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Abstract  

The peak temperature (Tp) and different temperature (ΔT) are the basic information in the differential thermal analysis (DTA). Considering the kinetic relation and the heat equilibrium in DTA, a correctional differential kinetic equation (containing Tp and ΔT parameter) is proposed. In the dehydration reaction of CaC2O4·H2O, the activation energy calculated from the new equation showed some smaller than that from Kissinger equation, but some bigger than that from Piloyan equation.

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Abstract  

There are two different opinions in the literature on the combustion mechanism of the Si-Pb3O4 system. Differential thermal analysis, X-ray diffraction and infra-red spectroscopy have been used to examine the thermal behaviour of the mixture to characterize its combustion products and judge the validity of both proposed reaction paths. It was concluded from the results that the Si-Pb3O4 system exhibits rather complicated reaction mechanism including both gas-solid and solid-solid (proceeding below oxidant decomposition temperature) reactions whose importance depends on the fuel content of the mixture.

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Abstract  

The thermal properties and devitrification behaviour of substituted InF3 glasses were studied by means of differential thermal analysis. A comparison of various simple quantitative methods to assess the level of stability of multicomponent fluoride glass systems was also made. Most of these methods are based on critical temperatures. In this paper, a new parameter,k d(T), is introduced to the stability criteria. The stabilities of several substituted InF3 glasses were evaluated experimentally and correlated with the activation energies of crystallization via this new kinetic criterion and compared with those evaluated by other criteria.

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Abstract  

The purpose of this work was to employ the differential thermal analysis (DTA) technique to compare variations in the collapse energy of the zeolite Y crystalline structure in a fresh catalyst and in the same catalyst impregnated with nickel and vanadium. A small exothermic signal in the DTA curve at 950–1150 °C indicated the collapse of the crystalline structure. The areas of the exothermic signals in the DTA curves of the two samples indicated a reduction in the curve of the metal impregnated catalyst. These results were compared with X-ray data, leading to the conclusion that metal impregnation affects the zeolite Y crystalline structure and that the DTA technique is a potentially useful tool for measuring the integrity of zeolite Y in catalysts.

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Abstract  

With the computer simulations, it has been found that in Differential Thermal Analysis (DTA) the overlapped peaks do not satisfy the linear overlapping principle, and the relationship between the overlapped peaks is rather complex that is a function of sample thermal conductivity, specific heat, quantity and latent heats, etc. If the first point where the two peaks begin to overlap is at the posterior half of the first peak curve and the two overlapped peaks can be identified by two different peaks, from the curve of overlapped peaks we can know that the temperature corresponding to the first point deviating from the sample's first phase change curve is the sample's second phase change temperature.

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Abstract  

The two step oxidation of UO2+x and reduction of U3O8 powders observed during Differential Thermal Analysis (DTA) has been exploited to determine their Specific Surface Areas (SSAs). The results obtained by this method have been compared with the Braunauer, Emmett and Teller (BET) method and are found to be in good agreement in the SSA range of 2–4 m2/gm in the case of UO2+x obtained from ADU route and 4–8 m2/gm in the case of AUC route. A precision of ±0.1 m2/gm is obtained. The maximum temperature of oxidation and reduction of these oxides are dependent upon their preparative routes such as Ammonium Diuranate (ADU) and Ammonium Uranyl Carbonate (AUC).

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Abstract  

Differential thermal analysis was carried out on the self-propagating high-temperature synthesis reaction 3TiO2+4Al+3C→3TiC+2Al2O3. The results allow the ignition temperature of the reaction to be estimated and the reaction mechanism to be identified. The ignition temperature was 900°C and the results suggest that the reaction proceeds by an initial reaction between titania and aluminium (3TiO2+4Al→3Ti+2Al2O3) and the titanium formed reacts with the carbon (Ti+C→TiC).

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A basic formula of differential thermal analysis is evolved for the case when the heat transfer coefficient between the specimen cell and the reference cell is not zero. The more general formula obtained differs from the classical formula by including the parameters of the reference cell and the heat transfer coefficient between the cells. It indicates that utilization of the classical formula is not correct if heat exchange occurs between the cells. To utilize the generalized formula, additional measurements of the temperature changes of the reference material are required. However, if the time constants of the two cells are identical, the formula can be changed to assume the form of the classical formula for DTA if a correction factor is introduced which takes into account the effect of heat exchange between the cells.

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The kinetics of strontium tungstate crystallization from sodium tungstate melts in platinum crucibles were studied by differential thermal analysis at crystallization temperaturesT 0=800, 900 and 1000° by continuous cooling at ratesR T=40, 120 and 200° per hour. Heterogeneous nuclei that first formed on the metal platinate particles in the solution during the induction periods (t) grew to small crystallites (¯l). The main crystal growth started after the development of some excess solute concentration (Δ¯C) at the end of the induction temperatures (¯T). For the first 80% crystallization, the average crystal lengths (l τ) varied with the growth time (τ) according to the relation where is the diffusion rate constant at temperatures nearT, andM is the metal salt molecular weight. The initial growth rates and the ratiosl τ 2/τ depended onΔ¯C instead ofR T The last 20% growth was controlled only by the rate of development of the excess solute concentration.

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Journal of Thermal Analysis and Calorimetry
Authors: R. Gonzales-Santos and R. Roque-Malherbe

Dithionates (CaS2O6·4H2O, SrS2O6·4H2O, BaS2O6·2H2O, MnS2O6·4H2O, MgS2O6·6H2O, CoS2O6·6H2O, NiS2O6·6H2O, ZnS2O6·6H2O and CuS2O6·4H2O) were subjected to thermodielectric analysis. The thermoanalytical curves show low temperature effects from 60 to 350°. These are related with the dehydration and decomposition of the dithionates, which could be fully correlated with the knowledge of the thermal behavior of these compouds obtained with other thermal methods.

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