• Title/Summary/Keyword: Yttria

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Change of phase transformation and bond strength of Y-TZP with various hydrofluoric acid etching

  • Mi-Kyung Yu;Eun-Jin Oh;Myung-Jin Lim;Kwang-Won Lee
    • Restorative Dentistry and Endodontics
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    • v.46 no.4
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    • pp.54.1-54.10
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    • 2021
  • Objectives: The purpose of this study was to quantify phase transformation after hydrofluoric acid (HF) etching at various concentrations on the surface of yttria-stabilized tetragonal zirconia polycrystal (Y-TZP), and to evaluate changes in bonding strength before and after thermal cycling. Materials and Methods: A group whose Y-TZP surface was treated with tribochemical silica abrasion (TS) was used as the control. Y-TZP specimens from each experimental group were etched with 5%, 10%, 20%, and 40% HF solutions at room temperature for 10 minutes. First, to quantify the phase transformation, Y-TZP specimens (n = 5) treated with TS, 5%, 10%, 20% and 40% HF solutions were subjected to X-ray diffraction. Second, to evaluate the change in bond strength before and after thermal cycling, zirconia primer and MDP-containing resin cement were sequentially applied to the Y-TZP specimen. After 5,000 thermal cycles for half of the Y-TZP specimens, shear bond strength was measured for all experimental groups (n = 10). Results: The monoclinic phase content in the 40% HF-treated group was higher than that of the 5%, 10%, and 20% HF-treated groups, but lower than that of TS-treated group (p < 0.05). The 40% HF-treated group showed significantly higher bonding strength than the TS, 5%, and 10% HF-treated groups, even after thermal cycling (p < 0.05). Conclusions: Through this experiment, the group treated with SiO2 containing air-borne abrasion on the Y-TZP surface showed higher phase transformation and higher reduction in bonding strength after thermal cycling compared to the group treated with high concentration HF.

Formation of Phases and Mechanical Properties of YSZ-Based Thermal Barrier Coating Materials Doped with Rare Earth Oxides (희토류 산화물이 첨가된 YSZ 기반의 열차폐 코팅용 소재의 상 형성 및 기계적 특성)

  • Yong Seok Choi;Gye Won Lee;Sahn Nahm;Yoon suk Oh
    • Journal of Powder Materials
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    • v.30 no.5
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    • pp.402-408
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    • 2023
  • This study focused on improving the phase stability and mechanical properties of yttria-stabilized zirconia (YSZ), commonly utilized in gas turbine engine thermal barrier coatings, by incorporating Gd2O3, Er2O3, and TiO2. The addition of 3-valent rare earth elements to YSZ can reduce thermal conductivity and enhance phase stability while adding the 4-valent element TiO2 can improve phase stability and mechanical properties. Sintered specimens were prepared with hot-press equipment. Phase analysis was conducted with X-ray diffraction (XRD), and mechanical properties were assessed with Vickers hardness equipment. The research results revealed that, except for Z10YGE10T, most compositions predominantly exhibited the t-phase. Increasing the content of 3-valent rare earth oxides resulted in a decrease in the monoclinic phase and an increase in the tetragonal phase. In addition, the t(400) angle decreased while the t(004) angle increased. The addition of 10 mol% of 3-valent rare-earth oxides discarded the t-phase and led to the complete development of the c-phase. Adding 10 mol% TiO2 increased hardness than YSZ.

Electrochemical Characteristics of Anode-supported Solid Oxide Fuel Cells (연료극 지지형 고체산화물 연료전지의 전기화학적 특성)

