A new process to produce advanced zirconia-based ceramic composites from low-value minerals

Abstract

A method to produce Al/sub 2/O/sub 3/-SiC-ZrO/sub 2/ powder composite by carbothermal reaction was investigated. Carbothermal reaction has been a creative technique to produce alumina-silicon carbide composite powder from inexpensive precursor materials such as kaolinite, kyanite, pyrophyllite, etc. The products obtained from carbothermal reactions have shown nanometric particle sizes, homogeneous mixture and most impurities were eliminated by volatilization. Zircon (ZrSiO/sub 4/), as an inexpensive source of zirconia, was mixed with kaolinite-carbon or kyanite-carbon to produce zirconia-based composites. Unfortunately zirconia cannot be obtained directly from carbothermal reaction of these minerals as the reaction to produce zirconium carbide is favored. Instead, this new process obtains Al/sub 2/O/sub 3/-SiC-ZrC composite powder at temperatures above 1500/spl deg/C at 1 atm. However, a subsequent controlled oxidation step can transform ZrC of this powder into a mixture of monoclinic and tetragonal ZrO/sub 2/. Thermodynamic data were generated to support test results. The Al/sub 2/O/sub 3/-SiC-ZrO/sub 2/ powder with 7.9% vol ZrO/sub 2/ and 23.4% vol SiC was sintered by hot pressing at 1800/spl deg/C resulting in pellets with 30% higher fracture toughness than the ones made of Al/sub 2/O/sub 3/-SiC composite. This encouraging result led to conclude that carbothermal reaction is a significant process to obtain ceramic composites by using different types of inexpensive minerals.