THE ASSESSMENT OF DISPERSION OF FINE CERAMIC POWDERS FOR INJECTION-MOLDING AND RELATED PROCESSES

A method for the assessment of dispersion of fine ceramic powders in an organic vehicle for use in injection moulding and related processes is described. The procedure combines the quantitative evaluation of maximum shear stress in twin-roll mixing with the examination of agglomerate breakdown by scanning electron microscopy using the back-scattered electron image technique. The effect of shear stress, mixing time and the strength of agglomerates on the dispersive mixing process was investigated. Two-spray-dried ZrO2 powders and one TiO2 powder were examined by mixing with a polystyrene vehicle. The results suggest that the maximum shear stress during mixing should be five to 10 times greater than the agglomerate strength in order to disperse the powder in an organic vehicle. Mixing time was found to be less important. The microscopical technique can be used on its own to examine the state of dispersion of powders in organic materials after dilution in the mixing device.