• 한국건축시공학회:학술대회논문집
• /
• 한국건축시공학회 2017년도 추계 학술논문 발표대회
• /
• pp.24-25
• /
• 2017

Gamma-C₂S (γ-C₂S) is a substance that is difficult to react with water under normal temperature but can absorb a large amount of CO₂ in the air. The addition of γ-C₂S to cementitious materials through the curing of CO₂ can improve the pore structure and improve the durability of the material. In this study, three kind of Ca-bearing materials : CaO, Ca(OH)₂, CaCO₃, were calcined 2.5h at 1450℃ to synthesize γ-C₂S after mixing with SiO₂ respectively. Among them, Ca(OH)₂ mixed with SiO₂ after calcining shows highest content. Synthesized γ-C₂S was added to the cement mortar, after water curing for 1 month, accelerated carbonation test was experimented. After 28d accelerated carbonation test, pore structure will be detectived by MIP. Based on the MIP result, following the calculation method of Fractal theory, the pore structure will be quantitative described.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2004년도 추계학술대회
• /
• pp.1162-1165
• /
• 2004

Size and crystalline phase changes of $Fe_{2}O_{3}$ nanoparticles formed in a $H_{2}/O_{2}$ flame have been investigated. At flame temperatures below $1350^{\circ}C$, the mean particle size increased monotonously with the distance from the burner edge; but in high-temperature flames above $1650^{\circ}C$, it suddenly decreased from 20 nm to ${\sim}3$ nm with the distance from the burner edge. The results of X-ray diffraction and HRTEM showed that this sudden reduction of the size of nanoparticles was accompanied by a partial phase transformation from ${\gamma}$-$Fe_{2}O_{3}$ into ${\alpha}$-$Fe_{2}O_{3}$. We suggest the structural instability due to ${\gamma}-$ to ${\alpha}-phase$ transformation as a mechanism for a rapid fragmentation of 20 nm particles into 3 nm ones.

• 한국분말재료학회지
• /
• 제14권1호
• /
• pp.19-25
• /
• 2007

This study was focused on the optimization of low-pressure ultrasonic spraying process for synthesis of pure ${\gamma}-Fe_2O_3$ nanoparticles. As process variables, pressure in the reactor, precursor concentration, and reaction temperature were changed in order to control the chemical and microstructural properties of iron oxide nanoparticles including crystal phase, mean particle size and particle size distribution. X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies revealed that pure ${\gamma}-Fe_2O_3$ nanoparticles with narrow particle size distribution of 5-15 nm were successfully synthesized from iron pentacarbonyl ($Fe(CO)_{5}$) in hexane under 30 mbar with precursor concentrations of 0.1M and 0.2M, at temperatures over $800^{\circ}C$. Also magnetic properties, coercivity ($H_c$) and saturation magnetization ($M_s$) were reported in terms of the microstructure of particles based on the results from vibration sampling magnetometer (VSM).

• Biotechnology and Bioprocess Engineering:BBE
• /
• 제9권6호
• /
• pp.506-513
• /
• 2004

Spirulina produces $\gamma$-linolenic acid (GLA), an important pharmaceutical substance, in a relatively low level compared with fungi and plants, prompting more research to improve its GLA yield. In this study, metabolic flux analysis was applied to determine the cellular metabolic flux distributions in the GLA synthetic pathways of two Spiru/ina strains, wild type BP and a high­GLA producing mutant Z19/2. Simplified pathways involving the GLA synthesis of S. platensis formulated comprise of photosynthesis, gluconeogenesis, the pentose phosphate pathway, the anaplerotic pathway, the tricarboxylic cycle, the GLA synthesis pathway, and the biomass syn­thesis pathway. A stoichiometric model reflecting these pathways contains 17 intermediates and 22 reactions. Three fluxes - the bicarbonate (C-source) uptake rate, the specific growth rate, and the GLA synthesis rate - were measured and the remaining fluxes were calculated using lin­ear optimization. The calculation showed that the flux through the reaction converting acetyl­CoA into malonyl-CoA in the mutant strain was nearly three times higher than that in the wild­type strain. This finding implies that this reaction is rate controlling. This suggestion was sup­ported by experiments, in which the stimulating factors for this reaction $(NADPH\;and\;MgCl_{2})$ were added into the culture medium, resulting in an increased GLA-synthesis rate in the wild type strain.

