• 자원환경지질
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• 제27권6호
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• pp.537-548
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• 1994

The Weolyu gold-silver deposits at Hwanggan, Chungcheongbukdo, is of a late Cretaceous $(74.24{\pm}1.63Ma)$ epithermal vein-type, and is hosted in the quartz porphyry of late Cretaceous age. Based on mineral paragenetic sequence interpreted from vein structure and mineral assemblages, three stages mineralization were distinguished. A variety of ore minerals occurs including pyrite, sphalerite, chalcopyrite, galena with small amount of electrum, native silver, argentite, pearceite, sb-pearceite, argyrotite. The gangue minerals are quartz, rutile, calcite, apatite, fluorite and rhodochrocite. Wall-rock alteration such as pyritization, chloritization, sericitization, silicification is observed near the quartz veins. Au-Ag minerals were crystallized at middle and late stage of the two mineralization sequences. Results from the analysis of fluid inclusion and thermodynamic calculation indicate that Au-Ag mineral deposits were formed primarily by cooling and dilution of hydrothermal fluids($165{\sim}313^{\circ}C$, 0.4~2.4wt.% equivalent NaCl) with some degree mixing of meteoric water.

• Restorative Dentistry and Endodontics
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• 제20권2호
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• pp.818-826
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• 1995

The present study was undertaken to investigate the crystal growth onto enamel mineral and synthetic hydroxyapatite seeds in media resembling the enamel fluid composition. Effects of fluoride at low concentrations on the precipitation were also examined in a benchtop crystal growth model adopting a miniaturized reaction column. X-ray diffraction and Fourier transform infrared spectroscopy(FTIR), as well as chemical analyses, were employed for characterization of both seed materials before and after experimentation. Remarkable findings were that (1) both biological and synthetic seeds at the same total surface areas yielded rather similar precipitation rates at all levels of fluoride concentration in solution and (2) the precipitation rate was accelerated in a manner depending on fluoride concentrations in media. FTIR differential analysis disclosed that the precipitating phase was characterized as poorly crystallized apatite, which incorporated subtle carbonate. Most of the fluoride ions in soution were readily incorporated into crystals. The overall results support the view that the seeded crystal growth model is of value to gain insight into the mechanism of enamel crystal growth under fluoride regimens.

• 한국자기공명학회논문지
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• 제6권2호
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• pp.84-88
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• 2002

Dating and dosimetry using electron spin resonance (ESR) in 20th Century developed at both Yamaguchi University and Osaka University have been reviewed with emphasis on new prospects and strategies in 21th century. Natural radiation have been generating radicals that accumulated in archaeological and geological materials. ESR detects these radicals and the ESR signal intensity is proportional to the radiation dose and therefore the age. The assessment of the total dose of natural radiation and the annual dose rate give their ESR ages. The ESR dating of stalactites and stalagmites ant Akiyoshi cave in Yamaguchi prefecture in 1975 was extended to anthropological dating using bones and tooth enamel excavated in Greek Petralona cave. Fossils of shells and corals gave the ages of marine terraces and sea-level changes. Quartz grains gave the ages of geothermal alteration and fault movements. Future ESR dating of ices at outer planets anf their satellite are also investigated as basic studies for ices od $H_2O,\;CO_2,\;SO_2$ as well as terrestrial hydrates in laboratory. Atomic bomb radiation dosimetry at Hiroshima and Nagasaki using ESR lead to the dosimetry of personnel, Chemobyl and JCO criticality accidents. Monitoring of radiation dose with sensitive materials with tissue equivalence are being developed. finally a new scanning ESR imaging apparatus (a near field microwave microscope) developed in our laboratory gave ESR images of Radicals from fossils to Si-CVD and diamond films as summarized in my book in 2002.

• Nuclear Engineering and Technology
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• 제54권3호
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• pp.997-1002
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• 2022

Oxyapatite[Ca₂Nd₈(SiO₄)₆O₂] glass-ceramics have been suggested as wasteforms for the immobilisation of rare-earth radioactive nuclides because of their high waste-loading capability and good chemical durability. In particular, a partitioning effect is predicted to contribute to an enhancement of corrosion resistance in glass-ceramics compared with that of conjugate glasses of the same composition. Because rare-earths are inherently insoluble nuclides, detection of changes in corrosion behavior between glass-ceramics and conjugate glasses under normal conditions is not easy. In this study, therefore, we revealed the partitioning effect by exposing glass-ceramics and glasses to solution of pH 2, 7 and 10 at 90 ℃ for 20 d. In addition, we proposed the corrosion mechanism for oxyapatite glass-ceramics under various corrosion conditions. Especially, the glassy phase dissolved first, followed by the oxyapatite phase during pH 7 corrosion.

