Production of Al2O3-SiC composites from micrometer α-Al2O3 powder obtained via sol-gel

Alumina (Al2O3) is an advanced ceramic material developed for different applications as refractories, precision tools, pacemaker, etc. Solid state sintering of alumina or matrix ceramic composites (CMCs) compacts starts from powders. Once method to produce high quality aluminum oxide powders is the sol-gel technique. Alumina begins as pseudo-crystallized aluminum hydroxide gel which is produced under moderate reaction conditions trough a colloidal suspension. In this work, Al2O3 powder was produced by precipitation of pseudoboehmite (PB) through sol-gel process. Subsequently, a mixture of Al2O3/SiC powders with 5 wt.% of SiC as reinforcement was produced. This mixture was used to manufacture green compacts by uniaxial pressing at 440 MPa. Afterward, some samples were applied a heat treatment (pre-sintered) at 1200°C for 6 h in air. Sintering was carried out in a vertical dilatometer Linseis L75 V up to 1500°C for 2h under argon atmosphere. Pseudobohemite, alumina powders and Al2O3/SiC composites were characterized through X-ray diffraction technique and Scanning Electron Microscopy (SEM). Dilatometric shrinkage data into densification curves obtained were analyzed. Images obtained with SEM showed a uniform Al2O3 powder morphology of submicron size, otherwise Al2O3/SiC composite images showed the interaction of the reinforcement particles on the ceramic matrix. Experimental results demonstrated the pre-sintering reduce the decomposition of SiC particles on the compact surface. This behavior was attributed to formation of SiO2 around the reinforcement particle due it act as protective barrier.