• Journal of Technologic Dentistry
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• v.21 no.1
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• pp.5-14
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• 1999

Glass ceramics for dental crown prosthesis were prepared by crystallization of CaO-MgO-SiO2-$P_2O_5-TiO_2$ glasses. Their crystallization behaviors have been investigated as a function of heattreatment temperature, holding time and chemical composition in relation to mechinical properties. Crystallization peak temperatures were determined by differential thermal analysis(DTA). Crystalline phases and mircostructures of heat-treated sample were determined by the means of powder X-ray diffraction(XRD) and scanning electron microscopy(SEM). The final crystalline phase assemblages and the microstructures of the samples were found to be dependent on glass compositions, heattreatment temperature, and holding time. 1st crystallization peak temperature(TP), affected strongly by apatite, was found to be increased or decreased. From the experiment, the following results were obtained : 1. The crystallization peak temperature($T_P$) formed by apatite increased until adding up to 9wt% $TiO_2$ to base glass composition, then decreased above that. 2. Apatite($Ca_{10}P_6O_{25}$), whitlockite(${\beta}-3CaO-P_2O_5$), $\beta$-wollastonite($CaSiO_3$), magnesium tianate($MaTiO_3$) and diopside(CaO-MgO-$2SiO_2$) crystal phase were precipitated in MgO-CaO-$SiO_2-TiO_2-P_2O_5$ glass system containing 9wt% and 11wt% of $TiO_2$ 3. Vickers hardness of samples increased with increasing heat-treatment temperature and Vickers hardness of S415T9 samples heat-treated at 1075 was approxi-mately 813Kg $mm^{-2}$ as maximum value. 4. Vickers hardness of samples increased due to precipitation of apatite, whitlockite, $\beta$-wollastonite, magnesium titanate, and diopside crystal phases within glass matrix.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.3 no.2
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• pp.176-184
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• 1993

The glasses, which the $\beta$-spodumene as the principal crystalline phase could be precipitated, were melted by adding >, $P_2O_5, TiO_2, ZrO_2 in the Li_2O-Al_2O_3-SiO_2$ system. In order to achieve the glass-ceramic body of near-theoritical density by sintering method, the optimum condition of heat treatment, the effect of glass powder size and the properties were investigated by DTA, XRD, bulk density, thermal expansion and SEM. Addition of $P_20_5$ imProved the tendency of sintering and the sample with 9wt% $P_20_5$ content was the most dense OOdy by sintering method. The optimum condition of heat treatmemt was sintered for densitification at $740^{\circ}C$ and crystallized at $950^{\circ}C$. In the optimum condition, the relative density was above 90% and the thermal expansion was negative about $-1{\times}10^{-7}/^{\circ}C$.

• Transactions of the Korean hydrogen and new energy society
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• v.22 no.6
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• pp.780-786
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• 2011

Mg hydride had high hydrogen capacity (7.6%), lightweight and low cost materials and it was promising hydrogen storage material at high temperature. However, commercial applications of the Mg hydride are currently hindered by its high absorption/desorption temperature, and very slow reaction kinetics. one of the approaches to improve the kinetic is $MgH_x$ intermixed with carbon. And it shows that carbon and carbon allotropes have a beneficial effect on hydrogen sorption in Mg. The graphene is a kind of carbon allotropes which is easily desorbed reaction at low temperatures because its reaction is exothermic. In this work, the effect of graphene concentration on the kinetics of Mg hydrogen absorption reaction was investigated. The $MgH_x$-Graphene composites has been prepared by hydrogen induced mechanical alloy (HIMA). The synthesized powder was characterized by XRD and simultaneous TG, DSC analysis. The hydrogenation behaviors were evaluated by using a sievert's type automatic PCT apparatus. In this research, results of kinetic profiles exhibit hydrogen absorption rate of $MgH_x$-5wt.% and 10wt.% graphene composite, as 1.25wt.%/ms, 10.33wt.%/ms against 0.88wt.%/ms for $MgH_x$ alone at 473K.

• Transactions of the Korean hydrogen and new energy society
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• v.21 no.3
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• pp.201-206
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• 2010

In present work, $La_{0.8}Ca_{0.2}CrO_3$ (LCC) ceramic interconnect layer for SOFC was prepared by using thermal plasma spray coating process. The LCC powders were synthesized by Pechini method and calcined at the temperature of $1000^{\circ}C$. The prepared LCC powder was characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), particle counter, BET analysis, respectively. In addition, basic and essential properties of LCC layer coated by thermal plasma spray coating process such as the morphology of surface and cross section for coated layer, gas leak rate, and electrical conductivity were analyzed and discussed. Based on these experimental results, it can be concluded that the LCC layer coated by thermal plasma spray coating process can be suitable as a ceramic interconnect of SOFC operated at $800^{\circ}C$.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2001.10a
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• pp.660-664
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• 2001

$Zn_xSr_{1-x}S$ thin films were prepared in the whole composition range by rf sputtering, using powder targets of a mixture of ZnS and SrS with the required mole fraction. The possibility of existence of $Zn_xSr_{1-x}S$ solid solutions was systematically investigated from the results of thin film growth, in terns of structural, optical characteristics and the chemical bonding of the constituent atoms. The XRD, XPS and optical results made it clear that the solid solutions with a single-phased zincblende structure and a single-phased rocksalt structure were formed at $0.86~0.93{\leq}x{\leq}1$ and $0{\leq}x{\leq}0.29$, respectively. The miscibility gap, including phase separation regions was found to exist in $0.3{\leq}x{\leq}0.86~0.91$, in which lattice constants, binding energy and absorption edges kept almost constant by the same values as those at border compositions. The experimental results on phase transition agreed well with the fraction of ionic character $f_{i}$ based on the Phillips'dielectric theory.

