• 한국세라믹학회지
• /
• 제35권10호
• /
• pp.1061-1069
• /
• 1998

The thermal instability of Al2TiO5 Ceramics was contrlled by solid solution with MgO SiO2 and ZrO2 through electrofusion in an arc furnace. The thermal expansion properties of Al2TiO5 composites show the hysteresis due to the strong anisotropy of The crystal axes of these material. These phenomena are ex-plained by the opening and closing of microcracks. The difference in microcracking temperatures e.g 587.6(ATG2), 405.9(ATG3) and 519.7$^{\circ}C$(ATG4) is caused by the difference in grain size and stabilizer type. The thermal shock behaviour under cyclic conditions between 750-1400-75$0^{\circ}C$ show no change in mi-crostructure and phase assemblage for all three stabilized specimens. After the thermal loading test at 110$0^{\circ}C$ for 100hrs. ATG1 and ATG2 materials decomposes completely to its components corundum and ru-tile in both cases. However with approximatelly 20% retention of the Al2TiO5 Thus in order to prevent decomposition of the stabilized material in the critical temperature range 800-130$0^{\circ}C$ it must be traversed within a short period of time.

• 자원환경지질
• /
• 제25권2호
• /
• pp.101-114
• /
• 1992

Occurrences of many kaolin-pyrophyllite deposits in the Youngnam area is related to the Late Cretaceous volcanic rocks, which are widely distributed through southern part from Tongnae-Yangsan to Miryang-Wolsung. The mode of occurrence and genesis of the kaolin-pyrophyllite deposits related to the volcanism was studied. This area is covered by andesitic rocks, rhyolite and rhyolitic welded tuff in ascending order. Lower most andesitic part is almost fresh. The altered rocks in the rhyolitic welded tuff can be classified into the following zones: silicified, pyrophyllite-kaolin, and argillic zone from the center part of ore deposit. The clay deposits occur as irregular massive, layer and funnel type about 5~20 m in width and is accompanied by thin diaspore bed outside of ore shoot. The clays chiefly consist of kaolinite, sericite, pyrophyllite, a little amount of diaspore, alunite, dumortierite, corundum and pyrite. The process of kaolinization-pyrophyllitization has a close relation to a local acidic hydrothermal solution originated from granitic rocks. Acidic hydothermal alteration occurrs mainly in the rhyolitic welded tuff. Initial solution containing $H_2S$ and others was oxidized near the surface and formed hydrothermal sulfuric acid solution.

• 한국광물학회지
• /
• 제3권1호
• /
• pp.44-57
• /
• 1990

Mineralogy of clay(Napseok) deposits in Yangsan area has been studied by the methods of field investigation and laboratory works including the polarizing microscopy, X-ray diffraction, infrared spectroscopy, thermal analysis, chemical analysis by electron micro-probe and atomic absorption spectrophotometer, and electron microscopy(SEM and TEM). The Napseok ores in both the Cheonbulsan and Yongcheon deposits consist mainly of sericite, pyrophyllite and quartz, with more or less tourmaline. The high temperature minerals such as corundum and dumortierite are found in the Cheonbulsan deposit, but not in the Yongcheon deposits. Dickite, nacrite, and halloysite are found in the Yongcheon deposit, but not in the Cheonbulsan deposit. The Napseok ores of the Yukwang deposit consist of sericite posits in the Yangsan area. Occurrence, chemistry and structural features of important minerals are described. Mineralogical data of sericite such as intensity raios and chemistry also support that the Napseok deposits of both the Chenobulsan and Yongcheon mines were formed at the higher temperature than those of the Yukwang mine. Presence of sericite-dickite-pyrophyllite ores in the Yongcheon deposit also suggests the lower temperautre than in the Cheonbulsan deposit.

• Journal of Magnetics
• /
• 제13권1호
• /
• pp.23-29
• /
• 2008

The magnetic and other physical characteristics of $Mn_xSi_{1-x}Te$ have been investigated by electron magnetic resonance (EMR), X-ray diffraction (XRD) and other experiments. $Mn_xSi_{1-x}Te$ is found to have corundum structure for manganese contents up to 10% and also to be ferromagnetic for temperatures below 80 K. While ferromagnetic resonance signal coexists with the usual paramagnetic resonance signal, invariance of the g-factor inferred from the electron paramagnetic resonance signals throughout all temperature ranges clearly confirms that the manganese ions are in the electronic 3d5 state. The temperature dependence of EMR line-width is the same as other diluted magnetic semiconductors. From the EMR signals relaxation times $T_2$ and $T_1$ of $Mn_xSi_{1-x}Te$ compounds are estimated to be about $4.4{\times}10^{-10}s$ and $9.3{\times}10^{-8}s$ respectively and are found to vary slightly with temperature or composition change. Exchange narrowing of the EMR line-width becomes dominant for the sample in which the substitution ratio, x = 30%. For one sample, in which x = 0.5%, spin glass-like behavior is indicated by EMR signals for temperatures lower than 60 K. This behavior may authentic for samples within a certain range of x.

