SURFACE OXIDATION OF SI3N4 GREEN COMPACTS - EFFECT OF SINTERING AIDS

It is well known that the surface chemistry of Si3N4 is strongly influ enced by both the synthesis route and the subsequent processing steps, such as the mixing/milling vehicle, the forming procedure, etc. All t hese processing variables can modify not only the rheological properti es of the slips, but also the formation of chemical species at the sur face which are directly related to the densification and the propertie s of the sintered compact. In addition, the additives normally used fo r sintering can also influence the surface chemistry. The aim of the p resent work is to determine the possible changes in the particle surfa ce of Si3N4 green compacts prepared by different forming procedures (s lip casting and isostatic pressing) with and without sintering aids (A l2O3 and Y2O3). The surface oxidation has been determined, in each cas e trying to separate the contribution to the oxidation induced by the processing parameters and the contribution provided by the presence of the sintering aids. X-ray photoelectron on spectroscopy (XPS) is an e xtremely useful technique for this purpose. In this work, high resolut ion XPS has been applied to reveal not only the chemical changes broug ht about by oxidation of Si3N4 green compacts but also to quantify the extent of surface oxidation. (C) 1996 Elsevier Science Limited.