• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.7
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• pp.1229-1234
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• 2008

In this work, ultra high-voltage (17 - 50 kV AC), reliable 80 pF mica capacitors for partial discharge system application were investigated. Mica was used as the dielectric of the capacitors. Using the conservative design rule, over 3 individual $50\;{\mu}m$ thick mica sheets with a size of 30mm{\times}35mm were used with lead foils to form a parallel capacitor element and 20 mica sheets were interleaved with lead foils to form a series stack of parallel capacitor element to meet the requirements of the capacitors. The dimensions of the fabricated 80 pF capacitors for 17 kV AC and 50 kV AC were $90\;mm{\times}90\;mm$ and $95\;mm{\times}180\;mm$, respectively. The high-frequency characteristics of the capacitance (C) and dissipation factor (D) of the developed capacitors were measured using a capacitance meter. The developed capacitors exhibited C of 79.5 - 87.5 pF, had D of 0.001% over the frequency ranges of 150 kHz to 50 MHz, had a self-resonant frequency of 65 MHz, and showed results comparable to those measured for the capacitors prepared recently by $Adwel^{Tm}$. The developed capacitors also showed excellent characteristics for thermal shock test and temperature cycling test.

• Journal of Adhesion and Interface
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• v.24 no.3
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• pp.95-99
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• 2023

In this study, LiDAR-detectable black materials are synthesized by coating and reduction of titanium dioxide onto plate-type natural mica, which evaluated practical LiDAR verification. In detail, black TiO₂@Mica materials are fabricated by utilizing a sol-gel reaction to coat titanium dioxide onto natural mica, followed by reduction using sodium tetrahydridoborate. Subsequently, Black TiO₂@Mica materials are dispersed in hydrophilic transparent varnish and sprayed onto the glass substrate to assess applicability as paints. As a result, Black TiO₂@Mica-based paints exhibit true blackness (L^*=12.1) and a higher NIR reflectance (30.2 R%). In addition, it was confirmed that as-synthesized Black TiO₂@Mica materials are successfully recognized by a LiDAR sensor. This phenomenon is attributed to Fresnel's reflection law, in which light reflection occurs at the interface between natural mica and titanium dioxide with different refractive indices. In this regard, the findings of the study are expected to contribute to the potential utilization of LiDAR-detectable materials in various fields such as autonomous vehicles, robotics, and drones.

• Asian Pacific Journal of Cancer Prevention
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• v.13 no.2
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• pp.715-718
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• 2012

The current research concerns the clinicopathological significance of MHC class I chain-related protein A (MICA) expression in oral squamous cell carcinomas (OSCCs). The expression and location of MICA protein in 14 normal oral mucous and 45 cancerous and para-cancerous tissues were assessed by immunohistochemistry and levels of MICA mRNA expression in 29 cancerous and para-cancerous tissues were determined by the real-time polymerase chain reaction. Data were analyzed with the SPSS16.0 software package. MICA was found to be located in the cytoplasm and plasma membrane. Expression was higher in para-cancerous than in cancerous tissues (P < 0.05). However, no statistical difference was found between the following: 1) para-cancerous tissue with normal mucosa; 2) normal mucosa with cancerous tissue;and 3) among different clinicopathological parameters in OSCC (P > 0.05). The level of MICA mRNA was higher in OSCCs than in para-cancerous tissues, and was correlated with the regional lymph node status and disease stage (P < 0.05). The levels of MICA protein and mRNA expression differ among normal oral mucosa, para-cancerous tissue, and cancerous tissue. MICA may contribute to the tumorigenesis and progression of OSCC.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.29 no.6
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• pp.270-275
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• 2019

Mica capacitor is being adopted for high voltage firing unit of guided weapon system because of its superior impact enduring property relative to ceramic capacitor. Reliability of localized mica high voltage capacitors was verified through environmental test like terminal strength test, humidity test, thermal shock test and accelerated life test for application to high voltage firing unit. Failure mode of mica capacitor is a decrease of insulation resistance and its final dielectric breakdown. Main constants of accelerated life model were derived experimentally and voltage constant and activation energy were 5.28 and 0.805 eV respectively. Lifetime of mica capacitor at normal use condition was calculated to be 38.5 years by acceleration factor, 496, and lifetime at accelerated condition and this long lifetime confirmed that mica high voltage capacitor could be applied for firing unit.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.16 no.5
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• pp.85-90
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• 2017

