• Journal of the Korean Crystal Growth and Crystal Technology
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• v.31 no.5
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• pp.218-227
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• 2021

A thick film NTC thermistor for low temperature co-firing was manufactured by printing and sintering a paste prepared using NTC powder of Mn_1.5Ni_0.4Co_0.9Cu_0.4O₄ composition, lead free frit, and RuO₂ on a 96 % alumina substrate. The effect of frit and RuO₂ on the electrical properties of thick film NTC thermistor was studied. The resistance of the thick film NTC thermistor was higher than that of the bulk phase sintered at the same temperature, but it was found that the negative resistance temperature characteristic appeared more clearly and linearly in the resistance - temperature characteristic. On the other hand, the area resistance decreased as the sintering temperature increased, and the area resistance increased as the amount of frit added increased. The B constant of the thick film NTC thermistor was 3000 K or higher. Among them, it was found that the B constant of the thick film NTC thermistor made of paste with 5 wt% of frit added and sintered at 900℃ showed the highest B constant. Also, it can be seen that the area resistance decreased with the addition of RuO₂, and the change in the area resistance decrease of the thick film NTC thermistor obtained by sintering the paste containing 5 wt% of RuO₂ at 900℃ is the most obvious.

• Korean Journal of Materials Research
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• v.28 no.12
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• pp.763-768
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• 2018

In this study, glass fibers are fabricated via a continuous spinning process using manganese slag, steel slag, and silica stone. To fabricate the glass fibers, raw materials are put into an alumina crucible, melted at $1550^{\circ}C$ for 2 hrs, and then annealed at $600^{\circ}C$ for 2 hrs. We obtain a black colored glass. We identify the non-crystalline nature of the glass using an XRD(x-ray diffractometer) graph. An adaptable temperature for spinning of the bulk marble glass is characterized using a high temperature viscometer. Spinning is carried out using direct melting spinning equipment as a function of the fiberizing temperature in the range of $1109^{\circ}C$ to $1166^{\circ}C$, while the winder speed is in the range of 100rpm to 250rpm. We investigate the various properties of glass fibers. The average diameters of the glass fibers are measured by optical microscope and FE-SEM. The average diameter of the glass fibers is $73{\mu}m$ at 100rpm, $65{\mu}m$ at 150rpm, $55{\mu}m$ at 200rpm, and $45{\mu}m$ at 250rpm. The mechanical properties of the fibers are confirmed using a UTM(Universal materials testing machine). The average tensile strength of the glass fibers is 21MPa at 100rpm, 31MPa at 150rpm, 34MPa at 200rpm, and 45MPa at 250rpm.

• Korean Journal of Materials Research
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• v.29 no.11
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• pp.727-733
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• 2019

In this study, the glass melting properties are evaluated to examine the possibility of using refused coal ore as replacement for ceramic materials. To fabricate the glass, refused coal ore with calcium carbonate and sodium carbonate in it (which are added as supplementary materials) is put into an alumina crucible, melted at $1,200{\sim}1,500^{\circ}C$ for 1 hr, and then annealed at $600^{\circ}C$ for 2 hrs. We fabricate a black colored glass. The properties of the glass are measured by XRD (X-ray diffractometry) and TG-DTA (thermogravimetry-differential thermal analysis). Glass samples manufactured at more than $1,300^{\circ}C$ with more than 60 % of refused coal ore are found by XRD to be non-crystalline in nature. In the case of the glass sample with 40 % of refused coal ore, from the sample melted at $1,200^{\circ}C$, a sodium aluminum phosphate peak, a disodium calcium silicate peak, and an unknown peak are observed. On the other hand, in the sample melted at $1,300^{\circ}C$, only the sodium aluminum phosphate peak and unknown peak are observed. And, peak changes that affect crystallization of the glass according to melting temperature are found. Therefore, it is concluded that glass with refused coal ore has good melting conditions at more than $1,200^{\circ}C$ and so can be applied to the construction field for materials such as glass tile, foamed glass panels, etc.