• 한국세라믹학회지
• /
• 제39권3호
• /
• pp.272-277
• /
• 2002

전구체로 ($NH_4)[Al(ethylenediaminetetraacetate)]{\cdot}2H_2O$ 착물을 이용한 수정된 열탄소환원질화법으로 질화알루미늄(AlN) 분말과 휘스커를 합성하였다. 이 분말은 질소분위기에서 별도의 환원용 탄소를 혼합하지 않고 1200$^{\circ}$C에서 1500$^{\circ}$C까지의 온도에서 하소시킨 다름 잔류탄소를 태워 버림으로써 얻어졌다. 이 질화과정을 Al-27 마법각 스핀 핵자기공명, 적외선 분광법 및 X-선 회절법으로 연구했다. 전구체 착물은 열분해되어 ${\rho}$-알루미나와 ${\gamma}$-알루미나로 되었다가 ${\gamma}-{\alpha}$알루미나 전이없이 AlN으로 바뀌었다. ${\gamma}$-알루미나가 AlN으로 바뀌면서 분말의 형상이 유지되는 것으로 보아 이 변환과정에서의 중간체는 알루미늄이나 aluminum suboxides와 같은 기체상이 아니고, 고체상의 $AlO_xN_y$임을 알 수 있다. (0001) 사파이어를 이용하면 AlN 휘스커를 합성할 수 있다.

• Bulletin of the Korean Chemical Society
• /
• 제26권1호
• /
• pp.131-135
• /
• 2005

Gallium nitride (GaN) powders and nanowires were prepared by using tris(N,N-dimethyldithiocarbamato)gallium(III) (Ga(DmDTC)$_3$) and tris(N,N-diethyldithiocarbamato)gallium(III) (Ga(DeDTC)$_3$) as new precursors. The GaN powders were obtained by reaction of the complexes with ammonia in the temperature ranging from 500 to 1100 ${^{\circ}C}$. The process of conversion of the complexes to GaN was monitored by their weight loss, XRD, and $^{71}$Ga magic-angle spinning (MAS) NMR spectroscopy. Most likely the complexes decompose to $\gamma$ -Ga$_2$S$_3$ and then turn into GaN via amorphous gallium thionitrides (GaS$_x$N$_y$). The reactivity of Ga(DmDTC)$_3$ with ammonia was a little higher than that of Ga(DeDTC)$_3$. Room-temperature photoluminescence spectra of asprepared GaN powders exhibited the band-edge emission of GaN at 363 nm. GaN nanowires were obtained by nitridation of as-ground $\gamma$ -Ga$_2$S$_3$ powders to GaN powders, followed by sublimation without using templates or catalysts.

