• 수산해양기술연구
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• 제32권2호
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• pp.157-163
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• 1996

To ceramic film, $SiO_2$ and $Al_2O_3$, coated on pure Fe and stainless steel(SUS41O) by RF magnetron sputtering, the adherence between mm and substarte was studied. The adherence index (${\chi}$) was determined by the measure of micro hardness test. Also, the corrosion resistance on oxide coatings was studied using electrochemical measurement. The main results obtained are as the following: 1) In the micro-hardness test, with $1{\mu}m$ thickness mm, it has only one the value of ${\chi}$. Above $2{\mu}$thickness fIlm, however, get another value of ${\chi}$as the cracks in fIlm. 2) The oxide fIlm adhere well on the mild materials such as pure steel than high intensity materials like stainless. 3) Alumina($Al_2O_3$) coated materials have better corrosion resistance than silica($SiO_2$)coated materials

• 대한치과기공학회지
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• 제14권1호
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• pp.95-118
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• 1992

Glass ceramics for crown were prepared by adding 3$\sim$11 wt% TiO2 to the weight percent composition of 34.7 CaO, 27.8 SiO2, 18.3P2O5, 12.6MgO and 6.6 TiO2. The starting glasses were prepared by melting the powdered batch in alumina crucible at 1350$\sim$1400 for 1 hr and then quenching into a distilled water. The nucleation and crystallization of the crystalline glass ceramics for crown were studied by DTA, SME and X-ray diffraction analysis. Frit containing 9.11 wt% TiO2 had crystallization temperature of 850$\sim$1075 and major crystalline phase was identified by X-ray diffraction as diopside(CaO-MgO-2SiO2). Activation energies for the crystallization processes were obtained from DTA by varing rates for the fits, and were calculated from modified Ozawa and Kissinger equations. Activation energy for the crystallization processes of the S-4 frit was 489.6 KJ/mol.

• 산업기술연구
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• 제14권
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• pp.119-125
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• 1994

Ultra-precision machine tool equipped with the diamond bite tip is used to machine optical products, drums of VTR or computer hard disk. It needs nano technology in the surface roughness of workpiece. To perform the nano scale machining, ultra-precision machine tool must be designed and manufactured in consideration of the vibration characteristics. In this paper, using the finite element analysis, we investigate the modal parameters of the ultra-precision machine tool structures, which use cast iron, granite and alumina ceramic for the bed materials. To verify the numerical results, we manufacture a model of ultra-precision machine tool using granite bed and perform impulse test. Through the theoretical and experimental analyses, we could compare and estimate the vibration characteristics of the three models for the ultra-precision machine tools.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 하계학술대회 논문집 C
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• pp.1529-1531
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• 2003

Thick film mechanical sensors can be categorized into four main areas piezoresistive, piezoelectric, piezocapastive and mechanic tube. In this areas, the thick film strain gage is the earliest example of a primary sensing element based on the substrates. The latest thick film sensor is used various pastes that have been specifically developed for pressure sensor application. The screen printing technique has been used to fabricate the pressure sensors on alumina substrate($Al_2O_3$). Thick film capacitive of strain sensing characteristics are reported and dielectric paste based on (Ti+Ba) materials. The electric property of dielectric paste has been studied and exhibit good properly with good gage factor comparable to piezoresistive strain gage. New piezocapacitive strain sensor was designed and tested. The output of capacitive value was good characteristics.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.87-88
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• 2006

Ceramic-Metal Functionally Graded Materials (FGM) are of great interest for application as Thermal Barrier Coating (TBC) or Wear Resistant Coating (WRC). Spark Plasma Sintering (SPS) is a promising techniques for time-saving consolidation of laminated/graduated powder systems: SPS is a pressure-assisted electrical sintering method which directly applies a pulsed DC current as heat source. In the present work, production of $Al_2O_3-Ni$ FGMs by means of Spark Plasma Sintering is considered; effect of sintering condition on density, hardness and fracture toughness is studied. Problems correlated to this new processing technology are discussed.

• 동력기계공학회지
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• 제10권4호
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• pp.133-138
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• 2006

Effective thermal conductivity of particulate reinforced composite has been predicted by Eshelby's equivalent inclusion method modified with Mori-Tanaka's mean field theory. The predicted results are compared with the experimental results from the literature. The model composite is polymer matrix filled with ceramic particles such as silica, alumina, and aluminum nitride. The preliminary examination by Eshelby type model shows that the predicted results are in good agreements with the experimental results for the composite with perfect spherical filler. As the shape of filler deviates from the perfect sphere, the predicted error increases. By using the aspect ratio of the filler deduced from the fixed filler volume fraction of 30%, the predicted results coincide well with the experimental results for filler volume fraction of 40% or less. Beyond this fraction, the predicted error increases rapidly. It can be finally concluded from the study that Eshelby type model can be applied to predict the thermal conductivity of the particulate composite with filler volume fraction less than 40%.

