• The Journal of Advanced Prosthodontics
• /
• v.10 no.4
• /
• pp.259-264
• /
• 2018

PURPOSE. The purpose of this study was to evaluate the effect of the zirconia surface architecturing technique (ZSAT) on the bond strength between veneering porcelain and zirconia ceramic. MATERIALS AND METHODS. 20 sintered zirconia ceramic specimens were used to determine the optimal surface treatment time, and were randomly divided into 4 groups based on treatment times of 0, 1, 2, and 3 hours. After etching with a special solution, the surface was observed under scanning electron microscope, and then the porcelain was veneered for scratch testing. Sixty 3 mol% yttria-stabilized tetragonal zirconia polycrystal ceramic blocks were used for tensile strength testing; 30 of these blocks were surface treated and the rest were not. Statistical analysis was performed using ANOVA, the Tukey post-hoc test, and independent t-test, and the level of significance was set at ${\alpha}=.05$. RESULTS. The surface treatment of the zirconia using ZSAT increased the surface roughness, and tensile strength test results showed that the ZSAT group significantly increased the bond strength between zirconia and veneering porcelain compared to the untreated group (36 MPa vs. 30 MPa). Optimal etching time was determined to be 2 hours based on the scratch test results. CONCLUSION. ZSAT increases the surface roughness of zirconia, and this might contribute to the increased interfacial bond strength between zirconia and veneering porcelain.

• Journal of Powder Materials
• /
• v.28 no.5
• /
• pp.381-388
• /
• 2021

Zirconia has excellent mechanical properties, such as high fracture toughness, wear resistance, and flexural strength, which make it a candidate for application in bead mills as milling media as well as a variety of components. In addition, enhanced mechanical properties can be attained by adding oxide or non-oxide dispersing particles to zirconia ceramics. In this study, the densification and mechanical properties of YSZ-TiC ceramic composites with different TiC contents and sintering temperatures are investigated. YSZ - x vol.% TiC (x=10, 20, 30) system is selected as compositions of interest. The mixed powders are sintered using hot pressing (HP) at different temperatures of 1300, 1400, and 1500℃. The densification behavior and mechanical properties of sintered ceramics, such as hardness and fracture toughness, are examined.

• Journal of the Korean Society for Heat Treatment
• /
• v.36 no.4
• /
• pp.215-222
• /
• 2023

3Y-TZP (3 mol% yttria-stabilized tetragonal zirconia polycrystals, 3Y-TZP) ceramics are emerging as dental implant materials due to their superior optical and mechanical properties as well as excellent biophysical properties, in spite of low bioactivity. In this study, we investigated to sintered properties and microstructural defects of dental zirconia implants fabricated by ceramic injection molding and post-HIP (Hot isostatic pressing) processing and analyzed the processing parameters related with the obtainment of its high sinterd density. Sintered and microstructural parameters, i.e, apparent density, grain size and phase composition of zirconia implants fabricated by injection molding were dependent on the fixtute size and implant type. Maximum sintered density of 99.2% and minimum grain size of 0.3-0.4 ㎛ were obtained from large-scaled 2-body sample. In 1-body ceramic implant, high sintered density of 99.5% was obtained, but it had a little monoclinic phase and wide grain size distribution.

• Korean Journal of Materials Research
• /
• v.8 no.6
• /
• pp.505-512
• /
• 1998

In this study, two-layer thermal barrier coatings composed of plasma sprayed 0.3mm $ZrO_2(8wt% Y_2o_3)$ ceramic coating layer and O.lmm $NiCrAlCoY_20_3$ bond coating layer on AISI 316 were investigated microstructure of the coating, oxidation of the metallic bond coating and adhesive strength to evaluate the durability of coating layer after cyclic and isothermal test at 90$0^{\circ}C$. And quantitative phase analysis of $ZrO_2(8wt% Y_2o_3)$ ceramic coating was performed as a function of thermal exposure time using XRD technique. The results showed that the amount of m - 2rO, phase in the coating was slightly increased with increasing thermal exposure time at 90$0^{\circ}C$. The c/a ratio of t' - $ZrO_2$ in the as-sprayed coating was 1.0099 and slightly increased to 1.0115 after 100 hours heat treatment. It was believed that $Y_2O_3$ in high yttria tetragonaJ(t') was transformed to low yttria tetragonaJ(t) by $Y_2O_3$ diffusion with increasing thermal exposure time. The adhesive strength was gradually decreased as thermal exposure time increased. After the isothermal test, the failure predominantly occured in ceramic coating layer. On the other hand. the specimens after cyclic thermal test were mostly failed at bond coating/ceramic coating interface. The failure was oeeured by decreasing the bond strength between bond coating and oxide scale which were formed by oxidation of the metallic elements within bond coating and by thermal stress due to thermal expansion mismatches between the oxide scale and ceramic coating.

• Journal of the Korean Ceramic Society
• /
• v.48 no.6
• /
• pp.487-492
• /
• 2011

The effect of the application of lanthanum strontrium manganite and yttria-stabilized zirconia (LSM-YSZ) nano-composite fabricated by pulsed laser deposition (PLD) as a cathode of solid oxide fuel cell (SOFC) is studied. A gradient-structure thin-film cathode composed of 1 micron-thick LSM-YSZ deposited at an ambient pressure ($P_{amb}$) of 200 mTorr; 2 micron-thick LSM-YSZ deposited at a $P_{amb}$ of 300 mTorr; and 2 micron-thick lanthanum strontium cobaltite (LSC) current collecting layer was fabricated on an anode-supported SOFC with an ~8 micron-thick YSZ electrolyte. In comparison with a 1 micron-thick nano-structure single-phase LSM cathode fabricated by PLD, it was obviously effective to increase triple phase boundaries (TPB) over the whole thickness of the cathode layer by employing the composite and increasing the physical thickness of the cathode. Both polarization and ohmic resistances of the cell were significantly reduced and the power output of the cell was improved by a factor of 1.6.

