Mischmetal-nickel (Mm-Ni) alloys with single (Al) and multiple (Al, Co, Mn, Fe) substitutions for Ni are studied for their structural, hydrogen storage and thermodynamic properties. The alloys considered are MmNi5, MmNi4.7Al0.3, MmNi4.5Al0.5, MmNi4.2Al0.8 and MmNi4Al for single substitution, and MmNi3.9Co0.8Mn0.2Al0.1, MmNi3.8Co0.7Mn0.3Al0.2, MmNi3.7Co0.7Mn0.3Al0.3, MmNi3.6Co0.6Mn0.3Al0.3Fe0.2 and MmNi3.5Co0.4Mn0.4Al0.4Fe0.3 for multiple substitutions. The XRD patterns of all the alloys show single phase with the reflection peaks related to the CaCu5 hexagonal structure. All the multiple substituted alloys absorb and desorb hydrogen at sub-atmospheric pressures. The equilibrium pressure and hysteresis decrease, while enthalpy of formation (ΔH) and plateau slope increase with increase in unit cell volume, indicating an increase in the stability of the alloys. © 2008.

M. Prakash Maiya

Department of Mechanical Engineering

Balasubramanian Viswanathan

ENTHALPY OF FORMATION

MISCHMETAL-NICKEL ALLOY

PLATEAU PRESSURE

Substitution

Unit cell volume

Aluminum

Atmospheric pressure

enthalpy

Hydrogen

Hydrogen storage

HYDROGEN STORAGE ALLOYS

hysteresis

Manganese

Manganese compounds

Nickel

Nickel alloys

Organic polymers

Slope stability

Thermodynamics

Welds

Iron alloys

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Journal of Alloys and Compounds

The static and dynamic pressure-concentration isotherms (PCIs) of MmNi5-xAlx (x = 0, 0.3, 0.5 and 0.8) hydrides were measured at different temperatures using volumetric method. The effect of Al substitution on PCI and thermodynamic properties were studied. The plateau pressure and maximum hydrogen storage capacity decreased with Al content whereas reaction enthalpy increased. The plateau pressure, plateau slope and hysteresis effect was observed more for dynamic PCIs compared to static PCIs. Different mathematical models used for metal hydride-based thermodynamic devices simulation are compared to select suitable model for static and dynamic PCI simulation of MmNi5-based hydrides. Few important physical coefficients (partial molar volume, reaction enthalpy, reaction entropy, etc.) useful for development of thermodynamic devices were estimated. A relation has been proposed to correlate aluminium content and physical coefficients for the prediction of unknown PCI. The simulated and experimental PCIs were found matching closely for both static and dynamic conditions. © 2014 Hydrogen Energy Publications, LLC. All rights reserved.

International Journal of Hydrogen Energy

Experimental and theoretical studies on static and dynamic pressure-concentration isotherms of MmNi5-xAlx (x = 0, 0.3, 0.5 and 0.8) hydrides

In the present study, a novel four alloys three-stage hydrogen based sorption heat transformer (4A – HSHT) is proposed to achieve higher heating output and efficiency with wide range of operating temperatures. The 4A – HSHT system can able to produce multiple heating outputs compared to conventional single stage metal hydride heat transformer (MHHT) with higher COP. The screening of metal hydrides is carried out to identify the best suited working pair for 4A – HSHT which results in the pair of La0.9Ce0.1Ni5 – MmNi4.4Al0.6 – LaNi4.7Al0.3 – MmNi3.7Co0.7Mn0.3Al0.3 hydrides for operating temperature range of 180 °C for heating output, 140 °C for heat supply and 45 °C for heat sink. The thermodynamic performance of 4A – HSHT is investigated using experimentally measured pressure concentration isotherm (PCI) and thermodynamic properties of chosen metal hydrides. The thermodynamic performance i.e. COP, specific heat output and heating capacity are estimated as 0.75, 81.8 W/kg and 0.9 kW, respectively for 2.75 kg of each alloy with 64 min of cycle time followed by the discussion on effects of heating output temperature on COP and specific heat output. The detailed flow chart demonstrating the methodology of material selection and thermodynamic simulation is presented. In addition, the various issues related to the implementation of practical devices based on metal hydride sorption systems are discussed including recent developments. © 2019 Elsevier Ltd

