Glass transition, softening, crystallization, melting are events which cause a change in the characteristic properties of a compound like its heat capacity or its thermal expansion coefficient. These changes can be observed by both DSC and TMA measurements.
The Setsys 92, equipped with a furnace composed of a metal heating coil surrounding an inner silica tube, allows experiments to be carried out up to 1200°C. Thus, glasses can be characterized by different parameters such as : the glass transition temperature, the softening point, the true and average coefficients of thermal expansion ?.
With the SetsysTMA, it is possible to study the thermomechanical behavior of powder samples. The powder is contained in a crucible, the height and external diameter of which are respectively 20 mm and 10 mm. A flat-ended probe, with a diameter end of 7 mm, is brought into contact with the sample within the crucible.
For numerous industrial applications, metallic alloys need to have a high resistance to oxidation and corrosion and good mechanical properties, especially between 700 and 1000°C. Among them, Nickel-based superalloys are often used with additive elements such as Chromium to resist oxidation and Molybdenum, Titanium and Niobium to reinforce the initial metallic matrix.
Refractory clays contain only small amounts of fluxing impurities but high amounts of silica, alumina and water and therefore capable of withstanding high temperatures. A refractory clay is considered as a fire-clay if its melting point exceeds 1600°C.
Shales are very fine-grained varieties of sedimentary rocks composed of clay, quartz, mica and other minerals. Sintered carboniferous shales can be used as building materials.
Hydroxyapatite, a derivative of a calcium phosphate mineral, is the main inorganic component of vertebrate bone and tooth tissue. Sintered hydroxyapatite ceramics should have medical applications as bone fillers or artificial tooth roots.
Direct calorimetry is a method which consists in monitoring the heat production of living organisms : it gives direct information about their aerobic and anaerobic metabolism.
The SetsysTMA equiped with a cryostat allows thermomechanical measurements to be carried out at very low temperature (down to -150°C), like the determination of the glass transition temperature of polymeric materials. The glass transition temperature can be defined as the temperature at which a material loses its glass-like rigid properties and becomes more flexible in nature like rubber. This event is accompanied by a student increase of the thermal expansion coefficient of the material.
The epoxy resins are thermoset polymers often used in the elaboration of composite materials for aircraft industry. The resulting composite compounds have good mechanical properties and can be utilized up to 150°C to 200°C.
Sulfur is a base compound for the processing of rubber through the vulcanisation process. During this process a fine powdered ?-sulfur is incorporated into the crude rubber then heated. When heated, ?-sulfur will transform into ?-sulfur but this transformation must be avoided for a good vulcanisation because the ?-sulfur aggregates and then creates heterogeneity inside the vulcanized compound. It must be pointed out that the process has been monitored only on using a very slow scanning of 2 K.h-1. All the attempts at higher scanning rate were not successful : it demonstrates that only a very sensitive instrument can be used and that a conventional DSC will not be sensitive enough.
A fertilizer is generally a medium, which can supply to plant roots elements like N, P, K, Mg, S, Ca..
They are provided under a mixture of NH4NO3, phosphates, P2O5, K2O, MgO, SO3..
When they are stored these mixtures can age. A calorimetric experiment carried out at a fixed temperature can give information about the fertilizer behavior at this temperature.
A propellant is generally a mixture of two substances which decompose strongly after ignition. But also in storage conditions this mixture can react very slowly and this process must be surveyed.
It is accomplished by carrying out isothermal experiments with less than one gram of sample at different temperatures (50°C, 60°C, 70°C, 80°C for example). The lost time between two experiments is only 1000s ? 17 min. (see application sheet TN335).
The knowledge of the behavior of pharmaceutics has a certain importance as it can give information about an eventual decomposition process. For the certification of drug stability certain tests are generally required : a calorimetric experiment will enable the analysis of a substance required for prescribed conditions.
The helix-coil transition of DNA is often called the “fine structure of DNA melting”. The DSC method is so sensitive that it can detect small structural changes, even those due to cleavage of plasmid DNA with different restriction enzymes and the deletions of small portions of the DNA. Therefore, detailed DSC studies of the helix-coil transition, one of the most important physical properties related to such gene functions as replication, recombination, and transcription, are useful for further understanding of the structure of DNA.
The micro-DSC provides information on the enthalpy, temperature and heat capacity changes that accompany conformational transitions of biological molecules in solution.
hGH (or somatotropin) is synthesized in the anterior pituitary (hypophysis). A malfunction of the pituitary gland can lead to pituitary dwarfism. As treatment a hGH solution can be injected. An experiment in the temperature scanning mode will provide information about the thermal stability of the hormone : the processes of denaturation and aggregation can then be investigated.
