• The Korean Journal of Ceramics
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• v.1 no.2
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• pp.86-90
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• 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.

• Journal of the Korean Ceramic Society
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• v.11 no.3
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• pp.27-32
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• 1974

The effect of impurities of andalusite on the morphology of the crystallization of mullite was investigated. The raw, concentrated and purified andalusite were fired at 145$0^{\circ}C$. and 150$0^{\circ}C$. Each of three grades of andalusite was examined in a scanning electron microscope, X-ray diffractometer and etc. The raw andalusite showed deeply etched textures and prismatic crystals which are estimated to be an average of 2.5u in width and 15u in length. Concentrated andalusite showed poorly formed and elongated prismatic crystals. Purified andalusite showed condensed needle-like crystals which are estimated to be an average of 0.4$\mu$ in width and 2.0$\mu$ in length, but at the boundary of the original andalusite grain, prismatic crystals were seen. It is supposed that the purified andalusite is able to utilize as a raw material for high alumina refractories with refractoriness S.K. 38.

• Journal of the Korean Ceramic Society
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• v.17 no.1
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• pp.8-12
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• 1980

CaO was added to the $MgAlCrO_4$ spinel, a main component of the mag-chro refractroies, by 0, 1, 5 and 10 mol% before sintering at 135$0^{\circ}C$ in air. The X-ray diffraction analysis produced an additional X-ray diffraction pattern of 8CaO.$6Al_2O_3$.$2CrO_3$ besides that of $MgAlCrO_4$. The formation of 8CaO.$6Al_2O_3$.$2CrO_3$ was interpreted as due to the presence of CaO.8CaO.$6Al_2O_3$.$2CrO_3$ was unstable and easily vaporized. It was concluded that formation of the unstable pollutant 8CaO.$6Al_2O_3$.$2CrO_3$ could be prevented in reducing atmospheres. It was found that the basic refractories containing $Al_2 O_3 -CaO-Cr_2 O_3$ system would be more stable and much less toxic in reducing at mospheres than in oxidizing stmosphere.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.27 no.2
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• pp.99-104
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• 2017

Refractories used in low-rank coal gasification reactors are usually exposed in a highly corrosive $H_2S$ gas at less than $1000^{\circ}C$, and their mechanical properties such as erosion resistance and fracture strength decline with the exposure time. However, the cause of the degradation of the mechanical properties has little reported yet. In this paper, two kinds of castable refractories with different refractoriness had been exposed in a $H_2O/N_2/H_2S$ mixed gas with high $H_2S$ content for 100 hours at $900^{\circ}C$, and the changes of microstructure, crystalline phases and erosion resistance were compared before and after the corrosion test. The weight of the refractories decreases due to the elution of silica in the specimens after the corrosion test. The capillary porosities of the samples are reduced, but the erosion resistance of the samples is fatally weakened after the corrosion test. There also are changes in constituent phases; dmitryivanovite ($CaAl_2O_4$) and amorphous silica ($SiO_2$) disappear, and gypsum ($CaSO_4{\cdot}2H_2OS$) and kaolinite ($Al_2Si_2O_5(OH)_4$) newly appear after the corrosion test. It is obvious that the phase change from dmitryivanovite that works as a binding agent in the castable refractory to gypsum is the main reason of the degradation of the erosion resistance, because the mechanical properties of gypsum are much poorer than those of dmitryivanovite.

• Journal of the Korean Ceramic Society
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• v.12 no.2
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• pp.3-9
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• 1975

The continuous grading method of pyrophyllite particles was adopted to prepare the refractories for ladle. The optimum conditions of fabrication adjusting the binders, the amount of water, the forming pressure and the firing temperature were investigated. The various properties, such as strength, density, porosity, thermal shock, corrosion resistance to slag were measured and compared with properties of ladle bricks presently used at local steel plants. The specimen studied in the present investigation showed a rather superior properties to theconventional product available locally.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.05c
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• pp.103-107
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• 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.

