FeTi계 수소저장합금의 수소화반응에 있어서 Hysteresis현상

金大龍 慶北大學校 1989 論文集 Vol.47 No.-

Hysteresis phenomena in hydrogen absorption and desorption equilibria of FeTi-type hydrogen storage alloys were studied. In all systems, hysteresis energy loss during the hydriding and dehydriding cycles was observad. This hysteresis was reduced by small substitutions of Fe in FeTi by other transition elements. Hysteresis energy loss reduced significantly during the first few cycles of hydriding and dehydriding, and saturated gradually as the particle size become uniform. There was no evidence of the so-called aliquot size effect on hysteresis observed in other systems. The origin of the hysteresis phenomena and true equilibrium pressure in the FeTi-type intermetallic compounds-hydrogen system were also discussed. The hysteresis energy loss is mainly due to plastic works in solid solution and hydride phase caused by a large volume change during the hydriding and dehydriding reaction.

Molybdenum의 高溫酸化特性

金大龍 경북대학교 공과대학 1978 工大硏究誌 Vol.7 No.-

The oxidation behaviors of molybdenum were studied by thermogravimetric method in air-water vapor and argon-water vapor mixtures at the temperature range of 575°~805℃ and 615°~1004℃, respectively. In air-vapor mixtures, linear weight losses with time by the vaporization of MoO_3 were observed at temperatures above 678℃, and the activation energy for the vaporization was determined to be 86.103kcal/mol. Any appreciable effect of water vapor content on the oxidation reaction was not observed. In argon-water vapor mixtures, vaporization of MoO_3 was not observed because thermodynamically Mo+2H_2O→MoO_2+2H_2O is the only possible reaction in this system. Weight was continuously increased with time up to 1004℃ and parabolic rate law was obeyed in all temperatures. The activation energy for the parabolic oxidation was determined to be 21.886kcal/mol which was quite different from that of linear oxidation in air, and oxidation rates in argon-water mixtures were increased with the increase of partial pressure of H_2O in the mixtures.

(CFM)Ni_4.5Fe_0.25Cu_0.25의 水素貯藏特性에 미치는 熱싸이클의 影響

金大龍 경북대학교 산업기술연구소 1989 産業技術硏究誌 Vol.17 No.-

It is well known that hydrogen storage alloys were intrinsically degraded during a large number of cycles of hydriding and dehydriding. In this work, the effect of thermal cycles on the hydrogen storage characteristics of (CFM)Ni_4.5Fe_0.25Cu_0.25(CFM=cerium free mischmetal) was studied at a constant pressure by means of high pressure sievert apparatus and cyclic heating system. The hydrogen absorption capacity was decreased with increasing of the number of cycles and upper cycling temperature. Losses in capacity during the thermal cycles were not recovered by heat treatment. Even though applied pressure of the cycles was lower than the equilibrium pressure, capacity losses were also observed and hysteresis factor, especially absorption equilibrium plateau pressure was drastically increased. These results are explained by annealing effect, micro-phase separation and structure reordering during the thermally induced hydriding and dehydriding cycles.

Fe_0.9M_0.1Ti(M=Cr, Mn, Fe, Co, Ni 및 Al)-H 系에 대한 熱力學的 硏究

金大龍,尹秉河,姜大甲 경북대학교 1985 論文集 Vol.40 No.-

The influence of partial substitutions of Fe in FeTi by transition metals(Cr, Mn. Fe, Co, Ni) and aluminum on the thermodynamic stability was systematically investigated. Intermetallic compounds examined were Fe_0.9M_0.1 Ti(M = Al, Cr, Mn, Co, Ni and Al). Pressure-composition isotherms of each intermetallics for both absorption and desorption of hydrogen were obtained using a modified sievert's apparatus. In all systems, equilibrium pressure for hydriding reaction at a given temperature was larger than for dehydriding reaction and this difference results in hysteresis energy loss during the hydriding and dehydriding cycles. Enthalpy data of the systems were also calculated from the P-C-T data. Stability of the hydrides was increased more or less significantly by small substitutions of Fe by other elements. It was considered that these effects of substitutions should be explained by interstitial hole size of the intermetallic compounds.

