Aqueous processing of WC-Co powders:: Suspension preparation and granule properties

This paper focuses on how a thorough understanding of the surface chemistry of complex systems can assist in the design of a water-based process. We have investigated different aspects of the powder processing, including slurry preparation and granule characterisation. We have followed the oxidation and dissolution kinetics of WC and WC-Co mixtures, and found that the presence of Co suppresses the dissolution of WC. We have used the atomic force microscope (AFM) colloidal probe technique to measure the surface forces resulting in electrosteric stabilisation of WC-Co suspension with poly(ethylene imine) (PEI). The AFM was also used to measure the friction forces between individual spray-dried granules and a pressing tool wall. It was found that friction is largely affected by binder content and relative humidity. Moreover, a new technique to measure the density of spray-dried granules is presented.