Insulin is the hormone which reduces the blood sugar concentration. It is synthesized by the pancreas. A disturbance in the synthesis leads to diabetes. Thus diabetic people need periodic injection of insulin. This insulin is now synthesized by genetic engineering. Insulin tends to denature and aggregate when it is in injection ready solution. It is of great interest to get information about these processes, as they must be avoided in practice.
Carrageenans are extracted from red algae and used in food processing for their gelation properties. This polysaccharide shows an order-disorder transition when heat-treated. The kappa-carrageenan, obtained under aggregating conditions in the presence of K+ ion, shows a single molecular process when heated and cooled. The kappa-carrageenan forms rigid, thermally reversible, high strength gels e.g. dessert gels, petfood gels, air freshener gels. The MicroDSC technique is well adapted to investigate the formation and the melting of such gels
DPPC or DIPALMITOYL PHOSPHATIDYLCHOLINE is one of the main constituents of cell membranes. Its dispersion in water presents two endotherms : at low temperature a gel / gel transition involving a molecular packing rearrangement between two gel-state forms, and a gel / liquid crystalline phase transition, involving the melting of the hydrocarbon chains.
With a normal DSC, experiments are generally carried out at a high scanning rate (5 K.min-1). In these conditions the determination of solid-mesophase or mesophase-isotropic liquid transitions can be performed easily. Bus as far as the mesophase-mesophase transitions analysis is concerned, much smaller scanning rate are required (a few K.h-1 or less). The main drawback is that in these conditions CONVENTIONNAL DSC IS NOT SENSITIVE ENOUGH. For these reasons micro-DSC, A VERY SENSITIVE DSC IS OF GREAT INTEREST.
The capability of the micro-DSC of scanning the temperature upwards and downwards is also essential as it can provide information about the reversibility of the different transitions. This facility is especially important with the MONOTROPIC crystals which present mesophases only in the cooling mode.
Silicon carbide have good properties (tensile strength, ..) for a large range of temperatures.
These materials have transformations at high temperature, which can modify the mechanical properties.
Liquid-solid phase diagrams can be calculated using thermal analysis techniques.
In the field of very high temperatures, mixing of ceramics with a high melting point can be investigated.
Like alloys, mixtures of ceramics have almost the same applications but at higher temperatures. For example, in some new motors cars, ceramics are introduced to protect the hot zones in the cylinders.
The neodymium doped LaMgAl11O19 compounds are used in LASER manufacturing.
These compounds melt at high temperatures (around 1900°C). As crystal elaboration is carried out from a melted state bath, temperature must be well known. From a crystal nucleous soaked in the bath, a very slow stretching is carried out. The knowledge of the crystallization as well as possible supercooling must be determinate.
Carbon and graphite fibers are the only ceramic materials made by one chemical element. Their properties are well known : low expansion coefficient, good resistance to thermal shocks, excellent chemical resistance, use at very high temperatures, easy to use, high thermal conductivity.
This compound is found in large quantity in the earth’s crust and corresponds to Mg2SiO4 formula where magmas are originated from.
With TAG, it is determined that the decomposition of forsterite begins at around 1780°C.
Collagen is the principal structural protein found in mammalian tissues, such as skin, bone, cartilage, cardiovascular tissue.. Generally extracted from bovine tissue, collagen is used for clinical applications such as hemostatic sponge, wound-dressing material, suture, nerve repair.
Protease is a peculiar type of enzyme : its “mission” is to degrade other proteins. It is incorporated into washing powder : it is then the agent which will clean linen stained with blood, eggs,.. As it is to be used in a washing process it is important to know up to what temperature it can withstand denaturation
Metallic carbides are known to resist changes at very high temperatures. They have excellent characteristics of chemical inertia and mechanical resistance.
It is important to study the thermal behavior of such products for their applications.
Boride based ceramics also have high melting point. They have particularly interesting applications in reducing gases or under vacuum at very high temperature. Titanium boride (TiB2) is especially required due to its refractory properties, its hardness and its electrical characteristics.
It is used as cutting tool and for aircraft noses as well.
UO2 powder used as nuclear fuel is mixed with gadolinium oxide (Gd2O3).
Gadolinium oxide is a neutron collector. The normal working temperature of these elements is about 1600°C but we can measure the properties and behavior of these material in the case of a temperature raise up to 2000°C.
