• 한국세라믹학회지
• /
• 제36권2호
• /
• pp.167-171
• /
• 1999

130$0^{\circ}C$, 10시간 산소 분위기에서 소결한 이산화티탄의 소결체를 이용하여 수소 환원 속도를 조사하였다. 10% 수소(Ar balnce)를 분당 300ml 흘리면서 1200, 1250 및 130$0^{\circ}C$에서 각 4~20시간 환원하여 얻어진 시편의 환원 전과후의 무게 감소 및 환원 층의 두께를 측정하여 수소환원 속도가 평가되었다. 이산화티탄의 소결체가 수소환원 될 때 환원 생성물의 생성은 parabolic rate 법칙을 잘 만족하고 있음을 관찰할 수 있었으며, 이로부터 확산이 환원속도를 지배하고 있음을 알수 있었다. 얻어진 환원속도 상수의 Arrhenius plot로부터 계산된 겉보기 활성화 에너지는 약 210$\pm$10 kJ/mol 이었다.

• Biotechnology and Bioprocess Engineering:BBE
• /
• 제11권3호
• /
• pp.223-229
• /
• 2006

In this study, we have conducted kinetics and modelling studies of Centella asiatica cell growth and substrate uptake, in an attempt to evaluate cell growth for a better understanding and control of the process. In our bioreactor cultivation experiment, we observed a growth rate of 0.18/day, a value only 20% higher than was seen in the shake flask cultivation trial. However, the observed maximum cell dry weight in the shake flask, 10.5g/L, was 14% higher than was achieved in the bioreactor. Ninety seven percentage confidence was achieved via the fitting of three unstructured growth models; the Monod, Logistic, and Gompertz equations, to the cell growth data. The Monod equation adequately described cell growth in both cultures. The specific growth rate, however, was not effectively predicted with the Logistic and Gompertz equations, which resulted in deviations of up to 73 and 393%, respectively. These deviations in the Logistic and Gompertz models may be attributable to the fact that these models were developed for substrate-independent growth and fungi growth, respectively.

• 한국생물공학회:학술대회논문집
• /
• 한국생물공학회 2003년도 생물공학의 동향(XIII)
• /
• pp.634-638
• /
• 2003

For the investigation of the properties of aqueous fibroin solution, the variation of molecular weight by agregation of silk, morphology and difference of molecular weight at pI value was investigated. The distribution of molecular weight investigated using gel filtration chromatography and formation of aggregates were confirmed by using Field emission scanning electron microscope. The precipitation of fibroin solution at its pI value was compared by molecular weight distribution and the formation of fibroin aggregated were investigated. The aggregation kinetics were investigated at various condition.

• Elastomers and Composites
• /
• 제51권2호
• /
• pp.122-127
• /
• 2016

Thermal decomposition kinetics for two different types of polyurethane elastomers prepared with 2,2'-dichloro-4,4'-methylenedianiline (MOCA) and 3,5-dimethyl-thiotoluenediamine (Ethacure-300), based on PTMG/TDI isocyanate prepolymer, were studied using non-isothermal thermogravimetric analysis (TGA). Thermograms were obtained and analyzed using Friedman (FR) and Kissinger-Akahira-Sunose (KAS) methods for activation energy, $E_a$. The results obtained showed that decomposition reaction of both samples was observed similarly to occur through three different stages, i.e., initial stage with vaporization of low molecular weight materials, second stage of urethane linkage decompositions, and later stage of polyol segment decompositions. However, activation energy values at each stage for the sample cured with Ethacure-300 was much lower than those for the sample with MOCA, exhibiting relatively lower thermal stability for the sample with Ethacure-300 than that with MOCA.

• Archives of Pharmacal Research
• /
• 제8권1호
• /
• pp.7-14
• /
• 1985

Membrane-coated tablet of isonicotinic acid hydrazide (INAH) which releases INAH at the zero-order kinetics was deveoped. It consisted of a soluble tablet core surrounded by a porous membrane which controls the diffusion rate. Tablet cores were prepared by compressing granules of INAH and polyvinyl chloride (PVC) dissolved in methyl ethyl ketone in which micronized sucrose were suspended. Diffusion rate of INAH from the tablet through the membrane was constant until the loaded INAH in the core was almost released. The rate was independent of pH of the dissolution medium. Water-soluble sucrose particles behaved as a poreproducing material in the water-insoluble PVC film coat. The pH independency of the rate was probably due to the high solubility of INAH in the water of wide pH range. The diffusion rate of INAH could be controlled by chnaging the composition of the membrane or the coat weight. This membrane-coated INAH tablet seemed to be a powerful candidate for the controlled release drug delivery system (DDS) of INAH or other highly watersoluble drugs.

