thermal equilibration time is an important parameter for high accuracy measurements and needs to be taken into consideration at the start of the measurements. Based on a computational analysis, a 5 min wait time is required for achieving thermal equilibrium when the instrument enclosure temperature is different than the ambient temperature.
Dervis Emre Demirocak, Sesha S. Srinivasan, Manoj K. Ram, D. Yogi Goswami, Elias K. Stefanakos, International Journal of Hydrogen Energy 38 (2013) 1469-1477

L0021 – Mullite compacts obtained by colloidal filtration of alumina powders dispersed in colloidal silica suspensions

This work deals with the manufacture of mullite-matrix composites by a colloidal filtration route. Avariation of the transient viscous sintering process is studied in which submicrometer sized alumina particles are dispersed in a nanosize colloidal silica
O. Burgos-Montes, M.I. Nieto, R. Moreno, Ceramics International 33 (2007) 327-332

L0010 – Dimensional stability and defect chemistry of doped lanthanum chromites.

Acceptor doped lanthanum chromites are potential interconnect materials to be used in high temperature Solid Oxide Fuel Cells (SOFC). However, instability of these materials when exposed to low oxygen partial pressure causes a volume expansion that can be detrimental to the SOFC performance. The stability of La0.8Sr0.2Cr0.97V0.03O3 is determined as function ofpO2 and temperature by isothermal thermogravimetry and dilatometry. The experimental data are analysed using a simple model for the defect chemistry. The relation between expansion behaviour and change in defect chemistry is discussed using a simple structural model.
P.H. Larsen, P.V. Hendriksen and M. Mogensen, Journal of Thermal Analysis and Calorimetry 49 (1997) 1263-1275

HE0085 – Reversible hydrogen storage in the Li-Mg-N-H system. The effects of Ru doped single walled carbon nanotubes on NH3 emission and kinetics

In this study, the LiNH2?MgH2 (2:1.1) complex hydride system (Li?Mg?N?H is investigated in terms of hydrogen ab/desorption kinetics and the concomitant NH3 emission levels. By selecting more intense ball milling parameters, the hydrogen ab/desorption kinetics were improved and the NH3 emission reduced. However, it is shown that NH3 emission cannot be completely eliminated during ball milling. Single walled carbon nanotubes (SWCNTs) and 20 wt.% Ru doped SWCNTs are utilized as catalysts to study their effects on NH3 emission and kinetics characteristics of the Li?Mg?N?H system. The SWCNT doped sample did not show any kinetics improvement, whereas the SWCNT-20Ru doped sample showed similar kinetics performance as that of the base sample. More importantly, the presence of SWCNT increased the NH3 emission as compared to the base sample. On the other hand, SWCNT-20Ru doping reduced the NH3 emission compared to the SWCNT doping, but did not eliminate it completely. As revealed from the mass spectrometry signals, the SWCNT-20Ru catalyst starts to decompose NH3 at a temperature as low as 200 °C.
Dervis Emre Demirocak, Sesha S. Srinivasan, Manoj K. Ram, John N. Kuhn, Ranjani Muralidharan, Xiao Li, D. Yogi Goswami, Elias K. Stefanakos, International Journal of Hydrogen Energy 38 (2013) 10039-10049

L0020 – Synthesis and sintering of porous La0.8 Sr0.2 MnO3 powder

In this research, La0.8Sr0.2MnO3 precursors were synthesized from metallic nitrates by sol-gel method using polyacrylic acid (PAA) as the chelating to prepare pure and porous powders for the cathode application in solid oxide fuel cell (SOFC). The LSM powders after dried and sintered at suitable temperatures were characterized by X-ray diffractometry (XRD), scanning, and transmission electron microscopes (SEM and TEM). The LSM powder with nano-crystalline synthesized by adding (P)AA/LSM = 2 was obtained after calcined at 500°C for 2h, and still kept porous character up to 1000°C.
H-R. Hsu, S-C. Wang, W-C.J. Wei, Bulletin of the College of Engineering, N.T.U. 89 (2003) 83-90

L0041 – Surface resistance and sensitivity to hygrometry of various ceramic compositions for multilayer capacitors

Developing new dielectric compositions for multilayer ceramic capacitors, the authors of this work have observed an influence of hygrometry on the insulation resistance behavior of some of them. The swiftness of the phenomenon let us suppose a surface mechanism. Prompted by these observations, we have investigated the sensitivity of various conventional ceramic compositions to hygrometry by measuring their surface resistance versus the moisture rate in air. The studied materials are formulations for type I and type II ceramic capacitors. In order to understand some breakdown phenomena in ceramic multilayer capacitors, we have also investigated the influence of the screen printed electrodes composition.
J. Bernard, D. Houivet, J-M. Haussonne, Journal of the European Ceramic Society 25 (2005) 2977-2979

L0030 – Ionic conductivities and phase transitions of lanthanide rare-earth substituted La2Mo2O9

The ion conductivities and phase transitions of lanthanum molybdate (La2Mo2O9) substituted with lanthanide rare-earths are investigated using impedance spectroscopy, dilatometry, and X-ray powder diffraction. Among the substituted La2Mo2O9 of 10 mol% Ce, Nd, Sm, Gd, Dy, Er, Yb, the specimens containing Er, and Dy exhibit depressed alpha-beta phase transformation and high conductivities. Their 700°C conductivities are approximately five to seven times that of La2Mo2O9, around 0.26 S cm-1, comparable with those of (LaSr)(GaMg)O3 and Gd-substituted CeO2. Among the three compositions of 10 mol% Gd, Dy, Er showing depressed phase transition, Er- and Dy-substituted La2Mo2O9 possess relatively low thermal expansion coefficient 11 x 10^(-6) K-1, compared with that of the Gd-substituted La2Mo2O9, 18 x 10^(-6) K-1, which is near that of La2Mo2O9. Hence, Dy and Er are valuable dopants in improving the La2Mo2O9 properties. Across the lanthanide series, 10 mol%-substituted La2Mo2O9 demonstrates systematic variations in the conductivity-temperature relation. Hysteresis phenomena in both of conductivity and thermal expansion are also observed in those compositions which display phase transition.
D-S. Tsai, M-J. Hsieh, J-C. Tseng, H-Y. Lee, Journal of the European Ceramic Society 25 (2005) 481-487

L0051 – Sintering and microstructure of rare earth phosphate ceramics REPO4 with RE = La, Ce or Y

Sintering of rare earth phosphates REPO4 (RE = La, Ce or Y) was studied using dilatometry. The presence of a secondary rare earth metaphosphate phase RE(PO3)3 as sintering aid was investigated. It proved to accelerate the densification but it activated fast grain growth, which was very detrimental to the microstructural design of processed ceramics. A temperature of 1400-1450°C was required to sinter pure LaPO4 and CePO4 ceramics with fine grains. Both compounds behave similar while YPO4 did not densify even at 1500°C. The influence of specific surface area of starting powders, temperature and holding time on the sintering rate and microstructures of dense REPO4 materials is also reported.
D. Bregiroux, S. Lucas, E. Champion, F. Audubert, D. Bernache-Assollant, Journal of the European Ceramic Society 26 (2006) 279-287

L0040 – Low temperature sintering of MgTiO3 with bismuth oxide based additions

MgTiO3 is a classical material for type I MLCC. However, its densification temperature is too high to allowco-sintering with copper electrodes. Investigations into low temperature sintering of MgTiO3 show the complexity of this problem particularly when co-sintering with copper electrodes and thus a reducing atmosphere are involved in the process. Though feasibility of MgTiO3/copper MLCC seem to be possible [Bernard, J., Houivet, D., El Fallah, J. and Haussonne, J. M., MgTiO3 for base metal multilayer ceramic capacitors. J. Eur. Ceram. Soc., 2004, 24, 1877-1881] studies have pointed out several remaining problems such as sensibility to hygrometry [Bernard, J., Houivet, D., El Fallah, J. and Haussonne, J. M., Effect of hygrometry on dielectric materials. J. Eur. Ceram. Soc., 2004, 24, 1509-1511]. Investigations into low temperature sintering of MgTiO3 are thus still necessary to find a formulation which is not detrimental to dielectric behaviour. Sintering aid capabilities and/or good dielectric properties of bismuth oxide based additives make them good candidate materials to lower MgTiO3 sintering temperature without altering its final properties. In this study bismuth titanate is either formed in situ by reaction-sintering of Bi2O3-B2O3 additives with MgTiO3 or obtained by pre-calcination of Bi2O3 and TiO2 powders and then added to MgTiO3 prior to sintering. Bismuth titanate appears as a good sintering aid that allows sintering of MgTiO3 under 1000°C. It is however highly sensitive to the nature of the sintering atmosphere, oxidizing or reducing. Dielectric properties of sintered specimens are compatible with type I capacitors applications.
F. Belnou, J. Bernard, D.d Houivet, J-M. Haussonne, Journal of the European Ceramic Society 25 (2005) 2785-2789

L0029 – Sintering shrinkage of WC-Co materials with bimodal grain size distributions

Sintering shrinkage and densification rate were investigated for WC-Co materials with different grain size distributions. Unimodal distributions were compared to bimodal mixtures with size ratio close to four. A bimodal carbide mixture with 25% fine particles showed similar shrinkage behaviour to a material with unimodal distribution around the same mean value. With 50% fine particles the initial shrinkage was slightly faster than a unimodal material with the same mean size, while the late shrinkage was considerably slower. The effects of particle size distribution on particle packing and sintering are discussed, and the effect on viscosity modelled.
A. Petersson, J. Agren, Acta Materialia 53 (2005) 1665-1671

L0050 – Ba(Zn1/3Nb2/3)O3 sintering temperature lowering for silver co-sintering applications

The complex perovskite oxide Ba(Zn1/3Nb2/3)O3 have been broadly studied due to its attractive dielectric properties which place this material as a good candidate for manufacturing type I capacitors or hyperfrequency resonators. The development of Base Metal Electrodes Multi Layer Ceramic Capacitors (BME-MLCC) require a low sintering temperature to be co-sintered with a low cost metal such as copper or silver. Unfortunately, BZN requires a high temperature (1350°C according to the literature) to reach a satisfactory density (>90% of the theoretical one). The aim of this work is to lower the BZN sintering temperature to allow a co-sintering with copper or silver electrodes. For this goal, different sintering agents (lithium salts and glass phases) have been tested on the nominal compound. It is shown that an addition of 10 molar% B2O3 combined with 5 molar% LiF authorises a sintering temperature lowering near to 350°C. If a slight non-stoichiometry in A site is combined to these sintering agents, it is possible to reach a sintering temperature lower than 950°C without affecting the basic material properties. For each composition obtained, the ceramic is characterised in terms of final density, microstructure and dielectric properties. The silver co-sintering is also performed.
F. Roulland, S. Marinel, Ceramics International 32 (2006) 377-383

