Synthesis of Ceramic Milling Balls by Cold Forming

Abstract

This research work is concerned with testing several raw materials and solid industrial waste to produce ceramic milling balls by cold forming. The following materials have been tested as density promotors: Zirconia bricks (waste), phosphate concentrate, celestite concentrate and Pb-glass. Kaolin was used to provide the required plasticity for forming and feldspar as sintering agent. The balls were formed by hand and in a few tests by hydraulic pressure for comparison. The samples were dried for 24-48 hrs (120˚C) and fired under various temperatures ranging between 1000˚C and 1300˚C. Several parameters were determined including volume shrinkage, weight loss, bulk density, specific gravity, water absorption and compressive strength. The results showed that the best specifications were achieved in the balls made form 65% Zr-bricks (waste), 20% kaolin and 15% K-feldspar, fired at 1300˚C for 6 hrs soaking time. These balls had bulk density of 2.65-2.86 gm/cm3, porosity 0.14-0.54%, water absorption 0.05-0.21% and compressive strength 1350 MN/m2. Volume shrinkage after firing was 14-15% and weight loss 2.5-4.0%. These specifications are better than those of the balls formed by cold process and imported to Iraq. Whereas the imported balls formed by melt-casting of alumina show higher density and higher compressive strength. The present results also showed that forming under hydraulic pressure does not improve the density of the balls after firing whereas longer soaking time had significant impact in increasing the bulk density and improving the compressive strength, both of which reflect better sintering