  • Yoon Sung Pil;Han Jonghee;Nam Suk Woo;Lim Tae-Hoon;Hong Seong-Ahn;Hyun Sang-Hoon;Yoo Young-Sung
    • Journal of the Korean Electrochemical Society
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    • v.4 no.2
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    • pp.58-64
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    • 2001
  • YSZ ($8mol\%$ yttria-stabilized zirconia)-modified LSM $(La_{0.85}Sr_{0.15}MnO_3)$ composite cathodes were fabricated by formation of YSZ film on triple phase boundary (TPB) of LSM/YSZ/gas. The YSZ coating film greatly enlarged electrochemical reaction sites from the increase of additional TPB. The composite cathode was formed on thin YSZ electrolyte (about 30 Um thickness) supported on an anode and then I-V characterization and AC impedance analyses were performed at temperature between $700^{\circ}C\;and\;800^{\circ}C$. As results of the impedance analysis on the cell at $800^{\circ}C$ with humidified hydrogen as the fuel and air as the oxidant, R1 around the frequency of 1000 Hz represents the anode Polarization. R2 around the frequency of 100Hz indicates the cathode polarization, and R3 below the frequency of 10 Hz is the resistance of gas phase diffusion through the anode. The cell with the composite cathode produced power density of $0.55\;W/cm^2\;and\;1W/cm^2$ at air and oxygen atmosphere, respectively. The I-V curve could be divided into two parts showing distinctive behavior. At low current density region (part I) the performance decreased steeply and at high current density region (part II) the performance decreased gradually. At the part I the performance decrease was especially resulted from the large cathode polarization, while at the part H the performance decrease related to the electrolyte polarization.

Effect of various surface treatment methods of highly translucent zirconia on the shear bond strength with resin cement (고투명도 지르코니아의 다양한 표면처리 방법이 레진시멘트와의 전단결합강도에 미치는 영향)

  • Yu-Seong Kim;Jin-Woo Choi;Hee-Kyung Kim
    • The Journal of Korean Academy of Prosthodontics
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    • v.61 no.3
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    • pp.179-188
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    • 2023
  • Purpose. The purpose of this study was to evaluate the effect of surface treatments on the shear bond strength of two types of zirconia (3-TZP and 5Y-PSZ) with resin cement. Materials and methods. Two different types of zirconia specimens with a fully sintered size of 14.0×14.0×2.0 mm3 were prepared, polished with 400, 600, and 800 grit silicon carbide paper, and buried in epoxy resin. They were classified into four groups each control, sandblasting, primer, and sandblasting & primer. Cylindrical resin adhered to the surface-treated zirconia with resin cement. It was stored in distilled water (37℃) for 24 hours, and a shear bond strength test was performed. The normality of the experimental group was confirmed with the Kolmogorov-Smirnov & Shapiro-Wilk test. The interaction and statistical difference were analyzed using a two-way ANOVA. A post-hoc analysis was performed using Dunnett T3. Results. As a result of two-way ANOVA, there was no significant difference in shear bonding strength between zirconia types (P > .05), but there was a significant correlation in the sandblasting, primer, and alumina sandblasting & primer group (P < .05). Dunnett T3 post-test showed that, regardless of the type of zirconia, shear bonding strength was sandblasting & primer > Primer > sandblasting > control group (P < .05). Conclusion. There was no difference in shear bond strength between the types of zirconia. The highest shear bond strength was shown when the mechanical and chemical treatments of the zirconia surface was performed simultaneously.

The Effect of Veneering Techniques on the Color Parameters of Y-TZP Based All Ceramic Restoration of Varying Ceramic Core Thickness (지르코니아 코어 두께에 따른 전부도재관의 상부도재 축성방법이 보철물 색조에 미치는 영향)

  • Huh, Sung-Yoon;Son, Ho-Jung;Kim, Hae-Young;Kim, Jae-Hong
    • Journal of dental hygiene science
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    • v.12 no.2
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    • pp.123-129
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    • 2012
  • The aim of study was to compare the color parameters and mean color difference of porcelain specimens by different veneering technique in order to examine the effect of veneering technique on esthetics of yttria-stabilized tetragonal zirconia polycrystalline(Y-TZP) all ceramic restoration. Three groups of square-shaped core ceramic specimens(14mm in diameter and 0.3, 0.5, 0.7 mm) and two groups of veneering ceramic specimen were prepared for analysis. Color parameter($L^*,a^*,b^*$) and color difference of zirconia core squares and core-veneer specimens were measured with ShadeEye $NCC^{(R)}$ spectrophotometer, respectively. Mean color difference(${\Delta}E^*$)were calculated using color difference formula. Two-way analysis of variance(ANOVA) combined with a Tukey multiple-range test were used to analysis the data(${\alpha}=0.05$). ${\Delta}E^*$ values were not significantly affected by core thickness and veneering porcelain(p=0.083). The color differences(${\Delta}E^*$) of core-veneer specimens with 0.5, 0.7 mm-A1,A2,A3.5 shade were mostly below 3.7 which was within the clinically acceptable range, while color differences between 0.3 mm-A1,A2 showed more than 3.7. All-ceramic system has color characteristics that clinicians have to consider when selecting materials. Also, manufacturers of different porcelain systems must make every effort to achieve color reproducibility.

