Factors Influencing Slow Thermal Decomposition

Effects of Particle-Size Distribution on Thermal Decomposition 

Gamer and Gomm [1] found that lead azide crystals decompose from the surface inward and that samples of fine particles decompose at faster rates than samples of coarse particles. Other authors [48, 49] noted a similar relationship between decomposition rate of lead azide powders and particle size but did not account for these effects quantitatively. Indeed, the general lack of reproducibility in azide data may be attributed to variations in particle size among several factors known to influence decomposition rates. 

Recently, Hutchinson et al [47] measured the effect of particle size on the decomposition of lead azide. The fraction decomposed at time t a(t) for samples 

The constant kip represents the linear rate of advance of the reacting interface into the particle. The time at which a particle starts to decompose, was found to be related to r through the equation 

Despite the different approaches, the agreement in results for reaction penetration rate is remarkable. Thus the value for kip in Kleinberg and Hutchinson s analysis is 2.8 X 10 pm/sec for lead azide at 513°K which is to be compared with 2.3 X lO /im/sec derived from Fox s results at the same temperature [10,47]. 

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