Development of bending strength of porcelain body by the substitution of quartz by RHA at different soaking times: A comparison between experimental and predicted results

The effect of soaking time and substitution of quartz by rice husk ash (RHA) on bending strength of porcelain was investigated. RHA was used as a substitute for quartz with different replacement levels (0 wt% to 25 wt%). The mixed powder was pressed into pellets and at a mould pressure of 91 MPa. All the pellets were sintered at the temperatures of 1200 οC for 1 h, 2 h and 3 h soaking time, at a heating rate of 5 οC per minute. The bending strength and bulk density were the highest at a soaking time of 2 h MPa on 20 wt% of RHA. Porcelain containing RHA has about 7 % weight reduction compared with standard porcelain. The improvement in the properties could be attributed to decrease in porosity as a result of increase in mullite and glassy phase simultaneously. Statistical software Design Expert 7.1 was used. Cubic versus quadratic equation was used in order to design a model on the effect of the parameters on the response. For predicting the optimal point after performing experiments, Cubic versus quadratic equation (Equation 4.1) was fitted to correlate the relationship between independent variables (soaking and RHA wt%) and response (bending strength) and interactive effect of the process variables. Regression coefficients of the quadratic model was evaluated by analysis of variance (ANOVA). All the terms in the model were tested by student’s F-test and significance of the F-values at probability levels (p ≤0.05) were analyzed. The experimental results were compared with the predicted result and there was good agreement between the two results