Despite having many attractive properties, ZrO2 ceramic has a low fracture toughness which limits its wide application. One of the most obvious tactics to improve its mechanical properties has been to add a reinforcing agent to formulate a nanostructured composite material. Nanopowders of ZrO2 and Cr were synthesized from CrO3 and Zr powder by high energy ball milling for 10 h. Dense nanocrystalline 2/3Cr-ZrO2 composite was consolidated by a high-frequency induction heated sintering method within 5 min at 600˚C from mechanically synthesized powder. The method was found to enable not only rapid densification but also the inhibition of grain growth, preserving the nano-scale microstructure. Highly dense 2/3Cr-ZrO2 composite with relative density of up to 99.5% was produced under simultaneous application of a 1 GPa pressure and the induced current. The hardness and fracture toughness of the composite were 534 kg/mm2 and 7MPa·m1/2, respectively. The composite was determined to have good biocompatibility.

Thermal barrier coatings(TBCs) are being applied in many industrial fields such as thermal power generation, aviation and seasonal fields. ZrO2-Y2O3(8%) thermal spray coating powders are commercially used as thermal-barrier coating materials to protect against oxidation and corrosion of heat-resistant alloys at elevated temperatures. Currently, ZrO2-Y2O3(8%) thermal-spray powder is made using the industrial co-precipitation process, which is very complex and requires a lot of time. In this study, orthorhombic ZrO2 and Y2O3 powders were fabricated by mechanical mixing, which is more economical than the co-precipitation process. A tetragonal, yttria-stabilized zirconia(YSZ) coating-layer was produced by plasma spraying, using orthorhombic ZrO2-Y2O3(8%) powder. Our experimental results indicate that ZrO2-Y2O3(8%) mixed powder can be used economically in industry because it is no longer necessary to make this powder by liquid and gas-phase methods.

ZrO2 films were coated on aluminum etching foil by the sol-gel method to apply ZrO2 as a dielectric material in an aluminum(Al) electrolytic capacitor. ZrO2 films annealed above 450˚C appeared to have a tetragonal structure. The withdrawal speed during dip-coating, and the annealing temperature, influenced crack-growth in the films. The ZrO2 films annealed at 500˚C exhibited a dielectric constant of 33 at 1 kHz. Also, uniform ZrO2 tunnels formed in Al etch-pits 1μm in diameter. However, ZrO2 film of 100-200 nm thickness showed the withstanding voltage of 15 V, which was unsuitable for a high-voltage capacitor. In order to improve the withstanding voltage, ZrO2-coated Al etching foils were anodized at 300 V. After being anodized, the Al2O3 film grew in the directions of both the Al-metal matrix and the ZrO2 film, and the ZrO2-coated Al foil showed a withstanding voltage of 300 V. However, the capacitance of the ZrO2-coated Al foil exhibited only a small increase because the thickness of the Al2O3 film was 4-5 times thicker than that of ZrO2 film.

Lanthanum/gadolinium zirconate coatings are deposited via suspension plasma spray with suspensions fabricated by a planetary mill and compared with hot-pressed samples via solid-state reaction. With increase in processing time of the planetary mill, the mean size and BET surface area change rapidly in the case of lanthanum oxide powder. By using suspensions of planetary-milled mixture between lanthanum or gadolinium oxide and nano zirconia, dense thick coatings with fully-developed pyrochlore phases are obtained. The possibilities of these SPS-prepared coatings for TBC application are also discussed.

Yttria-stabilized zirconia (YSZ) coatings are fabricated via suspension plasma spray (SPS) for thermal barrier applications. Three different suspension sets are prepared by using a planetary mill as well as ball mill in order to examine the effect of starting suspension on the phase evolution and the microstructure of SPS prepared coatings. In the case of planetary-milled commercial YSZ powder, a deposited thick coating turns out to have a dense, vertically-cracked microstructure. In addition, a dense YSZ coating with fully developed phase can be obtained via suspension plasma spray with suspension from planetary-milled mixture of Y2O3 and ZrO2.

