Papers by Keyword: Transition Metal

Abstract: This paper presents the results obtained from the hydrogenation and decrepitation of three LaNi-based alloys, La_0.7Mg_0.3Al_0.3Mn_0.4Co_0.5Ni_3.8, La_0.7Mg_0.3Al_0.3Mn_0.4Cu_0.5Ni_3.8 and La_0.7Mg_0.3Al_0.3Mn_0.4Sn_0.5Ni_3.8, in the as-cast condition. The procedure for decrepitating the alloys to be used in the negative electrode of the batteries was carried out using a combination of various hydrogen pressures (2-9 bar) at room temperature. At 2 bar of H₂ it was revealed that Co, Cu and Sn have influence on the microstructures of the hydrogenated alloys and on the efficiency of hydrogen decrepitation. None of these alloys required thermal heating to activate and start the hydrogen absorption process. The decrepitated materials were characterized by scanning electron microscopy (SEM). The electrochemical measurements were performed using the tested negative electrode between two Ni (OH)₂ electrodes as a battery cell.

Abstract: This paper reports the results of investigations of the hydrogenation and decrepitation of some LaNi-based hydrogen storage cast ingot alloys. A decrepitation procedure for battery negative electrode alloys has been applied using a combination of hydrogen pressure and heating from room temperature to 773K. It has been shown that the Pr and Mg content have a significant influence on the microstructures of the hydrogenated alloys and decrepitation efficiency. Alloys with high concentration of Pr and Mg required an activation quenching treatment for starting the absorption of hydrogen. The decrepitated materials were characterized by scanning electron microscopy (SEM). Electrodes for alloy discharge capacity studies were produced using a nickel screen and electrochemical measurement were carried out in a standard three-electrode cell. The H content of the negative electrode, expressed as the number o H atoms (n) per formula unit, was determined using the measured storage capacity.

Abstract: In order to investigate Hafnium transition metal alloys HfM (M= Co, Ir, Os,Pt, Rh, Ru) phase diagrams in the region of 50/50% atomic ratio, we performed ab initio Full-Potential Linearized Augmented Plane Waves calculations of the enthalpies of formation of HfM compounds at B2 (CsCl) structure type. The obtained enthalpies of formation are discussed and compared to some of the existing models and available experimental data.

Abstract: In recent years, attention has been drawn to produce heterogeneous catalyst to replace homogeneous catalyst in biodiesel industry. This study was focused on the synthesis of three different types of alginate based heterogeneous catalyst (Ferric-alginate, Copper-alginate, and Nickel alginate) and the effect of the catalyst on esterification of oleic acid. Morphology and elemental analysis was conducted to investigate the properties of the catalyst. The new heterogeneous catalysts were used to catalyze the esterification of oleic acid at reaction temperature of 60°C and 2 hours reaction time. Fe-alginate has achieved the highest free fatty acids (FFAs) conversation rate of 82.03%. The results and findings proved that transition metal-alginate heterogeneous catalyst has the potential and ability to esterify the free fatty acids prior biodiesel production from high free fatty acids feedstock.

Abstract: In the theoretical study of thermophysical properties of materials at high temperature and pressure anharmonic effects are important. In this regard, in the present communication, anharmonic effects are taken into account by coupling recently proposed mean field potential (MFP) in conjunction with local pseudopotential for fcc transition metals Ni, Pd and Pt. Using present approach, we have computed volume variation of binding energy at 0K, vibrational free energy of lattice ions (F_ion), Helmholtz free energy and relative volume thermal expansion up to melting temperature of Ni, Pd and Pt. Further, applicability of present coupling scheme has been tested by investigating equation of state (EOS) at 300K which explains the microscopic internal structure of material. Our results are in good agreement with experimental and other theoretical findings which demonstrate the capability of present coupling scheme of MFP with local pseudopotential alongwith its computational simplicity.

