• Transactions of Materials Processing
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• v.20 no.4
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• pp.303-308
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• 2011

Using a mechano-luminescent(ML) paint, which allows the visualization of fast propagating crack under conventional loading conditions, a catastrophic fracture mechanism associated to crack tip melting and wake bridging in bulk metallic glass, is described in this paper. Fracture occurs in two steps with, first, crack initiation from the mechanically machined sharp notch tip in a rectangular shaped compact tension specimen and melting of its tip due to intense shear deformation within very few deformation bands. Then, the crystalline phase in the glass matrix gradually converts the molten crack into a conventional bridged crack as it propagates.

• Proceedings of the KOSOMBE Conference
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• v.1996 no.05
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• pp.130-132
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• 1996

It is well known when porous calcium phosphate ceramics are used as a bone graft substitute, new tissues or blood vessels are grown into the porous implant due to their excellent biocompatibility. In this study, the ${\beta}$-crystalline form of calcium metaphosphate, $Ca(PO_{3})_{2}$ is prepared by the controlled thermolysis of monocalcium phosphate, $Ca(H_{2}PO_{4})_{2}$. The diameter of cylindrical pores formed during cooling was controlled by a holding time at the melting point of a monocalcium phosphate and by the change of a recrystallization temperature, to obtained the most appropriate size (about $200{\mu}m$) of pores. It was observed that the increasing holding time at the melting point of monocalcium phosphate results in the decreases of pore sizes.

• Bulletin of the Korean Chemical Society
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• v.16 no.1
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• pp.17-21
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• 1995

A new series of polyarylate copolyesters were prepared by melt polycondensation of 1,4-diacetoxy-2,5-(α-phenylisopropyl)benzene with mixture of terephthalic acid and isophthalic acid in varying ratio. And their general properties such as the glass transition temperature, crystalline melting temperature, crystallinity and solubility were studied. The intrinsic viscosity values of the present polymers measured in a mixed solvent of phenol/p-chlorophenol/1,1,2,2-tetrachloroethane ranged from 0.45 to 0.66 depending on the composition and molecular weight. The copolyesters containing greater than 20 mole % of isophthalic acid were found to be amorphous, whereas the homopolymer derived from terephthalic acid was semicrystalline with a melting point of 414℃. The glass transition temperatures of the polymers ranged from 165 to 180℃ depending on the composition. The copolyesters containing 50 mole % and greater of isophthalic acid moiety were soluble at room temperature in such common solvents as tetrahydrofuran, chloroform and N,N-dimethylformamide.

• Fibers and Polymers
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• v.1 no.2
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• pp.76-82
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• 2000

A series of random copolyesters having various compositions were synthesized by bulk copolymerization of bishydroxyethyl terephthalate (BHET) with 1,4-cyclohexane dimethanol (CHDM) or dimethyl isophthalate (DMI). CHDM and DMI content was less than 10 wt%. For the synthesized copolyesters, isothermal crystallization rate, melting behavior, and equilibrium temperature were investigated by calorimetry and by Avrami and Hoffman-Weeks equation. Crystalline lattice and morphology were studied by WAXD and SEM. Regardless of the composition, the value of the Avrami exponent was about 3, which indicates that crystallization mechanism of the copolyester was similar to those of PET homopolymer. Incoporation of CHDM or DMI units in PET backbone decreased the crystallization rate of the copolyesters. Surface free energy of copolyesters was evaluated using the newly proposed equation. The value of surface free energy was about 189$\times$$10^{-6}$/$J^{2}$/$m^{4}$ regardless of comonomer contents. This result is in good agreement with that of PET homopolymer.

• Journal of the Korean Ceramic Society
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• v.34 no.11
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• pp.1182-1186
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• 1997

La0.8Ca0.2Cr0.98O3 powder was prepared using the modified Pechini process. Various crystalline phases formed during thermal decomposition were investigated. (La,Ca)CrO4 phase, first formed from the precursor, was transformed to (La,Ca)CrO3 and CaCrO4 above 80$0^{\circ}C$, which remained up to 110$0^{\circ}C$. However, only (La,Ca)CrO3 phase consisting of orthorhombic and intermediate rhombohedral polymorphs was observed after sintering at 125$0^{\circ}C$. The specimens sintered at 140$0^{\circ}C$ exhibited 98% of relative density and rather wide grain size distribution with average grain size of 3-4 ${\mu}{\textrm}{m}$. Densification and grain growth of the specimens observed above 125$0^{\circ}C$ were presumably attributed to liquid phase sintering resulted from melting of Ca3(CrO4)2 phase.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1989.06a
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• pp.111-113
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• 1989

