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

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 [approximate]50mol% because of inhomogeneity related to mixing a low fraction of siloxane polymer (liquid) with the filler (solid).