Abstract: Emission spectra of Sn, Sb, Pb and Bi doped silica glasses co-doped with Al and P prepared by modified chemical vapor-phase deposition (MCVD) using solution doping technique are presented. Bi doped silica glasses present emission/excitation (Em/Ex) bands around 470/(330, 220nm) 600/(470, 350, 270nm), 730 and 830/(820, 420, 380, 250nm), with the intensity ratio of these bands depends on the composition, indicating that different emission sources (valence states or defects) are present together. The Em/Ex of Sb doped silica glasses also depend on composition, and are similar of Bi doped silica glasses. The lifetime at 830 and 1400 in Bi or Sb doped silica glasses are similar and around 60 and 850μs, respectively. The lifetime around 600nm was 3.2 and 11μs, respectively to Bi and Sb doped silica glasses. The Sn doped silica glass present Em/Ex bands around 305/265nm, 400/(270, 340nm) and 430/280nm. The Pb doped silica glass present Em/Ex around 370/290nm and 540/320nm. No significant change in the emission bands in the visible range are observed when the Sn or Pb doped silica glass are co-doped with Al or P. The present results of Em/Ex suggest that Bi and Sb can be candidate for fiber lasing in visible range (around 600nm) using the available LD pumping (ex: 405nm). Despite Sn and Pb doping shows strong emission around 400nm, unfortunately until now there is no LD that can be used as pumping source.

Abstract: Oil palm empty fruit bunch (EFB) is one of the palm biomass produced in abundance after oil extraction in Malaysia. This study was focused to utilize this waste biomass as a beneficial raw materials. EFB was used to prepare new solid acid catalyst for biodiesel production. EFB was converted into solid catalyst via direct impregnation method and it was used to catalyse esterification of oleic acid. Transition metal sulfide salt, Fe₂(SO₄)₃ was impregnated on EFB fibres. Effect of different calcination temperature was studied on the properties of catalyst. The result shows that Fe₂(SO₄)₃ based solid acid catalyst which calcined at 500°C exhibited the highest catalytic activity with 93.90% esterification rate was achieved. The morphology and surface chemistry and function group determination for the solid acid catalyst were characterized by SEM-EDX and FTIR.

Abstract: For the purpose of improving the electric discharge machinability of PCD, the authors have proposed a method using an electrode made of a specific transition metal which is easy to react with diamond. As a result, Ti, Nb, Ta, Mo, and W among various reactive metals brought very high efficiency, higher than 3 times of existing electrode materials (Cu, CuW) in the EDM of PCD. It was thought that the higher removal efficiency was due to the material properties such as mixing enthalpy between transition metal atom and carbon atom and a crystal structure of body centered cubic (bcc) lattice.

Abstract: The Fe²⁺/modified silica catalysts have been substituted with four types of transition metals such as Fe³⁺, Cr³⁺, Mn³⁺ and Mo. The catalytic activity of these catalysts has been tested for the oxidative degradation of Reactive Black 5 (RB5) at 30°C and pH 4.5. The substituted Fe²⁺/modified silica with Fe³⁺ (Fe²⁺:Fe³⁺/ m-SiO₂) exhibited the highest catalytic performance compared to others transition metals by degrading the RB5 nearly to 95%. This catalyst possessed on high stability by maintaining its performance during the three successive cycles of reaction. These findings can be ascribed to the plausible enhancement in the formation of hydroxyl radicals (HO^●) due to the effective redox between Fe²⁺ and Fe³⁺

Abstract: A specific transition metal is used as a dopant element in silicon carbide powders to create the compensation effect. According to ab-initio simulation, vanadium, chromium, and manganese-induced compensation decrease the lifetime of the acceptor carrier and cause higher resistance when boron is the main impurity. Since the silicon carbide lattice has low solubility, excess metal precipitates on the surface of powders, particularly on the grain boundaries. The compositions of matrix and precipitation in the powders reveal obvious differences between the two areas. The X-ray diffraction (XRD) pattern shows the structure of VSi₂, which indicates the existence of a second phase. Dual-beam focused ion beam (DBFIB) is used to further analyze the geography inside the powders. A cross-section view by DBFIB shows a second phase in the grains with a composition similar to that in the grain boundary. Metal-doped silicon carbide powders are used as starting materials to conduct crystal growth with better dopant element distribution.