Thermal analysis characteristics

An examination of the magnetic susceptibility, thermal analysis characteristics, and X-ray powder patterns of samples of V02+ c( — 0.02 x < 0.03) prepared by heating V205-V203 mixtures in silica tubes has shown that the homogeneity range for V02 is very narrow.393"... 

The standard thermal analysis characteristics acting during plastic injection molding are conduction, convection and radiation. Standard analyses show that special attention must be paid to the set-up of the boundary conditions for these physical characteristics, depending on specific aspects such as thermal contact resistance (TCR). 

Polypropylene molecules repeatedly fold upon themselves to form lamellae, the sizes of which ate a function of the crystallisa tion conditions. Higher degrees of order are obtained upon formation of crystalline aggregates, or spheruHtes. The presence of a central crystallisation nucleus from which the lamellae radiate is clearly evident in these stmctures. Observations using cross-polarized light illustrates the characteristic Maltese cross model (Fig. 2b). The optical and mechanical properties ate a function of the size and number of spheruHtes and can be modified by nucleating agents. Crystallinity can also be inferred from thermal analysis (28) and density measurements (29). 

Thermal analysis of homopolymer samples are simpler than those of blends. Separate thermal analysis of individual polymer components are made before doing the same for a blend in order to get more accurate and proper information on thermal characteristics. 

The thermal reactions of CaC204 H20 have been very fully investigated and this substance has been used as a thermal analysis reference material [1058], Dehydration, decomposition to the carbonate, and dissociation to CaO are all well separated, though kinetic characteristics are influenced by the presence of C02, 02 and H20 as well as by the reaction conditions, including heating rate, sample size, and sample container. Kinetic parameters for the oxalate decomposition reaction have been summarized by Gurrieri et al. [1059]. Values of E are close to 314 8 kJ mole-1. Decompositions [1057,1060,1061] of Sr (643—743 K) and Ba (663—743 K) oxalates involves some disproportion of CO, yielding residual carbon. 

This second group of tests is designed to measure the mechanical response of a substance to applied vibrational loads or strains. Both temperature and frequency can be varied, and thus contribute to the information that these tests can provide. There are a number of such tests, of which the major ones are probably the torsion pendulum and dynamic mechanical thermal analysis (DMTA). The underlying principles of these dynamic tests have been covered earlier. Such tests are used as relatively rapid methods of characterisation and evaluation of viscoelastic polymers, including the measurement of T, the study of the curing characteristics of thermosets, and the study of polymer blends and their compatibility. They can be used in essentially non-destructive modes and, unlike the majority of measurements made in non-dynamic tests, they yield data on continuous properties of polymeric materials, rather than discontinuous ones, as are any of the types of strength which are measured routinely. 

Differential Thermal Analysis (DTA). One of the characteristics of a rubber useful in tire rubber compounds is that it is amorphous at room temperature but readily undergoes strain induced crystallization. For this reason, copolymers were prepared in order to appropriately adjust the crystalline melt temperature. 

The phase transformation relationships for the solvatomorphs of naproxen sodium have been reported [71], The dihydrate phase is obtained upon crystallization from water, and a monohydrate phase could be prepared by the dehydration of the dihydrate phase in a desiccator (RH = 0%) for two days. The anhydrate phase could be obtained from either the monohydrate or dihydrate by drying the substance in an oven at 120 °C for two hours. Thermal analysis data was used to demonstrate the existence of two types of water in the dihydrate phase, and that each could be removed at a characteristic temperature. 

In a manner similar to that just described for differential thermal analysis, DSC can be used to obtain useful and characteristic thermal and melting point data for crystal polymorphs or solvate species. This information is of great importance to the pharmaceutical industry since many compounds can crystallize in more than one structural modification, and the FDA is vitally concerned with this possibility. Although the primary means of polymorph or solvate characterization s centered around x-ray diffraction methodology, in suitable situations thermal analysis can be used to advantage. 

One of the more recently exploited forms of thermal analysis is the group of techniques known as thermomechanical analysis (TMA). These techniques are based on the measurement of mechanical properties such as expansion, contraction, extension or penetration of materials as a function of temperature. TMA curves obtained in this way are characteristic of the sample. The technique has obvious practical value in the study and assessment of the mechanical properties of materials. Measurements over the temperature range - 100°C to 1000°C may be made. Figure 11.19 shows a study of a polymeric material based upon linear expansion measurements. 

There are eight different combinations of outcomes from the thermodynamics, impact sensitivity, and thermal analysis considerations. Each combination has unique characteristics, and hazard progression can be established (see Table 3.6). 

Zeman, S., "The Relationship between Differential Thermal Analysis Data and the Detonation Characteristics of Polynitroaromatic Compounds," Thermo-chimica Acta, 41 (1980). 

These parameters need to be considered for reactions that go towards the intended completion as well as for possible upsets (see section C). Measuring methodologies for determining characteristic material property values (Stoffkenngrofcen), e.g., differential thermal analysis ("DTA"), calorimetry, and adiabatic experiments, and their possible use and applications are given in the literature /1, 2, 3, 41. 

Figure 1.1.20 shows the differential thermal analysis (DTA) data for the cores, of chromium hydrous oxides particles prepared in the absence of hematite, and of coated particles. It is obvious that the latter behave as the coating material, when alone. This example clearly indicates the possibility of having the surface site characteristics of chromium hydrous oxide induced onto ellipsoidal iron oxide particles. The latter morphology cannot be achieved by diiecl precipitation of the same chromium compound. 

Physical characteristics of active API (aspect, thermal analysis, particle size distribution, optical activity, polymorphic forms, moisture content, loss on drying, microbial content, etc.)... 

Evidence for the presence of hydrosilicates in the preparations could also be obtained from differential thermal analysis (2). An examination of the curves given in Fig. 2 showed an endothermal deflection at 125-175° C., which must be caused by the expulsion of adsorbed water, since the X-ray diffraction diagram revealed no change. Upon further heating, the preparations display an endothermal deflection characteristic for the compounds present, viz. ... 

An autocatalytic decomposition can be followed by isothermal aging and periodic sampling for a chemical analysis of the substance. The reactant concentration first remains constant and decreases after an induction period (Figure 12.7). This is characteristic for self-accelerating or autocatalytic behavior. The chemical analysis may also be replaced by a thermal analysis using dynamic DSC or other calorimetric methods, following the decrease of the thermal potential as a function of the aging time. 

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