Applied Thermal Engineering

Studies on thermodynamic performance of three stage sorption heat transformer

The performance of metal hydrides based simultaneous cooling and heat transformation system (MHCHT) using a combination of La0.9Ce0.1Ni5–MmNi4.4Al0.6–MmNi3.7Co0.7Mn0.3Al0.3 hydrides is evaluated. The MHCHT is thermodynamically analysed using statically and dynamically measured PCIs and thermodynamic properties. In addition, a set of governing equations is solved in order to study the heat and hydrogen transfer between the reaction beds. The experimental PCI measurement data are compared with the numerical results and a reasonably good agreement is observed between them. From the results, the slope and hysteresis factors are determined for further thermal analyses. It is observed that the performance parameters i.e. cooling capacity, heat transformation capacity and coefficient of performance (COP) of MHCHT are significantly decreased by 42.4%, 26.7% and 19.1% respectively when dynamic property data are considered compared to static property data. In addition, the thermodynamic cycle is analysed by considering the variation in pressure during hydrogen transfer process between the metal hydride beds. © 2019 Hydrogen Energy Publications LLC

Performance analysis of metal hydride based simultaneous cooling and heat transformation system

This short review discusses the classification, pressure concentration isotherm (PCI) characterisation and applications of metal hydrides. Special attention is paid to describe the design criterion and fabrication of Sievert's apparatus and PCI characterisation methods of metal hydrides. Different classes of metal hydrides and their properties are broadly discussed. Also, some of the important applications of metal hydrides are presented. The absorption and desorption PCIs of four Lanthanum based alloys namely La0.9Ce0.1Ni5, La0.8Ce0.2Ni5, LaNi4.7Al0.3 and LaNi4.6Al0.4 are measured using volumetric method in the temperature range of 20 to 80 °C. Later, different PCI simulation models are compared, and Zhou's model is used to simulate the experimentally measured PCIs at different temperatures. It is found that the simulation results are in good agreement with the experimentally measured results. Copyright © 2016 John Wiley &amp; Sons, Ltd. Copyright © 2016 John Wiley &amp; Sons, Ltd.

International Journal of Energy Research

Metal hydrides for energy applications - classification, PCI characterisation and simulation

Metal hydride based heat transformer, heat pumping and cooling systems are the most important thermodynamic applications of metal hydrides due to the ability to utilise waste heat as input. For attaining higher efficiency and extensive operating temperature range, novel four alloys multi stage multi effect thermodynamic system is proposed. This paper brings systematic study of four alloys based thermodynamic cycle for simultaneous cooling, heat pumping and heat transformation. The performance of this thermodynamic cycle was studied using different combination of AB5 – type (La and Mm based) metal hydrides. The effect of operating temperatures (such as hot, driving, intermediate and cold temperatures) and different metal hydride combinations on the thermodynamic cycle performance was studied. Additionally, the cycle performance i.e. coefficient of performance (COP), specific alloy output (S), cooling capacity (CC), etc. were compared with three alloys based simultaneous heating and cooling system. The study shows that the employment of four alloy system for the development of metal hydride based thermodynamic system improves cycle efficiency as well as specific alloy output and facilitates extensive operating temperature range. © 2016 Hydrogen Energy Publications LLC

Thermodynamic analysis of novel multi stage multi effect metal hydride based thermodynamic system for simultaneous cooling, heat pumping and heat transformation

