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정순효,하헌필,변지영 대한금속재료학회 2004 대한금속·재료학회지 Vol.42 No.8
A previously developed fixed grid finite volume method was used to investigate hydrogen removal process involving surface reaction, diffusion, β/α phase boundary movement and phase transformation that occurs during dehydrogenation of cylindrical β-titanium specimens. Effects of temperature, initial hydrogen content and radius of specimen on times for dehydrogenation were studied. It was found that dehydrogenaion occus through the following 4 steps: (1) lowering of hydrogen concentration at the surface of the β specimen to equilibrium value, (2) lowering of hydrogen concentration gradient to a value matching the surface reaction flux. (3) the (β/α phase transformation by inward movement of the β/α phase boundary and (4) further removal of hydrogen in the a phase specimen to final value. Time for hydrogen removal in the first step increases with increase of temperature and initial hydrogen content, due to the rapid increase of amount of hydrogen to be removed comparing with the increase of hydrogen removal rate. It increases with specimen radius. Time for hydrogen removal in 2nd step decreases with increase of temperature due to increase of hydrogen removal rate and decrease of amount of hydrogen to be removed, but it increases with specimen radius and initial hydrogen content. Time for hydrogen removal in 3rd step (β/α phase transformation) decreases with increase of temperature due to decrease of diffusion and reaction resistance and due to increase of partition coefficient, but it increases with specimen radius due to increase of diffusion and reaction resistance. It increases with initial hydrogen content. Time for hydrogen removal in 4th step decreases with increase of temperature due to decrease of diffusion and reaction resistance as well as equilibrium concentration, but it increases with specimen radius due to increase of diffusion and reaction resistance.
정순효,하헌필,변지영 대한금속재료학회 2004 대한금속·재료학회지 Vol.42 No.5
A fixed grid, finite volume model was applied to investigate hydrogen absorption, diffusion and moving boundary α/βphase transformation that occurs during hydrogenation and homogenization annealing of cylindrical titanium specimens. Effects of parameters such as temperature, specimen radius, amount of added hydrogen on the times required for hydrogenation, for completion of α/βphase transformation and for homogenization were studied. It was found that hydrogen absorption rate is mostly influenced by surface reaction rather than solid-state diffusion. Time for hydrogenation becomes somewhat shorter with increase of temperature, due to decrease of hydrogen saturation concentration in spite of large increase of diffusivity and reaction rate constant. It increases almost linearly with increasing specimen radius or with amount of hydrogenation, showing positive deviation from linearity due to increase of diffusion resistance or surface hydrogen concentration. The completion of α/βphase transformation and homogenization are finished quickly with raising temperature due to increase of diffusivity and decrease of equilibrium hydrogen concentration in the βphase. They are nearly proportional to the square of specimen radius. With increase of the amount of added hydrogen, the completion of α/β phase transformation and homogenization are finished quickly during annealing due to the progress of α/β phase transformation during hydrogenation (Received August 23, 2003)
V<sub>2</sub>O<sub>5</sub>/TiO<sub>2</sub> 촉매의 선택적 환원촉매반응에서 격자산소의 역할
하헌필,최희락,Ha, Heon-Phil,Choi, Hee-Lack 한국재료학회 2006 한국재료학회지 Vol.16 No.5
In situ electrical conductivity measurements on $V_2O_5WO_3/TiO_2$ catalysts were carried out at between 100 and $300^{\circ}C$ under pure oxygen, NO and $NH_3$ to investigate the reaction mechanism for ammonia SCR (selective catalytic reduction) de NOX. The electrical conductivity of catalysts changed irregularly with supply of NO. It was, however, found that the electrical conductivity change with ammonia supply was regular and the increase of electrical conductivity was mainly caused by reduction of the labile surface oxygen. The electrical conductivity change of catalysts showed close relationship with the conversion rate of NOx. Variation of conversion rate in atmosphere without gaseous oxygen also showed that labile lattice oxygen is indispensable in the initial stage of the de NOx reaction. These results suggest that liable lattice oxygen acts decisive role in the de NOx mechanism. They also support that de NOx reaction occurs through the Eley?Rideal type mechanism. The amount of labile oxygen can be estimated from the measurement of electrical conductivity change for catalysts with ammonia supply. This suggests that measurement of the change can be used as a measure of the de NOx performance.
이석현,권동욱,( Ha Heon Phil ),김종식 한국공업화학회 2020 한국공업화학회 연구논문 초록집 Vol.2020 No.-
Rare-earth metals (RM) were reported to readily fuse with V<sub>2</sub>O<sub>5</sub> to build a series of RM<sub>1</sub>V<sub>1</sub>O<sub>4</sub> architectures, which are iso-structural one another and include open V sites accessible to NO<sub>X</sub>/NH<sub>3</sub>. We found that Ce<sub>1</sub>V<sub>1</sub>O<sub>4</sub> can undergo its structural modification with a variable quantity of RM elements. This resulted in the formation of bimetallic RM<sub>X</sub>Ce<sub>1-X</sub>V<sub>1</sub>O<sub>4</sub> geometries, whose RM compositions (X) were varied from 0 to 1. Herein, we highlighted our recent study on the synthesis of TiO<sub>2</sub>-supported RM<sub>X</sub>Ce<sub>1-X</sub>V<sub>1</sub>O<sub>4</sub> catalysts and the contrast of their surface properties, all of which can exceptionally promote the consequences of selective NO<sub>X</sub> reduction (SCR) and NH<sub>3</sub> oxidation (SCO) in comparison with RM<sub>1</sub>V<sub>1</sub>O<sub>4</sub> or Ce<sub>1</sub>V<sub>1</sub>O<sub>4</sub>. Er served as a model element for the RM, and formed Er<sub>X</sub>Ce<sub>1-X</sub>V<sub>1</sub>O<sub>4</sub> phases on TiO<sub>2</sub> via wet-impregnation, and tested in the SCR/SCO at 200-600℃.