• Tribology and Lubricants
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• 제25권1호
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• pp.49-55
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• 2009

The frictional properties of automotive brake pads with four different ceramic materials such as magnesia, hematite, alumina, and zircon were investigated. A Krauss type friction tester using gray iron disks was used to examine the friction coefficient, intensity of friction force oscillation, and the tribe-surfaces. Results showed that the friction coefficient increased as the hardness of abrasives increases. Friction oscillation was also increased with hardness of the abrasives. However, the friction materials containing less abrasive particles produced stable friction films on the sliding surface. The transition between two-body and three body abrasion during sliding also played a crucial role in destructing the friction film on the pad surface and in determining various frictional properties.

• 대한기계학회논문집A
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• 제20권4호
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• pp.1356-1362
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• 1996

Fracture toughness of heterogeneous brittle materials such as poly crystalline ceramics used to present the size (thickness) effect as well as statistically distributed results. There is belief that both(size effect and scatter) must be associated with each other. However, no generally accepted theory has been established so far. Using statistical approach, a probabilistic modeling for the fracture toughness which describes the thickness effect was attempted in this paper, Weibull distribution of specific fracture energy(SFE)at local areas and Griffith criterion are applied to the model. In addition, the newly developed model was verified with experimental results of alumina.

• 한국결정성장학회지
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• 제23권1호
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• pp.44-50
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• 2013

E-glass 섬유는 항공기, 자동차, 레져기구의 복합재료 보강용으로 가장 널리 사용되는 유리섬유이다. 그러나 최근 E-glass 섬유의 원재료비 상승, 환경문제 및 화학적 저항성과 기계적 특성을 향상시키기 위해 산화붕소 함량을 8 %에서 0(제로)까지 감소시키는(소위 'Boron free E-glass'라고 불리는) 연구가 진행되고 있다. 본 연구에서는 'BF(Boron free E-glass)' 조성의 벌크유리와 섬유유리를 제조하고, 열적특성 및 광학적특성을 평가하였다. 5~10 %의 서로 다른 알루미나 함량을 갖는 배치를 $1550^{\circ}C$에서 2시간 용융하여 'BF(Boron free E-glass)'가 얻어졌고, 81~86 %의 높은 가시광투과율, $4.2{\sim}4.9{\times}10^{-6}/^{\circ}C$의 낮은 열팽창계수, $907{\sim}928^{\circ}C$의 연화점을 갖는 투명하고 맑은 유리가 얻어졌다. 'BF' 섬유 시편에 대한 화학적내구성 시험에 있어서는 알루미나 함량이 높아질수록 더 좋은 침식저항성을 나타냄을 확인할 수 있었다.

• 대한치과기공학회지
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• 제35권1호
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• pp.57-64
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• 2013

Purpose: Waste parts of zirconia blocks and powders were remained after CAD/CAM process. In order to make these residual zirconia fit for practical use, zirconia single cores were produced by drain casting process. Methods: Remained zirconia blocks were reduced to powders with zirconia mortar, and screened with 180 mesh sieve. Zirconia slip was prepared from waste parts of zirconia by ball milling. Plaster molds for forming cores by slip casting were also prepared. Formed cores were removed from mold after partial drying. Dried cores were biscuit fired at $1,100^{\circ}C$ for 1hour. Biscuit fired cores were treated with tools to control the fitness and thickness. Finished cores were $2^{nd}$ fired at $1,500^{\circ}C$ for 1hour. Microstructure of cross section of core was observed by SEM. Results: When mill pot was filled with 100g of zirconia and alumina mixed powder, 300g of zirconia ball, and 180g of distilled water, the optimum slip for drain casting was obtained. Gypsum plaster for ceramic forming was more suitable then yellow stone plaster for casting process. SEM photograph showed the microstructure of fully dense with uniform grain size of zirconia and well dispersed alumina grains into the zirconia matrix. Conclusion: Zirconia single cores were produced by drain casting process. Drain casting is useful process to make these residual zirconia fit for practical use. Further study will be focused on the preparation of the bridge type cores by casting.