GUIDE TO INJECTION-MOLDING OF CERAMICS AND HARDMETALS - SPECIAL CONSIDERATION OF FINE POWDER

The small particle size of ceramic and hardmetal powders significantly increases the risk of particle agglomeration with an associated incre ase in viscosity of plastisols used in powder injection moulding. The agglomeration is counteracted by adding surface active compounds to th e powder containing plastisol. A model is presented for the functionin g of such additives in injection moulding or fine (ceramic, hardmetal) powder. The idea is to create a thin, dense adsorbed layer which redu ces the attractive van der Waals forces without adding considerably to particle size, thus decreasing viscosity without creating perfect sta bility. In this manner, the pseudoplasticity necessary for the injecti on moulding is retained. The approach outlined shows that the adsorbat es working as dispersants should be short molecules such as stearic ac id, stearyl alcohol, and octadecyl silanes, all built around a C18 cha in. (C) 1997 EPMA.