Nicholas J.E. Adkins

Development of AB5 type hydrogen storage alloys with low Co content for rechargeable Ni–MH batteries with respect to electric vehicle applications

Abstract Rechargeable alkaline nickel–metal hydride (Ni–MH) batteries have recently started to penetrate the consumer battery market. In contrast to the widely used Ni–Cd batteries they display up to 50% higher storage capacity and, due to the absence of Cd, an improved environmental compatibility. The electrochemically active material at the negative electrode is a hydrogen storage alloy. In most commercial applications so-called AB 5 alloys having a CaCu 5 type crystal structure have been used so far. These commercial AB 5 alloys are usually of the type Mm(Ni,Co,Al,Mn) 5 , containing typically 10 wt% Co. Mm denotes Mischmetal, a cost-effective mixture of the rare earths La, Ce, Pr and Nd. The large amount of Co is added to produce an alloy with a reasonable cycle life, but increases the alloy cost considerably. The Ni–MH system is considered as a promising energy source for pure electric vehicles and hybrid cars. However for this application it is necessary to decrease the Co content in these alloys without diminishing the cycle life endurance. Hydrogen storage alloy production by gas atomisation represents a promising way to achieve this goal.

Relationship between composition, volume expansion and cyclic stability of AB5-type metalhydride electrodes

Abstract Metal hydride alloys as electrode material for battery application contain up to 15 at.% cobalt. Alloys without cobalt show a much shorter cycle life compared to cobalt containing alloys. The mechanism of how cobalt influences the cycle life is still not well understood. The aim of this work is to investigate the influence of cobalt on the properties of the electrode. A series of alloys with different cobalt content and several other substituents for nickel (Fe, Cu,...) were prepared in two different ways. A set of samples was conventionally melted. A second set of samples was prepared by gas atomization. The volume expansion upon hydriding was analyzed by means of X-ray diffraction. Electrochemical measurements, e.g., discharge capacity as a function of cycle number, were performed. The volume expansion upon hydriding decreases with increasing cobalt content of the alloy. Cobalt substitution for nickel improves the cycle life of an electrode, especially at elevated temperatures (40°C). However, alloys where cobalt is partially substituted by iron show an even better cyclic stability and rate capability.

Net-Shape Manufacturing using Hybrid Selective Laser Melting/Hot Isostatic Pressing

Purpose The purpose of this study is to develop a manufacturing technology using hybrid selective laser melting/hot isostatic pressing (SLM/HIP) process to produce full density net-shape components more rapidly and at lower cost than processing by SLM alone. Design/methodology/approach Ti-6Al-4V powder was encapsulated in situ by the production of as-SLMed shell prior to the HIP process. After HIPping, the SLM shell is an integral part of the final component. Finite element (FE) modelling based on pure plasticity theory of porous metal coupled with an iterative procedure has been adopted to simulate HIPping of the encapsulated Ti-6Al-4V powder and SLMed shell. Two demonstrator parts have been modelled, designed, produced and experimentally validated. Geometrical analysis and microstructural characterisation have been carried out to demonstrate the efficiency of the process. Findings The FE model is in agreement with the measured data obtained and confirms that the design of the shell affects the resulting deformed parts. In addition, the scanning electron microscope (SEM) and Electron backscatter diffraction EBSD (EBSD) of the interior and exterior parts reveal a considerably different grain structure and crystallographic orientation with a good bonding between the SLMed shell and HIPped powder. Originality/value An approach to improve SLM productivity by combining it with HIP is developed to further innovate the advanced manufacturing field. The possibility of the hybrid SLS/HIP supported by FEA simulation as a net shape manufacturing process for fabrication of high performance parts has been demonstrated.

