AUGITE-BASED CERAMICS OBTAINED BY SOLID-STATE SINTERING OF LOESS

Loess from the Danubian Plain (Bulgaria) was used as the raw material for the solid-state synthesis of ceramics.The mineral phase composition of the loess fraction used was determined by powder X-ray phase analysis, and the chemical composition by X-ray fluorescence analysis. The semi-quantitatively determined mineral phases are quartz, plagioclase, K-feldspar, mica, carbonates (calcite and dolomite), chlorite and amphibole. The major oxides of the chemical composition of loess fraction are (in wt. %): SiO2 - 53,61; Al2O3 - 12.57; Fe2O3 - 7.05; P2O5 - 0,23; TiO2 - 1.37; CaO - 19.36; and MgO - 1.48. Experiments were performed with sintering of pure loess without additives, and with addition of MgO and Na2O in order to obtain a composition corresponding to that of the pyroxene augite - (Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)2O6. Ceramics were obtained at three temperatures: 1000, 1100 and 1200°C. The phase composition, spectral characteristics and colour coordinates of the obtained ceramics were determined. The results show that when magnesium and sodium are added to the loess raw material, the ceramics obtained after sintering at 1100 and 1200°C have a predominant content of augite and have a yellow-beige colour.