Fabrication of 8YSZ-$Al_2O_3$ solid oxide full cell (SOFC) electrolyte by a spark plasma sintering method (방전 플라즈마 소결법을 이용한 8YSZ-$Al_2O_3$ 고체 산화물 연료전지 전해질 제조)

  • Kim Jae Kwang;Choi Bong Geun;Yang Jae Kyo;Choa Yong Ho;Shim Kwang Bo
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.15 no.1
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    • pp.16-20
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    • 2005
  • In order to improve electrical conductivity and mechanical properties of 8YSZ SOFC electrolyte material, we used Al₂O₃ as an additive and applied the spark plasma sintering (SPS) method. The sintered bodies were densified above 96 % of theoretical density at 1200℃ and possessed microstructures composed of homogeneous grains less than 1 ㎛ in size. The addition of Al₂O₃ improved fracture toughness and bending strength by inhibiting grain growth of 8YSZ and increased total ionic conductivity because grain interior conductivity appeared to remain constant and grain boundary conductivity increased. It was assumed that the dissolution of Al₂O₃ into 8YSZ which was inevitable problem at commercial sintering method was effectively prohibited by the SPS technique with a relatively low sintering temperature and the reaction between Al₂O₃ and SiO₂ present at grain boundary to produce the crystalline Al/sub 2-x/Si/sub l-y/O/sub 5/ phase, resulting in the increase of grain boundary conductivity.

Effects of $Y_2O_3$ addition and sintering time on denazification and thermal conductivity of AlN ceramics during hot-press sintering ($Y_2O_3$ 첨가와 소결 시간이 AlN 세라믹스의 일축 가압 소결 거동 및 열전도도에 미치는 영향)

  • Chae, Jae-Hong;Park, Joo-Seok;Ahn, Jong-Pil;Kim, Kyoung-Hun;Lee, Byung-Ha
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.18 no.6
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    • pp.237-241
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    • 2008
  • Hot-press sintering of AlN ceramics were carried out with $Y_2O_3$ as sintering additive at a sintering temperature $1,750{\sim}1,850^{\circ}C$. The effect of $Y_2O_3$ addition and sintering time on sintering behavior and thermal conductivity of AlN ceramics was investigated. $Y_2O_3$ added AlN showed noticeably higher denazification rate than pure AlN. The thermal conductivity of AlN specimens was promoted by the addition of $Y_2O_3$ in spite of the formation of YAG secondary phase in AlN grain boundaries and grain boundary triple junction because $Y_2O_3$ addition could reduced the oxygen contents in AlN lattice which is primary factor of thermal conductivity. Typically, the thermal conductivity of 5 wt% $Y_2O_3$ added specimen was dramatically improved by the increase of sintering time because the elimination of YAG secondary phases from the grain boundary due to the evaporation, as well as the grain-growth of AlN grains.

Effect of Metal Chloride Coloring Liquids on Color and Strength Changes of Tetragonal Zirconia Polycrystals (금속염화물 착색제 침투가 정방정 지르코니아 다결정체의 색조와 강도 변화에 미치는 영향)

