COLLOIDAL PROCESSING AND LIQUID-PHASE SINTERING OF SIC

Colloidal dispersion and pressure-casting to prepare SiC green pieces of two types and pressureless sintering of SiC were sequentially condu cted to obtain homogeneous, dense SiC bodies, Polyethyleneimine (PEI) was selected as a dispersant, and Al(2)O3/Y2O3 additives served as a s intering aid for the ceramic systems. The dispersion behavior of the S iC in solutions with PEI dispersant was characterized by their surface potential and isoelectric point (IEP), and interpreted according to t he chemistry and adsorption of the PEI dispersant. The resulting cryst alline phases and grain morphologies of sintered SiC were investigated by quantitative X-ray diffractometry (QXRD), scanning and transmissio n electron microscopies (SERI and TEM) and high resolution transmissio n electron microscopy (HRTEM). alpha-SiC was sintered at ambient press ure to a higher density than beta-SIC with Al2O3 and Y2O3. The densifi cation and resulting microstructure depended greatly on the polytypes of the starting SiC powders, types of packing powder to buy samples, a nd types and amount of sintering additives, The effects of seeding wit h 6H-SiC powder on phase evolution, the transformation temperature and densification of the beta-SiC matrix are discussed.