Laws governing the combustion of the Ni + Al system under a low ambient gas pressure

Abstract

The ambient pressure dependences of the combustion rate and combustion-induced elongation for an initial Ni + Al mixture and Ni + Al mixtures subjected to vacuum heat treatment (VHT), mechanical activation, and additional activation in water (dispersion) have been studied. Most of the studies have been conducted for mixtures based on PNK-brand nickel (carbonyl); a separate set of experiments has been conducted for PNE-brand nickel (electrolytic). These powder brands contain different amounts of impurity gases and have different particle sizes. It has been shown that VHT, the ambient gas pressure, and the type of the used nickel have a substantial effect on the combustion rate of these mixtures. For the mixtures based on PNK nickel, the increase in the combustion rate after VHT is more significant than that after mechanical activation despite a more thorough mixing of the precursors and changes in the mixture microstructure. The qualitative change in the behavior of the dependence of the combustion rate of the dispersed mixtures on the external gas pressure has been interpreted in terms of a convective–conductive combustion model. The studies have made it possible to prove the previously made conclusion about the gasless combustion of Ni + Al mixtures (PNK nickel) under high ambient gas pressures.