• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.7
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• pp.2367-2374
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• 1996

A generalized Scheil equation for the solute redistribution in the absence of the back diffusion during the dendritic solidification of binary alloys is derived, in which coarsening of the secondary dendrite arms is taken into account. The obtained equation essentially includes the original Scheil equation as a subset. Calculated results for typical cases show that the coarsening affects the microsegregation significantly. The eutectic fraction predicted for coarsening is considerably smaller than that for fixed arm spacing. The most important feature of the present equation in comparison with the Scheil equation lies in the fact that there exists a lower limit of the initial composition below which the eutectic is not formed. Based on the generalized Scheil equation and the lever rule, a new regime map of the eutectic formation on the initial composition-equilibrium partition coefficient plane is proposed. The map consists of three regimes: the eutectic not formed, conditionally formed and unconditionally formed, bounded by the solubility and diffusion controlled limit lines.

• Journal of the Korean Ceramic Society
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• v.33 no.4
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• pp.405-410
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• 1996

The partial substitution of LiTaO3 with Al2O3 caused the variation of dielectric properties and a lower melting temperature yielding an easier growth of single crystal. The lattice constants and Raman band broadening were measured for the LiTaO3 solid solution in which the cations of Li+ and Ta5+ were partially substituted by Al3+ cation. The LiTaO3 type limit phases were obtained. ; Li1.15Al0.45Ta0.7O3 for cationic excess Li1.15Al0.45Ta0.7O3 for stoichiometry Li0.85Al0.05TaO3 for cationic deficit. The second phase was formed beyond the solubility limit. The limit phase (Li0.85Al0.05TaO3) in the region of cationic deficit showed the lowest Cuire temperature of 61$0^{\circ}C$ and melting point of 152$0^{\circ}C$ compared to the solid solutions in other regions (TMp=1$650^{\circ}C$, Tc=69$0^{\circ}C$ for LiTaO3)

• Korean Journal of Materials Research
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• v.20 no.6
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• pp.326-330
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• 2010

$CoSb_3$ Skutterudites materials have high potential for thermoelectric application at mid-temperature range because of their superior thermoelectric properties via control of charge carrier density and substitution of foreign atoms. Improvement of thermoelectric properties is expected for the ternary solid solution developed by substitution of foreign atoms having different valances into the $CoSb_3$ matrix. In this study, ternary solid solutions with a stoichiometry of $Co_{1-x}Ni_xSb_3$ x = 0.01, 0.05, 0.1, 0.2, $CoSb_{3-y}Te_y$, y = 0.1, 0.2, 0.3 were prepared by the Spark Plasma Sintering (SPS) system. Before the SPS synthesis, the ingots were synthesized by vacuum induction melting and followed by annealing. For phase analysis X-ray powder diffraction patterns were checked. All the samples were confirmed as single phase; however, with samples that were more doped than the solubility limit some secondary phases were detected. All the samples doped with Ni and Te atoms showed a negative Seebeck coefficient and their electrical conductivities increased with the doping amount up to the solubility limit. For the samples prepared by SPS the maximum value for dimensionless figure of merit reached 0.26, 0.42 for $Co_{0.9}Ni_{0.1}Sb_3$, $CoSb_{2.8}Te_{0.2}$ at 690 K, respectively. These results show that the SPS method is effective in this system and Ni/Te dopants are also effective for increasing thermoelectric properties of this system.

• Analytical Science and Technology
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• v.5 no.1
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• pp.127-134
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• 1992

Effects of boron addition on microstructure and phases of plasma are melted tungsten have been investigated by optical microscopy, scanning electron microscopy, Auger electron spectroscopy, X-ray diffractometer, measurements of grain size and hardness. The change in the microstructure upon boron addition was studied by optical microscopy. It was observed that the grain refinement was induced upon content within the limit of solubility. When the boron content was above the solubility limit, two phases of primary tungsten and eutectic structure were observed and confirmed by AES and XRD analysis. It was also shown that recrystallization temperature was increased and recrystallized grain size was reduced as boron content increased.

• Korean Journal of Materials Research
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• v.21 no.9
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• pp.515-519
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• 2011

The purpose of this study was to determine the optimal firing condition and composition for $Al_2TiO_5$ crystal, which is suitable for stable coloration in glazes at high temperatures, using $Cr_2O_3$ as chromophore for the synthesis of $Al_2TiO_5$ system pigments. $Al_2TiO_5$ has a high refractive index and good solubility of chromophore in the $Al_2TiO_5$ lattice, making this structure a good candidate for the development of new ceramic pigments. Pigments were synthesized by using $Al_2O_3$ and $TiO_2$ mainly. Various amounts of $Cr_2O_3$ such as 0.01, 0.02, 0.03, 0.04 and 0.05 mole were also added. Each compound was synthesized at $1300^{\circ}C$, $1400^{\circ}C$, and $1500^{\circ}C$ for 2 hours and cooled naturally. The crystal structure, solubility limit, and color of the synthesized pigments were analyzed by XRD, SEM, Raman spectroscopy, UV and UV-vis. The changes in color as the result of applying 6 wt% of the synthesized pigments to lime barium glaze were expressed as CIE-L*a*b* values. A $Cr_2O_3$ 0.03 mole doped $Al_2TiO_5$ brown pigment was successfully synthesize at $1400^{\circ}C$, and the values of CIE-L*a*b* parameters were L* = 44.62, a* = 3.10, and b* = 17.25. In the case of the pigment synthesized at $1500^{\circ}C$, the brown color was obtained at 0.01 mole and 0.02 mole $Cr_2O_3$, and the CIE-L*a*b* values were 55.34, 1.73, 28.64, and 49.39, 0.51, 21.33, respectively. At $1500^{\circ}C$, the maximum limit of solid solution was 0.03 mole $Cr_2O_3$. The glazed sample showed green color, and the values of the CIEL* a*b* parameters were L* = 45.69, a* = -0.98, and b* = 20.38.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.3
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• pp.327-333
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• 1999

