• 한국잠사곤충학회지
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• 제16권2호
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• pp.55-75
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• 1974

가잠에 있어서의 세포질다각체 바이러스의 경난전달감락을 구명하기 위하여 육각형 세포직다각체 바이러스를 전대잠에 접종하고 이에 감염된 자아의 교배조와 비감염된 자아의 교배에서 얻어진 대잠에 있어 유발현상의 차이, 유발.간섭현상의 차이를 관찰하고 분석하여 경난전달감염적 가능성을 밝혔다. 여기에서 얻어진 실험결과는 다음과 같다. 1. 이형 바이러스인 사각형 세포질다각체 바이러스에 의한 육각형 세포질다각체 바이러스의 유발실험에서 감염된 바이러스의 종류를 육각형의 단일감염과 육각형과 사각형의 혼합감염을 모두 기준삼을 때 감염자아겨배군에서는 대조군보다 40내지 60%가 더 높은 유발정도를 보였다. 2. formalin 첨식에 의한 육각형 세포질다각체 바이러스의 우발실험에서 육각형 세포질다각체 바이러에 의한 유발만을 기준 삼을 때 실험군은 대조군에 비햐여 40%의 높은 유발정도를 보였다. 이 실험에서 첨식한 2 또는 3%의 formalin농도는 우발정도에 있어서 차이를 가져오지 못했다. 3. 냉장처리에 의한 육각형 세포질다각체 바이러스의 유발실험에서 육각형 세포질다각체 바이러스에 의한 유발만을 기준삼을 때 실험군 대조군에 비하여 약 50%의 높은 유발정도를 보였다. 이 실험에서 적용한 12 또는 24시간의 첨식처리군간에 의의있는 차이가 인정되지 않았다. 4. 유발.간섭현상에 관한 실험에서 유발과 간섭되는 바이러스를 육각형 세포질다각체 바이러스에 국한시켰을 때 이차 바이러스인 사각형 세포질다각체 바이러스의 처리농도가 높아질수록 일차 바이러스인 육각형 세포질다각체 바이러스 량이 1$\times$$10^{8}$/ml에 이르러서는 대조군과 동일한 수준에 놓이게 되었다. 한편 유발과 간섭되는 바이러스를 사각형 세포질다각체 바이러스에 국한시켰을 때는 얕은 농도의 이차 바이러스는 유발된 일차 바이러스에 의하여 간섭받았고, 이차 바이러스 량이 1$\times$$10^{7}$ /ml에서부터 이차 바이러스에 감염된 가잠이 증가되었으나 대조군보다는 약 30%가 미달되는 감염률을 보였다. 5. 유발.병원성 증진현상에 간한 실험에서 유발과 증진되는 바이러스를 사각형과 육각형 세포질다각체 바이러스의 혼합감염 된것에 국한시켜 보면 이차 바이러스인 사각형 세포질다각체 바이러스의 농도가 높아져서 1$\times$$10^{7}$ /ml에 이르면 혼합감염은 최고도에 이르러 실험군과 대조군간의 차이는 40%를 넘게 되었다. 여기에서 대조군은 이차 바이러스의 농도과 관계없이 아무런 영향을 받지 않았다. 사사 ： 이 연구를 수행함에 있어서 시종 지도해 주신 김낙정 교수님, 최병희 교수님 그리고 박광의 교수님께 심심한 사의를 드리며 본 논문이 완성될 수 있도록 노고를 아끼지 않고 지도하여주신 전윤성 교수님과 정길택 교수님께 또한 심심한 사의를 드립니다. 그리고 본 논문을 위한 실험을 수행함에 있어 전자현미경사용에 적극 협조해 주신 이순형 학형과 누에 사육시험을 도와 준 금근영, 임대준군에게 아울러 감사드립니다. 본 실험에 공시한 세식질다각체 바이러스를 분양하여 주신 동경대학 농학부 도부인 교수님께 또한 감사드립니다.

• 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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• 제25권5호
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• pp.488-494
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• 1988

Effects of MnO2 addition on themicrostructure, dielectric and piezoelectric properties of Rhombohedral, Tetragonal and Morphotropic phase boundary(MPB) in Pb(Ni1/3Nb2/3)O3-PbTiO3-PbZrO3 system were investigated and respectively the amount of MnO2 addition was 0, 0.2, 0.5, 1.0, 3.0wt%. In the tetragonal region, compared with the Rhombohedral and Morpotropic phase boundary, Mechanical quality factor(Qm), Curie temperature(Tc) and Dissipation factor were promoted by addition of MnO2. According to the results of the microstructure, dielectric and piezoelectric properties, the solid solution range of MnO2 addition in this system was 0.2-0.5wt%.

