• Journal of the Korean Chemical Society
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• v.24 no.3
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• pp.193-200
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• 1980

The crystal structure of N-acetyl-L-cysteine, $C_5H_9NO_3S,$ has been determined from three dimensional photographic intensity data $(CuK{\alpha}$ radiation) by single crystal X-ray diffraction analysis. There is one formula unit in the triclinic unit cell with a = 7.04(3), b = 5.14(2), c = 8.25(3) ${\AA}$, ${\alpha}$ = 106(2), ${\beta}$ = 51(1), ${\gamma}$ = 124(2)$^{\circ}$ and space group P$_1$, The structure was solved by the direct method and refined by the full matrix least-squares method. The final R value is 12.3% for 629 observed reflections. The C-carboxyl group and the N-acetyl group are very neary planar. The molecule appears to form with neighboring molecules a hydrogen bond, $O-H{\cdot}{\cdot}{\cdot}O(3)$ of length 2.59${\AA}$.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.22 no.2
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• pp.99-104
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• 2012

The co-precipitation technique has been applied to synthesize biphasic calcium phosphate (BCP). $Ca(NO_3)_2{\cdot}4H_2O$ and $(NH_4)_2HPO_4$ as the starting materials was used. X-ray diffraction (XRD) and Fourier transformed infrared (FT-IR) spectroscopy were used to characterize the structure of as-synthesized and calcined BCP powders. After immersion in Hanks' Balanced Salt Solution (HBSS), for 1 week a precipitation started to be formed with individual small granules on the specimen surface. An MTT assay indicated that BCP powders have no cytotoxic effects on MG-63 cells, and that they have good biocompatibility.

• 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 $-1{\times}10^{-7}/^{\circ}C$.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.20 no.5
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• pp.243-248
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• 2010

Si-substituted biphasic calcium phosphates (Si-BCP) were prepared by co-precipitation method. X-ray diffraction and fourier transform infrared spectroscopy were used to characterize the structure of Si-BCP powders. The Si-BCP powders with various Ca/(P+Si) molar ratio were carried out on structural change of hydroxyapatite (HAp) and ${\beta}$-tricalcium phosphate ($\ss$-TCP). The in-vitro bioactivity of the Si-BCP powders was determined by immersing the powders in SBF solution, after that observing the chemical composition and morphology change by X-ray diffraction, scanning electron microscope and energy dispersive spectroscopy.

• Transactions on Electrical and Electronic Materials
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• v.2 no.1
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• pp.27-31
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• 2001

$\beta$-$In_2S_3$ and $\beta$-$In_2S_3$:$Co^{2+}$ thin films were grown using the spray pyrolysis method. The thin films crystallized into tetragonal structures. The indirect energy band gap of the thin films was found to be 2.32 eV for $\beta$-$In_2S_3$ and 1.81 eV for $\beta$-$In_2S_3$:$Co^{2+}$(Co:1.0 mol%) at 198K. The direct energy band gap was found to be 2.67 eV for $\beta$-$In_2S_3$ and 2.17 eV for $\beta$-$In_2S_3$:$Co^{2+}$(Co:1.0 mol%). Impurity optical absorption peaks were observed for the ${\beta}$-$In_2S_3$:$Co^{2+}$ thin films. These impurity absorption peaks are assigned, based on the crystal field theory, to the electron transitions between the energy levels of the $Co^{2+}$ ion sited in $T_{d}$ symmetry.

• Journal of the Korean Society for Heat Treatment
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• v.17 no.6
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• pp.346-355
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• 2004

The flame quenching process has been employed to modify the surfaces of commercial marine propeller material, aluminum bronze alloy (Cu-8.8Al-5Ni-5Fe), and the microstructure, hardness and wear properties of the flame-quenched layers have been studied. The thermal history was accurately monitored during the process with respect to both the designed maximum surface temperature and holding time. The XRD and EDX analyses have shown that at temperatures above $T_{\beta}$, the microstructure consisting of ${\alpha}+{\kappa}$ phases changed into the ${\alpha}+{\beta}^{\prime}$ martensite due to an eutectoid reaction of ${\alpha}+{\kappa}{\rightarrow}{\beta}$ and a martensitic transformation of ${\beta}{\rightarrow}{\beta}^{\prime}$. The ${\beta}^{\prime}$ martensite phase formed showed a face-centered cubic (FCC) crystal structure with the typical twinned structure. The hardness of the flame-quenched layer having the ${\alpha}+{\beta}^{\prime}$ structure was similar to that of the ${\alpha}+{\kappa}$ structure and depended sensitively on the size and distribution of hard ${\kappa}$ and ${\beta}^{\prime}$ phases with depth from the surface. As a result of the sliding wear test, the wear resistance of the flame-quenched layer was markedly enhanced with the formation of the ${\beta}^{\prime}$ martensite.

