| For the purpose of improving the thermal stability of the Eco-Friendly and medium temperature transparent glaze for household porcelains, the two representative medium temperature daily-use porcelain bodies from Jingdezhen and Chaozhou were investigated. The great difference in thermal stability of the two porcelain bodies was analyzed from the points of view of compositions, microstructures and performances. Chaozhou porcelain bodies with high thermal stability were selected as the basic bodies for the next experiment of preparing medium temperature transparent glaze. The medium temperature transparent glaze was prepared by using suitable raw materials and adjusting the prescription composition. The influence of main technical parameters on the glazed effect and thermal stability was investigated. The prescription of basic transparent glaze was optimized by orthogonal experimental method. In view of the glass-ceramic, the LAS-based crystals with low thermal expansion were synthesized through adjusting the appropriate process parameters, and then were added into the basic glaze to increase its thermal stability. The effects of addition amounts of LAS-based crystals on thermal stability and appearance of the transparent glaze were investigated. XRF, dilatometry, TG-DTA, XRD, SEM, EDS and gloss meter test were employed to characterize the as-prepared glaze.The results show that Jingdezhen and Chaozhou porcelain bodies are of high coefficient of thermal expansion (a) due to their low aluminum and high silicon content and low a value due to their high aluminum and low silicon content, respectively. The former has no cracking when they were treated from170℃to20℃for one time, and the latter has excellent thermal ability without cracking when they were treated from600℃to20℃for one time. The reason why the thermal stability of Chaozhou porcelain bodies is high is that the main crystalline phase of Chaozhou porcelain bodies was well-developed, crossed, and slender nanorod-like primary mullite crystals, which strengthened and toughened the bodies and gave Chaozhou porcelain bodies excellent thermal stability. However, Jingdezhen porcelain bodies were just the opposite.The formula of base glaze is K-feldspar32%, kaolin12%, steatite5%, calcite22%, quartz24%, barium carbonate2%, zinc oxide3%and additional CMC0.2%. The base glaze has the performances of thermal expansion coefficient of7.2×10-6/℃in the range of room temperature to600℃, gloss of116and without cracking when they were treated from170℃to20℃for one time. The optimum processing of the glaze could be obtained when fired at1200℃at the increasing temperature rate of400℃/h, kept for30min and then cooled naturally.The experimental results of synthesizing LAS system crystals show that the optima formula is Li:Al:Si=1:1:1. LiAlSiO4(β-eucryptite) crystal can be synthesized at1200℃for2h. The transformation process of the synthetic products Li2SiO3â†'LixAlxSi1-xO2â†'LiAl(SiO3)2â†'LiAlSi2O6â†'LiAlSiO4.The glaze layer structure was composed of glass phase and fine β-eucryptite crystals with the addition of the LAS system crystals. The grain size, quantity and distribution of β-eucryptite crystallites with low thermal expansion which were precipitated in glaze were very different according to the different additive amounts. The optimum addition amount was5%, and a large number of β-eucryptite crystallites with the size of0.2-0.4μm were generated and evenly distributed in the glaze matirx at this time. The high thermal stability of transparent glaze with a of6.0×10-6℃in the range of room temperature to600℃, gloss of110and no cracking cooled from200℃to20℃for one time was finally obtained. |
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