• Journal of the Korean Magnetics Society
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• v.5 no.1
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• pp.58-63
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• 1995

The crystallographic and magnetic properties of the ferrimagnetic $Ni_{0.5}Co_{0.5}Fe_{2}O_{4}$ have been studied by X-ray and $M\"{o}ssbauer$ measurements. The Crystal structure is found to be spinel structure with the lattice constant $a_{0}=8.346{\pm}0.005\;{\AA}$. $M\"{o}ssbauer$ spectra of $Ni_{0.5}Co_{0.5}Fe_{2}O_{4}$ have been taken at various temperatures rallging from 13 to 780 K. The isomer shifts indicate that the valence states of the Fe ions for tetrahedral(A) and octahedral(B) sites have ferric character. Debye temperatures for the A and B sites are found to be $441{\pm}5\;K$ and $321{\pm}5\;K$, respectively. Atomic migration from the A to the B sites starts near 500 K and increases rapidly with increasing temperature to such a degree that 51 % of the ferric ions at the A sites have moved over to the B sites by 700 K.

• Journal of the Korean Magnetics Society
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• v.9 no.1
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• pp.1-6
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• 1999

The crystallographic and magnetic properties of the ferrimagnetic $CoFe_{1.9}Ga_{0.1}O_4$ have been studied by X-ray, M$\"{o}$ssbauer measurements. The crystal structure is found to be inverse spinel structure with the lattice constant $a_0=8.386{\pm}0.005{\AA}$. M$\"{o}$ssbauer spectra of $CoFe_{1.9}Ga_{0.1}O_4$ have been taken at various temperatures ranging from 13 to 840 K. The isomer shifts indicate that the valence states of the Fe ions for tetrahedral (A) and octahedral (B) sites have ferric character. Debye temperatures for the A and B sites are found to be 882$\pm$5 K and 209$\pm$5 K, respectively. Atomic migration form the A to the B sites starts near 350 K and increases rapidly with increasing temperature to such a degree that 73% of the ferric ions at the A sites have moved over to the B sites by 700 K. by 700 K.

• Korean Journal of Materials Research
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• v.11 no.3
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• pp.203-206
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• 2001

The effects of SrTiO$_3$ addition and sintering temperature on the microstructure and magnetic properties of yttrium iron garnet (YIG) were investigated. The lattice Parameter increasing of sintered YlG with small amount of SrTiO$_3$ addition was supposed to be substituted $Y^{+3}$, Fe$^{+3}$ ions to Sr$^{+2}$,Ti$^{+4}$ ions which are relatively large in ionic ranius. A YIG specimen sintered at 142$0^{\circ}C$ with 0.2mol% SrTiO$_3$ showed above 98% densification of theoretical density. Saturation magnetization (M$_s$) at room temperature decreased a little bit with increasing SrTiO$_3$, addition but no great chance. In addition, the coercivity (H$_c$) was almost not changed by sintering temperature.

• Korean Journal of Soil Science and Fertilizer
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• v.32 no.4
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• pp.429-439
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• 1999

Potentiometric titration data were collected for some humic acids purified from Korean upland and paddy soils over a range of pH (3.0 - 11.0) with $NaNO_3$ background electrolyte concentrations (0.01, 0.10, 0.50 and 1.00 M). The data were applied to model A and V which included both intrinsic heterogeneity of humic materials and electrostatic interaction influences on binding sites. The elemental analysis were conducted for various type of humic samples. The $E_4/E_6$ ratio proposed negative correlation with the total carboxyl groups ($r^2$= 0.9988). The charge ($cmol_c\;kg^{-1}$) on the humic acids became more negative as the ionic strength increased. In both continuous and batch titrations, the ionic strength effect was greater in Namweon series (pH 6.39) than others at pH 5.00. The effect of ionic strength on surface charge appears to be greater in batch titrations. This could suggest that continuous titrations do not represent an equilibrium state and the effects of electrolyte concentration was not fully realized during the course of titrations. Both models described experimental data obtained from continuous and batch titrations well over a range of ionic strengths. Model A is more simpler than model V but adaptes more fitted parameters. Thus, the observed change in apparent binding constants with surface charge is regarded solely due to electrostatic influences rather than functional group heterogeneity. However, Model V is more mechanistically realistic in a number of discrete ligand binding sites.

