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pISSN : 1225-1429 / eISSN : 2234-5078

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2019, Vol.29, No.6

  • 1.

    Effect of hydrogenation surface modification on dispersion and nucleation density of nanodiamond seed particle

    Choi ByoungSu | 전희성 | UM JI HUN and 3other persons | 2019, 29(6) | pp.239~244 | number of Cited : 0
    Abstract PDF
    Two hydrogenation surface modifications, namely hydrogen atmosphere heat treatment and hydrogen plasmatreatment, were found to lead to improved dispersion of nanodiamond (ND) seed particles and enhanced nucleation density fordeposition of smooth ultrananocrystalline diamond (UNCD) film. After hydrogenation, the C-O and O-H surface functionalitieson the surface of nanodiamond particles were converted to the C-H surface functionalities, and the Zeta potential wasincreased. As the degree of dispersion was improved, the size of nanodiamond aggregates decreased significantly andnucleation density increased dramatically. After hydrogen heat treatment at 600oC, average size of ND particles was greatlyreduced from 3.5 m to 34.5 nm and a very high nucleation of ~3.9 × 1011nuclei/cm2was obtained for the seeded Si surface.
  • 2.

    Porous Sn-incorporated Ga2O3 nanowires synthesized by a combined process of powder sputtering and post thermal annealing

    이하람 | HYON CHOL KANG | 2019, 29(6) | pp.245~250 | number of Cited : 0
    Abstract PDF
    We investigated the post-annealing effect of Sn-incorporated -Ga2O3 (-Ga2O3 : Sn) nanowires (NWs) grown onsapphire (0001) substrates using radio-frequency powder sputtering. The -Ga2O3 : Sn NWs were converted to a porousstructure during the vacuum annealing process at 800oC. Host non-stoichiometric Ga2O3x, is transformed into stoichiometricGa2O3, where Sn atoms separate and form Sn nano-clusters that gradually evaporate in a vacuum atmosphere. As a result,the amount of Sn atoms was reduced from 1.31 to 0.27 at%. Pores formed on the sides of -Ga2O3 : Sn NWs wereobserved. This increases the ratio of the surface to the volume of -Ga2O3 : Sn NWs.
  • 3.

    Abnormal grain growth of ZnO ceramics

    KIM YOUNG JUNG | 2019, 29(6) | pp.251~256 | number of Cited : 0
    Abstract PDF
    In the process of ZnO ceramic sintering at a temperature of 1385oC, higher than the normal sintering temperature,some grains were growth up to mm scale. When sintered at 1400oC for 8 hours, the size of the grains that are not involved inthe abnormal growth is as large as 30~40 m, but the size of the abnormal grown grain reaches 1,000 m, which is morethan 10,000 times bigger in volume than the normal one within 8 hr growth. As a cause of rapid and abnormal graingrowth, primary particle size distribution, compaction density variation within sample and doping of impurities could beconsidered. The primary particle size distribution could be considered main reason for abnormal grain growth but no solidevidence was obtained. Through the observation of the microstructure, it is presumed that the giant grains grow absorbingthe neighbor grains through a grain rotation process.
  • 4.

    Effect of Si sludge addition on the properties of lightweight geopolymers

    김민정 | KIM, YOOTAEK | 2019, 29(6) | pp.257~263 | number of Cited : 0
    Abstract PDF
    Lightweight geopolymers were fabricated with non-milled IGCC slag and Si sludge as a bloating material. Therelationship between addition amount of Si sludge and physical/chemical properties of lightweight geopolymers wasinvestigated. When the geopolymers were made by mixing IGCC slag, alkali activator, and more than 10 wt.% Si sludge,the temperature of the geopolymer pastes reached higher than 130oC in a few minutes. This exothermic reaction acceleratedthe geopolymer reaction; however, it was difficult to make geopolymer specimens because of a rapid bloating reaction. Both compressive strength and density of the specimens tend to decrease with an addition of Si sludge; however, there waslittle difference in both compressive strength and density with addition of Si sludge more than 10 wt.%. Because there wasa limit to get low density geopolymers by simply increasing the addition of Si sludge, the control of pore size anddistribution of geopolymer is more important by controlling flow rate of the paste through the control of W/S ratio. Therefore, it is important to control process conditions, appropriate W/S ratio for the bloating than the control of Si sludge. The optimum W/S ratio was 0.20 for the addition of Si sludge less than 30 wt.% and W/S ratio should be more than 0.28for the addition of Si sludge more than 30 wt.%, although there was no practical application in fact.
  • 5.

