• Title, Summary, Keyword: Decomposition behavior

Search Result 378, Processing Time 0.046 seconds

Synthesis of $\beta$-Alumina By Oxalate Coprecipitation Method and Its Crystallization Behavior (Oxalate 공침법에 의한 $\beta$-Alumina 합성과 결정화 거동)

  • 박용민;양유철;김형욱;박성수;손영국
    • Journal of the Korean Ceramic Society
    • /
    • v.32 no.4
    • /
    • pp.455-461
    • /
    • 1995
  • To investigate the synthesis of $\beta$-Al2O3 and its crystallization behavior by oxalate coprecipitation method, the optimum pH range for oxalate coprecipitates has been theoretically calculated from the solubility products and the equilibrium constans of each metal ionic species and their solubility diagram wa obtained. The optimum pH range for oxalate coprecipitates at room temperature was estimated as <4. In experiment, we found that the optimum condition for oxalate coprecipitates was pH<1, which was not doped with pH controller. The Na+ ions were easily exchanged for the NH4+ ions of NH4OH which was used as pH controller, and those NH4+ ions were supposed to affect the crystallization behavior of $\beta$-Al2O3. The thermal decomposition of all complexes was almost complete below 40$0^{\circ}C$. The primary product of the decomposition process was m-Al2O3, which transformed to $\beta$"- or $\beta$-Al2O3 at temperature higher than 100$0^{\circ}C$. We found that the powder prepared at 120$0^{\circ}C$ had only $\beta$"- and $\beta$-Al2O3.EX>-Al2O3.

  • PDF

A Study on Bubble Behavior Generated by an Air-driven Ejector for ABB (Air Bubble Barrier) (II): Comparison of Bubble Behavior with and without Ejector (공기구동 이젝터를 이용한 ABB (Air Bubble Barrier)의 기포거동 특성 연구 (II): 기포거동 특성의 비교 분석)

  • Seo, Hyunduk;Aliyu, Aliyu Musa;Kim, Hyogeum;Kim, Kyung Chun
    • Journal of the Korean Society of Visualization
    • /
    • v.15 no.2
    • /
    • pp.59-67
    • /
    • 2017
  • To verify floatability of ABB (Air bubble barrier), we compared bubble swarm behavior with and without the air-driven ejector. Experiment was conducted using the fabricated air-driven ejector with 5 mm nozzle on the bottom of 1 m3 water tank. Reynolds number of air in the nozzle was ranged 1766-13248. We analyzed data with statistical method using image processing, particle mage velocimetry (PIV) and proper orthogonal decomposition (POD) analysis. As a result of POD analysis, there was no significant eigenmode in bubbly flow generated from the ejector. It means that more complex turbulent flows were formed by the ejector, thereby (1) making bubbles finer, (2) promoting three-dimensional energy transfer between bubble and water, and (3) making evenly distributed velocity profile of water. It is concluded that the air-driven ejector could enhance the performance of ABB.

Seismic response analysis of embankment dams under decomposed earthquakes

  • Nasiri, Fatemeh;Javdanian, Hamed;Heidari, Ali
    • Geomechanics and Engineering
    • /
    • v.21 no.1
    • /
    • pp.35-51
    • /
    • 2020
  • In this study, the seismic response analysis of embankment dams was investigated through numerical modeling. The seismic behavior of dams under main earthquake records and wavelet-based records were studied. Earthquake records were decomposed using de-noising method (DNM) and down-sampling method (DSM) up to five levels. In decomposition process, low and high frequencies of the main earthquake record were separated into two signals. Acceleration response, spectral acceleration, and Fourier amplitude spectrum at the crest of embankment dams under different decomposition levels were evaluated. The seismic behavior under main and decomposed earthquake records was compared. The results indicate an acceptable agreement between the seismic responses of embankment dams under wavelet-based decomposed records and main earthquake motions. Dynamic analyses show that the DNM-based decomposed earthquake records have a better performance compared to DSM-based records. DNM-based records up to level 4 and DSM-based records up to level 2 have a high accuracy in assessment of seismic behavior of embankment dams. The periods corresponding to the maximum values of acceleration spectra and the frequencies corresponding to the maximum values of Fourier amplitude spectra of embankment dam crest under main and decomposed records are in good agreement. The results demonstrate that the main earthquake records can be replaced by wavelet-based decomposed records in seismic analysis of embankment dams.

Thermal Decomposition Characteristics of Azo compounds (아조(Azo)화합물 열분해특성)

  • Kim, Kwan-Eung
    • Journal of the Korean Society of Safety
    • /
    • v.17 no.2
    • /
    • pp.39-44
    • /
    • 2002
  • This study was investigated the thermal decomposition characteristics of azo type sponge blowing agent azodicarbonamide(ADCA) using differential scanning calorimeter(DSC). The experimental results showed that the exothermic onset $temperatures(T_{o})$ for ADCA were about $201{\sim}206^{\circ}C$ and evolution heats(Q) were about $144{\sim}150cal/g$. The exothermic onset $temperatures(T_{o})$, exothermic maximum $temperature(T_{m})$ and exothermic final $temperature(T_{f})$ were decreased by decreasing particle size of ADCA and evolution heats(Q) were increased with it. $T_{o}$ and Q for $6.1{\sim}7.2{\mu}m$ ADCA were increased by increasing heating rate at constant sample weight and activation energy was about 37.29kcal/mol. A positive gas pressure was employed in the elucidation of the decomposition behavior of ADCA because it sublimes during linear heating at atmospheric pressure. $T_{o}$ and Q of ADCA tended to increase with a pressure in air or nitrogen. In the case of azo dye, experimental results showed that $T_{o}$ were about $280{\sim}420^{\circ}C$ and Q were about $2{\sim}30cal/g$.

