• Bulletin of the Korean Chemical Society
• /
• 제30권2호
• /
• pp.373-377
• /
• 2009

A pathway for the formation of normal $CoAl_2O_4$ particles is suggested. The optimal amount of malonic acid was determined, and the characteristics of the obtained powders were investigated. Normal $CoAl_2O_4$ powders were prepared using solutions of malonic acid and metal nitrates. X-ray diffraction, Brunauer-Emmett-Teller (BET) and scanning electron microscope (SEM) measurements, as well as Fourier transform infrared (FTIR) and ultraviolet/visible (UV-Vis) spectroscopy were carried out. Normal $CoAl_2O_4$ crystallites were formed by a solid state reaction between $CoAl_2O_4$ and amorphous aluminum oxide. The optimal molar ratio of malonic acid to the nitrate anions present in the initial solution was found to be 0.30~0.35. The particles were composed of agglomerates of primary particles. The primary particles were 40 nm in size. This size was relatively constant regardless of the preparation temperature. However, the size of the agglomerated particles increased to 220 nm with increasing temperature.

• KSBB Journal
• /
• 제15권6호
• /
• pp.548-555
• /
• 2000

온도 및 pH에 동시에 민감한 하이드로젤 poly(N-isopropy­l lacrylamide-co-N,N-dimethylaminopropy Imethacrylamide)을 온도 (13, 15.5, 18, 20.5 및 $23^{\circ}C$)와 pH (10.3, 11.3 및 12.3)를 달리 하여 합성하고 이 젤들의 외형, 기계적 강도, 젤 표면모양, LCST, 수축 pH 및 젤의 팽윤 특성을 연구하였다. 합성온도 및 합성 pH가 낮을수록 젤의 외형은 투명하였 고 기계적 강도는 높았다. SEM 관찰 결과 단백질 보다 더 큰 pore들 때문에 분리효율이 감소되는 것으로 사료된다. 합 성온도나 합성 pH의 증가는 LCST를 낮추었다. 외부온도가 LCST보다 낮은 $25^{\circ}C$ 에 서는 모든 합성온도와 합성 pH에 대 하여 젤은 전 pH에 걸쳐 팽윤된 상태에 있었다. $40^{\circ}C$에서는 LCST보다 높은 온도임에도 불구하고 poly (NIPAAm-co­D DMAPMAAm) 하이드로젤은 pH가 중성 및 산성 영역에서 팽윤되었다. 합성온도가 증가함에 따라 젤 부피가 가장 큰 폭으로 변하는 수축 pH가 더 높아졌다.

• 약학회지
• /
• 제30권5호
• /
• pp.228-231
• /
• 1986

The effect of temperature and pH on the degrdation of minoxidil in the aqueous solution was investigated and the stability of pharmaceutical preparation for solution was also studied. The degradation of minoxidil in the aqueous solution was first order type reaction and the rate constant at $20^{\circ}C$ in pH 7.0 phosphate buffer solution was 9.464${\times]10^{-3} day^{-1}$ and calculated activation energy was 11.7 kcal/mol. The degradation of minoxidil was acid-base catalytic reaction and the most stable range of pH was about 5.0. The liquid pharmaceutical preparation was very stable in 3 months.

• 약학회지
• /
• 제12권3_4호
• /
• pp.41-49
• /
• 1968

The optimum reaction conditions for the preparation of the precipitated calcium carbonate of an average particle size of 0.05.mu. in diameter was set in which the Box-Wilson Plan was applied. The reaction conditions are as follows; 1) concentration of milk of lime; 6.56% w/w 2) temperature; 14.24.deg. C #) velocity of carbon dioxide introducing; 1.95l/min. The crystal form was found that of calcite in X-ray diffraction analysis. The particle size was determined by the sedimentation volume measurement. The shape was identified by the elctron micro-diffraction pattern and the electron microscopic photographs.

• 한국식품영양과학회지
• /
• 제28권4호
• /
• pp.942-947
• /
• 1999

This study was conducted to evaluate sanitary practices of employees in business & industry foodservice operations of Pusan and the Kyung Nam areas, and to suggest a guideline for an effective sanitation training program. The questionnaire was used in this study as a survey method. Questionnaire were administered to 246 employees. The results were as follows. 55.3% of employees have had regular(monthly) food sanitation education. The mean rating of food sanitary knowledge for all employees was 65.9/100. When the education level was higher and the age younger, the mean rating of was also higher. Among the ratio of correct answers for food sanitary knowledge areas, a equipment sanitation was the highest (80.5%), and time temperature was the lowest(45.3%). The mean rating of sanitary procedures for food storage was 4.80/5.00, pre preparation 4.04/5.00, personal hygiene 3.54/5.00, equipment sanitation 3.20/5.00, and food preparation 2.56/5.00. Employees regularly educated in food sanitation rated significantly higher for food preparation than those who were of irregulary educated. The higher mean rating group(over 66) for the food sanitary knowledge showed significantly higher rates in sanitary procedures(food preparation, equipment sanitation, and personal hygiene) than that of the lower group(below 65). The practice of personal hygiene was positively correlated (p<0.001) with sanitary concept and food preparation, among the food sanitary knowledge areas.