    A study on the design development of a domestic disinfector using UV LED

    주왕 | 성영 | Kang, Seung-Min and 1other persons | 2019, 29(6) | pp.264~269 | number of Cited : 0
    Abstract PDF
    The design for household sterilizer applying UV LED was studied. Based on UV LED sterilization distance andtime data, the concept of home disinfectioner design was presented. Using technologies such as computer aided designsoftware, 3D printing and laser cutting, etc., three different UV LED operating method models were produced. The finaldesign was derived by conducting an analysis of the product’s merits and demerits on the three plans from the result ofeach model.
  • 6.

    Reliability assessment of mica high voltage capacitor through environmental test and accelerated life test

    박성환 | 함영재 | 김정석 and 3other persons | 2019, 29(6) | pp.270~275 | number of Cited : 0
    Abstract PDF
    Mica capacitor is being adopted for high voltage firing unit of guided weapon system because of its superiorimpact enduring property relative to ceramic capacitor. Reliability of localized mica high voltage capacitors was verifiedthrough environmental test like terminal strength test, humidity test, thermal shock test and accelerated life test forapplication to high voltage firing unit. Failure mode of mica capacitor is a decrease of insulation resistance and its finaldielectric breakdown. Main constants of accelerated life model were derived experimentally and voltage constant andactivation energy were 5.28 and 0.805 eV respectively. Lifetime of mica capacitor at normal use condition was calculatedto be 38.5 years by acceleration factor, 496, and lifetime at accelerated condition and this long lifetime confirmed thatmica high voltage capacitor could be applied for firing unit.
  • 7.

    A study on the photocatalyst filter design using UV-C

    Han, Sang yun | Kang, Seung-Min | 2019, 29(6) | pp.276~282 | number of Cited : 0
    Abstract PDF
    The purpose of this study was to analyze the structure of general filter using ultrafine filter (Profilter), dustcollector filter, HEPA (HAPA-High Efficiency Particulate Air) filter, deodorized filters, etc. of air purifiers and to studynew types of purified filters that can improve ultrafine dust, harmful gases, and sterilization cleanup performance. Thestudy was also conducted by adding photocatalyst filters to the existing step-by-step filtration filter types, which were proposedin the design three coupling structure filters of the left and right UV-LED installation frames and the photocatalyst coatinghoneycomb frame. Future research is needed on the effect of photocatalyst filters. This study was to investigate theapplication and structure of photocatalyst filters to air purifiers.
  • 8.

    Application of ultra-high-temperature ceramics to oxidation-resistant and anti-ablation coatings for carbon-carbon composite

    김현미 | Sungchurl Choi | 조남춘 and 2other persons | 2019, 29(6) | pp.283~293 | number of Cited : 0
    Abstract PDF
    As applications in extreme environments such as aerospace, high-energy plasma and radio-active circumstancesincreases, the demand for materials that require higher melting points, higher mechanical strength and improved thermalconductivity continues to increase. Accordingly, in order to improve the oxidation/abrasion resistance of the carbon-carboncomposite, which is a typical heat-resistant material, a method of using ultra high temperature ceramics was reviewed. Theadvantages and disadvantages of CVD coating, pack cementation and thermal plasma spraying, the simplest methods forsynthesizing ultra-high temperature ceramics, were compared. As a method for applying the CVD coating method to C/Ccomposites with complex shapes, the possibility of using thermodynamic calculation and CFD simulation was proposed. Inaddition, as a result of comparing the oxidation resistance of the TaC/SiC bi-layer coating and TaC/SiC multilayer coatingproduced by this method, the more excellent oxidation resistance of the multilayer coating on C/C was confirmed.
  • 9.

    The effect of rotation on the macro-steps formation during 4H-SiC solution growth

    SHIN Yunji | park tae yong | Si-Young Bae and 1other persons | 2019, 29(6) | pp.294~297 | number of Cited : 0
    Abstract PDF
    New insights about macro-step formation has been investigated. The phenomena of surface instability caused bythe interaction between step flow and fluid flow was describe in mechanical way. The rotation of the seed crystal in aclockwise direction was applied with a speed varied from 30 to 200 rpm during the TSSG process on the Si- and C-faces4H-SiC. The macro-steps were formed along the two specific directions at different locations on the crystal for each, i.e.,[10-10] or [01-10] directions or both. From the results, it is suggested that the macro-steps were generated from the microstepsby interaction between step flow and fluid flow during the rotation of seed crystal. Furthermore, The fluid flow couldbe effective to control the micro- and/or macro-step behavior during solution growth.
  • 10.

