• Korean Journal of Materials Research
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• v.19 no.8
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• pp.407-411
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• 2009

Reflection properties, such as specular reflection and diffuse reflection, are very important optical properties for the reflector, which has high reflectance in the display and architecture industry. Calcite is lowcost, nontoxic, and stable over a wide temperature range. Therefore, it is one of the most widely using fillers in many industries and has some advantages over titania as a filler to improve reflectance. However, optical properties, especially those of ceramic-filled composites, have not been analyzed. We studied the reflectance of calcite composites with their surface roughness. The reflectance of the composites was determined using a UV-visible spectrometer. The surface morphology and the micro-structure of the composites were investigated by atomic force microscope. The reflectance of the composites was improved by increasing the content of calcite in the calcite-frit composite. The reflectance is related with the surface roughness in the composites. However, the reflectance depends on the calcite contents in materials with similar surface roughness.

• International Journal of Fluid Machinery and Systems
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• v.4 no.1
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• pp.67-75
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• 2011

Recent results are presented concerning the development of magnetofluidic leakage-free rotating seals for vacuum and high pressure gases, evidencing significant advantages compared to mechanical seals. The micro-pilot scale production of various types of magnetizable sealing fluids is shortly reviewed, in particular the main steps of the chemical synthesis of magnetic nanofluids and magnetic composite fluids with light hydrocarbon, mineral oil and synthetic oil carrier liquids. Design concepts and some constructive details of the magnetofluidic seals are discussed in order to obtain high sealing capacity. Different types of magnetofluidic sealing systems and applications are reviewed. Testing procedures and equipment are presented, as well as the sealing capabilities of different types of magnetizable fluids.

• Geomechanics and Engineering
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• v.36 no.1
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• pp.9-18
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• 2024

With the rapid development of highways and railways, series of traffic safety issues emerged because of mudstone disintegration. To research on the mechanism and further guarantee the stability and safety of transportation infrastructure built on or near mudstone formations, the mudstone disintegration test of mudstone was carried out based on mudstone and sandy mudstone. The element types, cementation characteristics and pore characteristics of the tested specimens were studied by means of Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD) and Image Pro Plus (IPP). The disintegration index of mudstone was approximately 1%, and even some specimens were difficult to be calculated, while the disintegration index of sandy mudstone is approximately 8.7%. According to the results, the two mudstones belong to grade II and III disintegration respectively, of which the sandy stone presents more extensive disintegration than mudstone. This phenomenon was distinguished that, the clay minerals of mudstone are approximately 25% more abundant than those of sandy mudstone, and the unit pore area is 20 ㎛² larger, which result in different microstructure and water absorption capacities. In the liquid phase, the ions in the mudstone specimens were exchanged and combined with water molecules in the environment during the whole disintegration process. This results in continuous spalling and fragmentation of clay minerals, the emergence of secondary fractures, and the deepening of primary fractures.

• Journal of the korean academy of Pediatric Dentistry
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• v.37 no.1
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• pp.82-90
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• 2010

This study examined the effect of adhesive tape supplemented with sodium fluoride on the prevention of dental erosion in vitro. Sound bovine tooth samples were selected and divided randomly into the following 4 groups according to the material treatments: group 1, APF gel; group 2, fluoride varnish; and groups 3 and 4, fluoride tape supplemented with 5% NaF in either a methyl cellulose or poly vinyl acetate carrier, respectively. All specimens were submitted to alternate cycles of acid exposure in a cola beverage (pH 4.3) and artificial saliva for $6\;{\times}\;5\;min/day$ over a 5 day period. The micro-hardness was recorded each day and the lesion depth was measured after 5 days. The micro-hardness of the experimental sides of groups 2, 3 and 4 were significantly higher than that of their control sides and the experimental side of group 1 during the experimental period (p<0.05) except on the 5th day. The enamel surfaces of treatment groups 2, 3 and 4 showed significantly higher resistance to mineral loss in terms of the erosion depth (p<0.05) than group 1 and their control sides. There was no statistically significant difference among group 2, 3 and 4, indicating that the fluoride varnish and tapes produce similar results. Fluoride adhesive tapes are effective in reducing the progression of erosion and can be recommended for young patients who are more susceptible to dental erosion.

• Geophysics and Geophysical Exploration
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• v.25 no.4
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• pp.167-176
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• 2022

We designed a borehole deviation survey tool applicable for steel-cased holes, K-DEV, and developed a prototype for a depth of 500 m aiming to development of own equipment required to secure deep subsurface characterization technologies. K-DEV is equipped with sensors that provide digital output with verified high performance; moreover, it is also compatible with logging winch systems used in Korea. The K-DEV prototype has a nonmagnetic stainless steel housing with an outer diameter of 48.3 mm, which has been tested in the laboratory for water resistance up to 20 MPa and for durability by running into a 1-km deep borehole. We confirmed the operational stability and data repeatability of the prototype by constantly logging up and down to the depth of 600 m. A high-precision micro-electro-mechanical system (MEMS) gyroscope was used for the K-DEV prototype as the gyro sensor, which is crucial for azimuth determination in cased holes. Additionally, we devised an accurate trajectory survey algorithm by employing Unscented Kalman filtering and data fusion for optimization. The borehole test with K-DEV and a commercial logging tool produced sufficiently similar results. Furthermore, the issue of error accumulation due to drift over time of the MEMS gyro was successfully overcome by compensating with stationary measurements for the same attitude at the wellhead before and after logging, as demonstrated by the nearly identical result to the open hole. We believe that the methodology of K-DEV development and operational stability, as well as the data reliability of the prototype, were confirmed through these test applications.

