Thermal properties of silicon carbide and combustion mechanisms of aluminum nanoparticle

Silicon Carbide (SiC) and Alumina (Al2O3) are two important engineering materials for their outstanding electronic, thermal and physical properties. Applications of SiC to high-temperature and high-power devices require knowledge of its thermal properties. We have studied the specific heat and thermal conductivities of both cubic SiC and amorphous SiC as functions of temperature. Results show different heat transport behaviors for crystalline and amorphous SiC. A layer of about 4 nm Al2O3 is naturally formed on the surface of aluminum nanoparticles (ANPs). Presence of this layer affects the combustion behavior of ANPs. Using multi-million-atom molecular dynamics (MD) simulations, we have investigated the combustion behavior of a single ANP. Transition of the combustion mechanism from diffusion to ballistic transportation of atoms is found when the temperature of the preheated aluminum core of the ANP is changed from 3000K to 9000K. Higher initial temperature of the aluminum core results the mechanical breakdown of the alumina shell in the expansion phase of the ANP. Breaking of the shell provides direct oxidation paths for core aluminum atoms, which results faster oxidation reaction and then faster energy release. Thus, the mechanism of the combustion is transferred from thermodynamics to mechanochemistry regime. Furthermore, when the shell structure of the ANP is changed from thicker crystalline to thinner amorphous, this transition of combustion mechanism is found at lower temperatures. Specially, for initial core temperature of 9000K, the ANP with amorphous shell explodes and results complete shattering of the shell. No large fragment of oxide is found after the explosion except for clusters of tens of oxidized Al atoms, that form a superficial particle and reactivity of which is greatly enhanced.