• 한국세라믹학회지
• /
• 제41권2호
• /
• pp.111-117
• /
• 2004

고순도 3Y-TZP에 알루미나를 0.3∼l.2wt%까지 첨가하여 attrition milling을 하고 slip-casting하여 시료를 제조하였다. 1390∼151$0^{\circ}C$까지 열처리하여 소결체의 소결특성을 기제적 물성과 미세구조 분석을 통하여 확인하였다. XRD를 이용하여 monoclinic-ZrO$_2$의 생성량을 정량적으로 확인하였으며, 147$0^{\circ}C$ 이장에서 열처리한 시료의 경우 m-ZrO$_2$의 생성으로 밀도의 저하를 보였으며, 비정상 입자성장을 유발하여 경도가 저하되었다. 알루미나의 첨가량이 0.9wt% 미만, 열처리 온도143$0^{\circ}C$에서 microhardness가 1360Hv 이상의 소결체를 제조할 수 있었다.

• 한국세라믹학회지
• /
• 제30권11호
• /
• pp.881-890
• /
• 1993

MAS system has narrow sintering temp. range due to the liquid phae sintering and thereby densify rapidly. And especially, its poor mechanical properties limitedthe industrial application. In this study, the improvement of mechanical properties and densification is suggested by the consideration of the toughening mechanisms and isolated pore generation mechanism which is derived by the liquid phase sintering theory in 3Y-TZP added composites. After Pressureless sintering up to 140$0^{\circ}C$ for 5hr, the dihedral angle and contact angle are analyzed by the observation of microstructure. As a result of microstructure analysis, the sintering stage of the specimen sintered for 5hr is analyzed as solid-skeleton stage. And the isolated pore generation mechanisms are considered as (1) The swelling of the liquid phase is predominent due to the facts that dihedral angle is larger than 60$^{\circ}$, contact angle is large and that liquid volume fraction is smaller than 10%. (2) The porous characteristics of the MAS system is also suggested as: the SiO2-rich liquid film is firstly formed at the srface and therefore this reduces the contiguity of the pore, which induces the isolated pore. The strength and fracture toughness increased with the addition of 3Y-TZP and the main fracture toughness improvement mechanisms are analyzed as the crack deflection.

• 한국세라믹학회지
• /
• 제42권2호
• /
• pp.140-144
• /
• 2005

The microstructures and mechanical properties of Tetragonal Zirconia Polycrystals (TZP) sintered bodies, which made by pressureless and spark plasma sintering techniques, were investigated using XRD, SEM, and TEM techniques. In the spark plasma sintered samples, the TZP grains were equiaxed type including many sub-grain boundaries regardless of sintering conditions. The biaxial strength of TZP having an average of 80 nm grains in diameter was high in value with 1025 MPa, but fracture toughness showed a low value due to the absence of a fracture toughening mechanism such as transformation toughening. In the Pressureless Sintered (PLSed) samples, the grain size of TZP was strongly dependent on the sintering temperature; i.e., it gradually increased as the sintering temperature increased. The value of fracture toughness increased as the grain size increased by the stress-induced phase transformation and Borne crack deflection.

• 한국세라믹학회지
• /
• 제41권7호
• /
• pp.508-512
• /
• 2004

치과 임프란트의 상부구조물로 응용하기 위해 Zr $O_2$, $Y_2$ $O_3$, Nb$_2$ $O_{5}$를 각각 90.24, 5.31, 4.45mo1%씩 혼합한 정방정 지르코니아 고용체에 알루미나를 부피비로 10-90%를 10vo1%간격으로 첨가하여 (Y, Nb)-TZP/알루미나 복합체를 제조하였다. 최적의 기계적 물성은 알루미나를 10vo1% 첨가했을 때 이축 곡강도는 900MPa이었으며 파괴인성은 8.9MPam$^{1}$2/이었고 20$0^{\circ}C$ 오토크레이브하에서 10시간 열처리했을 때 저온열화가 관찰되지 않았다. 복합체를 임프란트 상부구조물로 제작하여 40명의 환자에게 총 65개를 시술한 후 2년 동안 관찰한 결과 부작용이나 나사의 풀림 또는 파절이 전혀 일어나지 않아 우수한 임상결과를 보였다.

