OXIDATION BEHAVIOR OF REACTION-BONDED ALUMINA COMPACTS USING AN AL88SI12 ALLOY PRECURSOR

The oxidation behaviour of attrition-milled Al88Si12/Al2O3 powder mixt ures was investigated for the formation of mullite/Al2O3 composites by the reaction bonded alumina (RBAO) process. Cylindrical powder compac ts were heated at 5-degrees-C min-1 to temperatures between 450 and 14 00-degrees-C. Oxidation occurred rapidly between ca. 400 and 750-degre es-C. Dense, outer reaction layers which formed at the lower temperatu res inhibited complete oxidation and led to fracture of the body durin g continued heating to higher temperatures (above ca. 850-degrees-C) W hile the incorporation of ZrO2 improved the oxidation of the samples, X-ray analysis indicated that the Si in the alloy reacted with the ZrO 2 to form phases which prevented the formation of mullite at the tempe ratures used in the experiments.