Shock-induced chemical reactions in titanium–silicon powder mixtures of different morphologies: Time-resolved pressure measurements and materials analysis

Abstract

The response of porous titanium (Ti) and silicon (Si) powder mixtures with small, medium, and coarse particle morphologies is studied under high-pressure shock loading, employing postshock materials analysis as well as nanosecond, time-resolved pressure measurements. The objective of the work was to provide an experimental basis for development of models describing shock-induced solid-state chemistry. The time-resolved measurements of stress pulses obtained with piezoelectric polymer (poly-vinyl-di-flouride) pressure gauges provided extraordinary sensitivity for determination of rate-dependent shock processes. Both techniques showed clear evidence for shock-induced chemical reactions in medium-morphology powders, while fine and coarse powders showed no evidence for reaction. It was observed that the medium-morphology mixtures experience simultaneous plastic deformation of both Ti and Si particles. Fine morphology powders show particle agglomeration, while coarse Si powders undergo extensive fracture and entrapment within the plastically deformed Ti; such processes decrease the propensity for initiation of shock-induced reactions. The change of deformation mode between fracture and plastic deformation in Si powders of different morphologies is a particularly critical observation. Such a behavior reveals the overriding influence of the shock-induced, viscoplastic deformation and fracture response, which controls the mechanochemical nature of shock-induced solid-state chemistry. The present work in conjunction with our prior studies, demonstrates that the initiation of chemical reactions in shock compression of powders is controlled by solid-state mechanochemical processes, and cannot be qualitatively or quantitatively described by thermochemical models.

Mesoscale simulation of the configuration-dependent shock-compression response of Ni+Al powder mixtures

“…Prior work on the Ti+Si system has revealed evidence of particlesize-dependent dynamic material response [5]. Recovery experiments performed on mixtures of Ti and Si (5:3 molar ratio) of varying particle sizes revealed distinct differences in the particle-level mechanical behavior of the components.…”

“…Intermediate particle sizes (< 45µm) exhibited simultaneous deformation and mixing. These disparate micromechanical behaviors exact direct influence over the propensity for initiating ultra-fast shock-induced chemical reactions, with only the intermediate particle sizes displaying signatures of reaction, evidenced by increases in shock velocity above a threshold stress of 1.5 GPa [5].…”

Ti-Si photocatalyst for producing hydrogen synthesized by shock wave

“…According to Thadhani et al [6], Ti-Si could be reaction at the flyer velocity of <1.0km/s after enough ballmilling treatment for pre-activated powder mixture. However, to avoid pollution from impurity during the ball milling process, the mixtures of Ti and Si were directly shocked after pressing into the container.…”

Meso-Scale Experimental & Numerical Studies for Predicting Macro-scale Performance of Advanced Reactive Materials (ARMs)

“…8 While processes of thermal ignition in such reactive materials are well understood, 9 the mechanisms of impact-initiated reactions and their kinetics remain to be established. Our prior work 10,11,12 showed that shockinitiation of chemical reactions is influenced by differences in the elastic/plastic properties of reactant materials and their morphological characteristics. Under uniaxial-strain loading, micro-size spherical Ni+Al powder mixtures showed crush-up to full density at ~0.5 GPa, while the crush-up stress for flake-Ni+Al mixtures of similar size is ~2 GPa, and that of nano-sized Ni+Al was ~6 GPa.…”