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Impact ignition and combustion of micron-scale aluminum particles pre-stressed with different quenching rates

TitleImpact ignition and combustion of micron-scale aluminum particles pre-stressed with different quenching rates
Publication TypeJournal Article
Year of Publication2018
AuthorsHill, KJ, Tamura, N, Levitas, VI, Pantoya, ML
JournalJournal of Applied Physics
Volume124
Pagination9
Date Published09
Type of ArticleArticle
ISBN Number0021-8979
Accession NumberWOS:000445367200029
Keywordscore, physics, reactivity, shell, strain, x-ray-diffraction
Abstract

Pre-stressing aluminum (Al) particles by annealing and quenching alters dilatational strain and is linked to increased particle reactivity. The quenching rate associated with pre-stressing is a key parameter affecting the final stress state within the Al particle, with faster quenching rates theoretically favoring a higher, more desirable stress state. Micron scale Al particles are annealed to 573 K, then quenched at different rates (i.e., 200 and 900 K/min), mixed with bismuth oxide (Bi2O3), and the Al + Bi2O3 mixtures are examined under low-velocity, drop-weight impact conditions. Both quenching rates showed increased impact ignition sensitivity (i.e., between 83% and 89% decrease in ignition energy). However, the slower quenching rate showed a 100% increase in pressurization rate compared to untreated particles, while the faster quenching rate showed a 97% increase in peak pressure, indicating that these two quenching rates affect Al particles differently. Surprisingly, synchrotron X-ray diffraction data show that the 200 K/min quenched particles have a higher dilatational strain than the untreated particles or the 900 K/min quenched particles. Results are rationalized with the help of a simple mechanical model that takes into account elastic stresses, creep in the alumina shell, and delamination of shell from the core. The model predicts that Al powder quenched at 200 K/min did not experience delamination. In contrast, Al quenched at 900 K/min did not have creep but does have delamination, and under impact, delamination led to major fracture, greater oxygen access to the core. and significant promotion of reaction. Thus, the increase in quenching rate and shell-core delamination are more important for the increase in Al reactivity than pre-stressing alone. Published by AIP Publishing.

DOI10.1063/1.5044546
Custom 1

Not AL

Alternate JournalJ. Appl. Phys.