• 한국세라믹학회지
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• 제17권2호
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• pp.96-100
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• 1980

The castable refractory, CaO.$2Al_2O_3$ is a useful alumina cement for iron, steel and cement for iron, steel and cement industries, however it is difficult to produce CaO.$2Al_2O_3$because of its high melting point(180$0^{\circ}C$) and narrow firing range. In this study, the coprecipitation method was used to produce CaO.$2Al_2O_3$ for lower temperature firing . This method involved the titration of mixed solution of calicum and aluminate which extracted from domestic kaolin with $NH4_OH$ solution under blowing $CO_2$ gas into the solution. The coprecipitate and its clacined products were analyzed by X-ray diffraction and DTA. The calcined products fired between 400 and 90$0^{\circ}C$ were amorphous, but at 100$0^{\circ}C$ the coprecipitate was converted into one compound, CaO$2Al_2O_3$. From those experimental results, it was found that we could synthesizze CaO.$2Al_2O_3$ at about 100$0^{\circ}C$ which is lower than conventional firing temperature by around 80$0^{\circ}C$. The refractoriness of this alumina cement was SK 34 and the compressive strength ( 1 day) was about 250kg/$\textrm{cm}^2$.

• 한국세라믹학회지
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• 제47권5호
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• pp.357-364
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• 2010

This study was performed to get basic information about properties of high blaine slag cement(HSC) to use shotcrete(or sprayed concrete and mortar). Particle size distribution, setting time and compressive strength test, analysis like as SEM, DSC thermal analysis, XRD was carried out to investigate principle properties of HSC. Setting time of HSC was delayed slightly, but influence of accelerators was more bigger than ordinary portland cement(OPC). Compressive strength of HSC at 28 days was more higher than OPC regardless of using accelerators. Results of analysis showed early period hydration products of HSC is more small and located widely, because of the interface of between cement particle and water is increased as specific surface of cement increase. From the SEM observation and analysis of DSC and XRD results, aluminates accelerators bring on some hydration products like as calcium aluminium hydrates, alkali free accelerators increases ettringite and monosulfates. Aluminates accelerators has a advantage of setting time and early strength, alkali free accelerators increases strength after 7 days.

• 한국산학기술학회논문지
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• 제15권1호
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• pp.21-26
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• 2014

치과에서 사용되는 구강 치료용 요오드 용기는 개폐 시 용기의 캡에 부착되어 있는 칼날에 의해 치료용 실은 절단이 된다. 금속의 칼날은 요오드 용액과 반응하여 단기간에 부식이 되는 문제로 인해 환자의 위생에도 영향을 준다. 이러한 문제를 해결하기 위해 최근 세라믹 칼날로 대체되어진 제품들도 개발되어 생산되는데, 이때 세라믹 칼날은 수작업과 기계가공을 통해 만들어 진다. 본 연구에서는 세라믹 칼날을 분말사출성형공정으로 대량 생산할 수 있도록 20Cavity의 균일 충전을 위한 유동 시스템을 제안하였다. Moldflow를 이용하여 20cavity 유동성에 대한 시뮬레이션을 진행하였고, 금형제작과 수정을 통해 금형을 완성하였다. 사출성형 후 탈지와 소결공정을 통해 완성하고, 금형에 세라믹 칼날을 인서트 사출하여 캡 제품을 완성하였다. 본 연구를 통해 유효한 절단 성능을 갖는 세라믹칼날 대량생산 가능성을 검증하였다.

• Advances in materials Research
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• 제8권2호
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• pp.117-135
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• 2019

The lifetime of a gas turbine combustor is typically limited by the durability of its liner, the structure that encloses the high-temperature combustion products. The primary objective of the combustor thermal design process is to ensure that the liner temperatures do not exceed a maximum value set by material limits. Liner temperatures exceeding these limits hasten the onset of cracking which increase the frequency of unscheduled engine removals and cause the maintenance and repair costs of the engine to increase. Hot gas temperature prediction can be considered a preliminary step for combustor liner temperature prediction which can make a suitable view of combustion chamber conditions. In this study, the temperature distribution of ceramic panels for a V94.2 gas turbine combustor subjected to realistic operation conditions is presented using three-dimensional finite difference method. A simplified model of alumina ceramic is used to obtain the temperature distribution. The external thermal loads consist of convection and radiation heat transfers are considered that these loads are applied to flat segmented panel on hot side and forced convection cooling on the other side. First the temperatures of hot and cold sides of ceramic are calculated. Then, the thermal boundary conditions of all other ceramic sides are estimated by the field observations. Finally, the temperature distributions of ceramic panels for a V94.2 gas turbine combustor are computed by MATLAB software. The results show that the gas emissivity for diffusion mode is more than premix therefore the radiation heat flux and temperature will be more. The results of this work are validated by ANSYS and ABAQUS softwares. It is showed that there is a good agreement between all results.

