• 치위생과학회지
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• 제15권5호
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• pp.577-584
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• 2015

본 연구에서는 $1,040^{\circ}C$에서 예비소결한 Y-TZP 시편을 크롬 염화물 0.03~0.08 wt%, 테르븀 염화물 0.03~0.07wt%를 함유한 금속염화물 수용액에 3분간 침지하고서 $1,450^{\circ}C$에서 2시간 동안 소결하였으며, 이를 금속염화물 침투가 Y-TZP 소결체의 색상, 소결밀도, 굴곡강도 및 미세조직의 변화에 미치는 영향을 조사한 결과, 다음과 같은 결론을 얻었다. 지르코니아 예비소결체에 대한 크롬과 테르븀 염화물 침투로 A1, A2 및 A3에 근사한 색조의 재현이 가능하였다. 크롬과 테르븀 염화물을 첨가했을 때 지르코니아의 결정립 크기가 증가하였다. Y-TZP 소결체의 2축 굴곡강도는 크롬과 테르븀 염화물 침투에 의해서 유의한 변화를 보이지 않았다(p>0.05). X-선 회절 분석결과, 크롬과 테르븀 염화물의 첨가 여부와 함량에 따른 지르코니아 결정상의 차이점은 관찰되지 않았다. 이상의 결과로 크롬과 테르븀 염화물을 사용하여 지르코니아의 색상을 조절할 수 있음을 확인하였고, 착색된 지르코니아의 색상은 Vita shade guide의 색상과 다소 차이가 있었지만 임상에서 이중구조 세라믹 보철물 재작 시 사용 가능할 것으로 생각된다.

• 치위생과학회지
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• 제14권1호
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• pp.29-34
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• 2014

본 연구는 최근 심미보철물 제작에 널리 사용되는 지르코니아의 저온열화가 수복물의 안정성 및 내구성에 영향을 미치는 여부를 확인하기 위하여 전단결합강도를 측정하였다. 디스크 형태의 시편을 각각 7개씩 제작한 후 전장도재를 축성하여, ISO 13356 규격에 의거한 조건으로 고압증기 멸균기에 저온열화의 정도를 조절하기 위하여 3, 5, 10시간 동안 수열처리를 진행하였다. 제한된 조건하에 시행된 실험을 통해 전단결합강도를 확인하였으며, 측정 후 파절양상을 관찰 하였다. 저온열화 처리 전후의 시편에 대한 전단결합강도의 변화는 각 실험군별 유의한 차이가 있었다(p<0.05). 10시간을 저온열화 처리한 시편이 가장 낮은 전단결합강도로 나타났으며, 처리시간이 길어질수록 전단결합강도가 낮아지는 경향을 보였다. 파절 양상으로 저온열화 처리를 하지 않은 시편에서 응집성 파절을 보였으며, 저온열화 처리가 길어질수록 혼합형 파절 경향으로 전환되었다. 결론적으로 본 연구는 저온열화 현상이 진행될수록 지르코니아 코어와 전장도재 간의 결합강도가 낮아지는 경향을 확인하였다. 본 실험결과를 토대로 치과용 지르코니아를 이용한 보철물 제작과정과 환자에게 장착 후 안정적인 사용을 위하여 저온열화 현상에 대한 주의가 필요할 것으로 생각된다.

• 한국결정성장학회:학술대회논문집
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• 한국결정성장학회 1996년도 제11차 KACG 학술발표회 Crystalline Particle Symposium (CPS)
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• pp.55-85
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• 1996

