• 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.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.24 no.6
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• pp.268-273
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• 2014

$Y_2O_3$ ceramic specimens were fabricated from the granular powder, obtained by spray drying process from the slurry. The slurry was prepared by mixing PVA binder, NaOH for Ph control, PEG and $Y_2O_3$ powder. The $Y_2O_3$ specimen was shaped in size of ${\phi}14mm$ and then sintered at $1650^{\circ}C$. The characteristics, microstructure, densities and plasma resistance of the $Y_2O_3$ specimens were investigated with the function of forming pressure and sintering time. $Y_2O_3$ specimens were exposed under the $CHF_3/O_2/Ar$ plasma, the dry etching treatment of specimens was carried out by the physical reaction etching of $Ar^+$ ion beam and the chemical reaction etching of $F^-$ ion decomposed from $CHF_3$. With increasing sintering time, $Y_2O_3$ specimens showed relatively high density and strong resistance in plasma etching test.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.19 no.1
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• pp.33-38
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• 2009

The effect of ${Y_2}{O_3}$ as a sintering additive on thermal conductivity and microstructure of pressureless sintered AIN ceramics was investigated at sintering temperature range from 1,700 to $1,900^{\circ}C$. ${Y_2}{O_3}$ added AIN specimens showed higher densification rate than pure AIN because of the formation of the yttrium aluminates secondary phase by reaction of ${Y_2}{O_3}$ and ${Al_2}{O_3}$ of AIN surface. The thermal conductivity of AIN specimens was promoted by the addition of ${Y_2}{O_3}$ in spite of the formation of secondary phase in AIN gram boundaries and grain boundary triple junction, because ${Y_2}{O_3}$ addition could reduced the oxygen contents in AIN lattice which is primary factor of thermal conductivity. The them1al conductivity of AIN specimens was promoted by increasing sintering time because the increases of average grain size and the elimination of secondary phases from the grain boundary due to the evaporation. Particularly. the thermal conductivity of AIN specimen sintered at $1,900^{\circ}C$ for 5 hours improved over 20 %. $141\;Wm^{-1}K^{-1}$, compared with the specimen sintered at $1,900^{\circ}C$ for 1 hour.

• Journal of the Institute of Electronics Engineers of Korea TE
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• v.39 no.4
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• pp.341-349
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• 2002

Electrical, mechanical and sinterability properties of yttria-stabilized zirconia doped with 5.35wt% $Y_2$O$_3$(Y$_2$O$_3$- containing stabilized zirconia : YSZ) were studied as a function of $Al_2$O$_3$, CoO, Fe$_2$O$_3$ and MnO$_2$ addition. The ratio of monoclinic phase to tetragonal phase was changed by the addition of $Al_2$O$_3$, CoO, Fe$_2$O$_3$ and MnO$_2$ to 8.00 wt% and sintered density decreased with increasing $Al_2$O$_3$, CoO, Fe$_2$O$_3$ and MnO$_2$ addition. Fracture toughness increased with the increase of monoclinic to tetragonal phase ratio and was maximum at about 18%. When transition metals such as CoO, Fe$_2$O$_3$ or MnO$_2$ was added more than 1.5 wt%, the electrical conductivity of YSZ increased. But $Al_2$O$_3$ hardly affected the electrical conductivity of YSZ. The addition of $Al_2$O$_3$, CoO, Fe$_2$O$_3$ and MnO$_2$ into YSZ resulted in the more complex behavior of fracture toughness and hardness variation and the specimen with 1.5wt%-Fe$_2$O$_3$, 3.0wt%-Al$_2$O$_3$ and 1.5wt%-CoO showed the monoclinic to tetragonal phase ratio of 18% and the highest toughness of 10.8 MPa.m$^{1}$2/ and Vickers hardness of 1201 kgf/mm$^2$.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.29 no.6
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• pp.308-316
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• 2019

Electron beam physical vapor deposition (EBPVD) is a conventional method to fabricate thermal barrier coating (TBC) of high temperature airfoil engine parts, such as blade etc. for its high temperature structural stability from the nature of columnar growth behavior. For the high quality of TBC by EBPVD, the structural factors, such as growth behavior, thickness uniformity and so on, should be managed to obtain the coating which satisfied the required specifications of usable level of mechanical and thermal properties. In this study, the growth behavior and structure variations of 7YSZ (7 wt% yttria stabilized zirconia) coatings with different configurational deposition parameters for the specimens which have turbine blade shape mock-up were investigated. Growth behavior of coatings were studied by comparing computational modeling of evaporation behavior with actual deposition process using e-beam source.