L0039 – Low sintering temperature of MgTiO3 for type I capacitors

Magnesium titanate MgTiO3 is a well-known compound for type I multilayer ceramic capacitors. Nevertheless, the sintering temperature of the pure ilmenite MgTiO3 is around 1350°C. Such a high sintering temperature together with the high sensitivity of the dielectric material to reduction when heated in a low-oxygen containing atmosphere implies that MgTiO3-based MLCC include palladium-rich inner electrodes. The high level of variation of both the costs of Pd and Ag justifies research leading to the use of cheaper metals such as silver or base metals such as nickel or copper. When using low-melting temperature metals (silver melts at 960°C and copper at 1085°C), the sintering temperature of the dielectric material has to be lowered.We report here on our investigations into the use of fluorine containing additives for the reducing of the sintering temperature of magnesium titanate, showing the ability of this material to be sintered at temperatures much lower than 1000°C. Both dielectric and electric properties of such ceramics are compatible with type I capacitors requirements.
J. Bernard, F. Belnou, D. Houivet, J-M. Haussonne, Journal of the European Ceramic Society 25 (2005) 2779-2783

L0028 – Synthesis and characterisation of the double perovskite Ba2(Zn0.5Ti0.5X)O6 (X = Nb, Ta) ceramics

Ba2(Zn0.5Ti0.5X)O6 compounds from the general ABO3 perovskite family were synthesized by the classical solid-state route for X = Nb and Ta with various A/B ratios (1.005, 1 and 0.995). After the calcination step at 1100°C, both compounds (X = Nb and Ta) contain mainly the cubic disordered 'Ba2(Zn0.5Ti0.5X)O6' phase but traces of BaTiO3 and secondary phases are often detectable. Nevertheless, after the sintering stage at higher temperature (from 1300 to 1500°C) and for all A/B ratios investigated, Ti enters into the cubic perovskite structure, resulting in the formation of a unique 'Ba2(Zn0.5Ti0.5X)O6' phase. Attractive dielectric properties have been measured on the tantalum-based compound for A/B = 0.995 (Q 2000 at 7.4 GHz and e = 39.6) as well as on the niobium-based phase for A/B = 1.005 (Q 2200 at 6.1 GHz and e = 54.8). All these characteristics were confirmed at 1 MHz and a linear dependence of the permittivity versus temperature from 60 to 180°C has also been evidenced for both formulations. Sinterability, dielectric properties and microstructure of such compounds are discussed with respect to the stoichiometry.
S. Marinel, F. Roulland, Materials Research Bulletin 40 (2005) 962-969

L0049 – Titanium effect on phase transformation and sintering behavior of transition alumina

The sintering behavior of doped gamma-alumina powders studied by dilatometry and electron microscopy is analysed with a particular emphasis on the role of titanium on the various densification steps. Compared with other doping elements, such as Mg, Y and Zr, which do not improve alpha-phase densification, titanium enhances this densification step by a fast decrease of internal colony porosity. This internal densification of single crystalline zones is attributed to the lengthening of the elementary bricks in titanium-doped samples.Atransient increase in densification rate is also observed, corresponding to the precipitation when during grain growth, grain boundaries become saturated with titanium. Final densities close to the theoretical values are obtained.
S. Lartigue-Korinek, C. Legros, C. Carry, F. Herbst, Journal of the European Ceramic Society 26 (2006) 2219-2230

L0038 – High decrease in CaZrO3 sintering temperature using complex fluoride fluxes

The effects of complex fluoride flux on the sintering and the electric/dielectric properties of CaZrO3 ceramics are investigated. Four fluoride mixtures are tested: LiF-CaF2-SrF2, LiF-CaF2-BaF2, LiF-SrF2-BaF2 and LiF-BaF2-B2O3. They are used because each of their associated phase diagrams shows the existence of an eutectic composition having a low melting temperature. This liquid phase is used to promote the densification at low temperature. The effect of various additions (nature and quantity) are also investigated to optimise the resulting thermal and physical properties. In terms of sintering behaviour, the results are unambiguous, leading to a drastic decrease of the densification temperature with all the non-boric additions (<1000°C). The dc/ac measurements carried out on the materials sintered at low temperature (900 and 1000°C) and either in air or in reductive atmosphere follow the same trend when using non-boric additions, with high permittivities (>25), low dielectric losses (<10x10^(-4)), low temperature coefficients of the permittivity (<100 ppm/K) and high insulating resistivities (up to 10^15; the high frequency measurements lead to similar conclusions revealing high QF products (up to 40 THz) using non-boric additions. The effect of the sintering temperature, the sintering atmosphere, the flux composition and its amount on these properties are also discussed.
M. Pollet, S. Marinel, F. Roulland, Journal of the European Ceramic Society 25 (2005) 2773-2777

L0027 – Influence of titanium nitride addition on the microstructure and mechanical properties of TiC-based cermets

In this paper, the TiC-based cermets with addition of TiN were fabricated by a conventional powder metallurgy process. The titanium nitride (TiN) and titanium carbide (TiC) used as starting powders have been synthesized by the self-propagating high temperature synthesis (SHS) method. This exothermic reaction, easy to process, allows to obtain fine and original powders from lowcost raw materials. Cermets obtained by sintering powders of TiC and Mo2C with nickel binder phase are investigated. The effect of TiN adding on the microstructure and the mechanical properties of these composites are studied. Microstructures have been observed by scanning electron microscopy (SEM). Room temperature mechanical properties such as Young s modulus, fracture toughness and microhardness have been measured and related to morphology and chemical composition of the samples. Tribological experiments were also performed and the friction coefficient of a cermet containing titanium nitride was compared with that of other hard materials. The SHS starting powders used present some particularities, as it was shown in a previous study [Mate´riaux a` base de carbures et nitrures, pour coupe et usure, obtenus a` partir de poudre SHS, PhD Thesis, INSA Lyon, 2004]. The purpose of this work is to show that results concerning the impact of TiN addition on microstructure and mechanical properties obtained on bulk specimens, from these original starting powders, are similar to the ones obtained on alloys from commercial starting powders.
J. Russias, S. Cardinal, Y. Aguni, G. Fantozzi, K. Bienvenu, J. Fontaine, International Journal of Refractory Metals & Hard Materials 23 (2005) 358-362

L0048 – Effect of type of primary processing on the microstructure, CTE and mechanical properties of magnesium/alumina nanocomposites

Magnesium based composites containing 2.5wt.% of nano-sized Al2O3 (50nm) particulates reinforcement were synthesized using an innovative disintegrated melt deposition technique and blend-press-sinter powder metallurgy technique followed by hot extrusion. Microstructural characterization of the materials revealed uniform distribution of reinforcement, grain refinement and the presence of minimal porosity. Properties characterization revealed that the presence of nano-Al2O3 particulates led to an increase in dimensional stability, hardness, elastic modulus, 0.2% yield strength, UTS and ductility of pure magnesium. Amongst the composites, the ingot metallurgy processed material exhibited superior modulus and ductility while powder metallurgy processed material exhibited superior yield strength and ultimate tensile strength. The results further revealed that the overall combination of tensile properties of these materials remained superior when compared to high strength magnesium alloy AZ91 reinforced with much higher weight percentage of SiC. Fractography studies revealed that the typical brittle fracture of pure magnesium changed to ductile due to the incorporation of nano-Al2O3 particulates. An attempt is made in the present study to correlate the effect of nano-sized Al2O3 particulates as reinforcement and processing type with the microstructural and tensile properties of magnesium.
S.F. Hassan, M. Gupta, Composite Structures 72 (2006) 19-26

L0037 – Low temperature sintering of the binary complex perovskite oxides xBa(Zn1/3Ta2/3)O3 + (1-x)Ba(Mg1/3Ta2/3)O3

The interest for the complex perovskites oxides is known since several years. Ba(Zn1/3Ta2/3)O3 (BZT) and Ba(Mg1/3Ta2/3)O3 (BMT) have been broadly studied due to their attractive dielectric properties suitable for applications such as multilayer ceramic capacitors or hyperfrequency resonators. They hence exhibit at 1MHz very low dielectric losses combined with a high relative dielectric constant which is stable with the temperature. Unfortunately, these materials needs a too high temperature to reach a satisfying density. The BMT sintering temperature is indeed higher than 1500°C, which is too high to envisage a co-sintering with copper (Tf = 1083°C) or nickel (Tf = 1450°C). To lower the sintering temperature, a glass phase addition is performed on the complex formulations xBa(Zn1/3Ta2/3)O3 + (1-x)Ba(Mg1/3Ta2/3)O3 (with x = 0, 1/3, 1/2, 2/3 and 1). These mixtures are envisaged to explore their dielectric properties. The sintering temperature lowering reached is higher than 400°C when 10 molar% of borate oxide is added to the mixtures and their dielectric properties are very attractive (? = 25 and ?? =-59 ppm/°C for x = 1/3) for the fabrication of base metal electrodes multi layer ceramic capacitors (BME-MLCC).
F. Roulland, G. Allainmat, M. Pollet, S. Marinel, Journal of the European Ceramic Society 25 (2005) 2763-2768

L0047 – Variation of the lattice parameter and thermal expansion coefficient of (U,Dy)O2 as a function of DyO1.5 content

Thermal expansions of (U,Dy)O2 solid solutions were investigated between room temperature and 1673K by using a thermo-mechanical analyzer. The lattice parameter of (U,Dy)O2 pellets is lower than that of UO2 and it decreases as Dy content increases. The linear thermal expansion and average thermal expansion coefficients of (U,Dy)O2 are higher than that of UO2. For the temperature range from room temperature to 1673 K, the average thermal expansion coefficient values for UO2 and (U0.8Dy0.2)O2 are 10.97x10^(-6) and 11.37x10^(-6) K-1, respectively.
S-H. Kim, H-S. Kim, Y-W Lee, D-S. Sohn, D-S. Suhr, Journal of Alloys and Compounds 407 (2006) 263-267

L0036 – Dielectric properties of Ba(Mg,Zn)1/3Nb2/3O3 and effect of B2O3 and LiF addition

The dielectric and microwave properties of (x)BaZn1/3Nb2/3O3-(1-x)BaMg1/3Nb2/3O3 (BMZN) mixture were investigated. The complex perovskite-type ceramics Ba(Zn1/3Nb2/3)O3 (BZN) and Ba(Mg1/3Nb2/3)O3 (BMN) have a high dielectric constant (?r = 39 and 33, respectively), but while BZN has a relative low firing temperature (?1350°C), BMN has a too high sintering temperature (>1500°C) to make it attractive in some technological applications. Mixing these two dielectric ceramics in different proportions and adding some sintering agents (like glassy B2O3 and LiF) the sintering temperature can be decreased, and XRD patterns indicates the formation of a solid solution for all x values investigated. The dielectric properties are preserved or even improved for some specific combinations. For BMZN (x = 1/4), without any dopants, the Qf factor is 76.7 THz for f = 7.6 GHz and the temperature coefficient of the resonant frequency tf is -4 ppm/°C, which is the best value for BMZN. These values make BMZN compounds suitable for microwave resonator applications. We highlight in this paper that BMZN materials can be successfully sintered at low temperature (i.e. 940°C), opening opportunities to manufacture base metal electrodes multilayer ceramic capacitors (BME-MLCC).
A. Veres, S. Marinel, F. Roulland, Journal of the European Ceramic Society 25 (2005) 2759-2762

L0046 – Elaboration and characterisation of apatite based mineral supports for microfiltration and ultrafiltration membranes

The development and the characterisation of new supports for microfiltration and ultrafiltration membranes from apatite applied to filtration are presented. The choice of this material is based primarily on its low cost (considering its abundance in the Tunisian ores). The support, with tubular configuration, was prepared from natural apatite: apatite powders were crushed for 30 min and sieved to 200 mm. The resulting powders, mixed with organic additives and water, could be extruded to elaborate a porous structure. The firing temperature of the support is 1160°C. The morphologies of the surface and the cross-section observed on scanning electron microscope (SEM) are homogeneous and do not present any macro defects (cracks, etc.). The mean pore diameter, measured by mercury porosimetry, is 6 mm and the pore volume is 48%.
S. Masmoudi, A. Larbot, H. El Feki, R. Ben Amar, Ceramics International 33 (2007) 337-344

