Two-step heat-treatment strategy for removing residual carbon in AlN powders synthesized by carbothermal reduction–nitridation

Abstract

Aluminum nitride (AlN) synthesized via the carbothermal reduction-nitridation (CRN) process inevitably contains residual carbon originating from the carbon source used during synthesis. In this study, a two-step heat-treatment strategy was employed to effectively remove the residual carbon. First, the samples were heat-treated in an air atmosphere to oxidize and eliminate carbonaceous species. Subsequently, an additional heat treatment was conducted under a mixed H2–N2 atmosphere to further reduce the remaining carbon. As a result, the residual carbon was converted into hydrocarbon species, including methane, and efficiently removed, leading to a significant reduction in the carbon content. However, when the heat-treatment duration exceeded a critical threshold, an unexpected increase in residual carbon was observed. This behavior is attributed to the release of carbon originally present as CN defects within the AlN lattice under the reducing atmosphere, followed by the formation of Al2OC. Consequently, carbon species that were not initially detected became measurable in the subsequent carbon–sulfur (C–S) analysis.