Low temperature carburization of high surface area tungsten powders

Abstract

Abstract Reductive decomposition of WO 3 precursor powder gives high surface area α-W at temperatures above 650 °C, β-W at temperatures below 575 °C, and mixtures of α-W and β-W (in various ratios) at intermediate temperatures. The carburization behavior of these powders in flowing CO over the temperature range 350 °–700 °C is sensitive to the initial crystalline state of the powder. The α-W powder can be carburized directly to WC phase in an appropriately high carbon activity environment, whereas the carburized β-W powder becomes trapped in a metastable W 2 C state. A simple model is presented to account for this difference in carburization behavior of α-W and β-W phases.