熔融 Cd 中 Zn 과 Cu, Ag, In, Bi, Pb 및 Sn의 相互作用係數

尹秉河,金大龍 慶北大學校 1982 論文集 Vol.34 No.-

Zinc activities in dilute Cd-Zn and Cd-Zn-X(where, X; Cu, Ag, In, Bi, Pb and Sn)molten alloys have been measured in the temperature range of 450 to 570℃, using an e.m.f. measuring technique. The concentration cell utilized was pure Zn(1)|[ZnCl_2 (in fused KCl+LiCl eutectic electrolyte)]|[Cd-Zn or Cd-Zn-X(1)] The activities of zinc deviated positively from the Raoult's law. The activity coefficients of zinc in the ternary systems were decreased with increasing Cu and Ag, but increased with increasing In, Bi, Pb and Sn. The interaction parameters of the zinc-zinc and zinc-third element were found to be a linear functions of the reciprocal absolute temperature and were expressed by the following relations. ε^Zn_Zn = -930.7/T-6.4074 ε^Cu_Zn = -4070/T-4.3644 ε^Ag_Zn = -7261/T-5.1039 ε^In_Zn = -9769/T+3.5979 ε^Bi_Zn = 1585.6/T+3.1725 ε^Pb_Zn = -8410/T+2.0508 ε^Sn_Zn = 984/T-0.1943

熔融 Zn-Cd, Zn-Bi, Cd-Bi系 및 Zn-Cd-Bi系에서 각 成分金屬의 活動度 측정

尹秉河,金大龍,金炳宰 慶北大學校 1984 論文集 Vol.38 No.-

Activities of the component metal in Zn-Cd, Zn-Bi-Cd alloys have been determined at 823 K by touch instant electromotive force method. The cell employed was ◁표삽입▷ (원문을 참조하세요) Activities of each component metal which obtained by T.I.E. method showed similar tendencies with the compare of the equilibrium concentration cell method. But activities of the noble metals showed small difference in some range. This difference was made from the substitution reactions in the molten electrolyte, and from calculation's error.

低溫 鹽素化 反應에 依한 Silicon 製造

尹秉河,林龍進,金大龍,金圭鎬 경북대학교 공과대학 1980 工大硏究誌 Vol.9 No.-

The preparation of high purity silicon by the hydrogen reduction of sicl_4 which producted from the chlorination of commercial ferrosilicon was carried out. The chlorination rates and reaction ratio of ferrosilicon were increased with inoreasing of temperature and Cl_2 flow rate. The optimum Cl_2 flow rate and particle size of ferrosilicon was about 50ml/min and 30-40mesh, respectively. Reaction rate and reaction ratio were increased in the presence of NiCl_2, but CaCl_2, znCl_2, Cu powder and Cu-turnings were acted as an acticatalystic effects. By the addition of 10% NiCl_2 catalysis at 250℃, 66% reaction ratio for four hours was obtained. Silicon chlorides products were purified by the combination of the fractional distillation and silica gel adsorption techniques, and, using these purification techniques, all metallic and nonmetallic impurities were eliminated to unit ppm purified SiCl_4 was reduced in a graphite tube by hydrogen in the temperature range of 900-1200℃, The yields of the silicon products were increased with increasing of temperature and H_2/SiCl_4 mole ratio, and yields at 1100℃ and 1200℃ with mole ratio of 50 was 30% and 43%, respectively. Growth morphologies of silicon crystal were fine needle or cobweblike growth up to 1100℃ and coarse needle or sawtoothlike at 1200℃. These growth morphologies were little changed with precipitation substrates. The purity of silicon product which was analyzed after etching of HF and hydrochloric acid was higher than 99.99%.

瞬間接觸起電力法에 依한 熔融 Cd中의 Zn과 Cu, Ag, In, Bi, Pb 및 Sn와의 相互作用 파라미터

金大龍(Dai-Ryong Kim),尹秉河(Byung-Ha Yoon) 한국표면공학회 1982 한국표면공학회지 Vol.15 No.4

수소저장합금의 마이크로캡슐화

김대룡(Dai Ryong Kim),김용철(Yong Cheol Kim),금동욱(Dong Uk Keum) 한국수소및신에너지학회 1989 한국수소 및 신에너지학회논문집 Vol.1 No.1

Although it has been well known that many metal hydrides are promising to use for hydrogen storage and other applications, some difficulties still remain. Metal hydrides, particularly in powder form, have very poor thermal conductivity. The hydrogen storage alloys degrade intrinsically or extrinsically during repeated hydriding and dehydriding. Elimination of these problems is very important in the practical applications. In order to prevent degradation and to improve the thermal conductivity, the hydrogen storage characteristics of rare-earth type alloy encapsulated with Cu or Ni by means of chemical plating have been investigated. No changes has occured in hydrogen absorption capacity and equilibrium pressure even though the alloy powder is microencapsulated. The first hydrogen absorption rate of the alloy encapsulated increased considerably comparing to uncapsulated sample. In the case of encapsulating the fine powder (>10um) and subsequent compacting by 8ton/cm², shape of compact is maintained regardless of hydriding and dehydriding. The degree of degradation of the alloy caused by impurity gas of CO or O₂ was decre ased prominently by encapsulation.

Na2SO4를 피복한 니켈의 가속산화

김대용 ( Dai Ryong Kim ) 한국부식방식학회 1979 Corrosion Science and Technology Vol.8 No.4