Journal of ThermalAnalysis, Vol.38 (1992)2657-2668 ON THE OXIDATION BEHAVIOUR OF MONOLITHIC TiB2 AND AI203-TiB2 AND Si3N4-TiB2 COMPOSITES A. Tampieri, E. Landi and A. Bellosi CNR-IRTEC, RESEARCH INSTITUTE FOR CERAMICS TECHNOLOGY, FAENZA, ITALY In view of the susceptibility of TiB2 to oxidation, the thermal stability of monolithic TiB2 and of A1203-30 vol% "l'iB2 and Si3N4-20 vol% TiB2 composites was investigated. The temperature at which TiB2 ceramic starts to oxidize is about 400~ oxidation kinetics being controlled by diffusion up to T = 900~ and in the first stage of the oxidation at 1000~ and 1100~ (up to 800 rain and 500 min respectively), and by a linear law at higher temperatures and for longer periods. Weight gains in the AIzO3-TiB2 composite can be detected only at temperatures above =700~ and the rate governing step of the oxidation reaction is characterized by a one-dimen- sional diffusion mechanism at T = 700~ and T = 800~ and by two-dimensional diffusion at higher temperatures. Concerning the Si3N4-TiB2 composite, three different oxidation behaviours related to the temperature were observed, i.e. up to =1000~ the reaction detected regards only the second phase; at ~1000< T< =1200~ the diffusion of O2 or N2 through an oxide layer is proposed as the rate-governing step; at T > =1200~ a linear kinetic indicates the formation of a non protec- tive scale. Keywords: monolithic TiB2 and AhO3-TiB2 and Si3N4-TiB2composites, oxidation kinetics Introduction Titanium diboride has been studied extensively for its potential applications and it has received great attention because of its high melting point, hardness, electrical conductivity and wettability by molten AI [1 -3]. The addition of TiB2 to an A1203 or Si3N4 matrix greatly increases hardness, strength and fracture toughness; in addition, these composites can be used as electrodes, wear parts, cutting tools, high temperature heaters and heat ex- changers. John Wiley& Sons, Limited, Chichester AkadMmiaiKiadt, Budapest