• Journal of the Korean Chemical Society
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• v.38 no.10
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• pp.753-762
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• 1994

Dephosphorylation of diphenyl- or isopropylphenyl-4-nitrophenylphosphinate (DPNPIN or IPNPIN) mediated by $OH^-$ or o-iodosobenzoate ion ($IB^-$) are relatively slow in aqueous solution. The reactions in CTAX micellar solutions are, however, very accelerated, because CTAX micelles can accommodate both reactants in their Stern layer in which they can easily react, while hydrophilic $OH^-$(or $IB^-$) and hydrophobic phosphinates are not mixed in water. Even though the concentrations (> $10^{-3}$ M) of $OH^-$(or $IB^-$) in CTAX solutions are much larger amounts than those ($6{\times}10^{-6}$ M) of phosphinates, the rate constants of the dephosphorylations are largely influenced by change of the concentration of the ions, which means that the reactions are not followed by the pseudo first order kinetics. In comparison to effect of the counter ions of CTAX in the reactions, CTACl is more effective on the dephosphorylation of DPNPIN (or IPNPIN) than CTABr due to easier expelling of $Cl^-$ ion by $OH^-$(or $IB^-$) ion from the micelle, because of easier solvation $Cl^-$ ion by water molecules. The reactivity of IPNPIN with $OH^-$(or $IB^-$) is lower than that of DPNPIN. The reason seems that the 'bulky' isopropyl group of IPNPIN hinders the attack of the nucleophiles. The mechanism of reaction of IPNPIN with IB- ion concluded as 'nucleophilic' instead of 'general basic' by a trapping experiment and a measured kinetic isotope effect.

• Applied Biological Chemistry
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• v.28 no.2
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• pp.68-75
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• 1985

Laboratory experiments were conducted to investigate the effect of compost and humic acid treatment on adsorption of Cd, Zn, and Cu in soils. Three soils differing in physical and chemical properties used in this experiments were Bonyrang (Typic Udifluvents) SL, Gangseo (Aquatic Eutrochrepts) L, and Gyorae (Typic Distrandepts) SiL. Adsorption of Cd, Zn, ana Cu on the soils followed Langmuir isotherm up to 75 ppm of initial concentration. The adsorption maxima of Cd, Zn, and Cu for the Bonryang soil, the lowest in pH, organic matter content, and CEC, were the lowest of the three soils. Although the Gyorae soil derived from volcanic ash was the highest in organic matter content and CEC, the adsorption maxima of heavy metals for the Gyorae soil were lower than those for the Gangseo soil of which organic content and CEC were intermidiate. The adsorption maxima/CEC ratios for the Bonryang, the Gangseo, the Gyorae soils were found to be in the range of $23{\sim}27%,\;28{\sim}57%$, and $11{\sim}14%$ respectively The bonding energy constants of Cd, Zn, and Cu for the soils were in the order of Gangseo>Bonryang>Gyorae soils. The adsorption maxima of Cd, Zu, and Cu for the Bonryang soil increased with compost treatment by $100{\sim}210%,\;90{\sim}230%$, and $130{\sim}290%$ respectively, while little difference was observed when the soil was treated with humic acid Bonding energy constants of Cd, Zn, and Cu for the Bonryang soil increased significantly with compost treatment, and showed insignificant correlation with humic acid treatment.

• Applied Chemistry for Engineering
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• v.5 no.5
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• pp.825-835
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• 1994

Synthesis of ETBE as an octane number enhancer from ethanol and isobutene in a flow reactor under atmospheric pressure was studied. Amberlyst-15 and Amberlyst XN-1010 were used as catalysts within the temperature range of $70-140^{\circ}C$. The activity of Amberlyst 15 was higher than that of Amberlyst XN-1010. The reaction rate data obtained under differential reactor condition were tested by a linear regression method to determine the reaction mechanism and kinetic parameters. The ETBE synthesis reaction seems to be proceeded via the LHHW(Langmuir-Hinshelwood-Hougen-Watson) machanism. The activation energy of the surface reaction was estimated by the reaction rate constants as well as the adsorption equilibrium constants. Apparent activation energies are 18.64 and 24.19kcal/mol for Amberlyst-15 and Amberlyst XN-1010, respectively.

• Composites Research
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• v.37 no.2
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• pp.132-138
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• 2024

In this study, a molecular dynamics simulation study was performed to investigate the size-dependent electroelastic properties of single-walled boron nitride nanotubes(BNNT). To describe the elasticity and polarization of BNNT under mechanical loading, the Tersoff potential model and rigid ion approximation were adopted. For the prediction of piezoelectric constants and Young's modulus of BNNTs, piezoelectric constitutive equations based on the Maxwell's equation were used to calculate the strain-electric displacement and strain-stress relationships. It was found that the piezoelectric constants of BNNTs gradually decreases as the radius of the tubes increases showing a nonnegligible size effect. On the other hand, the elastic constants of the BNNTs showed opposites trends according to the equivalent geometrical assumption of the tubular structures. To establish the structure-property relationships, localized configurational change of the primarily bonded B-N bonded topology was investigated in detail to elucidate the BNNT curvature dependent elasticity.