지르코니아 분말은 ZrO2 결정상이 온도변화에 따라 부피변화를 수반하는 상전이변태를 나타낸다. 단사정 ZrO2가 110$0^{\circ}C$에서는 정방정으로, 2$700^{\circ}C$ 내외에서는 입방정으로 결정구조가 가역적으로 변한다. 이 ZrO2에 금속산화물을 고용시키면 형석 (CaF2:Florite)형의 입방정 결정구조가 실온에서도 안정하게 존재하게 된다. 안정화제 산화물은 caO, MgO등 2가 산화물외에 3가 또는 4가의 금속산화물로서 Sc2O3, Y2O3, Sm2O3, Nd2O3, Gd2O3, Y2O3, CeO2 등이며 이들은 금속이온의 원자가가 변하기 쉬운 희토류 산화물이다. 안정화 지르코니아는 형석형 결정구조이며 결정화학적으로 보면 금속양이온이 산소이온에 대해서 정육면체형의 8배위를 하고 있다. 이때 이온반경비(양이온/음이온)에 따라 Zr+4자리와 O-2자리의 격자위치와 모양이 형성되므로 비틀어진 정육면체구조이건 이상적인 정육면체 형석구조를 이룬다. 이는 지르코니아의 결정상의 2상-3상인 부분안정화 지르코니아다결정체(PSZ : partially stabilized zirconia)이거나 단일상-2상인 정방정 지르코니아다결정체(TZP : tetragonal zirconia polycrystal)의 결정구조를 가지는데 기인한다. PSZ는 주로 MgO, CaO를 안정화제로 고용시켜 입방정 영역에서 소결하고 이를 다시 입방정과 정방정의 상 영역에서 열처리하여 입방정 입자내부에 정방정을 석출 형성시킨 것이며 TZP는 Y2O3 및 CeO2를 고용시켜 PSZ와 다르게 일반적인 상압소결한 정방정 결정상의 미립자이다. 산화지르코늄 분말은 지르콘사에서 열분해시킨 지르코늄소결.융해괴(caustic fusion clinker)를 산처리하여얻어진 지르코늄산용액(zirconyl acid solution : cloride, sulfide, nitride 등)으로부터 제조된다. 고순도 산화지르코늄은 용액 결정석출법에 의해 ZrOCl2.8H2O, 5ZrO2.3SO3.15H2O, ZrO(NO3)2.xH2O 등의 지르코늄 수화물만을 재결정화시킨 것으로부터 얻을 수 있으며 이 지르코늄염 수용액으로부터 입자미세구조를 효과적으로 제어하여 산화지르코늄 및 안정화 지르코니아 분말제조가 가능하다. 안정화 지르코니아 분말은 ZrO2와 안정화산화물의 고용을위하여 가열처리를 필요로 하며 일정온도에서 최적상태로 숙성하므로서 2가지 상(phase) 이상의 고용체를 가지게 된다. 안정화 지르코니아 분말은 고용처리온도를 낮추고 효과적으로 생성시키기 위해서는 지르코늄 및 안정화제염을 혼합하고 습식 직접합성하여 저온에서 고용체의 합해진상 영역을 생성시키는 것이다. 이는 지르코니아 원료분말의 미세구조를 제어하므로서 가능하며 이때 화학성분조성과 크기형태가 균일하게 분포된 입자분말을 얻을 수 있다.

• 한국재료학회지
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• 제28권6호
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• pp.349-354
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• 2018

Particle size reduction is an important step in many technological operations. The process itself is defined as the mechanical breakdown of solids into smaller particles to increase the surface area and induce defects in solids, which are needed for subsequent operations such as chemical reactions. To fabricate nano-sized particles, several tens to hundreds of micron size ceramic beads, formed through high energy milling process, are required. To minimize the contamination effects during high-energy milling, the mechanical properties of zirconia beads are very important. Generally, the mechanical properties of $Y_2O_3$ stabilized tetragonal zirconia beads are closely related to the mechanism of phase change from tetragonal to monoclinic phase via external mechanical forces. Therefore, $Y_2O_3$ distribution in the sintered zirconia beads must also be closely related with the mechanical properties of the beads. In this work, commercially available $100{\mu}m-size$ beads are analyzed from the point of view of microstructure, composition homogeneity (especially for $Y_2O_3$), mechanical properties, and attrition rate.

• 한국분말재료학회지
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• 제4권3호
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• pp.179-187
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• 1997

Milling media of steel and zirconia were used to produce $MoSi_2$ by mechanical alloying (MA) of Mo and Si powders. The effect of milling media on MA of Mo-65.8at%Si powder mixture has been investigated by SEM, XRD, DTh and in-situ thermal analysis. The powders mechanically alloyed by milling medium of steel for 8 hours showed the structure of fine mixture of Mo and Si, and those mechanically alloyed by milling medium of zirconia for longer milling time showed the structure of fine mixture of Mo and Si. The tetragonal $\alpha$-$MoSi_2$ Phase and the tetragonal $Mo_5Si_3$ phase appeared with small Mo peaks in the powders milled by milling medium of steel for 4 and 8 hours. The $\alpha$-$MoSi_2$ phase and the hexagonal $\beta$-$MoSi_2$ phase were formed after longer milling time. The $\alpha$-$MoSi_2$ phase appeared with large Mo peaks in the powders milled by milling medium of zirconia for 4 hours. The phases, $\alpha$-$MoSi_2$ and $\beta$-$MoSi_2$. were formed in the powders milled for longer milling time. DTA and annealing results showed that Mo and Si were transformed into $\alpha$-$MoSi_2$ and $Mo_5Si_3$, while $\beta$-$MoSi_2$ into $\alpha$-$MoSi_2$. In-situ thermal analysis results demonstrated that there were a sudden temperature rise at 212 min and a gradual increase in temperature in case of milling media of steel and zirconia, respectively. The results indicate that MA can be influenced by materials of milling medium which can give either impact energy on powders or thermal energy accumulated in vial.