• Journal of the Mineralogical Society of Korea
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• v.31 no.1
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• pp.47-55
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• 2018

Talc, hydrous magnesium phyllosilicate, is one of the most popular industrial minerals due to their chemical stability and adsorptivity. While micro-sized talc has long been used as a filler and coating, nano-sized talc recently is attracting attention as additives for improving the stability of nanocomposites. In this study, we produced the nano-sized talc powder by mechanical method using high energy ball mill and investigated the changes in particle size and crystallinity with increasing milling time up to 720 minutes. X-ray diffraction results show that the peak width of talc gradually as the milling proceeded, and after 720 minutes of pulverization, the talc showed an amorphous-like X-ray diffraction pattern. Lase diffraction particle size analysis presents that particle size of talc which was ${\sim}12{\mu}m$ decreased to ${\sim}0.45{\mu}m$ as the milling progressed, but no significant reduction of particle size was observed even after grinding for 120 minutes or more. BET specific surface area, however, steadily increases up to the milling time of 720 minutes, indicating that the particle size and morphology change steadily as the milling progressed. Scanning electron microscope and transmission electron microscope images shows that layered particles of about 100 to 300 nm was aggregated as micro-sized particles after pulverization for 720 minutes. As the grinding time increases, the particle size and morphology of talc continuously change, but the nano-sized talc particles form micro sized agglomerates. These results suggest that there is a critical size along the a, b axes in which the size of plates is reduced even though the grinding proceeds, and the reduction of plate thickness along the c axis leads the increase in specific surface area with further grinding. This study could enhance the understanding of the mechanism of the formation of nano-sized talc by mechanical grinding.

• Journal of Veterinary Clinics
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• v.27 no.4
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• pp.325-329
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• 2010

The osteogenic potential of hydroxyapatite/poly $\varepsilon$-caprolactone composite (HA/PCL) scaffolds with matrigel was evaluated in a rat calvarial defect model. Calvarial defect formation was surgically created in Sprague Dawley rats (n = 18). HA/PCL scaffold was grafted with matrigel (M-HA/PCL group, n = 6) or without matrigel (HA/PCL group, n = 6). A critical defect group (CD group, n = 6) did not received a graft. Four weeks after surgery, bone formation was evaluated with radiography, micro computed tomography (micro CT) scanning, and histologically. No bone tissue formation was radiographically evident in the CD group. Bone tissue was radiographically evident in the HA/PCL and M-HA/PCL groups, however, there was more bone-similar opacity in the M-HA/PCL group. Micro CT analysis revealed that the bone volume of the M-HA/PCL group was higher than the HA/PCL group, however, no significant difference was found between the HA/PCL and M-HA/PCL groups. Bone mineral density in the M-HA/ PCL group was significantly higher than in the HA/PCL group (p < 0.05). Histologically, new bone was formed only from existing bone in the CD group, showing concavity without bone formation in the defect. In the HA/PCL group, new bone formation was only derived from existing bone, while in the M-HA/PCL group the largest bone formation was observed, with new bone tissue forming at the periphery of existing bone and around the HA/PCL scaffold with matrigel. The results indicate that the combination of HA/PCL scaffold with matrigel may be an effective means of enhancing bone formation in critical-sized bone defects.

• Economic and Environmental Geology
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• v.47 no.5
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• pp.467-477
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• 2014

Naturally occurring asbestos (NOA) occurs in rocks and soils as a result of natural weathering and human activities. The asbestos have been associated with ultramafic and mafic rocks, and carbonate rock. The previous studies on NOA were mainly limited to ultramafic and mafic rock-hosted asbestos in Korea. But, studies on carbonatehosted asbestos are relatively rare. Therefore, the purposes of this study were to investigate mineralogical characteristics of carbonate-hosted and metapelite-hosted NOA and to examine genesis of NOA occurred in the both rocks. The study area was Daerori, Seosan, Chungnam Province, Korea. The major rock formation consisted of limestone and schist which have been known to contain asbestos. Sampling was performed at outcrop which contained carbonate rock showing acicular asbestos crystals as well as pegmatitic intrusion that contacted with carbonate rock. PLM, XRD, EPMA, and EDS analyses were used to characterize mineral assemblages, mineralogical characteristics, and crystal habits of amphiboles and other minerals. BSEM images were also used to examine the genesis of asbestos minerals. The amphibole group was observed in all of the carbonate rocks, and actinolite and tremolite were identified in all rocks. These mineral habits were mainly micro-acicular crystals or secondary asbestiform minerals on the surface of non-asbestiform minerals appearing split end of columnar crystals produced by weathering. BSEM images showed residual textures of samples. The residual textures of carbonate rocks showed dolomite-tremolite-diopside mineral assemblages that formed during prograde metasomatism stage. Some carbonate rock also showed diopside-tremolite-talc mineral assemblages which were formed during retrograde metasomatism stage, as the residual textures. In result the presence of asbestos actinolite-tremolite in the carbonate rocks were confirmed in the areas where actinolite-tremolite asbestos was influenced by low temperature hydrothermal solution during metasomatism stage. These asbestos minerals showed the acicular asbestiform minerals, but even non-asbestiform minerals, a bundle or columnar shape, could transform to asbestiform minerals as potential NOA by weathering because the end of columnar shape of non-asbestiform minerals appeared as multiple acicular shaped fibers.