• Proceedings of the Korea Technical Association of the Pulp and Paper Industry Conference
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• 2000.11a
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• pp.138-138
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• 2000

국내의 백상지 공정은 공정에 투입되는 청수의 양을 줄이면서 동시에 폐수 배출 양을 감 소시키기 위해 많은 노력을 하고 있다. 공정으로 유입되는 청수의 양과 처리된 폐수의 양을 줄이기 위한 방법으로 PDFCpolydisk filter)를 도입하여 백수를 여과하여 showertf sealing 에 재사용하고 있으며 공정수 재활용에 따른 유기 물질과 무기물질의 계 내로의 축적을 방 지하기 위한 효과적인 폐수 처리방법을 모색하고 있다. 일반적으로 청수를 백수로 대체할 경우 공정 백수 내에 TDSCtotal dissolved solid), T TSSCtotal suspended solid), CODCchemical oxygen demand), 전기 전도도와 칼숨 경 도 등이 증가되며 음이온성 저해 물질Canionic trash)이 증가하여 보류 및 지력증강용 첨가제의 효율 을 떨어뜨릴 뿐만 아니라 마모, 슬라엄, 펠트 막힘 등의 문제를 유발하게 된다고 알려져 있다. 청수를 백수로 대체함에 따라 생기는 이러한 문제를 해결하면서 효율적인 청수 절약 방안 을 세우기 위해서는 무엇보다도 문제를 유발하는 원인 물질의 축적 양을 예측하는 것이 중 요하다고 판단된다. 본 연구는 백상지 공정의 폐쇄화 수준이 높아짐에 따른 공정 백수 내의 유기물질의 축적 현상을 분석하는 것올 목적으로 하였다. 이를 위해 산화전분을 유기물질의 대표하는 물질로 설정하였다. 이는 백상파지와 함께 초지계 내로 유업되는 산화전분은 파지의 4%를 차지할 정도로 유입량이 많을 뿐만 아니라 음이온성을 띄고 있어서 지료에 홉착율이 낮고 양이온성 고분자의 효율을 저해하며 슬라임의 원인이 되기도 하는 물질이기 때문이다. 산화전분의 축적 현상을 분석하기 위하여 pilot 설비 상세 설계도를 참고하여 하루 생산량 이 16 T/D이고 백상파지만이 파지로 유입되는 백상지 생산 공정을 모델로하였으며, 산화전 분의 홉착과 용출 모델을 만들어 상용 시율레이터를 이용하여 시율레이션 프로그램을 작성 하였다. 시률레이션 프로그램에서는 장섬유 미세섬유, 충전제를 지료 구성 성분으로 설정하였고 O Orccotoma 등이 사용한 일과 보류도 모델을 응용하여 보류도 모델올 만들었다. 산화전분은 백상파지에 포함된 형태로만 초지계 내로 유입되며 백상파지가 해리되는 과정에서 완전히 백수에 용출되었다가 지료 구성 성분에 홉착되는 것으로 가정하였다. 지료 홉착된 산화전분 의 양은 용존 산화전분 총량에 비례하는 것으로 가정하였으며, 이 때 이 비례상수를 전분 홉착율이라 정의하였다. 시율레이션 결과, 공정 폐쇄화가 진행됨에 따라 백수 내의 산화 전분 농도는 증가하게 되 며, 폐쇄화 수준이 높아질수록 백수 내 전분 농도의 증가량은 더 높아졌다. 백수 내의 전분 농도의 증가량은 백상파지 첨가량이 증가할수록, 표면 사이징 양이 증가할수록 커졌다.

• Journal of the Korean Chemical Society
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• v.40 no.6
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• pp.420-426
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• 1996

The critical micelle concentration(CMC) and the counterion binding $constant(\beta)$ at the CMC of the mixtures of Sodium dodecylsulfate(SDS) with Sodium dodecylbenzenesulfonate(DBS) in aqueous solutions have been determined from the concentration dependence of electrical conductance at several temperatures from $15^{\circ}C$ to $35^{\circ}C.$ Thermodynamic parameters(${\Delta}C_p,\;{\Delta}G_m^{\circ},\;{\Delta}H_m^{\circ}$ 및 ${\Delta}S_m^{\circ}$ and ${\Delta}C_p$), associated with the micelle formation of SDS/DBS mixtures, have been estimated from the temperature dependence of CMC and $\beta$ values. The measured values of ${\Delta}G_m^{\circ}\;and\;{\Delta}C_p$ are negative but the values of ${\Delta}S_m/^{\circ}$ are positive in the whole measured temperature region. The significance of these thermodynamic parameters and their relation to the theory of the micelle formation of SDS/DBS mixtures have been also considered.