Controlled Ca impurity implanted inner crack-like pore in the high purity alumina bi-crystal had been created by micro-fabrication technique, which includes ion implantation, photo-lithography, Ar ion milling, and hot press. The morphological change and the growth od crystals formed by heat treatment in Ca doped high purity single crystal alumina, were observed using optical microscopy. The dot was developed and hexagon like crystal appeared on inner surface of crack-like pore after heat treatment. Bar type crystals, probably CaO . $6Al_2O_3$, were observed on the inner surface of 100ppm Ca implanted specimen after 1 hour heat treatment at $1,500^{\circ}C$, but this bar type crystal disappeared after 1 hour heat treatment at $1,600^{\circ}C$. This disappearance means that there should be little increase of Ca solubility limit to alumina and/or changes of diffusion coefficient of Ca in alumina around this temperature.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.1
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• pp.160-168
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• 1998

In order to investigate the color variation and the solubility limit in wagnerites by metal ion substitution, wagnerite ($A_2XO_4Z$) was synthesized and then, substituted by coloring metal ions, especially $CO^{2+},Ni^{2+}$ and $Cu^{2+}$ ions. When calcium was replaced with Mg, Co, Ni and Cu divalent ions, solid solutions were formed with a limited solubility. Single phase wagnerites were synthesized by the substitution of Ca with Mg and Co, and their colors were white and purple, respectively. Substitutions with $Li^+$ were succeeded in the specific composition and the substitution of vanadium for $X^{5+}$ were attempted, resulting in the wagnerites of dark purple, dark gold and light yellow colors. The substitution of chlorine was, also, attmepted for the fluorine site.

• Macromolecular Research
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• v.14 no.2
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• pp.199-204
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• 2006

Remarkably high and stable separation performance for olefin/paraffin mixtures was previously reported by facilitated olefin transport through ${\pi}$-complex membranes consisting of silver ions dissolved in poly(hexamethylenevinylene) (PHMV). In this study, the ${\pi}$-complex formation of $AgBF_4,\;AgClO_4\;and\;AgCF_{3}SO_3$ with PHMV and their ionic interactions were investigated. FT-Raman spectroscopy showed that the C=C stretching bands of PHMV shifted to a lower frequency upon incorporation of silver salt, but the degree of peak shift depended on the counter-anions of salt due to different complexation strengths. The symmetric stretching modes of anions indicated the presence of only free ions up to [C=C]:[Ag]=1:1, demonstrating the unusually high solubility of silver salt in PHMV. Above the solubility limit, the ion pairs and higher-order ionic aggregates started to form. The coordination number of silver ion for C=C of PHMV was in the order $AgBF_4$ > $AgClO_4$ > $AgCF_{3}SO_3$, but became similar at [C=C]:[Ag]=1:1. The different coordination number was interpreted in terms of the different transient crosslinks of silver cations in the complex, which may be related to both the interaction strength of the polymer/silver ion and the bulkiness of the counteranion.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2004.09a
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• pp.33-36
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• 2004

Two biokinetic models (\circled1 Mrichaelis-Menten kinetics with competitive inhibition \circled2 with both competitive inhibition and Haldane inhibition) for reductive dechlorination were developed and compared with results from batch kinetic tests conducted over a wide range of PCE and TCE concentrations with two different dechlorinating cultures. At PCE concentrations lower than 300 $\mu$M, both model simulated the experimental results well. However, The kinetic model that incorporated both competitive and Haldane inhibitions much better simulated experimental data for PCE concentrations greater than 300-400 $\mu$M, and TCE concentrations at half its solubility limit (4000 $\mu$M). The PM culture showed Haldane inhibition constants of 900, 6000, 7000 $\mu$M for TCE, c-DCE and VC, indicating very weak Haldane inhibition for c-DCE and VC, while the EV culture had lower Haldane inhibition constants for TCE, c-DCE, and VC of 900, 750, and 750 $\mu$M, respectively. The BM culture had better transformation abilities than the individual cultures over a wide range of PCE and TCE concentrations. Modeling results indicated that a combination of competitive and Haldane inhibition kinetics is required to simulate dechlorination over a broad range of concentrations up to the solubility limits of PCE and TCE.

• Journal of the Korean Ceramic Society
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• v.42 no.5 s.276
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• pp.308-313
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• 2005

In this study the electrical conductivity of excess BaO in $BaTiO_3$ was measured to investigate the relationship between defects and solubility in the temperature range of $900^{\circ}C$ to $1300^{\circ}C$ under various oxygen partial pressure. First of all, quenched $BaTiO_3$ powders of various Ba/Ti ratios were analysed by X-ray diffraction to confirm whether second phase is formed or not. As the results, we observed the solubility of BaO in the temperature range of $1200^{\circ}C$ to $1400^{\circ}C$, and it was also found that the conductivity minima move to lower $PO_2$ with increasing excess BaO within solubility limit.