• 대한치과보철학회지
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• 제34권2호
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• pp.309-319
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• 1996

This study was performed to evaluate the fracture toughness of seven commercially available dental ceramics by indentation fracture method. All specimens were fabricated to the final dimensions of approximately 12mm in diameter 2mm in thickness. The characte-ristic indentation dimensions of Vickers or Knoop indentation were measured to calculate the fracture toughness values and Young’s moduli. The results obtained were summarized as follows; 1. Young’s modulus and Vickers hardness of Vita In-Ceram showed the maximum values of $154.4{\pm}49.2$ Gpa and $12.60{\pm}0.71$Gpa, respectively. Results of Scheff test exhibited the significant difference between Vita In-Ceram group and others(p<0.01). 2. Maximum fracture toughness of $2.562{\pm}0.37 MPam^{1/2}$ for Vita In-Ceram and the maxi-mum one of $0.908{\pm}0.132MPam^{1/2}$ for Vitadur-N were calculated. Results of Scheff test showed the significant difference between Vita In-Ceram group and Vita Hi-Ceram(p<0.05) : also between Vita In-Ceram or Vita Hi-Ceram and others(p<0.01). 3. The alumina-based core ceramics showed the aspect of Palmqvist crack for the indentation load of 49.0N, but others showed the median/lateral crack for the indentation load of 9.8N.

• 한국세라믹학회지
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• 제45권2호
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• pp.105-111
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• 2008

Symmetric three layer composites have been prepared by freeze casting and then pressureless sintered at $l700-1800^{\circ}C$ in $N_2$ gas atmosphere. The relative sintered density of multilayer composites having microstructural characteristics of later intermediate-stage densification increased with sintering temperature and reached about 95% theoretical value at $1800^{\circ}C$. Although the indentation strength of the multilayer composites was generally reduced with increasing Vickers indentation load up to 294N, the damage resistance of multilayer composites was superior compared to monolithic layer 95AL/5SN material. The three-point bend strength of the layered materials remained at the values 266-298 MPa after indentation with a load of 49N, while that of the monolithic 95AL/5SN material was 219 MPa. The fracture toughness of the multilayer material was $5.4-6.6\;MPa\;m^{1/2}$.

• 대한치과보철학회지
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• 제35권4호
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• pp.781-792
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• 1997

This study was peformed to evaluate the dynamic fatigue characteristics of the dental ceramics for all-ceramic crown. A feldspathic porcelain of VMK68. glass ceramic of IPS-Empress, and glass infiltrated alumina ceramic of In-Ceram were used. Disc specimens were prepared to the final dimensions of 12 mm in diameter and 1 mm in thickness. The biaxial flexure test was conducted using a ball-on-three-ball method. 240 specimens were tested in $37^{\circ}C$ water by testing 20 samples at each of four loading rates:0.05, 0.2, 1, and 5mm/min. 60 specimens were tested in a moisture-free environment by testing 20 samples at 5mm/min. The inert strength of VMK68 was 80.25MPa, and the fatigue parameters were n=29.1, ${\sigma}_{fo}=52.90MPa$. The inert strength of IPS-Empress was 104.76MPa, and the fatigue parameters were n=32.46, ${\sigma}_{fo}=67.52MPa$. The inert strength of In-Ceram was 429.33MPa, and the fatigue parameters were n=31.46, ${\sigma}_{fo}=258.36MPa$. 10-year failure stresses of VMK68, IPS-Empress, and In-Ceram were 20.3MPa, 24.8MPa, and 93.6MPa, respectively. Failure strength and fatigue life showed the highest value in In-Ceram, and then, IPS-Empress and VMK68.

• 대한화학회지
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• 제54권1호
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• pp.131-136
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• 2010

다양한 철 원소의 조성을 갖는 인산알루미늄 철을 합성하여 표면 성질과 벌크 성질을 조사하였다. 벤질 알코올과 디에틸 말론산의 transesterification반응에 의해 촉매 특성을 결정 하였다. 에틸 벤질 말론산과 디벤질 말론산을 유일한 생성물로 얻었다. 철 성분이 0.025 몰 퍼센트인 FeAlP의 경우에 특이한 촉매 특성과 조직상의 특성이 나타난다. 디에스터의 형성은 중간 정도 크기의 산성 자리에서 이루어진다. 물질 안에 수화된 알루미나와 polycondensed인산이 존재할 경우에는 에스터교환 반응에서 인산 알루미늄 철의 촉매 특성이 감소하게 된다.

• 한국재료학회지
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• 제11권7호
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• pp.622-624
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• 2001

The CVD film of methoxysilane derived from diphenyldimethoxysilane(DPDMS) was formed on the outer surface of a porous ${\alpha}-alumina$ support tube coated(via dipping-drying-calcining) with a boehmite sol(0.3 mol-Al/L). The resulting silica membrane($500^{\circ}C,\;P_{fe}\;=\;130\;Pa$) showed a permeance of $5.18{\times}10^{-8}\;mol\;{\cdot}\;m^{-2}{\cdot}s^{-1}{\cdot}Pa^{-1}\;for\;CO_2$ and a permselectivity of 13.35 for $CO_2/N_2\;at\;30^{\circ}C$.

