| Combustion synthesis (CS) is a novel method for synthesizing and producing advanced inorganic materials, which provides energy- and time-saving advantages over conventional processing routes. The thermal explosion (TE) mode of CS was found to be suitable for the synthesis of intermetallic compounds, metal- and intermetallic-matrix composites.Since ignition temperature is very important in optimizing TE processing routes and establishing appropriate safety precautions for its industrial operation. To provide a reasonable method for determination of the ignition temperature, the ignition phenomena in the TE process of synthesizing TiAl3 were investigated. According to the critical conditions introduced by the Semenov's theory of spontaneous ignition, the criterion for evaluating the ignition temperature (T c) of the thermal explosionsystem at a linear heating rate (?) was derived to be dT/dt = ?, d2T/dt2= 0.Applying this criterion, the T c s of the thermal explosion (TE) synthesis of Ti-75at%Al samples at different heating rates were evaluated using non-isothermal differential scanning calorimetry (DSC). And the ignition temperature (Tc0) for isothermal TE is predicted to be 683 癈 by^he multiple linear regression (MLR) of T cs evaluated according to the criterion at different heating rates, which closes to the range of 700 ~ 705 ? obtained from the isothermal DSC observation. These two Tc0 values prove that the T cs evaluated at different heating rates are reliable, and the criterion for evaluating the T c of the TE system at a linear heating rate is feasible for TE synthesis in binary metallic TE systems like Ti-75at%Al system.Many experimental factors such as heating rate, particle size, green density of____________________________________ Abstract__________________________________________sample have all been found to influence the T'c in TE synthesis. However, the effect of sample volume on T c was rarely reported. In order to explore the relation between T'c and sample size in the TE process of synthesizing TiAl3, the above testified criterion was applied to the linear heating DSC curves of Ti-75at.%Al samples with different sizes. The result shows that the T'c has a strong sample size dependence. The larger the sample size, the lower is the ignition temperature. By linear fitting of data points in 2lnT"c-ln(1/r+1/h) Vs -E/RTC plot, the activation energy of the ignition process is evaluated 169kJ/mol by a data-fitting method derived by applying the Semenov theory of spontaneous ignition to the cylindrical samples with different sizes.Despite some successes have been made in the applied investigations of CS, the studies on kinetic mechanism of CS process are still stagnant because of the complex nature of combustion reaction: non-equilibrium conditions, higher-temperature and extremely large temperature gradients. Nowadays, the research on the kinetics of CS has lagged behind that on application. Such a situation is more obvious in the research field of TE synthesis.In the evaluation of the kinetic parameters of TE synthesis, several remarkable papers have emerged using conventional thermal analysis (TA) methods in recent years. Unfortunately, some kinetic investigations are troublesome in identifying the complexities of the solid-state reaction mechanism or even obtaining the reasonably consistent kinetic results from isothermal and non-isothermal data of identical process, due to the misuse of thermokinetic analysis methods. In order to identify the complexity of the chemical kinetics without the distortion by self-heating effect, Friedman method was applied to the non-isothermal differential scanning calorimetry(DSC) data of the TE synthesis reaction of Ti+3Al-TiAl3. According to the shape of the dependence of activation energy (E) on extent of conversion (a), three processes were determined with the E of 109, 175 and 89 kJ/mol. These values of E are close to those of chemical reaction of Ti+3Al-TiAl3, the diffusion of Al between Ti and Al through TiAl3-laye...
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