engleski

Sol-gel Derived Mullite-gahnite Composite

Mullite-gahnite composites with different phase-ratio were prepared by the sol-gel process. Crystallization path was determined by differential thermal analysis (DTA). X-ray diffraction (XRD) was used to study the development of crystal phases. Calcined amorphous precursors were further compacted and sintered. The course of thermal reactions is dominated by the intermediate formation of two spinel phases. The former phase was attributed to gahnite and the latter to Al-Si spinel. With temperature increase Al-Si spinel transforms to mullite releasing excess alumina, which reacts with amorphous SiO2-rich phase in the second step of mullitization. Zn loading decreases mullite and α-alumina while increases gahnite and amorphous phase. Mullite composition, temperatures and rates of the crystallization processes depend on the gahnite content. Microstructure was investigated by scanning electron microscopy (SEM). The observed microstructure, characterized by fine gahnite particles distributed among mullite acicular grains, is known to be highly favourable for ceramics with high mechanical requirements. The microstructure is also affected by the gahnite content, where the sample with the highest gahnite amount yields the largest mullite grains.

Mullite; Gahnite; Crystallization

nije evidentirano