• Journal of Korea Foundry Society
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• v.31 no.5
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• pp.293-301
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• 2011

Representative magnesium alloys applied to the die-casting are AZ91, AM60, etc., and the application of these alloys is restricted to components operating at moderate temperatures, due to grain boundary siding of ${\beta}$-phase($Mg_{17}Al_{12}$) at temperatures above $120^{\circ}C$. Heat-resistant magnesium alloys such as AE42, AE44 have been developed, but that have been too burdensome to produce because of the expensive rare earth materials. Research work for the development of low-priced heat-resistant magnesium alloy is actively in progress and positive results are being reported. This study aims to investigate the effect of Ca additions on mechanical properties of Mg-4Al-2Sn heat resistant magnesium alloys. Mg-4Al-2Sn alloys with Ca (0wt.%, 0.3wt.%, 0.7wt.%, 1wt.%) have been produced through the die-casting process for the development of low-priced heat-resistant magnesium alloy, and high temperature tensile tests are performed using the specimens. The results showed that mechanical properties of Mg-4Al-2Sn-xCa increased with the addition of Ca up to 0.7wt.% Ca and further addition of Ca deteriorated the mechanical properties of the alloys. A significant amount of porosity was observed at the sample with 1wt%. Ca and the longer freezing range of the alloy was believed to cause the formation of porosity.

• Journal of Korea Foundry Society
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• v.32 no.6
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• pp.289-295
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• 2012

Mg-Al-Sn-Si system alloy, as a promising cheap heat-resistant Mg alloy for automobile engine part, has been investigated. Refinement of microstructure and precipitation of thermally stable secondary phases are important goal for the design of heat-resistant Mg alloy. In this study, the effect of Ce on the microstructure and room temperature mechanical properties of Mg-Al-Sn-Si alloy was investigated. High thermally stable $Mg_2Si$ phases in Mg-Al-Sn-Si alloy is very useful intermetallic compound. However, the $Mg_2Si$ phases often result in poor mechanical properties due to the coarse chinese type $Mg_2Si$ phases. The experimental specimens were fabricated by fluxless melting under $CO_2+SF_6$ atmosphere and poured into the permanent pre-heated at $200^{\circ}C$. It was told that Ce addition can modify $Mg_2Si$ phases and refine microstructure and improve the tensile strength, yield strength and elongation.

• Transactions of Materials Processing
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• v.22 no.3
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• pp.165-170
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• 2013

High temperature deformation behavior of a heat-resistant duplex stainless steel, used as a retort in the Pidgeon process for Mg production, was investigated in this study. 25Cr-8Ni based duplex stainless steels were cast into rectangular ingots, with dimensions of $350mm{\times}350mm{\times}100mm$. Nitrogen and yttrium were added at 0.3wt.% each to enhance the heat-resistance of the steel. Phase equilibrium was calculated using the thermodynamic software FactSage$^{(R)}$ and the database of FSStel. For comparison, cast 310S steel, a widely used heat-resistant austenitic stainless steel, was also examined in this study. Dilatometry was conducted on the as-cast ingots for the temperature range from RT to $1200^{\circ}C$ and the thermal expansion coefficients were evaluated. The nitrogen addition was found to have an effect on the thermal expansion behavior for temperatures between 800 and $1000^{\circ}C$. High temperature tensile and compression tests were conducted on the ingots for temperatures ranging from 900 to $1230^{\circ}C$, which is the operation temperature employed in Mg production by the Silico-thermic reduction process. The steel containing both N and Y showed much higher strength as compared to 310S.

