Partially water-soluble binder formulation for injection molding submicrometer zirconia

A binder system containing 60% by volume of a water-soluble major constituent was formulated and tested for powder injection molding ceramic materials. The main components of the binder phase were a low molecular weight polyethylene glycol, an oxidized high density polyethylene, polyvinyl butyral and stearic acid. Ceramic powder-binder mixes containing these binder components and up to 45% by volume of a submicrometer stabilized zirconia powder were prepared and characterized. The apparent viscosity of these mixes at a temperature of 190 degrees C and a shear rate of 100 s-(1) was determined to he 700-800 Pas. Binder removal from parts produced by injection molding these feedstocks was accomplished using a two-stage process. The water-soluble constituent, polyethylene glycol, was removed by dissolution in water at 50 degrees C. Tests showed that approximately 90% of the polyethylene glycol could be removed from a 2-mm thick part during a 2 h immersion in water. The remaining binder constituents were removed using a thermal treatment to 500 degrees C at a heating rate of 100 degrees C/h. Thermogravimetric analysis revealed a good separation of the decomposition regions for the various components when heated in an argon atmosphere. A final sintering step in air at 1500 degrees C produced parts having a density above 99%.