• Korean Chemical Engineering Research
• /
• 제40권6호
• /
• pp.741-745
• /
• 2002

Sol-Gel법에 의해 출발물질로 zirconium-n-butoxide(ZNB)와 yttrium nitrate를 사용하여 yttria-stabilized zirconia(YSZ) 나노분말을 제조하였다. 또한 ZNB의 가수분해 동안 첨가된 물량의 변화가 얻어진 YSZ 나노분말의 결정상과 기공특성에 미치는 영향을 조사하였다. 하소온도 변화에 따른 결정상 변화는 첨가된 물량에 관계없이 동일한 양상을 보였다. 즉, $100^{\circ}C$에서 건조된 분말은 모두 비정질상이었으며, $400^{\circ}C$에서 입방정상의 결정구조로 전환되었고, $1,000^{\circ}C$에서 정방정상과 단사정상이 나타나 $1,400^{\circ}C$까지 정방정상과 단사정상이 공존하는 결정구조를 보였다. ZNB의 가수분해 중 물의 양이 비교적 적게 첨가된 경우로($H_2O/ZNB=20$이하) 제조된 분말은 mesopore의 기공분포를 보인 반면, 물의 양이 비교적 많이 첨가된 경우에서는 ($H_2O/ZNB=50$이상) micropore의 기공분포를 보였다.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2012년도 추계학술대회 논문집
• /
• pp.591-592
• /
• 2012

• 구강회복응용과학지
• /
• 제26권3호
• /
• pp.253-264
• /
• 2010

최근 개발된 Yttrium-stabilized-tetragonal-zirconia-polycrystal(Y-TZP ceramic)은 생체 친화적이며 높은 굴곡 강도, 파절 저항성, 파괴 인성을 지니고 CAD-CAM을 통해 milling이 가능하여 많은 치과 영역에서 사용되고 있다. 구치부 zirconia framework을 사용하는 고정성 수복물의 경우에는 상부 장석 도재의 상대적으로 높은 빈도의 파절을 보이고 있다. 복합레진은 취성이 적고 법랑질 보다 마모도가 낮으며 수리가 용이하다. 높은 교합압 부위에서 전장용 복합레진을 사용한 임플란트 수복은 기능적인 장점을 지니며 흥미롭게 여겨지고 있다. 이번 연구의 목적은 Y-TZP ceramic에 몇 가지 표면 처리를 시행하여 전장용 복합레진을 적용 시켰을 때 도재 전장시과 비교하여 임상적 활용을 위한 유용한 전단결합강도를 지니는지를 알고자 함이다.

• 한국세라믹학회지
• /
• 제52권5호
• /
• pp.299-303
• /
• 2015

The electrolyte is an important component in determining the performance of Fuel Cells. Especially, investigation of the conduction properties of electrolytes plays a key role in determining the performance of the electrolyte. The electrochemical properties of Yttrium stabilized zirconia (YSZ) were measured to allow the use of this material as an electrolyte for solid oxide fuel cells (SOFC) in the temperature range of $700-1000^{\circ}C$ and in $0.21{\leq}pO_2/atm{\leq}10^{-23}$. A Hebb-Wagner polarization experimental cell was optimally manufactured; here we discuss typical problems associated with making cells. The partial conductivities due to electrons and holes for 8YSZ, which is known as a superior oxygen conductor, were obtained using I-V characteristics based on the Hebb-Wagner polarization method. Activation energies for holes and electrons are $3.99{\pm}0.17eV$ and $1.70{\pm}0.06eV$ respectively. Further, we calculated the oxygen ion conductivity with electron, hole, and total conductivity, which was obtained by DC four probe conductivity measurements. The oxygen ion conductivity was dependent on the temperature; the activation energy was $0.80{\pm}0.10eV$. The electrolyte domain was determined from the top limit, bottom limit, and boundary (p=n) of the oxygen partial pressure. As a result, the electrolyte domain was widely presented in an extensive range of oxygen partial pressures and temperatures.

• 대한화학회지
• /
• 제34권6호
• /
• pp.555-560
• /
• 1990

$YBa_2Cu_3O_{7-x}$ 초전도 필름을 초음파에 의한 aerosol spray 법을 이용하여 YSZ (yttria stabilized zirconia) 및 SrTi$O_3$의 (100) 결정면 위에 만들었다. 초전도상은 세 단계의 과정을 거쳐서 형성되었다 : (가) 이트륨, 바륨, 구리의 질산염을 화학 양론비로 섞어 만든 용액을 250$^{\circ}C$로 가열된 기질에 분무하여, (나) 형성된 필름을 공기 중에서 550$^{\circ}C$로 예열하고, (다) 흐르는 산소 분위기에서 950$^{\circ}C$로 소결한 뒤 노냉하였다. 필름의 저하을 dc four-point probe 법으로 측정하여 액체질소 온도 이상에서 초전도성을 확인하였다.

• 한국재료학회지
• /
• 제29권4호
• /
• pp.233-240
• /
• 2019

This study analyzes the mechanical properties, including the attrition rate, of $50{\mu}m$ size yttria-stabilized zirconia (YSZ) beads with different microstructures and high-energy milling conditions. The yttria distribution in the grain and grain-boundary of the fully sintered beads relates closely to Vickers hardness and the attrition rate of the YSZ beads. Grain size, fractured surfaces, and yttrium distribution are analyzed by electronic microscopes. For standardization and a reliable comparison of the attrition rate of zirconia beads with different conditions, Zr content in milled ceramic powder is analyzed and calculated by X-ray Fluorescence Spectrometer(XRF) instead of directly measuring the weight change of milled YSZ beads. The beads with small grain sizes sintered at lower temperature exhibit a higher Vickers hardness and lower attrition rate. The attrition rate of $50{\mu}m$ YSZ beads is measured and compared with the various materials properties of ceramic powders used for high-energy milling. The attrition rate of beads appears to be closely related to the Vickers hardness of ceramic materials used for milling, and demonstrates more than a 10 times higher attrition rate with Alumina(Hv ~1650) powder than $BaTiO_3$ powder (Hv ~315).

