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 baffles on the uniformity of distribution of SiC in the mixture. A three-blade paddle with different blade angles and a variable-pitch blade impeller (A-3) were used for stirring the mixture at various rotational speeds. The results show that SiC concentration variation during stirring in the absence of baffles was 7.5 vol.%, whereas in the presence of four vertical baffles the concentration variation was reduced to 2 vol.%. The power consumption for homogeneous mixing varied between 17.5 and 175 W vol.−1 depending upon the type of impeller and its rotational speed. A semi-empirical correlation for obtaining uniform mixing has been developed based on the Reynolds number, the power number and the Froude number for stirred SiC–water slurries. The results on inhomogeneity 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 molten aluminum–SiC system used to cast metal–matrix composites.