• 한국재료학회지
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• 제16권8호
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• pp.485-489
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• 2006

The preparation conditions of $YBO_3$:Eu phosphor particles having the maximum photoluminescence intensity under vacuum ultraviolet in the spray pyrolysis were optimized. The $YBO_3$:Eu phosphor particles prepared from spray solution with stoichiometric amount of boric acid had the maximum photoluminescence intensity. The $YBO_3$:Eu phosphor particles with pure phases were formed at low post-treatment temperatures because of fast reaction of yttrium and boron components without volatilization of boron component. The prepared $YBO_3$:Eu phosphor particles by spray pyrolysis had fine size, narrow size distribution and regular morphology. The photoluminescence intensity of the prepared $YBO_3$:Eu phosphor particles under vacuum ultraviolet was 103% of the commercial $(Y,Gd)BO_3$:Eu phosphor particles.

• 한국표면공학회지
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• 제30권3호
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• pp.183-190
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• 1997

Fabrication and crystallization characteristics of yttria($T_2O_3$) stabilized zirconia(YSZ) thin film by sol-gel process were studied. YSZ sol was synthesized with zirconium n-propoxide($Zr(OC_3H_7)_4)$) and yttrium nitrate pentahydrate ($Y(NO_3)_3.5H_2O$). YSZ film was prepared by depositing the polymeric sol on porous $Al_2O_3$ substrate by spin-coating, and the film characteristics were investigated by FRIR, TG-DTA, XRD, DSC, optical microscopy and SEM. The film topology was uniform and cracks were not found. It was found that the annealing temperature and the concentration of stabilizer affect the crystallization of YSZ film. The YSZ film began to crystallize from amorphous to tetragonal phase at 40$0^{\circ}C$, and it was not converted to cubic structure until $1100^{\circ}C$. It seemed that the grains were formed over $700^{\circ}C$and the average grain size was obtained about 0.2$\mu\textrm{m}$.

• Journal of Astronomy and Space Sciences
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• 제35권1호
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• pp.19-30
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• 2018

The analysis of the high-resolution spectra of 31 Magellanic Clouds Cepheid variables enabled the identification of thorium lines. The abundances of thorium were found with spectrum synthesis method. The calculated thorium abundances exhibit correlations with the abundances of other chemical elements and atmospheric parameters of the program stars. These correlations are similar for both Clouds. The correlations of iron abundances of thorium, europium, neodymium, and yttrium relative to the pulsational periods are different in the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC), namely the correlations are negative for LMC and positive or close to zero for SMC. One of the possible explanations can be the higher activity of nucleosynthesis in SMC with respect to LMC in the recent several hundred million years.

• 대한화학회지
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• 제57권1호
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• pp.52-62
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• 2013

The interaction of titanium (IV), yttrium (III), zirconium (IV), palladium (II) and cerium (IV) with deprotonated enrofloxacin leads to the formation of the neutral or cationic mononuclear complexes. The isolated solid complexes have been characterized with physicochemical and spectroscopic techniques and thermogravimeteric analyses. The spectroscopic data indicate that the enrofloxacin ligand is on the deprotonated mode acting as bidentate ligand coordinated to the metal ions through the ketone oxygen and a carboxylato oxygen and the metal ions completed the coordination number with water molecules. The thermal decomposition mechanisms proposed for enrofloxacin and their metal complexes were discussed. The activation energies, $E^*$, enthalpies, ${\Delta}H^*$, entropies, ${\Delta}S^*$ and Gibbs free energies, ${\Delta}G^*$, of the thermal decomposition reactions have been derived from thermogravimetric (TG) and differential thermogravimetric (DTG) curves, using Coats-Redfern (CR) and Horowitz-Metzeger (HM) methods. The antimicrobial activity has been evaluated against six different microorganisms.

• Journal of Korean Vacuum Science & Technology
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• 제2권1호
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• pp.43-48
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• 1998

The effect of mcirostructure on the electrical properties of yttria stabilized zirconia (YSZ) was analyzed by modeling layer arrangements and mixed phase structure. The YSZ thin films were deposited by RF magnetron sputtering using 30mol% YSZ and 8 mol% YSZ targets with yttrium pellets on porous alumina substrates. The structure, composition and electricla properties of the YSZ films were investigated as functions of sputtering conditons and layer arrangements by XRD, TEM, XPS and acimpedance spectroscopy. The results showed that the triple palyered YSZ films had highermicrohardness, lower compressive stress state and higher ionic conductivity by one order than single and double layered YSZ films. However, sputtered YSZ films have low conductivity compared to YSZ pellets or doctor bladed YSZ thin plates. These results were probably due to the influence of insulating alumina substrates, impractical for most stacking geometries and inductance induced by relatively long platinum, lead wire on YSZ conductivity.

