Effect of Addition of Talc on the Properties of Feldspar-Kaolinitic Clay Blends during Heating

Abstract

Effects of low addition of talc (up to 8 wt%) on thermal transformations of feldspar-kaolinitic clay blends were investigated by X-ray diffraction, scanning electron microscope and Fourier-transform infrared spectroscopy. The variations of some properties (firing shrinkage, water absorption, density and bending strength) versus talc additions were measured. It was found that talc additions did not affect the presence of neoformed phases (mullite, spinel and glassy phase) but markedly influenced their contents. With up to 4 wt% talc addition, the amount of the formed phases increased with the increase of talc content; consequently shrinkage increased along with strength and density. Apparently, talc derivative oxide (MgO) facilitated the sintering process. For >4 wt% talc, the effect of alkali fluxes reduced because of the abundance of MgO, and consequently the glassy phase content decreased. Therefore, the variations of properties changed except for water absorption and total porosity, which manifested a continuous decline.

Keywords:

• Vitreous ceramics
• Talc
• Thermal transformations
• Physical properties
• Microstructure