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508 articles

AN198 – Hydration of cement (C3S) at different temperatures Private content

The setting time of a cement has to be well known in order to determine its industrial applications Tricalcic silicate (C3S) is the active component of cements, giving a high resistance which obtained rapidly. A thermal investigation of C3S hydration by means of calorimetry allows us to determine the setting time and the kinetics of hydration, and also the influence of temperature on the parameters.

AN181 – Styrene – butadiene (7%) polymerization Private content

The control of polymerization assumes the knowledge of the reaction rates. It is essential to know the quantities of heat which must be removed by the cooling systems to obtain maximum productivity. The isothermal calorimetric test gives the curve for the conversion of monomer into polymer versus time. Its analysis determines the kinetics of polymerization necessary for the previous previsions. An example is given for the polymerization of a mixture of styren and butadien (7%) at different temperatures (130,140,150°C).

AN183 – Heat capacity of elastomers Private content

Elastomers show an important variation of their heat capacity near the glass transition. The knowledge of the heat capacity before and after transition is of a great utility for the uses and applications of the compounds. In DSC methods, heat capacity (Cp) is proportional to thermal power evolved when the sample is heated. Two runs are necessary in order to determine precisely Cp : the first one with empty cells (sample and reference), the second one using the same cells, with the sample. The difference between the two curves characterizes the heat capacity of the sample.

AN184 – Polymerization of polyurethan (polyol + polyisocyanate) Private content

Reticulated polyurethan is obtained through the reaction of a glycol and a diisocyanate, according to the following reaction :

X (O = C = N – R – N = C = O) + x (OH – R ‘ – OH) – –> X (O – C = NH .. R – HN – C = O)
Il l

The reaction is calorimetrically followed by using the mixing cell with a metallic menbrane (see description in C80 chapter).

AN185 – Thermal Stability of various elastomers Private content

Uses of natural rubber are numerous and well known (tires, pipes, shoes, ..). In some cases, synthetic rubbers are prefered due to their specific properties and their lower cost importance. Thermogravimetry allows to compare their resistance to temperature. The investigation is run on the following elastomers : natural rubber, butyl rubber, cis-polybutadien, polychloropren (Neoprene).

AN186 – Elastomer o-rings stability by TGA

Many elastomers are used as seals, adhesives and flexible parts. Their resistance to heat, solvents and pressure especially make them excellent candidates to manufacture gaskets and o-rings. Three different o-rings are investigated by thermogravimetry with the Labsys TG 1150°C to compare their resistance to temperature: NBR (Nitrile butadiene rubber), EPDM (ethylene propylene diene monomer) and Viton (fluoropolymer).

AN187 – Isothermal stability of polybutadiene Private content

Elastomers are often employed in severe conditions of use, particularly of temperature (joints, pipes, ..). Optimal conditions of use must be well defined in order to know when to make replacement. Isothermal thermogravimetry gives information on the resistance of elastomer to a given temperature and determines its decomposition kinetics.
The investigation is run on cis-polybutadiene.

AN190 – Thermal analysis of mineral salts used in the cement industry Private content

Cement is obtained from the baking of mixture of clays and limestones in which silica is one of the main components. Mineral salts are numerous in the initial compound, and sometimes traces of nitrates.
A controlled amount of gypsum can be added to the manufactured cement in order to retard its setting rate.
The thermal behaviour of the three different salts (silica, nitrate, gypsum) is investigated by DSC .

AN191 – Heat capacity of crude cement and clinker Private content

Heat capacity is a very important thermodynamic parameter, when determining the heat balance of a reaction. The specific heats of the different components, before and after the reaction, have to be known in order to define the correct heating of the system.
The heat capacity of crude cement and clinker is measured according to the stepwise method.
An increment of temperature is scanned, and the calorimetric peak, corresponding to the sample heated is integrated, as shown below.