• Korean Journal of Metals and Materials
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• v.46 no.5
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• pp.304-309
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• 2008

Magnesium alloys containing $Mg_2Si$ particles, as a promising cheap heat-resistant magnesium alloy for automobile power train parts applications, are attracting more attention of both material scientists and design engineers. Modification of the Chinese script shape $Mg_2Si$ particle is a key for using this alloy in sand or permanent mould casting. In the present work, the modification effect of Sr and Sb on the corrosion properties of the Mg-5Al-2Si alloy was investigated. Sr or Sb addition promoted the formation of fine polygonal shape $Mg_2Si$ particles by providing the nucleation sites. Sr was more effective element than Sb for shape modification of Chinese script shape $Mg_2Si$. Such improved microstructure of the modified alloy resulted in large improvement in corrosion resistance as compared to unmodified Mg-5Al-2Si alloy.

• Transactions of the Korean Society of Automotive Engineers
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• v.17 no.3
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• pp.45-53
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• 2009

Die casting process of Mg alloys for high temperature applications was studied to produce an engine oil pan. The aim of this paper is to evaluate die casting processes of the Aluminium oil pan and in parallel to apply new Mg alloy for die casting the oil pan. Temperature distributions of the die and flow pattern of the alloys in cavity were simulated to diecast a new Mg alloy by the flow simulation software. Dies have to be modified according to material characteristics because melting temperature and heat capacity are different. We changed the shape and position of runner, gate, vent hole and overflow by the simulation results. After several trial and error, oil pans of AE44 and MRI153M Mg alloys are produced successfully without defect. Sleeve filling ratio, cavity filling time and shot speed of die casting machine are important parameter to minimize the defect for die casting Magnesium alloy.

• The Journal of Internal Korean Medicine
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• v.19 no.2
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• pp.300-316
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• 1998

The various oriental herbal medicines, which have usually been used for treatment of reducing fever, purging intense heat and detoxication, were screened to determine the antibacterial activity and the minimal inhibitory concentration against antibiotics-resistant Staphylococcus aureus. The results obtained were as follows: 1. Among the 23 oriental medicines tested, the water-soluble extract of Coptis japonica showed very excellent antibacterial activity against antibiotics-sensitive and -resistant S. aureus. A little activity was found in the extracts of Scutellaria baicalensis, Eriobotrya japonica and Prunus mume against antibiotics-sensitive S. aureus and in that extracts of P. mume, Schizandra chinensis and S. baicalensis against antibiotics-resistant S. aureus. When C japonica was used, the high antibacterial activity was shown against Bacillus subtilis and other extracts showed a little or no antibacterial activity against B. subtilis and E. coli as a control. 2. The highest antibacterial activities against antibiotics-resistant S. aureus were found in the ethanol-soluble extract of C japonica. Other ethanol-soluble extracts of S, baicalensis, S. chinensis and P. mume showed a little activity against both antibiotics-sensitive and antibiotics-resistant S. aureus. 3. Among the medicinal herbs tested, the water- and ethanol extracts of C. japonica showed very excellent antibacterial activity against the pathogenic S. aureus and both Escherichia coli and Bacillus subtilis used as a control. 4. When the water-soluble extracts of C. japonica and S. baicalensis, minimal inhibitory concentrations (MICs) against antibiotics-sensitive S. aureus were $20mg/m{\ell}\;and\;30mg/m{\ell}$, respectively. The MICs of the ethanol-soluble extracts of C. japonica and P. scabriosaefolia were $7.5mg/m{\ell}\;and\;12mg/m{\ell}$, respectively. 5. For the MICs against antibiotics-resistant S. aureus, the water-soluble extracts of C. japonica and P. mume showed $15mg/m{\ell}\;and\;10mg/m{\ell}$, respectively. The MICs of the ethanol-soluble extracts of C. japonica and P. mume were $13mg/m{\ell}\;and\;20mg/m{\ell}$, respectively. As a result, the highest antibacterial activity was found in both water- and ethanol-soluble extracts of C. japonica against antibiotics-resistant S. aureus. And the water- and ethanol-soluble extracts of S. baicalensis, S. chinensis and P. mume showed comparatively high antibacterial activities against both antibiotics-sensitive and -resistant S. aureus.

