Influences of pyrophyllite and CaO/K<inf>2</inf>O on phase transformation and properties of ceramic body and glaze for single firing

Abstract

© 2020 Author(s). The research observed the phase transformation and properties of the stoneware body and clear glaze as a function of pyrophyllite content and CaO/K2O ratio during single firing. The body batches were formulated and formed by RAM press. The glaze suspensions were also formulated and sprayed on dried products. The products were single-fired at 1220°C for 540min in a gas kiln in reduction atmosphere and then were normal cooled to ambient temperature. The phase transformation and microstructure of bodies and glazes were evaluated. The technological properties were also investigated. The results showed that the vitrification and properties of single-fired samples were developed relating to the increase of pyrophyllite content. The stoneware body composing (wt%) kaolin 35, K-feldspar 30, ball clay 15, quartz 20 mixed with bentonite 1 and pyrophyllite 3 wt% could be formed by RAM press. As a result of the XRD pattern, the major phases were mullite (3Al2O3.2SiO2) and free silica (SiO2). The properties of the product were shown that the linear shrinkage at 10.82%, water absorption at 0.17% and MOR at 153.21MPa. The clear glaze could be sprayed on the dried products without defects. After single firing at 1220°C, the glaze was completely melted presenting clear layer without crazing. The melting of glaze had started before the stoneware body reached to complete vitrification. The properties of clear glaze were also developed with the increase of CaO/K2O ratio. The maximum vickers microhardness of the glazes was approximately at 925.57 HV and the maximum glossy at 76.3GU for CaO/SiO2 at 6.00. These properties are compatible with those of commercial stoneware and tableware.