Oxidation of detonation nanodiamonds in a reactive formulation

Nanodiamonds have been used as reducing agent in energetic compositions. The reactive formulations prepared by mixing detonation nanodiamond (DND) with potassium chlorate (PC) decompose according to two combustion modes, i.e. continuous or intermittent, depending on the nanodiamond proportion and pressing level used to shape the pellets. The analysis of a series of experimental results has led to build a predictive prevalence diagram of the combustion mode. In the continuous combustion domain, the reaction rate varies as a power law of the nanodiamond content: V = V₀χ_DND]^? α. The pre-exponential factor gives an interesting estimate of the self-sustaining rate of the oxidation of pure nanodiamond loose powder (≈ 0.8 mm/s). Furthermore, the increase of the nanodiamond ratio in the composition makes the burning more regular, and slows down the combustion rate. The effect of pressing on the morphology of DND/PC compositions was intensively studied and led to the understanding of the combustion mechanisms. The porosity of interstitial DND powder acts as a thermal shield and favours the diffusion of the gaseous species released by the combustion in the fresh composition, leading to a convective propagation. This mechanism accounts for the continuous combustion. The thermal conductivity of DND powder measured experimentally is three orders of magnitude smaller than a typical value for bulk diamond (λ_D = 500 W·m^? 1·K^? 1). This result is in agreement with the values calculated from Maxwell's model, for spherical DND particles in a continuous fluid (air).