• Journal of the Korean Ceramic Society
• /
• v.36 no.4
• /
• pp.391-402
• /
• 1999

Characteristics of composite electrolytes which were prepared by coating a thin film of YSZ (yttria sta-bilized zirconia : (ZrO2)0.92 (Y2O3)0.08) on YDC (yttria doped ceria : Ce0.8Y0.2O1.9) with mixed conductivity have been investigated in order to develop the low-temperature solid oxide fuel cell. The thickness (t) of spin-coated YSZ thin films after the heat-treatment at 600$^{\circ}C$ was increased proportionally to the sol con-centrations (C) while the decrease in its thickness with the spin rate ($\omega$) could be expressed in the e-quation of ln t=9.49-0.53 ln $\omega$(0.99mol//s sol conc.) When the sol concentration and the spin rate being less than 0.99 mol/l and higher than 1000 rpm respectively reliable YSZ/YDC composite electrolytes could be obtained by multi-coating although several micro-cracks were observed in singly coated YSZ film surfaces. The dense YSZ film with a 1$\mu\textrm{m}$ thickness was prepared by coating of 0.99 mol/l YSZ sol five-times at 2000 rpm followed by heat-treatment at 1400$^{\circ}C$ for 2h, The adhesion between YSZ film and YDC substrate was found to be very good. The open circuit voltages of H2/O2 single cell with YSZ/YDC composite electrolytes were 0.79∼0.82 V at 800$^{\circ}C$ and 0.75∼0.77V at 900$^{\circ}C$ The open circuit voltage was inversely proportioned to the thickness ratio of YSZ thin film (1$\mu\textrm{m}$) to YDC substrate(0.28-2.22 mm)

• Journal of the Korean Ceramic Society
• /
• v.38 no.11
• /
• pp.987-992
• /
• 2001

A refractory grade low-cost silicon nitride powder was chemically analyzed, purified, and gas pressure sintered with the sintering additives. As-received powder contained a significant amount of free-Si, 0.72 wt% of Fe, 0.5 wt% of al and 0.31 wt% of Ca. Oxygen and carbon contents of the powder were 3.3 wt% and 0.4 wt%, respectively, and it consisted of 96% of $\beta$-phase and 4% of $\alpha$-phase. After lowering the Fe content and nitriding treatment, the powder was sintered with 6 wt% yttria and 2 wt% alumina for 1 h between 1823 K and 2123 K in order to examine the sintering behavior. Fully dense samples were obtained by sintering at 2123k for 2h. For comparison, a commercially available high-grade powder was also sintered at the same time. The low-cost powder showed much slower densification rate than the high-grade powder. Fully dense sample prepared from the low-cost powder contained a number of coarse grains with a low aspect ratio, and its hardness, fracture toughness, flexural strength and thermal shock resistance were not as good as those of the sample prepared with the high-grade powder.

• Journal of the Korean Ceramic Society
• /
• v.38 no.7
• /
• pp.602-607
• /
• 2001

Zirconia powder containing 3 mol% yttria (3Y-PSZ) was casted on the cast iron substrate by plasma spraying method. Coated specimens were then heat treated at 500$\^{C}$ in nitrogen plasma. Wear tests were performed on nitrogen heat treated and non heat treated samples at temperatures from 25$\^{C}$ to 600$\^{C}$. Wear results showed that the friction coefficient and the wear loss of both the treated and the non-treated samples showed maximum value at 400$\^{C}$. These results were explained by low temperature thermal degradation due to the monoclinic transformation. Nitrogen plasma treatment significantly improved the tribological performance. The effect of nitrogen heat treatment on tribological behavior was explained by the increased micro-hardness and decreased monoclinic faction.

• Journal of the Korean Ceramic Society
• /
• v.24 no.3
• /
• pp.235-242
• /
• 1987

This study was about to make zirconia ceramics with yttria, using spraying precipitation method for the purpose of powder control. The powder properties and the characterization of sintered body, were studied. As the results, 1. The synthesized powder had homogeneity of spherical shape, and average particle size was 2-3 um. 2. Crystallization temperature increased with Y2O3 content. 3. Apparent density of sintered body (fired above 1500$^{\circ}C$) was higher than 98% of theoretical value in 3 mol% Y2O3 content. 4. High KIC values(19kg/㎣/2) in 3 mol % Y2O3 content resulted from sintering density increasement.

• Journal of the Korean Ceramic Society
• /
• v.35 no.3
• /
• pp.273-279
• /
• 1998

Unite cell of soid oxide fuel cell (SOFC) that consists of a dense yttria-stabilized zirconia(YSZ) electrolyte a porous nickel-YSZ cermet anode and a porous strontium- doped lanthanum manganate(LSM) cathod was fabricated from using pore former through co-firing technique. Initial sintering shrinkage rates of each layer were identified for fabricating SOFC. Heterogenous sintering was very effective in tailoring shrinkage rate for three layers. The powder tailoring necessary for shrinkage rate matching are as follows ; electrolyte of 60% TZ8YS/ 40% TZ8Y mixture anode of 51wt% NiO/49 wt% (70wt% TZ8YS/30 wt% UT ZrO2) mixture and cathode of 80% LSM/20% UT ZrO2 mixture . The overall sintering shrinkage rate differences of three layers using these compositions were maintained in a few percent.