WHISKER ALIGNMENT BY SLIP EXTRUSION

Si3N4 or Al2O3 ceramic slips containing 20-30 vol.% SiC whiskers and s mall quantities of a dispersant and gelling agent were prepared by ult rasonic dispersion and ball milling. The viscosity was minimized by ad justing the pH of the slip and the amount of organic additives. The sl ip was extruded into a gelling solution through a hypodermic syringe f itted with a 0.5 mm internal diameter stainless steel needle. The conv ersion of the extruded slip into a flexible thread was accomplished by an ion exchange reaction in the gelling solution. The orientation of the whiskers in the extruded thread was determined by infiltrating an epoxy resin into the dried thread and measuring the distribution of th e angle between the whiskers visible on a polished cross-section and t he extrusion direction. The degree of whisker alignment in the thread was defined in terms of a statistical orientation factor f0 which vari ed from 0 to 1 as the whisker distribution changed from randomly orien ted to complete alignment in the extrusion direction. Optimum whisker alignment was achieved at large needle length-to-diameter ratios, low slip viscosities and high extrusion velocities.