Correlation of shock initiated and thermally initiated chemical reactions in a 1:1 atomic ratio nickel-silicon mixture

Abstract

Shock initiated chemical reaction experiments have been performed on a 1:l atomic ratio mixture of 20-to 45,um 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.

Shock synthesis of silicides—I. experimentation and microstructural evolution

“…This initial discovery was followed by activity in Japan [2,3] and the USSR [4][5][6][7][8]. In the U.S., the pioneering work of Graham and co-workers [9][10][11] was followed by investigations by Vreeland and co-workers [12,13], Horie et al [14,15], Boslough [16], Thadhani and co-workers [17,18], and Yu et al [19,20].…”

Shock compression of reactive powder mixtures

“…An explanation for reaction initiation based upon thermal energy was developed by Krueger et al, 33,98 following their work on Ni+Si powder. Micrometre-scale powders (Ni: 20-45µm, Si: -325 mesh) were mixed at a 1:1 atomic ratio and pressed to 60% TMD within a steel containment fixture.…”

“…98 Ultra-fast chemical reactions, labelled "shock-induced" reactions, which register as increases in shock velocity (and perhaps pressure) in timeresolved traces, have instead been proven sensitive to powder configuration, which in turn is influenced by differences in intrinsic and extrinsic properties of the reactants. 36-40, 87, 104 Time-resolved studies of the effect of particle size, particle morphology, and powder pretreatment have shown that extrinsic properties, specifically those that influence the local particle-scale mechanics of deformation, can greatly alter the propensity of a powder mixture to undergo shock-induced chemical reaction, even in the case of systems with larger differences in intrinsic properties.…”

Shock wave initiation of the Ti5Si3 reaction in elemental powders

“…Krueger et al 3 found an energy threshold for shock wave initiation of the NiSi reaction in porous Ϫ325 mesh ͑Ͻ45 m͒ NiϩSi powders. The threshold corresponded to the energy to initiate the reaction thermally in a differential scanning calorimetry ͑DSC͒ for a zero porosity NiϩSi mixture which had previously been consolidated by a shock wave with an energy just below the threshold energy.…”