Hydrothermal Reduction of Co_3O_4-Suspensions with Hydrogen - A Novel Approach to Coated Tungsten Carbide Powders

摘要

Uniform carbide-microstructures in WC/Co hardmetals require homogeneous distribution of the cobalt phase already in the green powder compact. Usually extensive, cost-intensive powder milling and a balanced ratio of WC to Co powder size are required to achieve a homogeneous mixture of the starting materials prior to sintering. In the past several attempts have been made to reduce or avoid ball milling, including co-precipitation, co-reduction/carburisation and coating of the carbide powders by means of chemical, physical or electro-chemical methods.rnThis research focused on a new route to carbide coating comprising oxide-pressure-precipitation of submicron to nano sized Co_3O_4-suspensions from cobalt solutions, mixing with WC-suspensions and subsequent hydrothermal reduction of those suspensions in hydrogen atmosphere. The effects of WC addition and catalyst addition on the progress of cobalt oxide reduction are discussed. The resulting cobalt and composite powders were characterised via powder diffraction, SEM and TEM. Sintering tests confirmed the homogenous Co distribution.