• 한국재료학회지
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• 제31권1호
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• pp.1-7
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• 2021

The characteristics and morphology of precipitated calcium carbonate (PCC) particles produced by carbonation process with various experimental conditions are investigated in this study. The crystal structures of PCC formed by carbonation process are calcite and aragonite. The crystal structure of PCC particles synthesized without adipic acid additive is calcite only, regardless of the reaction temperature. Needle-like shape aragonite phase started to form at reactor temperature of 80℃ with the adipic acid additive. Particle size of the single phase calcite PCC synthesized without adipic acid additive is about 1 ~ 3 ㎛, with homogenous distribution. The aragonite PCC also shows uniform size distribution. The reaction temperature and concentration of adipic acid additive do not show any significant effects on the particle size distribution. Aragonite phase grown to a large aspect ratio of needle-like shape showed relatively improved whiteness. The measured whiteness value of single calcite phase is about 95.95, while that of the mixture of calcite and aragonite is about 99.11.

• 한국재료학회지
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• 제15권5호
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• pp.348-352
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• 2005

Gallium oxyhydroxide (GaOOH) powders were heat-treated in a flowing ammonia gas to form GaN, and the reaction kinetics of the oxide to nitride was quantitatively determined by X-ray diffraction analysis. GaOOH turned into intermediate mixed phases of $\alpha-\;and\;\beta-Ga_2O_3$, and then single phase of GaN. The reaction time for full conversion $(t_c)$ decreased as the temperature increased. There were two-types of rapid reaction processes with the reaction temperature in the initial stage of nitridation at below $t_c$, and a relatively slow processes followed over $t_c$ does not depends on temperatures. The nitridation process was found to be limited by the rate of an interfacial reaction with the reaction order n value of 1 at $800^{\circ}C$ and by the diffusion-limited reaction with the n of 2 at above $1000^{\circ}C$, respectively, at below $t_c$. The activation energy for the reaction was calculated to be 1.84 eV in the temperature of below $830^{\circ}C$, and decreased to 0.38 eV above $830^{\circ}C$. From the comparative analysis of data, it strongly suggest the rate-controlling step changed from chemical reaction to mass transport above $830^{\circ}C$.

• 한국세라믹학회지
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• 제35권10호
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• pp.1030-1039
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• 1998

In fly ash-lime system the effects of reaction condition amounts of gypsum and cement and CaO/SiO2 ratio on the hydrates by hydrothermal reaction were investigated. The tobermorite phases were not observed in hy-drothermal reaction of fly ash lime because of the hydrate rate was very slow. The compressive strength and the hydration rate increased with increasing the amount of gypusm and cement and the optimum amounts of gypsumo and cement were 5wt and 20wt% respectively. The specimen which CaO/SiO2 ratio is 0.85 was shown the maximum compressive strength and the tobermorite phase within reaction time 2 hours.

• Bulletin of the Korean Chemical Society
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• 제18권11호
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• pp.1186-1191
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• 1997

Solvolyses of methanesulfonyl chloride (CH3SO2Cl) in water and methanol have been studied theoretically using ab initio self-consistent reaction field (SCRF) molecular orbital method. All stationary structures including transition state on the potential energy surface in solution have been found and compared with the gas phase structures. The overall reaction occurs via a concerted SN2 mechanism with a non-cyclic trigonal bipyramidal transition state, and the activation barrier is lowered significantly in solution. The transition state for the hydrolysis reaction is looser than that for the methanolysis reaction, and this is in accord with the experimental findings that an SN2 type mechanism, which is shifted toward an SN1 process or an SAN process in the hydrolysis and alcoholysis reaction, respectively, takes place. The catalytic role of additional solvent molecules appears to be a purely general-base catalysis based on the linear transition structures. Experimental barrier can be estimated by taking into account the desolvation energy of nucleophile in the reaction of methanesulfonyl chloride with bulk solvent cluster as a nucleophile.

• 한국결정성장학회지
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• 제12권3호
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• pp.126-132
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• 2002

$ZrOCl_2{\cdot}8H_2O$ 수용액과 KOH 수용액의 반응으로부터 얻은 침전물을 $100^{\circ}C$에서 24 시간 동안 숙성시켜 정방정상 지르코니아를 제조한 후 수열합성 조건을 변화시킴으로써 비등방성 형상의 나노 결정형 지르코니아 분말을 합성하였다. 수열합성 시 반응온도와 반응시간이 증가할수록 정방정상인 구형 입자는 감소하고 상대적으로 단사정상 spindle-like 입자와 막대상 입자가 증가하였다. NaOH 용액의 농도가 증가함에 따라 입성장과 함께 정방정상에서 단사정상으로의 상전이가 촉진되었으며, 저온에서 반응시간이 짧은 경우 합성한 분말들은 반응초기에 응집된 입자들이 NaOH 용액에 부분적으로 용해되면서 응집입자 및 결정입자 크기가 감소되어 비표면적이 증가하였다가 반응시간이 길어지고 반응온도가 높아짐에 따라 입성장에 의하여 점차 비표면적이 감소하였다.