• KSBB Journal
• /
• 제14권2호
• /
• pp.205-211
• /
• 1999

본 연구에서는 A.cycloclast ATCC 21921 균주를 사용하여 $\gamma$-butyrobetaine으로부터 L-carnitine을 생산하는 최적 조건에 대한 연구를 수행하였다. 배양액 내에 $\gamma$-butyrobetaine 만을 포함하였을때는 최대 L-carnitine 생산량이 29g/L이었고 전환수율도 30.9 mol%로 매우 낮았다. L-carmtine 생산에 미치는 탄소원의 영향을 관찰한 결과 glycerol을 첨가할 경우 L-carnitine 생산량이 4.6g/L 그리고 전환수율이 88.2 mol%로 $\gamma$-butyrobetaineaks을 포함하였을 때보다 월등히 향상되었다. Betaine, chohne와 같은 quaternary ammonium compounds 들이 L-carnitine 생산에 미치는 영향을 조사해본 결과, 이들에 의하여 L-carntine 생산 속도가 빨라지고 전환수율도 증가함을 알 수 있었다. 한편, 기질인 $\gamma$-butyrobetaine 농도 3% 이상에서 세포 생장은 저해되고 L-carnitine 생산은 기질 농도 2-3%에서 가장 우수함을 알 수 있었다. 본 연구에서 구한 최적 생산 조건, 다시 말해서 glycerol과 choline을 배양액에 포함하고 기질의 농도를 2%^로 하여 플라스크에서 회분식 배양을 하였을 때, 배양 4일 만에 최대 7.2g/L의 L-carrutine을 생산할 수 있었고 이때 $\gamma$-butyrobetaine으로부터 L-carnitine에로의 전환수율은 98.7mol%이었다.

• Nuclear Engineering and Technology
• /
• 제54권8호
• /
• pp.2999-3005
• /
• 2022

The new experimental setup has been built at the 11b channel of the IBR-2 research reactor at FLNP, JINR, to study the elemental composition of samples by registration of prompt gamma emission during thermal neutron capture. The setup consists of a curved mirror neutron guide and a radiation-resistant HPGe high-purity germanium detector. The detector is surrounded by lead shielding to suppress the natural background gamma level. The sample is placed in a vacuum channel and surrounded by a LiF shield to suppress the gamma background generated by scattered neutrons. This work presents characteristics of the experimental setup. An example of hydrogen concentration determining in a diamond powder made by detonation synthesis is given and on its basis, the sensitivity of the setup is calculated being ~4 ㎍.

• Journal of Ceramic Processing Research
• /
• 제20권spc1호
• /
• pp.109-112
• /
• 2019

γ-dicalcium silicate(γ-C2S) is known as a polymorphism of belite. Due to its high CO2 fixed capacity and the low CO2 emission production process, γ-C2S has attracted more and more attention of researchers. For the further development of application of γ-C2S in building construction industry. In this study, we aim to investigate the method for synthesizing high purity of γ-C2S. The influence of different raw materials and calcination temperatures on the purity of γ-C2S was also evaluated. Several Ca bearing materials were selected as the calcium source, the materials which' s main component is SiO2 were used as the silicon source. Raw materials were mixed and were calcined under different temperatures. The results reveal that the highest purity could be obtained using Ca(OH)2 and SiO2 powder as raw materials. And for the practical application, a relatively economic synthesis method using natural mineral materials- limestone and silica sand as raw materials was developed, by this method, the purity of the synthetic γ-C2S was 77.6%.

• 대한화학회지
• /
• 제44권6호
• /
• pp.513-517
• /
• 2000

TTF (tetrathiafulvalene) 유도체의 전구체로서 5,6-dimethyl-1,3-dithiolo[4,5-b][1,4]dithiin-2-thione (화합물 3)을 로손반응에 의하여 합성하였다. 치환기의 종류에 따라 1,4-dithiin이나 티오펜이 포함된 두 가지의 서로 다른 생성물이 얻어졌고, 이들은 $^{13}C$ NMR과 고 분해능 전자충돌(HREI) 질량분석 분광학으로 특성화하였다. 화합물 3의 합성은 X-선 구조분석으로도 확인되었다. 결정학적 자료: 삼사정계, 공간군 P1, a=4.145(2)${\AA}$, b=10.600(2)${\AA}$, c=12.279(2)${\AA}$, ${\alpha}=71.440(10)^{\circ},\;{\beta}=84.30(2)^{\circ},\;{\gamma}=87.31(2)^{\circ}$, Z=2, $R(wR_2$)=0.0559(0.1416). 두 가지 생성물의 생성 기구를 비교하여 설명하였다.