Initiation of Lead Azide by High-Intensity Light

Abstract

Radiation from an argon flash-bomb is used to initiate detonation in lead azide aggregates. Optical methods are employed to measure initiation delay as a function of energy absorbed by the azide. It is found that the product of the rate of energy absorption and the initiation delay is constant. This is interpreted in terms of a thermal initiation mechanism as follows: Absorption of flash-bomb radiation causes a continuing increase in azide surface temperature; above a critical temperature Tc, exothermic decomposition of the azide becomes very rapid and leads to thermal explosion and detonation in very short times. Typical initiation delays are of the order of 1 μsec and Tc∼900°K. Reaction-rate parameters calculated on the basis of this model, using measured initiation delays, are in good agreement with those obtained from thermal decomposition studies without explosion. It is shown that, for the experimental conditions used, purely photochemical reactions are unimportant.

Features of initiating the light-sensitive explosive composites for safe blasting of borehole charges in coal mines

“…Conclusion as for the essential role of a thin surface layer of the substance in the process is confirmed by a series of other results. For instance, paper [17] states that lead azide initiation does not depend upon the material pureness, dispersion, and sample density. Moreover, the paper highlights the effect of dispersion of the substance decomposition products upon the ignition parameters being characteristic for considerable indices of explosive absorption.…”

A theory of light-induced explosion

“…It follows that (1,5) do= -6 exp(=) U= + V -. [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] It is evident from the expressions for 6 and wo, that three of the important factors governing the growth of reaction to explosion are the heat of reaction Q, the light intensity I, and the length of the reacting system r. Eq. 2-19 can be used to obtain the maximum value of the parameter 6 (kcrit) or the parameter co (COcit) for which a solution of Eq.…”

“…A primary explosive such as lead azide satisfies the latter requirement (1) and it has been established (6, 7) that a photochemical ignition mechanism may be excluded under ordinary conditions. The thermal chemical properties (1,6) and absorption spectrum (8, 9) of lead azide are reasonably well established and the calculations discussed below were made using values of the density p = 3.62 g/cm3, thermal conductivity X = 4 X 10-4 cat g-K-' cm-', specific heat at constant pressure Cp = 0.117 cal g'1 K-', heat of reaction Q = 115,000 cal/mol, activation energy E = 37,000 cal/mol, and a value of 1014 s-l for the pre-exponential factor A (1 cal = 4.184 J). It is assumed that we are probing the sample with monochromatic light in a spectral region for which the fraction of light absorbed a may be set equal to 1.…”