INHOMOGENEITIES IN SILICON-CARBIDE DISTRIBUTION IN STIRRED LIQUIDS - A WATER MODEL STUDY FOR SYNTHESIS OF COMPOSITES

An experimental study was conducted on the mixing quality of two-phase slurries in the model SiC-water system using a gravimetric technique with a view to determining the influence of impeller geometry and baff les on the uniformity of distribution of SiC in the mixture. A three-b lade paddle with different blade angles and a variable-pitch blade imp eller (A-3) were used for stirring the mixture at various rotational s peeds. The results show that SiC concentration variation during stirri ng in the absence of baffles was 7.5 vol.%, whereas in the presence of Four vertical baffles the concentration variation was reduced to 2 vo l.%. The power consumption for homogeneous mixing varied between 17.5 and 175 W vol.(-1) depending upon the type of impeller and its rotatio nal speed. A semi-empirical correlation for obtaining uniform mixing h as been developed based on the Reynolds number, the power number and t he Froude number for stirred SiC-water slurries. The results on inhomo geneity of silicon carbide in water concentration during mixing are in close agreement with the modeling studies by previous workers on the water-SiC system, and with limited experimental studies on the real mo lten aluminum-SiC system used to cast metal-matrix composites. (C) 199 8 Elsevier Science S.A. All rights reserved.