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Sundara Ramaprabhu
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Sundara Ramaprabhu
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Sundara Ramaprabhu
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Sundara, Ramaprabhu
Ramaprabhu, Sundara
Ramaprabhu, S.
Ramaprabhu, Sundar
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10 results
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- PublicationMagnetic behaviour of hydrogenated Ho1-xMmxCo2 (x = 0-0.4) alloys(14-05-2010)
;Srinivas, G.We report the temperature and filed dependence of magnetic behaviour of the Ho1-xMmxCo2 (x = 0, 0.1, 0.2, 0.3 and 0.4; Mm = mischmetal) alloys and their crystalline hydrides. The change of magnetic transition temperature (TC), order of magnetic transition and total magnetization of the alloys with increasing Mm content is studied. The alloys exhibit strong composition and field dependence of thermal hysteresis and spin-reorientation below TC. The effect of hydrogen absorption on the magnetic behaviour of alloys is studied, and the results are correlated to the unit cell volume expansion and decrease in the conduction electron density. © 2010 Elsevier B.V. All rights reserved. - PublicationCorrelation between hydrogen storage properties and amount of alloy particles in Mg-based composites(12-07-2007)
;Kandavel, M.The results obtained from the systematic investigation of the effect of amount of alloy particles in Mg + x wt% (Ti0.1Zr0.9)1.1Mn0.9V0.1Fe0.5Ni0.5 (x = 5, 15, 25, 30, 35, 40, 50, 60 and 75) on the hydrogen storage properties have been discussed. Mg + x wt% (Ti0.1Zr0.9)1.1Mn0.9V0.1Fe0.5Ni0.5 (x = 5, 15, 25, 30, 35, 40, 50, 60 and 75) composites have been synthesized by reaction ball milling. The composites have been characterized by powder X-ray diffractograms (XRD) and scanning electron microscopy (SEM). To examine the effect of amount of catalyst on the hydrogen storage properties of these composites, pressure-composition absorption/desorption isotherms have been obtained in the pressure range 0.1-100 bar at 300 °C using pressure reduction technique. Maximum storage capacity of around 4.7 wt% at 300 °C has been obtained in Mg + 5 wt% (Ti0.1Zr0.9)1.1Mn0.9V0.1Fe0.5Ni0.5. The dependence of plateau pressure on the unit cell volume of Mg phase in these composites is discussed. Hydrogen absorption kinetics of these materials were performed at 300 °C. The kinetics data were analyzed using rate equations to understand the mechanism of hydriding reaction process. © 2006 Elsevier B.V. All rights reserved. - PublicationInvestigations of hydrogen storage properties in certain Zr-based AB2 alloys(01-04-2002)
;Mary Philipose, Shanthi ;Mani, N. ;Kesavan, T. R.The hydrogen storage properties of ZrMnFe0.45Co0.45V0.1 and ZrMn0.9V0.1Fe0.5Co0.5, which are of C14 hexagonal structure, are studied in the ranges of 0.3 ≤ P (bar) ≤ 30 and 30 ≤ T (°C) ≤ 100. The partial substitution of V at the Mn site or at the Fe/Co site in ZrMnFe0.5Co0.5 leads to the expansion of the lattice, the percentage of volume expansion being larger for ZrMnFe0.45Co0.45V0.1 than for ZrMn0.9V0.1Fe0.5Co0.5. The pressure-composition (P-C) isotherms of ZrMnFe0.45Co0.45V0.1 and ZrMn0.9V0.1Fe0.5Co0.5 show the existence of α, (α + β) and β regions. The hydrogen desorption isotherms of the alloys show that the hysteresis is small. The plateau pressures of ZrMnFe0.45Co0.45V0.1-H in the temperature ranges investigated, are lower than those in ZrMn0.9V0.1Fe0.5Co0.5-H, due to the larger size of the tetrahedral interstitial sites in the former alloy. The dependence of the relative partial molar enthalpy of dissolved hydrogen (ΔHH) and the partial molar entropy of dissolved hydrogen (ΔSH) in ZrMnFe0.45Co0.45V0.1-H and ZrMn0.9V0.1Fe0.5Co0.5-H on the hydrogen concentration show the presence of α, (α + β) and β phases. The chemical potential of dissolved hydrogen (ΔμH) in ZrMnFe0.45Co0.45V0.1-H is larger than that in ZrMn0.9V0.1Fe0.5Co0.5-H due to the larger size of the tetrahedral interstitial sites in the former alloy. © 2002 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved. - PublicationSolubility and diffusion of hydrogen in AB2-type Laves phase alloys(08-12-2005)
