• 대한화학회지
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• 제56권5호
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• pp.609-616
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• 2012

Ba-ferrite ($BaFe_{12}O_{19}$) nanoparticles were synthesized by chemical coprecipitation method in an aqueous solution. The particle size and the crystallization temperature of the Ba-ferrite nanoparticles were controlled varying the precipitation temperature. The precipitate that was prepared at $0^{\circ}C$ showed the crystal structure of Ba-ferrite in X-ray diffraction when it was calcined at the temperature above $580^{\circ}C$, whereas what was prepared at $50^{\circ}C$ showed the crystallinity when it was calcined at the temperature higher than about $700^{\circ}C$. The particle sizes of the synthesized Ba-ferrite were in a range of about 20-30 nm when it was prepared by being precipitated at $0^{\circ}C$ and calcined at $650^{\circ}C$. When the precipitation temperature increased, the particle size also increased even at the same calcination temperature. The magnetic properties of the Ba-ferrite nanoparticles were also controlled by the synthetic condition of precipitation and calcination temperature. The coercive force could be appreciably lowered without a loss of saturation magnetization when the Ba-ferrite nanoparticles were prepared by precipitation and calcination both at low temperatures.

• Carbon letters
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• 제14권1호
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• pp.45-50
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• 2013

Polyacrylonitrile (PAN) copolymers of different molecular weights were synthesized by a suspension polymerization and precipitation polymerization method. The rheology behaviors of the synthesized PAN copolymers were investigated in relation to their molecular weight, solid content and melting temperature. The influence of "historical effects" on the spinning solution of PAN was studied by analyzing the laws of viscosity considering the diversification time and temperature. The viscosity disciplines of each spinning solution conformed well to the rheological universal laws in a comparison of the suspension polymerization product with that of precipitation polymerization. Viscosity changes in the swelling process of dissolution were gentler in the suspension polymerization product; a small amount of water will quickly debase the solution viscosity, and high-speed mixing can greatly shorten the time required by the spinning solution to reach the final viscosity.

• Macromolecular Research
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• 제11권1호
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• pp.53-61
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• 2003

A molecular-thermodynamic model is developed for the salt-induced protein precipitation. The protein molecules interact through four intermolecular potentials. An equation of state is derived based on the statistical mechanical perturbation theory with the modified Chiew's equation for the fluid phase, Young's equation for the solid phase as the reference system and a perturbation based on the protein-protein effective two body potential. The equation of state provides an expression for the chemical potential of the protein. In a single protein system, the phase separation is represented by fluid-fluid equilibria. The precipitation behaviors are simulated with the partition coefficient at various salt concentrations and degree of pre-aggregation effect for the protein particles. In a binary protein system, we regard the system as a fluid-solid phase equilibrium. At equilibrium, we compute the reduced osmotic pressure-composition diagram in the diverse protein size difference and salt concentrations.

• 한국대기환경학회지
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• 제20권3호
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• pp.381-396
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• 2004

In order to understand the precipitation acidity and chemical composition of ion species in Iksan area as well as to know the difference of chemical characteristics in precipitation samples from the viewpoint of precipitation sampling method, precipitation samples were collected by wet-only automatic precipitation sampler and bulk manual precipitation sampler in Iksan, from March 2003 to August 2003. The mean pH of precipitation was 5.0. There was a little significant difference in the mean value of pH between automatic and manual sampler. However, pH values of some precipitation samples were lower in automatic sampler than in manual sampler, especially in case of precipitation samples with small rainfall for March 2003. The mean concentrations of each ions in precipitation were generally a little higher in precipitation samples collected by the manual sampler than in those collected by the automatic sampler because of accumulation of dry deposition on the surface of glass funnel installed at the manual sampler during the sampling period or no rainfall. Dominant species determining the acidity of precipitation, were N $H_4$$^{[-10]}$ and nss-C $a^{2+}$ for cations and nss-S $O_4$$^{2-}$ and N $O_3$$^{[-10]}$ for anions. The mean concentration of N $H_4$$^{+}$ and nss-C $a^{2+}$ were 31 $\mu$eq/L and 9 $\mu$eq/L for the automatic sampler and 40 ueq/L and 16 ueq/L for the manual sampler, respectively. In addition, nss-S $O_4$$^{2-}$ and N $O_3$$^{[-10]}$ were 27 $\mu$eq/L and 13 $\mu$eq/L for the automatic sampler and 32 $\mu$eq/L and 17 $\mu$eq/L for the manual sampler, respectively. Although the concentrations of the acidifying ions of nss-S $O_4$$^{2-}$ and N $O_3$$^{[-10]}$ were about 3 times higher than those for foreign pristine sites, precipitation acidity were estimated to be natural due to the neutralization reaction of the alkaline species of N $H_4$$^{+}$ and nss-C $a^{2+}$ with its higher concentrations. Considering the ratios of nss-S $O_4$$^{2-}$/N $O_4$$^{[-10]}$ nss-S $O_4$$^{2-}$, it was found that ammonium sulphate was dominant in Iksan precipitation. The major non-sea salt ions were maximum concentrations for March, but decreased with increasing of precipitation amount.on amount.