    A study of sintering behavior of spray coating in CaO-Al2O3-SiO2 glasses on Al2O3 substrate

    Hyein Na | Jewon Park | Jae-hyuk Park and 3other persons | 2019, 29(6) | pp.298~307 | number of Cited : 1
    Abstract PDF
    Two types of CaO-Al2O3-SiO2 (CAS) glass powder applied spray coating on the surface of sintered Al2O3 wereresearched for sintering behavior; (1) Si-rich, glass containing high content SiO2, (2) Ca-rich, containing high content CaO. Foaming of bubbles remaining inside the Ca-rich glass was produced at a viscosity of approximately 107~109poise,resulting in decreasing shrinkage (interfering with sintering) and increasing surface roughness. In case of Si-rich glass, therewas no serious foaming bubbles phenomenon like Ca-rich below 1000oC, however cristobalite crystals with low densityoccurred at 1200oC and then produced re-foaming of bubbles, resulting in abnormal sintering behavior. These phenomenonis considered to be a decrease in viscosity due to an increase in the Ca content of the glass according to the formation oflow-density cristobalite crystals. Therefore, in case of CAS glass, it is necessary to consider the increase of surfaceroughness and the sintering interference because of foaming bubbles phenomenon at low temperature sintering. Especially,when containing high SiO2 content, abnormal foaming phenomenon due to crystallization at high temperature should bepredicted.
  • 11.

    Deposition uniformity of 7 wt% YSZ as a thermal barrier coating with different configurational arrangement for turbine blade shape mock-up by electron beam physical vapor deposition

    Oh Yoon Suk | 채정림 | Ho-lim Ryu and 4other persons | 2019, 29(6) | pp.308~316 | number of Cited : 0
    Abstract PDF
    Electron beam physical vapor deposition (EBPVD) is a conventional method to fabricate thermal barrier coating(TBC) of high temperature airfoil engine parts, such as blade etc. for its high temperature structural stability from thenature of columnar growth behavior. For the high quality of TBC by EBPVD, the structural factors, such as growth behavior,thickness uniformity and so on, should be managed to obtain the coating which satisfied the required specifications ofusable level of mechanical and thermal properties. In this study, the growth behavior and structure variations of 7YSZ(7 wt% yttria stabilized zirconia) coatings with different configurational deposition parameters for the specimens which haveturbine blade shape mock-up were investigated. Growth behavior of coatings were studied by comparing computationalmodeling of evaporation behavior with actual deposition process using e-beam source
  • 12.

    Production and evaluation of raw materials for porcelain using clay mineral

    Jong-Young Kim | 2019, 29(6) | pp.317~328 | number of Cited : 0
    Abstract PDF
    In this work, we investigated clay and raw materials from China (black clay, red clay, white clay) and Korea(Cheonan clay, Obu clay) used for the manufacture of porcelain products. According to chemical analysis results, feldsparcomponents containing CaO, K2O, Na2O and quartz are found in clay materials besides primary clay such as kaollinte, forthe clay materials from Korea, which is found more in clay materials from Korea than from China. For the Fe2O3 content,governing whiteness of porcelain products, more iron oxide (> 5 %) is found in Korean clays (Cheonan clay, obu clay, redclay) compared to those form China (black, white clay). Through X-ray diffraction analysis, kaolinite and Halloysite arefound to be main phases for all the raw materials and second phases such as quartz and pyrophyllite are found. Using theseclay materials, raw materials for porcelain products were produced, and the physicochemical properties were investigatedfor sintered samples. Absorption rate is in order of Baekja-A < Baekja-B < Yeonbuncheong < Jinbuncheong < Cheongja, andthe sample, sintered at 1250oC in reductive atmosphere, exhibits the lowest absorption rate. Comparing the color of thesintered samples, the samples sintered in oxidative atmosphere (L*value: 86~95 %) show higher whiteness value than thosesintered in reductive atmosphere (L*value: 81~93 %). For the Cheongja and Buncheong, the samples sintered in reductiveatmosphre shows higher whiteness, L*values, and low a*/b*value, which is due to reduction of iron oxide (Fe2O3).
  • 13.