L0035 – Dielectric and electromechanical characterisation of fine-grain BaTi0.95Sn0.05O3 ceramics sintered from glycolate-precursor powder

Nanocrystalline BaTi0.95Sn0.05O3 (BTS-5) powder was synthesised from glycolate-precursors, and used to sinter fine-grain BTS-5 ceramics. We compare sintering behaviour, microstructure as well as dielectric and electromechanical properties of the advanced ceramics with ceramics sintered from classical mixed oxide powder.
L. Geske, V. Lorenz, T. Müller, L. Jäger, H. Beige, H-P. Abicht, V. Mueller, Journal of the European Ceramic Society 25 (2005) 2537-2542

L0045 – Electrical and microstructural characterization of spinel phases as potential coatings for SOFC metallic interconnects

Several spinel samples, i.e., MnxCr3-xO4 (0.5
W. Qu, L. Jian, J.M. Hill, D.G. Ivey, Journal of Power Sources 153 (2006) 114-124

L0034 – Electrical, thermal and catalytic properties of CeO2-Sm0.5Ti0.5O1.75 ceramics

The electrical conductivity of the ceramic composite, (CeO2)(1-x)(Sm0.5Ti0.5O1.75)x, where 0
S. Koutcheiko, Y. Yoo, I. Davidson, Ceramics International 31 (2005) 965-971

L0044 – Enhancing strength and ductility of Mg/SiC composites using recrystallization heat treatment

In the present study, magnesium composites with sub-micron size silicon carbide (SiC) particulate reinforcements were successfully synthesized using an innovative Disintegrated Melt Deposition technique followed by hot extrusion. The extruded materials were characterized for their microstructural, thermal and mechanical properties. Systematic investigations on the microstructure of the extruded samples revealed a fairly uniform distribution of SiC particulates with limited clustering. Good SiC/Mg interfacial integrity and limited porosity was observed for all the samples. The results of the properties characterization revealed that SiC in sub-micron length scale are more effective in lowering CTE, and enhancing hardness, 0.2% yield strength, and ultimate tensile strength when compared to SiC particulates in micron length scale. Subsequently, isothermal heat treatment at 150°C for 5 h was carried out for the composite samples. The results of tensile testing revealed that the heat treated samples showed an improvement of 0.2% YS, UTS and ductility. Particular emphasis is placed in this study to investigate the effect of heat treatment at the recrystallization temperature on the tensile properties of magnesium.
S. Ugandhar, M. Gupta, S.K. Sinha, Composite Structures 72 (2006) 266-272

L0033 – Sintering, microstructure and grain growth of Fe-doped Ce0.9Gd0.1O2 d ceramics derived from oxalate coprecipitation

The precursor powder of Ce0.9Gd0.1O2 d ceramics was prepared by oxalate coprecipitation. 0.1-3 at% (atomic percent) Fe2O3 was added into the powder via the conventional mixed-oxide method. The effects of doping level, and sintering temperature and time on the densification, microstructure and grain growth of Ce0.9Gd0.1O2 d ceramics were investigated by means of dilatometry measurement, density testing and scanning electronic microscopy (SEM) observation. In the Fe content range used, the sintering temperature decreased consistently with increasing Fe level (from 1310°C at 0.1 at% Fe to 1104°C at 3 at% Fe). Small additions of Fe2O3 promoted the densification rate significantly. The densification rate reached a maximum at 1 at% Fe, then decreased with further increase in Fe content. For 0.5 at% Fe-doped Ce0.9Gd0.1O2 d ceramic, over 97% relative density was complete during heating ramp fromroomtem perature to 1350°C at a heating rate of 10°C/min, as compared to only 86% for the undoped ceramic. The Fe doping level was also found to have a remarkable influence on the grain growth behavior, which depended on sintering temperature. At lower temperatures (e.g., 1250°C), a pinning effect on grain growth was found above 1 at% Fe additions. However, such a pinning effect became less important with increasing temperature. A slight increase in grain size was actually observed in the Fe-doped ceramic sintered at 1500°C as the Fe content increased from0.1 to 3 at%. The analysis based on the grain growth kinetics indicated that the undoped Ce0.9Gd0.1O2 d ceramic followed a parabolic law for grain growth, while the 0.5 at% Fe-doped ceramic had a grain growth exponent of 4.
T.S. Zhang, J. Ma, Y.J. Leng, Z.M. He, Journal of Crystal Growth 274 (2005) 603-611

L0054 – Electrical and thermal properties of La0.7Sr0.3Ga0.6Fe0.4O3 ceramics

Single-phase La0.7Sr0.3Ga0.6Fe0.4O3 (LSGF) ceramic powder was prepared in one step at 1500°C by solid-state reaction in air. The phase is a hexagonal (space group R-3c) at room temperature but becomes cubic at temperatures above 600°C. A high-density (97%) LSGF ceramic shows electrical conductivity of 4.3 S/cm (Ea = 0.32 eV) at 600°C in air. The thermal expansion coefficient of LSGF changes drastically in air due to oxygen loss and phase transition. High-density LSGF ceramic is relatively stable in forming gas (8% H2, 92% Ar). However, the powder decomposes in forming gas above 700°C with formation of LaSrGaO4. LSGF reacts with NiO at 1000°C. The ability of LSGF to split the C-H bond in methane at intermediate temperatures has been also evaluated.
S. Koutcheiko, P. Whitfield, I. Davidson, Ceramics International 32 (2006) 339-344

L0043 – Stress relaxation of bulk and ribbon glassy Pd40Cu30Ni10P20

Detailed measurements of linear heating and isothermal stress relaxation of bulk and ribbon glassy Pd40Cu30Ni10P20 below the glass transition temperature have been performed. Using the activation energy spectrum reconstructed from these measurements, the temperature dependence of the shear viscosity has been calculated. It has been found that this dependence agrees with that derived directly from the creep measurements. This provides strong support for understanding the stress relaxation as a result of the stress-oriented irreversible structural relaxation with distributed activation energies.
O.P. Bobrov, K. Csach, V.A. Khonik, K. Kitagawa, S.N. Laptev, M.Yu. Yazvitsky, Scripta Materialia 54 (2006) 369-373

L0032 – Thermal analysis of the cyclic reduction and oxidation behaviour of SOFC anodes

The reduction and oxidation (redox) kinetics of a Ni/YSZ cermet were studied at temperatures between 400 and 850°C by thermogravimetric analysis (TGA) and reduction and oxidation activation energies were determined. In addition, the volume change after redox cycling was examined by thermomechanical analysis (TMA). Samples with fine microstructure similar to a typical SOFC anode functional layer (AFL) and samples with coarse microstructure similar to a typical anode substrate were characterized. Coarse structured samples experienced no volume change or cracking upon redox cycling. Fine structured anode samples did not change in volume after reduction, but expanded between 0.9% and 2.5% after oxidation. The samples were significantly cracked after oxidation. The amount of expansion and cracking was reduced by lowering the Ni content of the anode and by reducing the oxidation temperature. The reduction of the NiO/YSZ samples followed linear kinetics with an activation energy of 78 kJ/mol. Ni/YSZ oxidation followed parabolic kinetics at temperatures lower than 700°C. A divergence from parabolic kinetics was seen at higher temperatures (700-850°C). This divergence has been seen in many other kinetic studies and is usually attributed to short-circuit diffusion mechanisms. An activation energy of 87 kJ/mol was calculated for oxidation.
D. Waldbillig, A. Wood, D. G. Ivey, Solid State Ionics 176 (2005) 847-859

L0053 – Processing of Al2O3/Y-TZP laminates from water-based cast tapes

Laminated structures have been investigated due to their capability for the reinforcement of ceramics. Crack deflexion and bifurcation, surface strengthening and threshold strength are the mechanisms associated to the fracture of laminated ceramic. In all the cases, a precise control of the thickness and composition of the layers is necessary. In this sense, colloidal processing techniques have proved their adequacy for the fabrication of designed layered structures. This paper deals with the fabrication of layered ceramics by stacking water-based cast tapes at room temperature and using low pressures. In order to control the pressing procedure, the engineering strain-stress curves recorded during the stacking of the tapes were analyzed. Afterwards, the sintering conditions have been optimized by adjusting the green density of the tapes to avoid differential sintering and the associated cracks. Monolithic and layered materials free of cracks have been fabricated using optimized processing conditions.
A.J. Sanchez-Herencia, J. Gurauskis, C. Baudin, Composites: Part B 37 (2006) 499-508

L0042 – Cofiring behavior and interfacial structure of NiCuZn ferrite/PMN ferroelectrics composites for multilayer LC filters

The cofiring behavior, interfacial structure and cofiring migration between NiCuZn ferrite and lead magnesium niobate (PMN)-based relaxor ferroelectric materials were investigated via thermomechanical analyzer (TMA), X-ray diffractometer (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Mismatched sintering shrinkage between NiCuZn ferrite and PMN was modified by adding an appropriate amount of sintering aids, Bi2O3, into NiCuZn ferrite. Pyrochlore phase appeared in the mixture of NiCuZn ferrite and PMN, which is detrimental to the final electric properties of LC filters. EDS results indicated that the interdiffusion at the heterogeneous interfaces in the composites, such as Fe, Pb, Zn, existed which can strengthen combinations between ferrite layers and ferroelectrics layers.
C. Miao, J. Zhou, X. Cui, X. Wang, Z. Yue, L. Li, Materials Science and Engineering B 127 (2006) 1-5

L0031 – A study of Pr0.7Sr0.3Fe(1-x)NixO(3-d) as a cathode material for SOFCs with intermediate operating temperature

Pr0.7Sr0.3Fe(1-x)NixO(3-d) (PSFN; x=0.2-0.5) compounds were synthesized and characterized by powder X-ray diffraction (XRD), thermal expansion coefficient (TEC) measurements, electrical conductivity and electrochemical impedance spectroscopy on coneshaped electrodes on a Ce0.9Gd0.1O1.95 (CGO10) electrolyte. The main phase of the powders belongs to the orthorhombic crystal system. The conductivities are fairly high, e.g., around 450 at 600°C for the x=0.3 compound. The TEC of the compounds is close to the values of ceria-based electrolytes. PSFN showed hysteresis in the temperature dependence of the conductivity, TEC and area-specific polarization resistance Rpol. It is considered that the hysteresis was caused by relatively slow adjustment of the oxygen stoichiometry. The electrochemical performance Rpol 1 of the PSFN compounds is similar to that of La0.6Sr0.4Fe0.8Co0.2O(3-d).
S-I. Hashimoto, K. Kammer, P.H. Larsen, F.W. Poulsen, M. Mogensen, Solid State Ionics 176 (2005) 1013-1020

L0052 – Effect of ceria on properties of yttrium-doped strontium titanate ceramics

