Nitridation Behavior of Kaolin with Reduced Alumina Content Obtained by Acid Treatment

,; ,; ,; ,; ,; ,

J. Korean Ceram. Soc. > Volume 29(5); 1992 > Article

Journal of the Korean Ceramic Society 1992;29(5): 347.

산처리에 의하여 알루미나 함량을 줄인 카올린의 질화거동

배원태, 정원도, 조철구

경상대학교 무기재료공학과

Nitridation Behavior of Kaolin with Reduced Alumina Content Obtained by Acid Treatment

ABSTRACT

Various kaolin samples with different alumina content were prepared from calcined admixture of kaolin and ammonium sulfate by varying the treatment time in sulfuric acid. Samples were nitridated under N2 or N2-H2 atmosphere with changing the amount of added carbon, the reaction time and temperature. As the alumina content lowered, the size of kaolin particles decreased and the specific surface area increased. XRD analysis indicated that ${alpha}$-quartz remained by decomposition of halloysite and meta-halloysite. Experimental results of nitridation behavior are summerized as follows; 1) Nitridation under N2 atmosphere. With the increase of C/SiO2 ratio and with the decrease of Al2O3 content, disappearance of XRD pattern peaks of mullite, ${alpha}$-quartz and ${alpha}$-Al2O3 were accelerated at 1300$^{circ}C$. SiC was the main phase in the reaction product of acid-treated kaolin samples nitridated at 1300$^{circ}C$ for 10 hours regardless of C/SiO2 ratio. But the XRD peak intensities of ${beta}$-Si3N4, ${beta}$-sialon and SiC did not show much difference when untreated raw kaolin was fired at the same condition. When the ratio of C/SiO2 was 3.5, ${beta}$-sialon and ${beta}$-Si3N4 existed in the reaction product of about 22% alumina containing kaolin sample fired at 1350$^{circ}C$ for 7 hours. Only ${beta}$-sialon existed in the same sample fired at 1400$^{circ}C$ for 10 hours. ${beta}$-sialon was obtained from all of the acid-treated kaolin samples fired at 1400$^{circ}C$ for 40 hours, but AlN and SiC remained in the untreated kaolin sample. Z value of the ${beta}$-sialon obtained from the 22% alumina containing kaolin sample fired at 1400$^{circ}C$ for 40 hours was about 1.3(XRD) and 1.5(EDS). 2) Nitridation under 80N2+2OH2 mixed gas atmosphere with the C/SiO2 ratio of 1 Mullite was not found, but ${alpha}$-Si3N4, and ${beta}$-sialon were present in the reaction product of about 22% alumina containing kaolin sample fired at 1300$^{circ}C$ for 10 hours. When untreated kaolin sample was nitridated at the same condition, mullite remained. AlN and SiC were not found in the reaction product of about 22% alumina containing kaolin sample fired at 1350$^{circ}C$ for 5 hours. On the other hand, AlN and SiC remained in the product of untreated kaolin fired at the same condition.