• 한국세라믹학회지
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• 제26권3호
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• pp.341-346
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• 1989

In order to evaluate the oxidation behavior of $\beta$-Sialon, $\beta$-Sialon ceramics was prepared from Si3N4, Al2O3, AlN and Y2O3 system. The specimens were oxidized in an oxygen atmosphere at 1, 20$0^{\circ}C$ for 9days. Oxidation behavior was evaluated by weight gain oxidation process, surface roughness. Microscopy, EDX and X-ray diffraction analysis were also used for the evaluation. The weight and surface roughness ofoxidized specimens were increased with increasing the oxidation time. Oxidized products were mullite, $\alpha$-cristobalite, yttrium aluminum oxide and yttrium silicate oxide.

• 한국세라믹학회지
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• 제34권2호
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• pp.195-201
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• 1997

본 논문은 kaolinite(Al2O3.2SiO2.2H2O)-aluminum trihydroxide(Al(OH3) 혼합물을 소결전에 planetary ball mill을 사용하여 건식 중에서 혼합분쇄한 후, 이 혼합물을 사용하여 소결하는 동안에 mullite의 생성거동을 연구한 것이다. 혼합물의 입자크기 감소는 분쇄 초기에 현저하였으며, 분쇄기간이 증가함에 따라 미립자들이 응집하는 현상을 보였다. 혼합물의 결정구조는 planetary ball milling에 의한 혼합분쇄에 따라 쉽게 비정질화되었으며, 비정질화되는 정도는 분쇄시간이 증가함에 따라 증가하였다. Kaolinite의 초기 분순물로 존재했던 anatase를 제외한 mullite상만이 상대적으로 낮은 소결온도인 1523K에서 혼합분쇄한 혼합물의 소결체에서 나타났다. 한편, 분쇄하지 않은 혼합물의 소결체의 경우는 이 온도에서 mullite 상 이외에 corundum, cristobalite, Al-Si spinel상이 공존하는 형태로 나타났다. 따라서, 혼합분쇄처리는 출발원료의 미소 규모에 있어서 균일혼합 및 분산을 촉진시키며, 또한 결정구조변화에 따른 열분해온도의 변화일으켜, 상대적으로 낮은 온도에서 고순도의 mullite를 직접 생성하는데 효과적이였다.

• 공학논문집
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• 제2권1호
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• pp.133-138
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• 1997

Mullite 분말을 합성하는 제조공정에서 기존의 분말합성법은 $1300^{\circ}C$이상의 높은 온도와 긴 반응시간과 cost 면에서 비싸다는 문제점을 안고 있다. 따라서 본 연구에서는 비교적 제조공정이 간단하고 짧은 반응시간내에 낮은 온도에서 미립의 산화물계 분말을 합성할 수 있는 연소 합성법으로 mullite 분말을 합성하였다. 금속의 질산염, 미립의 $SiO_2$분말과 연료를 적정 mole비로 혼합하여 공정변수에 따라 mullite를 합성하고, 그의 물성을 조사하였다. Hot plate에서의 실험은 연료의 양에 관계없이 mullite는 합성되지 않았다. 그러나, $500^{\circ}C$ 열처리로 실험에서는 mullite와 약간의 alumina, cristobalite가 보였고, 특히 aluminum nitrate, silica, urea 각각의 조성이 화학양론비였을 때 거의 완벽한 mullite를 얻을 수 있었다.

• 한국세라믹학회지
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• 제15권4호
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• pp.213-223
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• 1978

