• Journal of the Korean Ceramic Society
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• v.30 no.8
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• pp.651-656
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• 1993

Granulated Y-TZP powders were coated by using Sol-Gel method and the coating effect of Al2O3 on the isothermal phase transformation in Al2O3 coated Y-TZP powders was investigated. During aging, tetragonal phase in Y-TZP powder were isothermally transformed to monoclinic, but the tetragonal phase in Al2O3 coated Y-TZP powders was continuously retained in spite of long aging. It can be considered that the improvement of thermal stability of tetragonal phase in Al2O3 coated Y-TZP powders may be due to the increase of constraint effect near tetragonal phase, and the suppression of surface transformation by obstructing the reaction between the surface of Y-TZP and H2O.

• Journal of the Korean Ceramic Society
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• v.34 no.2
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• pp.171-174
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• 1997

It was experimentally identified, for the first time, that oxygen phonons play an important role in the low temperature degradation(tetragonallongrightarrowmonoclinic phase transformation) of yttria stabilized tetragonal zir-conia polycrystals (Y-TZP). The degradation accompanied by immersing the samples in the boiling water were markedly reduced by substituting of 18O for 16O in Y-TZP. This was attributed to the heavier mass of 18O which leads to the smaller probability to find oxygen atoms beyond certain critical displacements.

• Journal of the Korean Ceramic Society
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• v.27 no.2
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• pp.226-232
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• 1990

The degradation phenomena and thermal stability of 2.5Y-TZP at low-temperature were studied by means of XRD, Raman spectra and microstructural analysis. The degradation of heat-treated 2.5Y-TZP at 20$0^{\circ}C$-20hr in air was observed on the TZP surface, be caused by the cracks generated from tlongrightarrowm transformation, and the cracks was propagated inside the polycrystalline body. The ZrO2 grain boundaries and grains near the crack were revealed as if these were diffused and dissolved. And it was also observed mlongrightarrowt transformation as the degraded TZP was refired at 140$0^{\circ}C$, and it was thought to be the fact that the moisture in atmosphere during the aging process contributed to the degradation. The thermal stability of 2.5Y-TZP was improved dramatically with an addition of 3w/o CeO2 or a provision of high Y2O3 concentration on the TZP surface.

• Journal of the Korean Ceramic Society
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• v.38 no.5
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• pp.418-423
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• 2001

16 mole%의 CeO$_2$가 고용된 Ce-TZP 소결체 사이에 140~240$mu extrm{m}$ 두께의 Ce-TZP-5~30 vol% $Al_2$O$_3$중간층이 삽입된 층상복합체를 분말건식가압성형법에 의해 제조하였다. 소결온도는 $Al_2$O$_3$가 5~30 vol.% 첨가될 때 90% 이상의 소결밀도를 얻을 수 있도록 1$600^{\circ}C$로 정하였다. 이러한 3층 복합체에서 바깥의 Ce-TZP 지역에서의 파괴 형태는 입내파괴를 보여주었지만 $Al_2$O$_3$가 함유된 중간층에서는 입계파괴가 전이되면서 인성증가를 보여주었다. 이러한 층상 복합체의 경우 중간 층에 들어가는 Ce-TZP 중의 $Al_2$O$_3$함량이 30 vol.% 정도에 이르면 층간의 서로 다른 소결밀도 및 수축율, 열팽창계수 때문에 층간 소결 결함이 생겨 층간에서 균열의 전파가 큰 영향을 받음을 알 수 있었다. 반면 중간층의 $Al_2$O$_3$함량이 적을 경우 층간 결함이 생기지 않아 층간에서 균열의 전파가 별 영향을 받지 않음을 알 수 있었다.

• Korean Journal of Materials Research
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• v.19 no.8
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• pp.412-416
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• 2009

In this study, 3 mol% yttria-tetragonal zirconia polycrystal (3Y-TZP) nanoparticles were synthesized by the glycothermal method under various reaction temperatures and times. The co-precipitated precursor of 3Y-TZP was prepared by adding $NH_4OH$ to starting solutions, and then the mixtures were placed in an autoclave reactor. Tetragonal yttria-doped zirconia nanoparticles were afforded through a glycothermal reaction at a temperature as low as $220^{\circ}C$, using co-precipitated gels of $ZrCl_4$ and $YCl_3{\cdot}6H_2O$ as precursors and 1,4-butanediol as the solvent. The synthesized 3Y-TZP particles were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and Raman spectroscopy. The 3Y-TZP particles have a stable tetragonal phase only at glycothermal temperatures above $200^{\circ}C$. To investigate phase transition, the 3Y-TZP particles were heat treated from 400 to $1400^{\circ}C$ for 2 h. Raman analysis indicated that, after heat treatment, the tetragonal phase of the 3Y-TZP particles remained stable. The results of this study, therefore, suggest that 3Y-TZP powders can be prepared by the glycothermal method.