• Journal of the Mineralogical Society of Korea
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• v.23 no.2
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• pp.125-139
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• 2010

Behavior of heavy metals and arsenic in the tailings of Songcheon Au-Ag mine was characterized via both mineralogical and geochemical methods. Mineral composition of the tailings was investigated by X-ray diffractometry, energy-dispersive spectroscopy, and electron probe micro-analyzer (EPMA) and total concentrations of heavy metals and arsenic and their chemical forms were analyzed by total digestion of aqua regia and sequential extraction method, respectively. The results of mineralogical study indicate that the tailings included mineral particles of resinous shape mainly consisting of galena, sphalerite, pyrite, quartz, and scorodite, and specifically socordite was identified in the form of matrix. EPMA quantitative analyses were performed to evaluate the weatherability of each mineral, and the results suggest that it decreased in the sequence of arsenopyrite > galena > sphalerite > pyrite. The weathering pattern of galena was observed to show distinctive zonal structure consisting of secondary minerals such as anglesite and beudantite. In addition, almost all of arsenopyrite has been altered to scorodite existing asmatrix and galena, sphalerite, and pyrite which have lower weatherability than arsenopyrite were identified within the matrix of scorodite. During the process of alteration of arsenopyrite into scorodite, it is likely that a portion of arsenic was lixiviated and caused a great deal of detrimental effects to surrounding environment. The results of EPMA quantitative analyses verify that the stability of scorodite was relatively high and this stable scorodite has restrained the weathering of other primary minerals within tailings as a result of its coating of mineral surfaces. For this reason, Songcheon tailings show the characteristics of the first weathering stage, although they have been exposed to the surface environment for a long time. Based on the overall results of mineralogical and geochemical studies undertaken in this research, if the tailings are kept to be exposed to the surface environment and the weathering process is continuous, not only hazardous heavy metals, such as lead and arsenic seem to be significantly leached out because their larger portions are being partitioned in weakly-bound (highly-mobile) fractions, but the potential of arsenic leaching is likely to be high as the stability of scorodite is gradually decreased. Consequently, it is speculated that the environmental hazard of Songcheon mine is significantly high.

• International Journal of Oral Biology
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• v.33 no.1
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• pp.33-43
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• 2008

In the process of bone remodeling, mineral phase of bone is dissolved by osteoclasts, resulting in elevation of calcium concentration in micro-environment. This study was performed to explore the effect of high extracellular calcium ($Ca{^{2+}}_e$) on mineralized nodule formation and on the expression of progressive ankylosis (Ank), plasma cell membrane glycoprotein-1 (PC-1) and osteopontin by primary cultured mouse calvarial cells. Osteoblastic differentiation and mineralized nodule formation was induced by culture of mouse calvarial cells in osteoblast differentiation medium containing ascorbic acid and ${\beta}$-glycerophosphate. Although Ank, PC-1 and osteopontin are well known inhibitors of mineralization, expression of these genes were induced at the later stage of osteoblast differentiation during when expression of osteocalcin, a late marker gene of osteoblast differentiation, was induced and mineralization was actively progressing. High $Ca{^{2+}}_e$(10 mM) treatment highly enhanced mRNA expression of Ank, PC-1 and osteopontin in the late stage of osteoblast differentiation but not in the early stage. Inhibition of p44/42 MAPK activation but not that of protein kinase C suppressed high $Ca{^{2+}}_{e^-}$induced expression of Ank, PC-1 and osteopontin. When high $Ca{^{2+}}_e$(5 mM or 10 mM) was present in culture medium during when mineral deposition was actively progressing, matrix calcifiation was significantly increased by high $Ca{^{2+}}_e$. This stimulatory effect was abolished by pyrophosphate (5 mM) or levamisole (0.1-0.5 mM), an alkaline phosphatase inhibitor. In addition, probenecid (2mM), an inhibitor of Ank, suppressed matrix calcification in both control and high $Ca{^{2+}}_{e^-}$treated group, suggesting the possible role of Ank in matrix calcification by osteoblasts. Taken together, these results showed that high $Ca{^{2+}}_e$ stimulates expression of Ank, PC-1 and osteopontin as well as matrix calcification in late differentiation stage of osteoblasts and that p44/42 MAPK activation is involved in high $Ca{^{2+}}_{e^-}$induced expression of Ank, PC-1 and osteopontin.