Inorganic compounds, like oxalate, have well known decomposition reactions. With the calcium oxalate, the following reactions occur when heating up to 900°C.
CaC2O4, H2O –> CaC2O4 + H2O –> CaCO3 + CO –> CaO + CO2
The temperature of the furnaces of the TAG is scanned by the controller.
Scanning rates when heating or cooling can be set from 0.01 K.min-1 up to 99.99 K.min-1.
Studying alloys requires a high temperature limit (1750°C) with accurate heating and cooling scanning rates in order to determinate melting and crystallization points and also the evolution of these points after several cycles.
The µDSCIII can be used at two levels for checking enzymes : defining the temperature limit of use of the enzyme (see application note AN285), and also for simulating an enzymatic reaction. Mixing vessels, consisting in two inlet tubes and one outlet tube, are available. In the example the reaction between a fungal gluco-amylase solution and a maltose solution is investigated, giving a transformation of the sugar.
Milk powders have different composition for various utilization from baby milk to diet milk, but all include water, under the form of humidity or bound with other constituents.
By thermogravimetric analysis, these two kinds of water can be separated.
Stale milks and climate conditions modify these concentrations, and this analysis makes it possible to control these evolutions.
A reaction can be studied with thermogravimetric method to determinate kinetic parameters. For one temperature, the derivative of the mass loss (DTG), usually constant, gives the speed of the reaction, the total mass loss, and the conversion rate.
The active gas option is used to introduce hydrogen into the furnaces and to get a rapid atmosphere change. As platinum becomes brittle at high temperatures, under hydrogen, tungsten-rhenium thermocouples and tungsten crucibles are utilized.
Silicon carbide fibers are known for their tensile strength and also thermal behavior at high temperature. It is used as fiber in composite materials.
SiC fibers are analyzed in oxidizing atmosphere, they are heated up to 1500°C during 10 hours under air flow, to simulate, for example, an entry into the earth’s atmosphere of a space shuttle. Mechanical properties can also be evaluated after this test.
This classical example shows dehydration of pentahydrate copper sulfate CuSO4, 5H2O with argon sweeping at a rate of 1 l/h.
TGA and DTA curves are plotted without any digital correction.
Note : levels, separating the successive mass losses, are clearly horizontal, especially at the beginning of the heating. The DTA curve is stable.
Symmetrical configuration is especially efficient when the available sample mass is small or when the variations in the expected mass are low.
Some catalysts can be regenerated. A quick thermal analysis is able to separate the different compounds absorbed when being used and choose the appropriate cycle of regeneration. Such products are expensive and regeneration has to be done in the best conditions.
To provide products like sulfur which are reacting with platinum at low concentrations, a “protected probe” without exposed platinum can be utilized up to 1750°C.
Alloys have transitions or phase transformations. These transformations can be detected only by DTA, so a good sensitivity and a controlled atmosphere are needed to avoid others effects (oxidation, nitridation, ..). When a transition occurs it corresponds to a variation of heat capacity which is detected by a change of baseline on the DTA curve. This transition also changes the properties of alloys.
Sensitive materials like “silicon plates” are prepared under controlled atmosphere. Gas adsorption depends on the pressure and gas nature. When heating, theses gas can be desorbed and quantified thanks to thermogravimetry.
The TAG must be used in a symmetrical configuration, to get a very high sensitivity of less than 1 µg. To be sure of the results, three cycles of temperature must be run ; the difference between the third and the second runs gives balance stability and measurement reproducibility.
Enzymes are specific catalysts of biochemical reactions. They are usually proteins which are denatured by temperature. A temperature scan gives a knowledge of the enzyme stability and thus of its working temperature range. For example, fungal gluco-amylase is used in the fermentation industry for enzymatic reaction (see application note AN286). The Micro DSCIII enables the thermal stability of the enzyme and the optimum temperature for its use to be determined.
Palm oil is mainly constituted of esters of glycerol and fatty acids named glycerides. The composition of glycerides in oil is an important characteristic to control its quality. This composition can be determined following the specific phase transitions between polymorphic forms and solid-liquid phases of the constituents. It is shown that MicroDSC VII Evo is an equipment perfectly designed to characterize palm oil in terms of research and quality control.