    Synthesis of splinter-type and plate-type potassium titanate as reinforcements in brake pad for automobile

    김성훈 | Jong-Young Kim | 심우영 and 2other persons | 2019, 29(6) | pp.329~337 | number of Cited : 0
    Abstract PDF
    We synthesized potassium titanates having splinter and plate shape and evaluated frictional and wear properties ofbrake pad using them as reinforcements in friction materials. For splinter-shaped potassium titanates, potassium tetratitanate(K2O·4TiO2, PT4) with plate shape was prepared, then K ion of the titanate was leached by acid to make potassium hexatitanate(K2O·6TiO2, PT6), which was transformed to splinter-shaped PT6 by thermal treatment at 800oC. Plate-shaped potassiummagnesium titanate (K0.8Mg0.4Ti1.6O4, PMT) was prepared by adding Mg in the potassium titanate using KCl as a flux. Using PT6 and PMT as reinforcements in friction materials of brake pad, we evaluated frictional and wear properties using 1/5-scale dynamometer. According to dynamometer test results, both reinforcements shows similar friction coefficient and fade &recovery behavior to conventional material and plate-shaped PMT exhibits higher wear resistance than splinter-shaped PT6.
  • 14.

    Microstructure and mechanical properties of B4C-SiC composites

    소성민 | 김경훈 | 박주석 and 2other persons | 2019, 29(6) | pp.338~344 | number of Cited : 0
    Abstract PDF
    B4C-SiC composites were fabricated using hot press sintering method without sintering additives at 1,900~2,000oCunder a pressure of 40 MPa. The crystal phase, relative density, microstructure, and mechanical properties of B4C-SiCcomposites were evaluated. When B4C and SiC were uniformly dispersed in the composite, grain growth was inhibited, anda sintered body with a fine and uniform microstructure, with improved mechanical properties, was fabricated. The relativedensity of B4C-SiC composites sintered under 2,000oC of temperature and 40 MPa of pressure was over 99.8 %, and thebending strength and Vicker’s hardness at 50 wt% of B4C were 645 MPa and 30.6 GPa, respectively.
  • 15.

    Formulation and ink-jet 3D printability of photo curable nano silica ink

    이제영 | Ji-Hyeon Lee | Jae-Hyeon Park and 4other persons | 2019, 29(6) | pp.345~351 | number of Cited : 1
    Abstract PDF
    Recently, ink-jet printing technology has been applied for various industries such as semiconductor, display, ceramictile decoration. Ink-jet printing has advantages of high resolution patterning, fast printing speed, high ink efficiency andmany attempts have been made to apply functional materials with excellent physical and chemical properties for the ink-jetprinting process. Due to these advantages, research scope of ink-jet printing is expanding from conventional two-dimensionalprinting to three-dimensional printing. In order to expand the application of ink-jet printing, it is necessary to optimize therheological properties of the ink and the interaction with the substrate. In this study, photo curable ceramic complex inkcontaining nano silica particles were synthesized and its printability was characterized. Contact angle of the photo curablesilica ink were modified by control of the ink composition and the surface property of the substrate. Effects of contactangle on printing resolution and three-dimensional printability were investigated in detail.
  • 16.

    Printability of coating layer with nano silica sol for inkjet printing high-end photo paper

    김혜진 | Nahm, Sahn | Han Kyu Sung and 2other persons | 2019, 29(6) | pp.352~358 | number of Cited : 0
    Abstract PDF
    In recent years, printing paper with a function of information delivery and aesthetic value has attracted a greatattention with increasing market demand for coated paper that is capable of high quality printing. The coated paper forinkjet printing with high-quality of photorealistic grades requires the coating layer with a good wettability and poroussurface structure in order to improve the printability of ink. In this study, the coated paper was prepared using polyvinylalcohol (PVA) and surface treated nano silica sol with silane coupling agent. It was confirmed that the coating layer withsurface treated nano silica sol showed a uniform pore distribution and flat surface roughness. Glossiness of the preparedprinting paper was similar to that of commercial high quality photo paper. Especially, the coated paper with surface treatednano silica sol showed improved printability with excellent roundness of the printed dot of ink. These results indicates thatthe coating layer with excellent wettability and uniform pore distribution can be formed by using the nano-silica particleswith improved dispersibility through the surface treatment of the silane coupling agent.
  • 17.

    Fabrication and characteristics of suspension-plasma-sprayed yttrium oxide coatings

    김민숙 | 소성민 | HyungSun Kim and 4other persons | 2019, 29(6) | pp.359~364 | number of Cited : 0
    Abstract PDF
    The suspension plasma spraying is a modification of conventional plasma spray techniques that has beendeveloped to overcome the challenge of using fine particles in plasma spray processes. In this study, microstructuredevelopments and mechanical property of yttrium oxide (Y2O3) coatings prepared by the suspension plasma spray coatingtechnique have been investigated to determine the effect of processing parameters including plasma gun current and totalgas flow. The results showed that a highly dense Y2O3 coating having low porosity of 0.2 vol% without any lamellarstructures can be achieved at the optimum condition of gun current 200 A and total gas flow 220 L/min.
  • 18.

