Effect of talc addition on pyroplastic deformation of an alumina strengthened porcelain

Abstract

The influence of talc addition on the pyroplastic deformation of alumina-strengthened porcelain was investigated in this study. Along with the lower content of feldspar, the addition of talc contributed to the crystallization of the cordierite during the firing process, and the resulting cordierite crystals formed complicated filler structures. The porcelain samples made with the addition of talc showed an unprecedented pyroplastic deformation characteristic with almost no changes in the pyroplastic deformation index value during further firing at over 100°C after the water absorption reached almost zero. This improvement of pyroplastic deformation was thought to synchronize with the crystallization of cordierite.©2016 The Ceramic Society of Japan. All rights reserved.Key-words : Pyroplastic deformation, Talc, Cordierite, Porcelain, Filler [Received June 1, 2016; Accepted June 30, 2016] In the long history of porcelain manufacturing, controlling the deformation of a porcelain body during its firing process is one of the most important problems due to its tendency to decrease the precise shape reproducibility of the final product after the firing process. During the firing process, shrinkage deformation and pyroplastic deformation are two main factors responsible for the distortion of the final products. Shrinkage deformation occurs in the first stage of firing before the full dense temperature, and pyroplastic deformation is dominant during the final stage of firing.1) Pyroplastic deformation affects the optimum firing temperature range, and is related to many factors such as chemical composition, particle size of raw materials, and firing pattern.The chemical reactions, phase development, and microstructural evolution of a porcelain body during the firing process have been studied extensively with some researches focused on pyroplastic deformation.2)9) Tuncel et al. have studied the effect of chemical composition on pyroplastic deformation at 1250°C, and demonstrated that the Na 2 /K 2 O ratio had a more prominent effect on pyroplastic deformation compared to changes in the SiO 2 /Al 2 O 3 ratio. 10) Deng et al. reported the effect of the distribution of mullite in the glass matrix on pyroplastic deformation.11) Other studies revealed that the dissolution of quartz in the melt resulted in increasing the viscosity of the liquid phase, thus, reducing the pyroplastic deformation. 12)14) These studies mainly focused on the viscosity of the liquid phase or mullite phase formation in the glass matrix. However, there are only few reported studies on the role of filler in the pyroplastic deformation of porcelain. Austin et al. have reported that the addition of alumina, with higher refractoriness than quartz, in vitreous whiteware was effective in decreasing deformation during firing, 15) which suggests the characteristic of filler is a sensitive factor on pyroplastic deformation of a porcelain body. On the other hand, Kobayashi studied the crystallization and densification of cordierite ceramics, and reported a hig...

Evaluation of the water absorption and pyroplastic deformation of alumina-strengthened porcelain with talc-addition

“…13 where the formation of a continuous network of cordierite is emphasized to construct the rigid microstructure. Different from the previous study, 13) although porcelain 2T contains smaller amount of the talc, 2 versus 18 mass %, it achieves the aim of both small WA and small PI in a wide fire temperature range from 1240 to 1384°C. On the contrary, STD can only achieve such purpose at 1240°C (see Figs.…”

“…9), 12) In addition to the effect of glass matrix and mullite formation on reducing PD, some researchers also proposed to increase the viscosity of the liquid phase by introducing or forming crystals with a high melting point as a filler. 13) Talc is a mineral which includes magnesium, which enhances the glass matrix formation in porcelain. 11) Furthermore, the cordierite which crystallizes during the firing of porcelain with talc can be used as a strengthening filler or to reduce PD.…”

“…11) However, they ignored the effect of the enhanced crystallization of cordierite on the liquid phase viscosity. Kamochi et al 13) investigated the effect of talc addition to alumina-strengthened porcelain on PD. The fired porcelain had a very low pyroplastic deformation index (PI) of less than 1.5 © 10 ¹6 mm ¹1 even at a firing temperature 100°C higher than that at which the maximum densification was observed.…”

Low water absorption and pyroplastic deformation of alumina‐strengthened porcelain with petalite and Gairome clay

“…PD suppression also contributes to realizing new geometries of ceramic products that could otherwise easily be deformed with conventional porcelain. Although many efforts have been made toward suppressing the PD of porcelain, 4,[6][7][8][9][10][11][12] it remains a great challenge to develop dense porcelain with little PD because of the previously mentioned trade-off relationship. A large amount of low-viscosity liquid phase during firing, for instance, accelerates densification but also increase PD.…”