The melting curve of a fat is generally complex: for a given fat, there is not a melting point, but more a melting range. In processing fat, it is also interesting to know, for a given temperature, what is the amount of fat melted. The DSC technique is now widely used to determine solid-liquid ratios in fats, called the Solid Fat Index (SFI). This method is based on measuring the heat of fusion successively at different temperatures. By reference to the total melting heat, the fraction of fat melted is determined. This technique is faster than dilatometry, and give results comparable with NMR. DSC gives the possibility of tempering the fat at different temperatures prior to index determining.
The main problem caused by lipid oxidation is the formation of volatile compounds, which smell. This limits the time of conservation of different foods. When food containing lipids is heated, the temperature increases the degree of oxidation. This is especially true for edible oils used for frying. The pressure of oxygen has also an important effect on the kinetics of the oxidation reaction. The high-pressure crucible with gas flow under pressure is used in the DSC121 to characterize the effect of oxygen pressure on the oxidation of peanut oil.
For the frozen products, the DSC method can provide four different characteristics : the temperature at the beginning of freezing (especially for the solutions), the amount of ice at given temperature (also for the solutions), the temperature at the beginning of melting, the detection of possible phenomena of recrystallization. The temperature at the beginning of freezing is especially interesting for the industrial operations of extract freezing. It also defines the temperatures range of freeze drying for which the completely frozen water is evaporated under vacuum. In the example, the temperature of freezing of an extract of liquid coffee is measured.
Dry milk and whey powder contain amorphous lactose. But the storage of these products under high relative humidity induces lactose crystallization (a-lactose monohydrate). This produces a dense powder, which becomes unusable for consumption. The DSC technique enables the a-phase to be detected by measuring the dehydration of the a-lactose monohydrate. This is a very easy and useful test for checking of whey powder and dried milk.
Differential scanning calorimetry analysis can field information on the composition of multi-component systems, frequently encountered in foods, such as muscles. Muscle is a complex system consisting of different classes of proteins (myofibrillar, sarcoplasmic, collagenous). The DSC thermogram of the whole muscle shows the contribution of the proteins by their denaturation and enables identification of the main protein components (actin, myosin, sarcoplasmic proteins). Variations in this « fingerprint » of the muscles can be observed on the thermograms due to differences in the structure of proteins, different amounts of protein components, the state of the muscle. The µDSCIII is especially adapted for this type of analysis.
The surface reactivity of powdered coal depends on the thermal treatment during its preparation. The characterization of the surface is done through the desorption of solvents with different structures. For such an investigation, a special flow cell (see application sheet TN262) is used.
N-heptane is the carrier liquid, and butanol and C32H66 (both dissolved in n-heptane) are to be absorbed on the powdered coal, which has been heated under inert atmosphere at 260°C.
Fats are either liquid at room temperature (oils) or plastic (solid fats). Crude fat or oil undergoes a series of manufacturing processes before it is marketed. These include treatment with alkali to remove impurities, dehydration, hydrogenation, fractionation.. Depending on the treatment, the consistency of fat is different. The DSC method, by measuring the melting of the triglycerides contained in the fat, shows what is the effect of the manufacturing process on the crude fat.
Different types of sugars are present in food products (sucrose, fructose, maltose, saccharose..). Many of them are used in the food industry, as a powder or liquid. During food processing, they are heated, cooled, quenched according to different heat treatments. The DSC test is useful in this case to characterize the thermal behavior of the sugar when heated or cooled, to know if the sugar is in a crystalline or amorphous form according to the preparation. In the example the melting of three different sugars is measured.
Cheese is the curd of milk, basically a gel of casein. It contains mainly water, fat and proteins, the ratio of which depends on the type of cheese. If the curd is heated up to melting, a cream of cheese is obtained. The DSC test can give information on the thermal processing of cheese, also about possible storage at low temperature (refrigerator). On the example, a sample of cheese cream is cooled, then heated to show the thermal transformations in the product.
- A soft cheese and a hard cheese
DSC 131 Evo experimental conditions:
- Atmosphere: Nitrogen, atmospheric pressure
- Sample mass: about 50 mg in a 100µl
- sealed aluminum crucible
- The temperature is scanned from -50°C up to 40°C at 5°C.min-1.
When the samples of cheese are heated, different endothermic peaks corresponding to melting of fats and water are seen. When cooled down to – 50°C, a large exothermic peak is observed corresponding to the freezing of water contained in cheese.
This DSC test indicates what is the lowest temperature for a temperature controlled storage without the cheese freezing. Hard cheese can be stored at lower temperature compared to soft cheese.
