Determination of the firing schedule for a self glazing porcelain

Abstract

In this study the aim was the production of a self glazing porcelain which depended upon the formation of the anorthite phase (CaO. Al2O3. 2SiO2), by single firing. A frit was prepared by mixing 24.5 % K2CO3, 31.7 % SiO2 and 43.8 % H3P04 at 1050 °C in order to satisfy the molar ratio of K2O : B203 : SiO2 =1:2:3 known as the Seger formula. A batch having a composition of 50 % kaolin, 35 % wollastonite and 15 % frit was prepared. The differential thermal analysis (DTA) and linear dilatometry (LD) curves of this batch were determined. The firing schedule (FS) curve which shows the variation of temperature as a function of time was derived from the LD and DTA curves. The batch was fired for 210 min. including cooling, such that the maximum temperature was 1050 °C according to the FS and a self glazing porcelain was obtained. From the X-ray diffraction patterns it was determined that anorthite phase was formed in the porcelain. It was concluded that a great amount of energy would be saved by the production of a single firing porcelain which depends on the formation of the anorthite phase instead of the production of a double-stepped firing porcelain which depends on the formation of the mullite phase (3Al203.2SiO2).