• 한국세라믹학회지
• /
• 제31권11호
• /
• pp.1401-1413
• /
• 1994

The synthesis of kaolinite mineral from domestic diatomite for silica resource, commercial vailable gibbsite or alumina for alumina resource were made under various hydrothermal treatment, and the sythetic effect of acidic mineralizers, temperature treatment with time duration, particle size of alumina on formation of kaolinite mineral and the plastic properties of synthesized kaolinite were investigated. The various acidic mineralizers which are HCl, HNO3, H2SO4 and Oxalic acid were employed for hydrothermal reaction in the range of 0.01 mol/ι to 2 mol/ι concentration of each mineralizers. It was found that HCl in the level of 1 mol/ι solution produced highly yields of well-crystallized and platy form kaolinite mineral and gave the most effective extraction of iron oxide, compared to that of others, that HNO3 produced highly yield of kaolinite but lower extraction of iron oxide, that H2SO4 produced low yield of kaolinite and formed alunite mineral, and that oxialic acid formed spherical crystalline kaolinite and gave low extraction of iron oxide. Moreover, it showed that kaolinite minerals were well synthesized in a wide range of less than 2 mol/ι acids, but were poorly synthesized at more than 2 mol/ι acids. However, boehmite and kaolinite were coexistently formed in the temperature range of 18$0^{\circ}C$ and 20$0^{\circ}C$ when the calcined diatomite and gibbsite were involved. The well-ordered kaolinite mineral as a platy form was highly synthesized in the temperature range of 220 and 24$0^{\circ}C$, when the same marterials as above were used with treatment of 1 mol/ι HCl solution. The results also revealed that the size of crystalline platy form kaolinite, synthesized from alumina and calcined diatomite with treatment in 1 mol/ιHCl solution at 24$0^{\circ}C$, was much larger than that of gibbsite and calcined diatomite shown previously, and that kaolinite and corundum minerals were coexistently formed under any hydrothermal treatment conditions. The plasticity of synthesized kaolinite from under 2 ${\mu}{\textrm}{m}$ alumina and calcined diatomite was very poor, and that of the synthesized kaolinite from raw diatomite and gibbsite gave higher than that of calcined diatomite and gibbsite.

• 한국세라믹학회지
• /
• 제56권4호
• /
• pp.350-353
• /
• 2019

Porous alumina ceramics with addition of 0, 5, 10, 15, and 20 wt% Al(H₂PO₄)₃ were sintered at 1300, 1350, and 1400℃. The effects of the Al(H₂PO₄)₃ addition on crystal phases, water absorption, open porosity, pore size distribution, microstructures, and flexural strength were studied extensively. The experimental results revealed that only characteristic peaks of corundum were indexed in the XRD patterns of the as-prepared porous ceramics. The water absorption and open porosity of the porous Al₂O₃ ceramics increased remarkably with an increase in Al(H₂PO₄)₃ addition. The flexural strength first increased to a maximum value when 5 wt% Al(H₂PO₄)₃ was added and then decreased as additional Al(H₂PO₄)₃ was further added. SEM images showed that the average Al₂O₃ grain size in the porous ceramics changed in an opposite way as the flexural strength. The porous Al₂O₃ ceramics with 10 wt% Al(H₂PO₄)₃ addition exhibited comparable flexural strength to the ceramics without Al(H₂PO₄)₃ addition, although the latter had much higher porosity.

• 자원환경지질
• /
• 제24권2호
• /
• pp.83-96
• /
• 1991

Haenam pyrophyllite deposit occurred in the rhyolitic tuff of late Cretaceous age is located in the northern part of Haenam-gun, Jeonranam-do. The ore of the Haenam deposit is predominantly composed of pyrophyllite and illite accompanying such clay minerals as kaolinite, chlorite, and smectite. Pyrophyllite ore at the center of altered mass is often associated with kaolin minerals and high temperature minerals such as corundum, andalusite, and diaspore. On the basis of mineral assemblage the Haenam deposit can be devided into three alteration zones from the center to the margin of the deposit; the pyrophyllite zone, kaolinite zone, and illite zone. All alteration zones are associated with appreciable amounts of chalcedonic quartz. Those mineral assemblages indicate that hydrothermal solution which produced the Haenam deposit is strongly acidic solution with high silica and hydrogen activity and low $SO_4{^{2-}}$ activity. Discriminant analysis shows that $Na_2O$, $K_2O$, and $Al_2O$, of major elements are discriminant elements which classify alteration zones, while in case of trace elements Cr, Ni, and Sr turned out to be discriminant elements in this deposit. According to the mineral assemblage and illite geothermometry, pyrophyllite ore is considered to have been formed at about $240-290^{\circ}C$. K-Ar isotopic age for illite from this deposit indicates that it was formed at much the same age of later stage volcanics in the area, suggesting that the hydrothermal alteration of these deposits is associated with later volcanism of the area.

