Study of kinetics and mechanism of sintering under constant heating rates

The kinetics and mechanism of the molybdenum and sodium fluorides sintering under non-isothermal conditions, with constant heating rates from 2-50degC/min, have been studied. It was shown that the value of the expression [d 1n C/d(1/T]/[d 1n y/d(1/T)], which characterizes the responsible mass transfer mechanism is 1.55 for molybdenum compacts and approximately equal 2.55 for the sodium fluoride. Experimental activation energy for the early stage of the molybdenum compact sintering is equal to approximately 93.000 cal/mol. The temperature distribution of activation energies of the sintering process of sodium fluoride is analogous to the temperature distribution of the relative linear shrinkage, and is continually increasing from 40100 cal/mol up to 48500 cal/mol. After reaching the maximum value the activation energy starts decreasing and is 3/000 cal/mol. The obtained results show that in the case of molybdenum compact sintering the volume diffusion is predominant mechanism, but during the sodium fluoride sintering the most probable is the simultaneous role of the grain boundary diffusion and volume diffusion mechanisms