This work reports the preparation and properties of the ceramic mixtures of the A-site deficient perovskite Sr0.94Y0.04TiO3 (SYT) with CeO2 in a range of ratios with a view to establishing their potential as anode materials for solid oxide fuel cells. Good electrical conductivity that decreased with increasing CeO2 content was observed on reduction in forming gas. The composition with 50 wt.% of CeO2 showed the conductivity of 7.0 S/cm at 900°C in forming gas. The thermal expansion of SYT-CeO2 ceramics in forming gas and in air were investigated in the range 25-900°C at a ramping rate of 3°C/min and thermal expansion coefficients were determined. The addition of ceria was found to have a positive influence on the catalytic behavior of SYT-CeO2 ceramics towards steam methane reforming.
S. Koutcheiko, Y. Yoo, A. Petric, Isobel Davidson, Ceramics International 32 (2006) 67-72

L0073 – Abnormal thermal expansion and thermal stability of Ti3Al(1-x)SixC2 solid solutions

Ti3Al(1-x)SixC2 solid solutions exhibited abnormal high coefficients of thermal expansion at temperatures of >940°C during heating, which was ascribed to the precipitation of Si as Ti5Si3. Ti5Si3 phase usually located at the grain boundaries of the solid solutions.
J.X. Chen, Y.C. Zhou and J. Zhang, Scripta Materialia 55 (2006) 675-678

L0062 – Modelling WC-Co sintering shrinkage – Effect of carbide grain size and cobalt content

Phenomenological models based on the constitutive parameters uniaxial viscosity, viscous equivalent of Poisson's ratio and sintering stress are used to describe WC-Co sintering shrinkage. Shrinkage is divided into three subsequent stages. The influences of carbide grain size and cobalt content are accounted for and model parameters numerically adjusted to dilatometer results. The model successfully represents published shrinkage data for different materials and milling procedures.
A. Petersson, J. Ågren, Materials Science and Engineering A 452-453 (2007) 37-45

L0072 – Indentation creep behavior of a Zr-based bulk metallic glass

The deformation behavior of a Zr44Ti11Cu10Ni10Be25 bulk metallic glass (LM-1B) was studied in the supercooled liquid region by indentation creep test. Before indentation the glass transition and the crystallization temperatures were determined by calorimeter as 625 and 725 K, respectively. The phases formed during crystallization were identified by X-ray diffraction. The indentation creep experiments were carried out at different temperatures and loads. It was found that the creep can be regarded as Newtonian flow at strain rates between 5x10^(-5) and 5x10^(-4) s-1. The values of the viscosity and the activation energy of deformation were determined in the temperature range of 667-687 K.
D. Fatay, J. Gubicza, J. Lendvai, Journal of Alloys and Compounds 434-435 (2007) 75-78

L0061 – Wetting, densification and phase transformation of La2O3/A2O3/B2O3-based glass-ceramics

A lead-free, non-alkali La2O3-Al2O3-B2O3 (LAB) glass with Al2O3 filler had been investigated for low temperature co-firing ceramic (LTCC) application. The glass forming window and several physical properties of the LAB systems were investigated by ICP, TMA, XRD, DSC, and SEM/EDS. The results show that the densification and crystallization temperatures of LAB/Al2O3 were between 700°C and 950°C and depended greatly on the formulation. Crystalline phase LaBO3 (LB) and LaAl2B3O9 (L2A3B) crystallized starting at 825°C and 925°C, respectively. High degree of densification and crystallization of one glass-Al2O3 composition (L30A) was observed with the microstructure composed of tabular L2A3B grains interlocking with submicron Al2O3 and LB grains.
C-L. Chen, W-C.J. Wei, A. Roosen, Journal of the European Ceramic Society 26 (2006) 59-65

L0071 – Influence of the synthesis route on sol-gel SiO2-TiO2 (1:1) xerogels and powders

Five different sol-gel routes are used in order to synthesize mixed SiO2-TiO2 materials. Simple mixing of the Ti and Si precursors, prehydrolyzing of TEOS, modification of the Ti alkoxide with acetic acid, isoamyl alcohol and acetylacetone lead to translucent gels with different time of gelation. Different techniques such as TGA, DTA, XRD and IR spectroscopy are used to characterize each material. IR spectroscopy revealed the presence of Si-O-Ti and Si-O-Si bonds for all the xerogels letting suppose a composite microstructure of the gels. Pre-hydrolyzing of TEOS and modification of Ti alkoxide with isoamyl alcohol are the most appropriate routes to retain the anatase phase up to 1100°C.
S. Vives, C. Meunier, Ceramics International xxx (2007) xxx-xxx

L0060 – Processing and characterization of ultra-thin yttria-stabilized zirconia (YSZ) electrolytic films for SOFC

Sub-micron yttria-stabilized zirconia (YSZ) electrolyte layer was prepared by a liquid state deposition method and with an average thickness of 0.5 Am to improve the performance of the anode-supported solid oxide fuel cell (SOFC). The YSZ precursors, containing yttrium and zirconium species and an additive, poly-vinyl-pyrrolidone (PVP), were spin-coated on a Ni/YSZ anode substrate. Several properties, including crystalline phases, microstructures, and current-voltage (I -V) characteristics, were investigated. The thin film of 4 mol% Y2O3-doped ZrO2 (4YSZ) consisted of cubic, tetragonal, and a trace of monoclinic phases, and showed a crack-free layer after sintering at 1300°C. The anode supported SOFC, which consists of the Ni-YSZ anode, 4YSZ electrolyte, and Pt/Pd cathode, showed power densities of 477 mW/cm2 at 600°C, and 684 mW/cm2 at 800°C. Otherwise, the surface cracks of the other YSZ-coated samples (e.g. 8YSZ) can be repaired by a multi-coating method.
Y-Y. Chen, W-C.J. Wei, Solid State Ionics 177 (2006) 351 - 357

L0082 – Fabrication of gapless triangular micro-lens array

This study presents a new process to fabricate gapless triangular micro-lens array (GTMA) optical film. The process includes ultraviolet (UV) lithography, photoresist reflow process, Ni-Co electroplating and hot embossing technique. After photoresist triangular column array is defined by UV lithography, reflow technique is applied to melt photoresist triangular column array into the shape of triangular micro-lens array. With this reflowed triangular micro-lens array, metal Ni-Co is deposited and covered uniformly on the triangular micro-lens array using electroplating process. The growth rate of Ni-Co is controlled at 0.4-0.6 µm/min at electroplating current density of 1 A/dm2 (ampere square decimetre, ASD). After this electroplating process, a mold of GTMA is obtained, which is served as the primary mold. Next, with passivation technique applied on this primary mold's surface, a secondary mold is obtained by applying the electroplating process again. This secondary mold is served as master for the subsequent hot embossing process to replicate the GTMA pattern onto polymeric material of polymethyl methacrylate (PMMA) sheet. The Ni-Co mold with hardness over hardness of vicker (Hv) 650 is obtained. The stiffness and hardness of the mold play important roles in GTMA hot embossing process. In addition, this PMMA-based GTMA film used as optical film offers a 100% fill factor and high optical coupling efficiency to improve luminance. The optical measurement shows that this optical film with GTMA pattern increases 15.1% of luminance for backlight module (BLM) of liquid crystal display (LCD).
C.T. Pan, C.H. Su, Sensors and Actuators A Physical 134 (2007) 631-640

L0070 – Proton conduction in ceria-doped Ba2In2O5 nanocrystalline ceramic at low temperature

Sintered pellets of Ce-doped Ba2In2O5 (BIC) were prepared from nanopowders. The electrical conductivities were measured using ac impedance spectroscopy under different atmospheres and temperatures. The electrical conductivity of sintered BIC was found sensitive to environmental humidity when the temperature was below 300°C. However, in the presence of hydrogen, the electrical conductivities were independent of water content in the range of 0-30 vol%. The electrical conductivities of BIC were significantly affected by the presence of hydrogen in a temperature range of 100-300°C. The estimated protonic transference number and the measured open circuit voltage suggested the existence of electronic conduction. The coefficient of thermal expansion of BIC is 11.2x10^(-6) K-1 from 25 to 1250°C.
R. Hui, R. Maric, C. Decès-Petit, E. Styles, W. Qu, X. Zhang, J. Roller, S. Yick, D. Ghosh, K. Sakata, M. Kenji, Journal of Power Sources 161 (2006) 40-46

L0059 – High-temperature thermal characterization

G. Etherington, Ceramic Industry, feb 2007

L0081 – The rock salt oxide Li2MgTiO4: Type I dielectric and ionic conductor

The exploration of the Li-Ti-Mg-O system, using both sol-gel technique and solid state reaction method, allowed a new phase, Li2MgTiO4, with disordered rock salt structure (a = 4.159 Å ) to be synthesized. The latter is shown to be a good type I dielectric material, with a relative constant of 15 at high frequency and low dielectric loss (tand < 10^(-3)) over the temperature range - 60 to 160°C. It is also observed that the sintering temperature of this phase is strongly lowered by adopting the sol-gel technique compared to solid state reaction (1150°C instead of 1300°C). Finally we show that this phase exhibits cationic conductivity above 400°C (s600°C = 9 x 10^(-5) S cm-1).
M.V.V.M. Satya Kishore, S. Marinel, V. Pralong, V. Caignaert, S. D'Astorg, B. Raveau, Materials Research Bulletin 41 (2006) 1378-1384

L0069 – A study on sintering aids for Sm0.2Ce0.8O1.9 electrolyte

In this study, an addition of Co oxide or Cu oxide to Sm0.2Ce0.8O1.9 (SDC) was studied to improve the sinterability of SDC. It has been found that both Co and Cu oxide are very effective as sintering aids, and the SDC sintering temperature can be reduced from 1400°C without aids to below 1000°C with only 1 at.% of either Cu oxide or Co oxide. As compared to the pure SDC, a slight decrease of ionic conductivity was observed in SDC with Cu sintering aid. There is no obvious effect on electrochemical property of SDC with Co sintering aid under 2.5 at.%.
X. Zhang, C. Decès-Petit, S. Yick, M. Robertson, O. Kesler, R. Maric, D. Ghosh, Journal of Power Sources 162 (2006) 480-485

L0058 – The current detour effect observed on materials with random microstucture: experimental evidence from Li3xLa2/3-xTiO3 studied by impedance spectroscopy

Impedance spectroscopy (IS) has been used to study the influence on the low frequency part of the impedance diagrams of the microstructure of a fast ionic conductor, Li3xLa2/3-xTiO3 with x = 0.10 (named hereafter LLTO). This oxide has been synthesised by sol-gel method. After synthesis, the powder of LLTO displays a large distribution of grain size and agglomerates. The grain size distribution and the porosity of the ceramic have been changed by heat-treatment from 600°C to 1200°C in air. The impedance spectra of these ceramics, recorded at different temperatures from room temperature (RT) to 400°C, show a low-frequency depressed arc, which is characteristic of the grain boundary response of the ceramic. Its shape depends strongly on the heat-treatment of the ceramic, and therefore, on its microstructure. It is a simple arc when the pellet is well sintered but becomes very complex for non-sintered ceramics with high resistive grain boundary and pores. The observed "fish" shape indicates the presence of current "detours effect" in the material. This effect means that current detours around blocking grain boundary and/or pores occur to lower the impedance. Consequently, the brick layer model (BLM), which assumes an ideal microstructure, and then no current "detours effect", can not be used to analyse these impedance data.
M. Vijayakumar, O. Bohnke, Journal of the European Ceramic Society 26 (2006) 3221-3231

