• Bulletin of the Korean Chemical Society
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• 제33권3호
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• pp.779-789
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• 2012

In the kinetic theory of dense fluids the many-particle collision bracket integral is given in terms of a classical collision operator defined in the phase space. To find an algorithm to compute the collision bracket integrals, we revisit the eigenvalue problem of the Liouville operator and re-examine the method previously reported [Chem. Phys. 1977, 20, 93]. Then we apply the notion and concept of the eigenfunctions of the Liouville operator and knowledge acquired in the study of the eigenfunctions to cast collision bracket integrals into more convenient and suitable forms for numerical simulations. One of the alternative forms is given in the form of time correlation function. This form, on a further manipulation, assumes a form reminiscent of the Chapman- Enskog collision bracket integrals, but for dense gases and liquids as well as solids. In the dilute gas limit it would give rise precisely to the Chapman-Enskog collision bracket integrals for two-particle collision. The alternative forms obtained are more readily amenable to numerical simulation methods than the collision bracket integrals expressed in terms of a classical collision operator, which requires solution of classical Lippmann-Schwinger integral equations. This way, the aforementioned kinetic theory of dense fluids is made fully accessible by numerical computation/simulation methods, and the transport coefficients thereof are made computationally as accessible as those in the linear response theory.

• 한국세라믹학회지
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• 제33권12호
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• pp.1301-1310
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• 1996

Generally it requires high sintering temperatures more than 135$0^{\circ}C$ to make semiconductive BaTiO3 ceramics. Also it is very difficult to achieve a homogeneous mixing in solid-state reaction method. Therefore the liquid phase distributed to non-uniform dilute the characteristics of PTCR. In order to improve the uniformity this study is used the sol-gel coating method. Using this method we studied the new manufacturing process that had a high reproducibility and mass production capability. Tetraethyl orthosilicate (TEOS) was used as a source of Si. The semiconductive BaTiO3 ceramics which was produced by sol-gel method for the SiO2 addition and sintered between 124$0^{\circ}C$ and 130$0^{\circ}C$ showed almost same resistivity at room temperature among 125$0^{\circ}C$ and 130$0^{\circ}C$. As the results We could be sintered the semiconducting BaTiO3 ceramics at lower temperature even at 125$0^{\circ}C$ maintaining the same specific resistivity ratio ($\rho$max/$\rho$min) at 130$0^{\circ}C$. The specific resistivity both below and above the Curie temperature were increased by slow cooling and the steepness of the plots in the reasion of transition from low to high resistance increased as the cooling rate decreased.

• Membrane and Water Treatment
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• 제8권1호
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• pp.19-34
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• 2017

Boron exists in dilute concentrations in sea water, ground water and waste waters. Reactive liquid extraction can be used for removing boron to make the treated water suitable for drinking and irrigation, with its final concentration less than 0.5 ppm. The results of equilibrium experiments are reported on the removal of boron using 2-butyl-2-ethyl-1, 3-propanediol (BEPD as a nonionic carrier) in sunflower oil, a non-traditional solvent. The results of removal of boron from aqueous solutions in the concentration range 0.5-20 ppm are presented. It is shown that this new liquid membrane system, is able to remove boron from ground waters at their natural pH of 6-8 (without any chemical addition for pH adjustments). The removal efficiency is good when the process is upgraded to a hollow-fibre membrane contactor and approximately 45% boron can be removed in a single-stage contact. There are additional advantages of this new approach that includes reduced operational health and safety and environmental issues. The results reported here provide guidelines to the development of boron removal process using renewable, biodegradable, safe and cheap solvent system such as sunflower oil.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 하계학술대회 논문집 Vol.4 No.1
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• pp.155-159
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• 2003

Polycrystalline $Ti_{1-x}Co_xO_2$ thin films on $SiO_2$ (200 nm)/Si (100) substrates were prepared using liquid-delivery metalorganic chemical vapor deposition. Microstructures and ferromagnetic properties were investigated as a function of doped Co concentration. Ferromagnetic behaviors of polycrystalline films were observed at room temperature, and the magnetic and structural properties strongly depended on the Co distribution, which varied widely with doped Co concentration. The annealed $Ti_{1-x}Co_xO_2$ thin films with $x{\leq}0.05$ showed a homogeneous structure without any clusters, and pure ferromagnetic properties of thin films are only attributed to the $Ti_{1-x}Co_xO_2$ (TCO) phases. On the other hand, in case of thin films above x=0.05, Co clusters formed in a homogeneous $Ti_{1-x}Co_xO_2$ Phase, and the overall ferromagnetic (FM) properties depended on both $FM_{TCO}$ and $FM_{Co}$. Co clusters with about 10nm-150nm size decreased the value of Mr (the remanent magnetization) and increased the saturation magnetic field.

• 대한화학회지
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• 제33권5호
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• pp.459-467
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• 1989

계면활성제가 수용액 중에 용해되면 용액내에서 micelle이라는 응집체를 형성하며, micelle은 그 내부에 oil를 용해시켜 swollen micelle을 형성하게 된다. 실제로 물-oil-계면활성계의 상평형도상에서 micelle과 swollen micelle은 동일영역에 존재하게 되나 일반적으로 micelle과 swollen micelle의 형성에 관해서는 서로 다른 관점으로 취급되어 왔다. 본 연구에서는 이러한 계면활성제 응집체의 형성에 관한 일관된 열역학적 모델을 제시하고자 한다. 모든 경우에 저농도 영역에서 이상용액 이론을 적용하였으며, micelle 형성에너지는 소수성 작용에너지와 계면에서의 표면에너지의 합으로 표시하였다. 이론식으로부터 임계마이셀농도, 평균응집분자수, 용해비 등을 예측하였으며 실험관측치와 비교하였다.

