급냉응고시의 열분석에 관한 연구

하헌필,조순형,윤의박 대한금속재료학회 1986 대한금속재료학회 학술대회 개요집 Vol.1986 No.0

Ni-Cr-Sn-Bi합금의 anti-galling 특성에 미치는 Te의 영향

하헌필,김경탁,심재동,김용규,Ha Heon-Phil,Kim Kyung-Tak,Shim Jae Dong,Kim Yong Kyu 한국재료학회 2005 한국재료학회지 Vol.15 No.1

Ni-Cr-Sn-Bi alloys were prepared by air melting and sand casting method and their anti-galling behaviors were examined. Anti-galling properties were dominantly influenced by Bi-rich low temperature precipitates. Alloying effects on the anti-galling properties were investigated for several alloying elements to improve anti-galling properties of the alloy. An alloy with $1-3wt\%$ of Te showed markedly improved anti-galling properties. Metallographic and tribological tests were carried out to find out reasons for excellent properties. It was found that Te containing alloy has finely distributed precipitates of Bi-rich phase. The addition of Te changed the morphology of the Ni-rich primary phase from globular to fine dendritic. As a result, the anti-galling phase precipitated between dendrite arms with fine distribution showed excellent anti-galling properties.

Band-Gap Energy and Thermoelectric Properties of 90% $Bi_2Te_3-10% Bi_2Se_3$ Single Crystals

하헌필,현도빈,황종승,오태성,Ha, Heon-Pil,Hyeon, Do-Bin,Hwang, Jong-Seung,O, Tae-Seong Materials Research Society of Korea 1999 한국재료학회지 Vol.9 No.4

Dopant를 첨가하지 않은 시료와 donor dopant로 $CdI_2$를 첨가한 $Bi_2Te_3-10%$ 단결정을 Bridgman법으로 성장시키고 Hall 계수, 전하이동도, 전기비저향, Seebeck 계수, 열전도도 빛 성능지수를 77~600K의 온도범위에서 측정하였다. Dopant를 첨가하지 않은 90% $Bi_2Te_3-10% Bi_2Se_3$ 단결정에서 포화정공농도는 $5.85\times10_{18}cm^{-3}$ 이고 degenerate 온도는 127K 이었￡며, 전하 이동에 대한 산란인자는 -0.23 이고 전자이동도와 정꽁이동도의 비 ($\mu_e/\mu_h)$는 1.45 이었다. 90% $Bi_2Te_3-10% Bi_2Te_3$ 단결정의 OK 에서의 밴드갭 에너지는 0.200 eV 로서 $Bi_2Te_3-Bi_2Se_3$계 단결정에서눈 $Bi_2Se_3$의 놓도가 증가할수록 밴 드갭 에너지가 증가하였다. Donor dopant로 $CdI_2$를 첨가한 90% $Bi_2Te_3-Bi_2Se_3$ 조성의 n형 단결정에서 성능지수의 최대값은 $CdI_2$를 0.05 wt% 첨가한 경우에 약 230K에서 $3.2\times10^{-3}/K$를 나타내었다. The temperature dependences of the Hall coefficient, carrier mobility, electrical resistivity, Seebeck coefficient, thermal conductivity, and figure-of-merit of the undoped and $CdI_2$-doped 90% $Bi_2Te_3-10% Bi_2Se_3$, single crystals, grown by the Bridgman method, have been characterized at temperatures ranging from 77K to 600K. The saturated carrier concentration and degenerate temperature of the undoped 90% $Bi_2Te_3-10% Bi_2Se_3$ single crystal are $5.85\times10_{18}cm^{-3}$ and 127K, respectively. The scattering parameter of the 90% $Bi_2Te_3-10% Bi_2Se_3$ single crystal is determined to b -0.23, and the electron mobility to hole mobility ratio ($\mu_e/\mu_h)$ is 1.45. The bandgap energy at 0K of the 90% <$Bi_2Te_3-10% Bi_2Se_3$ single crystal is 0.200 eV. Adding $CdI_2$as a donor dopant, a maximum figure-of-merit of $3.2\times10^{-3}/K$</TEX at 230K was obtained for 0.05wt% $CdI_2$-doped specimen.