• Journal of dental hygiene science
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• v.13 no.3
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• pp.290-295
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• 2013

The purpose of this study was to investigate the shear bond strength between various commercial all-ceramic system core and veneering ceramics, and evaluate the clinical stability by comparing the conventional metal ceramic system. The test samples were divided into three groups: Ni-Cr alloy (metal bond), yttria-stabilized, tetragonal zirconia polycrystal (Y-TZP) (zirconia bond), lithium disilicate (lithium disilicate bond). The veneering porcelain recommended by the manufacturer for each type of material was fired to the core. After firing, the specimens were subjected to shear force in a universal testing machine. Load was applied at a crosshead speed of 0.50 mm/min until failure. Average shear strengths (mega pascal) were analyzed with a one-way analysis of variance and the Tukey test (${\alpha}$=0.05). The mean shear bond strength${\pm}$SD in MPa was $44.79{\pm}2.31$ in the Ni-Cr alloy group, $28.32{\pm}4.41$ in the Y-TZP group, $15.91{\pm}1.39$ in the Lithium disilicate group. The ANOVA showed a significant difference among groups (p<0.05). None of the all-ceramic system core and veneering ceramics could attain the high bond strength values of the metal ceramic combination.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.8 no.1
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• pp.33-39
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• 2010

The electrolytic reduction of a spent oxide fuel involves a liberation of the oxygen in a molten LiCl electrolyte, which results in a chemically aggressive environment that is too corrosive for typical structural materials. Accordingly, it is essential to choose the optimum material for the processing equipment that handles the high molten salt. In this study, hot corrosion studies were performed on bare as well as coated superalloy specimens after exposure to lithium molten salt at $675^{\circ}C$ for 216 h under an oxidizing atmosphere. The IN713LC superalloy specimens were sprayed with an aluminized NiCrAlY bond coat and then with an $Y_2O_3$ top coat. The bare superalloy reveals an obvious weight loss due to spalling of the scale by the rapid scale growth and thermal stress. The chemical and thermal stability of the top coat has been found to be beneficial for increasing to the corrosion resistance of the structural materials for handling high temperature lithium molten salts.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.22 no.2
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• pp.73-77
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• 2012

Co-(0.8 wt%) and Ce-(0.4 wt%) doped cubic zirconia ($ZrO_2$ : $Y_2O_3$ = 80 : 20, 70 : 30, 60 : 40, 50 : 50 wt%) single crystals grown by a skull melting method were heat-treated in $N_2$ at $1000^{\circ}C$ for 5 hrs. The orange, yellowish brown and brown colored as-grown single crystals were changed into either brownish red, yellow and green color after the heat treatment. Before and after the heat treatment, the YSZ (yttria-stabilized zirconia) single crystals were cut for wafer form (${\phi}6.5mm{\times}t2mm$). The optical and structural properties were examined by UV-VIS spectrophotometer and X-ray diffraction. Absorption by $Ce^{3+}(^2F_{5/2,7/2}(4f){\rightarrow}^2T_g(5d^1))$, $Co^{2+}(^4A_2(^4F){\rightarrow}^4T_1(^4F)$ or $^4T_1(^4P))$ and $Co^{3+}$, change of ionization energy and lattice parameter were confirmed.

• Korean Chemical Engineering Research
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• v.50 no.3
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• pp.562-566
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• 2012

A novel design of tubular segmented-in-series(SIS) solid oxide fuel cell (SOFC) sub module was presented in this paper. The tubular ceramic support was fabricated by the extrusion technique. The NiO-YSZ anode and the yttria-stabilized zirconia (YSZ) electrolyte were deposited onto the ceramic support by dip coating method. After sintering at $1350^{\circ}C$ for 5 h, a dense and crack-free YSZ film was successfully fabricated. Also, the multi-layered cathode composed of LSM-YSZ composite, LSM and LSCF were coated onto the sintered ceramic support by dip coating method and sintered at $1150^{\circ}C$. The performance of the tubular SIS SOFC cell and sub module electrically connected by the Ag-glass interconnect was measured and analysed with different fuel flow and operating temperature.

• Korean Chemical Engineering Research
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• v.49 no.6
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• pp.786-789
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• 2011

In order to estimate the possibility of applying electrolytes generally used in solid oxide fuel cells(SOFCs) to direct carbon fuel cells(DCFCs), properties of YSZ(yttria stabilized zirconia) electrolyte were evaluated. In this study, vacuum slurry coating method was adapted to coat thin layer on anode support substrate. After sintering the electrolyte at $1400^{\circ}C$ for 5hrs, microstructure was analyzed by using SEM image. Also, gas permeability and ionic conductivity were measured to find out the potential possibility of electrolyte for DCFCs. The YSZ electrolyte represented dense coating layer and low gas permeability value. The ionic conductivity of YSZ electrolyte was high over $800^{\circ}C$. After measurement of the electrolyte properties, direct carbon fuel cell was fabricated and its performance was measured at $800^{\circ}C$.