A model for Phase Transformation of Microalloyed Low Carbon Steel Combined with Nb Precipitation Kinetics (Nb 석출 거동을 고려한 저탄소강의 상변태 모델)

  • Kim, D.W.;Cho, H.H.;Park, S.;Kim, S.H.;Kim, M.J.;Lee, K.;Han, H.N.
    • Transactions of Materials Processing
    • /
    • v.26 no.1
    • /
    • pp.48-54
    • /
    • 2017
  • The dissolution and precipitation of Nb, which has been known as strong carbide-forming element, play a key role in controlling phase transformation kinetics of microalloyed steels. In this study, we analyzed both numerically and experimentally the precipitation behavior of Nb-microalloyed steel and its effect on the austenite decomposition during cooling. Nb precipitation in austenite matrix could be predicted by the thermo-kinetic software MatCalc, in which interfacial energy between precipitate and matrix is calculated. The simulated precipitation kinetics fairly well agrees with the experimental observations by TEM. Austenite decomposition, which is strongly affected by Nb precipitation during cooling, was measured by dilatometry and was modeled on the basis of a Johnson-Mehl-Avrami-Kolmorgorov(JMAK) equation. It was confirmed that the dissolved Nb delays the austenite decomposition, whereas, the precipitated Nb accelerates phase transformation during the austenite decomposition.

Fabrication of Lotus Nickel Through Thermal Decomposition Method of Compounds under Ar Gas Atmosphere

  • Kim, Sang-Youl;Hur, Bo-Young;Nakajima, Hideo
    • Korean Journal of Materials Research
    • /
    • v.19 no.5
    • /
    • pp.270-275
    • /
    • 2009
  • Lotus-type porous nickel with cylindrical pores was fabricated by unidirectional solidification under an Ar gas atmosphere using the thermal decomposition method of the compounds such as sodium hydroxide, calcium hydroxide, calcium carbonate, and titanium hydride. The decomposed gas does form the pores in liquid nickel, and then, the pores become the cylindrical pores during unidirectional solidification. The decomposed particles from the compounds do play a rule on nucleation sites of the pores. The behavior of pore growth was controlled by atmosphere pressure, which can be explained by Boyle's law. The porosity and pore size decreased with increasing Ar gas pressure when the pores contain hydrogen gas decomposed from calcium and sodium hydroxide and titanium hydride, ; however it they did not change when the pores contain containing carbon dioxide decomposed from calcium carbonate. These results indicate that nickel does not have the solubility of carbon dioxide. Lotus-type porous metals can be easily fabricated by the thermal decomposition method, which is superior to the conventional fabrication method used to pressurized gas atmospheres.

Experimental and Numerical Study of the Thermal Decomposition of an Epoxy-based Intumescent Coating (실험과 계산을 통한 에폭시 계열 내화도료의 열분해에 관한 연구)

  • Kim, Yangkyun
    • Fire Science and Engineering
    • /
    • v.30 no.1
    • /
    • pp.31-36
    • /
    • 2016
  • This study investigates the characteristics of thermal decomposition of an epoxy-based intumescent paint using thermogravimetric analysis (TGA) and numerical simulation. A mathematical and numerical model is introduced to describe mass loss profiles of the epoxy-based intumescent coating induced by the thermal decomposition process. The decomposition scheme covers a range of complexity by employing simplified 4-step sequential reactions to describe the simultaneous thermal decomposition processes. The reaction rates are expressed by the Arrhenius law, and reaction parameters are optimized to fit the degradation behavior seen during thermogravimetric (TG) experiments. The experimental results show a major 2-step degradation under nitrogen and a 3-step degradation in an air environment. The experiment also shows that oxygen takes part in the stabilization of the intumescent coating between 200 and $500^{\circ}C$. The simulation results show that the proposed model effectively predicts the experimental mass loss as a function of time except for temperatures above $800^{\circ}C$, which were intentionally not included in the model. The maximum error in the simulation was less than 3%.

Catalytic Decomposition of NF3 by Thermal Decomposition and Hydrolysis of γ-Al2O3 (γ-Al2O3 촉매상에서 열분해와 가수분해에 의한 NF3 촉매분해 특성)

  • Kim, Yong Sul;Park, No-Kuk;Lee, Tae Jin
    • Applied Chemistry for Engineering
    • /
    • v.26 no.2
    • /
    • pp.154-158
    • /
    • 2015
  • In this study, the catalytic activity of ${\gamma}-Al_2O_3$ was investigated for the decomposition of $NF_3$. Reactions for $NF_3$ decomposition were carried out in the range of reaction temperature of $330{\sim}730^{\circ}C$ and GHSV of $3,000{\sim}15,000mL/g-cat{\cdot}h$ in a fixed-bed catalytic reactor system. Thermal decomposition of $NF_3$ was also performed in order to compare with the catalytic decomposition of $NF_3$. The conversion of $NF_3$ by the catalytic decomposition at $400^{\circ}C$ was four times higher than that of the thermal decomposition. It was confirmed that the reaction behavior of $NF_3$ over ${\gamma}-Al_2O_3$ exhibited two reaction pathways in the presence of steam. Fluorine in $NF_3$ over ${\gamma}-Al_2O_3$ was chemically absorbed to $AlF_3$ by the gas-solid reaction in the absence of steam. The catalytic decomposition of $NF_3$ occurred by hydrolysis with steam. It was also confirmed by FT-IR analysis that $NF_3$ was completely decomposed to NOx and HF above $500^{\circ}C$.