;Kandavel, M.; ;Jung, M.Wipf, H.Solubility of H2 gas and diffusion of H interstitials were studied in Ti0.1Zr0.9Mn0.9V 0.1Fe0.5Ni0.5, (Ti0.1Zr 0.9)1.1Mn0.9V0.1Fe 0.5Ni0.5 and Ti0.1Zr0.9Mn 0.9V0.1Fe0.5Co0.5 alloys with C14 hexagonal structure. Data were taken between 400 and 600 ° C, for H 2 gas pressures up to 100 mbar and H concentrations up to 0.012 H atoms per host-metal formula unit (solid solution phase). H2 absorption is exothermic, and the partial enthalpy of solution per H atom is -(210±10) and -(248±10) meV for the two alloys Ti 0.1Zr0.9Mn0.9V0.1Fe 0.5Ni0.5 and (Ti0.1Zr0.9) 1.1Mn0.9V0.1Fe0.5Ni0.5, respectively. The diffusion coefficient of the H interstitials was determined for all three samples from the kinetics of H2 gas absorption. At 500 ° C, the diffusion coefficients are ∼5×10-5 cm2s -1, with activation energies between 292 and 423 meV. © 2005 Elsevier B.V. All rights reserved. - PublicationHydrogen storage studies in Zr0.9Ho0.1MnFe0.5Co0.5 and Zr0.9Ho0.1MnFe0.5Ni0.5(01-04-2002)
;Sitaram, V. ;Mani, N. ;Kesavan, T. R.The hydrogen storage properties and the thermodynamics of dissolved hydrogen in the C14 hexagonal Laves phase Zr0.9Ho0.1MnFe0.5Co0.5 and Zr0.9Ho0.1MnFe0.5Ni0.5 alloys are studied. The partial replacement of Ho in Zr site in ZrMnFe0.5Co0.5 and ZrMnFe0.5Ni0.5 alloys leads to the expansion of their lattices. The pressure-composition (p-c) isotherms of Zr0.9Ho0.1MnFe0.5Co0.5 and Zr0.9Ho0.1MnFe0.5Ni0.5 in the pressure and temperature ranges 0.6 ≤ P(bar) ≤20 and 30 ≤ T(°C) ≤100 show sloppy plateau (α + β) region. The average relative partial molar enthalpy of dissolved hydrogen at the (α + β) region in Zr0.9Ho0.1MnFe0.5Co0.5-H and Zr0.9Ho0.1MnFe0.5Ni0.5-H are -15.5 kJ(mol H)-1 and -14.5 kJ(mol H)-1, respectively. Similarly the average relative partial molar entropy of dissolved hydrogen at the two-phase region in Zr0.9Ho0.1MnFe0.5Co0.5-H and Zr0.9Ho0.1MnFe0.5Ni0.5-H are -51 J K-1(molH)-1 and -50 J K-1(molH)-1, respectively. The presence of α, (α + β)- and β-phases as seen in the p-c isotherms, is seen from the powder diffractograms of the alloy hydrides. The kinetics of hydrogen absorption in these alloys are quite fast which is between 15 and 20 min at room temperature. © 2002 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved. - PublicationHydrogen absorption and desorption properties of Ho1 - x Mmx Co2 alloys(01-09-2007)
;Srinivas, G.; The hydrogen absorption-desorption pressure-composition (PC) isotherms and kinetics of Ho1 - x Mmx Co2 (x = 0, 0.1, 0.2, 0.3 and 0.4, Mm = mischmetal) have been carried out in the temperature and pressure ranges 50-200 {ring operator} C and 0.001-1 bar using Sieverts-type apparatus. The effect of Mm on the equilibrium plateau pressure and hydrides stability has been discussed. The kinetics of hydrogen absorption at near equilibrium plateau region have been analyzed by a rate function. The reaction rate constants in the two-phase coexistence region and diffusion coefficient in the hydride phase region were calculated and its pressure and temperature dependence have been discussed. The hydrogen desorption from interstitial sites of Ho1 - x Mmx Co2 H has been performed using differential scanning calorimetry (DSC) and thermogravimetry (TG) analysis. The results are explored to identify the preferential occupation of different interstitial sites of hydrogen atoms and complete desorption temperature. The observed phase transformations as a function of hydrogen concentration and temperature have been discussed. © 2006 International Association for Hydrogen Energy. - PublicationHydrogen absorption characteristics in Mmx Tb1 - x Co2 (x = 0, 0.05, 0.1, 0.15, 0.2)(01-08-2007)
;Krishna Kumar, M.Hydrogen absorption pressure-composition (P-C) isotherms of C15 Laves phase Mmx Tb1 - x Co2 (x = 0, 0.05, 0.1, 0.15, 0.2) alloys have been investigated by pressure reduction method using Sieverts' apparatus, in the ranges 30 ≤ T {ring operator} C ≤ 200 and 0.01 ≤ P (bar) ≤ 20, respectively. The P-C isotherms show the presence of a single plateau region in the temperature and pressure ranges studied. The dependences of the plateau pressure at any given temperature and the hydrogen storage capacity at any particular pressure and temperature on the Mischmetal (Mm) content have been discussed. The dependence of the thermodynamics of dissolved hydrogen in these alloy hydrides on the hydrogen concentration has been studied. The absorption of hydrogen is accompanied by a maximum of 16-18% unit cell volume expansion in the host material without any structural changes as evidenced by the powder X-ray diffraction studies of alloy hydrides. Instead, hydrogen induced amorphization (HIA) at higher hydrogen concentration has been observed. The dependence of HIA on Mm content has been discussed. In addition, the kinetics of hydrogen absorption have been studied in the temperature range 50 ≤ T {ring operator} C ≤ 200 and activation energy for the α + β and β phase and the diffusion coefficient in the β phase have been calculated from the hydrogen absorption kinetics and the results have been discussed. © 2006 International Association for Hydrogen Energy. - PublicationHydrogen absorption and kinetic studies in Zr0.2Ho0.8Fe2(01-11-1996)