L0080 – A novel low temperature sintering process for PMnN-PZT ceramics

Samples with the composition of 0.07Pb(Mn1/3Nb2/3)O3-0.468PbZrO3-0.462PbTiO3 was prepared in this study. A novel process was adapted to lower the sintering temperature without properties deterioration. The sintering process includes a vacuumed heating stage, a air-venting heating stage, and a final sintering at 1050°C with certain holding time without PbO compensating atmosphere. The influence of holding time at the final sintering stage on the characteristics of the ceramics was studied. The air-venting stage caused a large shrinkage (about 10%) and then slowing down the shrinking rate when the sample was heated up from 800 to 1050°C. The relationships between the crystalline characteristics and physical properties, such as microstructure, the mechanical quality factor (Qm), and electromechanical coupling factor (kp), are discussed in this paper.
C-Y. Chen, Y. Hu, H-L. Lin, Materials Chemistry and Physics 99 (2006) 26-29

L0068 – Electrical properties of low-density polyethylene/multiwalled carbon nanotube nanocomposites

Low-density polyethylene (LDPE)/multiwalled carbon nanotube (CNT) nanocomposites were prepared via melt compounding. The electrical properties of LDPE/CNT nanocomposites as a function of CNT volume content, frequency and temperature were investigated. The results showed that dielectric constant of LDPE/CNT nanocomposites increases slightly with increasing CNT content up to 1.9 vol.%. Thereafter, the dielectric constant of the nanocomposites increases sharply. The dielectric constant of LDPE/3.6 vol.% CNT nanocomposite is more than two orders of magnitude larger than that of pure LDPE. The frequency dependence of electrical properties of LDPE/3.6 vol.% CNT nanocomposite can be well described by the percolation theory.
G.D. Liang, S.C. Tjong, Materials Chemistry and Physics 100 (2006) 132-137

L0057 – Deformation of steel powder compacts during sintering: Correlation between macroscopic measurement and in situ microtomography analysis

Powder compacts obtained by warm pressing of steel powder containing lubricant were found to swell during a typical delubrication cycle and shrink during sintering. The final dimensional changes of the denser compact were strongly anisotropic. Dilatometry measurements showed that final deformation resulted from microstructure induced by prior die pressing and from various phenomena arising at different stages of the cycle, each of them leading to a specific anisotropic effect. To corroborate this assumption the microstructure evolution of the denser material throughout sintering has been observed using in situ synchrotron X-ray computed microtomography. In addition to visual examination, quantitative analysis of 3D images consisted in searching for a relationship between the morphology and the orientation of pores in 2D sections and measuring local strain with an image correlation technique. From this information a schematic description of the main phenomena responsible for the deformation of steel powder compacts during sintering is proposed.
A. Vagnon, O. Lame, D. Bouvard, M. Di Michiel, D. Bellet, G. Kapelski, Acta Materialia 54 (2006) 513-522

L0079 – The effects of the physical states of a simulated fission product on the linear thermal expansion of (U0.924Ce0.076)O2

The linear thermal expansions of an (U0.924Ce0.076)O2 pellet, doped a simulated fission product (Nd2O3 or Ru), were measured from room temperature to 1673K in a flowing argon atmosphere using TMA. Nd2O3 and Ru represent the physical states of a fission product, a dissolved oxide and a metallic precipitate, respectively. Using the measured data, the mean coefficients of a linear thermal expansion was obtained as a function of the temperature, and the effects of the physical states of a simulated fission product on the thermal expansion were investigated. In the case of the Nd2O3 forming a dissolved oxide, the thermal expansion of the sample increased and the increment was proportional to the Nd contents, because the melting point of the Nd2O3 was lower than that of UO2 and although the metallic precipitate hardly affected the crystal structure, the linear thermal expansion also increased with an increasing Ru contents.
D-J. Kim, Y-S. Kim, J-H. Yang, S-H. Kim, Y-W. Lee, H-S. Kim, Journal of Alloys and Compounds 421 (2006) 151-155

L0067 – Low temperature sintering of ZnTiO3/TiO2 based dielectric with controlled temperature coefficient

Structure, microstructure and dielectric properties of ZnTiO3 and rutile TiO2 mixtures (ZnTiO3 + xTiO2 with x = 0, 0.02, 0.05, 0.1, 0.15 and 0.2) sintered using ZnO-B2O3 glass phase (5 wt.% added) as sintering aid have been investigated. For all compounds, the sintering temperature achieves 900°C. The X-ray diffraction patterns indicate for x = 0.1 that the material is composed by three phases identified as ZnTiO3 hexagonal, TiO2 rutile and ZnO. The presence of ZnO is explained by the introduction of Ti into Zn site to form the (Zn1-xTix)TiO3+x solid solution in resulting the departure of ZnO from the ZnTiO3 structure. The ZnTiO3 + 0.15TiO2 composition sintered at 900°C with glass addition exhibits attractive dielectrics properties (Er = 23, tan(delta) < 10^(-3) and a temperature coefficient of the dielectric constant near zero (t = 0 ppm/°C)) at 1 MHz. It is also shown that the introduction of TiO2 allows to tune the temperature coefficient of the permittivity. All these properties lead this system compatible to manufacture silver based electrodes multilayer dielectrics devices.
A. Chaouchi, S. Marinel, M. Aliouat, S. d'Astorg, Journal of the European Ceramic Society 27 (2007) 2561-2566

L0056 – Piezo-spectroscopic characterization of alumina-aluminium titanate laminates

A multilayered alumina-aluminium titanate composite was prepared by a colloidal route from aqueous suspensions. The structure of the laminate was symmetric and constituted of two external Al2O3 layers (width=1750 µm), one central Al2O3 layer (width=1200 µm) and two intermediate thin (width=315-330 m) Al2O3-Al2TiO5 layers. Additional monolithic materials with the same compositions as those of the layers were fabricated as reference materials. Young's modulus of the monoliths was determined by three point bending. Dilatometry determinations were performed on green specimens, following the same heating and cooling schedules as those used for sintering the laminate, in order to determine the actual dimensional changes on cooling after sintering. The dimensional changes of the sintered specimens on heating and on cooling were also determined. Microscopic distributions of residual stresses were evaluated by fluorescence piezo-spectroscopy, and they revealed the existence of weak tensile and compressive hydrostatic stresses in the aluminium titanate and alumina layers, respectively. The level and sign of these stresses was in good agreement with those predicted based on analysis of the Young's modulus and the dimensional variations during cooling after sintering of the monoliths with the same compositions as those of the layers. Dimensional variations during cooling after sintering were different from those for sintered materials, which presented hysteresis between heating and cooling. In spite of the presence of compressive residual stresses in the external layers of the laminate, strength values of notched samples of the laminated specimens were lower than those for monoliths of the same composition as the external layers.
G. de Portu, S. Bueno, L. Micele, C. Baudin, G. Pezzotti, Journal of the European Ceramic Society 26 (2006) 2699-2705

L0078 – Development of Mg/Cu nanocomposites using microwave assisted rapid sintering

In the present study, magnesium composites containing different amounts of nano-size Cu particulates were successfully synthesized using powder metallurgy (PM) technique incorporating microwave assisted two-directional sintering. The sintered specimens were hot extruded and characterized in terms of physical, microstructural and mechanical properties. Microstructural characterization revealed minimal porosity and the presence of a continuous network of nano-size Cu particulates and Mg2Cu intermetallic phase decorating the particle boundaries of the metal matrix. Coefficient of thermal expansion (CTE) value of magnesium matrix was improved marginally with the addition of nano-size Cu particulates. Mechanical characterization revealed that the addition of nano-size Cu particulates lead to an increase in hardness, elastic modulus, 0.2% yield strength (YS), ultimate tensile strength (UTS) and work of fracture of the matrix. An attempt is made in the present study to correlate the effect of increasing amount of nano-size Cu reinforcement on the microstructure and properties of monolithic magnesium.
W.L.E. Wong, M. Gupta, Composites Science and Technology 67 (2007) 1541-1552

L0066 – Synthesis and sintering of a monazite-brabantite solid solution ceramic for nuclear waste storage

Various geological arguments suggest that monazite can be an interesting waste-form for actinides such as Np, Pu, Cm and Am. We set up a simple procedure for making dense pellets of monazite-brabantite solid-solution ceramics with composition Ca0.092Th0.092 Ce0.089La0.727PO4. It consists of co-milling CaCO3, ThO2, CeO2, La2O3, and NH4H2PO4, 1250°C calcination, milling, cold-pressing, and sintering at 1450°C for 4 h. X-ray investigations showed that the reaction scheme from oxides to monazite is complex and involves various P+La-based intermediate compounds. The final density of the the product is around 95% of the theoretical density. The texture is homogeneous with a typical grain of size 5-20 mm. This process is designed to be adapted to hot cells and telemanipulators.
J-M. Montel, B. Glorieux, A-M. Seydoux-Guillaume, R. Wirth, Journal of Physics and Chemistry of Solids 67 (2006) 2489-2500

L0055 – Ce4+ modified cordierite ceramics

A dense, low thermal expansion cordierite ceramic was prepared by the co-precipitation method and Ce4+ addition. Ce4+ addition can inhibit m-cordierite crystallization and improve a-cordierite crystallization. Adding 3.2 wt.% Ce4+ enables density and mechanical strength to reach maximum values with a minor increase in thermal expansion coefficient.
Z.M. Shi, X. Bai, X.F. Wang, Ceramics International 32 (2006) 723-726

L0076 – Modelling of the grain growth and the densification of SnO2-based ceramics

This work consisted in the kinetic study of grain growth and densification processes for SnO2 and Sn0.94Zr0.06O2 ceramics between 1100 and 1200°C. From dilatometric experiments, it appeared that zirconia additions inhibited the final densification rate. For pure SnO2, the rate limiting step of the densification mechanism would correspond to the grain boundary or volume diffusion. From normal grain growth kinetics, the corresponding limiting step has been identified, i.e. either the surface diffusion in pores or grain boundary diffusion for ZrO2 free-SnO2 and Sn0.94Zr0.06O2, respectively. All of these results permit establishing the corresponding sintering map. For pure SnO2 ceramic, the experimental data have been well restored by modelling.
A. Maître, D. Beyssen, R. Podor, Ceramics International xxx (2007) xxx-xxx

L0065 – Effects of solid fission products forming dissolved oxide (Nd) and metallic precipitate (Ru) on the thermal conductivity of uranium base oxide fuel

The effects of solid fission products on the thermal conductivity of uranium base oxide nuclear fuel were experimentally investigated. Neodymium (Nd) and ruthenium (Ru) were added to represent the physical states of solid fission products such as 'dissolved oxide' and 'metallic precipitate', respectively. Thermal conductivity was determined on the basis of the thermal diffusivity, density and specific heat values. The effects of the additives on the thermal conductivity were quantified in the form of the thermal resistivity equation - the reciprocal of the phonon conduction equation - which was determined from the measured data. It is concluded that the thermal conductivity of the irradiated nuclear fuel is affected by both the 'dissolved oxide' and the 'metallic precipitate', however, the effects are in the opposite direction and the 'dissolved oxide' influences the thermal conductivity more significantly than that of the 'metallic precipitate'.
D-J. Kim, J-H. Yang, J-H. Kim, Y-W. Rhee, K-W. Kang, K-S. Kim, K-W. Song, Thermochimica Acta 455 (2007) 123-128