Mischmetal (Mm) nickel (Ni) alloys with different aluminium (Al) contents are tested for hydrogen storage characteristics under dynamic operating conditions. The compositions considered are MmNi5, MmNi4.7Al0.3, MmNi4.5Al0.5, MmNi4.2Al0.8 and MmNi4Al. Pressure concentration isotherms (PCI), plateau slopes and absorption rates are measured. Activation energies are calculated by fitting Arrhenius equation to the absorption data. As expected, the plateau pressure of MmNi5 decreased with increase in Al content. Apparent reaction enthalpy values (as distinct from enthalpy of formation calculated from static measurements), plateau slope, and activation energies increased, and absorption rate decreased with increase in Al content. The study confirms MmNi4.5Al0.5 as a preferred candidate for reversible hydrogen storage at room temperature with nominal supply pressure and fast kinetics. © 2008 Elsevier B.V. All rights reserved.

Influence of aluminium content on the dynamic characterstics of mischmetal based hydrogen storage alloys

Hydrogen absorption isotherms for the CaCu5 hexagonal structured alloys MmNi3.8Al0.4Fe0.4Co 0.4, MmNi3.5Al0.5Fe0.5Co 0.5, MmNi3.4Mn0.4Al0.4Fe 0.4Co0.4, MmNi3.368Mn0.333V 0.333Al0.3Fe0.333Co0.333 and MmNi3Mn0.333V0.333Al0.333Fe 0.333Co0.333Cu0.333 with Fe and Co in the mole ratio 1:1 have been obtained in the temperature and pressure ranges 30 ≤ T/°C ≤ 100 and 0.1 ≤ P/bar ≤ 30 using a high pressure unit based on the pressure reduction method. The powder X-ray diffractograms of the unannealed alloys show the formation of single phase. The lattice constants and the unit cell volume of these alloys increase with substitution of Mn, V, Cu, Fe, Al and Co at the Ni site in MmNi5. The hydrogen absorption isotherms show the presence of a single plateau region (α+β) in the temperature and pressure ranges studied. The hydrogen absorption studies show no marked change in the plateau slope due to the presence of Fe and Co in 1:1 mole ratio. The maximum hydrogen intake capacity (r = nH/n f.u.) is around 4.75 in MmNi3.8Al0.4Fe 0.4Co0.4 at 30 °C and at 30 bar. The dependence of the thermodynamics of dissolved hydrogen in these alloy hydrides on the hydrogen concentration shows the different phase regions α, α+β and β seen in the hydrogen absorption isotherms. At any particular temperature investigated, the chemical potential of dissolved hydrogen in these alloy hydrides decreases with the substitution of Mn, V, Cu, Fe, Al and Co at the Ni site, which has been correlated with the increase in the volume of the unit cell of the alloys. The desorption isotherms of MmNi 3.8Al0.4Fe0.4Co0.4 at 30 and 50 °C show that the hysteresis is very small with free energy loss per cycle about 0.4 kJ/mol H at 30 °C. The kinetics of hydrogen absorption at 30, 50, 75 and 100 °C have been studied for MmNi3.8Al 0.4Fe0.4Co0.4. The different phases identified by both kinetic and thermodynamic studies confirm those seen in the hydrogen absorption isotherms. The average activation energies Ea in the α, (α+β) and β phases are found to be 0.38 eV, 0.32 eV and 0.054 eV, respectively. The diffusion coefficient at 303 K in MmNi 3.8Al0.4Fe0.4Co0.4-H is about 2.55 × 10-10 cm2 s-1. The powder X-ray diffractograms of the alloy hydrides show that these alloys do not undergo any structural transformation upon hydrogenation. © 2003 Elsevier B.V. All rights reserved.

Effect of substitutional elements on hydrogen absorption properties in Mm-based AB5 alloys

A panoramic overview of hydrogen storage alloys from a gas reaction point of view

Hysteresis in MmNi5 systems with aluminium, manganese and tin substitutions

Hydrogen storage properties of MmNi5−xMnx system based on Indian mischmetal

Structural, hydrogen storage and thermodynamic properties of some mischmetal-nickel alloys with partial substitutions for nickel

Journal	Journal of Alloys and Compounds
ISSN	09258388
Open Access	No