THE EFFECT OF YTTRIUM ON THE EARLY STAGES OF OXIDATION OF ALUMINA FORMERS - COMMENTS

A new approach to the effect of yttrium on the early oxidation stages of alumina formers is proposed. It relies on the elucidation of proces ses occurring in unstable aluminas. Different mechanisms by which yttr ium can accelerate or retard the phase transformation of unstable alum inas into alpha-Al2O3 are discussed. Using a model of the defect struc ture of unstable aluminas it is concluded that doped yttrium should re tard the transformation as long as its amount does not exceed a critic al value. It is shown that the proposed approach enables fairly consis tent description of effect of yttrium and to explain various existing controversies.