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Laser ignition of pyrotechnic mixtures: Ignition mechanisms

 

作者: Henric O¨stmark,   Nils Roman,  

 

期刊: Journal of Applied Physics  (AIP Available online 1993)
卷期: Volume 73, issue 4  

页码: 1993-2003

 

ISSN:0021-8979

 

年代: 1993

 

DOI:10.1063/1.353165

 

出版商: AIP

 

数据来源: AIP

 

摘要:

A laser method for studying the ignition processes of a pyrotechnic mixture is presented. The experimental equipment consists mainly of a 250 W CO2laser, an explosive chamber, a power meter, and a mechanical shutter. Using the laser ignition apparatus a parametrical study of the ignitability of a pyrotechnic mixture (Mg/NaNO3) was conducted. The influence of the following parameters on the ignition energy was studied: pulse width, beam radius, particle size, different sorts of Mg, and gas pressure. These measurements are complemented by some ignition measurements on a Mg/BaO2mixture where the influence of catalysis is studied. Furthermore some high‐speed photography of the ignition process is presented. The thermal explosion theory is then applied to these measurements for a calculation of some of the important parameters followed by a discussion of the ignition mechanisms. The activation energy (Ea=148 kJ/mol), frequency factor (K0=7.1×1017s−1), and absorption coefficient (&agr;=3.1104m−1) were calculated from the measurements. Using the experimentally determined parameters a 2D finite‐element computer modeling of the ignition was carried out, showing that the ignition energy can be calculated with a fair degree of accuracy but that the time to ignition cannot be modeled with a pure heat transfer model. The study is concluded with a discussion of ignition mechanisms for pyrotechnic mixtures, which especially points out that the ignition mechanism for Mg/NaNO3is a melting of the oxidizer followed by a decomposition of the oxidizer, diffusion of the produced oxygen through the oxide layer on the magnesium particles with a consecutive reaction of oxygen and magnesium.

 

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