Effects of mechanical activation on the fluxing properties of Gua Musang Feldspar

Abstract

In this study, the relationship between milling duration and contamination, softening point, particle size and colour of Gua Musang Feldspar samples upon firing was determined. Feldspar is one of the components used in the manufacturing of clay-based ceramic products. The function of feldspar in the production of ceramics is to reduce the firing temperature, so that the energy upon firing can be saved in actual industrial production. The feldspar component is the first to melt in a typical clay-feldpar-silica triaxial porcelain compositions. The softening temperature of feldspar in the firing process is greatly affected by changes in the characteristics of the feldspar used, i.e., particle size, type and amount of alkali oxide content, etc. Other than size reduction, milling also invokes contamination due to the milling media. Contamination during milling at various milling duration using zirconia and stainless steel milling media was determined. Stainless steel was found to be unsuitable for use as the milling media because it affected the colour of the powder before and after firing. Even though contamination still took place when a zirconia milling media was used, zirconia was found to be a better choice because the contamination was much smaller, i.e., less than 1% at the longest milling duration of 20 hours. Hence, it would not affect the firing properties of the ceramic products and the original colour of the feldspar still remained the same as before milling. As milling proceeded into an ultrafine region, it became more and more difficult to obtain further reduction in size because a mill limit was reached. It was ascertained that as the milling duration increased, the softening point of the GMF showed a marked decrease in temperature from 925^oC to 775^oC, a difference of 150 ^oC. Characterisation studies with commercial potash and soda feldspars confirmed that the Gua Musang Feldspar is a type of soda feldspar.