• Korean Journal of Materials Research
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• v.8 no.10
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• pp.879-883
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• 1998

In the vacuum casting process for superalloys, molten metal are poured into the heated ceramic mold up to $1000^{\circ}C~1700^{\circ}C$. The mold has to have the high temperature strength during casting and made by hlgh purity alumina. In this sturdy, the mold was made by low purity alumina and changed silica contents intended to have high strength The 7.7wt.% SiOz specimens have 10- 55% higher strength than others in room and high temp. Therefore, the cast mold has been developed in this study for single crystal vacuum cast by controlling the ratio of fused alumina and colloidal silica which are used commercially for conventional casting in industries.

• Journal of the Korean Ceramic Society
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• v.40 no.9
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• pp.891-896
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• 2003

Novel fabrication technique was developed for high strength Reaction-Bonded SiC (RBSC) hot gas filter for use in IGCC (Integrated Gasification Combined Cycle) system. The room and high temperature fracture strengths for Si-melt infiltrated reaction-bonded SiC were 50-123, and 60-66 MPa, respectively. The average pore size was 60-70 $\mu\textrm{m}$ and the porosity was about 34 vol％. RBSC infiltrated with molten silicon showed improved fracture strength at high temperature, as compared to that of clay-bonded SiC, due to SiC/Si phase present within SiC phase. The thickness for SiC/Si phase was increased with increasing powder particle size of SiC from 10 to 34 $\mu\textrm{m}$. Pressure drop with dust particles showed similar response as compared to that for Schumacher type 20 filter. The filter fabricated in the present study showed good performance in that the filtered powder size was reduced drastically to below 1 $\mu\textrm{m}$ within 4 min.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.8
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• pp.338-343
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• 2017

In this study, blast furnace slag powder was used in concrete to help reduce carbon dioxide emissions and to recycle industrial waste. Blast furnace slag powder is a byproduct of smelting pig iron and is obtained by rapidly cooling molten high-temperature blast furnace slag. The powder has been used as an admixture for cement and concrete because of its high reactivity. Using fine blast furnace slag powders in concrete can reduce hydration heat, suppress temperature increases, improve long-term strength, improve durability by increasing watertightness, and inhibit corrosion of reinforcing bars by limiting chloride ion penetration. However, it has not been used much due to its low compressive strength at an early age. Therefore, this study evaluates the effects of steam curing for increasing the initial strength development of concrete made using slag powder. The relationship between compressive strength, SEM observations, and XRD measurements was also investigated. The concrete made with 30% powder showed the best performance. The steam curing seems to affect the compressive strength by destroying the coating on the powder and by producing hydrates such as ettringite and Calcium-Silicate-Hydrate gel.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.29 no.1
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• pp.24-31
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• 2019

The current study demonstrates an efficient procedure to create ingots from $Al_2O_3$ powder using the skull melting method to use these ingots as a starting material in conventional methods for growing synthetic single-crystal sapphire. Dimension of the cold crucible was 24 cm in inner diameter and 30 cm in inner height, 15 kg of $Al_2O_3$ powder was completely melted within 1 h at an oscillation frequency of 2.75 MHz, maintained in the molten state for 3 h, and finally air-cooled. The areal density and components of the cooled ingot by parts were analyzed through scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS). The areal density and $Al_2O_3$ content of the ingot were related to the temperature distribution inside the cold crucible during high-frequency induction heating, and the area with high temperature was high tends to be high in areal density and purity.

• Korean Journal of Metals and Materials
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• v.48 no.4
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• pp.277-288
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• 2010

The hot corrosion properties of heat-resistant steels were investigated in an oxidation atmosphere including artificial ash and sulfur dioxide. The heat-resistant steels of T22, T92, T122, T347HFG, Super304H and HR3C were evaluated at 620, 670 and $720^{\circ}C$ for 400 hours. The relationship between the corrosion rate and the temperature followed a bell-shaped curve with a peak rate at around $670^{\circ}C$. The corrosion rates showed a decreasing tendency as the chrome contents of these steels increased from 2.15 wt.% to 24.5 wt.%, and austenitic steels had a lower corrosion rate than ferritic steels. Sulfidation by $SO_2$ as well as molten salt corrosion also had an effect on the total corrosion rate, especially showing an increase in the corrosion rate in ferritic steels. Regardless of the chrome content in the steels and irrespective of the test temperature, the corrosion scale was composed of an outer oxide and an artificial ash mixed layer, a middle oxide layer and inner sulfide, and a mixed oxide layer. As the chrome content increased, the proportion of chrome oxide in the corrosion scale increased. Before spalling of the corrosion scale, voids and cracks were initiated in the sulfide and the mixed oxide layer or at the interface with the substrate.

• Journal of Korea Foundry Society
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• v.41 no.6
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• pp.516-520
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• 2021

During sand casting, the binders produces gases in cores because high temperature molten metals dissolve the binders into gases and causes gas defects in the casting products. In the present study, quantitative analysis of inorganic binder gas generation was performed using Thermo Gravimetry (TG) and Mass Spectrometer (MS) analyses. The specimen was prepared using organic binders in liquid and solid state, and a mixture of sand and binders. Moisture loss by catalysts was calculated by TG results from liquid and solid binder specimens; it was found that components of gases were different. Quantitative analysis was discussed for generated gases with individual gas component results obtained using TG and MS. It is expected that gas generation can be predicted in the casting simulation using the technique proposed in the present study.

