engleski

Mullite ceramics prepared by sintering of sol-gel derived pre-mullite powders

The excellent high temperature properties of mullite make itan attractive ceramic material for high-temperature mechanical applications. Although extensive vork has been done related to the processing and characterization of sol-gel derived materials having mullite compositions AlVI2(AlIV2+2XSi2-2X)O10-X with 0.22<X<0.58, a complete understanding of the relationship of initial process variables with microstructure and sintering behaviour of mullite has not yet been fully achieved. The aim of this work is to provide additional information about the influence of the precursor synthesis on the resulting properties of the mullite ceramics. The structural evolution with temperature of prepared amorphous gels has been studied by X-ray diffrection (XRD). The microstructure and morphology of sintered ceramics has been investigated by scanning and high-resolving transmission electron microscopy (SEM, HRTEM) and energy dispersive X-ray spectrometry (EDXS). The first crystalline phase (Al-Si spinell) occurs at 980oC, which further transforms into mullite solid solution at about 1250oC. The microstructure of the prepared ceramics is similar to that observed by Kanka and Schneider characterized by elongated mullite crystals (maximum size 5 to 7 um) embedded in a finer "mullite matrix". The size of a smaller equiaxial "mullite-matrix" crystals was <1 um. The EDX microanalysis in triple junctions and across the mullite/mullite grain boundaries revealed SiO2 rich glassy phase. The observed morphology is characteristic for materials with liquid-phase sintering mechanism

-

nije evidentirano