• 한국세라믹학회지
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• 제31권8호
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• pp.829-834
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• 1994

The aim of this study is to investigate the changes in dielectric properties, Young's modulus and remnant compressive strength with compressive cyclic loading in PZT of tetragonal, MPB and rhombohedral composition. Higher relative dielectric constants appeared in the poled condition than the unpoled condition for all the compositions. After poling treatment remarkably higher relative dielectric constants were observed particularly in MPB, tetragonal compositions. Until five percent of the expected fatigue life was exhausted, the dielectric constant increased with compressive cyclic stress in MPB and rhombohedral while it remained nearly constant in tetragonal. During the subsequent compressive cyclic stress, dielectric constant decreased in all the three compositions. As the compressive cyclic stress is applied the change of Young's modulus was coincided with the change of remnant compressive strength.

• 대한치과의사협회지
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• 제49권5호
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• pp.260-264
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• 2011

Zirconia ($ZrO_2$) is a crystalline dioxide of zirconium. Dental zirconia blocks for CAD/CAM are usually fabricated with powders of tetragonal zirconia polycrystals (TZP) stabilized with 3mol% yttria. Because of its mechanical properties similar to those of metals and color similar to tooth, it is evaluated to attain the two purposes at a time, strength and aesthetic in prosthetic dentistry. The ability of transformation of Y-TZP from tetragonal to monoclinic helps to prevent crack propagation and contributes the increase of strength and fracture toughness. Two different types of blocks, soft and hard, are used to prepare the zirconia frameworks. The fuzzy-sintered block is difficult in machining, so pre-sintered soft 3Y-TZP block is usually used to mill by computer aided machining.

• 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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• 제33권1호
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• pp.49-55
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• 1996

The aim of this study is to investigate the change of bending strength and fatigue strength in the unpoled and poled Pb(Zr, Ti)O3 ferroelectrics of tetragonal morphotropic phase boundary (MPM) and rhombohedral com-position in terms of internal stress which is measured by XRD method. Before poling treatment the highest bending strength was found in rhombohedral composition. After poling treatment the bending strength decreas-ed in all compositions but it decreased most remarkably in tetragonal composition. The most prominent de-crease of bending strength after poling treatment in tetragonal was attributed to the occurrence of microcracks due to highanisotropic internal stress around grain boundary which was induced of bending strength after poling in MPB and rhombohedral composition was not due to the occurrence of microcracks but to the increase in tensile internal stress perpendicular to the direction of crack propagation by domain alignment. Fatigue strength was higher before poling treatment than after poling treatment for various compositions.

• 한국해양공학회지
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• 제13권2호통권32호
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• pp.35-40
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• 1999

Effects of CuO addition on the sintering ability and the phase stability of Y-TZP. (Yttria doped Tetragonal Zirconia Polycrystals) were studied. The CuO dopants were found to be quite effective in reducing the sintering temperature to obtain full density and refining the grain size. The maximum allowable concentration of the dopants was limited to 0.3%mol% for CuO to maintain fully tetragonal phase. With the addition of these dopants, the flexual strength decreased by 20% in comparison with the undoped specimen but the fracture toughness increased by 15%.

• 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.

• 한국세라믹학회지
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• 제29권10호
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• pp.806-814
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• 1992

The aim of this study was to investigate the change in compressive strength, freacture behavior and degradation of piezoelectric properties with compressive cyclic loading in Pb(Zr, Ti)O3 of tetragonal, morphotropic phase boundary and rhombohedral composition. The highest compressive strength was found in rhombohedral composition. After poling treatment the strength increased by 8.4% and 6.5% in tetragonal and morphotropic phase boundary compositions respectively while changed little in rhombohedral. The increase of compressive strength after poling treatment is believed to be due to the internal stress around grain boundary by domain alginment toward electric field direction in the microstructures having tetragonality and the occurrence of domain switching to the direction perpendicular to electrical field during fracture. Fracture mode relatively change from transgranular to intergranular was observed in the large grain sized tetragonal and morphotropic phase boundary compositions before and after poling but the transgranular fracture mode always remained in the rhombohedral composition. From the X-ray diffractometer analysis the domains parallel to the electric field direction is known to undergo rearrangement during the cyclic loading into random direction that is responsible for the degradation of piezoelectric property.