• 대한치과기공학회지
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• 제29권1호
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• pp.49-57
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• 2007

This study was to add crushed frit with different grain sizes to 3Y-TZP so that it could determine the mechanical properties depending on sintering temperature. In this study, 3 types specimens were prepared in powder with respective additions of 20wt.% frit, which was sized through 24-, 48- and 72-hour ball milling with zirconia. Then, sintered pellets were tested in experiments under the temperature variations for different compositions. As a result, this study came to the following findings: 1. It was found that the higher sintering temperature and the longer ball milling time of frit led to the higher sintered density. 2. Bending strength tended to increase with higher sintering temperature and longer ball milling time of frit. 3. Hardness tended to increase with higher sintering temperature and longer ball milling time of frit. 4. However, it was found that fracture toughness didn't vary significantly depending on sintering temperature. From these findings, it was concluded that the smaller frit grain size and the narrower particle size distribution of frit lead to the better mechanical properties.

• 한국세라믹학회지
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• 제40권6호
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• pp.601-607
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• 2003

재료의 선택에 따른 생체친화성을 고찰하기 위해서 조골세포의 세포배양실험을 실시하였으며, 이로부터 세포의 부착형상, 증식, 분화의 정도를 살펴보았다. 본 실험에서 세포배양모재는 체내식립재료로 주목을 받고 있는 TiO$_2$, 3Y-TZP, HA (Hydroxyapatite) 그리고 Ti를 사용하였으며 대조군으로 Thermanox를 선택하였다. 일반적으로 모든 시편들은 같은 세포배양시간일때 거의 유사한 세포부착형상을 보였다. 그러나, HA위의 세포들은 나머지 시편들보다 좀 더 두꺼운 형상을 보였으며 빠른 세포의 부착 및 퍼짐으로 인한 overlapping이 자주 관찰되었다. 세포의 증식 및 분화의 경우에도 생체활성의 특성을 지니는 HA가 가장 높은 값을 보였으며 생체불활성재료인 경우에는 Ti, TiO$_2$, 3Y-TZP모두 유의한 차이를 보이지 않고 비슷한 경향을 나타내었다.

• 한국세라믹학회지
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• 제41권2호
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• pp.111-117
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• 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
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• 제42권2호
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• pp.140-144
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• 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
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• 제31권3호
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• pp.321-329
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• 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.

• 한국세라믹학회지
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• 제30권11호
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• pp.881-890
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• 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.

• Journal of Korean Dental Science
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• 제5권2호
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• pp.48-53
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• 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
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• 제16권2호
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• pp.121-125
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• 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.

• 한국재료학회지
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• 제20권7호
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• pp.379-384
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• 2010

The usual ceramic process of mixing and milling in state of oxides $ZrO_2$ and $CeO_2$ was adopted in this study in a wet process to manufacture Ce-TZP. $CeO_2$-$ZrO_2$ ceramics containing 8~20 mol% $CeO_2$ were made by heat treatment at $1250\sim1500^{\circ}C$ for 5hr. The maximum dispersion point of every slurry manufactured with a mixture of $ZrO_2$ and $CeO_2$ was neat at pH10. A stable slurry with average particle size of 90 nm can be manufactured when it is dispersed with the use of ammonia water and polycarboxylic acid ammonium. The sintered Ce-TZP ceramics manufactured with the addition of $CeO_2$ in a concentration of less than 10 mol% progressed to the fracture of the specimen due to the existence of a monoclinic phase of more than 30% at room temperature. More than 99% of the tetragonal phase was created for the sintered body with the addition of $CeO_2$ beyond 18 mol%, but the degradation of the mechanical properties on the entire specimen was brought about due to the $CeO_2$ existing in a percentage above 3%. Consequently, the optimal Ce-TZP level combined in the oxide state was identified to be 16 mol% of $CeO_2$ contents.

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