AN192 – Dehydration of calcium sulfate CaSO4, 2H2O (gypsum) Private content

Gypsum is used to prepare plaster products. Small amounts of gypsum are also contained in cements. Because of the characteristic nature of the gypsum peaks, the dehydration studies can be employed for the quantitative and qualitative determination of the components in any mixtures (dihydrate, hemihydrate).
Dehydration of gypsum occurs in two stages :
CaSO4, 2 H2O –> CaSO4, ½ H2O (plaster) –> CaSO4 (anhydrite)

AN180 – Glass transition of various synthetic elastomers Private content

Elastomers are frequently used for applications at low temperatures. Their point of brittleness or glass transition must be determined with precision in order to define the minimal temperature of use. The glass transition of an elastomer can be characterized by a variation of heat capacity, which makes thermal analysis a very useful method for detecting this phenomenon.

AN142 – Tg of a solution prior to its freeze-drying

Freeze-drying of a solution consists in first cristallyzing it totally, then sublimating the formed ice on installing vacuum. In order to obtain a final product of good quality, it is necessary to install vacuum at a temperature lower than the glass temperature (Tg) of the frozen solution.

AN143 – Oxidation Induction Time (OIT) of polyethylene by DSC Private content

Oxidation induction time (OIT) is defined as the time that takes oxidation of a sample to occur under oxygen at a given temperature. Applied to polymers, this measurement enables the evaluation of its oxidative stability. As an example, the process of aging of water pipes submitted to chlorinated water could be forecasted by performing OIT analysis. The OIT measurement is defined in the ISO11357-6 standard.

AN144 – Determination of cristallinity of PET by DSC Private content

PolyEthylene Terephtalate (PET) is a polyester widely employed in daily life (e.g. in water bottles, textile fibers, credit cards). The crystallinity is a very important characteristic because it is directly related to the properties of the polymer (e.g. toughness, clarity, stability). It is defined as the ratio between the crystalline and amorphous phases in the polymer. DSC is one of the main analytical techniques to determine the crystallinity ratio in a semicristalline polymer.

AN102 – Enthalpies of fusion and heat capacities for ice and tetrahydrofuran hydrate in the range 85 to 270 K

Clathrate hydrates are non-stoichiometric solid compounds in which individual « guest » atoms or molecules of suitable size and shape are held in the cavities provided by the hydrogen-bonded lattice of the « host » water molecules. Recent reports that large reserves of natural gas are present as clathrate hydrates in permafrost regions and beneath the oceans have generated interest in the study of their thermophysical properties such as heat capacity and thermal conductivity. An understanding of such properties will be required regardless of the production scheme used to recover natural gas from these deposits.

AN104 – Thermophysical properties of the composite ceramic-salt system (SiO2/Na2SO4)

A composite ceramic-salt packed bed configuration is being developed for high-temperature thermal storage. The thermophysical properties of the more particular hybrid system SiO2/ Na2SO4 have been investigated in the range from room temperature above the melting point of the salt, 884°C. The Na 2SO4 fraction in the composite materials was varied between 20 and 50 %. The following properties were measured: specific enthalpy, coefficient of thermal expansion and thermal diffusivity.

AN089 – Heat of mixing of polymer alloys by heat of solution method Private content

Direct measurement of the heat of mixing (interaction) of polymers is not feasible due to their high viscosity. The indirect approach described here is a heat of solution method, in which a
Hess’s Law cycle is used to determine the heat of mixing from the individual heats of solution of the alloy and its constituent polymers in a common solvent.

AN078 – Starch gelatinization in pasta cooking : differential flux calorimetry investigations

Pasta cooking conditions were simulated in a differential flux calorimeter. The profile of the endothermic starch gelatinization peak was observed to directly describe the process
according the first-order kinetics. Isothermal calorimetry provide much more reliable results than do other traditional approaches allowing here assessment of the gelatinization kinetics and simple thermodynamic treatment.

AN024 – Melting and gelation of iota-kappa carrageenan by MicroDSC

Carrageenans are linear sulfated polysaccharides extracted from Red Algae and used in food processing for their gelation properties. Three types of carrageenan exist: iota, kappa and lambda. Gelation is only obtained with the kappa and iota forms. Iota carrageenan produces soft gels whereas the gels obtained with the kappa form are strong. The MicroDSC technique is well adapted to investigate the formation and the melting of such gels