Reformulation of bone china body for the reduction of pyroplastic deformation

This work is aimed to decrease the pyroplastic deformation using sodium feldspar and potassium feldspar in bone china revealing the viscosity and crystalline phase effect. For this, we reformulated the traditional bone china recipe considering the amount and ratio of fluxing agents. In the first group, sodium feldspar (coded as Na-F) and potassium feldspar (coded as K-F) were introduced individually into the body from 20 to 35 wt.%. In the second group, we fixed the feldspar amount to 35 wt.% but changed the Na-F/K-F ratio to 1/3–1/2–1/1–2/1–3/1. Optical dilatometry measurements revealed that K-feldspar reduced the sintering temperature by about 50°C compared to Na-feldspar. Densified 35% K-F and 35% Na-F bodies showed very low pyroplastic index (PI) such as 5.36 × 10–6 cm−1 (at 1150°C) and 7.46 × 10−6 cm−1 (at 1200°C), respectively, whereas Na-F/K-F 1/3 sample exhibited the lowest PI (3.58 × 10−6 cm−1) at very low sintering temperature (at 1150°C). Microstructural analysis showed that the dissolution of residual quartz grains and the homogeneity of the distribution of the crystal phases support decrease in pyroplastic deformation.