• Journal of the Korean Ceramic Society
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• v.39 no.3
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• pp.259-264
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• 2002

In this study, sintering properties of Artificial Lightweight aggregates(ALAs) prepared from coal ash as a function of sintering temperature (900$^{\circ}$C, 1000$^{\circ}$C, 1100$^{\circ}$C) and time (2min, 5min, 10min) when limestone added as lightweight mineral was investigated. Increasing the sintering temperature resulted simultaneously from a decline of quartz mineral as well as growth of mullite mineral. Addition of limestone to ALAs newly formed sintered minerals such as clinoptilolite and plagioclase. Sintering effect of ALAs prepared from coal ash and limestone was more affected by a sintering temperature than time. As sintering temperature and time increae, transition of macropore to micropore and formation of closed pores were happened, consequently shrank the total pore volume of ALAs. The surface of ALAs sintered at 1000$^{\circ}$C for 5min was nearly not detected open pores due toe amalgamation effect of molten slag layer but homogeneous distributions of closed pores with micro-scale were examined in cross sectional area ALAs. Sintering temperature and time which present the most adequate state, in the preparation of ALAs, are corresponded to 1000$^{\circ}$C and 5min, respectively.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.12 no.3
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• pp.179-189
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• 2014

Pyroprocessing has been developed for the purpose of resolving the current spent nuclear fuel management issue and enhancing the recycle of valuable resources. An electrolytic reduction of the pyroprocessing is a process to reduce oxides into metals using LiCl as an electrolyte and requires a post-treatment process due to the inclusion of residual salt in porous metal products. A vacuum distillation has been adopted for various molten salt systems and could be applied to the post-treatment process of the electrolytic reduction. The residual salt in the metal products includes LiCl, alkali chlorides, and alkaline earth chlorides. In this paper, vapor pressures of chlorides have been estimated and the composition changes on the residual liquid during the vacuum distillation process have been calculated. A model combining a material balance and vapor-liquid equilibrium relations has been proposed under a constant vapor discharging flow rate and liquid composition changes have been calculated using the vapor pressures with respect to a dimensionless time. The behaviors have been compared with temperature and molten salt composition changes to simulate the process condition variation. The distillation of the residual salt has been dominated by LiCl which is the main component of the salt and CsCl of which vapor pressure is higher than that of LiCl would be readily removed. RbCl exhibits similar vapor pressure with LiCl and maintains its composition. However, $SrCl_2$ and $BaCl_2$ of which vapor pressures are much lower than that of LiCl are concentrated with time and expected to be possibly precipitated during the distillation when the initial compositions are increased.

• Applied Chemistry for Engineering
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• v.10 no.5
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• pp.652-659
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• 1999

The trend of poisoning of reforming catalyst along with the position of anodic catalyst bed was studied. Keeping the conditions that steam to carbon ratio was 2.5, operating voltage was 0.75 V, current density was $140mA/cm^2$, the unit cell was operated during 24 hrs at a steady state. And then the cell was stopped, the catalysts packed in the position of inlet, middle and outlet were sampled individually and then the amount of carbon, Li and K poisoned were analysed. After 100 hrs operated, the catalysts at the same positions were analysed at the same manner. The result of this experiment was as followings. After 24 hrs operated, the poisoning amounts of Li and K in the catalyst were 0.27 wt% at inlet, 0.23 wt% at middle and the highest value 1.59 wt% at outlet. After 100 hrs, the amount of poisoning is the highest in the catalyst packed at the inlet of unit cell. The performance simulation of unit cell explained these trends of poisoning catalysts. The simulation told that the catalyst in the region of the inlet of unit cell treated the 90% of initial methane flow rate and the highest electrochemical reaction happened in this region. So the catalysts of this region were the most poisoned with carbon, Li and K and also the rate of poisoning is faster than that of the catalyst at other regions. The temperature at the region of outlet of unit cell was $30^{\circ}C$ higher than that of other regions, so more Li, and K vaporized than at other regions and little reforming reaction at this region made the catalysts poisoning rate low.

• Journal of the Korean Ceramic Society
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• v.42 no.4
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• pp.260-268
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• 2005

A heat-resisting diatomite protection tube, using diatomite as a main component, was manufactured through an extrusion molding of ceramic slurry in different component ratios. And its mechanical strength, carbon analysis and microstructural non-homogeneity were investigated. After fixing $60wt\%$ of porous diatomite whose particle size was $50\~100\;{\mu}m$, the optimum mixture ratio with composition variables by changing $1\;wt\%$ of each component that was silica sol$(4.3\~7.3\;wt\%)$ as an inorganic binder, CMC (Sodium CarboxyMethyl Cellulose $(6\~9\;wt\%)$) as an organic binder and paper powder$(4.7\~7.7\;wt\%)$ was obtained. As a result of the investigation on a composition containing $60\;wt\%$ diatomite, $5.3\;wt\%$ silica sol, and $7\;wt\%$ CMC, a heat-resisting protection tube that could be used as a molten steel probe for measuring the temperature and components of molten steel was developed. The bending strength, compressive strength, and elastic modulus of the protection tube developed, that contained $\le2.3\;wt\%$ carbon, were 7.1 MPa, 7.5 MPa, and 1090 MPa, respectively.