Volatilization Characteristic And Crystallization Property For CaO-Al₂O₃-based Mold Powder

Volatilization characteristic and crystallization property of mold powder are important properties.Volatilization characteristic can affect the uniformity of slag composition directly and the property stability of slag.Crystallization can directly affect the heat transfer and bubrication between solidified shell and crystallizer.Both of them affect the smooth operation of continuous casting and improvement of billet quality.In this paper,CaO-Al2O3-based mold powder was the object of study.The volatilization characteristic and crystallization property of the mold powder were studied by thermogravimetric analysis and scanning electron microscopy.Under this experimental condition,the main conclusions were summarized as follows:(1)The initial weight loss temperature of CaF2 was 1026?.CaF2-SiO2 system reacted to form SiF4 at 890?,which increased the volatility of the system.Na2CO3 decomposition and Na2O volatilization occurred above 865? simultaneously.The addition of SiO2 and Al2O3 reduced the initial weight loss temperature of Na2CO3 and increased the weight loss rate.(2)B2O3 only volatiled less than 2%above 1000?.The initial weight loss temperature of Li2CO3 was 657?,which resulted from decomposition of Li2CO3 and the weight loss rate was up to 56.39%.(3)The effects of different fluxing agents on the volatilization of CaO-Al2O3-based mold powder were as follows:Li2O<CaF2<B2O3<Na2O.(4)When no fluxes were added,the crystallization phases of CaO-SiO2-Al2O3 slag were CaO Al2O3,2CaO SiO2,12CaO· 7Al2O3.The addition of 10%CaF2 could promote the crystallization of CaO·2SiO2.9CaF2.The addition of 10%Na2O inhibited the crystallization of 2CaO SiO2 from the crystalline phase of the basic slag.The addition of Li2O could obviously promote the crystallization of LiAlO2 which was a new phase.The addition of 10%Li2O and 10%B2O3 promoted the crystallization of Ca-Si-Al composite oxides.