• Journal of Korean Dental Science
• /
• 제5권2호
• /
• pp.48-53
• /
• 2012

Various ceramic implant systems made of yttria-stabilized tetragonal zirconia polycystal (Y-TZP) have become commercially available in recent years. A search of the literature was performed to assess the clinical success of dental Y-TZP implants and whether the osseointegration of Y-TZP is comparable to that of titanium, the standard implant material. No controlled clinical studies in humans regarding clinical outcomes or osseointegration could be identified. Clinical data were restricted to case studies and case series. Only 7 animal studies were found. Osseointegration was evaluated at 4 weeks to 24 months after placement in different animal models, sites and under different loading conditions. The mean bone-implant contact percentage was above 60% in almost all experimental groups. In studies that used titanium implants as a control, Y-TZP implants were comparable to or even better than titanium implants. Surface modifications may further improve initial bone healing and resistance to removal torque. Y-TZP implants may have the potential to become an alternative to titanium implants but cannot currently be recommended for routine clinical use, as no long-term clinical data are available.

• Tribology and Lubricants
• /
• 제16권2호
• /
• pp.121-125
• /
• 2000

Silicon nitride ceramic has been verified as an excellent rolling bearing material because of its high strength and outstanding rolling fatigue life properties. However under some corrosive circumstances it showed drawbacks such as hardness reduction and severe wear caused by corrosion. In this work, the variations of the rolling wear and hardness of three kinds of ceramics were studied for the specimen aged 15 days in alkali water (90 $\pm$ 2$\^{C}$,25 wt% NaOH ). All of the specimens, ① Si$_3$N$_4$, ② 3Y-TZP and ③ 3Y-TZP alloyed with 5 wt% CeO$_2$, were sintered and post-HIPed, and then polished up to 0.02 $\mu$mRa of surface roughness. Rolling wear tests were conducted by MJ type rolling fatigue life tester under the initial theoretical maximum contact stress of 3.16 GPa and the spindle speed of 1,000 rpm. Spindle oil was used as a lubricant. The specimens were not worn before aging. For the specimen aged in alkali water, Si$_3$N$_4$ and 3Y-TZP were worn by rolling wear tests, and hardness was decreased. While aging the specimens, the phase was transformed from tetragonal to monoclinic in 3Y-TZP and the microstructure change occurred in Si$_2$N$_4$. 3Y-TZP specimens alloyed with 5 wt% CeO$_2$ were not worn after aging and no phase transformation occurred while aging.

• 한국윤활학회:학술대회논문집
• /
• 한국윤활학회 1999년도 제30회 추계학술대회
• /
• pp.154-159
• /
• 1999

Silicon nitride ceramic has been verified as an excellent rolling bearing material because of its high strength and outstanding rolling fatigue life properties. However under some corrosive circumstances it showed drawbacks such as hardness reduction and severe wear caused by corrosion. In this work, the variations of the rolling wear and hardness of three kinds of ceramics were studied for the specimen aged 15 days in alkali water (90$\pm$2$^{\circ}C$, 25 wt% NaOH). All of the specimens, \circled1Si$_3$N$_4$, \circled23Y-TZP and \circled33Y-TZP alloyed with 5 wt% CeO$_2$, were sintered and post-Hipped, and then polished up to 0.02 ${\mu}{\textrm}{m}$Ra of surface roughness. Rolling wear tests were conducted by MJ type rolling fatigue life tester under the initial theoretical maximum contact stress or 3.76 Gra and the spindle speed of 1,000 rpm. Spindle oil was used as a lubricant. The specimens were not worn before aging. For the specimen aged in alkali water, Si$_3$N$_4$and 3Y-TZP were worn by rolling wear tests, and hardness was decreased. While aging the specimens, the phase was transformed from tetragonal to monoclinic in 3Y-TZP and the microstructure change occurred in Si$_3$N$_4$. 3Y-TZP alloyed with 5 wt% CeO$_2$specimens were not worn after aging and no phase transformation occurred while aging.