• 자원환경지질
• /
• 제36권4호
• /
• pp.269-274
• /
• 2003

금번 연구는 환태평양 귀금속 광화대 중 국내기업이 이미 진출한 나라를 대상으로 하였고, 캄보디아 빠일링 지역에 분포하는 보석광상에 대하여 조사를 수행하였다. 빠일링 보석광상은 현무암이 풍화된 라테라이트에 형성되어 있으며 표토 가까운 곳(깊이 1m 정도)에서는 주로 저품위의 강옥이, 이보다 깊은 곳에서는 고품위의 강옥이 산출된다. 또한, 풍화토의 색깔이 적색인 경우에는 루비, 청색의 경우에는 사파이어가 많이 산출되며, 일반적으로 적색토가 청색토의 상위에 놓인다. 보석류의 산출 및 성인은 풍화토와는 관계가 없으며, 적어도 화산암 상부에 원래 만들어져 있던 이들 보석류가 암석이 풍화를 받으면서 다량으로 산출되는 것이다. 이들 보석류는 화산암의 분출 시 또는 분출 후에 층의 상부 내지는 다른 화산암의 분출로 인해 두 층간 사이에서, 고온의 상태 하에서 보석이 만들어진다고 사료되며, 보석을 함유하는 화산암은 보석을 함유하지 않는 화산암과는 분출시 조금 달랐을 것으로 사료되나, 암석의 화학성분은 다른 지역에서 산출되는 화산암과 별다른 차이가 없다.

• 한국세라믹학회지
• /
• 제35권1호
• /
• pp.5-10
• /
• 1998

Mullitization in a multicomponent oxide system(alumina-kaolin-quartz-feldspar-talc) was studied as a function of sintering temperature from 1200 to 1500$^{\circ}C$ based upon a quantitative X-ray diffraction analysis. In the present study mullite grew as wiskers and its formation reaction showed characteristic there stages as follows In the first stage(1255-1295$^{\circ}C$) an appreciable mullitization(nucleation) occurred while corun-dum dissolution into glass (increasing glass content ) limited the rate of the reaction. At 1295-1335$^{\circ}C$ (second state) the reaction was significantly enhanced with a considerable glass consumption and with no appreciable change in corundum content. Finally (above 1335$^{\circ}C$) the reaction rate was attenuated re-markably with an apparent decrease in glass consumption rate. The impingement of mullite whiskers by oth-er whiskers and crystals was speculated to cause mullite growth in thickness direction with a slow growth rate resulting in the diminished reaction rate in the final stage.

• Bulletin of the Korean Chemical Society
• /
• 제9권6호
• /
• pp.333-337
• /
• 1988

Spinel $CoFe_2O_4$ solid solutions containing up to 50 mol% CoO were synthesized with spectroscopically pure CoO and ${\alpha}-Fe_2O_3$ polycrystalline powders. The spinel structures of the $CoFe_2O_4$ solid solutions were analyzed from XRD patterns and the Mossbauer spectra showed that the quenched $CoFe_2O_4$ had a partially inversed spinel structure ($Co_{0.23}Fe_{0.77}$) < $Co_{0.77}Fe_{1.23}$ > $O_4$, while the slowly cooled $CoFe_2O_4$ was completely inversed spinel ($Co_{0.04}Fe_{0.96}$) <$Co_{0.96}Fe_{1.04}$ > $O_4$. The $CoFe_2O_4$ specimens containing 10, 20, 30 and 40 mol% CoO turned to be a mixture of corundum and spinel structures. Electrical conductivities were measured as a function of temperature from 300 to $900^{\circ}C$ under oxygen partial pressures from $10^{-3}$ to 1 atm. The temperature dependencies of the electrical conductivity show different behaviors in the low- and high-temperature regions. The average activation energies are 0.23 eV and 0.80 eV in the low- and high-temperature regions, respectively. It is suggested that $Co^{2+} {\to} CO^{3+} + e^-$ and $Fe^{2+} {\rightleftharpoons} Fe^{3+} + e^-$ are the main conduction mechanisms responsible for the electronic conduction in the low- and high-temperature regions, respectively.