In this study, intermediate-mixed powders were prepared by loading zirconia powders initially in a ball-mill jar and loading alumina powders afterward; the initial-mixed powders were produced by loading zirconia and alumina powders together in the ball-mill jar. The effect of such differences in mixing method on the mechanical properties was investigated. In intermediate-mixed powders, the volume fraction of large particles slightly increased and, simultaneously, zirconia particles formed agglomerates that, due to early ball-mill loading of the zirconia powders only, were more dispersed than were the initial-mixed powders. For the intermediate-mixed powders, zirconia agglomerates were destroyed more quickly than were initial-mixed powders, so the number of dispersed zirconia particles rose and the inhibitory effect of densification due to the addition of a second phase was more obvious. In the microstructure of intermediate-mixed powders, zirconia grains were homogeneously dispersed and grain growth by coalescence was found to occur with increasing sintering temperature. For the initial-mixed powders, large zirconia grains formed by localized early-densification on the inside contacts of some zirconia agglomerates were observed in the early stages of sintering. The intermediate-mixed powders had slightly lower hardness values as a whole but higher fracture toughness compared to that of the initial-mixed powders.

This paper investigates the effect of prolonged high temperature exposure on concentric laminated Al2O3-ZrO2 composites. An ultrafine scale microstructure with a cellular 7 layer concentric lamination with unidirectional alignment was fabricated by a multi-pass extrusion method. Each laminate in the microstructure was 2-3μm thick. An alternate lamina was composed of 75%Al2O3-(25%m-ZrO2) and t-ZrO2 ceramics. The composite was sintered at 1500˚C and subjected to 1450˚C temperature for 24 hours to 72 hours. We investigated the effect of long time high temperature exposure on the generation of residual stress and grain growth and their effect on the overall stability of the composites. The residual stress development and its subsequent effect on the microstructure with the edge cracking behavior mechanism were investigated. The residual stress in the concentric laminated microstructure causes extensive micro cracks in the t-ZrO2 layer, despite the very thin laminate thickness. The material properties like Vickers hardness and fracture toughness were measured and evaluated along with the microstructure of the composites with prolonged high temperature exposure.

Ultra-fine zirconium carbide (ZrC) powder with nano-sized primary particles was synthesized by the carbothermal reduction method by using nano-sized and nano-sized graphite powders mixture. The synthesized ZrC powder was well dispersed after simple milling process. After heat-treatment at for 2 h under vacuum, ultra-fine ZrC powder agglomerates (average size, ) were facilely obtained with rounded particle shape and particle size of ~200 nm. Ultra-fine ZrC powder with an average particle size of 316 nm was obtained after ball milling process in a planetary mill for 30 minutes from the agglomerated ZrC powder.

Li2O-LiCl 용융염을 이용한 전해환원기술은 사용후핵연료로부터 우라늄 금속을 회수하기 위해 연구되고 있다. 이 전해환원기술에서는 Li2O가 촉매로 이용되기 때문에 그 농도를 유지하는 것은 매우 중요한 운전인자이다. ZrO2는 피복관의 주성분이 Zr이기 때문에 사용후핵연료에 불가피하게 함유되며, 본 연구에서는 Li2O를 촉매로 이용하는 전해환원공정에서 ZrO2의 거동을 살펴보았다. Li2O와 ZrO2의 화학반응과 전해환원공정 중에서의 생성물을 분석한 결과, Li2ZrO3와 Li4ZrO4가 주요하게 관찰되었고, 이는 Li2O의 손실을 가져오는 원인이 된다. 즉, ZrO2는 Li2O를 소모하는 역할을 하며, 반응생성물은 전기화학적으로 안정하기 때문에 Li2O의 손실이 불가피하게 된다.

This paper introduces an effect of a preparing -Ag composite on its mechanical properties and microstructure. In present study, -Ag was prepared by reduction-deposition route and wetting dispersive milling method, respectively. Two type of Ag powders (nano Ag and micron Ag size, respectively) were dispersed into powder during wetting dispersive milling in D.I. water. Each sample was sintered at for 2hr in atmosphere, and then several mechanical tests and analysis of microstructure were carried out by bending test, hardness, fracture toughness and fracture surface microstructure. As for microstructure, the Ag coated showed homogeneously dispersed Ag in in where pore defect did not appear. However, -nano Ag and -micro Ag composite appeared Ag aggregation and its pore defect, which carried out low mechanical property and wide error function value.

The characteristics of ceramics were influenced by the additives and the heat treatment that controls the microcrack behavior at grain boundaries. The effect of additives on ceramics were investigated in terms of mechanical properties and thermal expansion at high temperature. The were synthesized at , and for 2h by reaction sintering. The formation of phase was increased by additives that enhanced the volume of the microcrack that can lead to low thermal expansion. The mechanical properties of the stabilized ceramics were increased remarkably at , and due to the oneset of mechanical healing of grain-bondary microcracks at a high temperature. The amount of microcrack was decreased at lower sintering temperature that causes the increase of mechanical properties at high temperature.

