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

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 H 2 –N 2 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 C N defects within the AlN lattice under the reducing atmosphere, followed by the formation of Al 2 OC. Consequently, carbon species that were not initially detected became measurable in the subsequent carbon–sulfur (C–S) analysis.