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Journal of Thermal Analysis and Calorimetry
Authors: Abduljelil Iliyas, Kelly Hawboldt, and Faisal Khan

Introduction With safety issues associated with processing, storage, and transportation of sulfide mineral ores/concentrates due to their self-heating propensity in the presence of air, increasing emphasis is placed upon

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Abstract  

In order to identify the kinetic process of self-heating in DSC experiment for Ti+3Al→TiAl3 reaction, two approaches, linear-fitting approach developed from Semenov"s theory of spontaneous ignition and variation of Friedman method, were carried out with cylindrical Ti-75 at% Al samples. Following these approaches, two identical activation energies are obtained as 16915 kJ mol-1 and 1705 kJ mol-1, respectively. Compared with the activation energies of reactions and interdiffusions between Ti and Al, the possible rate-controlling process of self-heating in DSC experiment for Ti+3Al→TiAl3 reaction is the interdiffusion between Ti and Al through TiAl3-layer.

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Abstract  

It has been shown that the exothermic decomposition of KMnO4 in vacuum is accompanied by a significant self-heating effect. It manifests itself in the reduction of the molar enthalpy of the reaction, determined by the third-law method. In comparison with the value 138.3±0.6 kJ mol−1 that is valid for the decomposition of KMnO4 under atmospheric pressure at 493–553 K, the molar enthalpy in vacuum (10−4-10−7 bar) at 484–511 K varies in the range of 136 to 126 kJ mol−1. This is related to the reduction of the thermal conductivity of residual air in the furnace and, as a result, to the self-heating of the reactant, that accelerates the exothermic reaction. A simple method of evaluation of the self-heating effect has been developed. By analogy with the known method for evaluation of the self-cooling effect, it is based on the determination of the molar enthalpy by the third-law method at two different temperatures. The increase of sample temperature above the furnace temperature Tf in the case of the exothermic decomposition of KMnO4 in a high vacuum and T f≥490 K reaches a few tens of degrees.

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Results of testing the liability of various samples of fertilizer grade ammonium nitrate (AN) to self-heating are presented. Test methods applied comprises: DTA, TG, determination of mass loss at constant temperature, pH-measurement of aqueous solutions. The assessment of liability to self-heating is based on comparison to the relevant results of a standard AN product.

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Metastable effects on martensitic transformation in SMA

Part VIII. Temperature effects on cycling

Journal of Thermal Analysis and Calorimetry
Authors: V. Torra, C. Auguet, A. Isalgue, F. Lovey, A. Sepulveda, and H. Soul

Abstract  

The use of Shape Memory Alloys (SMA) in technical applications as damping in civil engineering structures requires the characterization of the alloy for each specific application. This involves the evolution of the mechanical properties and damping capacity with the number of cycles, frequency, maximum deformation, applied stresses, and the evolution of the alloy with aging time and temperature. In particular, the temperature effects associated to self-heating need to be evaluated. In continuous cycling the effects of latent heat, the associated dissipation induced by the hysteresis, the heat flow to surroundings and the cycling frequency induce different states of temperature in the specimen, which in turn produces changes in the transformation-retransformation stresses. In this article, the temperature effects associated to cycling are outlined for different cycling frequencies. The results show that, for relatively faster frequency the temperature arrives at an oscillatory state superimposed to an exponential increase. For lower frequencies, some parts of the sample attain temperatures below room temperature. The experimental results are represented with an elementary model (the 1-body model or the Tian equation used in calorimetric representation) of heat transfer. For the higher fracture where life requirements are associated to damping in stayed cables for bridges, the results show (for the NiTi alloy) a reduction of the hysteresis width as the frequency increases for deformations up to 8%. For reduced deformation, under 2% appears an asymptotic behavior where the frictional area is practically independent of the cycling frequency (up to 20 Hz). In addition, it is shown that more than 4 million of working cycles can be attained if the maximum applied stress is kept below a threshold of about 200 MPa. Although under this condition the deformation must remain lower than 2% a reasonable damping capacity can still be obtained.

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commercial Sanyo 18650 lithium-ion batteries under adiabatic condition by VSP2 calorimeter method and obtained the essential parameters of thermal hazard via VSP2, such as initial exothermic temperature ( T 0 ), self-heating rate (d T d t −1 ), d P d t −1

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data, such as temperature and pressure traces versus time. A PC-controlled adiabatic calorimeter (VSP2), the well-known turn-on heat-wait-search (H–W-S) mode for detecting the self-heating rate, was adopted for VSP2. Under heating conditions, the main

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temperature ( T 0 ), heat of decomposition (Δ H d ), maximum temperature ( T max ), maximum pressure ( P max ), self-heating rate (d T d t −1 ), pressure rise rate (d P d t −1 ), etc., by using differential scanning calorimetry (DSC) and vent sizing package

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Fauske & Associates, LLC [ 22 ]. The test data of a sample such as self-heating rate; control reaction of temperature, pressure, and time and reaching maximum heating temperature and pressure; and other related data were obtained by VSP2. In addition, the

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