When measuring melting points of fats or oils, some anomalies can be detected due to supercooling, but mainly to the fact that solid triglycerides exist in different crystalline forms (polymorphism), each of them with a different melting point. The crystalline form depends on the rate of cooling or heating, on the storage conditions (time, temperature…) These crystalline forms have an influence on the functional properties of the fat : e.g. butter spreading, milky aspects of oils.
The reaction between two organic liquids most often liberates a large amount of heat. In an industrial reactor, when the reaction takes place, large volumes of each component are involved. It is important to know what will be the heat evolved and the rate of reaction, in order to drive correctly the reactor.
The calorimeter is well adapted for this type of simulation. As many reactions occur in alkaline medium, the mixing vessel with metallic membrane is indicated for these experiments, like the reaction between formol and butanal in soda.
Starch is a vegetal polysaccharide from different origins (potato, maize,..). It is industrially used in many foodstuffs, especially in fast cooking products. When mixed with water at low temperature, wetting of starch occurs. When heated in water, a gel is formed. The temperature of gelation depends on the origin of starch. The mixing vessel with membrane is used to investigate the wetting and gelation of starch in water.
The knowledge of thermal stability of products to be transformed under heating is of the first importance. This is often the case in food industry where raw products are heated in reactors, e.g. coffee when roasted.
It appears that during the roasting operation, large quantities of heat are liberated.
In order to determine the risk of thermal hazard or spontaneous ignition of the product, a simulation is operated by calorimetry, using the vacuum high pressure vessel. This vessel enables a pressure of inert gas (20 bars) to be applied during the reaction, in order to simulate the real industrial conditions.
Many solid porous compounds, especially zeolites, are well known for their adsorbing properties. In order to measure their adsorption capacity, a special experimental set-up has been designed for the C80 calorimeter.
This device allows the characterization of the adsorption of vapor on a solid under reduced pressures. The liquid to be absorbed is initially frozen then kept at a well-defined temperature, determining a well-known vapor pressure.
This vapor is absorbed on the solid, previously regenerated under vacuum. The solid is contained in a vacuum high-pressure vessel. An example of the use of such a device is given by the adsorption of benzene vapor on a zeolite.
The heats involved during dehydration processes of some mineral compounds can be used for energy storage as the heat of vaporization of water has a high value (? 42 kJ.mol-1). Hydrated salts are especially interesting for such applications. Calorimetry is the ideal method for testing the capacity of energy storage and for determining the range of temperature in which the transformation occurs. The gas circulation normal pressure vessel is used for such an investigation. Water vapor during dehydration is evacuated through the tube.
Carrageenan is a polysaccharide, largely used in the food industry especially for its gelation properties. In solution, the polysaccharide exhibits ion selectivity. A specific site binding is observed with certain ions in preference to others. The calorimetric test is used to measure the heat of binding of iota carrageenan with different ions from mineral salts.
The determination of drug polymorphism is an important problem for the pharmaceutical research. Depending on the polymorphic form present in a drug, its characteristics can be very different. The detection of the polymorphic forms is not easy. DSC has been used with some success, but cannot be used for all products (thermal stability limitation). As the polymorphic forms have different behaviors especially dissolution properties, the calorimetric test of dissolution is used to investigate their differentiation.
Raw edible oils contain a certain amount of free fatty acids, which have to be neutralized before their use. In industrial plants, an excess of soda is added to neutralize the free acidity. The problem is the adjustment of the amount of soda to be added, knowing the oil acidity. The simulation of the operation is made in a calorimeter on different edible oils, using the reversal mixing vessel.
The dissolution test is a standard one for the mixing calorimetry. It is a way to check the calibration of the calorimeter. The dissolution of potassium chloride in water is used as a reference test.
With the C80 calorimeter, the best results are obtained with the reversal mixing vessel.
Four forms of calcium sulfate are known : dihydrate : CaSO4, 2H20 (gypsum), hemihydrate : CaSO4, ½ H20 (plaster) and two anhydrites CaSO4 : natural and insoluble anhydrite and soluble anhydrite III (obtained by heating plaster up to 200°C).
Plaster and anhydrite III, which are soluble in water, are used in the building industry, because of their setting properties.
The reversal mixing vessel is particularly well adapted for the investigation of plaster setting. Water and plaster are initially separated in the vessel, then mixed.
The heat capacity determination by the calorimetric method is well known and very easy to run. The sample is heated in the calorimeter, and the heat flow detected by the heatflux transducer is directly proportional to its heat capacity. In practice, two successive tests are necessary : one test with empty vessels on both sides (measure and reference), and a second test with the sample in the “measure” vessel, the “reference” vessel remaining empty. The experimental conditions must be strictly identical for both experimentation. The heat flow deviation between the two curves characterizes the variation of the sample heat capacity versus temperature.