Mica-glass ceramics has features such as micro-sized crystals, high strength, chemical resistance, semitransparent optical properties, etc. Due to its superior material properties, mica glass ceramics have increasing applications in dental and medical components, insulation boards, chemical devices, etc. In many applications, especially for dental and medical components, ultra-precise polishing is required. However, it is known to be a very difficult-to-grind material because of its high hardness and brittle properties. Thus, in this study, a newly developed ultra-precise polishing method is applied to obtain nano-level surface roughness of the mica glass ceramics using magnetorheological (MR) fluids and nano abrasives. Nano-sized ceria particles were used for the polishing of the mica glass ceramics. A series of experiments were performed under various polishing conditions, and the results were analyzed. A very fine surface roughness of Ra=6.127 nm could be obtained.

• Journal of the Society of Cosmetic Scientists of Korea
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• v.34 no.4
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• pp.269-274
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• 2008

In this study we successfully altered the structural characteristics of the mica surface and were able to control oil-absorption by using the microwave enhanced etching (MEE) technique, which has originally been used in semiconductor industry. When microwave energy is applied to the mica, the surface of the mica is etched in a few minutes. As the result of etching, oil-absorption of the mica was enhanced and surface whiteness was improved by modifying the silicon dioxide layer. Additionally, the high whiteness was maintained even though the etched mica absorbed the sebum or sweat. The surface modification of mica was performed by microwave irradiation after the treatment of hydrofluoric acid. The degree of etching was regulated by acid concentration, irradiation time, the amount of energy and slurry concentration. The surface morphology of the etched mica appears to be the shape of the 'Moon'. The characteristics of surface area and roughness were examined by Brunauer-Emmett-Teller (BET) surface area analysis, atomic force microscopy (AFM), scanning electron microscopy (SEM), spectrophotometer and goniophotometer.

• The Journal of the Petrological Society of Korea
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• v.12 no.3
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• pp.119-134
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• 2003

Yuksipryeong two-mica granite presents strongly peraluminous characteristics in both mineralogy and geochemistry. It has high aluminum saturation index with 1.15∼l.20 and high corundum with 2.20∼2.98 wt% CIPW norm. As the color index is <16% and FeO$\^$T/+ MgO + TiO$_2$is average 1.9 wt％, it corresponds to leucogranite. Yuksipryeong two-mica leucogranite shows negative linear trend for TiO$_2$, Al$_2$O$_3$, FeO, Fe$_2$O$_3$, MgO, CaO, K$_2$O, P$_2$O$\_$5/, Rb, Ba, and Sr as SiO$_2$increases, and the positive relation of Zr and Th, which result from feldspar, biotite, apatite and zircon fractionation. Pegmatitic dike has higher SiO$_2$and P$_2$O$\_$5/, but lower another major elements. Yuksipryeong two-mica leucogranite has lower Rb, but higher Ba and Sr than Manaslu, Hercynian two-mica leucogranites, and S-type granites in Lachlan Fold Belt. Pegmatitic dike has higher Rb and Nb but lower Ba, Sr, Zr, Th, and Pb contents than Yuksipryeong two-mica leucogranite, resulting in removing or mobilizing for some trace elements from the granitic melt. Yuksipryeong two-mica leucogranite has total REEs with 95.7∼l23.3 ppm, and chondrite-normalized REE pattern is very steep ((La/Yb)$\_$N/ = 6.9∼24.8), light REEs (LREEs)-enriched End heavy REEs (HREEs)- depleted pattern with low to moderate Eu anomalies (Eu/Eu＊= 0.7∼0.9). While pegmatitic dike has low total REEs with 7.0 ppm, and chondrite-normalized REE pattern is flat-pattern ((La/Yb)$\_$N/ = 2.1) with strong negative Eu anomalies (Eu/Eu＊= 0.2). The melt compositions having formed two-mica leucogranites depend on not only the source rock but also the amounts of the residual remaining after melting of source rocks. The CaO/Na$_2$O and Rb/Sr-Rb/Ba ratios depend mainly on the composition of source rocks in the strongly peraluminous granite, that is, plagioclase/clay ratio of the source rocks. Yuksipryeong two-mica leucogranite has higher CaO/Na$_2$O and lower Rb/Sr-Rb/Ba ratios than Manaslu and Hercynian two-mica leucogranites (Millevaches and Gueret) derived from clay-rich, plagioclase-poor (polite), which suggest that the probable source rocks for Yuksipryeong two-mica leucogranite is clay-poor, plagioclase-rich quartzofeldspathic rocks. As the concentrations of Al$_2$O$_3$remain nearly constant but those of TiO$_2$increases as increasing temperature in the strong peraluminous melt, the Al$_2$O$_3$/TiO$_2$ratio may reflect relative temperature at which the melts have formed. Comparing the polite-derived Manaslu and Hercynian two- mica leucogranites, Manaslu two-mica leucogranite has higher Al$_2$O$_3$/TiO$_2$ratio than latter, and its melt have formed at relatively lower temperature ($\leq$ 875$^{\circ}C$) than Hercynian two-mica leucogranites. Likewise, comparing the quartzofeldspathic rock-derived granites, Yuksipryeong two-mica granite has higher Al$_2$O$_3$/TiO$_2$, ratio than S-type granites in Lachlan Fold Belt (>875$^{\circ}C$). The melt formed Yuksipryeong two-mica leucogranite are considered to have been formed at temperature at below the maximum 875$^{\circ}C$C$.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.19 no.4
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• pp.190-195
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• 2009