• The Journal of Advanced Prosthodontics
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• 제7권5호
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• pp.400-405
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• 2015

PURPOSE. The purpose of this study is to mix dental ceramic powder in varying ratios and evaluate the effect of the mixing ratio on color and translucency. MATERIALS AND METHODS. The ceramic powder of shade A3 of the same product was mixed with the shade A2 of three products: IPS e.max Ceram (Ivoclar Vivadent, Schaan, Liechtenstein), Vintage Halo (SHOFU Inc., Kyoto, Japan), and Ceramco 3 (Ceramco-Dentsply, Burlington, NJ, USA) in the following fixed ratios (0 wt%, 25 wt%, 50 wt%, 75 wt%, and 100 wt%) and then fired. A total of 150 specimen of ceramic fired were manufactured in a regular size (W: 8.5 mm, L: 10.5 mm, and H: 1.5 mm). For color and translucency, $L^*$, $a^*$, and $b^*$ were measured and Two-way analysis of variance (ANOVA) and One-way analysis of variance (ANOVA) were used for data analysis (${\alpha}$=0.05). RESULTS. The higher the mixing ratio was, $L^*$, $a^*$, and $b^*$ of IPS e.max Ceram were all increased, and $L^*$ of Vintage Halo was reduced and $a^*$ and $b^*$ were increased. $L^*$ and $a^*$ of Ceramco3 were reduced and $b^*$ of Ceramco3 was increased. Color difference (${\Delta}E^*ab$) was increased in all three products as the mixing ratio got higher. Increased mixing ratios resulted in decreased translucency parameter (TP) values for IPS e.max Ceram but increased TP values for Vintage Halo and Ceramco3. CONCLUSION. In this limited study, CIE $L^*$, $a^*$, and $b^*$ were influenced by the mixing ratio of the A3 powders and porcelain powder mixtures represented a various color and translucency.

• 콘크리트학회논문집
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• 제25권5호
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• pp.565-572
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• 2013

CBPC(chemically-bonded phosphate ceramic) 바인더는 사소 MgO와 인산의 강력한 산-염기 반응을 이용한 초속경 보수재료로서, 시멘트와는 달리 CaO의 함량을 10% 이하로 줄인 재료이다. 이번 실험에서는 CBPC 바인더에 천연광물 및 산업부산물로 이뤄진 6가지 충전재들을 첨가하고 물리적 성능 및 수화 반응을 관찰하였다. 실리카퓸을 첨가한시편이 압축강도 및 동탄성계수가 상대적으로 높았고, 특히 장기강도 면에서 뚜렷한 증가율을 보였다. 또한 XRD 분석을 통해 실리카퓸을 첨가한 시편에서 마그네슘의 수화물인 M-S-H gel and $MgCO_3$ 피크를 관찰 할 수 있었다. 칼슘 성분이 다량 포함된 충전재를 넣은 시편의 경우 강도 및 내구성 면에서 좋지 않은 결과를 낳은 것으로 보아, 칼슘과 마그네슘 수화물은 서로 화학적으로 결합하지 않으므로 섞지 않는 것이 좋다는 결론을 도출했다. 결과적으로 MgO를 기반으로 하는 모르타르에는 순수하게 실리카 성분으로만 이루어진 실리카 흄과 같은 충전재가 알맞은 것으로 나타났다.

