• The Korean Journal of Ceramics
• /
• 제1권2호
• /
• pp.86-90
• /
• 1995

Theoretical predictions for thermodynamically stable phases which formed when alkali(sodium and potassium) vapors reacted with alumina-chromia refractories under coal gasifying atmosphere were confirmed experimentally using a laboratory-scale coal gasifying reaction system and a commercial alumina-chromia refractory using SEM, XRD, and EDAX. Alkali concentration profiles in the refractory as a function of time were also determined. The results showed that the compounds that formed were $X_2O{\cdot}Al_2O_3, X_2O{\cdot}Cr_2O_3, X_2O{\cdot}5Al_2O_3, X_2O{\cdot}7Al_2O_3, X_2O{\cdot}11Al_2O_3(X=Na^+ \;or\; K^+)$, depending upon the alkali concentration and time of exposure at high temperatures. The presence of sulfur in gasifying atmospheres did not appear to affect the alkali reaction produces. Alkali pentration into the alumina-chromia refractory was deep and the formation of the $Na_2O{\cdot}Al_2O_3/K_2O{\cdot}Al_2O_3$ compunds resulted in the serious deformation of the refractory due to the large volume expansion at the reaction surface. The hot face of the alumina-chromia refractory in service under an alkali environment is prone to failure by alkali attack.

• 공업화학
• /
• 제20권6호
• /
• pp.638-645
• /
• 2009

가스화기에서 사용된 고알루미나계 내화물을 분석하여 용융 슬래그에 의한 손상 메커니즘을 조사하였다. 내화물 시료에서 슬래그에 의해 심하게 손상된 부분의 깊이는 부착된 슬래그를 포함하여 12~40 mm이었으며 슬래그 접촉면과 평행 방향으로 형성된 균열을 가지고 있었다. 슬래그와 접촉한 내화물은 미세구조에 따라 손상도가 다르게 나타났다. Fused $Al_2O_3$ 그레인의 경우 경계에서만 깨짐과 기공형성이 관찰되었고, tablet $Al_2O_3$의 경우 슬래그가 입자사이로 침투하여 입자 테두리에 Fe-Al 화합물이 관찰되었다. 결합제로 쓰인 calcium aluminate는 고온의 슬래그 접촉면에서는 슬래그에 용해되어 관찰되지 않았다. 큰 grain 주변에는 냉각 시 재결정된 것으로 보이는 막대형의 $Al_2O_3$ 상이 형성되었고 큰 기공들이 관찰되었다. 따라서 고알루미나계 내화물은 고온의 슬래그 경계면에서 결합제가 석탄 슬래그에 용융되고, 냉각 시 막대형의 알루미나를 형성하며, 이 과정에서 구조적인 변화에 의한 크랙이 형성되면서 구조적 스폴링에 의한 물리적 손상의 영향을 받는 것으로 보인다.

• 한국분말야금학회:학술대회논문집
• /
• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
• /
• pp.1099-1100
• /
• 2006

The mechanical properties of ceramics materials can be tailored by designing their microstructures. We have reported that development of texture can be controlled by slip casting in a strong magnetic field followed by heating even for diamagnetic ceramics such as alumina. A strong magnetic field of 12T was applied to the suspension indcuding alumina powder to rotate each particle during slip casting. The sintering was conducted at the desired temperature in air without a magnetic field. C-axis of alumina was parallel to the magnetic field. Bending strength of textured alumina depended on the direction of oriented microstructure.

• 한국세라믹학회지
• /
• 제38권2호
• /
• pp.238-238
• /
• 2001

본 연구에서는 kaolin을 이용하여 반기상법, gel coating법, seed 첨가법으로 mullite를 합성하였으며 mullite 15 wt%를 고 알루미나질 내화물 원료에 첨가하여 내화물 시편을 제조하였다. 제조된 시편의 물성을 분석한 결과 seed 첨가법으로 제조된 mullite를 첨가한 시편의 물성이 338.60 MPa의 꺾임강도와 9,427 kgf/㎠의 압축강도값을 나타내었다. 제조된 시편의 내화도 및 잔존선팽창수축률을 측정한 결과 나머지 두가지 방법으로 합성한 mullite나 일반적인 고 알루미나질 내화물에 비하여 좋은 특성을 나타내었다.