Na-tetrasilicic fluorine mica powders were synthesized by skull melting method. The staring materials having chemical composition of $Mg_3(OH)_2Si_4O_{10}:Na_2SiF_6:SiO_2=8.3:24.8:66.9$ mol% were charged into a cold crucible of 13 cm in diameter and 14cm in height and heated by R.F. generator at working frequency of 2.84 MHz. The materials were maintained for 1hr as a molten state and cooled down in the container. In this study, the specific electric resistance of mica was estimated and the columnar and plate shaped mica were synthesized.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.2
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• pp.119-126
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• 2002

The mica/epoxy composite used in generator(rated 22 kV and 500 MW) stator windings was aged at 180$\^{C}$ for up to 1000 hours in air and hydrogen. The degradation mechanism was investigated through the defect of evolution and microstructural analysis by performing SEM(Scanning Electron Microscope). As the thermal aging time increases, the number of voids per unit volume increases at the mica/epoxy interface of generator stator windings. The aged specimens in hydrogen showed retarded generation and growth of voids. Accelerated aging tests were conducted using the combination of thermal and electrical aging in air and hydrogen. The aging was carried out at a combined stress such as thermal aging at 110$\^{C}$, electrical aging at 5.5 kV/mm and frequencies 420 Hz in air, and electrical aging at 5.5 kV/mm and frequencies 420 Hz in hydrogen (pressure 4 kg/㎠). Thermal and electrical aging generates large voids at the mica/epoxy interface in air. Electrical aging in hydrogen also generates small voids, delaminations and cracks in mica tapes.

• Journal of the Korean Ceramic Society
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• v.36 no.7
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• pp.691-697
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• 1999

TiO2 powder was adsorbed on the surface of mica using the heterocoagulation method in water TiO2 powder was prepared from hydrolysis of titanium-iso propoxide in a mixed solvent of anhydrous ethanol and water. When the molar ratio of water to titanium iso-propoxide was 0.25 monodispersed spherical TiO2 particles were obtained. The prepared TiO2 powder showed anatase phase after heat treatment at 50$0^{\circ}C$ for 2 h and then transformed to rutile phase after heat treatment at 100$0^{\circ}C$ for 2h. The iso-electric points of TiO2 and Mica were pH 3.9 and pH 3.25 respectively which were measured by the Z-potential analysis in water base. The maximum Z-potential difference between two powders was observed in the range of pH 3.6~3.7 TiO2 powder was adsorbed on the surface of mica by heterocoagulation method in pH 3.6~3,7 The properties of prepared TiO2 powder was haracterized by TG-DTA, XRD and SEM The morphology and thermal properties of TiO2-adsorbed mica were examined.