A comprehensive review is presented of the extractive metallurgy of rare earths. The topics covered are: world rare earth resources and production; ore processing and separation of individual rare earths; reduction, refining, and ultrapurification of rare earth elements; methods for rare earth materials analysis; and a selection of the numerous rare earth applications. World rare earth reserves are abundant and would last for well beyond the next century. However, all of the 16 naturally occurring rare earth elements are not equally distributed in the ore minerals. This, compounded with the problems specific to the isolation and recovery of each of the rare earths, sets the stage for an unequal rare earth availability. The close chemical similarity of rare earths looses its importance when divergent physical properties determine the processes for rare earth element reduction and refining. The rare earth metals, alloys, and compounds have been as pure as could be determined. Finally, the commercial...

Extractive Metallurgy of Rare Earths

A review of polymer electrolyte membranes for direct methanol fuel cells

Transportation of people and commodities being a socio-economic criterion needs clean energy and the demand is kept on increasing with modernization. Consequently, generation of a fuel with safer, efficient, economic and reasonably environmental friendly features is the key issue towards fulfilling such demands. Hydrogen seems to be an ideal synthetic energy carrier due to its lightweight, exclusive abundance and environmentally benign oxidation product (water). However, storage remains a big challenge. In this communication, recent developments in the production of hydrogen fuel, applications and storage together with the environmental impacts of hydrogen as energy carrier are emphasized.

Hydrogen the future transportation fuel: From production to applications

Temperature effect and thermal impact in lithium-ion batteries: A review

An apparatus comprising a deformable lens element can be provided wherein a deformable lens element can be deformed to change an optical property thereof by the impartation of a force to the deformable lens element.

Apparatus and method comprising deformable lens element

The electrode characteristics, the hydrogen equilibrium properties, the crystallographic and mechanical properties of simple ternary alloys of the type LaNi5−xMx(M ≡ Ni, Mn, Cu, Cr, AlandCo) were examined. The effect of substituting elements to improve the cycle life increased in the order: M ≡ Mn, Ni, Cu, Cr, AlandCo. The lower the capacity, the smaller the volume expansion ratio, the slower the pulverizing rate and the lower the Vickers hardness were, the longer the cycle life became. The alloy LaNi2.5Co2.5, which showed the highest durability as a negative electrode, satisfied all these requirements.

Some factors affecting the cycle lives of LaNi5-based alloy electrodes of hydrogen batteries

It has been found that the respective substitutions of La and Ni in LaNi{sub 5} by small amounts of Zr and Al remarkably improve the cycle life of the alloy anode, scarcely causing a lowering of capacity. In order to clarify the mechanism, the relations between chemical compositions and anode properties for La{sub 1 {minus} {ital x}}Zr{sub {ital x}}Ni{sub 5 {minus} {ital y}}Al{sub {ital y}}, such as capacity, cycle life, rate capability, temperature behavior, and self-discharge character, were examined. With increasing Zr content in the presence of Al ({ital y} = 0.5) the cycle life (CL) increased greatly: CL = 180 for {ital x} = 0, CL = 580 for {ital x} = 0.1, CL = 690 for {ital x} = 0.15, and CL = 810 for {ital x} = 0.2. The self-discharge was also depressed by the Zr addition. However, hydrogen overpotentials showed a tendency to increase with increasing Zr content, leading to the lowering of discharge potentials and capacities at high currents and low temperatures. The results obtained here were discussed in terms of surface oxide film which worked as a barrier for preventing the diffusion of hydrogen and for protecting the alloy from further corrosion. It wasmore » suggested that the small amounts of substituted Zr and Al play an important role by getting the surface oxide film more dense and protective.« less

Metal Hydride Anodes for Nickel‐Hydrogen Secondary Battery

Effects of Microencapsulation of Hydrogen Storage Alloy on the Performances of Sealed Nickel/Metal Hydride Batteries

The addition of small amounts of elements such as silicon, aluminium and titanium to LaNi2.5Co2.5 greatly influenced anode performance characteristics such as usable temperature range, capacity and its decay rate during repeated cycles, rate capability, low temperature dischargeability and self-discharge rate. The capacity decay was suppressed by the addition of silicon, but the rate capability decreased and the self-discharge rate increased. The alloy containing titanium exhibited a much longer cycle life, but much lower storage capacity and worse low temperature dischargeability. The addition of aluminium was very useful for improving the usable temperature range, cycle life and charge retention, and it did not cause too great a decrease in capacity and/or increase in overpotentials.

The influence of small amounts of added elements on various anode performance characteristics for LaNi2.5Co2.5-based alloys

The self-discharge mechanism of nickel-hydrogen batteries using metal hydride anodes is investigated and discussed by dividing the capacity loss during the storage in open-circuit conditions into two parts, i.e., reversible and irreversible ones. The reversible capacity loss is attributed to the desorption of hydrogen from the metal hydride anode and the irreversible capacity loss to the deterioration of the hydrogen-absorbing alloy. Microencapsulation of the alloy with a thin copper layer is found to improve the self-discharge characteristics.

Keisuke Oguro

Papers

Some factors affecting the cycle lives of LaNi5-based alloy electrodes of hydrogen batteries

Metal Hydride Anodes for Nickel‐Hydrogen Secondary Battery

Effects of Microencapsulation of Hydrogen Storage Alloy on the Performances of Sealed Nickel/Metal Hydride Batteries

The influence of small amounts of added elements on various anode performance characteristics for LaNi2.5Co2.5-based alloys

Self‐Discharge Mechanism of Nickel‐Hydrogen Batteries Using Metal Hydride Anodes