The purpsoe of this study was to produce domestic stamping materials; sling mass which could be used as unburned refractory for iron melt'ladle. Batch compositions were based on Belgian Ladelite; mineral compositions were composed of 84 wt% of quartz and 16 wt% of clay, and particle sizes were divided into 12 wt% of 1410/297㎛, 18wt% 297/149㎛, 20wt% of 149/74㎛, 11wt% 74/44㎛ and 39wt% 44㎛ under. The effect of variable batch compositions were also investigated such as substitution of pyrophylite or industrial grade alumina for quartz and of zircon for portion of quartz and clay, increase of clay and addition on sericite. Samples were pressed at 100kg/㎠ with 7.4wt% of water or 7.4wt% of 4 wt% PVA solution. Dried and Fired properties of samples such as linear shrinkage, apparent porosity, modulus of rupture, refractoriness and corrosion resistance to blast furnace slag were investigated. The results are summarized as follows. 1. Dried samples are shrinked, but fired at 700-1400℃ expanded. Samples fired at 700-1000℃ and 1200-1400℃ tended to expand with incresing of firing temperature, but fired at 1000-1200℃ tended to shrink with increase of firing temperature. 2. Apparent porosity of samples fired at 700℃ is increased, but fired at 1200-1400℃ decreased with increasing of firing temperature. 3. Modulus of rupture of samples fired at 700℃ is decreased, but fired at above 700℃ increased with increasment of firing temperature. 4. Dried samples with 7.4 wt% of 4 wt% PVA solution better improve modulus of rupture than with 7.4 wt% of water, but the firing strength of the sampels fired at 700-1000℃ is showed reversely. 5. In quartz-clay system, mineral phases of samples fired at above 1200℃ are consisted of α-quartz, α-cristobalite and mullite. Respectively as firing temperature was rising up, intensity of α-cristobalite and mullite is in creased. 6. Quartz-Kibushi clay system, Kimcheun quartz(substitutuion of portion of industrial grade alumina for quartz) Hampyeung clay system and pyrophyllite-clay system are better in corrosion resistance to blast furnace slag than burned pyrophyllite brick. 7. 84 wt% of pyrophyllite-16wt% of clay system is superior in modulus of rupture and corrosion resistance to blast furnace slag to 84 wt% of quartz-16 wt% of clay system.

• 한국세라믹학회지
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• 제50권6호
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• pp.470-475
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• 2013

In this study, we report that effects of a filler with a high coefficient of thermal expansion on a sealant for high-temperature ($750{\sim}850^{\circ}C$) SOFC. We designed a $SiO_2-BaO-ZnO-B_2O_3-Al_2O_3$ glass system with a softening temperature higher than $750^{\circ}C$. The properties of the glass system show not only low volumetric shrinking but also low swelling. The glass system did not create a crystal phase during along-term heat treatment. We fabricated a seal gasket with 0, 10, 15, and 20 wt% cristobalite added as filler materials with glass powder. The coefficient of thermal expansion of the seal gasket increased according to cristobalite content. During along-term heat treatment, the leak rate decreased by about 5% after a heat treatment in an oxidizing atmosphere at $750^{\circ}C$ for 2000 h, also decreasing by about 6% after a heat treatment in a reducing atmosphere at $750^{\circ}C$ for 1000 h.

• 한국세라믹학회지
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• 제12권1호
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• pp.23-28
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• 1975

The object of this study is to find the optimum conditions for crystal growth and kinds of crystal in ZnO-Al2O3-SiO2 glass composition. At first, the base glass composed of ZnO (44.7%), Al2O3(14.0%) and SiO2(41.3%) was melted in propane gas furnace at 1450-150$0^{\circ}C$ for an hour, and then it was poured into the stainless steel mould heated previously at $600^{\circ}C$ to obtain the thin glass test piece. Four crystal forms from base glass such as stuffed keatite, zinc orthosilicate, zinc aluminosilicate, and cristobalite were crystallized during heat treatment between 80$0^{\circ}C$ and 110$0^{\circ}C$. For the investigation of crystal growth, X-ray diffractometer and thermal differential analysis were used and the growth rate of the four crystal forms were obtained by the method of Archimedes specific gravity and intensity comparison of X-ray diffraction peak. The results obtained were as follows. 1) Stuffed keatite peaks which started to appear after two hours at 80$0^{\circ}C$ were maximum after 11 hours and this crystal breaks down to willemite irreversibly at about 100$0^{\circ}C$. 2) Development of gahnite started at 85$0^{\circ}C$ and increased with temperature growth. 3) Stuffed keatite which had been transformed slowly into willemite at 100$0^{\circ}C$ was decreased with time and willemite increased until four hours. 4) Cristobalite began to be developed after treatment of 110$0^{\circ}C$.

• 한국산업보건학회지
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• 제29권3호
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• pp.271-277
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• 2019

Objectives: A 46-year-old woman who had worked on cleaning stainless steel containers with Initially unknown powders died from acute silicosis. To determine whether the acute silicosis was related to his work environment, we conducted exposure assessment the level of exposure to respirable crystalline silica(RCS) during cleaning stainless steel containers with unknown powders. Methods: The exposure assessment of RCS were undertaken according to the National Institute for Occupational Safety and Health(NIOSH) method 7500. The components of the unknown powder were analyzed using X-ray Diffraction. Results: The unknown powder was found to be natural diatomaceous earth, which contained 12% and 9% quartz and cristobalite, respectively, crystalline silica. In the case of cleaning stainless steel containers with diatomaceous earth powder, the primary measurement resulted in 1.3 times higher occupational exposure limit of MOEL(in sum of quartz and cristobalite concentration) and 3.9 times higher in secondary measurement. The workbench was equipped with a local exhaust system, but because there was no hood at the end of the duct, the wind speed at the opening of the duct was 12 m/sec, whereas the controlled wind speed at the working position was only 0.3 m/sec below the legal standard. Conclusions: There is an urgent need to install the hood, conduct safety and health education for employers and workers, and periodically monitoring and manage the working environment.

