Summary and Appraisal

It should be emphasized that most data on energy levels in the solid are derived from optical absorption measurements and photoconductivity studies, and the assumption is usually made that these optical values can be converted to thermal energies appropriate to thermal decomposition. Most of the optical data apply to bulk material. The effect of the surface (where decomposition takes 

As originally indicated by direct observation, decomposition can be described simply by a contracting envelope model. It seems unlikely that curve-fitting based on detailed kinetics data will provide much further insight into reaction mechanisms unless careful control is made of such factors as particle size, purity, and defect content. The recent results for lead azide suggest that many of the anomalies disappear when particle size is taken into account. It would be interesting to discover how many of the discrepancies in behavior, previously reported by different workers on the same material, could be resolved by closer attention to this single factor. 

The effects of impurities are more difficult to quantify. Recent work has paid attention to the preparation and characterization of ultrapure materials and the possibility of introducing ionic impurities and new energy levels into the band gap of the parent azide. This approach will undoubtedly lead to a better understanding of reaction mechanisms. 

Gurney, Electronic Processes in Ionic Crystals, Oxford University Press, Oxford, 1948, Chapter 8. 

Mitchell, Chemistry of the Solid State, W. E. Garner, ed., Butterworths, London, 1955, Chapter 13, p. 311. 

---

Bach PB, Brown C, Gelfand SE, McCrory DC. Management of acute exacerbations of chronic obstructive pulmonary disease A summary and appraisal of published evidence. Ann Intern Med 2001 134 600-620. 

---