• 농약과학회지
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• 제9권3호
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• pp.185-190
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• 2005

최초의 침투이행성 농약 살균제, 카르복신 1의 유도체인 16을 고체상에서 합성하였다. 1,3-옥사티올란 유도체를 아실화 반응성을 갖고 있는 4-하이드록시-3-나이트로벤조페논 고체상 6에 연결하여 9를 82%의 수율로 합성하였다. 고체상의 1,3-옥사티올란 9의 황원자를 MCPBA로 산화한 다음 생성된 설폭사이드 10을 산촉매 존재하에서 환팽창하여 상응하는 고체상에 연결된 다이하이드로-1,4-옥사티인 유도체 12를 합성하였다. 고체상의 1,3-옥사티올란 9의 산화물을 p-메톡시아닐린과 반응시켜 1,3-옥사티올란 14, 1,3-옥사티올란 설폰 15, 다이하이드로-1,4-옥사티인 16, 그리고 아세토아세트아닐라이드 유도체 17을 각각 41%, 35%, 14%, 10% 수율로 얻었다.

• Journal of Welding and Joining
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• 제14권4호
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• pp.99-108
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• 1996

The microstructure and bond strength are examined on the SiC/SiC and SiC/mild steel joints brazed by the Ag-Ti based alloys with different Ti contents. In the SiC/SiC brazed joints, the thickness of the reaction layers at the bond interface and the Ti particles in the brazing alloy matrices increase with Ti contents. When Ti is added up to 9 at% in the brazing alloy. $Ti_3SiC_2$ phase in addition to TiC and $Ti_5Si_3$ phase is newly created at the bond interface and TiAg phase is produced from peritectic reaction in the brazing alloy matrix. In the SiC/mild steel joints brazed with different Ti contents, the microstructure at the bond interface and in the brazing alloy matrix near SiC varies similarly to the case of SiC/SiC brazed joints. But, in the brazing alloy matrix near the mild steel, Fe-Ti intermetallic compounds are produced and increased with Ti contents. The bond strengths of the SiC/SiC and SiC/mild steel brazed joints are independent on Ti contents in the brazing alloy. There are no large differences of the bond strength between SiC/SiC and SiC/mild steel brazed joints. In the SiC/mild steel brazed joints, Fe dissolved from the mild steel does not affect on the bond strength of the joints. Thermal contraction of the mild steel has nearly no effects on the bond strength due to the wide brazing gap of specimens used in the four-point bend test. The brazed joints has the average bond strength of about 200 MPa independently on Ti contents, Fe dissolution and joint type. Fracture in four-point bend test initiates at the interface between SiC and TiC reaction layer and propagates through SiC bulk. The adhesive strength between SiC and TiC reaction layer seems to mainly control the bond strength of the brazed joints.

• 대한환경공학회지
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• 제31권2호
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• pp.102-108
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• 2009

연속회분식반응기에서 측정되는 기초상용계측기의 프로파일은 공정 내에서 수행되는 유기오염물질 및 영양염류 제거반응의 진행 정도에 대한 정보를 제공할 수 있다. 특히 호기성 반응구간에 측정되는 pH나 DO, ORP의 변곡점 등의 정보를 이용한 반응 종료 감지는 널리 알려진 응용사례라고 할 수 있다. 그러나 이러한 정보들은 반응의 종료 여부에 대한 정보를 제공할 뿐, 현재 공정에 가해지는 부하에 대한 정보를 제공하지는 못한다. 본 논문에서는 운전자에게 공정 유입수 내의 호기적 반응을 요하는 부하, 즉 암모니아 부하 및 유기물 부하의 고/중/저에 관한 정보를 제공할 수 있는 기초상용계측기의 정보를 활용한 진단 알고리즘을 개발하였다. 본 알고리즘으로 인해, 연속회분식반응기를 운전할 시에 수시로 변화하는 유입수의 부하를 습식분석 없이 자동 계측기 프로파일로부터 얻어낼 수 있을 것으로 사료된다.

• 한국환경과학회:학술대회논문집
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• 한국환경과학회 2003년도 봄 학술발표회 발표논문집
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• pp.135-136
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• 2003

• Bulletin of the Korean Chemical Society
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• 제23권3호
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• pp.503-506
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• 2002