Starch is a base product in foodstuffs, especially for rapid cooking.
When the grains of starch are in the same time in presence of water and heated an effect of gelation occurs, for a well-defined temperature. This temperature depends on the origin of the starch.
The storage of chemical heat consists in using the reversible endothermic and exothermic reactions of a chemical equilibrium. This is the case of the reaction between two solids materials : hydrated baryta and potassium nitrate :
Ba(OH)2 – 8H20 + 2KNO3 <--> Ba(NO3)2 + 2KOH + 8H20.
The calorimetric standard vessel enables the investigation of a large amount of mixture at low heating or cooling rates. In order to have a better homogeneity of the solid mixture during the reaction, the reversing mechanism of the calorimeter can be used to shake the mixture.
In chemical industries, the determination of the thermal hazards or decomposition risk for organic products is one of the most important experimentation to be run before any transformation or storage of the products.
The thermal methods give an interesting mean of experimentation and simulation for such a determination. The organic sample set in a closed standard high pressure vessel is heated quickly at a fixed temperature and the thermal behavior of the sample is observed by recording the calorimeter signal.
The standard high-pressure vessel is well adapted for the heating of solutions above 100°C. An interesting application is the detection of the limit of solubility of salt mixtures. The corresponding temperature is detected when the calorimetric signal changes abruptly, showing the end of the thermal effect of dissolution. In the example a mixture of potassium and sodium chlorides in water is investigated at different ratios.
Zeolites are hydrated silicates of aluminum, and either sodium or calcium or both, of the general formula Na2O-AI2O3-nSiO2.xH2O. They are well known for their adsorption and catalyst properties, used more and more for industrial applications. An example of adsorption of water vapor on a zeolite is given to show the possibilities of the experimental set-up described on application note TN231. The amount of adsorbed water depends on the type of zeolite, the temperature and the pressure of water vapor. The calorimetric test is very useful to measure the adsorption capacity of a zeolite and to compare the efficiency of different zeolites.
Isothermal calorimetry is well adapted to measure the adsorption capacity of zeolite for different compounds. The incremental vapor pressure method is used in the following example, showing the adsorption of benzene on a zeolite. The experimental adsorption device, described on application note TN231, allows running such an investigation.
Thermogravimetry is frequently used in characterizing the natural or synthetic types of catalysts and zeolites, and especially in distinguishing the loss of adsorbed and structural (hydroxyl) water. For their use as adsorbents or catalysts, it is also important to know how the dehydration process occurs. An example of determination of adsorbed and structural water in a catalyst is shown hereunder.
CO2 Catalyst catalysis barbon dioxide
The latent heat is the energy evolved by a material when it undergoes to a structure change. The effective storage of this heat requires the use of materials with large melting heat, which can be recovered during solidification. For latent heat storage below 130°C, hydrated salts are frequently used. Mostly they are tightly encapsulated in order to prevent evaporation or contamination of the material.
A glass ampoule containing a large amount of FeCl3 – 6H2O is placed in a standard vessel, and the melting of the hydrated salt is easily investigated.
The temperature range of the C80 calorimeter is large enough to investigate some phase changes or transitions in materials. The experimentations are run on large amounts of sample, with low heating rates. That gives precise quantitative measures, and solves also the problem of sampling for some inhomogeneous materials.
Using a standard vessel, a sample of ammonium nitrate is heated at 0.2K.min-1 for detecting different characteristic transitions.
The CALVET microcalorimeters are particularly well adapted for the determination of differential heats of adsorption of reactive gas on solid catalysts (see P.C. GRAVELLE, Catal.Rev.Sci,1977, 16(1), 37-110).
A well-known volume of reactive gas is injected on the catalyst. The adsorbed volume is evaluated and the heat of adsorption measured. Then the curve of variation of the heat of adsorption versus the degree of surface coverage can be drawn.
Anthracite is a higher species of coal, which contains a low content of volatiles. A rapid characterization of anthracite is obtained by the proximate analysis. This industrial determination gives the contents of moisture, volatiles, fixed carbon and ash in the sample.
