Low-temperature synthesis of high-purity AlN from Al powder

Abstract

This study developed and optimized a novel and cost-effective method for producing AlN particles by heating Al powder in a nitrogen atmosphere at temperatures lower than the melting point of Al. As the size of the initial Al particles decreased, nitridation was accelerated because of the high specific surface area (more sites to initiate nitridation) and porosity (more pathways for nitrogen gas). The nitridation rate was initially slow for larger Al particles because of the time required to achieve a sufficiently low oxygen content, whereas almost complete nitridation of 1 μm Al powder rapidly occurred. The nitridation degree was <50% for 10 μm Al powder, while high-purity AlN particles (>95% nitridation) were obtained from the smaller Al particles. Process optimization demonstrated efficient and industrially relevant strategies for producing AlN from Al particles. The use of a mixture of different Al particle sizes greatly increased the degree of nitridation compared to the use of only 10 μm Al particles because of the high specific surface area and limited coarsening of Al by limiting the molten Al phase. The addition of Ar gas regulates the nitridation rate to avoid exhausting the nitrogen supply, which results in a very high degree of nitridation (98.7%). These findings demonstrate the production of high-purity AlN from Al powder at much lower temperatures than those currently used for commercial AlN fabrication. This could significantly reduce the manufacturing cost and promote wider use of AlN to take advantage of its attractive properties for electronics and other applications.