Journal of the Korean Ceramic Society (한국세라믹학회지)

The Korean Ceramic Society (한국세라믹학회)
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Effect of Fluorides on Mullitization of $SiO_2-Al_2O_3$ System; Korean Kaolin

플루오르화물이 $SiO_2-Al_2O_3$계 원료의 물라이트화에 미치는 영향

  • 최상욱 (인하대학교 공대 요업공학과) ;
  • 이철규 (인하대학교 공대 요업공학과)
  • Published : 1980.02.01
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Abstract

The effect of the addition of various fluoreides on the mullitization of Korean crude kaolin was studied by X-ray powder diffraction and scanning electron microscopic methods. Kaolin without any addition of fluoreides began to be transformed into the mullite at 1, 10$0^{\circ}C$. Mullite peaks were discernible in the X-ray diffraction patterns of the specimens which contained fluorides equivalent to about 2 wt % fluorine, and which were sintered at 1, 05$0^{\circ}C$. The higher the concentration of fluorine in kaolin, the lower was the initiatinig temperature of mullitization. Experiments , for example, showed that mullite could be formed at 95$0^{\circ}C$ from kaolin mixed with 3.4% fluorine. Of the fluoride, addtives, sodiumsiliconfluoride $(Na_2SiF_6)$ was must effective in mullite formation of kaolin. In order of accelerating mullitization, the fluorides except $Na_2SiF_6$ could be placed in following sequence ; (1) sodium (NaF) (2) aluminium$(AlF_3)$ (3)potassium(KF) (4) ammonium$(NH_4F)$ (5) magnesium$(MgF_2)$ (6) calcium$(CaF_2)$. It was considered that the intrinsic characteristics of fluorides, such as size of ionic radiu, charge , bond strength between cation and anion, and electronegativity of cation affected millitization of halloysite, a main constituent mineral of kaolin.

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References

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