L0075 – Effects of the sintering atmosphere on Nb-based dielectrics

The effects of a forming atmosphere on the stability, the sintering and the dielectric properties of Ba5Nb4O15, BaNb2O6, ZnNb2O6 and Zn3Nb2O8 ceramics were investigated, because of the primary importance of the sintering atmosphere in relation to copper sintering. These Nbbased materials were sintered in air and in Ar/H210%. Zn-containing samples are very sensitive to the reductive atmosphere. ZnO volatilises at 800-850°C and the resulting compound does not exhibit the expected properties. BaNb2O6 and Ba5Nb4O15 are more stable in term of relative weight loss. Nevertheless, the phase analysis reveals a modification of the BaNb2O6 phase, what induces the degradation of the dielectric property stability versus temperature. The properties of Ba5Nb4O15 are not modified by a sintering in reductive atmosphere. A relative permittivity of 38.8, a permittivity temperature coefficient of -150 ppm°C-1 and an insulating resistivity of 10^10.9 V cm were obtained for this latter.
S. d'Astorg, S. Marinel, Ceramics International xxx (2007) xxx-xxx

L0064 – Microwave synthesis and characterization of metastable (Al/Ti) and hybrid (Al/Ti + SiC) composites

Two-directional microwave assisted rapid sinteringwas carried out to fabricate Al/Ti metastable composites and Al/(Ti + SiC) hybrid composites. The length scale of Ti was in microns (20µm) and of SiC in nanometers (50 nm). Microstructural characterization revealed uniform distribution of Ti particulates and SiC nanoparticulates in the Al matrix, relatively low amount of porosity and good matrix-reinforcement interfacial integrity. Coefficient of thermal expansion of the Al matrix reduced due to the presence of Ti and Ti + SiC reinforcements. The results revealed that addition of SiC nanoparticulates to Al-Ti formulations assisted in increasing microhardness, macrohardness, Al-Ti interfacial hardness, 0.2% YS and UTS while the ductility was marginally affected. Particular emphasis was placed to study the feasibility of using hybrid reinforcements in the Al matrix synthesized by using microwaves.
S.K. Thakur, T.S. Kong, M. Gupta, Materials Science and Engineering A 452-453 (2007) 61-69

L0074 – Preparation and properties of dense Ce0.9Gd0.1O(2-d) ceramics for use as electrolytes in IT-SOFCs

Gd-doped ceria solid solutions have been recognized to be leading electrolytes for use in intermediate-temperature fuel cells. In this communication, it reported on the preparation, solubility and densification of Ce0.9Gd0.1O(2-d) ceramics derived from carbonate coprecipitation. The dissolution of Gd2O3 in CeO2 lattice was identified to complete during coprecipitation process by studying lattice parameter against temperature. The calcining temperature was found to have a significant influence on the densification behavior and final sintered density for the carbonatecoprecipitated powder. The samples prepared from the powder calcined at <700°C had an expansion at ~1250 to 1400°C during sintering, and thus lowered sintered density. 800°C was identified to be an optimal calcining temperature for carbonate-coprecipitated powder. The powder calcined at 800°C for 2 h had a mean crystalline size of ~25 nm with nearly spherical shape and narrow particle-size distribution, which had a maximum densification rate at ~1190°C. This temperature (of maximum densification rate) could further be reduced to ~1080°C for the carbonate-coprecipitated powder by adding 0.5 at.% FeO1.5 (atomic ratio). At 1200°C for 5 h, over 98% relative density with an average grain size of ~1.2µm was obtained for the 0.5 at.% Fe-loaded Ce0.9Gd0.1O(2-d) ceramics. Fe loading was also found to have a positive effect on grain boundary conductivity of Ce0.9Gd0.1O(2-d) ceramics. An increase in the grain boundary conduction by over two times was achieved in the present work for the 0.5 at.% Fe-loaded Ce0.9Gd0.1O(2-d) ceramics.
T.S. Zhang, J. Ma, L.H. Luo, S.H. Chan, Journal of Alloys and Compounds 422 (2006) 46-52

L0063 – Rheological behaviour of kaolin/talc/alumina suspensions for manufacturing cordierite foams

This paper deals with the preparation and rheological charaterization of concentrated suspensions (40 vol.% solids) of mixtures of kaolin/talc/alumina to relative weight contents of 40/43.8/16.2, respectively. These concentrated suspensions were thixotropic and viscosus, the rheological properties being largely influenced by a number of processing parameters, the most relevant being the nature and content of deflocculant and the pH value. Best results were obtained for a polyacrylic-based polyelectrolyte and pH 11. Green densities of 59 % of TD were obtained. Dynamic and static sintering studies were performed and the analysis of the resulting phases was made by XRD. From these tests it was concluded that cordierite phase needed a thermal treatment of 1300ºC to be formed. The sintered slip cast materials have a large residual porosity because of the coarse particle size of the raw materals. Macroporous cordierite foams are obtained by impregnation of polyurethane foam into the optimized slip and heating at 1350ºC/1h with a burning out step at 550ºC/30 min.
J.B. Rodrigues Neto, R. Moreno, Applied Clay Science 37 (2007) 157-166

L0108 – Effect of transition metal oxides on densification and electrical properties of Si-containing Ce0.8Gd0.2O(2-d) ceramics

Ce0.8Gd0.2O(2-d) (CGO20) ceramic has been considered as one of the most promising electrolytes for intermediate temperature (IT) fuel cells. It has been reported that some transition metal oxides (TMO), such as MnO2, Fe2O3 and Co3O4, are effective sintering aids for the densification of ceria-based electrolytes. However, very little information is available regarding the effect of TMO addition on the electrical properties of Si-containing CGO20 ceramics. In this study, 0.5 at.% (atomic percent) TMOs have been loaded into the CGO20 with ~30 ppm (pure) and ~200 ppm (impure) SiO2, respectively, and the sintering behavior and ionic conductivity have been investigated. It has been found that Co3O4 is the most effective sintering aid, and the sintering temperature of CGO20 can be reduced by over 200°C by adding 0.5 at.% CoO4/3. All the TMOs used show a slight effect on the grain-boundary (GB) conductivity of the pure CGO20. However, SiO2 additions, together with MnO2 and Co3O4, have found to be extremely detrimental to the GB conduction of CGO20. As compared to the impure CGO20, the GB resistance has been increased by over six times for the impure one with addition of only 0.5 at.% CoO4/3. On the other hand, in contrast to the Mn or Co doping case, small addition of Fe2O3 has a scavenging effect on SiO2 impurity, and significantly improves the GB conduction of the impure CGO20. Therefore, Fe2O3 could be used as an effective sintering aid, as well as a grain-boundary scavenger for SiO2 contaminated ceria-based electrolytes.
T.S. Zhang, J. Ma, Y.J. Leng, S.H. Chan, P. Hing, J.A. Kilner, Solid State Ionics 168 (2004) 187-195

L0097 – Synthesis of fine La0.8Sr0.2MnO3 powder by different ways

La0.8Sr0.2MnO3 (LSMO) powders were successfully synthesized by three routes (sol-gel, spray dryer and conventional solid state method). The precursors were characterized by particle size analysis, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The sintering stage of all powders was also investigated by dilatometer. Finally, the sintered LSMO ceramics have been investigated magnetically and electrically in view to study the ferromagnetic-paramagnetic and/or metal-insulator transition. The magnetoresistance MR up to 42% above room temperature has been observed.
D. Grossin, J.G. Noudem, Solid State Sciences 6 (2004) 939-944

L0085 – Thermal expansion of near stoichiometric (U,Er)O2 solid solutions

Thermal expansions of (U,Er)O2 solid solutions were investigated between room temperature and 1673 K by using a thermo-mechanical analyzer. Lattice parameters of the (U,Er)O2 pellets are lower than that of UO2 and they decrease as the Er contents increase. The linear thermal expansion and average thermal expansion coefficients of (U,Er)O2 are higher than that of UO2. For the temperature range from room temperature to 1673 K, the average thermal expansion coefficient values for UO2 and (U0.8Er0.2)O2 are 10.94x10^(-6) and 11.42x10^(-6) K-1, respectively.
S-H. Kim, H-S. Kim, Y-W. Lee, D-S. Sohn, D-S. Suhr, Materials Letters 60 (2006) 1480-1483

L0107 – The kinetics of surface area reduction during isothermal sintering of hydroxyapatite adsorbent

The behaviour of non-stoichiometric hydroxyapatite (HA) during the calcination in a solid bed was investigated. The structural properties are described in terms of the specific surface area. Calcination led to a significant decrease of the specific surface area by particle coalescence and densification. Hydroxyapatite begins to shrink near 780°C and reaches 97% theoretical density at 1100°C. The specific surface area and density variations are caused both by sintering and chemical reaction. Sintering data from these solids were correlated as a function of time and temperature. The rate of sintering is assumed to obey an Arrhenius equation. These results are compared with a number of literature models describing the mechanism of sintering kinetics using the specific surface area, and a good agreement is observed. The kinetic equation used is based on sintering driven by the curvature gradient in the interparticle neck region associated with initial stage sintering. Then, the decline in specific surface area is accurately described by the empirical equation of the form dS/dt = -B(T)k^b. The changing value of b, also known as the "order" of the reaction, suggests that the diffusion mechanism for loss of surface area may be a function of the temperature.
S. Bailliez, A. Nzihou, Chemical Engineering Journal 98 (2004) 141-152

L0096 – Preparation of spherical zirconia powder in microemulsion system and its densification behavior

The water droplets in the microemulsion system of cyclohexane/water/TritonX-100/hexyl alcohol can act as the nano-reactors which solubilize zirconium oxychloride and ammonia separately. The precipitation reactions will take place in the confined spaces determined by the droplets size. The minute original reactors help us obtain nano-size spherical zirconia amorphous powder with uniform diameter distribution and weak aggregate. Such powder begins to crystallize at the temperature about 475°C, and its shrinkage of densification will be elementarily finished from 1080 to 1280°C. The powder is formed by dry pressing process. The 99% relative density and 100% tetragonal phase can be obtained when the green body is sintered at 1400°C for 2 h.
T. Ma, Y. Huang, J. Yang, J. He, L. Zhao, Materials and Design 25 (2004) 515-519

L0084 – Development of a novel hybrid aluminum-based composite with enhanced properties

In the present study, a novel aluminum-based hybrid composite containing titanium particulates (discontinuous/particulates reinforcement) and iron mesh (continuous/interconnected reinforcement)was synthesized using a solidification processing route involving disintegrated melt deposition coupled with hot extrusion. Microstructural characterization studies conducted on hybrid composite revealed reduced grain size (~44%) when compared to monolithic aluminum, uniform distribution of unreacted and reacted titanium in matrix, and absence of reaction products at the iron-wire/aluminum matrix interface. Results of properties characterization revealed that the presence of hybrid reinforcement led to a reduction in coefficient of thermal expansion (~7.6%) and an increase in hardness, elastic modulus (~10%), 0.2% yield strength (20%) and ultimate tensile strength (~27%). The enhancement in properties realized in hybrid composite was found to be much higher when compared to conventional Al/SiC composite formulations containing relatively higher weight percentages of SiC particulates.
M. Gupta, M.O. Lai, C.Y.H. Lim, Journal of Materials Processing Technology 176 (2006) 191-199

L0106 – The mechanical behavior of magnesium alloy AZ91 reinforced with fine copper particulates