The proximate analysis is easily achieved by thermogravimetry according to the following scheme :
– Heating to 110°C and isothermal level during 5 minutes => moisture
– Rapid heating to 950°C under inert gas and isothermal level during 10 minutes => volatiles
– Switch from inert gas to oxygen at 950°C => fixed carbon
– Test residue => ash
The proximate analysis, as described in application sheet AN222, allows classifying a coal and gives information for its industrial use. Coal is particularly classified according to its volatiles content : anthracite (8 to 18 %), semi-bituminous (18 to 26 %), bituminous (26 to 40 %), semi-bituminous (40 to 50 %).
The thermogravimetric test allows giving a rapid result for a coal.
All the operations heating and gas switching are automatically achieved by the controller associated with the thermoanalyzer.
The thermogram of coal combustion (application note AN214) shows two steps in the oxidation reaction. The first peak has been often associated with the combustion of volatiles.
But when a coal is maintained under oxygen at 110°C in a thermobalance, a mass increase is detected, corresponding to an oxygen adsorption on coal. The result of this interaction is the modification of coal structure and the formation of complex compounds. The first peak detected by DSC seems to be associated to this coal transformation before the burning of fixed carbon.
The combination of thermal analysis with evolved gas analysis is frequently used in order to characterize the exhausted gases of a reaction. Such a connection requires a continuous circulation of gas through the instrument, with an easy fitting of the EGA apparatus. The open structure of the Calvet DSC111 is particularly interesting for such a combination. The quantitative measurement of both heat evolved by a sample and the amount of gas emitted is made possible, giving a great interest for the better comprehension of the reactions occurring during the experiment. This is particularly powerful for gas-solid interactions, like adsorption in the catalysis field. Two types of combination are described : DSC-gas chromatography and DSC-mass spectrometry using the silica reactor (see application note TN225).
The use of the DSC-GC combination (see application note AN226) is illustrated by the investigation of hydrogen adsorption on a platinum catalyst, called Eurocat. The catalyst contains 6.26% platinum deposited on silica.
Hydrogen is diluted to 5.4% in argon, and injected on the sample through an injection loop (0.5 ml), in the carrier gas (argon). Before adsorption investigation, the catalyst is initially pretreated in the DSC by heating under hydrogen up to 450°C, and held at this temperature during 2 hours. Then, the surface of catalyst is completely desorbed under a flow of argon, before cooling at the temperature of investigation.
After adsorption of a gas on a catalyst, it is interesting to know what type of adsorbed species have been formed. One mode of investigation is to desorb the catalyst by heating and record the desorption thermogram : that is the temperature programmed desorption. On the thermogram, peaks will appear corresponding to the different species formed during the gas adsorption. An example is given by the desorption of a platinum catalyst after hydrogen adsorption (see application note AN227).
The platinum catalyst, described on the application note AN227, has relatively large amount of platinum. In order to give a limit of detection to the DSC-GC combination device, an experimentation has been run on a catalyst containing only 0.2 % Palladium (support : alumina), for the adsorption of carbon monoxide (10% in helium). The effect of metal dispersion on the support is also investigated for a catalyst containing 0.75% Palladium.
Helium is used as a carrier gas. Catalysts have been initially preheated under H2 at 250°C, then desorbed under helium.
If the calorific value of coal is of first importance, the value of the enthalpy is also necessary to establish the heat balance of the system under study.
By the isothermal drop method, the total heat necessary for heating the sample from a temperature T1 (generally ambient temperature) up to higher temperature T2, is measured.
The method is used for measuring the enthalpy of a powdered coke (30-40 mesh) at different temperatures.
The surface reactivity of powdered coal depends on the thermal treatment for its preparation. The characterization of the surface is done through the adsorption of solvents with different structures. For such an investigation, a special flow cell (see application note TN220) is used.
n-heptane is the carrier liquid, and butanol and C32H66 (both dissolved in n-heptane) are to be adsorbed on the powdered coal, which has been heated under inert atmosphere at 260°C.
Melting of ashes is of a high importance in the use of coal. According to the conditions of use, it can be interesting or forbidden. Melting of ashes depends on their chemical composition, and also the type of atmosphere in which melting occurs.
A coal has rather fusible ashes when the melting point is about 1300°C. If melting does not occur below 1500°C, ashes are said refractory.
Setsys DTA is used to characterize the melting of two ashes.
Coal is particularly characterized by its calorific value which essentially depends on its carbon and volatile contents. The combustion of coal occurs on a wide range of temperature (from 200°C up to 600°C). Coke, which is a high carbon content product, burns at higher temperature, with only a step of combustion. Carbon graphite is an ideal case of combustion, the reaction yielding only water and carbon dioxide.
Coke is especially used in steel industry and in metallurgy. Its calorific content varies from 6500 to 7500 cal.g-1, and the combustion gives very few ashes.
