Rheological Properties Of SiC Suspensions Used For Recrystallized Ceramics

candidate material for kiln furniture, electric heating elements and boiler burners due to its low density and thermal expansion coefficient, high melting point, thermal conductivity, flexural strength and hardness, excellent resistance to thermal shock, abrasion and corrosion. The solid loading and rheological properties of SiC suspensions have considerable influence on the ceramic bulk density and homogeneous microstructure, then having effect on the comprehensive properties of SiC ceramic products. The aim of this investigation was, therefore, to research the influence of tetramethyl ammonium hydroxide (TMAH) used as a dispersant on the rheological properties of SiC suspensions used for recrystallized ceramics to prepare aqueous suspensions with high solid loading, low viscosity and good rheological properties.With TMAH addition, the stable dispersion in both fine SiC powders and suspensions was studied from different viewpoints such as infrared spectrum, zeta potential, phase analysis, rheological properties and sedimentation behavior. The results showed that, compared with zeta potentials of SiC powders without TMAH addition, the zeta potential absolute values with TMAH addition were considerably increased with a pH ranged from 3 to 11. Moreover, with an amount of 0.3wt% TMAH addition, the solid loading of fine SiC suspensions increased from 33vol% to 60vol%.The results in the present study also indicated that, the optimum particle size gradation of SiC was 7:3 in the weight ratio for coarse powders and fine powders with a median particle size of 100μm and 2.0μm, respectively. With a pH of 9.63 and a TMAH concentration of 0.1wt%, the SiC suspensions mixed with coarse and fine powders used for recrystallized ceramics could be prepared with the highest solid loading of 70.25vol%.The influence of TMAH used as the dispersant on the rheological properties of SiC suspensions used for recrystallized ceramics was also investigated. The results showed that the Newtonian fluid behavior appeared in high shear rate range in the flow curve of SiC suspensions, while in low and middle shear rate range, shear thinning behavior presented and the variation of viscosity with the increasing shear rate could be fitted by power law, which was an innovative idea in this study. As power law, the fitting equations wereη=0.354γ-0.3743,η=1.232γ-0.4495,η=1.188γ-0.2867 andη=1.513γ-0.2752 for SiC suspensions with a solid loading of 62.5vol% 65.0vol%, 67.5vol% and 69.0vol%, respectively.Additionally, the recrystallized SiC ceramic bodies with a bulk density of 2.37g/cm3 had been successfully obtained by slip casting using SiC suspensions with a solid loading of 70.25vol%.