In this study, a hybrid composite based on magnesium alloy AZ91A reinforced with copper particulateswas fabricated using the disintegrated melt deposition (DMD) processing technique followed by hot extrusion. Microstructural characterization of the as-extruded composite sample revealed a near uniform distribution of the copper particulates and other intermetallic phases through the magnesium alloy metal matrix, good integrity at the copper-magnesium alloy matrix interfaces and evidence of minimal porosity. Mechanical property quantification revealed that addition of copper particulates resulted in a significant increase in elastic modulus, 0.2% offset yield strength and ultimate tensile strength of the composite material. However, ductility of the composite was marginally affected when compared to the unreinforced monolithic counterpart. The overall mechanical properties of AZ91A/Cu composite were found to be higher than the silicon carbide particulate reinforced AZ91 composite, even for higher volume fractions of the particulate reinforcement. Influence of copper in the matrix of magnesium alloy AZ91A is examined in light of intrinsic microstructural features and mechanical properties of the composite.
K.F. Ho, M. Gupta, T.S. Srivatsan, Materials Science and Engineering A369 (2004) 302-308

L0095 – Effect of ZrO2 additions on sintering of SnO2-based ceramics

The effect of zirconia additions on sintering of CoO doped tin dioxide has been investigated in the temperature range 1100- 1250°C. A first study showed that the substitution of tin by zirconium reduces significantly the volatilisation rate of SnO2 for temperatures greater than 1400°C. It appeared that the zirconium content increase inhibits the densification kinetics of SnO2-based ceramics. Indeed, the relative density did not exceed 93% for a Zr content lower than 6 mol% in the Sn(1-x)ZrxO2 solid solution. This negative effect can be imputed to the elastic distortions caused by the introduction of Zr in the tin dioxide lattice. So, the diffusion rate of point defects such as oxygen or cobalt ions is lowered.
A. Maître, D. Beyssen, R. Podor, Journal of the European Ceramic Society 24 (2004) 3111--3118

L0105 – Experimental and numerical analysis of the deformation of ferrite segments during sintering

The thermo-mechanical behaviour of hard ferrite powder compacts at high temperature is investigated with a view to simulating dimensional changes occurring during sintering of industrial components. Emphasis is laid on the anisotropy in both shrinkage and viscosity, which is induced by the prior pressing operation performed under magnetic field. Anisotropic shrinkage and viscosity are described according to an original approach based on an orthotropic thermo-elastic equation, which assumes an analogy between the thermal and elastic terms of this equation and the viscous and free sintering deformations. Finite element calculations using this constitutive equation are then carried out on two industrial parts. The comparison between the obtained numerical results and experimental measurements proves the relevance of the proposed model.
F. Toussaint, D. Bouvard, Ph. Tenaud, E. Di Marcello, Journal of Materials Processing Technology 147 (2004) 72-78

L0094 – Microstructural evolution of Y2O3 and MgAl2O4 ODS EUROFER steels during their elaboration by mechanical milling and hot isostatic pressing

Different ODS EUROFER steels reinforced with Y2O3 and MgAl2O4 were elaborated by mechanical milling and hot isostatic pressing. Good compromise between strength and ductility could be obtained but the impact properties remain low (especially for the Y2O3 ODS steel). The materials were structurally characterized at each step of the elaboration. During milling, the martensite laths of the steel are transformed into nano-metric ferritic grains and the Y2O3 oxides dissolve (but not the MgAl2O4 spinels). After the HIP, all the ODS steels remain ferritic with micrometric grains, surrounded by nano-metric grains for the Y2O3 ODS steels. The mechanisms in the Y2O3 ODS steels are complex: the Y2O3 oxides re-precipitate as nano-Y2O3 particles that impede a complete austenitization during the HIP. The quenchability of the ODS steels is modified by the milling process, the oxide nature and the oxide content. Eventually, the advantages and drawbacks of each oxide type are discussed.
C. Cayron, E. Rath, I. Chu, S. Launois, Journal of Nuclear Materials 335 (2004) 83-102

L0104 – Rare earth phosphate powders RePO4 . nH2O (Re=La, Ce or Y) II. Thermal behavior

The thermal behavior, thermostructural and morphological changes, of rare earth phosphate powders RePO4 . nH2O (Re=La, Ce or Y) was investigated up to 1500°C using high temperature X-ray diffraction, FT-infrared and Raman spectroscopies and thermogravimetry coupled with differential thermal analysis. The hydration water of the compounds was zeolitic (for Re=La or Ce) or coordinated (for Re=Y) and was associated with a divariant or a monovariant equilibrium of dehydration, respectively. The high temperature anhydrous monoclinic phase LaPO4 or CePO4 formed irreversibly at about 750°C after the total dehydration of the hexagonal hydrated structure while the dehydration of the monoclinic YPO4 . 2H2O phase began from about 190°C with its simultaneous decomposition into tetragonal YPO4. A polytrioxophosphate secondary minor phase Re(PO3)3 resulting from adsorbed H3PO4 was formed at 950°C and decomposed at 1350°C. The particle morphology did not change with the temperature but grain coalescence occurred below 1000°C.
S. Lucas, E. Champion, D. Bernache-Assollant, and G. Leroy, Journal of Solid State Chemistry 177 (2004) 1312-1320

L0093 – Thermal stability and mechanical properties of a Zr-based bulk amorphous alloy

The thermal and mechanical properties of a Zr-Al-Cu-Ti-Ni bulk metallic glass were investigated. The glass transition and the crystallization were studied by calorimetry and X-ray diffraction. It was found that the crystallization occurred in two steps. The precipitating phases, and the activation energies were determined. It was established that the crystallization was controlled by the diffusion of the alloying Cu and Ni atoms. The creep behavior was investigated by indentation tests. The viscosity and the activation energy of the deformation process determined from indentation were in reasonable agreement with those obtained by compression tests.
D. Fatay, J. Gubicza, P. Szommer, J. Lendvai, M. Blétry, P. Guyot, Materials Science and Engineering A 387-389 (2004) 1001-1004

L0103 – Ce0.8Gd0.2O(2-d) ceramics derived from commercial submicron-sized CeO2 and Gd2O3 powders for use as electrolytes in solid oxide fuel cells

Twenty percentage of Gd2O3-doped ceria solid solution has been prepared as an electrolyte for solid oxide fuel cells via the conventional mixed-oxide method from high-purity commercial CeO2 and Gd2O3. The solubility of Gd2O3 in CeO2 in the temperature range of 1300-1700°C has been examined based on the measurements of the lattice parameter. It is found that the dissolution of Gd2O3 in CeO2 is completed at 1600°C for 5 h. The addition of Gd2O3 increases sintering temperature, retards densification, and also depresses grain growth as compared with undoped CeO2. The sample sintered at 1550°C for 5 h has the highest grain boundary conductivity, while the highest grain interior conductivity is achieved for the sample sintered at 1600°C for 5 h. It is also observed that below 500°C, the maximum total conductivity is exhibited by the former sample, but above 500°C, for the latter one.
J. Ma, T.S. Zhang, L.B. Kong, P. Hing, S.H. Chan, Journal of Power Sources 132 (2004) 71-76

L0092 – Improvements in sintered density and dimensional stability of powder injection-molded 316L compacts by adjusting the alloying compositions

Powder injection molding is a process that provides advantages when making small parts with high density and complicated shapes. However, dimensional control of powder injection-molded stainless steel parts is difficult due to the presence of the liquid phase and the large amount of shrinkage that occurs during sintering. This study examines whether such a problem can be overcome through adjustments in the alloy composition and by making use of Thermo-Calc analysis. The results show that, with an increase in the molybdenum content up to the maximum limit according to existing specifications, a compact can be sintered to high densities without the presence of the liquid phase, while maintaining it in the dual-phase region of gamma + delta. In addition, dimensional control is improved. A slower heating rate is also found to be beneficial. These results are explained through dilatometric analysis and phase diagrams that are calculated using the Thermo-Calc program.
G.J. Shu, K.S. Hwang, Y.T. Pan, Acta Materialia 54 (2006) 1335-1342

L0102 – Increasing elastic modulus, strength and CTE of AZ91 by reinforcing pure magnesium with elemental copper

Heat-treatable AZ91 and 3.9 vol.% copper particulate reinforced magnesium composite was synthesized using an innovative disintegrated melt deposition (DMD) technique followed by hot extrusion. Microstructural characterization of the composite material revealed retention and uniform distribution of reinforcement with defect free interface with the matrix. Physical properties characterization revealed improved dimensional stability of composite when compared to AZ91. Mechanical properties characterization revealed an increase in average values of modulus, 0.2% yield strength and ultimate tensile strength of un-heat-treated composite when compared to T6 heat-treated AZ91 while the ductility was adversely affected. An attempt is made in the present study to compare the microstructural, physical and mechanical properties of Mg/Cup composite with that of the commercially used AZ91 alloy.
S.F. Hassan, K.F. Ho, M. Gupta, Materials Letters 58 (2004) 2143-2146

L0091 – Studies of Fe-Co based perovskite cathodes with different A-site cations

Iron-cobalt based perovskite cathodes with different A-site cations ((Ln0.6Sr0.4)0.99Fe0.8Co0.2O(3-d), where Ln is La, Pr, Sm or Gd) have been synthesised, characterised by a powder XRD, dilatometry, 4-point DC conductivity measurements, and electrochemical impedance spectroscopy (EIS) on cone shaped electrodes. In addition to this scanning electron microscopy (SEM) was used to characterise the bars. XRD revealed that only the La-containing perovskite was hexagonal. The Pr and Sm perovskites were orthorhombic. The gadolinium-based perovskite was a two phase system consisting of an orthorhombic and a cubic perovskite phase. The thermal expansion coefficient (TEC) increased systematically with a decrease in the size of the A-site cation until the gadolinium-containing perovskite where the TEC decreases abruptly. The total electric conductivity was the highest for the La-based perovskite and the lowest for the Gd-based perovskite as determined by 4-point DC conductivity measurements on bars. A clear correlation between the size of the A-site cation and the electrochemical performance was revealed, as the area specific resistance (ASR) was the lowest for the compounds with the smallest A-site cation. This might be explained on the background of the creation of a two-phase structure with a unique microstructure when the size of the A-site cation is lowered, or that one of the phases has a high electro-catalytic activity towards the electrochemical reduction of oxygen.
K. Kammer, Solid State Ionics 177 (2006) 1047-1051

L0101 – Mullite phase formation in oxide mixtures in the presence of Y2O3, La2O3 and CeO2

The effect of oxides (Y2O3, La2O3, and CeO2), on phase formation of mullite, reaction sequence and microstructure evolution, in the mixtures of Al2O3 and SiO2, has been investigated. All three dopants showed a positive effect on the mullitization behavior, lowering the mullite formation temperature by about 100°C. The improved mullitization behavior was attributed to the formation of the low-viscosity liquid phase due to the addition of dopants. The reaction sequence was different in the three doping cases. Two types of yttrium silicate were found in the samples doped with Y2O3, with one being favored at low temperature and another at high temperature. No reaction was observed between CeO2 and Al2O3 or SiO2, while La2O3 was not detected by the X-ray diffraction (XRD) measurement for all doping levels. The samples with La2O3 had the best densification behavior among the three doping cases, while the effect of CeO2 on densification was slightly better than that of Y2O3. The difference in the effects of the three oxides on the mullitization and densification behavior of the doped samples implied the difference in the characteristics of the low-viscosity glass phases formed at high temperatures.
L.B. Kong, T.S. Zhang, J. Ma, F. Boey, R.F. Zhang, Journal of Alloys and Compounds 372 (2004) 290-299