• 한국결정성장학회지
• /
• 제13권1호
• /
• pp.24-30
• /
• 2003

The preparation of $PbTiO_3$ powder was carried out using the oxide starting material by hydrothermal method. The powder of a crystalline phase with perovskite structure was synthesized. The optimum conditions for the preparation of powder were as follows; hydrothermal solvent; 8M-KOH or 8M-NaOH, reaction temperature; 250~$270^{\circ}C$, run time; 10 h. The ,shape of synthesized powders were well developed crystalline faces with specific surface area of about 2.3 $\textrm m^2$/g in KOH solution and about 5.0 $\textrm m^2$/g in NaOH solution. The cell parameters of powder were a = 3.90$\AA$, c = 4.14 $\AA$ and cell volume was 57.30 $\AA^3$. The cell ratio (c/a) of powder was the same as the theoretical ratio with c/a = 1.06 and the phase transition temperature(Tc) of the powders was about $470^{\circ}C$.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 1995년도 춘계학술대회 논문집
• /
• pp.26-30
• /
• 1995

We describe the preparation and characterization of epitaxial thin films made with high temperature superconductor, $YBa_2Cu_3O_{7-\delta}$. The influence of processing parameters for YBCO thin films on MgO substrates in-situ grown by the pulsed laser deposition, including parameters of a laser beam energy, oxygen pressure, substrate temperature, target-substrate dis-tance is discussed. The characteristics of YBCO thin films were analyzed by using XRD, R-T measurement, AFM, crosssectional TEM, and RBS. For examples of microwave device applications, The fabrication and characterization of the microstrip lowpass filter and bandpass filter are also presented.

• 한국자동차공학회논문집
• /
• 제5권5호
• /
• pp.51-66
• /
• 1997

A heat transfer model of the intake valve in a spark ignition engine is presented, which is calibrated with a number of the valve temperature profiles measured during engine warm-up for the gaseous fuel(propane). The valve is divided into four identical elements for which the assumption of lumped thermal mass is applied. The calibration is made so that the difference between the measued and simulated valve temperatures becomes minimal. Then the model is applied to the cases of the liquid fuel(indolene) to estimate the amount of the liquid fuel vaporized from the intake valve by assuming that fuel evaporation accounts for the deficit of the heat balance budget. The results of the model show quantitative contribution of each heat transfer source to the heat balance. The behavior of the calculated mass fraction of the fuel vaporized from the intake valve explains how the liquid fuel evaporate during engine warm-up. The mass fraction at warmed-up condition is closely related with the fraction directly targeted on the valve back by the fuel spray geometry.

• 한국세라믹학회지
• /
• 제30권3호
• /
• pp.236-242
• /
• 1993

As the fundamental research on preparation of fine single crystalline ferroxaplana by means of glass-crystallization methods using steel twin-roller, the properties of ferroxplana crystallized from glass were studied. Most of the specimens quenched by twin-roller at about 130$0^{\circ}C$ were glass phase, the crystallization of these glasses underwent multi-steps and ferroxplana phase was only stable in the temperature range of 88$0^{\circ}C$ to 95$0^{\circ}C$. Above 95$0^{\circ}C$ ferroxplana begines to be decomposed in glass. Ferroxplana had such magnetic properties as M8=29emu/g, MHC=166Oe, and Curie Temperature, Tc=610$\pm$5K.

• 한국세라믹학회지
• /
• 제34권4호
• /
• pp.420-428
• /
• 1997

Alumino-borosilicate glasses containing nano-sized CuCl crystals for nonlinear optical application were prepared by the melting and precipitation process, and structural and optical properties were investigated by using XRD, TEM, SAXS, and optical spectroscopy. the average radius of the precipitated CuCl particles was about 2 nm. The blue shift of Z3 resonance peak with decreasing the precipitated CuCl particles size was found and the radius increased with decreasing the glass transition temperature of the matrix glass and with increasing the temperature and duration time of the precipitation heat treatment.