• Economic and Environmental Geology
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• v.4 no.4
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• pp.167-215
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• 1971

I. Purpose and Importance of the Study The purpose of the present study is to clarify to geological, mineralogical, and physico-chemical properties of the clay minerals deposits imbedded in the Tertiary sediments in the areas between. Pohang and Ulsan along southeastern coastal region of Korea. These clays are being mined and utilized for filter and insecticide after activation or simple pulverizing, nontheless activated clays are short coming as chemical industry in Korea has been rapidly grown in recent years. In spite of such increase in clay demand, no goological investigation on clay deposits nor physico-chemical properties of the clays have been carried out up to date. Consequently activated clays produced in Korea is not only of low grade but also of shortage in supply, so that Korea has to import activated clays of better grade. The importance of the present study lies, therefore, on that guiding principle could be laid down by knowing stratigraphical horizons, of clay deposits and fundamental data of improving grade of activated clays might be derived from the results of physico-chemical examinations. II. Contents and Scope of the study The contents of the study are pinpointed down in the following two subjects: 1) General geological investigation of Tertiary formations distributed in the areas between Pohang and UIsan, and detail geological study of the bentonitic clay deposits imbedded in them. 2) To clarifty physico-chemical characteristics of the clays by means of chemical analysis, X-ray diffraction and electron microscope. The scope of the study involves the following there points: i) Regional geological investigation-This investigation has been carried out in order to find out the distribution of Tertiary sediments and exact location of clay mineral deposits in the areas between Pohang and UIsan. ii) Detail geological investigation-This has been concentrated in and around the clay deposits which. had been found out by the regional investigation. iii) Laboratory researchs include i) age determination and correlation of Tertiary sediments by paleontological study, and ii) Chemical analysis, X-ray diffraction, and electron microscopic studies on clays, samples taken from various clay deposits. III. Research Results and Suggestions 1) The geology of the area investigated is composed mainly of Janggi and Beomgokri groups of Miocene age in ascending order rested on the upper Silla system, Balkuksa granite and volcanic rocks of upper Cretaceous age as base. 2) Janggi group is composed in ascending order of Janggi conglomerate, Nultaeri rhyolitic tuff, Keumkwangdong shale, two beds of lignite-bearing formations which consist of alternation of conglomerate, sandstone and mudstone, and andesitic, rhyolitic, and basaltic tuff beds. 3) Beomgokri group is mainly composed of andesitic to rhyolitic tuff interlayered by conglomerate and tuffaceous sandstone. In the areas around boundary between North-and South Kyeongsang-do is distributed Haseori farmation which is composed of conglomerate, sandstone, mudstone and andesitic to rhyolitic tuff, and which is correlated to Eoilri formation of Janggi group. 4) Clay deposits of the area are interbedded in Eoilri, Haseori, Nultaeri tuff, Keumkwangdong shale, upper and lower horizon of the lower lignite-bearing seam, and Keumori rhyolitic tuff formations of Janggi group; and are genetically classi.fied into four categories, that is, i) those derived from volcanic ash beds(Haseori and Daeanri deposits), ii) those of secondary residual type from rhyolitic tuff beds(Seokupri deposits), iii) Clay beds above and beneath the lignite seams, (Janggi and Keumkwangdong deposits), and iv) those derived from rhyolitic tuff beds(Sangjeong and Tonghae deposits). 5) Mineral constituents of clay deposits are, according to X-ray diffraction, montmorillonite accompanied in different degree by cristobalite, plagioclase, quartz, stilbite, and halloysite in rare occasion. The clays are grouped according to mineral composition into four types; i) those consist mostly of montmorillonite, ii) those composed of montmorillonite and cristobalite, iii) those composed of montmorillonite and plagioclase, and iv) those composed of montmorillonite, plagioclase and quartz. 6) Clays interbedded in Haseori formation and vicinity of lignite seams belong to the first type, are of good quality and derived either from volcanic ash bed, or primary clay beds near lignite seams. Clays belonged to other types are derived from weathering of rhyolitic tuff formations and their quality varies depending upon original composition and degree of weathering. Few clays in secondary residual type contain small amount of halloysite. 7) Judging from analytical data, content of silica($SiO_2$) varies proportionally with content of cristobalite, and alumina($Al_2O_3$) content does not vary with that of plagioclase, but increases in the sedimentary bedded type of deposits. 8) It is unknown whether or not these days could be upgraded by beneficiation since no grain size of these impurities nor beneficiation test had been studied. 9) Clay beds derived from valcanic ash layers or sedimentary layers at the vicinity of lignite seams are thin in thickness and of small, discontinueous lenticular shape, although they are of good quality; and those derived from rhyolitic tuff formations or residual type from tuff are irregular in both occurrence and quality. It is, therefore, not only very difficult but also meaningless to calculate its reserve, and reserve estimation, even if done, will greatly be deviated from practically minable one. Consequently, way of discovery and exploitation of clay deposits in the area under consideration is to check the geologically favorable areas whenever needed.

