• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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• pp.1155-1156
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• 2006

Hopkinson bar dynamic test under strain rates ranging from 2000 $s^{-1}$ to 8000 $s^{-1}$ at room temperature revealed that the flow stress of tungsten heavy alloys depended strongly on the strain, strain rate, and the content of molybdenum. The variation of flow stress was caused by the competition between work hardening and heat softening in the materials at different strain rates. The high temperature strength of the matrix phase was increased by the addition of molybdenum, which enhanced the strength of the tungsten heavy alloys in high strain rate test.

• 한국주조공학회지
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• 제29권6호
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• pp.257-264
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• 2009

The effects of silicon and molybdenum on the temperature-dependent properties of high silicon and high molybdenum ductile cast iron were investigated. Microstructure was composed of ferrite, cell boundary complex carbide, carbide precipitated in the grain and graphite. The number and size of carbide decreased with the increase of silicon content and increased with the increase of molybdenum content, however, the size of cell boundary carbide increased above 0.81wt%Mo. The room temperature tensile strength increased with the increase of silicon and molybdenum contents. That did not increase with the latter with more than 0.8wt%. Meanwhile the high temperature tensile strength showed the similar trend to that of room temperature one, that of the specimen with 0.55wt%Mo was the highest. The $A_1$ transformation temperature increased with the silicon and molybdenum contents, and showed similar tendency with the variation of strength. It was discussed due to the solubility limit of Molybdenum in ferrite, of which value was assumed to be in the vicinity of 0.81wt%Mo. The weight after oxidation at 1,173K showed the result caused by the difference in solubility of molybdenum in the matrix. That and the thickness change after oxidation did not show any consistent trend with the silicon and molybdenum contents.

• 자원환경지질
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• 제13권2호
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• pp.117-127
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• 1980

Molybdenum as by-products of Sangdong tungsten mine occurrs in the form of molybdenite in quartz vein. The molybdenum contents of scheelite in Sangdong ore bodies ranges from trace to 8%, therefore the scheelites show variable fluorescence colores under ultra-violet lamp (short wave). The fluorescence color are in order high content of molybdenum, yellow, white and blue. The yellow fluorescing scheelite is dominant in upper ore vein, otherwise the blue fluorescent variety is dominant in lower ore vein. The fluorescence color of scheelite in the main ore vein show zonal distribution becoming progressively more blue outerwards, contrary more yellow innerwards, and even in single scheelite crystal, simillar zonal pattern is observed, too. Molybdenite occurrs as flakes or elongated blades at the margins of the quartz vein only molybdenite bearing quartz veins but also other sulfides mineral bearing quartz veins have mainly blue flourescing scheelites. We suggest that the molybdenum contents of the early stage ore solution are progressively decreased by a subsequent crystallization of the yellow fluorescing scheelites.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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• pp.1153-1154
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• 2006

Effects of sintering conditions such as sintering temperature and heating rate on oxygen content, density, microstructure and toughness of sintered Mo were investigated. The oxygen content of the sintered Mo significantly depended on the sintering conditions. The oxygen content of the primary sintered(below 1673 K) Mo influenced the densifications. The number of pores at grain boundaries of the secondary sintered(at 2073 K)Mo depended on the oxygen content of the primary sintered Mo. Grain growth of the secondary sintered Mo was inhibited by the existence of pores at the grain boundaries. The secondary sintered Mo having larger number of pore and smaller grain size demonstrated higher strength.

• 한국표면공학회지
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• 제35권4호
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• pp.241-248
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• 2002

Hardfacing layers of Stellite 6 alloy with different molybdenum content are deposited on AISI 1045 carbon steel using plasma transferred arc welding (PTAW). The properties of the hardfacing layer are investigated in order to clarify the effect of molybdenum addition to the cobalt-base alloy. With an increase in molybdenum contents, the size of Cr-rich carbides in the interdendritic region is abruptly refined, but volume fraction of the carbide slightly increases. Also, with an increase of Mo, $M_{6}$ C type carbides are formed instead of Cr-rich $M_{7}$ $C_{3}$ type carbided, and this microstructural change enhanced the mechanical properties of Stellite 6 alloy.

• Nuclear Engineering and Technology
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• 제54권2호
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• pp.709-731
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• 2022

Loss of fracture resistance due to thermal aging degradation is a potential limiting factor affecting the long-term (80+ year) viability of nuclear reactors. To evaluate the effects of decades of aging in a practical time frame, accelerated aging must be employed prior to mechanical characterization. In this study, a variety of chemically and microstructurally diverse austenitic stainless steels were aged between 0 and 30,000 h at 290-400 ℃ to simulate 0-80+ years of operation. Over 600 static fracture tests were carried out between room temperature and 400 ℃. The results presented include selected J-R curves of each material as well as K_0.2mm fracture toughness values mapped against aging condition and ferrite content in order to display any trends related to those variables. Results regarding differences in processing, optimal ferrite content under light aging, and the relationship between test temperature and Mo content were observed. Overall, it was found that both the ferrite volume fraction and molybdenum content had significant effects on thermal degradation susceptibility. It was determined that materials with >25 vol% ferrite are unlikely to be viable for 80 years, particularly if they have high Mo contents (>2 wt%), while materials less than 15 vol% ferrite are viable regardless of Mo content.

