Study On The Mechanism And Preparation Of Highly Concentrated SiC Ceramic Suspensions

The highly concentrated ceramic suspensions with low viscosity and homogeneous stability are the base of the application of the consolidation in-situ forming technique and also the one of conditions to control effectively the microstructure of green body, reduce the defects inside of materials and improve the performance and reliance of ceramic materials.According to the basic mechanism of dispersion and stability and combining the chemical methods, AAM (Acrylamide) was grafted on the SiC (silicon carbide) powder surface treated by APS (3-aminopropyltriethoxysiIane) silane coupling agents by using the eerie ammonium nitrate as initiator, as a result the PAAM (polyacrylamide)-coated SiC powder was produced. By coating the silicon carbide, the colloidal characteristics of powders in the water were changed, the capacity of dispersion and stability were improved. So the base of processing the highly concentrated ceramic suspensions was established.During investigation, the technological methods of coating silicon carbide powders by the organic compound were searched after and the three technological parameters including time, temperature, concentrations during the coating process were established. The surface characteristics of uncoated and coated silicon carbide powders and the Theological property of suspensions as well the property of forming were analyzed by Fourier Transform Infrared Spectrometer, TEM, SEM, Zeta potential instrument, rotation viscometer and the flexural strength instrument.All of testing results indicate that PAAM has existed on the surface of silicon carbide powders. The surface characteristics of the coated silicon carbide powders were improved and the capability of stability and dispersion were increased. The experiments showed that the coated silicon carbide suspensions were flocculated easily in the basic condition and dispersed easily in the acid condition. When the pH value was 5, the 55vol.% homogenous ceramic suspensions with stability and proper rheological property were processed and could be provided with the requirement of consolidation in-situ forming techniques. We also presumed the model of preparing the highly concentrated ceramic suspension, made an analysis about the mechanism of the dispersion, stability and reducing water.The PAAM-coated silicon carbide powders (-1.1 Sum) were applied to the coarse particle (- 11 Sum) system in the investigation. The results showed the 67vol.%-70vol.% highly concentrated suspensions which had the proper rheological property were obtained with the 52wt% coarse powders +48wt% PAAM-coated silicon carbide powders. At the same time, the suspensions prepared by PAAM-coated powders (55vol.%) were slipped. After slip casting, the density and strength of green body were increased compared to the uncoated powders. The microstructure of green body was dense and dispersion was homogenous. All of those indicated the PAAM-coated powders had excellent processing performance.