• The Korean Journal of Ceramics
• /
• 제6권2호
• /
• pp.143-149
• /
• 2000

Monolithic refractory technology has been developed for RH vessels, with the purpose of reducing the total refractory cost. The technology includes the use of an improved monolithic refractory and microwave drying. The improved monolithic refractory was an alumina-spinel composition, of the type used in steel ladles, to which fine alumina was added to increase the density and corrosion resistance. The microwave drying method, previously developed and used to dry the monolithic lining in steel ladles, was modified for use in drying the dense, 500mm thick lining in RH vessels. This work has resulted in significant cost savings.

• 한국세라믹학회지
• /
• 제38권2호
• /
• pp.128-136
• /
• 2001

본 연구에서는 kaolin을 이용하여 반기상법, gel coating법, seed 첨가법으로 mullite를 합성하였으며 mullite 15 wt%를 고 알루미나질 내화물 원료에 첨가하여 내화물 시편을 제조하였다. 제조된 시편의 물성을 분석한 결과 seed 첨가법으로 제조된 mullite를 첨가한 시편의 물성이 338.60 MPa의 꺾임강도와 9,427 kgf/$\textrm{cm}^2$의 압축강도값을 나타내었다. 제조된 시편의 내화도 및 잔존선팽창수축률을 측정한 결과 나머지 두가지 방법으로 합성한 mullite나 일반적인 고 알루미나질 내화물에 비하여 좋은 특성을 나타내었다.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2002년도 춘계학술대회 논문집 유기절연재료 전자세라믹 방전플라즈마 일렉트렛트 및 응용기술
• /
• pp.103-107
• /
• 2002

Ethyl silicate was used as organic binder for alumina refractories. In the present work only 15% of the water required for complete hydrolysis of ethyl silicate was initially added. The balance was provided from the atmosphere under controlled conditions of temperature and rh. The purpose of detailing the possible binder problem areas is more to indicate that the binder can have an effect on ceramic operations.

• 한국세라믹학회지
• /
• 제38권3호
• /
• pp.238-244
• /
• 2001

본 연구에서는 Seed 첨가법에 의하여 제조된 mullite(Syn M)와 외국산 mullite 2종류(sintered mullite : SM, fused mullite : FM)를 고알루미나질 내화물 원료에 적용하여 내화물 시편을 제조하였으며 mullite에 따른 결정상, 미세구조, 부피비중, 강도를 조사하였다. SM, FM, Syn M의 mullite 함유량은 93.17%, 86.79%, 97.57%이었으며 mullite를 15 wt% 첨가하여 제조한 시편의 물성을 조사한 결과 Syn M을 함유한 시편이 꺾임강도 338.60 MPa, 압축강도 9,427kgf/$\textrm{cm}^2$을 나타내었다. 외국산 mullite를 첨가한 시편의 강도는 Syn M을 첨가한 것보다 약 5~10% 정도 낮은 강도를 보였다.

• 한국세라믹학회지
• /
• 제31권12호
• /
• pp.1437-1442
• /
• 1994

Self propagating synthesis and thermal explosion of combustion reactions were applied to Al/K2Cr2O7/Al2O3 system as the first stage for a production of magnesia-chromium refractory. Several factors related to products made by two combustion reactions were considered and properties of products were characterised. Two processes were required to preheat upto at least 80$0^{\circ}C$ for the thermal explosion and the self propagating synthesis. These processes were so violent and explosive that alumina as diluent was added to the system in order to absorb the reaction heat and reduce the reaction rate. The products consisted of crystal phases of KAl5O8, Cr2O3, Al2O3, K2CrO4, and K2Al2O4.3H2O. The amount of KAl5O8 and K2Al2O4.3H2O crystal phases of products were decreased with further addition of alumina.

• 한국주조공학회지
• /
• 제13권5호
• /
• pp.476-483
• /
• 1993

The influence of substrate materials on the degree of basal porosity during spray casting process has been investigated. Different conditions of droplet spreading on the substrate were induced by varying the substrate material. Flat sections of cast iron and aluminum have been spray deposited via spray casting process onto an aluminum substrate, a low carbon steel substrate, and an alumina based refractory substrate. Results for cast iron and aluminum sprayed onto the aluminum substrate showed significant improvements in the surface condition and degree of basal porosity with evidence of substrate deformation that round pits ranging from $5{\mu}m$ to $20{\mu}m$ in diameter are distributed on the surface of aluminum substrate. The lowest level of porosity was developed in alumina based refractory material. Several mechanisms for porosity formation were discussed with droplet impact pressure and droplet spreading. Adopting a spray cutting mechanism for removing the periphery of spray cone, porosity level was remarkably decreased.