• 자원리싸이클링
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• 제29권6호
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• pp.73-78
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• 2020

선탄 폐석의 유리 소재 원료로의 활용을 위해 선탄 폐석의 고온 상 전위 거동 및 Na2CO3의 첨가에 따른 유리질(비정질)화 실험을 실시하였다. 실험 결과 700~1,100 ℃에서 소성된 선탄폐석에는 mullite가 생성되고, 1,450 ℃에서는 mullite와 cristobalite만이 존재하였다. 선탄 폐석의 유리질화는 Na2CO3 첨가됨에 따라 진행되었으며, Na2CO3 10 wt.% 첨가 후 1,450 ℃ 온도에서 소성된 선탄 폐석의 유리질화는 97.9 wt.%로 나타났다. 그러나 Na2CO3가 20 wt.% 첨가된 선탄 폐석의 시료의 경우, 1,100 ℃에서의 2차 재소성 과정에서 nepheline(Na2O·Al2O3·2SiO2)이 생성되었으며, 이를 통해 선탄폐석의 유리질화를 위한 최적의 Na2CO3 첨가량은 10 wt.%로 나타났다.

• 한국세라믹학회지
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• 제40권5호
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• pp.494-500
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• 2003

금속 제련공정에서 배출되는 특정폐기물인 EAF(Electrical Arc furnace) dust를 점토와 혼합하여 건축용 벽돌을 제조함에 있어 A1203의 첨가가 소결범위에 미치는 영향을 연구하였다. $Al_2$O$_3$ 첨가되지 않은 시편은 1200-125$0^{\circ}C$에서 과량의 액상에 의해 기포가 형성되고 개기공(open pores)이 감소함으로 겉보기 밀도가 크게 감소하였으며 125$0^{\circ}C$ 이상에서는 기포가 시편 외부로 소멸되어 흡수율이 증가되었다. 그러나 $Al_2$O$_3$가 첨가된 Clay-Dust 계 소결체는 1200-125$0^{\circ}C$ 구간에서 소결온도에 따른 밀도 변화율이 크게 감소되었고, 125$0^{\circ}C$ 이상에서는 흡수율(%)의 증가율이 둔화되었다. $Al_2$O$_3$가 첨가되지 않은 시편은 1275$^{\circ}C$에서 소결된 경우 cristobalite상이 주된 상인 반면, mullite(3Al$_2$O$_3$ 2SiO$_2$)상은 소량 합성되었고, 원료성분인 hematite(FeAl$_2$O$_4$)는 소멸되지 않아 액상이 과량 생성되는 조성임을 확인하였다. 반면 $Al_2$O$_3$가 l5 wt% 첨가된 시편의 경우, 1275$^{\circ}C$에서 cristobalite는 완전 소멸되고 mullite상이 합성되어 주상이 되며, hematite 상이 일부 AI$_2$O$_3$와 반응하여 hercynite(FeAl$_2$O$_4$)상을 형성하여 액상 생성량이 많지 않을 것으로 분석되었다. 이상의 결과로부터 Clay-Dust계에 $Al_2$O$_3$를 첨가하면 액상의 발생량과 특성 및 결정상 종류를 변화시켜줌으로써 시편물성의 변화율을 감소시켜 소결온도 범위를 넓히는 효과가 있는 것으로 분석되었다.

• 한국결정성장학회:학술대회논문집
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• 한국결정성장학회 2000년도 Proceedings of 2000 International Nano Crystals/Ceramics Forum and International Symposium on Intermaterials
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• pp.151-163
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• 2000

A polymerized organic-inorganic complexation route is introduced for the synthesis of oxide ceramic powders. Polyvinyl alcohol was used as the organic carrier for precursor ceramic gel. Porous and soft powders, which have a high specific surface area, were obtained after calcinating the aerated precursors. The PVA content and its degree of polymerization had a significant influence on the homogeneity of the final powder. In particular, attrition milling process with the porous powder resulted in ultra-fine particles. In the case of the preparation of cordierite powder, nano-size powder, which has a high specific surface area of 181 ㎡/g, was obtained by the milling process. The complexation route was also applied to the synthesis of unstable phase in room temperature like beta-cristobalite, high temperature form of silica.