Particle surface properties of stainless steel-coated tungsten carbide powders

Tungsten carbide powders sputter-deposited with stainless steel were characterized in order to evaluate the surface properties in air and aqueous environments. The scanning electron microscopy with energy dispersive spectroscopy showed that a very high uniformity of the coating distribution on the WC particles was attained by the sputtering technique, enabling a complete surface coverage for low coating contents (greater than or similar to 1 wt.%). The DTA-TG thermal analysis in air atmosphere revealed that the coating layers increase the oxidation resistance of WC powders, in spite of the coating porosity. The electrophoretic measurements performed in aqueous solution, for different pH at a constant ionic strength (1 mM KCl), showed that the surface charge until pH similar or equal to 8 is essentially determined by the stainless steel coating, while for higher pH it becomes closer to that of the WC particles. The coating adhesion measured by a scratch test was found to decrease in the basic pH region. These results were discussed in terms of the effect of the short-range repulsion forces between the coating layer and the particle surface in aqueous suspensions. (c) 2006 Elsevier B.V. All rights reserved.