• Korean Journal of Microbiology
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• v.9 no.2
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• pp.86-93
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• 1971

Escherichiae-like organisms were isolated from rectal specimens of 56 children who were either in preschool age or in elementary school. The isolated strains were subjected to tests to screen enteropathogens producing heat-labile enterotoxin and susceptibility test to various antibiotics by disc diffusion method on agar plates. Production of heat-labile enterotoxin by the strains was assyed in the sensitive and reproducible cultured adrenal tumor cell system. The assay was sterodogenesis of the cell in the presence of heat-labile enterotoxin. Among 56 strains, gave positive reaction in the test of toxin production. This meant that about 10% of the children population objected to the study harbored the toxigenic strain of enteropathogenes. Some of these toxigenic strains were resistant to the antibiotics employed in the test. This study suggested that considerable population in Korea may harbor entertoxigenic E. coli as a part of intestinal normal flora. The toxigenic strains which are resistant to antibiotics may bring issue of public health in the future.

• Korean Journal of Plant Tissue Culture
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• v.28 no.2
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• pp.75-79
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• 2001

An experiment was carried out to introduce OsHSP17.9, a low molecular HSP gene isolated from rice plant to orchardgrass (Dactylis glomerata L.) using Agrobacterium. Mature seed-derived calli of orchardgrass were co-cultured with Agrobacterium tumefaciens EHA101 harboring the plasmid pIG-HSP17.9 for transformation. Calli selected by hygromycin were transferred to N$_{6}$ medium containing 1 mg/L NAA, 5 mg/L kinetin, 250 mg/L cefotaxime and 50 mg/L hygromycin and several hygromycin resistant plants were obtained. Stable incorporation of the introduced OsHSP17.9 to the genome of the hygromycin resistant plants was confirmed by PCR and Southern blot analysis. Transformation efficiency was variable between cultivars in which it was 16.5% in Potomac and 8.0% in Frontier. Constitutive expression of the transgene in the transformed orchardgrass tissues was identified by Northern blot analysis but transcript levels were different among individual plants.s.

• Journal of the Korean Ceramic Society
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• v.32 no.3
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• pp.385-393
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• 1995

Akali-resistant porous glass was prepared by phase separation in Na2O-B2O3-SiO2 system containing ZrO2 and MgO. ZrO2 was added for alkali-resistance and MgO for anti-cracking during leaching. Optimal content of ZrO2 for alkali-resistance was 7wt% and devitrification by heat treatment resulted from further addition. Pore size and pore volume were decreased and specific surface area was increased with ZrO2 addition due to depression in phase separation. Addition of 3mol% MgO to mother glass containing 7wt% ZrO2 was effective for anti-crack during leaching. In this case, with phase separation at 55$0^{\circ}C$ and 5$25^{\circ}C$ for 20 hrs. crack-free porous glasses could be prepared. The relation between pore size r and heat treatment time t at 55$0^{\circ}C$ was D=25.58＋18.16t. According to measurement of gas permeability, the mechanism of gas permeation was Knudsen flow. N2 and He permeability of porous glass which was prepared by heat treatment at 55$0^{\circ}C$ for 20 hrs. were 0.843$\times$10-7mol/$m^2$.s.Pa and 2.161$\times$10-7mol/$m^2$.s.Pa respectively.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.15 no.3
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• pp.1-6
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• 2019

The basalt fiber, which is found to be non-toxic and harmless to the human body, is expected to become a trend for industrial fibers as they have better properties of non-combustion, heat-resistant, soundproof, absorbent, moistureproof, wear-resistant, corrosion resistant, lightweight, and high strength properties. Thus, in this study, we analyzed the chemical compositions of basalt produced at seven sites on Jeju Island for making a high value inorganic insulation material. The results showed that the MgO content of basalt collected from the eastern part of Jeju Island was higher than 7.5 percent, while that of the western region was less than 6 percent.