• Journal of the Korean Ceramic Society
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• v.27 no.8
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• pp.971-978
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• 1990

The ifluence of transformability and stabilized effects in tetragonal phase on the isothermal phase transformation of Y-TZP at low temperature were investigated. The transformability of Y-TZP powders were gradually increased with calcination temeprature and reached maximum at critical temperature, but when the Y-TZP powders were calcined above critical temperature, transformability of Y-TZP were gradually decreased with increasing calcination temperature. It was concluded that maximum transformability was appeared because particle size effects decreased and constrain effects increased with calcined temperature. The isothermal phase transformation during aging at 25$0^{\circ}C$ only observed in Y-TZP stabilized by constrain effects and the amounts of transformation during aging at 25$0^{\circ}C$ only observed in Y-TZP stabilized by constrain effects and the amount of transformed monoclinic phase during aging decreased with increasing constrain effects. From these results, the mechanism of isothermal phase transformation and degradation behaviors at low temperature in Y-TZP was concluded that occurred by decreasing of constrain effects due to stress relaxation at grian boundary.

• Korean Journal of Clinical Pharmacy
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• v.27 no.2
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• pp.83-91
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• 2017

Background: Piperacillin/tazobactam (TZP) is an antibiotic against a broad spectrum of gram-positive, gram-negative, and aerobic and anaerobic strains of bacteria. Due to changes in its pharmacokinetic and pharmacodynamic parameters by TZP-treated patients' renal functions and obesity, it is important to administrate and monitor TZP based on their renal functions and Body Mass Index (BMI) levels. The purpose of this study was to determine the appropriateness of administration doses of TZP based on renal functions of obese cancer patients in a tertiary hospital. Methods: This study was retrospectively conducted with obese cancer patients with $BMI{\geq}30kg/m^2$ in a tertiary hospital, Korea from September 2004 to August 2014. Data were collected through Electronic Medical Record (EMR) which contained laboratory data and TZP dosing of each patient. Results: Among 7,058 patients during the study period, 102 prescriptions were selected based on inclusion and exclusion criteria and classified by their renal functions. Although TZP should be used based on patients' renal functions to adjust its dose, its initial dose and dosing interval were consistently used without considering patients' renal functions on a regular basis. Especially, in the comparison with FDA dosing standard of TZP, approximately twice patients with $20mL/min{\leq}CrCl{\leq}40mL/min$ received domestically 4.5 g instead of 2.25 g as the TZP starting dose. Conclusion: The appropriate doses of TZP were administered to almost all of obese cancer patients; however, the recommended TZP dose was different between Korea and other countries by twice the amount. Further related studies are necessary to clearly determine the results, to optimize TZP treatment for obese patients with cancer in clinical practice, and to design and develop new TZP formulations for them in pharmaceutical industry.

• Journal of the Korean Ceramic Society
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• v.27 no.1
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• pp.55-61
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• 1990

Effect of Al2O3 addition on the mechanical properties and microstructure of Ce-TZP were studied. 12, 14, 16Ce-TZP containing 0-40wt% Al2O3 were prepared by sintering at 155$0^{\circ}C$ for 2h. in air. Density, linear shrinkage, bending strength, Vickers hardness, microstructuer and the amount of stress induced phase transformation were examined. Vickers hardness increased linearly with increasing amounts of Al2O3. The amount of transformation and fracture toughness decreased linearly with increasing amount of Al2O3. Linear shrinkage and relative density decreased with increasing Al2O3 content in all composition of Ce-TZP. Grain growth of Ce-TZP was inhibited by Al2O3 dispersion and fracture mode of Ce-TZP/Al2O3 composites transformed from intergranular to transgranular fracture as the amount of Al2O3 increased. TEM observation revealed that Al2O3 particles were located mainly at grain boundaries of ZrO2.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.10 no.2
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• pp.122-127
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• 2000

Microstructural evolutions in ceria-stabilized zirconia (Ce-TZP) and alumina-dispersed Ce-TZP ceramics were investigated as functions of doping and annealing conditions. All of sintered specimens showed the relative density over 99 %. Sintered specimens had linear grain boundaries and normal grain shapes, but ceria-doped specimens had irregular grain shapes and nonlinear grain boundaries due to the diffusion-induced grain boundary migration during annealing at $1650^{\circ}C$ for 2 h. Mean grain boundary length of Ce-TZP with irregular grain shapes was higher than that of normal grain shapes, and was a value of 23pm at the maximum. Alumina particles dispersed in Ce-TZP inhibited the grain growth of zirconia particles. $Al_2O_3$Ce-TZP doped with ceria and annealed at $1650^{\circ}C$ for 2 h showed irregular grain shapes as well as small grain size. Added alumina particles showed the grain growth during sintering or annealing, and they changed the position from grain boundary to inside of the grains during the annealing. The specimens with normal grain shapes showed an intergranular fracture mode, whereas the specimens with irregular grain shapes showed a transgranular fracture mode during the crack propagation.

• Journal of the Korean Ceramic Society
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• v.42 no.6 s.277
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• pp.417-424
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• 2005

Although a lot of studies in fracture toughness of Y-TZP ceramics for structural applications have been done, it remains an important challenge to be able to improve fracture toughness of Y-TZP ceramics. In this research, milling method adding monoclinic zirconia and $Al_2O_3$ to 3Y-TZP was introduced to improve the fracture toughness of 3Y-TZP. Experimental results showed that addition of small amount of $Al_2O_3$ causes to make lots of oxygen vacancies (VO) by substituting $Al^{3+}$ for $Zr^{4+}$. It is believed that the produced vacancies provides useful routes far mass transfer. Y-TZP ceramics having higher microhardness and better fracture toughness was fabricated by sintering at $1400^{\circ}C$.