The shock initiation process was directly observed in different powder mixtures that produce little or no gas upon reaction. The samples of reactive powder were contained in recovery capsules that permitted the samples to be analyzed after being shocked and that allowed the initiation of reaction to be monitored using three different methods. The microsecond time-scale processes were observed via a fast two-color pyrometer. Light intensity detected from the bottom of reactive samples was slightly greater compared to inert simulants in the first 10 μs after shock arrival. However, this light was much less intense than that which would correspond to the bulk of the material reacting. Thus it seemed that only small, localized zones, or hot spots, had begun to react on a time scale of less than 30 μs. Light emissions were then recorded over longer time scales, and intense light appeared at the bottom of samples a few milliseconds to a few hundreds of milliseconds after shock arrival at the bottom of the test samples. Thus it appeared that the bulk of the material reacted as the hot spots spread via convective/diffusive means. This bulk reaction was also observed using thermocouples for a large number of mixtures and incident shock pressures. The delay time for the onset of bulk reaction was found to be not strongly dependent upon shock pressure but seemed to correlate with the burning speed of the mixtures. The shock initiation process appeared to take place via the initiation and growth of hot spots, as in high explosives, except that burning speeds are much slower in reactive powders that produce little gas.
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15 April 2011
Research Article|
April 21 2011
In-situ measurements of the onset of bulk exothermicity in shock initiation of reactive powder mixtures
François-Xavier Jetté;
François-Xavier Jetté
a)
1Department of Mechanical Engineering,
McGill University
, Montreal, Québec H3A 2K6, Canada
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Andrew J. Higgins;
Andrew J. Higgins
1Department of Mechanical Engineering,
McGill University
, Montreal, Québec H3A 2K6, Canada
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Samuel Goroshin;
Samuel Goroshin
1Department of Mechanical Engineering,
McGill University
, Montreal, Québec H3A 2K6, Canada
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David L. Frost;
David L. Frost
1Department of Mechanical Engineering,
McGill University
, Montreal, Québec H3A 2K6, Canada
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Yannick Charron-Tousignant;
Yannick Charron-Tousignant
2Department of Mechanical Engineering,
University of Ottawa
, Ottawa, Ontario K1N 6N5, Canada
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Matei I. Radulescu;
Matei I. Radulescu
2Department of Mechanical Engineering,
University of Ottawa
, Ottawa, Ontario K1N 6N5, Canada
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Julian J. Lee
Julian J. Lee
3
Defence R&D Canada Suffield
, Ralston, Alberta T1A 8K6, Canada
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a)
Author to whom correspondence should be addressed. Electronic mail: francois-xavier.jette@mail.mcgill.ca.
J. Appl. Phys. 109, 084905 (2011)
Article history
Received:
September 08 2010
Accepted:
January 08 2011
Citation
François-Xavier Jetté, Andrew J. Higgins, Samuel Goroshin, David L. Frost, Yannick Charron-Tousignant, Matei I. Radulescu, Julian J. Lee; In-situ measurements of the onset of bulk exothermicity in shock initiation of reactive powder mixtures. J. Appl. Phys. 15 April 2011; 109 (8): 084905. https://doi.org/10.1063/1.3553861
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