• Journal of the Korean Ceramic Society
• /
• v.14 no.3
• /
• pp.163-168
• /
• 1977

As a wet chemical drying process "hot petroleum drying method" was applied and developed for preparing uniformly fine oxide powder with high purity and sinterreactivity. Using this method solution of sulfates was dried in hot petroleum bath (~17$0^{\circ}C$) to sulfate powder from which corresponding mullite doped by Fe3+ ion was formed. Particle size, shape, decomposition by heat, and phase identification of sulfate andoxide powders determined by DTA, TGA, X-ray diffraction, analysis and electron microscopy: sulfate powder prepared by this drying method is an intimate mixture of the amorphous form of uniformly and finely distributed spherical particles (0.05-0.1$\mu$). Mullitization with the sulfate powder occurs at 110$0^{\circ}C$ in air. The morphology of mullite particle made by firing the sulfate powder at 135$0^{\circ}C$ in oxygen atmosphere is granular of 0.1-0.3$\mu$ in size. This drying process proved to be a very effective method for preparing fine, homogeneous, and highly sinterreactive multicomponent oxide powder without conventional ceramic process of mixing, milling, and granulating. This process can be also applied for preparing electronic ceramic materials which are requisite for high purity and homogeneity.mogeneity.

• Economic and Environmental Geology
• /
• v.29 no.3
• /
• pp.269-279
• /
• 1996

Dehydroxylation and mullitization of primary and secondary kaolins were investigated in order to compare and understand the differences in thermal behaviours by DTA and TG up to $1,100^{\circ}C$. Chemical analyses and EPMA of the samples revealed nearly ideal unit-cell formulae of kaolins. The weight losses of dickite and halloysite are 14% and 12.5% on the average, respectively. The activation energies of dehydroxylation of kaolin minerals were calculated according to Kissinger's approach which uses various heating rates in DTA to estimate the activation energy of thermal reactions. The activation energies of dehydroxylation of halloysites from Daemoung and Buksam mines are about $163kJmor^{-1}$ (white), $168kJmor^{-1}$ (pink), and $176kJmor^{-1}$ respectively. The activation energies of dickites collected from Sungsan and Ogmae mines are about $166kJmor^{-1}$ and $387kJmor^{-1}$. The asymmetric shape of endothermic peak in DTA, the relative intensities of OH-stretching bands in FTIR spectroscopy and the existence of residual XRD peaks of the samples which were heated at $550^{\circ}C$ for 2 hours indicate that Sungsan dickite may be more disordered than Ogmae dickite. The new phase formed in thermally treated samples in the range of $900^{\circ}C$ to $1,100^{\circ}C$ was identified as mullite by XRD on the basis of disappearing of the characteristic peaks of kaolins and increasing of amorphous background upon heat treatment. On further heating, loss of more water from dehydroxylate resulted in the formation of mullite and the characteristic X-ray diffraction patterns of mullite began to appear at about $900{\sim}1,000^{\circ}C$ in kaolins.

• Journal of the Korean Ceramic Society
• /
• v.43 no.4 s.287
• /
• pp.235-241
• /
• 2006

Mullite short fibers have been fabricated by adapting the Kneading-Drying-Calcination (KDC) process and characterized. The effect of the addition of foaming agent and calcination temperature on the formation of mullite fibers from coal fly ash, was examined. In the present work, ammonium alum $NH_4Al(SO_4)_2\;12H_2O$ synthesized trom coal fly ash and sodium phosphate $Na_2HPO_4\;2H_2O$ were used as foaming agents. After calcination at $1300^{\circ}C$ for 10 h and then etching with 20% HF solution at $50^{\circ}C$ for 5 h using a microwave heating source, the alumina-deficient $(AI_2O_3/SiO_2$ = 1.13, molar ratio) orthorhombic mullite fibers with a width of ${\sim}0.8mm$ (aspect ratio >30), were prepared from the coal fly ash with $AI_2O_3/SiO_2$ = 0.32, molar ratio by the addition of $NH_4AI(SO_4)_2\;12H_2O$, and with further addition of 2 wt% sodium phosphate. The excessive addition of sodium phosphate rather decreased the formation of mullite fibers, possibly due to the large amount of liquid phase prior to mullitization reaction.

• Journal of the Korean Ceramic Society
• /
• v.32 no.5
• /
• pp.626-634
• /
• 1995

The SiC-porcelain powder mixtures containing 51.9wt% SiC are produced as by-products from the surface abrasion process of porcelain cores. This raw powders were used as starting materials for the synthesis of SiC containing ceramics. The specimen, which was fired at 135$0^{\circ}C$ from raw powders, had SiC, $Al_{2}O_{3}$, , cristobalite, mullite as crystalline phases, and the fractured microstructure showed dispersed SiC crystalline particles almost wetted with glassy matrix and spherical pores. Although the oxidation of SiC containing powder compacts wetted with glassy matrix and spherical pores. Although the oxidation of SiC containing powder compacts started at the range of 600~80$0^{\circ}C$ form the analysis of weight gain, the presence of $SiO_{2}$ crystallien phase and cristobalite was confirmed at 100$0^{\circ}C$ by XRD analysis. Mullitization of specimens was accelerated by preheating before the final firing. The specimen sintered at 135$0^{\circ}C$ after 100$0^{\circ}C$ preheating consisted of SiC, cristobalite, mullite as crystalline phases, and revealed 2.24g/$cm^{3}$ bulk density, 11.73% water adsorption, porous microstructure with small amount of glassy phase. SiC contents of specimens, which was 51.9 wt% in the raw powders, reduced to 37~22 wt% after firing at 135$0^{\circ}C$ depending on the preheating condition.