Krueger, Barry R. and Mutz, Andrew H. and Vreeland, Thad, Jr. (1991) Correlation of shock initiated and thermally initiated chemical reactions in a 1:1 atomic ratio nickel-silicon mixture. Journal of Applied Physics, 70 (10). pp. 5362-5368. ISSN 0021-8979. http://resolver.caltech.edu/CaltechAUTHORS:KRUjap91b
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Shock initiated chemical reaction experiments have been performed on a 1:1 atomic ratio mixture of 20- to 45-µm nickel and –325 mesh crystalline silicon powders. It has been observed that no detectable or only minor surface reactions occur between the constituents until a thermal energy threshold is reached, above which the reaction goes to completion. The experiments show the energy difference between virtually no and full reaction is on the order of 5 percent. Differential scanning calorimetery (DSC) of statically pressed powders shows an exothermic reaction beginning at a temperature which decreases with decreasing porosity. Powder, shock compressed to just below the threshold energy, starts to react in the DSC at 621 °C while powder statically pressed to 23% porosity starts to react at about 30 °C higher. Tap density powder starts to react at 891 °C. The DSC reaction initiation temperature of the shock compressed but unreacted powder corresponds to a thermal energy in the powder of 382 J/g which agrees well with the thermal energy produced by a shock wave with the threshold energy (between 384 and 396 J/g). (Thermal energies referenced to 20 °C.) A sharp energy threshold and a direct correlation with DSC results indicates that the mean thermal energy determines whether or not the reaction will propagate in the elemental Ni+Si powder mixture rather than local, particle level conditions. From this it may be concluded that the reaction occurs on a time scale greater than the time constant for thermal diffusion into the particle interiors.
|Additional Information:||Copyright © 1991 American Institute of Physics (Received 11 March 1991; accepted 19 August 1991) This work was supported under the National Science Foundation’s Materials Processing Initiative Program, Grant No. DMR 8713258. We would like to thank Phil Dixon, formerly at the New Mexico Institute of Technology, for preparing the powder mixture, and Zezhong Fu of Caltech for her help with the DSC experiments. Barry Krueger died on October 29, 1990 as a result of injuries received in a motorcycle accident. His family, friends, and scientific colleagues mourn the loss of a truly gifted individual.|
|Subject Keywords:||NICKEL; SILICON; MIXTURES; POWDERS; SHOCK WAVES; CHEMICAL REACTION KINETICS; DIFFERENTIAL SCANNING CALORIMETRY; POROSITY; THERMAL DIFFUSIVITY; SCANNING ELECTRON MICROSCOPY; X–RAY DIFFRACTION ANALYSIS|
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|Deposited On:||25 Sep 2006|
|Last Modified:||26 Dec 2012 09:03|
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