• 자원환경지질
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• 제7권2호
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• pp.63-78
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• 1974

Daehwa tungsten-molybdenum deposits is fissure filled quartz veins occurring in Precambrian granite gneiss adjacent to the contact with Mesozoic biotite granite mass. Essential ore minerals are molybdenum and wolframite accompaning scheelite, cassiterite, chalcopyrite, pyrrhotite, pyrite and bismuthinites. Gangue minerals are quartz and little muscovte, fluorite, beryl and Carbonate minerals. Fluid inclusions in quartz, fluorite, beryl, scheelite and calcite have filling temperature ranges of $170-353^{\circ}C$. According to the studies of mineral paragenesis and filling temperature of fluid inclusion indicate that main tungsten and molybdnum mineralization have taken place with the minerals whose filling temperature ranges 205 to $353^{\circ}C$. Liquid $CO_2$ bearing fluid inclusions are characteristic in the quartz and early fluorite of tungsten and tungsten bearing molybdenum veins but hardly recognized from molybdemun veins. Estimated $CO_2$ concentration according to diagram proposed by the Takenouchi ranges from 10 to 20wt%. These facts suggest that tungsten mineralization may be related to the $CO_2$ content of the hydrothermal solution during the mineralizing period.

• 한국재료학회지
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• 제3권2호
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• pp.111-120
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• 1993

플라즈마 아크 용해에 의해 0.31-1.14at%Hf과 0.08-1.00at%C의 조성을 갖는 Mo시편을 제조하여, 열처리에 따른 미세조직 변화를 광학현미경, AES(Auger Electron Spectroscopy)및 투과전자현미경(TEM)으로 조사하였다. 산소함량이 약 830ppm인 초기분말을 압분체로 성형하여 용해한 결과, 산소함량 약 40-130ppm의 시편으로 제조할 수 있었으며, 이때 Hf및 C의 첨가량이 증가할수록 시편의 결정립은 미세화되었다. Mo-1.14at% Hf-1.00at % C 조성의 시편을 열처리한 결과 130$0^{\circ}C$에서 결정립내의 편상의 ${\beta}$-Mo 탄화물(molybdenum carbide)이 열역학적으로 더욱 안정한 $\alpha$-Mo 탄화물로 변태되기 시작하고, 1400-150$0^{\circ}C$온도 구간에서는 급내에 의해 고용되어 있던 Hf과 C이 반응하여 미량의 Hf탄화물이 석출되었으며, 150$0^{\circ}C$에서는 결정립계에 Hf 탄화물이 편석되었다. 1500-170$0^{\circ}C$에서는 결정립계에 편석된 Hf탄화물이 분해되고 열역학적으로 더욱 안정한 Hf 산화물(Hafnium oxide)이 석출되었으며, 결정립내에도 미세한 Hf 산화물이 석출되었다.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 1998년도 특별강연 및 춘계학술발표 개요집
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• pp.257-259
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• 1998

• Corrosion Science and Technology
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• 제9권1호
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• pp.20-28
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• 2010

According to the bipolar model, ion selectivity of some species in the passive film is important factor to control the passivation. An increase of cation selectivity of outer layer of the passive film can stabilize the film and improves the corrosion resistance. Therefore, the formation and roles of ionic species in the passive film should be elucidated. In this work, two types of solution (hydrochloric or sulfuric acid) were used to test high N and Mo-bearing stainless steels. The objective of this work was to investigate the formation of oxyanions in the passive film and the roles of oxyanions in passivation of stainless steel. Nitrogen exists as atomic nitrogen, nitric oxide, nitro-oxyanions (${NO_x}^-$), and N-H species, not nitride in the passive film. Because of its high mobility, the enriched atomic nitrogen can act as a reservoir. The formation of N-H species buffers the film pH and facilitates the formation of oxyanions in the film. ${NO_x}^-$ species improve the cation selectivity of the film, increasing the oxide content and film density. ${NO_x}^-$ acts similar to a strong inhibitor both in the passive film and at active sites. This facilitates the formation of chromium oxide. Also, ${NO_x}^-$ can make more molybdate and nitric oxide by reacting with Mo. The role of Mo addition on the passivation characteristics of stainless steel may differ with the test environment. Mo exists as metallic molybdenum, molybdenum oxide, and molybdate and the latter facilitates the oxide formation. When nitrogen and molybdenum coexist in stainless steel, corrosion resistance in chloride solutions is drastically increased. This synergistic effect of N and Mo in a chloride solution is mainly due to the formation of nitro-oxyanions and molybdate ion. Oxyanions can be formed by a 'solid state reaction' in the passive film, resulting in the formation of more molybdate and nitric oxide. These oxyanions improve the cation selectivity of the outer layer and form more oxide and increase the amount of chromium oxide and the ratio of $Cr_2O_3/Cr(OH)_3$ and make the film stable and dense.