• 한국수소및신에너지학회논문집
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• 제3권2호
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• pp.35-43
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• 1992

Thin Film yttrium, 500 nm thick, was prepared by electron beam evaportion on sapphire substrate. Film was hydrogenated at room temperature upto 1 bar hydorgen pressure without any activation process. Electrical resistivity was measured by four-point DC method in the temperature range between room temperature and 30 K for various hydorgen concentration x = 0 to 2.924 of $YH_x$ sample. Temperature dependent resistance of $YH_{2\;924}$ shows low temperature minmum at 105K ($36{\mu}{\Omega}cm$ deep), the metal-semiconductor transition at 260K, and a hysteresis, which are similar behavior to bulk $YH_x$(x>2) experimental results.

• 한국세라믹학회지
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• 제29권2호
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• pp.119-126
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• 1992

3 mol% Y2O3-doped ZrO2 powders were prepared by hydrolysis with 0.1, 0.2, 0.3, 0.4, 0.5, 0.6 mol/ιH2O/ethanol into 0.1 mol/ι zirconium and yttrium alkoside/ethanol. Spherical monodispersed yttria-partially stabilized zirconia particles with an average diameter of about 0.5 ${\mu}{\textrm}{m}$ were prepared by hydrolysis with 0.2 mol/ιH2O/ethanol. The as-prepared powder was amorphous and with heating it transformed into cubic up to 80$0^{\circ}C$ and into tetragonal over 100$0^{\circ}C$. 3 mol% Y2O3-doped ZrO2 powders calcined over and up to 80$0^{\circ}C$ were a mixture of tetragonal and monoclinic and only tetragonal as determined by X-ray diffraction, respectively.

• 한국세라믹학회지
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• 제36권8호
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• pp.799-804
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• 1999

Composites of SiC-Si3N4 consisted of uniformly distributed elongated $\beta$-Si3N4 grains and equiaxed $\beta$-SiC grains were fabricated with $\beta$-SiC,. $\alpha$-Si3N4 Al2O3 and Y2O3 powders. By hot-pressing and subsequent annelaing elongated $\beta$-Si3N4 grains were grown via$\alpha$longrightarrow$\beta$ phase transformation and equiaxed $\beta$-Si3N4 composites increased with increasing the Si3N4 content owing to the reduced defect size and enhanced crack deflection by elongated $\beta$-Si3N4 grains and the grain boundary strengthening by nitrogen incorporation. Typical flexural strength and fracture toughness of SiC-40 wt% Si3N4 composites were 783 MPa and 4.2 MPa.m1/2 respectively.

• 한국세라믹학회지
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• 제29권2호
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• pp.143-151
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• 1992

Partially stabilized alpha-sialon composition (X=0.1) powder was hot-pressed at 1800~200$0^{\circ}C$ for 0~90 min with 30 MPa. Sintering behavior, phase changes and mechanical properties for the specimens were studied. As sintering temperature was raised from 1800 to 190$0^{\circ}C$, the relative density tended to increase and reached 99% of theoretical at 190$0^{\circ}C$. However the amount of alpha-sialon decreased because alpha-sialon transformed to beta-Si3N4 and yttrium rich silicate glass. In the case of hot-pressing at 190$0^{\circ}C$ for various times, densification increased with sintering time and full densification above 99% of theoretical was attained by 30 min. The amount of alpha-sialon decreased with sintering time. The maximum strength of 825 MPa was obtained by hot-pressing at 190$0^{\circ}C$ for 60 min.

• 한국기계연구소 소보
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• 통권20호
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• pp.79-87
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• 1990

Advanced ceramics have some excellent properties as the material for the mechanical component. It is, however, very difficult to grind ceramics with high efficiency because of their high strength, hardness and brittleness. Thus it is required also by a strong boom of demands for development of Machinable ceramics with high machinability in the most of industries. In present research, experiments are carried out to compare the machinability of sample Machinable ceramics. A $\ell$N(Aluminum Nitride) with additives of BN(Boron Nitride), yttrium. CaO are turned with cut-off tool type tungsten carbide bite using conventional turning machine.