V₂O₅/TiO₂ 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.

계산과학기반 저온용 탈질촉매개발 및 응용

하헌필 한국공업화학회 2015 한국공업화학회 연구논문 초록집 Vol.2015 No.1

세계적으로 환경규제가 엄격해지고 배연가스 처리조건이 가혹해짐에 따라 고효율 고내구성을 가진 촉매특성이 요구된다. 최근에는 국제해사기구에서는 선박에서 배출되는 배기가스도 Tier III 조건을 만족하도록 규정하고 있다. 이에 따라 촉매가 배연가스 처리조건에 맞도록 저온에서 작동할 수 있을 뿐만 아니라 각종 촉매열화(deactivation)를 극복해야하는 것이 당면과제로 대두되고 있다. 본 발표에서는 계산과학을 기반하여 촉매를 설계하고 표면개질기술을 이용하여 촉매의 내구성 및 효율을 향상시킨 탈질촉매 개발내용을 보고하고 탈질촉매의 응용 및 기술이전 사례를 설명하고자 한다.

Nd promoted Vanadia-Ceria catalysts for low temperature NH₃-SCR

최현,하헌필,( Pullur Anil Kumar ),정영은,( Danh Thi Huong ),이관영 한국공업화학회 2015 한국공업화학회 연구논문 초록집 Vol.2015 No.0

Composite catalysts by doping Nd into vanadia-ceria are prepared to obtain further improved catalytic properties by homogeneous precipitation method using urea as a precipitation agent which exhibits high NOx conversion at 150-400C. The results showed that the Nd help to increase the activity of vanadia-ceria for NH₃- SCR, The SCR mechanism is investigated through various characterizations, such as XRD, BET-SA,XPS, NH₃- TPD, H₂- TPD and FE-SEM.

Vanadium oxide-based extruded honeycomb monolith catalyst for abatement of NOx with NH₃

정영은,하헌필,이관영,( Danh Thi Huong ),( Pullur Anil Kumar ),최현 한국공업화학회 2015 한국공업화학회 연구논문 초록집 Vol.2015 No.1

Vanadium based monolith type catalyst was carried out for the selective catalytic reduction(SCR) of NO_x by NH₃. The monolith catalyst can be adjusted to reduce the simulate exhaust gas of marine engine at wide temperature (150~500°C). The characteristics of the monolith catalysts were thoroughly characterized by surface area, temperature programmed desorption (TPD) of NO, SO₂ and NH₃, X-ray Fluorescence (XRF) spectrometer and scanning electron microscope (SEM). The Vanadum based monolith catalyst showed higher activity at low temperature about 200C under SO₂ and H₂O condition than commercial catalyst.

Pure powder와 Precursor를 Ball milling하여 NH₃ SCR의 NO Conversion을 활성 비교

최현,하헌필,이관영,정영은,( Pullur Anil Kumar ),( Danh Thi Huong ) 한국공업화학회 2015 한국공업화학회 연구논문 초록집 Vol.2015 No.1

The object of this study is to check the ball milling effect on the catalytic activity of V-based catalysts for NH₃-SCR. The catalysts prepared by varying the precursors and pure oxide of Ce through ball milling. X-ray diffraction (XRD) was used to analyze crystal size of oxides after ball milling. All the prepared catalysts were characterized by BET-SA, NH₃-TPR, H₂-TPR and XPS. Finally, the catalysts were evaluated for NOx reduction with NH₃ at different temperatures.

티타늄의 THP공정 중 수소화 과정 수치해석

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)

티타늄의 THP공정에서의 수소제거 과정 수치해석

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.