• Bulletin of the Korean Chemical Society
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• 제24권3호
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• pp.363-368
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• 2003

The major ionic components of precipitation collected at the 1100 Site of Mt. Halla and Jeju city have been determined. The reliability of the analytical data was verified by the comparison of ion balances, electric conductivities and acid fractions; all of their correlation coefficients were above 0.94. Ionic strengths lower than $10^{-4}$ M were found in 53% of the 1100 Site samples and 28% of the Jeju city samples. Compared with other inland areas, the wet deposition of $Na^+,\;Cl^-\;and\;Mg^{2+}$ was relatively larger, but that of $NH_4^+,\;nss-SO_4^{2-}$(non-sea salt sulfate) and $NO_3^-$ was lower. Especially the wet deposition increase of $Ca^{2+}$ in the spring season supports the possibility of the Asian Dust effect. The acidification of precipitation was caused mostly by $SO_4^{2-}\;and\;NO_3^-$ in the Jeju area, and the organic acids have contributed only about 7% to the acidity. The neutralization factors by NH₃were 0.47 and 0.48, and that of CaCO₃was 0.31 and 0.25 at the 1100 Site and Jeju city, respectively. Investigation into major influencing sources on precipitation components by factor analysis showed that the precipitation at the 1100 Site had been influenced mostly by an anthropogenic source, followed by soil and seawater sources. The precipitation at Jeju city was mainly influenced by oceanic sources, followed by anthropogenic and soil sources.

• Carbon letters
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• 제11권1호
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• pp.22-27
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• 2010

The precipitation polymerization of acrylonitrile (AN) was carried out in a mixture solution of dimethyl sulfoxide (DMSO) and water at $50{\sim}65^{\circ}C$ using ${\alpha},{\alpha}'$-azobisisobutyronitrile (AIBN) as an initiator. The increased molecular weight polyacrylonitrile (PAN) was prepared with increasing the $H_2O$/DMSO ratio from 10/90 to 80/20. The viscosity average molecular weight of $H_2O$/DMSO solvent was 4.4 times larger than that of $H_2O$/DMF solvent, and precipitation polymerization was accelerlated due to the far decreased chain transfer effect of DMSO. Based on the experimental results, the increased PAN molecular weight was regarded as the summation of two mechanisms: i) particle-particle aggregation and ii) particle-radical attachment. The theoretical equation derived from the mechanisms was well coincided with the experimental results showing the linear relationship between the viscosity average molecular weight and the H2O/DMSO ratio.

• 한국환경과학회지
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• 제6권5호
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• pp.461-472
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• 1997

This study was carried out to investigate the characteristics of chemical components and precipitation at Kimhae area from March, 1992 to June, 1994. The pH values, concentration of soluble ions($Cl^-$, $NO_2^-}$ $NO_3^-}$, $NO_4^{2-}$-, $PO_4^{3-}$. $F^-$, $Mg^{2+}$, $Ca^{2+}$, $Mn^{2+}$, $K^+) and non-soluble metals(Cr.Si. Zn, Pb, Cu, Fe, Mn, Mg, Ad. V. Cal were measured by pH meter, IC (ion Chromatography) and ICP(Inductively Coupled Plasma). The data were analyzed by the dally. hourly distribution characteristics of acidity and chemical components, as well as the correlation between them. The results are as follows. 1. The pH range of precipitation was from 3.45 to 6.80 in Kimhae area. and average value was pH 4.62 and main chemical components were $SO_4^{2-}$, $Cl^-$, $NO_3^-$. The highest pH value and concentration appeared in initial rain, which might result from urbanlzation and industrialization in this area and long term transportation from China. 2. The hourly correction distribution of main anions related to pH value In the rainwater showed $SO_4^{2-}$ > $NO_3^-$ > $Cl^-$. Hourly concentration of heavy metal and each ion was highly correlated with pH in the precipitation.

