Synthesis and Phase Relations of Potassium-Beta-Aluminas in the Ternary System K2O-MgO-Al2O3

K2O-MgO-Al2O3 3성분계에서 K+-β/β"-Al2O3의 합성 및 상관계

  • Ham, Choul-Hwan (Department of Industrial Chemistry, KonKuk University) ;
  • Lim, Sung-Ki (Department of Industrial Chemistry, KonKuk University) ;
  • Lee, Chung-Kee (Department of Industrial Chemistry, KonKuk University) ;
  • Yoo, Seung-Eul (Functional Materials Engineering Lab., Korea Automotive Technology Institute(KATECH))
  • 함철환 (건국대학교 공업화학과) ;
  • 임성기 (건국대학교 공업화학과) ;
  • 이충기 (건국대학교 공업화학과) ;
  • 유승을 (자동차부품연구원 기능소재연구실)
  • Received : 1999.09.20
  • Accepted : 1999.10.14
  • Published : 1999.11.10

Abstract

$K^+-{\beta}/{\beta}"-Al_2O_3$ in the ternary system $K_2O-MgO-Al_2O_3$ was directly synthesized by solid state reaction. The phase formation and phase relation were carefully investigated in relation to starting composition, calcining temperature and time, and dispersion medium. The optimal synthetic condition was also examined for the formation of ${\beta}"-Al_2O_3$ phase with a maximum fraction. As a composition range, the mole ratio of $K_2O$ to $Al_2O_3$ was changed from 1:5 to 1:6.2 and the amount of MgO used as a stabilizer was varied from 4.2 wt % to 6.3 wt %. The calcining temperature was selected between $1000^{\circ}C$ and $1500^{\circ}C$. At $1000^{\circ}C$, the ${\beta}/{\beta}"-Al_2O_3$ phases began to form resulted from the combining of ${\alpha}-Al_2O_3$ and $KAlO_2$ and increased with temperature rising. All of ${\alpha}-Al_2O_3$ phase disappeared to be homogenized to the ${\beta}/{\beta}"-Al_2O_3$ phase at $1200^{\circ}C$. Near the temperature at $1300^{\circ}C$, the fraction of ${\beta}"-Al_2O_3$ phase showed a maximum value with the composition of $K_{1.67}Mg_{0.67}Al_{10.33}O_{17}$. At temperatures above $1300^{\circ}C$, the fraction of ${\beta}"-Al_2O_3$ phase decreased gradually owing to $K_2O$ loss caused by a high potassium vapor pressure, and the appropriate calcining time was about 5 hours. Acetone was more effective than distilled water as a dispersion medium for milling and mixing.

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