  • Oh, Jong-Jin;Noh, Hyeong-Rok
    • Journal of dental hygiene science
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    • v.15 no.5
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    • pp.577-584
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    • 2015
  • The purpose of this study was to evaluate the effect of metal chloride infiltration treatment on color and strength changes of the yttria-stabilized tetragonal zirconia polycrystals (Y-TZP). Fifty disc specimens were prepared with a Y-TZP powder (ZPEX; Tosoh, Japan). Thirty different metal chloride solutions containing 0.03~0.08 wt% chromium and 0.03~0.07 wt% terbium ions were prepared. Presintered Y-TZP specimens were soaked in metal chloride coloring liquids for 3 minutes and sintered in air at $1,450^{\circ}C$ for 2 hours. The color of the specimens was measured with spectrophotometer and color difference (${\Delta}E^*$) was obtained based on the CIE $L^*$, $a^*$, $b^*$ color coordinate values. To evaluate the effect of metal chloride infiltration strength changes, the biaxial flexural test was performed at crosshead speed 0.5 mm/min. Colors of the sintered Y-TZP showed the colors of Vita shade guide A1, A2 and A3 with the infiltration of chromium and terbium chloride solutions. Density of the sintered Y-TZP increased by the infiltration of chromium and terbium chloride solutions. Bi-axial flexural strength of the sintered Y-TZP did not show statistically significant differences by the infiltration of chromium and terbium chloride solutions (p>0.05). Chromium and terbium chloride did not affect the crystal phase of zirconia, and all specimens showed tetragonal phase. Accordingly, this study suggests that chromium and terbium chlorides can make colored zirconia while adding in a liquid form. The color of colored zirconia differ from that of vita shade guide but it can use all ceramic restoration as substructure in dental clinic.

Cathode materials advance in solid oxide fuel cells (고체산화물연료전지 공기극의 재료개발동향)

  • Son, Young-Mok;Cho, Mann;Nah, Do-Baek;Kil, Sang-Cheol;Kim, Sang-Woo
    • Journal of Energy Engineering
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    • v.19 no.2
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    • pp.73-80
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    • 2010
  • A solid oxide fuel cells(SOFC) is a clean energy technology which directly converts chemical energy to electric energy. When the SOFC is used in cogeneration then the efficiency can reach higher than 80%. Also, it has flexibility in using various fuels like natural gases and bio gases, so it has an advantage over polymer electrolyte membrane fuel cells in terms of fuel selection. A typical cathode material of the SOFC in conjunction with yttria stabilized zirconia(YSZ) electrolyte is still Sr-doped $LaMnO_3$(LSM). Recently, application of mixed electronic and ionic conducting perovskites such as Sr-doped $LaCoO_3$(LSCo), $LaFeO_3$(LSF), and $LaFe_{0.8}Co_{0.2}O_3$(LSCF) has drawn much attention because these materials exhibit lower electrode impedance than LSM. However, chemical reaction occurs at the manufacturing temperature of the cathode when these materials directly contact with YSZ. In addition, thermal expansion coefficient(TEC) mismatch with YSZ is also a significant issue. It is important, therefore, to develop cathode materials with good chemical stability and matched TEC with the SOFC electrolyte, as well as with high electrochemical activity.

Evaluation of Thermal Durability for Thermal Barrier Coatings with Gradient Coating Thickness (경사화 두께를 갖는 열차폐 코팅의 열적 내구성 평가)

  • Lee, Seoung Soo;Kim, Jun Seong;Jung, Yeon-Gil
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.21 no.8
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    • pp.248-255
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    • 2020
  • The effects of the coating thickness on the thermal durability and thermal stability of thermal barrier coatings (TBCs) with a gradient coating thickness were investigated using a flame thermal fatigue (FTF) test and thermal shock (TS) test. The bond and topcoats were deposited on the Ni-based super-alloy (GTD-111) using an air plasma spray (APS) method with Ni-Cr based MCrAlY feedstock powder and yttria-stabilized zirconia (YSZ), respectively. After the FTF test at 1100 ℃ for 1429 cycles, the bond coat was oxidized partially and the thermally grown oxide (TGO) layer was observed at the interface between the topcoat and bond coat. On the other hand, the interface microstructure of each part in the TBC specimen showed a good condition without cracking or delamination. As a result of the TS test at 1100 ℃, the TBC with gradient coating thickness was initially delaminated at a thin part of the coating layer after 37 cycles, and the TBC was delaminated by more than 50% after 98 cycles. The TBCs of the thin part showed more oxidation of the bond coat with the delamination of topcoat than the thick part. The thick part of the TBC thickness showed good thermal stability and oxidation resistance of the bond coat due to the increased thermal barrier effect.