The combustion of coke can be investigated by DSC. But, as the sample masses are generally little, it is necessary to know what is the influence of the mass on the determination of the heat of combustion.
In the case of coal products, the calorific value is usually determined with bomb calorimeters. This type of method is accurate, but does not yield information on the combustion reaction. Differential Scanning Calorimetry allows another approach of the combustion investigation. The heat of combustion is measured, referring to a standard coal with a well known heat content (in this case coal 7 DE from DSM Holland).
According to the temperature of the test, different types of products are obtained during the pyrolysis of coal : gases, chars, condensable products (water, ammonia), benzols and coke as final product above 1000°C. The production of gases (hydrogen, methane, ethylene,..) begins at about 350°C. After this distillation, an intermediary coke is obtained at about 600°C. The formation of this compound and the production of gases is investigated by DSC, in an inert atmosphere.
The oil of bituminous shale, as described on application note AN217, burns in three different steps between 100°C and 500°C.
Coal shale is often used as a fuel in cement industry.
The same mass of sample is heated under oxygen in the CALVET HT1000 calorimeter. Oxygen is introduced in the crucible by means of a small tube plunging in the sample.
The interest of bituminous shales is growing, due to its organic part. But the cost of oil extraction from shale is a limitation. Some investigations are done in order to use the oil shale without treatment, as a fuel, like in cement industry. In this case, it is necessary to determine the range of temperature in which combustion of the organic part occurs, and also the heat evolved during combustion. The calorimetric test is well adapted to give those two experimental values. The CALVET HT1000 calorimeter is used for investigation of large samples at low scanning rates. Two bituminous shales with different oil contents are investigated.
Peroxides are known as very unstable materials : concentrated material may react explosively with combustible materials. The knowledge of the thermal stability of such a product must be well known before its use in organic reactions, or also storage. A sample of peroxide in solution in cyclohexane is investigated in a sealed crucible.
Diethylenglycol is largely used in organic chemistry due to its excellent solvent properties. The sodium derivative of diethylenglycol is an intermediate for organic synthesis. Diluted in diethylenglycol, diethylenglycol-Na has a relatively good thermal stability up to 250°C. Decomposition of DEG-Na at different concentrations in DEG is investigated in sealed crucibles. The pressure developped during decomposition is about 50 bars or more.
Ortho-nitrophenol is a hazardous solid used as an intermediate in organic synthesis. The thermal stability of the compound is investigated in different crucibles, with variable internal pressures. According to this pressure, the decomposition phenomena is very different.
Azodicarbonamide formula is NH2 – CO – N = N – CO – NH2. The compound belongs to the family of azo dyes. Azodicarbonamide decomposes at about 200°C. But the decomposition phenomena largely depends on the pressure above the sample. Different tests are run in an open crucible, a sealed crucible and a controlled high pressure crucible, in order to show that the pressure on the sample has a great influence on the decomposition rate.
2,4-dinitrotoluene (CH3 – C6H3 – (NO2)2), obtained by nitration of toluene, is an intermediate for organic synthesis and especially used in mixtures of explosives.
2,4-dinitrotoluene has a dangerous fire hazard. The decomposition of this material is investigated at different scanning rates, and the kinetics parameters are determined according to OZAWA and KISSINGER methods.
Nitrocumene (NO2- C6H4 – CH – (CH3)2) is an organic liquid used in synthesis. This liquid is thermally stable at medium temperatures and begins to decompose at about 250°C. The kinetics parameters of the decomposition are determined according to the FREEMAN-CAROLL method.
Paranitroacetanilide (NO2 – C6H4- NH – CO – CH3) is obtained by nitration of acetanilide, in concentrated sulfuric acid solution.
Hydrolysis of paranitroacetanilide is thermally stable up to 270°C. The kinetics parameters of the decomposition are determined according to the FREEMAN-CAROLL method.
Polyacrylonitrile (CH2 – CH -)n is mainly transformed in synthetic fibers or
l used for elaboration of different copolymers.
CN Polyacrylonitrile is thermally stable for
medium temperatures. Above 250°C, it undergoes a very strong decomposition. The kinetics parameters of the reaction are determined according to the FREEMAN-CAROLL method.
Investigation of azobisisobutyronitrile (ABIBN) in solution in di-N-butylphtalate is used as a reference test for the determination of kinetics parameters by the FREEMAN-CAROLL method. A single test is only needed to determine reaction order, reaction rate and activation energy.