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Kinetics of Weight Changes and Developments During Oxidation Sintered j?-SIALONS

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  • South East Applied Materials Research Centre

Abstract

PII: S0955-2219(97)00087-3 Journal of the European Ceramic Society 17 (1997) 1901-1909 PII: SO955-2219(97)00087-3 Kinetics of Weight Changes and Developments During Oxidation Sintered j?-SIALONS R. Ramesh, P. Byrne, S. Hampshire and M. J. Pomeroy Materials Research Centre, University of Limerick, Ireland Abstract The oxidation behaviour of yttria denscjied p-sialon materials (Si~6_Z~AIZ0,N~s_,~) with z-values of 0.2, 0.5, 1.0, 1.5, 2.0 and 3.0 at 1350°C is reported for times up to 256 h. The sialons can be grouped into two categories with respect to oxidation kinetics and predominant crystalline phases formed in the surface layers. For the z= O-2 to I.0 materials, changes in oxidation parabolic rate constant occur after 128 h and yttrium disilicate or cristobalite are the major crystalline oxidation products within the surface layers. For the higher z-value materials, no changes in parabolic oxidation rate are observed and mullite is the predominant phase formed. Examination of cross-sectioned specimens of the z =0.2 and 3.0 materials indicates changes in morphology consistent with those reported for the surface layers. The kinetics and mechanism of oxidation and morpholo- gical development of the oxide scale are discussed in terms of additive d$iision efects. 0 1997 Elsevier Science Limited. Resume’ Le comportement a l’oxydation de materiaux p- SiAlON (Si(6_Zl Al, 0, NC,_,,), denstjies par ajout dbxyde d’yttrium et ayant des valeurs de z de 0.2 ,0..5, l-0, 1.5, 2.0 et 3.0, a dte’ suivi a 1350°C pour des temps aliant jusqu ‘a 256 h. Ces materiaux peuvent etre group& en deux categories suivant les cinetiques dbxydation et la nature des phases cristallines for- mees en surface. Pour des valeurs de z comprises entre 0.2 et 1.0, des evolutions de la constante para- bolique de la vitesse d’oxydation apparaissent apres 128 h de traitement. Les principaux produits dbxy- dation a l’interieur de la couche formee sont le sili- cate djrttrium ou la

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