• Corrosion Science and Technology
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• 제15권3호
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• pp.120-124
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• 2016

The effect of alloying element Ca (0, 1, and 2 wt%) on corrosion resistance and bioactivity of the as-received and anodized surface of rolled plate AM60 alloys was investigated. A plasma electrolytic oxidation (PEO) was carried out to form anodic oxide film in $0.5mol\;dm^{-3}\;Na_3PO_4$ solution. The corrosion behavior was studied by polarization measurements while the in vitro bioactivity was tested by soaking the specimens in Simulated Body Fluid (1.5xSBF). Optical micrograph and elemental analysis of the substrate surfaces indicated that the number of intermetallic particles increased with Ca content in the alloys owing to the formation of a new phase $Al_2Ca$. The corrosion resistance of AM60 specimens improved only slightly by alloying with 2 wt% Ca which was attributed to the reticular distribution of $Al_2Ca$ phase existed in the alloy that might became barrier for corrosion propagation across grain boundaries. Corrosion resistance of the three alloys was significantly improved by coating the substrates with anodic oxide film formed by PEO. The film mainly composed of magnesium phosphate with thickness in the range $30-40{\mu}m$. The heat resistant phase of $Al_2Ca$ was believed to retard the plasma discharge during anodization and, hence, decreased the film thickness of Ca-containing alloys. The highest apatite forming ability in 1.5xSBF was observed for AM60-1Ca specimens (both substrate and anodized) that exhibited more degradation than the other two alloys as indicated by surface observation. The increase of surface roughness and the degree of supersaturation of 1.5xSBF due to dissolution of Mg ions from the substrate surface or the release of film compounds from the anodized surface are important factors to enhance deposition of Ca-P compound on the specimen surfaces.

• 대한치과보철학회지
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• 제34권1호
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• pp.169-186
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• 1996

The purpose of this study was to investigate the mechanical properities and biocompatibility with crystallization temperature and time of a bioactive glass-ceramic system $41.4wt%SiO_{2}-35.0wt%CaO-3.0wt%MgO-12.0wt%P_{2}O_{5}-8.6wt%Al_{2}O_{3}$ with same molar percent of $Al_{2}O_{3}\;and\;P_{2}O_{5}$. The crystallization behaviors were investigated with DTA, XRD and SEM. Fracture toughness with the change of crystallization temperature and time was measured by indentation fracture method. Also, biocompatibility was evaluated by culture of mouse fibroblast cell line L929. The results obtained were as follows ; 1. The major crystalline phases were apatite and anorthite, and relative intensity of anorthite phase was increased at $1004^{\circ}C$. 2. The hardness and fracture toughness were gradually increased with the increase in ceraming temperature to $1004^{\circ}C$. 3. When the glass ceramic was heat-treated for 4 hours at ceraming temperature of $1004^{\circ}C$, hardness and fracture toughness showed the maximum values $578.84k/mm^2\;and\;2.07MPa\;m^{1/2}$, respectively. 4. The growth rate and cytotoxic of L929 fibroblast cells for bioactive glass ceramic were better than those of stainless steel and titanium.

• 대한치과교정학회지
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• 제44권5호
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• pp.246-253
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• 2014

Objective: To evaluate the bioactivity, and the biomechanical and bone-regenerative properties of Ti6Al4V miniscrews subjected to anodization, cyclic precalcification, and heat treatment (APH treatment) and their potential clinical use. Methods: The surfaces of Ti6Al4V alloys were modified by APH treatment. Bioactivity was assessed after immersion in simulated body fluid for 3 days. The hydrophilicity and the roughness of APH-treated surfaces were compared with those of untreated (UT) and anodized and heat-treated (AH) samples. For in vivo tests, 32 miniscrews (16 UT and 16 APH) were inserted into 16 Wistar rats, one UT and one APH-treated miniscrew in either tibia. The miniscrews were extracted after 3 and 6 weeks and their osseointegration (n = 8 for each time point and group) was investigated by surface and histological analyses and removal torque measurements. Results: APH treatment formed a dense surface array of nanotubular TiO2 layer covered with a compact apatite-like film. APH-treated samples showed better bioactivity and biocompatibility compared with UT and AH samples. In vivo, APH-treated miniscrews showed higher removal torque and bone-to-implant contact than did UT miniscrews, after both 3 and 6 weeks (p < 0.05). Also, early deposition of densely mineralized bone around APH-treated miniscrews was observed, implying good bonding to the treated surface. Conclusions: APH treatment enhanced the bioactivity, and the biomechanical and bone regenerative properties of the Ti6Al4V alloy miniscrews. The enhanced initial stability afforded should be valuable in orthodontic applications.