• Resources Recycling
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• v.31 no.6
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• pp.44-51
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• 2022

In the steelmaking process using an electric arc furnace (EAF), light-burnt dolomite, which is a flux containing MgO, is used to protect refractory materials and improve desulfurization ability. Furthermore, a recarburizing agent is added to reduce energy consumption via slag foaming and to induce the deoxidation effect. Herein, a waste MgO-C based refractory material was used to achieve the aforementioned effects economically. The waste MgO-C refractory materials contain a significant amount of MgO and graphite components; however, most of these materials are currently discarded instead of being recycled. The mass recycling of waste MgO-C refractory materials would be achievable if their applicability as a flux for steelmaking is proven. Therefore, experiments were performed using a target composition range similar to the commercial EAF slag composition. A pre-melted base slag was prepared by mixing SiO₂, Al₂O₃, and FeO in an alumina crucible and heating at 1450℃ for 1 h or more. Subsequently, a mixed flux #2 (a mixture of light-burnt dolomite, waste MgO-C based refractory material, and limestone) was added to the prepared pre-melted base slag and a melting reaction test was performed. Injecting the pre-melted base slag with the flux facilitates the formation of the target EAF slag. These results were compared with that of mixed flux #1 (a mixture of light-burnt dolomite and limestone), which is a conventional steelmaking flux, and the possibility of replacement was evaluated. To obtain a reliable evaluation, characterization techniques like X-ray diffraction (XRD) analysis and X-ray fluorescence (XRF) spectrometry were used, and slag foam height, slag basicity, and Fe recovery were calculated.

• Economic and Environmental Geology
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• v.28 no.3
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• pp.185-197
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• 1995

Tungsten skarns in the Chungju mine which consists mainly of strata-bound type iron ore deposits are found in the vicinity of the contact between the age-unknown Kyemeongsan Formation and granitic rock intrusions of Mesozoic age($134{\pm}2Ma$). Tungsten skarns were formed extensively from alumina and silica-rich schistose rocks by the introduction of calcium and iron from hydrothermal solution. The skarns comprise a metasomatic column and are subdivided into four facies; garnet facies, wollastonite facies, epidote facies and chlorite facies. The skarn process in time-evolutional trend can be divided broadly into the four facies in terms of the paragenetic sequence of calc-silicates and their chemical composition. Skarn and ore minerals were formed in the following sequence; (1) garnet facies, adjacent to biotite granite, containing mainly garnet(>Ad96) and magnetite, (2) wollastonite facies containing mainly wollastonite and garnet(Ad95~60), (3) epidote facies, containing mainly epidote(Ps35~31), quartz, andradite-grossular(Ad63~50), and scheelite, (4) chlorite facies, adjacent to and replacing schist, containing mainly chrolite, muscovite, quartz, calcite, epidote(Ps31~25), hematite and sulfides. The mineral assemblage and mineral compositions. suggest that the chemical potentials of Ca and Fe increased toward the granitic rock, and the component Al, Mg, K, and Si decreased from the host rock to granitic rock. The homogenization temperature and salinity of fluid inclusion in scheelite, quartz and epidote of epidote facies skarn is $300-400^{\circ}C$ and 3-8wt.% eqiv. NaCl, respectively. ${\delta}^{34}S$ values of pyrite and galena associated with chlorite facies skarn is $9.13{\sim}9.51%_{\circ}$ and $5.85{\sim}5.96%_{\circ}$, respectively. The temperature obtained from isotopic com· position of coexisting pyrite-galena is $283{\pm}20^{\circ}C$. Mineral assemblages and fluid inclusion data indicate that skarn formed at low $X_{CO_2}$, approximately 0.01. Temperature of the skarn mineralization are estimated to be in the range of $400^{\circ}C$ to $260^{\circ}C$ and pressure to be 0.5 kbar. The oxygen fugacity($fo_2$) of the skarn mineralization decreased with time. The early skarn facies would have formed at log $fo_2$ values of about -25 to -27, and late skarn facies would have formed at log $fo_2$ values of -28 to -30. The estimated physicochemical condition during skarn formation suggests that the principal causes of scheelite mineralization are reduction of the ore·forming fluid and a decrease in temperature.

