Effects of Mixing Amount of CoO on Non-isothermal Crystallization Behaviors of Willemite Crystalline Glaze
Building ceramics covered with willemite crystalline glaze were prepared with roller kiln at low temperature in short time.The effects of the content of CoO(colorant)on the non-isothermal crystallization performance of willemite crystalline glaze were studied,while the mechanism of amorphous crystallization of the crystalline glaze was revealed by using Kissinger method and water quenching & rapid cooling treatment.The blue color of the crystalline glazed gradually deepened,while the area proportion,diameter and crystal phase content of the crystalline glaze increased first and then decreased with increasing content of CoO.All the three parameters reached the maximum values when the content of CoO was 0.6 wt.％.The mechanism of amorphous crystallization of the willemite crystalline glaze was the surface crystallization synergistically with volume crystallization.The addition of an appropriate content(0.6 wt.％)of CoO is beneficial to reducing the crystallization activation energy,improving Avrami exponent,enhancing the small angle branching ability,and effectively promoting the amorphous crystallization process of the crystalline glaze.However,the excessive content(1.0 wt.％)of CoO would actually weaken the amorphous crystallization of the crystalline glaze,leading to decrease in integrity of the petals and diameter size of the flower-shaped crystal patterns.Finally,building ceramics covered with the willemite crystalline glaze with a integral flower-shaped pattern structure,crystal pattern diameter size of 2.8 mm and bright blue color(b*value of-50.2),were obtained with roller kiln at a relatively low temperature and quick firing process(the ferro firing temperature of 1165 ℃ and firing time of 70 min).
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