• 한국광물학회지
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• 제10권2호
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• pp.114-125
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• 1997

The purpose of this study is to clarify the geological occurrence, mineralogical, physico-chemical and thermal properties of the sericite ore which located in Chungha area, Kyungsangbuk-do. The geology of this area are composed mainly of hornfels and some felsite porphyry. The sericitic ore is classified into sericite, sericite-quartz and quartz-sericite ore according to mineral assemblages. Mineral components in sericite ore are mainly sericite with minor quartz, apatite, sphene, zircon, ilmenite, bismuthinite, iron oxide and etc. Sericite-quartz ore are mainly composed of sericite and quartz. Accessary minerals are muscovite, epidote, zircon, sphene, iron oxide and etc. The chemical compositions of K2O, Al2O3, & Ignition loss in sericite and sericite-quartz ore increase than that of the host rock, while the composition of SiO2, Na2O & Fe2O3 decrease. Sericite and sericite-quartz ore are characterized by the specific gravity of 2.35 and 2.44, the pH of 4.36 cP and 2.36 cP respectively. The result of size analyses of sericite ore is 11.3% in grain volume concentration between 12.9 $\mu\textrm{m}$ and 11.1$\mu\textrm{m}$, and 32.3% between 9.6$\mu\textrm{m}$ and 12.9$\mu\textrm{m}$. The thermal expansivity of sericite and sericite-quartz ore show the similar pattern. The sericite ore shows the thermal expansivity of 0.31% at 50$0^{\circ}C$, 0.39~0.75% at 600~1,00$0^{\circ}C$ and 0.74% at 1,10$0^{\circ}C$. The sericite-quartz ore show the thermal expansivity of 0.29% at 50$0^{\circ}C$, 0.36~0.72% at 600~1,000% and 0.71% at 1,10$0^{\circ}C$.

• 암석학회지
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• 제8권2호
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• pp.81-91
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• 1999

옥천화강암은 옥천읍 일대에서 원형상으로 분포하며, 그 북부와 동부 및 남부에서 옥천층군을 관입한 쥬라기 암체이며 그 서부에서 백악기의 석영반암류에 의해 관입된다. 이 암체는 중립질의 흑운모 화강으로서 유색광물부(mafic enclave)가 종종 발달하며 북부 주변에서는 미약한 엽리구조를 이루기도 한다. 구성광물은 석영, 사장석, 알칼리장석, 흑운모, 스펜과 녹리석 등이다. 복부일부에 발달하는 미립질과 줄무늬 석영, 흑운모와 이차광물인 백운모 등이 이루는 엽리는 옥천화강암질 마그마의 유동중에 주변암에 의해 형성된 구조이다. QAP 모드분석에서 몬조화강암-화강섬록암에 도시되는 과알루미나암질로서 캘크 알칼리례열에 속하는 분화경향을 가진다. SiO2 대 주원소 그리고 미향원소 등의 관계도에서 단일 마그마의 분화경향을 뚜렷이 가진다. 콘드라이트로 표준화한 희토류원소는 경(LREE)에서 중(HREE)으로 갈수록 점진적으로 결핍되며 Eu/Eu*는 0.84의 부 이상값(negative anomaly)을 가져 대체로 국내 쥬라기 화강암류와 유사한 특성을 가진다. 동시충돌대의 지구조적환경에서 I-형의 지각물질이 용융하여 형성된 화강암질 마그마가 다소 빠르게 상승하여 옥천층군내에 정치된 암체이다.

• 자원환경지질
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• 제17권1호
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• pp.35-47
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• 1984

Combined mineralogical and geochemical studies were made on two hundred eighty one representative samples from uraniferous coaly meta-pelites of the Ogcheon metamorphic terrain. Different mineral occurrence of the areas investigated should be taken into account for chemical processes for uranium extraction. Secondary uranium minerals identified are metauranocircite, metatorbernite and autunite. These are disseminated mostly on the laumontites which infused and filled secondary openings in the coaly matrix, and are often closely associated with iron oxides. The uranium distribution show distinctly log normal. Geochemical correlation coefficient of uranium and organic carbon displays +0.624~+0.796. The relationship of the major components to uranium can be expressed by the following regression equation: Log $(U_3O_8{\times}10^4)$=1.40117-0.00076 (quartz) -0.00118 (muscovite) +0.00235 (biotite) +0.00323 (other silicates) - 0.01114 (apatite) +0.01124 (hematite) +0.00149 (limonite) -0.01823 (opaques)+0.03049 (organic carbon). Uranium in the coaly meta-pelites of the Ogcheon Group was deposited together under same physico-chemical environmental conditions. There is a considerable variation in the ${\delta}^{34}S$ values (11.2~16.8 per mil) of the pyrites from the U-bearing meta-pelites, which implies sedimentary origin. The two U-bearing coaly rocks analyzed have ${\delta}^{13}C$ values between -16.88~-18.00 per mil, which suggests organic.