L0090 – Physical properties of BaMg(1/3)Nb(2/3)O3-BaCo(1/3)Nb(2/3)O3 solid solutions

Structural, electric and magnetic properties of Ba3Mg(1-x)CoxNb2O9 based dielectric ceramic compounds have been studied. The samples, prepared by a solid state reaction method, were characterised by X-ray powder diffraction (XRPD), electron microscopy (SEM), dielectric (epsilon(T)) and magnetic measurements (khi-1(T)). The XRPD analyses showed that the crystal structure of these compounds does change by the increase of substitution degree, passing froma superstructure hexagonal-type, P3m1 (no. 164), space group (SG) to a simple structure cubic-type, Pm3m (no. 221), SG. However, the evolution of the elementary unit cell lattice parameter can be followed and it exhibit a linear increasing tendency with increase in the substitution, indicating the existence of a solid solution through out the investigated range of substitution (0-1). Themicrostructure analysis shows a variation inthe grain size and also the porosity of the samples with the degree of substitution. The results are in good agreement with that of dielectricmeasurements, which also showed that the dielectric constant (epsilon) increases with the increase of cobalt content. The magnetic characterization of cobalt substituted samples showed an antiferromagnetic type super-exchange interaction between thesemagnetic ions. At the same time, the values of effective magnetic momentum (µeff) are close to the value that corresponds to Co2+ free ions. The study highlights the possibility of modelling these materials by substitutions, in order to improve properties of negative-positive-zero (NPO) type dielectric applications.
A. Veres, S. Marinel, M. Pollet, Journal of Physics and Chemistry of Solids 67 (2006) 822-827

L0100 – Structure, nonstoichiometry and magnetic properties of the perovskites Sr(1-x)CaxMnO(3-d)

The structural, thermal and magnetic properties of the perovskite-type alkaline-earth manganites of the series Sr(1-x)CaxMnO(3-d) (0 < x < 1) were investigated. SrMnO(3-d) forms a hexagonal perovskite lattice and shows a first-order transformation to a highly defective cubic high-temperature modification. By substituting Ca for Sr (x > 0.25) the hexagonal perovskite is suppressed and a cubic (or orthorhombic) lattice becomes stabilized for all temperatures. For x = 0.5 and 0.75 cubic perovskites with a large nonstoichiometry (e.g., d = 0.25 for x = 0.5) are obtained at 1400°C. The defective perovskites are prepared by either quenching from high temperature or by cooling in an inert atmosphere. The oxygen vacancies are easily filled by subsequent reoxidation at low temperature (400-600°C) and stoichiometric samples are obtained. Orthorhombic perovskites are formed at T < 1200°C with the nonstoichiometry d increasing with increasing temperature (e.g., d = 0.06 at 1000°C and d = 0.14 at 1200°C for x = 0.5). Slow cooling in air results in almost complete reoxidation (d = 0). CaMnO(3-d) is an orthorhombic perovskite with a large range of nonstoichiometry (0 < d < 0.30). The cubic to hexagonal phase transformation of the Sr-rich samples is accompanied by a large expansion of the lattice that is reduced by Ca substitution. The Ca/Sr-manganites are antiferromagnets with TN of 170 K for x = 0.5 and d = 0.02 and 120 K for x = 1 and d = 0.05.
J. Töpfer, U. Pippardt, I. Voigt, R. Kriegel, Solid State Sciences 6 (2004) 647-654

L0088 – Mechanical and thermal expansion behavior of hipped aluminum-TiB2 composites

Aluminum-TiB2 composites reinforced with 5-20 vol.% ceramic particles were prepared by powder metallurgy (PM) method. Hot isostatic pressing was employed to consolidate the green PM products. The microstructure of metal matrix composites (MMCs) was found to depend greatly on the relative particle size (RPS) ratio between the aluminum and ceramic particles. Microstructural examination revealed that RPS value of 0.56 favors both the densification of MMC compacts and better uniform distribution of ceramic particles. Tensile measurements showed that the Young's modulus and ultimate tensile strength of the Al-TiB2p MMCs tend to increase with increasing TiB2p volume content at the expense of tensile ductility. Thermal expansion property of hipped MMCs was measured in the temperature range from 85 to 600°C. The results showed that the increase in the volume fraction of TiB2 reinforcement reduces the coefficient of thermal expansion (CTE) of the Al-TiB2 composites. Moreover, the CTE versus temperature plots exhibited an apparent peak minimum at ~380°C during the first heating stage for the composites reinforced with TiB2 >15 vol.%. This peak corresponds to the onset of relaxation for the compressive stress, leading to the Al matrix to deform plastically.
S.C. Tjong, K.F. Tam, Materials Chemistry and Physics 97 (2006) 91-97

L0099 – Ductility improvement of Ni-added molybdenum compacts through the addition of Cu and Fe powders

The sintered density of molybdenum can be significantly improved through the addition of a small amount of nickel. However, such addition impairs the ductility due to the formation of a NiMo intermetallic compound at the grain boundaries. This makes the plastic deformation process, such as rolling, drawing, and forging, impossible. This study shows that when copper is added, the sintered density can be further increased, but, not the ductility. This ductility problem of the Mo-Ni-Cu system can be improved when a small amount of iron is added and when the total amount of the alloying Ni, Cu, and Fe is over 6wt%, such as in the Mo-4Ni- 1Cu-1Fe system. Such improvement is attributed to the elimination of the brittle NiMo compounds in the matrix.
K.S. Hwang, H.S. Huang, International Journal of Refractory Metals & Hard Materials 22 (2004) 185-191

L0087 – Improving the performance of lead-free solder reinforced with multi-walled carbon nanotubes

In this study, varying weight fractions of multi-walled carbon nanotubes were successfully incorporated into 95.8Sn-3.5Ag-0.7Cu solder, to synthesize novel lead-free composite solders. The composite solders were synthesized via the powder metallurgy route of: blending, compaction, sintering and extrusion. The extruded materials were then characterized for their physical, thermal and mechanical properties. With the addition of increasing weight percentage of carbon nanotubes, the composite solders experienced a corresponding decrease in density values and wetting property improved. The melting temperatures of the composite solders were found to be unchanged with the carbon nanotube additions. Thermomechanical analysis of the composites also showed that the presence of reinforcements decreased the average coefficient of thermal expansion of the solder matrix. An improvement in the mechanical properties was also recorded with the presence of increasing carbon nanotubes. An attempt was made, to correlate the increasing presence of reinforcements with the physical, thermal and mechanical properties obtained.
S.M.L. Nai, J. Wei, M. Gupta, Materials Science and Engineering A 423 (2006) 166-169

L0109 – The synthesis mechanism of Ca3Al2O6 from soft mechanochemically activated precursors studied by time-resolved neutron diffraction up to 1000°C

The reaction pathway for the Ca3Al2O6 formation up to 1300°C, from mechanochemically treated mixtures of amorphous aluminum hydroxide and CaCO3; was studied in situ by differential thermal analysis, constant heating rate dilatometry and timeresolved neutron powder diffraction. The experiment was carried out, in an open system, on a sample with the nominal Ca3Al2O6 stoichiometry. The results obtained by neutron diffractometry and thermal analysis were in good agreement with the data obtained by scanning electron microscopy and X-ray diffraction on heat-treated and-quenched samples. The synthesis path implied the formation of cryptocrystalline Al2O3; crystalline CaO, CaAl2O4 and Ca12Al14O33 as transitory phases. Finally the nucleation and growth of the single phase Ca3Al2O6 took place at 1300°C and exhibited porous structure due to CO2 and H2O release.
J.M. Rivas Mercury, A.H. De Aza, X. Turrillas, and P. Pena, Journal of Solid State Chemistry 177 (2004) 866-874

L0098 – Correlation between densification rate and microstructural evolution for pure alpha alumina

Correlation between microstructural evolution and macroscopic measurements has been investigated on pure alpha alumina under non-isothermal conditions. The densification of different as-received and milled powders of alumina has been monitored during sintering. Densification rate curves as a function of relative density are sensitive to microstructure, such as initial parameters of microstructure (agglomeration, pore size, heterogeneities), and heating schedule (thermal pre-treatment, heating rate). Densifi- cation rate curves can be correlated with microstructural evolution during overall sintering and are expected to be a good help to choose raw materials.
D. Lance, F. Valdivieso, P. Goeuriot, Journal of the European Ceramic Society 24 (2004) 2749-2761

L0086 – Evidence of the formation of a new rock-salt type compound Li2MgTiO4 and of its role on the properties of the Li doped MgTiO3

This work deals with the sintering of MgTiO3 in presence of Lithium salt and more precisely with lithium halide. These last sintering agents lead to the formation of a new rock-salt type structure Li2MgTiO4. This new phase was synthesized by a classical solid-state route and their electric and dielectric properties were characterize. The formed material is a type I dielectric material with a permittivity close to 12 with dielectric losses inferiors to 0.3% in the range of -50 to 150°C. X-ray diffraction and investigation by TEM were also performed. The influences of the formation of this new phase on the properties of MgTiO3 are described here.
J. Bernard, D. Houivet, M. Hervieu, J.M. Haussonne, Solid State Sciences 8 (2006) 598-605

L0129 – Some studies on the phase formation and kinetics in TiO2 containing lithium aluminum silicate glasses nucleated by P2O5

Lithium aluminum silicate (LAS) glasses of compositions (wt%) 10.6Li2O–71.7SiO2–7.1Al2O3–4.9K2O–3.2B2O3–1.25P2O5–1.25TiO2 were prepared by the melt quench technique. Crystallization kinetics was investigated by the method of Kissinger and Augis–Bennett using differential thermal analysis (DTA). Based on the DTA data, glass ceramics were prepared by single-, two-, and three-step heat treatment schedules. The interdependence of different phases formed, microstructure, thermal expansion coefficient (TEC) and microhardness (MH) was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), thermo-mechanical analysis (TMA), and microhardness (MH) measurements. Crystallization kinetics revealed that Li2SiO3 is the kinetically favored phase with activation energy of 91.10 kJ/mol. An Avrami exponent of n = 3.33 indicated the dominance of bulk crystallization. Based upon the formation of phases, it was observed that the two-stage heat treatment results in highest TEC glass ceramics. The single-step heat treatment yielded glass ceramics with the highest MH.
A. Ananthanarayanan, A. Dixit, R. K. Lenka, R. D. Purohit, V. K. Shrikhande, G. P. Kothiyal, J Therm Anal Calorim (2011) 106, 839–844

L0118 – Use of TMA to predict deposition behaviour of biomass fuels

Deposits formation on boiler heat transfer surfaces is one of the main operational problems associated to biomass co-combustion. This paper proposes a novel method to rank deposition propensity of biomass fuels. The method combines thermo-mechanical analysis (TMA) with ash leaching procedures and is applied here to a set of biomass fuels. Based on the TMA penetration and shrinkage traces obtained for the original and the leached ashes, the fuels are classified regarding their deposition tendencies. The results have been successfully validated with chemical analysis of the liquid fraction from ash leaching. Initial results for the behaviour of coal–biomass mixtures are also presented
A.A. Tortosa Masia, B.J.P. Buhre, R.P. Gupta, T.F. Wall, Fuel 86 (2007) 2446–2456