DTA Experiments

Shock-modified zirconia powder was reacted with lead oxide in controlled differential thermal analysis (DTA) experiments and compared to the unmodified material by Hankey and co-workers [82H01]. This reaction yields... 

Shock-modified zirconia was studied in DTA experiments to temperatures of 1500°C [84H01]. As shown in Fig. 7.12, the temperature for transforma-... 

The shock-modified composite nickel-aluminide particles showed behavior in the DTA experiment qualitatively different from that of the mixed-powder system. The composite particles showed essentially the same behavior as the starting mixture. As shown in Fig. 8.5 no preinitiation event was observed, and temperatures for endothermic and exothermic events corresponded with the unshocked powder. The observations of a preinitiation event in the shock-modified mixed powders, the lack of such an event in the composite powders, and EDX (electron dispersive x-ray analysis) observations of substantial mixing of shock-modified powders as shown in Fig. 8.6 clearly show the first-order influence of mixing in shock-induced solid state chemistry. 

The unreacted samples and starting powder mixtures were studied in DTA experiments to investigate the effects of morphology on the shock modifica-... 

Data for the uncatalyzed polycondensation from STA (simultaneous TGA/DTA) experiments under high-flow inert gas at atmospheric pressure [8] are shown in Figure 2.28. These data also demonstrate the dependency of the overall polycondensation rate on the polymer film thickness. 

The thermal decomposition process of AP particles is altered significantly when 10% LiF is added, as shown in Fig. 7.25. The decomposition of AP particles without LiF commences at about 570 K and 50% mass loss occurs at 667 K, which corresponds to the exothermic peak. The TG curve consists of a two-stage mass-loss process. The first stage corresponds to the first exothermic reaction at 635 K, and the second stage corresponds to the second exothermic reaction in the high-temperature region between 723 K and 786 K observed in the DTA experi-... 

Initial studies were performed with [f-Bu2GaSbEt2]2 (3). DSC studies showed 3 to decompose in two steps around 190 and 215 °C as was confirmed by TGA/DTA experiments (Fig. 12) [36]. The first mass loss of almost 37% is only slightly larger than the calculated mass loss due to the elimination of two Ga-(t-Bu) groups (34%). Between 200 and 220 °C, an additional 9% mass loss was observed. Finally, a third mass loss of about 4% takes place above 500 °C, that most likely results from some decomposition of the material formed. 

Particular attention should be paid to both the stability in solution and the thermal stability. The condesation-hydrolysis equilibria of heteropolyanions in aqueous media are shown in Fig. 8. Each heteropolyanion is stable only at pH values lower than the corresponding solid line (55). Some solid heteropolyacids are thermally stable and applicable in reactions with vapor-phase reactants conducted at high temperatures. The thermal stability is measured mainly by X-ray diffraction (XRD), thermal gravimetric analysis, and different thermal analysis (TG-DTA) experiments. According to Yamazoe et al. (56), the decomposition temperatures of H3PM012O40 and its salts depend on the kinds of cations Ba2 +, Co2+ (673 K) < Cu2+, Ni2+ (683 K)[Pg.127]

DTA experiments were carried out by Elspeth C. Eberlin and Joan Z. Whiting. TMA experiments were carried out by Joan K. Lucas and Marie T. Borghetti. 

A number of additional DTA experiments were undertaken with various compositions within the binary system up to 66.6 at. % S (= MoS2 composition). In Fig. 7 a phase diagram is shown in which all results are incorporated. With respect to the above-mentioned classification of sulfide systems14), the Mo—S system, as well as the Cr—S system, exhibits Type 1 two regions of immiscible liquids one field of liquid immiscibility in the metal-rich portion at high temperatures, and a second two-liquid field in the sulfur-rich region beyond MoS2 which is not shown in Fig. 7. 

Recent high-temperature DTA experiments yielded the expected region of two liquids in the metal-rich portion above 1950 °C28),but neither the exact composition of the monotectic (liquid 1) nor that of the coexisting liquid 2 is known. The DTA results of a successful experiment with a mixture of Mo and M02.06S3, of 18 at.% S composition, definitely showed the eutectic temperature to be 1620 °C, the monotectic temperature to be 1950 °C, and a third effect at 2050 °C, which may indicate a homogeneous liquid above that temperature. 