Pure zirconia and x mol% calcia partially stabilized zirconia (x = 1.5, 3, and 8) nanopowders were synthesized by hydrothermal method with various reaction temperatures for 24 hrs. The precipitated precursor of pure zirconia and x mol% calcia doped zirconia was prepared by adding NH4OH to starting solutions; resulting sample was then put into an autoclave reactor. The optimal experimental conditions, such as reaction temperatures and times and amounts of stabilizer CaO, were carefully studied. The synthesized ZrO2 and x mol% CaO-ZrO2 (x = 1.5, 3, and 8) powders were characterized by XRD, SEM, TG-DTA, and Raman spectroscopy. When the hydrothermal temperature was as low as 160˚C, pure ZrO2 and x mol% CaO-ZrO2 (x = 1.5 and 3) powders were identified as a mixture of monoclinic and tetragonal phases. However, a stable tetragonal phase of zirconia was observed in the 8 mol% calcia doped zirconia nanopowder at hydrothermal temperature above 160˚C. To observe the phase transition, the 3 mol% CaO-ZrO2 and 8 mol% CaO-ZrO2 nanopowders were heat treated from 600 to 1000˚C for 2h. The 3 mol% CaO-ZrO2 heat treated at above 1000˚C was found to undergo a complete phase transition from mixture phase to monoclinic phase. However, the 8 mol% calcia doped zirconia appeared in the stable tetragonal phase after heat treatment. The result of this study therefore should be considered as the preparation of 8 mol% CaO-ZrO2 nanopowders via the hydrothermal method.

The preparation of Y2O3-doped ZrO2 nanoparticles in Igepal CO-520/cyclohexane reverse micelle solutions is studied here. In this work, we synthesized nanosized Y2O3-doped ZrO2 powders in a reverse micelle process using aqueous ammonia as the precipitant. In this way, a hydroxide precursor was obtained from nitrate solutions dispersed in the nanosized aqueous domains of a microemulsion consisting of cyclohexane as the oil phase, with poly (oxyethylene) nonylphenylether (Igepal CO-520) as the non-ionic surfactant. The synthesized and calcined powders were characterized by thermogravimetrydifferential thermal analysis (TGA-DTA), X-ray diffraction analysis (XRD) and transmission electron microscopy (TEM). The crystallite size was found to nearly identical with an increase in the water-to-surfactant (R) molar ratio. A FTIR analysis was carried to monitor the elimination of residual oil and surfactant phases from the microemulsion-derived precursor and the calcined powder. The average particle size and distribution of the synthesized Y2O3-doped ZrO2 were below 5 nm and narrow, respectively. The TG-DTA analysis showed that the phase of the Y2O3-doped ZrO2 nanoparticles changes from the monoclinic phase to the tetragonal phase at temperatures close to 530˚C. The phase of the synthesized Y2O3-doped ZrO2 when heated to 600˚C was tetragonal ZrO2.

The industrial manufacturing of YSZ products can be summarized as a three step process: a) hydrolysis of zirconyl chloride and mixing of other solutions, b) precipitation, and c) calcination. The addition of ammonia or OH- is essential in the precipitation process. However, a strong agglomeration was observed in the results of an ammonia or OH- addition. Thus, it is necessary to disperse the powders smoothly in order to improve the mechanical strength of YSZ. In this study, YSZ was synthesized using the urea stabilizer and hydrothermal method. YSZ powders were synthesized using a hydrothermal method with Teflon Vessels at 180˚C for 24 h. The mole ratio of urea to Zr was 0, 0.5, 1, and 2. The crystal phase, particle size, and morphologies were analyzed. Rectangular specimens (33 mm×8 mm×1±0.5 mm) for three-point bend tests were used in the mechanical properties evaluation. The crystalline of YSZ powders observed a tetragonal phase in the sample with a ratio of Zr:urea = 1:2 addition and a hydrothermal reaction time of 24 h. The average primary particle size of YSZ was measured to be 9 nm to 11 nm. The agglomerated particle size was measured from 15 nm to 30 nm. The three-point bending strength of the YSZ samples was 142.47 MPa, which is the highest value obtained for the Zr:urea = 1:2 ratio addition YSZ sample.