    Partial premixed combustion modeling of diffusion flame burner for SiO2 deposition as optical fiber cladding

    박형빈 | Yoonsoo Han | 2019, 29(6) | pp.365~371 | number of Cited : 0
    Abstract PDF
    In this study, the flame temperature distribution of the diffusion flame burner for SiO2 deposition was analyzedby the computational fluid analysis. This corresponds to the previous step for simulating the SiO2 preform deposition processfor manufacturing optical fibers using environmentally friendly raw materials. In order to model premixed combustion, heatflow, convection, and chemical reactions were considered, and Reynolds-averaged Navier-Stokes equations and k- modelswere used. As a result, the temperature distribution of the flame showed a tendency to increase the distance from thenozzle surface to the maximum temperature when the flow rate of the auxiliary oxygen increased. In addition, it wasconfirmed that the temperature distribution due to incomplete combustion was large in the combustion reaction with a largeequivalence ratio of the mixed gas.
  • 19.

    Antibacterial properties of traditional ceramic glazes containing copper oxide

    Ungsoo Kim | Choi Jung Hoon | hyunggoono and 3other persons | 2019, 29(6) | pp.372~378 | number of Cited : 0
    Abstract PDF
    Traditional ceramic glazes formulated with copper oxide (CuO) exhibited antibacterial properties on Staphylococcusaureus (Gram Positive) and Escherichia coli (Gram Negative). All the ceramic glazes containing CuO showed antibacterialbehavior when fired in reducing atmosphere. However, some of copper glazes presented antibacterial behavior and had noantibacterial properties at all when sintered in an oxidizing atmosphere. To elucidate the antibacterial mechanism, ceramicglazes were studied for phase and microstructure analysis, dissolution behavior and surface zeta potential. Metallic copperwas precipitated in the glaze layer when sintered in reducing atmosphere. Less than 0.05 ppm of Cu ion was dissolved fromglazes. Ca ion was most dissolved among all the samples. Glaze surface was highly negatively charged when CuO wasadded over 3 wt.% regardless of the sintering atmosphere. The antibacterial behavior of ceramic glazes seemed to be directlyrelated to the dissolution behavior of cations, but the antibacterial behavior of oxidized specimens was not explained by thedissolution behavior. Surface potential of ceramic glazes appeared to play an auxiliary role in antibacterial properties.
  • 20.

    Size control of Au nanoparticles by pH and effect of surface enhanced raman spectroscopy (SERS)

    Young Wook Lee | Tae Ho Shin | 2019, 29(6) | pp.379~382 | number of Cited : 0
    Abstract PDF
    Synthesis of gold nanoparticles (NPs) made an aqueous environment via the reduction of HAuCl4 by ascorbicacid (AC) with the surfactant of polyvinylpyrrolidone (PVP). Highly monodisperse gold particles with size ranges from 4to 20 nm were prepared in high-yield by pH control. The synthesized gold nanoparticles were analyzed for structural andoptical properties using transmission electron microscopy (TEM) and UV-vis spectroscopy. In this study, we could revealthat the prepared nanoparticles exhibited efficient surface-enhanced Raman scattering (SERS) properties, and their SERSactivities depends on size.
  • 21.

    Study on the growth of 4H-SiC single crystal with high purity SiC fine powder

    Dong-Geun Shin | 김병숙 | 손해록 and 1other persons | 2019, 29(6) | pp.383~388 | number of Cited : 0
    Abstract PDF
    High purity SiC fine powder with metal impurity contents of less than 1 ppm was synthesized by improved carbothermalreduction process, and the synthesized powder was used for SiC single crystal growth in RF heating PVT device attemperature above 2,100oC. In-situ x-ray image analyzer was used to observe the sublimation of the powder and single crystalgrowth behavior during the growth process. SiC powder was used as a source of single crystal growth, exhausted from theoutside of the graphite crucible at the growth temperature and left graphite residues. During the growth, the flow of rawmaterials was concentrated in the middle and influenced the growth behavior of SiC single crystals. This is due to the differencein temperature distribution inside the crucible due to the fine powder. After the single crystal growth was completed, the singlecrystal ingot was cut into a 1 mm thick single crystal substrate and finely polished using a diamond abrasive slurry. A darkyellow 4H-SiC was observed overall of single crystal substrate, and the polycrystals generated in the outer part may be causedby the incorporation of impurities such as the bubble layer mixed in the process of attaching the seed crystal to the seed holder.