• 한국재료학회지
• /
• 제27권8호
• /
• pp.445-450
• /
• 2017

YSZ (Yttria-stabilized zirconia) is a ceramic material that is used for electronic and structural materials due to its excellent mechanical properties and specific electrical characteristics according to the Yttrium addition. Hydrothermal synthesis has several advantages such as fine particle size, uniform crystalline phase, fast reaction time, low process temperature and good dispersion condition. In order to synthesize YSZ nanoparticles with high crystallinity, hydrothermal synthesis was performed at various concentrations of NaOH. The hydrothermal process was held at a low temperature ($100^{\circ}C$), with a short process time (2,4,8 hours); the acidity or alkalinity of solution was controlled in a range of pH 2~12 by addition of NaOH. The optimum condition was found to be pH 12, at which high solubility levels of Y(OH) and Zr(OH) were reported. The synthesized nano powder showed high crystallinity and homogenous composition, and uniform particle size of about 10 nm.

• The Journal of Advanced Prosthodontics
• /
• 제12권5호
• /
• pp.265-272
• /
• 2020

PURPOSE. The aims of this study were to investigate mechanical properties and hydrothermal degradation behaviour of the cubic-containing translucent yttrium oxide stabilized tetragonal zirconia polycrystal (Y-TZP). MATERIALS AND METHODS. Four groups of Y-TZP (T, ST, XT, and P), containing different amount of cubic crystal, were examined. Specimens were aged by autoclaving at 122℃ under 2 bar pressure for 8 h. Phase transformation was analyzed using X-ray diffraction (XRD) to measure phase transformation (t→m). Kruskal-Wallis test was used to determine the difference. Surface hardness, biaxial flexural strength, and fracture toughness in values among the experimental groups and verified with Wilcoxon matched pairs test for hardness values and Mann Whitney U for flexural strength and fracture toughness. RESULTS. XRD analysis showed no monoclinic phase in XT and P after aging. Only Group T showed statistically significant decreases in hardness after aging. Hydrothermal aging showed a significant decrease in flexural strength and fracture toughness in group T and ST, while group XT and P showed no effect of aging on fractural strength and fracture toughness with P<.05. CONCLUSION. Hydrothermal aging caused reduction in mechanical properties such as surface hardness, biaxial flexural strength, and fracture toughness of Y-TZP zirconia. However, cubic-containing zirconia (more than 30% by volume of cubic crystal) was assumed to have high resistance to hydrothermal degradation. Clinical significance: Cubic-containing zirconia could withstand the intraoral aging condition. It could be suggested to use as a material for fabrication of esthetic dental restoration.

• 한국지구과학회지
• /
• 제18권6호
• /
• pp.553-558
• /
• 1997

등축정계의 결정구조를 지니는 무색 투명한 저코니아($Zr_{0.73}Y_{0.27}O_{1.87}$) 결정을 $Y_2O_3$를 안정제로 사용하여 Bridgman-Stockbager법(또는 Skull 용융법)으로 합성하였다. 육성된 결정은 유리광택을 나타내며 동시에 약간의 지방 광택도 띤다. 저코니아 결정은 편광현미경하에서 등방성을 나타내며 이방성의 징후는 발견되지 않는다. 모스 경도는 $8{\sim}8\frac{1}{2}$이고 비중은 5.85이다. 자외선하에서는 약한 백색 형광을 낸다. 단결정법으로 결정한 저코니아의 결정구조는 등축정계이며, 공간군은 $Fm3m({O^5}_h)$이다. 단위포 상수(a)는 $5.1552(5){\AA}$이며, $V=136.99(5){\AA}$, Z=4, R=0.0488이다. 저코니움 원자는 각 모서리에 산소 원자가 자리잡고 있는 육면체의 중심에 위치하고 있으며, 각 산소 원자는 저코니움 원자로 되어 있는 사면체의 중심에 위치하고 있다. 결국 8:4의 배위수가 성립하는 구조를 하고 있다.

• 한국세라믹학회지
• /
• 제29권2호
• /
• pp.119-126
• /
• 1992

3 mol% Y2O3-doped ZrO2 powders were prepared by hydrolysis with 0.1, 0.2, 0.3, 0.4, 0.5, 0.6 mol/ιH2O/ethanol into 0.1 mol/ι zirconium and yttrium alkoside/ethanol. Spherical monodispersed yttria-partially stabilized zirconia particles with an average diameter of about 0.5 ${\mu}{\textrm}{m}$ were prepared by hydrolysis with 0.2 mol/ιH2O/ethanol. The as-prepared powder was amorphous and with heating it transformed into cubic up to 80$0^{\circ}C$ and into tetragonal over 100$0^{\circ}C$. 3 mol% Y2O3-doped ZrO2 powders calcined over and up to 80$0^{\circ}C$ were a mixture of tetragonal and monoclinic and only tetragonal as determined by X-ray diffraction, respectively.