• International Journal of Precision Engineering and Manufacturing
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• 제8권4호
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• pp.38-44
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• 2007

Combat vehicles are frequently maneuvered in battlefields when the lives of combatants are being threatened. These vehicles are important elements that influence the consequences of a battle. Their armor must be lightweight and provide excellent protection to ensure successful operations. Ceramic composite armor has recently been developed by many countries to fulfill these requirements. We reviewed previous research to determine an effective armor design, and then fabricated a composite armor structure using $Al_2O_3$ and glass fiber-reinforced polymer. Specimens were manufactured under controlled conditions using different backing plate thicknesses and bonding methods for the ceramic layer and the backing plate. The penetration of an armor-piercing bullet was evaluated from ballistic protection tests. The bonding method between the ceramic layer and the fiber-reinforced polymer influenced the ballistic protection performance. A bonding layer using rubber provided the best protection.

• 한국식품영양학회지
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• 제10권4호
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• pp.503-508
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• 1997

L. edodes의 배양액 및 균사체로부터 항암작용이 있는 단백 다당류의 추출 및 정제방법에 관한 실험을 실시하였다. 단백다당류 추출에서 비이온성 계명 활성제인 2% Triton X-100 용액으로 추출할 경우 상온에서 추출하여도 통상의 10$0^{\circ}C$ 열수 추출을 통해 얻을 수 있는 것보다 수율이 높았다. 그러나 계명활성제 용액에 4N NaCl을 첨가하여 추출하면 ethanol 침전과정에서 단백다당류의 침전물을 얻을 수 없었다. 열수 추출에 있어서 추출 온도는 10$0^{\circ}C$가 효과적이고 추출 시간은 4시간 정도면 충분하였다. 열수 추출 결과 ethanol 침전 및 동결건조를 통하여 얻어진 조단백 다당류의 정제 실험에서는 alumina를 충전제로 하는 gel filtration보다 sephadex에 의한 gel filtration 또는 DEAE-cellulose, DEAE-sephadex를 이용한 ion exchange chromatography가 보다 효과적이다.

• 한국재료학회지
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• 제13권5호
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• pp.309-312
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• 2003

Tin dioxide($_SnO2$) thin films were deposited on alumina substrate by metal-organic chemical vapor deposition (MOCVD) as a function of temperature and time. Thin films were fabricated from di-n-butyltin diacetate as a precursor and oxygen as an oxidation. The microstructure of deposited films was characterized by X-ray diffraction and field emission scanning electron microscopy(FE-SEM). The thickness was linearly increased with deposition time and $SnO_2$structure was found from $375^{\circ}C$ for the deposition time of 32 min. The maximum sensitivity to 500ppm CO gas was observed for the specimens deposited at $375^{\circ}C$ for 2 min at the operating temperature of $350^{\circ}C$. Gas sensitivity to CO increased with decreasing the film thickness. The sensing properties of response time, recovery and sensitivity of CO were changed with variations of substrate temperature and time.

• International Journal of Concrete Structures and Materials
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• 제10권1호
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• pp.15-28
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• 2016

With the aim to reduce the atmospheric $CO_2$, utilization of the carbonated lime produced from the aqueous carbonation reaction for the synthesis of a cementitious material would be a promising approach. The present investigation deals with the aqueous carbonation of slaked lime, followed by hydrothermal synthesis of a cementitious material utilizing the carbonated lime, silica fume, and hydrated alumina. In this study, the aqueous carbonation reaction was performed under four different conditions. The TGA, FESEM, and XRD analysis of the carbonated product obtained from the four different reaction conditions was performed to evaluate the efficacy of the reaction conditions used for the production of the carbonated lime. Additionally, the performance of the cementitious material was verified analyzing the physical characteristics, mechanical property and setting time. Based on the results, it is demonstrated that the material produced by the hydrothermal method possesses the cementing ability. Additionally, it is revealed that the mortar prepared using the alternative cementitious material yields $33.8{\pm}1.3MPa$ compressive strength. Finally, a plausible reaction scheme has been proposed to explain the overall performances of the aqueous carbonation as well as the hydrothermal synthesis of the cementitious material.

• Transactions on Electrical and Electronic Materials
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• 제4권2호
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• pp.1-4
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• 2003

The purpose of this study was to investigate the characteristics of slurry including phosphoric acid for chemical-mechanical planarization of copper and tantalum nitride. In general, the slurry for copper CMP consists of alumina or colloidal silica as an abrasive, organic acid as a complexing agent, an oxidizing agent, a film forming agent, a pH control agent and additives. Hydrogen peroxide (H$_2$O$_2$) is the material that is used as an oxidizing agent in copper CMP. But, the hydrogen peroxide needs some stabilizers to prevent decomposition. We evaluated phosphoric acid (H$_3$PO$_4$) as a stabilizer of the hydrogen peroxide as well as an accelerator of the tantalum nitride CMP process. We also estimated dispersion stability and zeta potential of the abrasive with the contents of phosphoric acid. An acceleration of the tantalum nitride CMP was verified through the electrochemical test. This approach may be useful for the development of the 2$\^$nd/ step copper CMP slurry and hydrogen peroxide stability.