Thermal analysis, differential, during

Melting temperatures of as-polymerized powders are high, ie, 198—205°C as measured by differential thermal analysis (dta) or hot-stage microscopy (76). Two peaks are usually observed in dta curves a small lower temperature peak and the main melting peak. The small peak seems to be related to polymer crystallized by precipitation rather than during polymerization. 

Succinonitrile that is kept at a temperature of 80°C for forty six hours caused a violent decomposition, after being heated to 195°C to eliminate some compound solidified in a pipe. Differential thermal analysis showed that the reaction was self-accelerated with a period of induction of thirty three hours at 200°C and an hour and a half at 280 C. No heat was given off during the period of induction. Once started, the decomposition is very fast and there is no inhibitor. The cyanide ion shortens the period of induction. 

Autocatalysis happens when a reaction product, formed during reaction, acts as a catalyst which accelerates the progress of the reaction even at constant temperature. An example is the acid-catalysed saponification of various esters and related compounds. Autocatalytic reactions can be easily experimentally identified by means of differential thermal analysis methods. 

Differential thermal analysis ("DTA") is a measuring method which makes it possible to study the heat transfer during physical and chemical reactions. This can be done with small samples (usually a few milligrams). This analysis is suited for studying the thermal stability of materials and can in many cases be used to assess the thermal potential of chemical reactions. 

Differential thermal analysis (DTA) is a technique in which the temperature difference between the sample tested and a reference material is measured while both are subjected to the controlled temperature program. Differential scanning calorimetry (DSC) is a technique in which the heat flow difference between the sample and reference material is monitored while both are subjected to the controlled temperature program. Thermogravimetric analysis (TGA) is a technique in which the weight of a sample is monitored during the controlled temperature program. 

The difference of temperature between the sample under estimation and a thermally-inert reference material is continuously recorded as a function of furnace temperature in differential thermal analysis (DTA). In actual practice both TGA and DTA are regarded as complementary techniques whereby information gathered by the usage of one approach is invariably supplemented and enhanced by the application of the other method. The range of phenomena measurable during a DTA-run is found to be much larger than in a TGA-run. 

More advanced techniques are now available and section 4.2.1.2 described differential scanning calorimetry (DSC) and differential thermal analysis (DTA). DTA, in particular, is widely used for determination of liquidus and solidus points and an excellent case of its application is in the In-Pb system studied by Evans and Prince (1978) who used a DTA technique after Smith (1940). In this method the rate of heat transfer between specimen and furnace is maintained at a constant value and cooling curves determined during solidification. During the solidification process itself cooling rates of the order of 1.25°C min" were used. This particular paper is of great interest in that it shows a very precise determination of the liquidus, but clearly demonstrates the problems associated widi determining solidus temperatures. 

Liu, Q., Lu, X., Yada, R. (2005). The effect of various potato cultivars at different times during growth on starch content determined by differential scanning calorimetry. Journal of Thermal Analysis and Calorimetry, 79(1), 13-18. 

TGA. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) are other means to confirm the above structural models. Figure 4.4.8 shows the thermal analysis data for sample I. Curve (a) shows a TG datum of a mass loss about 22% after heating over 350°C. The derivative curve (b) of mass loss curve (a) clearly shows that there are at least four steps during the decomposition of the sample. This finding was further confirmed by the DTA data curve (c) shown in the same figure. It is clearly seen that there are four endothermic peaks. The DTA and TGA curves were similar for all samples. Note that the relative ratios of mass... 

Powdering, or grinding, of samples is a simple preparation method required in a number of spectrometric and spectroscopic techniques, such as x-ray diffraction (XRD), nuclear magnetic resonance (NMR), differential thermal analysis (DTA), thermogravimetric analysis (TG), or ATR-FTIR spectroscopy. Control of the particle size during grinding must be taken into account in attempting to obtain reliable results. 

Mos of the solid carbonaceous material available to industry is derived from the pyrolysis of petroleum residues, coal, and coal tar residues. Understanding the reactions occurring during pyrolysis would be beneficial in conducting materials research on the manufacture of carbonaceous products. The pyrolysis of aromatic hydrocarbons has been reported to involve condensation and polymerization reactions that produce complex carbonaceous materials (I). Interest in the mechanism of pyrolysis of aromatic compounds is evidenced in a recent study by Edstrom and Lewis (2) on the differential thermal analysis of 84 model aromatic hydrocarbons. The study demonstrated that carbon formation was related to the molecular size of the compound and to energetic factors that could be estimated from ionization potentials. 

Differential thermal analysis was used as a further measure of thermal stability. The polymer powder was pressed at 200°C in air to form a film. The film sample was heated at 10°C/minute from 25°-500°C in a nitrogen atmosphere. The the temperature at the onset of decomposition— i.e.y dehydrochlorination—as well as the peak endothermic temperature of the polymer which had already been subjected to a temperature of 200°C during film formation, were obtained from the DTA plot (Figures 3 and 4). 

Several methods have been developed over the years for the thermochemical characterisation of compounds and reactions, and the assessment of thermal safety, e.g. differential scanning calorimetry (DSC) and differential thermal analysis (DTA), as well as reaction calorimetry. Of these, reaction calorimetry is the most directly applicable to reaction characterisation and, as the heat-flow rate during a chemical reaction is proportional to the rate of conversion, it represents a differential kinetic analysis technique. Consequently, calorimetry is uniquely able to provide kinetics as well as thermodynamics information to be exploited in mechanism studies as well as process development and optimisation [21]. 

An other method to study structures during cooling and warming is differential thermal analysis (DTA) (Figure 1.25). It measures the different course of temperature between the sample and a probe, which changes its thermal behavior uniformly but does not have a phase transition in the measured temperature range. Such an instrument is illustrated in Figure 1.26. 

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