고온 무가습 조건에서 고분자 전해질 막의 수화성 및 수소이온 전도도 향상을 위해 sulfonated poly(aryl ether sulfone) 전해질 고분자에 sulfated ZrO2 (s-ZrO2)를 함침시킨 유-무기 복합막을 제조하였다. X-ray diffraction를 통해 s-ZrO2 의 구조적 특징과 입자크기를 확인하였으며 추가적으로 FT-IR 분석을 통해, s-ZrO2입자에 술폰산기가 화학적으로 결합되어 있음을 확인 할 수 있었다. 다양한 s-ZrO2 조성비를 가진 유-무기 복합막의 이점을 확인하기 위해서 이온교환능력, 함수율, 수소이온 전도도를 측정하였다. 실험결과, s-ZrO2의 조성비를 달리한 유-무기 복합막의 수소이온 전도도는, 5 wt% s-ZrO2를 함유한 유-무기 복합막의 경우에서, 상온 수화조건 뿐만 아니라 100℃ 이상의 무가습 조건에서 매우 높은 수소 이온 전도도를 나타내었다. 특히 120℃ 무가습 조건에서도 5 wt% s-ZrO2를 함유한 유-무기 복합막이 0.0018 S cm -1의 매우 높은 전도도를 나타냄으로써 100℃ 이상의 고온에서도 높은 수화도를 유지하는 유-무기 복합막의 제조가 가능하였다.

In this study, partially stabilized zirconia was synthesized using a chemical Y2O3 stabilizer and hydrothermal method. First, YCl3-6H2O and ZrCl2O-8H2O was dissolved in distilled water. Y-TZP (a Y2O3-doped toughened zirconia polycrystalline precursor) was also prepared by conventional co-precipitates in the presence of an excess amount of NH4OH solution under a fixed pH of 12. The Y-TZP precursors were filtered and repeatedly washed with distilled water to remove Cl- ions. ZrO2-Xmol%Y2O3 powder was synthesized by a hydrothermal method using Teflon Vessels at 180˚C for 6 h of optimized condition. The powder added with the Xmol%- Y2O3 (X = 0,1,3,5 mol%) stabilizer of the ZrO2 was synthesized. The crystal phase, particle size, and morphologies were analyzed. Rectangular specimens of 33mm×8mm×3 mm for three-point bend tests were used in the mechanical properties evaluation. A teragonal phase was observed in the samples, which contains more than 3 mol% Y2O3. The 3Y-ZrO2 agglomerated particle size was measured at 7.01μm. The agglomerated particle was clearly observed in the sample of 5 mol % Y2O3-ZrO2, and and the agglomerated particle size was measured at 16.4 um. However, a 20 nm particle was specifically observed by FE-SEM in the sample of 3 mol% Y2O3-ZrO2. The highest bending fracture strength was measured as 321.3 MPa in sample of 3 mol% Y2O3-ZrO2.

The effects of an addition of ZrO2 on the microstructure and electrical properties of MgO films as a protective layer for AC plasma display panels were investigated. MgO + a 200 ppm ZrO2 protective layer prepared by e-beam evaporation exhibited a secondary electron emission coefficient (γ) that was improved by 21% compared to that of a pure MgO protective layer. The relative density and Vickers hardness increased with a further addition of ZrO2. These results suggest that the discharge properties and optical properties of MgO protective layers are closely related to the relative density and Vickers hardness. The good optical and electrical properties of γ, at 0.080, a grain size of 19 μm and an optical transmittance of 91.93 % were obtained for the MgO + 200 ppm ZrO2 protective layer sintered at 1700˚C for 5 hrs.

A ZrO2 coating solution containing ZrO2 photo-catalysis, which is transparent in visible light, was prepared by the hydrolysis of alkoxide, and thin films on the SiO2 glass substrate were formed in a dipcoating method. These thin films were heat-treated at temperatures ranging from 250˚C-800˚C and their characteristics were subjected to thermal analysis, XRD, spectrometry, SEM, EDS, contact angle measurement, and AFM. Tetragonal ZrO2 phase was found in the thin film heat treated at 450˚C, and anatase TiO2 phase was detected in the thin film heat-treated at 600˚C and above. The thickness of the films was approximately 300 nm, and the roughness was 0.66 nm. Thus, the film properties are excellent. The films are super hydrophilic with a contact angle of 4.0˚; moreover, they have self-cleaning effect due to the photo catalytic property of anatase TiO2.