High pressure/high temperature quenching and DTA experiments indicated that cubic a-daubreelite has a monoclinic /3-polymorph at pressures of more than 14 kb the reactions were discussed on the basis of a p-T diagram43. ... 

C The binary monotectic liquid appears in the sulfur-rich portion of the Cu—S system liquid immiscibility occurs above 1.8 S (liquid) monotectic (liquid) analogous DTA experiments with added MoS2 contents showed no change of this temperature. 

DTA experiments indicated a second transition zone 0 + a occurs between 1710 10 °C (X-phase) and 1575 15 °C (Y-phase). Finally a continuous liquidus-solidus relation characterizes the high-temperature a-solid solution series with melting temperatures of 1770 10 °C (X-phase) and 1700 35 °C (Y-phase). Melting experiments performed with various X—Y phase mixed crystals resulted in inhomogeneous quenched products. Since a small vapor loss could hardly be prevented, some exsolved molybdenum metal was always observed. 

The assignment of desorption peaks in TPD and DTA experiments as indicating different adsorption states formed on adsorption of a probe molecule at the adsorption temperature may be ambiguous, since a transformation of low-temperature adsorption states into other states may occur on steadily increasing the desorption temperature above the adsorption temperature. 

Comparison of these data with the curves of the catalytic deactivation leads to the conclusion that a higher initial activity of catalyst is related with the greater content of weakly bonded sulfur (easily replaced by oxygen in DTA experiment). Practically the catalyst deactivation results from accumulation of strongly bonded sulfur in the Mo surrounding. 

Mal tseva et al. investigated the decomposition of Ca(AlH4)2 by DTA experiments which showed several exothermic and endothermic reactions associated with hydrogen evolution [182]. From in situ X-ray diffraction studies and DSC analysis of solvent-free Ca(AlH4)2, it is evident that the decomposition proceeds in three steps (Eqs. (5.37)-(5.39)) [76] ... 

The one-dimensional form of Eq. (37) was used to describe the distribution of energy in the system. Also, the ignition temperature kinetics were used, where the cell instantly converts to TiC and AI2O3 when the ignition temperature (900°C) is reached (determined from DTA experiments). In addition, heat losses due to convection and radiation from the first cell were also taken into account. 

Figure 2. Results of the TGA/DTA experiments with RhSalenY and RuSalenY.

Critical cooling rate, Rc, can also be obtained on the basis of an empirical correlation between the crystallization onset temperature (7 ) obtained from the exothennic peaks in the DTA curves and the cooling rate, R, employed in the DTA experiment using the relation. 

Despite the theoretical advantages of the power compensated approach, the associated instrumentation is much more complex and, therefore, there are circumstances where the simpUcity of DTA has much to recommend it. DTA requires just two thermocouples and can, therefore, be used under demanding conditions. For example, high-pressure DTA experiments have been used extensively to generate phase diagrams of polyethylene and related low molar mass compounds— high-pressure DSC is rather more complex. 

Differential Thermal Analysis (DTA) experiments were carried out in dry air (Air Liquide, < 5 ppm impurities) between 25 and 500°C using a Thermal Analyst 2100 TA apparatus. Samples previously dried at 120°C were heated at 5°C.min . Preliminary experiments showed that no DTA peak was observed above 500°C. 

The discriminator is the balance within the furnace. The balance allows the measurement of any temperature changes between the sample and reference. For a DSC experiment, the individual heaters under both pans work to keep the temperatures the same (or the differential temperature equal to zero) and the power drawn to maintain this is measured. For a DTA experiment, the difference in temperature between the sample and the reference is recorded as a function of furnace temperature. The environment in the furnace is controlled. 

The development of EGD-EGA closely paralleled the introduction of controlled furnace atmosphere DTA and other thermal analysis techniques. In 1927, Orcel and Caillere (23) pointed out the importance of controlling the furnace atmosphere in DTA experiments on metallic chlorites. Some 20 years later, Berg (24) described perhaps the first EGD apparatus in which he... 

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