• Journal of the Korean Ceramic Society
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• v.41 no.9
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• pp.657-662
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• 2004

The kinetics of oxidation and disappearance of graphite in MgO-C refractories containing TiC were, in the temperature range from 1000 to 1200$^{\circ}C$, investigated to enhance the oxdation resistance of MgO-C refractproes. The air was blown into the furnace at flow rate of 0.2 litters per minute, and then weight decrease was measured with a thermo balance at 30 seconds intervals until the value of weight became unchanged. The value of effective diffusion coefficient (De) for the specimen of MgO-C was 1.39${\times}$10$\^$-4/ ㎡/sec. The diffusion of oxygen through decarburized layer was the rate deforming step in the overall oxidation process under present experimental conditions. The TiC additions enhanced the oxidation resistance of the MgO-C refractories.

• Journal of the Korean Ceramic Society
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• v.38 no.9
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• pp.829-833
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• 2001

There have been many studies about the chemical corrosion of converter's refractories. However, few studies have been reported for the stress corrosion induced by the weight of the refractories and by the two bottom shape models designed for the converter. In this study, the stress distributions of the two converter models were analyzed by FEM. Model 1 has the step edge shape and model 2 has the round edge shape. Simulation results show that model 2 of round bottom edge has higher gravitational stress just below the slag line than the model 1. Model 2 is considered to suffers more serious corrosion than model 1 during the middle working stage by the thermal and chemical factors.

• The Korean Journal of Ceramics
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• v.4 no.4
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• pp.279-285
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• 1998

The $UO_2$ pellets are usually sintered under hydrogen gas atmosphere. Hydrogen gas may cause unexpected early failure of the refractory bricks in the sintering furnace. In this work, nitrogen was mixed with hydrogen to investigate the effect of nitrogen gas on a failure machanism of the refractory bricks and on the microstructure of the $UO_2$ pellet. The hydrogen-nitrogen mixed gas experiments show that the larger nitrogen the mixed gas contains, the less the refractory materials are reduced by hydrogen. The weight loss measurements at $1400^{\circ}C$ for fire clay and chamotte refractories containing high content of $SiO_2$ indicate that the weight loss rate for the mixed gas is about half of that for the hydrogen gas. Based on the thermochemical analyses, it is proposed that the weight loss is caused by hydrogen-induced reduction of free $SiO_2$ and/or $SiO_2$ bonded to $Al_2O_3$ in the fire clay and chamotte refractories. However, the retardation of the hydrogen-induced $SiO_2$ reduction rate under the mixed gas atmosphere may be due to the reduction of the surface reaction rate between hydrogen gas and refractory materials in proportion to volume fraction of nitrogen gas in the mixed gas. On the other hand, the mixed gas experiments show that the test data for $UO_2$ pellet still meet the related specification values, even if there exists a slight difference in the pellet microstructural parameters between the cases of the mixed gas and the hydrogen gas.

• Journal of the Korean Ceramic Society
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• v.18 no.1
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• pp.41-47
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• 1981

The sintering characteristics of the SiC-Clay-Kaolin chamotte system were studied by addition of $Al_2O_3$ for the manufacture of silicate-bonded silicon carbide refractories at $1350^{\circ}C$. The sinterbilit of SiC-Binder mixture was measured by apparent porosity and compressive strength. And its mineral compositions were identified with X-ray diffractometer. The following results were obtained; 1) Optimum amount of mixed clay ($\textrm{Al}_2\textrm{O}_3$ 40 wt% mixed) as a binder was about 25wt% 2) Appropriate mixing ratio of mixed Kaolin chamotte ($\textrm{Al}_2\textrm{O}_3$ 40wt% mixed) was about 30wt% in the clay Kaolin chamotte binder. 3) Variation of apparent porosity and compressive strength of sintered SiC-binder mixture fired at $1350^{\circ}C$ were due to the sinterbility of clay.