• 암석학회지
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• 제17권3호
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• pp.133-143
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• 2008

지표지질의 지구화학적 변화 추적과 고고학 유물의 원료(점토질 토양)의 기원지를 밝혀내기 위한 도구로서의 희토류원소의 역할을 확인하고자 하였다. 실험용 지질시료로는 화강암과 편마암 그리고 이들로부터의 화학적 풍화과정을 거친 풍화암과 풍화토양을 선택하여 이들의 화학조성변화를 비교하였고, 고고학적 응용을 위한 시료로는 점토질 토양과 이를 이용하여 제조한 토기 및 도기를 채취하여 이들의 화학조성변화를 비교하였다. 연구결과에 의하면, 일반적인 화학조성간의 상대적인 비교로는 암석-풍화암-토양 혹은 점토질 토양-토기-도기로의 변화에 따른 지구화학적 특성변화의 상관성이 없는 반면에 PAAS(Post Archean Australian Shale)로 규격화한 희토류원소 분포도는 거의 동일한 양상을 띄었다. 이는 희토류원소의 분포도가 다른 지구화학적 연구기법에 기법에 비해 퇴적물의 기원물질 혹은 고고학적 유물의 재료를 밝혀내는데 더 유용함을 지시해준다고 볼 수 있다.

• 한국정밀공학회지
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• 제16권11호
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• pp.62-67
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• 1999

The RP&M(Rapid Prototyping and Manufacturing) is the most appropriate technology for the small-lot production system, in which the production cycle is getting shorter owing to various needs from consumers. Recently RP products which are made of plastics, wax, and paper are used to verify the design of samples. But these products cannot be applied to the real mold because the strength enough to be a mold cannot be given by soft materials such as plastics. So RP products are copied to AFR(Al powder Filled Resin) molds or metal molds, which is called the RP&M. In this paper, RP&M is applied to a casting process. A porous casting mold, which is made from ceramic powder and binder, is used for rapid tooling of aluminum shoes molds.

• 한국세라믹학회지
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• 제33권11호
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• pp.1209-1216
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• 1996

MoSi2-Al2O3 composites were prepared by thermal explosion mode of self-propagating high temperature syn-thesis (SHS) using element powders of MoO3 Mo Si and Al. The combustion products of MoSi2 which have 10, 20, 30 and 40 wt% Al2O3 showed the molten state in the range of Mo to MoO3 6:1-9.5:1, 2:1-8:1, 1:1-5:1, and 1:1-3:1 (molar ratio) respectively. The combustion products which made least seperation the molten phase from the slag phase were in Mo/MoO3=9, 5:1, 8:1, 5:1 and 3:1 (molar ratio) respectively. Particles size of MoSi2 and Al2O3 in the combustion product were decreased as the molar ratio of Mo to MoO3 increase. By XRD analysis only MoSi2 and $\alpha$-Al2O3 peaks were identified in the combusion products, In case of MoSi2 containing 20wt% Al2O3 5.1wt% Al existed into MoSi2 grains and 30.7wt% Si and 7.7wt% Mo existed into Al2O3 grains. The relative density of MoSi2 containing 10, 20, 30 and 40 wt% Al2O3 were 82.7, 85.2, and 81.9% respectively. The fracture strength of MoSi2-Al2O3 composites increased with increasing Al2O3 and that of MoSi2-20wt% Al2O3 composite was 195 MPa.

• 한국세라믹학회지
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• 제36권1호
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• pp.1-6
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• 1999

천연원료인 pink A급의 합천 kaolin에 산업부산물인 Al(OH)3와 boehmite를 각각 첨가하여 mullite를 합성하였다. 혼합방법으로는 분쇄와 혼합효과를 동시에 얻을 수 있는 attrition milling법을 행하였고 1.5 ton/$\textrm{cm}^2$으로 일측가압성형하여 시편을 제조, 열처리하였다. Al(OH)3 부산물을 첨가하였을 경우 Al2O3 함량이 71.8 wt%인 시편을 1$600^{\circ}C$에서 4시간 열처리하여 223MPa의 꺽임강도값을 얻었고 10시간 열처리하여 85%의 mullite가 생성되었다. boehmite를 첨가하였을 경우 1$600^{\circ}C$에서 10시간 열처리하였을 때 Al2O3 함량이 68wt%인 시편의 경우 147MPa의 꺽임강도값을 얻었고 Al2O3 함량이 71.8 wt%의 시편의 경우 95%의 고순도 mullite를 합성할 수 있었다.