;Kesavan, T. R.; ;Rama Rao, K. V.S.Das, T. P.The hydrogen absorption and the kinetics of hydrogen absorption are studied on the C15 type Laves phase pseudo-binary alloy Zr0.2Ho0.8Fe2 in the temperature and pressure ranges RT ≤ T ≤ 150 °C (RT = room temperature) and 0 ≤ P ≤ 70 bar respectively. The maximum hydrogen concentration of 8.1 hydrogen atoms per formula unit is attained at the equilibrium pressure of 67 bar at RT, which is the highest value observed so far in Zr-based C15 Laves phase alloys. From the dependence of thermodynamics of dissolved hydrogen on the hydrogen concentration, the two-phase region in the isotherm corresponding to the equilibrium pressure of about 67 bar at RT is identified as the γ-phase region. This is further confirmed through the X-ray powder diffractogram of the hydrogenated samples on the two-phase regions and from the kinetics of hydrogen absorption. The relative partial molar enthalpy (ΔH̄H) and entropy (AS̄H) of hydrogen at infinite dilution are found to be in the ranges -(3-13) kJ (mol H)-1 and -(14-33) J K-1 (mol H)-1 respectively. The unit cell volume expansion (ΔV/V) upto 26% is found at the maximum hydrogen concentration at RT without change in its cubic Laves phase structure. The average activation energies (Ea) in the (α + β) and β phases are found to be 24 kJ mol-1 and 2 kJ mol-1 respectively. - PublicationHydrogen absorption studies in Zr0.2Tb0.8Co3 and decrepitation and cyclic stabilities in Zr0.2Tb0.8Co3 and ZrMnFe(22-08-1997)
;Arun, C.Pressure-composition isotherms have been determined for a Zr0.2Tb0.8Co3 alloy in the ranges 10≤P (mbar)≤900 and 75≤T (°C)≤200. The hydrogen absorption study shows that the substitution of Zr for Tb in TbCo3 results in the shift of the plateau region to higher equilibrium pressures with a reduction in the hydrogen capacity. An X-ray study on the hydrogenated Zr0.2Tb0.8Co3 alloy reveals that the alloy does not decompose upon hydrogenation. Particle size measurements in Zr0.2Tb0.8Co3 and ZrMnFe alloys before and after hydrogenation show that the decrepitation in Zr0.2Tb0.8Co3 is far less than that in the much harder material ZrMnFe. A plateau pressure of near 1 bar at a temperature suitable for practical applications can be conveniently obtained by appropriate replacement of Tb by Zr in TbCo3. © 1997 Elsevier Science S.A. - PublicationHydrogen absorption characteristics in Zr0.2Ho0.8CoFe(27-03-1998)
;Kesavan, T. R.; ;Rama Rao, K. V.S.Das, T. P.Hydrogen absorption studies have been carried out on the Zr0.2Ho0.8CoFe alloy which has the C15 cubic Laves phase structure. The data were collected in the temperature and pressure ranges 27≤T(°C)≤150 and 0.05≤P(bar)≤45 respectively. A maximum hydrogen concentration of 9 hydrogen atoms per formula unit at 43 bar at RT is observed. The P-C isotherms show two plateau regions which are identified as the (α+β) and (β+γ) phases. These are confirmed from the variation of thermodynamic parameters as the function of hydrogen concentration and from the powder X-ray diffractograms of the samples taken at different hydrogen concentrations. The relative partial molar enthalpy (ΔH̄H) and entropy (ΔS̄H) of hydrogen are found to be in the ranges - (1-8) kJ (mol H)-1 and - (13-22) J K-1 (mol H)-1, respectively. The unit cell volume expansion (ΔV/V) up to 22% is found at the maximum hydrogen concentration at RT without a change in its crystal structure. The powder X-ray diffractogram of Zr0.2Ho0.8CoFeH9 does not indicate the occurrence of hydrogen induced amorphization (HIA) unlike the case of Zr0.2Ho0.8Co2H3 even though the atomic size ratio (RA/RB) of Zr0.2Ho0.8CoFe is more than the critical value estimated for the formation of an amorphous state upon hydrogenation. © 1998 Elsevier Science S.A.