This paper reports the optical characteristics of TeS$_{5}$ Ge$_{5}$ thin film. In phase diagram, TeS$_{5}$ Ge$_{5}$ has the eutetic point with the loweat melting point. Therfore, TeS$_{5}$ Ge$_{5}$ thin film will be melted by Diode Laser with low energy. TeS$_{5}$ Ge$_{5}$ thin films start to change the phase from amorphous to crystalline near 10$0^{\circ}C$, but perfectly change the phase at 28$0^{\circ}C$. As-deposit TeS$_{5}$ Ge$_{5}$ thin film start to change the phase to crystalline in enviroment og 66$^{\circ}C$ 80%RH.circ}C$ 80%RH.

• Journal of Technologic Dentistry
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• v.14 no.1
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• pp.95-118
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• 1992

Glass ceramics for crown were prepared by adding 3$\sim$11 wt% TiO2 to the weight percent composition of 34.7 CaO, 27.8 SiO2, 18.3P2O5, 12.6MgO and 6.6 TiO2. The starting glasses were prepared by melting the powdered batch in alumina crucible at 1350$\sim$1400 for 1 hr and then quenching into a distilled water. The nucleation and crystallization of the crystalline glass ceramics for crown were studied by DTA, SME and X-ray diffraction analysis. Frit containing 9.11 wt% TiO2 had crystallization temperature of 850$\sim$1075 and major crystalline phase was identified by X-ray diffraction as diopside(CaO-MgO-2SiO2). Activation energies for the crystallization processes were obtained from DTA by varing rates for the fits, and were calculated from modified Ozawa and Kissinger equations. Activation energy for the crystallization processes of the S-4 frit was 489.6 KJ/mol.

• Korean Journal of Materials Research
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• v.11 no.9
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• pp.786-791
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• 2001

$\alpha$,$\omega$-Bis(4-glycidyloxybenzylidene-4-aminophenyl)methane (BGBAM) was synthesized from the initial materials, 4-hydroxylbenzaldehyde (HBA), 4,4'-methylenedianiline (MDA) and epichlorohydrin. The DSC trace for BGBAM shows two endotherms associated with the liquid crystalline phase transition around $104.2^{\circ}C$ and the isotropic transition around $171.2^{\circ}C$, and it also has a broad exotherm in the range of $178~300^{\circ}C$ due to the anionic homopolymerization of BGBAM. DSC curve for the curing of BGBAM with hexamethylene diamine (HMD) shows an endothermic peak around $93^{\circ}C$ attributed to the melting of BGBAM. It also has three exothermic peaks around $128.4^{\circ}C$ and $180.2^{\circ}C$ associated with the epoxide-amine reaction and weak peak in the range of $200~263^{\circ}C$ related to the anionic homopolymerization between the unreacted epoxide groups. The activation energy values of cure reaction by Kissinger method are 66.5, 67.3 and 90.6 kJ/mol for $T_{pl},\; T_{p2}\; and \;T_{p3},\; respectively$. The kinetic parameters by isoconverional method are similar value to those from Kissinger method.

• Journal of the Korean Ceramic Society
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• v.28 no.10
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• pp.793-802
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• 1991

The multicrystalline machinable ceramics was fabricated by melting method using domestic pyrophyllite. After determination of optimum crystallization temperature and time from results of DTA, XRD and SEM, base glasses were heat treated by 2-step schedule. Main crystalline phases identified by XRD, EDX were Na-fluorophlogopite, ${\beta}$-spoduemen and ${\alpha}$-cordierite, and the crystallization condition of these crystals was varied with chemical composition, thermal history and nucleation agents. The thermal, chemical properties of prepared samples were excellent.

• YAKHAK HOEJI
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• v.8 no.2
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• pp.45-47
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• 1964

Two new orotic acid derivatives orotyl-DL-alanine and orotyl-L-tyrosine were synthesized. They were obtained as high melting crystalline masses by condensing DL-alanine and L-tyrosine each with orotyl chloride in aqueous sodium hydroxide solution, followed by acidifying the reaction mixture.