• Restorative Dentistry and Endodontics
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• 제45권4호
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• pp.52.1-52.11
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• 2020

Objectives: Yttria-stabilized tetragonal phase zirconia has been used as a dental restorative material for over a decade. While it is still the strongest and toughest ceramic, its translucency remains as a significant drawback. To overcome this, stabilizing the translucency zirconia to a significant cubic crystalline phase by increasing the yttria content to more than 8 mol% (8YTZP). However, the biocompatibility of a high amount of yttria is still an important topic that needs to be investigated. Materials and Methods: Commercially available 8YTZP plates were used. To enhance cell adhesion, proliferation, and differentiation, the surface of the 8YTZP is sequentially polished with a SiC-coated abrasive paper and surface coating with type I collagen. Fibroblast-like cells L929 used for cell adherence and cell proliferation analysis, and mouse bone marrow-derived mesenchymal stem cells (BMSC) used for cell differentiation analysis. Results: The results revealed that all samples, regardless of the surface treatment, are hydrophilic and showed a strong affinity for water. Even the cell culture results indicate that simple surface polishing and coating can affect cellular behavior by enhancing cell adhesion and proliferation. Both L929 cells and BMSC were nicely adhered to and proliferated in all conditions. Conclusions: The results demonstrate the biocompatibility of the cubic phase zirconia with 8 mol% yttria and suggest that yttria with a higher zirconia content are not toxic to the cells, support a strong adhesion of cells on their surfaces, and promote cell proliferation and differentiation. All these confirm its potential use in tissue engineering.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1998년도 추계학술대회 논문집
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• pp.311-314
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• 1998

The effects of the additions of transition metal oxides on ZrO$_2$ - Y$_2$O$_3$ (Y$_2$O$_3$ - containing tetragonal zirconia polycrystals : Y-TZP) system has been studied by investigating fracture toughness and phase stability of the sintered specimens. In the specimens sintered at 1450$^{\circ}C$ for 2hrs in air the phase transformation from tetragonal to monoclinic was observed. The ratios of monoclinic phase to tetragonal phase were changed with the additions of CoO, Fe$_2$O$_3$ and MnO$_2$, respectively, from 0.00 to 8.00wt%. The fracture toughness was increased with increasing the monoclinic to tetragonal phase ratio and was maximum at the ratio of about 18%. However, the hardness was decreased with increasing the ratio. The additions of CoO, Fe$_2$O$_3$ and MnO$_2$ together into Y-TZP resulted in more complex behaviors of fracture toughness and hardness. The specimen with the additions of 1.5wt% Fe$_2$O$_3$, 3.0wt% Al$_2$O$_3$ and 1.5wt% CoO showed the monoclinic to tetragonal phase ratio of 18% and the highest toughness of 10.8 MPa.m$\^$$\frac{1}{2}$/ and Vickers hardness of 1201kgf/mm$^2$.

• 한국결정성장학회:학술대회논문집
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• 한국결정성장학회 2000년도 Proceedings of 2000 International Nano Crystals/Ceramics Forum and International Symposium on Intermaterials
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• pp.243-248
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• 2000

Effect of NiO addition on microstructure, stability of tetragonal phase and mechanical properties was investigated. (Y, Ni)-TZP solid solution was obtained by pressureless sintering. The fracture toughness was increased by solid solution of NiO. Neither reaction phase nor glassy phase was observed at the grain boundaries. From these results, it was determined that solid solution of NiO was destabilized tetragonal phase of Y-TZP. Y-TZP/Ni nanocomposite that contained nano-sized Ni particles was also fabricated by internal reduction method. Some evaluations and discussions were carried out for both (Y, Ni)-TZP solid solution and Y-TZP/Ni nanocomposite.

• 한국세라믹학회지
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• 제28권7호
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• pp.541-548
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• 1991

Sinterability and stability of TZP ceramics co-stabilized by 12 mol% CeO2 and divalent or trivalent oxides less than 1 mol% were investigated. Divalent and trivalent oxides increased stability of tetragonal ZrO2. 100% tetragonal ZrO2 phase was obtained by doping 12 mol% CeO2 and 0.2 mol% CaO and MgO respectively when sintering was carried out at 1500$^{\circ}C$ for 2 hours. Divalent and trivalent oxides improved sinterability and inhibit grain growth of ZrO2. And it was found that CaO was the most effective sintering aid and grain growth inhibitor for ZrO2 in this study. Incorporation of divalent and trivalent oxides into 12Ce-TZP increased the strength of 12Ce-TZP and particulary 12Ce, 0.4Ca-TZP exhibited a flexural strength of about twofold greater than 12Ce-TZP.

• 한국세라믹학회지
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• 제30권12호
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• pp.1059-1065
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• 1993

The sliding wear behavior of the plasma sprayed zirconia containing 8wt% yttria was investigated over a range of room temperature to 800℃. Both of the friction coefficient and the wear loss increased reaching its maximum at about to 499℃. and then decreased again with increasing temperature up to 800℃. The worn surface at elevated temperature were observed and analyzed by scanning electron microscopy and X-ray diffractometer to study the mechanisms of high temperature wear behavior. Surface morphology of the worn samples changes with temperature. Monoclinic (m)/tetragonal (t) x-ray peak intensity ratio of wear debris and worn surface decreased with increasing temperature. Non-transformable tetragonal (t') to metastable tetragonal (t) phase transformation of worn surface increased with increasing temperature. The results indicate that dehumidification and above phase changes are contributing to the high temperature wear behavior of the plasma sprayed ZrO2-Y2O3 coatings.