• Economic and Environmental Geology
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• v.44 no.4
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• pp.273-288
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• 2011

Chon-Ashuu copper mining claim area is located, in terms of the geotectonic setting, in the northern part of the suture line which is bounded with the marginal part of Issik-kul micro-continent on the southern part of North Tien-Shan terrane. The geological blocks of Chon-Ashuu districts belong to the southern tip of Kazakhstan orocline. The rock formation of this area are composed of the continental crust or/and arc collage and the paleo-continental fragments-accretionary wedge complex of pre-Altaid orogenic materials. ASI(Alumina Saturation Index) of Paleozoic plutonic rocks in Chon-Ashuu area belong to the peraluminous and metaluminous rocks which were generated from fractional crystallization of Island and volcanic arc crusts in syn-post collisional plate. The geology of the ChonAshuu area consists of upper Proterozoic and Paleozoic rock formations. According to Harker variation diagrams for Chon-Ashuu arenaceous sedimentary rocks, the silty sandstone of Chon-Ashuu area showing the mineralogical immaturity were derived from Island arc or the marginal environments of active continent in Cambro-Carboniferous period. Numerous intrusive rocks of Chon-Ashuu area are distributed along north east trending tectonic structures and are bounded on four sides by the conjugate pattern. The most common type of the plutonic rocks are granodiorite and monzodiorite. According to the molecular normative An-Ab-Or composition (Barker, 1979), the plutonic rocks in Chon-Ashuu area are classified into tonalite - trondhjemite - granodiorite (TTG) series which are an aggregation of rocks which is the country rock of copper mineralization, that are formed by melting of hydrous mafic crust at high pressure.

• Restorative Dentistry and Endodontics
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• v.32 no.4
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• pp.343-355
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• 2007

The objectives of this study was to evaluate the durability of 4 resin cements by means of microtensile bond strength test combined with thermocycling method and fractographic FE-SEM analysis. Experimental groups were prepared according to thermocycling (0, 1,000, 5,000) and the kind of resin cements, those were Variolink II, Multilink, Panavia F 2.0, Rely X Unicem. Flat dentin surfaces were created on mid-coronal dentin of extracted third molars. Then fresh dentin surface was grounded with 320-grit silicon carbide abrasive papers to create uniform smear layers. Indirect composite block (Tescera, Bisco Inc., Schaumburg, IL, USA) was fabricated ($12\;{\times}\;12\;{\times}\;6\;mm^3$). It's surface for bonding to tooth was grounded with silicon carbide abrasive papers from 180- to 600-grit serially, then sandblasted witk $20\;-\;50\;{\mu}m$ alumina oxide. According to each manufacturer's instruction, dentin surface was treated and indirect composite block was luted on it using each resin cement. For Rely X Unicem, dentin surface was not treated. The bonded tooth-resin block were stored in distilled water at $37^{\circ}C$ for 24 hours. After thermocycling, the bonded tooth-resin block was sectioned occluso-gingivally to 1.0 mm thick serial slabs using all Isomet slow-speed saw (Isomet, Buehler Ltd, Lake Bluff, IL, USA). These sectioned slabs were further sectioned to $1.0\;{\times}\;1.0\;mm^2$ composite-dentin beams. The specimens were tested with universal testing machine (EZ-Test, Shimadzu, Japan) at a crosshead speed of 1.0 mm/min with maximum load of 500 N. The data was analyzed using one-way ANOVA and Duncan's multiple comparison test at $p\;{\leq}\;0.05$ level. Within the limited results, we conclude as follows; 1. The bond strength of Variolink II was evaluated the highest among experimental groups and was significantly decreased after 1,000 thermocycling (p < 0.05). 2. The bond strength of Multilink was more affected by thermocycling than the other experimental groups and significantly decreased after 1,000 thermocycling (p < 0.05). 3. Panavia F 2.0 and Rely X Unicem showed the gradually decreased tendency of microtensile bond strength according to thermocycling but there was no significant difference (p > 0.05). 4. Adhesive based-resin cements showed lower bond strength with or without thermocycling than composite based-resin cements. 5. Variolink II & Multilink showed high bond strength and mixed failure, which was occurred with a thin layer of luting resin cement before thermocycling and gradually increased adhesive failure along the dentin surface after thermocycling. The bonding performance of resin cement can be affected by application procedure and chemical composition. Composite based-resin cement showed higher bond strength and durability than adhesive based-resin cement.