Surface Modification And Characterization Of Compound Powder Of SiC-Al₂O₃-ZrO₂-C

Ultra-fine powders have been attracted widely because of theirs excelled property. However, theirs application is limited owing to higher surface energy of agglomerating easily. Therefore, the key that ultra-fine powders can be applied widely lies in the technology of surface modification for the purpose of good dispersion.The effects of the pH value and surface active reagent(Polyacrylic acid,PAA) on the dispersion of ultra-fine powders (SiC,Al₂O₃,ZrO₂,C) were investigated in this paper. The effects of surface modification were characterized by measuring zeta potential of powders and sedimentary volume and viscosity of suspension; The concentration of functional groups on surface of activated carbon was measured by the boehm titration and was used to characterize the effect of oxidation with HNO3 for the dispersion of activated carbon.The results of measuring and analyzing zeta potential and sedimentary volume and viscosity of suspension were indicated: when pH value was 9, as to SiC, with 0.5wt%PAA as dispersant, the absolute value of powder zeta potential was the highest and the sedimentary volume and viscosity of suspension were the least; as to Al₂O₃, with 0.3wt%PAA as dispersant, the absolute value of powder zeta potential was the highest and the sedimentary volume and viscosity of suspension were the least; as to ZrO₂, with 0.4wt%PAA as dispersant, the absolute value of powder zeta potential was the highest and the sedimentary volume and viscosity of suspension were the least; as to active carbon oxidated by HNO3, with 0.9wt%PAA as dispersant, the absolute value of powder zeta potential was the highest and the sedimentary volume and viscosity of suspension were the least; It was found that the content of acidic functional groups on surface of activated carbon was influenced greatly by concentration of HNO3: with raising of the concentration of HNO3, its content was increased firstly and had been highest when the concentration of HNO3 was 10mol/L, and then its content was not changed conspicuously. The increase of content of acidic functional groups on surface of activated carbon leads to the higher hydrophilic property and dispersion of suspension.The dispersion and rheology of suspension of compound powder were also investigated. It was found that the suspension of initial compound powder showed the rheological behavior of shear thinning and that the rheoogical behavior of modified suspension was better than the initial suspension. The pH value had great influence on the viscosity of suspension in range of 8-10.5and had no influence at surpassing 10.5, PAA also had great influence on the viscosity of suspension. When pH value was 10.5, with 0.8wt%PAA, the suspension of compound powder had the best rheology and showed the rheological behavior of Newton liquid. The highest solid content of suspension was 31vol% before modifying and was 32.5vol% after modifying.