• Polymer(Korea)
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• v.35 no.2
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• pp.130-135
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• 2011

Along with the fast development of electronics, the demands of portable electronics and wireless sensors are growing rapidly. The need for self-powering materials capable of powering the electrical devices attached to them is increasing, The piezoelectric effect of polyvinylidene fluoride (PVDF) can be used for this purpose. PVDF has a special crystal structure consisting of a ${\beta}$-phase that can produce piezoelectricity. In this paper, multilayer PVDF films were fabricated to increase the ${\beta}$-phase content. A solution of 10% concentration N;N-dimethylacetamide (DMAc) in PVDF (PVDF/DMAc) was used to fabricate the films via spin coating technique with the following optimum process parameters: a spin rate of 850 rpm, spin time of 60 s, drying temperature of $60^{\circ}C$, and drying time of 30 min, Compared with single-layer PVDF films, the multilayer films exhibited higher ${\beta}$-phase content. The ${\beta}$-phase content of the films increased gradually with increasing number of layers until 4, Maximum ratio of ${\beta}$-phase content was 7.72.

• Journal of the Korean Ceramic Society
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• v.22 no.3
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• pp.53-59
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• 1985

Nucleation and crystallization of $\beta$-eucryptite in a glass of molecular percentage composition Li2O.Al2O3.2SiO2 are studied. The glasses are made by quenching of the melts from 143$0^{\circ}C$ to room temperature. Heat-treatment for nucleation and crystal growth are caried out at various temperature in the range between 50$0^{\circ}C$ and 80$0^{\circ}C$ with different duration of time. The amounts of crystallization are estimated by the method of x-ray powder diffraction. As the results a time-temperature-transformation relation for crystallization is derived. The maximum rate of crystallization is observed at about 75$0^{\circ}C$ from the T-T-T-curve while the crystallization temperature is detected at 67$0^{\circ}C$ by DTA measurement. The crystallization temperature moved to 62$0^{\circ}C$ by adding 5 weight percents of TiO2 and it moved to 78$0^{\circ}C$ by adding 2 weight percents of V2O5. The crystallization temperature moved to 62$0^{\circ}C$ by adding 5 weight percent of TiO2 it moved to 78$0^{\circ}C$ by adding 2 weight percents of V2O5 The activation energy for crystallization from the pure glass is calculated as 68 Kcal/mol and it varied to 53 Kcal/mol and 110Kcal/mol when 5 weight percents of TiO2 and weight percents of V2O5 are added respectively.

• 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.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.53 no.7
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• pp.352-357
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• 2004

The composites were fabricated, respectively, using 61vol.% SiC - 39vol.% TiB$_2$ and using 61vo1.% SiC - 39vo1.% WC powders with the liquid forming additives of 12wt% $Al_2$O$_3$＋Y$_2$O$_3$ by pressureless annealing at 180$0^{\circ}C$ for 4 hours. Reactions between SiC and transition metal TiB$_2$, WC were not observed in this microstructure. The result of phase analysis of composites by XRD revealed SiC(6H), TiB$_2$ and YAG(Al$_{5}$Y$_3$O$_{12}$) crystal phase on the SiC-TiB$_2$, and SiC(2H), WC and YAG(Al$_{5}$Y$_3$O$_{12}$) crystal phase on the SiC-WC composites. $\beta$\$\longrightarrow$$\alpha$-SiC phase transformation was ocurred on the SiC-TiB$_2$, but $\alpha$\$\longrightarrow$$\beta$-SiC reverse transformation was not occurred on the SiC-WC composites. The relative density, the vicker's hardness, the flexural strength and the fracture toughness showed respectively value of 96.2%, 13.34GPa, 310.19Mpa and 5.53Mpaㆍml/2 in SiC-WC composites. The electrical resistivity of the SiC-TiB$_2$ and the SiC-WC composites is all positive temperature coefficient resistance(PTCR) in the temperature ranges from $25^{\circ}C$ to 50$0^{\circ}C$. 2.64${\times}$10-2/$^{\circ}C$ of PTCR of SiC-WC was higher than 1.645${\times}$10-3/$^{\circ}C$ of SiC-TiB$_2$ composites.posites.