Rapid Solid-State Metathesis Routes to Aluminum Nitride

Metathesis (exchange) reactions offer the possibility of controlling temperature through a judicious choice of precursors. Here, a reaction between AlCl3 and Ca3N2 is found to produce phase-pure aluminum nitride (AIN) in seconds. The CaCl2 byproduct salt, whose formation drives this highly exothermic reaction, is simply washed away after reaction completion. SEM images demonstrate that the AIN product is a micron-sized powder, while TEM shows wellformed crystallites. Thermodynamic calculations indicate that a reaction temperature of 2208 K could be reached under adiabatic conditions. Using an in situ thermocouple and a stainless steel reactor vessel to hold the precursors, a reaction temperature of 1673 K is measured 0.8 s after initiation. Switching to a thermally insulating ceramic vessel produces a maximum reaction temperature of 2010 K because of the more nearly adiabatic conditions. The high reaction temperature appears to be critical to forming phase-pure AIN. Experiments with UsN, instead of Ca3N2, produce lower temperatures (1513 K), resulting in both Al and AL2O3 impurities.