• Macromolecular Research
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• 제12권5호
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• pp.519-527
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• 2004

Stable poly(methyl methacrylate-co-divinylbenzene) (poly(MMA-co-DVB)) microspheres were prepared by precipitation polymerization using acetonitrile as the main medium under various polymerization conditions, including modifications of the agitation speed, monomer and initiator concentrations, DVB content in the monomer mixture, and the use of various cosolvents. Gentle agitation was required to obtain smooth spherical particles. The individually stable microspheres were obtained at monomer concentrations of up to 15 vol% in an acetonitrile medium. The number-average diameter increased linearly with respect to increases in the monomer and initiator concentrations. We found, however, that the uniformity of the microspheres was independent of the variation of the polymerization ingredients because nuclei formation was solely influenced by the crosslinking reaction of the monomers. We obtained higher yields for the polymerization at higher concentrations of monomer and initiator. The concentration of DVB in the monomer mixture composition played an important role in determining not only the size of the microspheres but also the yield of the polymerization. In addition, although we employed various cosolvents as the polymerization medium, we found that acetonitrile/2-methoxyethanol was the only system that provided spherical particles without coagulation. This finding indicates that the precipitation polymerization is strongly dependent on the solvent used as the medium.

• 공업화학
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• 제10권7호
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• pp.996-1002
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• 1999

알칼리 및 알칼리토금속(Cs, Rb, Ba, Sr), 전이금속(Zr, Fe, Mo, Ni, Pd, Rh), 란탄족(La, Y, Nd, Ce, Eu) 및 악티늄족(Np, Am) 등 17개 원소로 구성된 질산매질의 모의 방사성용액에서 옥살산에 의한 란탄족과 악티늄족 원소의 공침전 연구를 수행하였다. 옥살산 농도 0.5 M에서 질산농도의 영향과 아스코빅산 첨가에 따른 원소들의 침전율이 조사되었다. 각 원소들의 침전율은 질산농도에 따라 약간 감소하였으나 란탄족과 악티늄족은 99% 이상 침전되었다. 옥살산 침전시 아스코빅산이 첨가되는 경우 Pd이 금속으로 환원 침전되었고, 이때 Mo, Fe, Ni, Ba의 경우는 침전율이 약 10~20% 감소하는 것으로 나타났으나, 기타 원소들에 대해서는 영향이 나타나지 않았다. Pd(II) 이온은 질산농도 1.0 M 미만의 모의용액에서 아스코빅산 첨가시 Pd 금속으로의 환원침전이 일어났으며, 아스코빅산 농도가 0.01~0.02 M 부근에서 가장 크게 나타났다. 하이드라진이 아스코빅산과 같이 첨가될 때 Pd의 환원침전을 억제하는 것으로 나타났다.

• 한국재료학회지
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• 제25권6호
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• pp.274-278
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• 2015

The possibility of using the chemical precipitation method of up-cycled ammonium paratungstate (APT) was studied and compared with the thermal decomposition method. $WO_3$ particles were synthesized by chemical precipitation method using a 1:2 weight ratio of APT: Di-water. For thermal decomposition, APT powder was heated for 4h at $600^{\circ}C$ in air atmosphere. The reaction products were characterized by X-ray diffraction (XRD), X-ray fluorescence spectrometer (XRF), particle size analyzer (PSA), and field emission-scanning electron microscopy (FE-SEM). Thermogravimetric analysis (TGA) of the up-cycled APT allowed for the identification of the sequence of decomposition and reduction reactions that occurred during the heat treatment. TGA data indicated a total weight loss of 10.78% with the reactions completed in $658^{\circ}C$. The XRD results showed that APT completely decomposed to $WO_3$ by thermal decomposition and chemical precipitation. The particle size of the synthesized $WO_3$ powders by thermal decomposition with 2 h of planetary milling was around $2{\mu}m$ During the chemical precipitation process, the particle size of the synthesized $WO_3$ powders showed a round-shape with ${\sim}0.6{\mu}m$ size.