Preparation of Low-Shrinkage Mullite Based Ceramics from Polysiloxane as a Preceramic Polymer

Abstract

Monolithic mullite was synthesized from polymer (cross-linked polysiloxane)/filler (alumina) blends. By virtue of a chemical oxidation reaction of ZrSi₂, intentionally added in increasing fractions, a nearly zeroshrinkage mullite based composite could be obtained by conventional sintering. The composites specimen after sintering were composed of mullite and monoclinic ZrO₂, according to the ZrSi₂ fraction added to the starting mixture. Low-shrinkage mullite based ceramics could be obtained when the content of ZrSi₂ was between 30 and 50mol%. In the case of ZrSi₂ 50mol%, the shrinkage was as low as 4.5%, although some specimen was found cracked after sintering. The upper limit for ZrSi₂ addition was considered to be ≈50mol% because of inhomogeneity related to mixing a low fraction of siloxane polymer (liquid) with the filler (solid).