• Bulletin of the Korean Chemical Society
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• 제31권11호
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• pp.3195-3200
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• 2010

We have performed molecular dynamics simulations of atomistic models of $C_{60}$ molecules and DMPC bilayer membranes to study the static and dynamic effects of carbon nanoparticles on biological membranes. All four $C_{60}$-membrane systems were investigated representing dilute and concentrated solutions of $C_{60}$ residing either inside or outside the membrane. The concentrated $C_{60}$ molecules in water phase start forming an aggregated cluster. Due to its heavy mass, the cluster tends to adhere on the surface of the bilayer membrane, hindering both translational and rotational diffusion of individual $C_{60}$. On the other hand, once $C_{60}$ molecules accumulate inside the membrane, they are well dispersed in the central region of the bilayer membrane. Because of the homogeneous dispersion of $C_{60}$ inside the membrane, each leaflet is pushed away from the center, making the bilayer membrane thicker. This thickening of the membrane provides more room for both translational and rotational motions of $C_{60}$ inside the membrane compared to that in the water region. As a result, the dynamics of $C_{60}$ inside the membrane becomes faster with increasing its concentration.

• 한국수소및신에너지학회논문집
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• 제10권2호
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• pp.101-106
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• 1999

Hydrogen solubility in internally oxidized Pd-Mo(Al) alloys has been studied at 323 K from the measurements of pressure-composition(p-c) isotherms. Internal oxidation of $Pd_{0.985}Al_{0.015}$ and $Pd_{0.97}Mo_{0.03}$ alloys results in the precipitation of Al and Mo particles in a matrix of pure Pd. It has been observed that the presence of the aluminum and molybdenum oxide precipitates results in an enhanced hydrogen solubility in the dilute phase region of Pd-H in a Pd/aluminum(molybdenum)oxide composites. Hydrogen solubility enhancements due to the presence of residual stresses around ceramic particles have been observed from p-c isotherms determined at 323 K after oxidation at 1073 K. The solubility enhancements in completely internally oxidized alloys are greater than that in partially oxidized alloys. The stress fields near the ceramic precipitates are the major source of the solubility enhancements. Transmission electron microscopy indicates that alumina precipitates are nanometer-sized and coherent with the Pd matrix after oxidation.

• 태양에너지
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• 제12권2호
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• pp.18-27
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• 1992

졸-겔 기술에 의해 $WO_3$ 다충박막이 유리와 ITO coated glass 위에 증착되었다. 특성은 XRD, 분광광도계, DTA/TGA, SEM/EDAX 그리고 RBS에 의해서 분석되었다. 균질한 $WO_3$막은 유리기판위에 dipping속도 5mm/s에서 증착 되었으며 이 시료는 희석된 HCI 전해액을 사용하여 착색시킨 결과 낮은 근적외선 투과율을 나타내었다. DTA 결과 $380^{\circ}C{\sim}500^{\circ}C$ 범위의 gel data는 $WO_3$의 결정화 온도 형성을 결정하였으며 이 측정치는 졸-겔 박막의 결정화 온도와 일치하였다. RBS에 의해 착색되지 않은 $WO_3$ 졸-겔 막의 화학조성은 $WO_3$였다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2006년도 추계학술대회 논문집 광주전남지부
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• pp.39-42
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• 2006

Titania sols or powders were are very promising materials for environment as photocatalyst. The band gap energy of $TiO_2$ has been known to be 2.8 to 3.2 eV. But the measuring system of its band gap is usually depend on absorption properties. Thus, in this study, absorption properties of $TiO_2$ sols prepared by hydrothermal process were researched with the effect of various particle sizes and concentrations. The mean particle size in $TiO_2$ sols increased as 15 nm to 60 nm, absorption graph measured by UV-Vis spectrometer shows to move red-shift. When dilute solution added with $2^n$ in $TiO_2$, the band gap energy increases as linear function.

• Restorative Dentistry and Endodontics
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• 제20권2호
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• pp.818-826
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• 1995

The present study was undertaken to investigate the crystal growth onto enamel mineral and synthetic hydroxyapatite seeds in media resembling the enamel fluid composition. Effects of fluoride at low concentrations on the precipitation were also examined in a benchtop crystal growth model adopting a miniaturized reaction column. X-ray diffraction and Fourier transform infrared spectroscopy(FTIR), as well as chemical analyses, were employed for characterization of both seed materials before and after experimentation. Remarkable findings were that (1) both biological and synthetic seeds at the same total surface areas yielded rather similar precipitation rates at all levels of fluoride concentration in solution and (2) the precipitation rate was accelerated in a manner depending on fluoride concentrations in media. FTIR differential analysis disclosed that the precipitating phase was characterized as poorly crystallized apatite, which incorporated subtle carbonate. Most of the fluoride ions in soution were readily incorporated into crystals. The overall results support the view that the seeded crystal growth model is of value to gain insight into the mechanism of enamel crystal growth under fluoride regimens.