• 한국결정학회지
• /
• 제11권2호
• /
• pp.102-107
• /
• 2000

20vol% Al2O3-dispersed 2Y-TZP ceramics was prepared by mixing of 2Y-TZP and Al2O3 powder with different particle sizes, and investigated the influence of Al2O3 particle size and sintering condition on the microstructure and fracture toughness. Sintering conditions of the Al2O3-dispersed 2Y-TZP specimens showed high density at sintering condition of 1350℃ and 1500℃ for 1∼5h, and homogeneous microstructure. The grain size of tetragonal zirconia and the fracture toughness increased with the size of dispersed Al2O3 particle. The highest fracture toughness (∼17.2MPa·m1/2) of all specimens was obtained in the specimens with dispersed Al2O3 particle size of 1.0㎛ and sintered at 1500℃ for 2h.

• 한국세라믹학회지
• /
• 제31권3호
• /
• pp.321-329
• /
• 1994

Functionally gradient materials(FGM), which have the continuous or stepwise variation in a composition and microstructure, are being noticed as the material that solves problems caused by heterogeneous interface of coating or joining. And these materials also expect new functions occured by gradient composition itself. Therefore, to examine possibility of thermal barrier materials, TZP/Mo·FGM and TZP/Ni·FGM were fabricated by sintering method. As to the sintered specimens, sintering shrinkage, relative density and Vicker's hardness in each composition were examined. The phenomena due to the difference of sintering shrinkage velocity during sintering process and the thermal stress induced through differences of thermal expansion coefficient in FGM were discussed. And the structure changes at interface and microsturcture of FGM were investigated. As a results, the difference of shrinkage between ceramic and metal was about 14% in TZP/Mo and 7% in TZP/Ni. The relative density and hardness were considerably influenced by metal content changes. Owing to unbalance of sintering shrinkage velocity between ceramic and metal, various sintering defects were occured. To control these sintering defects and thermal stress, gradient composition of FGM should be narrow. The microstructure changes of FGM depended on the ceramic or metal volume percents and were analogous to the theoretical design.

• 미생물학회지
• /
• 제44권4호
• /
• pp.339-345
• /
• 2008

국내 대학병원에서 분리되어 imipenem 에 대한 최소억제농도가 $8{\mu}g/ml$ 이상인 51개의 포도당비발효 그람음성 간균들 중 metallo-${\beta}$-lactamase (MBL)을 생성하는 균주들을 분리하고, 그들 중에서 내성이 강한 Pseudomonas aeruginosa에 대한 항균제 병합요법의 효과를 알아보기 위하여 상승효과를 보이는 항균제 조합을 찾아보았다. 9개의 균주(Pseudomonas aeruginosa 2주 및 Achromobacter xylosoxidans subsp. xylosoxidans 7주)가 MBL 양성을 나타냈으며, PCR 결과 9주 모두에서 $bla_{VIM-2}$ 유전자가 관찰되었다. 이들 중에서 P. aeruginosa DK569는 aztreonam (MIC; $8{\mu}g/ml$)을 제외하고 실험한 모든 ${\beta}$-lactam 항균제, aminoglycoside, ciprofloxacin에 내성을 보여 aztreonam 함유 배지를 이용하여 상승효과률 보이는 항균제를 찾고자 하였다. One disk synergy test 에서 선별된 항균제 조합을 이용하여 생존률 검사 실험을 한 결과, aztreonam (AZT)와 piperacillin-tazobactam (TZP)의 병합은 항균제 노출 6시간 후에 AZT 또는 TZP의 단독 항균제 노출시 보다 균수가 1/18.7로 감소하였다. 그리고 AZT와 amikacin (AN)의 병합에서도 항균제 노출 6 시간 후에 AZT 또는 AN의 단독항균제의 투여보다 균수가 1/17.1 로 감소하였다. 결국 위 두 조합은 의미있는 상승효과를 보이지 못하여 위 세 항균제를 조합하여 실험하였다. 위의 세 항균제를 병합하였을 때 항균제 노출 8시간 후에 AZT, TZP 및 AN의 단독 투여에 비하여 병합요법에 의해 균수가 1/183.3 로 감소하여 의미있는 상승효과를 보였다. 이 결과는 치료가 쉽지 앓은 MBL 생성균에 의한 감염에 대한 치료에 AZT, TZP 및 AN의 세 가지 항균제 병합요법이 유용할 것이라는 것을 의미한다.