• The Journal of Natural Sciences
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• v.14 no.2
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• pp.41-54
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• 2004

$LaMnO_3$ and A site substituted $La_{0.9}Sr_{0.1}MnO_3$(a=$5.33\AA$, c=$13.27\AA$), B site substituted $LaMn_{0.9}Cu_{0.1}O_3$(a=$5.52\AA$, c=$13.31\AA$) mixed oxides were prepared by Citrate sol-gel method. The powder X-ray diffraction patterns of these oxides were indexed with single phase hexagonal perovskite structures. According to the TRR result, oxygen stoichiometry of these oxides were oxidative nonstoichiometry as like $LaMnO_{3.16}$, $La_{0.9}Sr_{0.1}MnO_{3.10}$ and $LaMn_{0.9}Cu_{0.1}O_{3.14}$ Reduction reactions of un-substituted $LaMnO_3$ was two steps, but specific site(A site of B site) partially substituted $LaMnO_3$ oxides were procees to three reactions.

• Journal of the Microelectronics and Packaging Society
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• v.26 no.4
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• pp.83-88
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• 2019

LiBaPO₄:Eu²⁺ phosphors with stoichiometric and nonstoichiometric compositions were prepared using a solid state reaction followed by heat treatment in reduced atmosphere, and the crystal structures and photoluminescence(PL) properties of the powders were investigated by x-ray powder diffraction and luminescence spectrometer. At 900℃, the Ba₃(PO₄)₂ phase as the intermediate phase was observed with the LiBaPO₄ phase as the main crystalline phase. Samples with a low europium concentration at 1,000℃ belonged to the trigonal structure, whereas samples with Eu²⁺ content more than 4 mol% showed monoclinic structure. In the nonstoichiometric compositions of 4 mol% Eu²⁺ and above, a single phase of Eu²⁺-doped LiBaPO₄, showing bluish green emission, was formed.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.10 no.4
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• pp.318-323
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• 2000

The intercalated compounds of alkylsulfonates into hydrated zinc were synthesized. From the high temperature powder X-ray diffraction (HTXRD), FT-IR, and molecular size, the temperature dependence of orientation for the intercalated alkylsulfonates were determined. In the temperatures range 1, alkylsulfonates were intercalated into hexa aqua zinc layer with the bilayer structure of $32.9^{\circ}$angle for ${Zn(H_2O_4]^{2+}[C_nH_{2n+1}SO_3]_2\;^-$. In the temperatures range 2, alkylsulfonates were intercalated into tetra aqua zinc layer with the bilayer structure of $55.2^{\circ}$angle for ${Zn(C_nH_{2n+1}SO_3)_2$. In the temperatures range 3, alkylsulfonates were directly bonded to zinc ion with the bilayer structure of $76.5^{\circ}$angle for ${Zn(C_nH_{2n+1}SO_3)_2$.

• Journal of the Korean Magnetics Society
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• v.9 no.1
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• pp.29-34
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• 1999

$Y_{2.5}La_{0.5}Fe_5O_{12}$ is fabricated by a sol-gel method and the magnetic properties of single phase garnet are investigated by using X-ray diffraction, vibrating sample magnetometer, scanning electron microscopy and M$\"{o}$ssbauer spectroscopy. The single phase powders garnet was fired at 100$0^{\circ}C$ for 8 hours. The crystal structures of samples are cubic garnet. Mossbauer spectroscopy were measured from 13 K to 750 K. M$\"{o}$ssbauer spectra show that the iron exist ferric trivalence in sample. The spin wave constants were determined $B_{3/2}=0.32{\pm}0.05,\; C_{5/2}=0.18{\pm}0.05$ and Debye temperature were determined 382 K at 24(d) site and 246 K at 16(a)-site. The saturation magnetization $M_s$ of powder is 25 emu/g. 25 emu/g.

• Bulletin of the Korean Chemical Society
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• v.33 no.6
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• pp.1845-1850
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• 2012

Layered metal hydroxides (LMHs) containing calcium were synthesized by coprecipitation in solution having two different trivalent metal ions, iron and aluminum. Two mixed metal solutions ($Ca^{2+}/Al^{3+}$ and $Ca^{2+}/Fe^{3+}$ = 2/1) were added to sodium hydroxide solution and the final pH was adjusted to ~11.5 and ~13 for CaAl-and CaFe-LMHs. Powder X-ray diffraction (XRD) for the two LMH samples showed well developed ($00l$) diffractions indicating 2-dimensional crystal structure of the synthesized LMHs. Rietveld refinement of the X-ray diffraction pattern, the local structure analysis through X-ray absorption spectroscopy, and thermal analysis also confirmed that the synthesized precipitates show typical structure of LMHs. The chemical formulae, $Ca_{2.04}Al_1(OH)_6(NO_3){\cdot}5.25H_2O$ and $Ca_{2.01}Fe_1(OH)_6(NO_3){\cdot}4.75H_2O$ were determined by inductively coupled plasma-atomic emission spectroscopy (ICP-AES). Particle morphology and thermal behavior for the synthesized LMHs were examined by field emission scanning electron microscopy and thermogravimetricdifferential scanning calorimetry.