• 한국세라믹학회지
• /
• 제30권11호
• /
• pp.974-978
• /
• 1993

Glass viscosity effects on the electrical properties and microstructure of RuO2 based thick film resistors (TFR) using alumina modified lead borosilicate glasses were studied. AT 85$0^{\circ}C$, the glass viscosities were increased from 4.24Pa.s to 51.5Pa.s when the alumina was added from none to 14 weight percent to the standard glass of 63% PbO, 25% B2O3 and 12% SiO2. The resistivities of resistors were generally decreased and the microstructure development was retarded as the viscosity of the glass increased. This is contrary to the generally accepted thought that the low resistivity is due to fast microstructure development kinetics in TFR. Even though the glass viscosity retards the microstructure development kinetics, the overall network formations are favored for higher viscosity of glass, such that the sheet resistivities were decreased as the glass viscosity increased.

• 대한설비공학회지:설비저널
• /
• 제16권4호
• /
• pp.415-420
• /
• 1987

The combustion kinetics of the imported bituminous coal was studied in the interme-diated heating rate. The activation energy and the frequency factor were obtained by experi-ment of the coal weight loss depending on the combustion time with Ih. furnace. The experi-ments were performed in the heating rates of $1,5,10^{\circ}C/sec\;or\;20^{\circ}C/sec\;at\;the\;600-900^{\circ}C$ maximum temperature, The values of the activation energy(E) which were calculated from the experimental data existed in the range from 3000cal/g-mol to 15000cal/g-mol, and those of the frequency $factor(1nk_O)$ were in the range from 4.5cm/sec to 11.5cm/sec.

• Korean Chemical Engineering Research
• /
• 제48권1호
• /
• pp.110-115
• /
• 2010

본 연구 목적은 두가지 종류의 국내 수입탄에 대한 열분해 반응율을 구하고 이를 비교하는 것이다. 이를 위해 TGA를 통하여 열분해 실험을 수행하였으며, 반응상수 분석은 New DAEM 방법을 이용하였다. 서로 다른 가열속도에서 각각 얻어진 TGA 질량변화 곡선으로부터, 활성화 에너지의 분포함수를 구한 후 최고빈도를 나타내는 활성화 에너지를 평균 활성화 에너지로 결정하였다. 그 결과 석탄의 종류에 따라 상기 반응에 대한 반응속도상수가 확실한 차이를 보였다. 이 같은 New DAEM 분석기법을 통해 얻은 반응상수를 적용시킨 CPD 모델을 가지고 예측한 결과가 TGA 실험치와 비교할 때보다 더 잘 일치함도 확인할 수 있었다.

• Korean Chemical Engineering Research
• /
• 제43권6호
• /
• pp.683-690
• /
• 2005

왕겨를 마이크로파로 탄화하고 그의 탄화속도를 기존의 열적 탄화에 의한 탄화속도와 비교하였다. 왕겨를 $300{\sim}600^{\circ}C$에서 각각 30분 동안 열적 탄화하고 그의 탄화속도를 분석한 결과 탄화온도가 증가할수록 질량감소 및 탄화도(C/H 몰비)가 현저히 증가했지만 왕겨에 마이크로파를 조사하면 입사전력과 조사시간이 증가해도 탄화가 일어나지 않았다. 그러나 $600^{\circ}C$에서 30분 동안 탄화시켜 C/H 몰비가 3.0 이상인 탄화왕겨 6 wt％를 왕겨에 혼합시키고 마이크로파를 조사한 결과 탄화가 잘 되었고 그의 속도식은 마이크로파 입사전력 및 조사시간에 의존하였으며 열적 탄화와 마찬가지로 Arrhenius 식으로 잘 표현되었다. 이때 마이크로파 탄화로 얻어진 활성화에너지는 열적 탄화에 비하여 크게 낮은 반면에 반응속도상수는 훨씬 컸다. 이는 마이크로파 흡수촉진 매체, 즉 촉매적 개시제(initiator)로 사용된 탄화왕겨에 대한 마이크로파 에너지의 내부 부피가열 특성에 기인한 것으로 판단된다. 마이크로파 흡수특성에 대한 왕겨의 회분과 탄화왕겨의 탄화도 및 혼합비율에 대한 영향을 검토하였다.

• Corrosion Science and Technology
• /
• 제19권1호
• /
• pp.43-50
• /
• 2020

In this study, the effects of KCl(s) and K₂SO₄(s) on the oxidation characteristics of 2.25Cr-1Mo steel were investigated for 500 h in 10O₂ + 10CO₂ (vol%) gas environmen at 650 ℃. Oxidation kinetics were characterized by weight gain, oxide layer thickness, and fitted models for the experiment data were proposed. The fitted models presented considerable agreement with the experimental data. The oxide layer was analyzed using the scanning electron microscope, optical microscope, and energy dispersive X-ray spectroscopy. The oxidation kinetics of 2.25Cr-1Mo steel with KCl and K₂SO₄ coatings showed significantly different oxidation kinetics. KCl accelerated the oxidation rate very much and had linear oxidation behavior. In contrast, K₂SO₄ had no significant effect, which had parabolic kinetics. The oxide layer was commonly composed of Fe₂O₃, Fe₃O₄, and FeCr₂O₄ spinel. KCl strongly accelerated the oxidation rates of 2.25Cr-1Mo steel in the high-temperature oxidation environment. Conversely, K₂SO₄ had little effect on the oxidation rates.