Life cycle assessment of sponge nickel produced by gas atomisation for use in industrial hydrogenation catalysis applications

PurposeThis paper presents a cradle-to-grave comparative life cycle assessment (LCA) of new gas atomised (GA) sponge nickel catalysts and evaluates their performance against the current cast and crush standard currently used in the industrial hydrogenation of butyraldehyde to butanol.MethodsA comparative LCA has been made, accounting for the energy used and emissions throughout the entire life cycle of sponge nickel catalysts—ranging from the upstream production of materials (mainly aluminium and nickel), to the manufacturing, to the operation and finally to the recycling and disposal. The LCA was performed following ISO14040 principles where possible, and subsequently implemented in the software package GaBi 4.3. The CML2001 impact assessment methodology was used, with primary focus on comparing catalysts for equivalent greenhouse gasses generated over their lifetime and their relative global warming potential and secondary focus on acidification potential. This is justified as the lifetime is dominated by energy use in the operational phase, and acidification is dominated by the production of nickel for which existing ISO14040 collected data has been used. A sensitivity analysis was used to provide a number of scenarios and overall environmental performances of the various sponge nickels considered when compared to the existing industrial standard.Results and discussionIt was found that the energy and emissions during the operation phase associated with a given catalyst significantly outweigh the primary production, manufacturing and recycling. Primary production of the nickel (and to a lesser extent molybdenum when used as a dopant) also has a significant environmental impact in terms of acidification potential, but this is offset by operational energy savings over the catalysts’ estimated lifetime and end of life recyclability. Finally, the impact of activity improvement and lifetime duration of sponge nickel catalysts was determined as both total life cycle energy for operational use and as a total life cycle global warming potential.ConclusionsFrom this assessment, the newly developed, higher activity spongy nickel catalysts produced by gas atomisation could have a significantly lower environmental impact than the current industry standard cast and crush method. Given the potential environmental benefits of such catalysts, applications in other processes that require a catalyst should also be investigated.

Accelerated Discovery of Thermoelectric Materials: Combinatorial Facility and High-Throughput Measurement of Thermoelectric Power Factor.

A series of processes have been developed to facilitate the rapid discovery of new promising thermoelectric alloys. A novel combinatorial facility where elements are wire-fed and laser-melted was designed and constructed. Different sample compositions can be achieved by feeding different element wires at specific rates. The composition of all the samples prepared was tested by energy dispersive X-ray spectroscopy (EDS). Then, their thermoelectric properties (power factor) at room temperature were screened in a specially designed new high-throughput setup. After the screening, the thermoelectric properties can be mapped with the possibility of identifying compositional trends. As a proof-of-concept, a promising thermoelectric ternary system, Al-Fe-Ti, has been identified, demonstrating the capability of this accelerated approach.

Log-Normal Melt Pulsation in Close-Coupled Gas Atomization

High speed photography coupled with sophisticated image analysis has been used to study low-frequency pulsation during close-coupled gas atomization. At high gas pressure the instantaneous melt delivery is described by two superimposed log-normal distributions, one with a high standard deviation but little melt at the atomizer tip, the second with low standard deviation but more melt at the atomizer tip. At low gas pressures the distribution is better described by a single log-normal distribution.

Analysis of Microstructural Inhomogeneities of Ti-Based Alloys Produced via Laser-Based Combinatorial Synthesis

Combinatorial synthesis from elemental feedstock is a novel way to develop new alloy combinations in a time-efficient approach. In this study, laser-based combinatorial synthesis using elemental feedstock has been used to create small coupons for the Ti-based ternary alloys (Ti-Al-Nb and Ti-Ni-Cu) systems. The aim of this study is to assess the microstructural inhomogeneities of the coupons using quantitative microscopy and X-ray diffraction, and to compare the microstructure to cast alloys. It was found that the microstructural inhomogeneity, in terms of the phase fraction distribution and the chemistry, is insignificant in most alloy combinations. Post-processing heat treatment was generally not essential to obtain an assessment of the utility of the alloy combination, but it can be used to improve the microstructural homogeneity.

Complementary EM study on highly active nanodendritic Raney-type Ni catalysts with hierarchical build-up

Nanostructured Raney-type Ni catalysts have been used in industry since the 1920s for the production of a wide range of chemicals. [1] In the EU supported project IMPRESS it has been shown that by using gas atomisation processing high surface area particles with significantly increased catalytic activity in hydrogenation reactions can be produced. [2,3] Structural investigations with complementary methods of electron microscopy in combination with X-ray powder diffractometry have enabled the link between processing, structure and catalytic activity to be explored. [4]