Applications rare earth metals

Traditional Lewis acids such as AICI3 or BFj OEt2 catalyze key steps in many reactions involving carbonyl compounds, leading to carbon-carbon bond formation. Because of their reactivity and instability these catalysts cannot be used in aqueous solution. For this area of application, rare earth metal catalysts open up new perspectives. 

Oil field uses are primarily imidazolines for surfactant and corrosion inhibition (see Petroleum). Besides the lubrication market for metal salts, the miscellaneous market is comprised of free acids used ia concrete additives, motor oil lubricants, and asphalt-paving applications (47) (see Asphalt Lubrication AND lubricants). Naphthenic acid has also been studied ia ore flotation for recovery of rare-earth metals (48) (see Flotation Lanthanides). 

The liquid-liquid extraction (solvent extraction) process was developed about 50 years ago and has found wide application in the hydrometallurgy of rare refractory and rare earth metals. Liquid-liquid extraction is used successfully for the separation of problematic pairs of metals such as niobium and tantalum, zirconium and hafnium, cobalt and nickel etc. Moreover, liquid-liquid extraction is the only method available for the separation of rare earth group elements to obtain individual metals. 

Rare earth metals, as well as alkali earth metals, can be used as oxygen getters in the purification of tantalum powder. Osaku and Komukai [608] developed a method for the production of tantalum and niobium metal powder by a two-step reduction of their oxides. The second step was aimed at reducing the oxygen content and was performed by thermal treatment with the addition of rare metals. The powder obtained by the described method is uniform, had a low oxygen level and was suitable for application in the manufacturing of tantalum capacitors. 

Applications Rare Earth and Transition Metal Ions, and Color Centers... 

Platinum is a relatively rare earth metal usually found with related metals osmium and iridium. While it has a number of industrial applications, its common consumer application is in catalytic converters. This application has actually increased platinum concentrations in roadside dust. The ability of platinum and its derivatives to kill cells or inhibit cell division was discovered in 1965. Platinum-based drugs, such as cisplatin, are used to treat ovarian and testicular cancer, and cancers of the head and neck, as well as others. Unfortunately, the toxic side effects of these agents often limit their usefulness. 

Praesodymium may be recovered from its minerals monazite and bastana-site. The didymia extract of rare earth minerals is a mixture of praesodymia and neodymia, primarily oxides of praesodymium and neodymium. Several methods are known for isolation of rare earths. These are applicable to all rare earths including praesodymium. They include solvent extractions, ion-exchange, and fractional crystallization. While the first two methods form easy and rapid separation of rare earth metals, fractional crystaUization is more tedious. Extractions and separations of rare earths have been discussed in detail earlier (see Neodymium and Cerium). 

An X-ray atomic orbital (XAO) [77] method has also been adopted to refine electronic states directly. The method is applicable mainly to analyse the electron-density distribution in ionic solids of transition or rare earth metals, given that it is based on an atomic orbital assumption, neglecting molecular orbitals. The expansion coefficients of each atomic orbital are calculated with a perturbation theory and the coefficients of each orbital are refined to fit the observed structure factors keeping the orthonormal relationships among them. This model is somewhat similar to the valence orbital model (VOM), earlier introduced by Figgis et al. [78] to study transition metal complexes, within the Ligand field theory approach. The VOM could be applied in such complexes, within the assumption that the metal and the... 

About 25 000 tons of RE Metals - calculated as oxide - are currently consumed in the world per year. This quantity is divided among a dazzling variety of applications. In order to bring a certain systemization into this variety, these applications and possible applications have been reviewed from 3 different aspects from a historic development, from the special properties of the rare earths and from the degree of separation of the individual elements or grcfup of elements of the rare earth metal series. 

Chemical Properties. In the uses of chemical properties the high affinity of the rare earth metals for os gen is primarily involved. This leads to their application as flints, vdierein their highly exothermic reaction with os gen in air is used. On the same properties rests their application as getter metals, vherein residual os gen, as for exanple in amplifier tubes, is bound up. 

The rare earth elements are physiologically inert and therefore present no danger to the environment. The tro pharmaceutical applications vhich go back to the thirties are based primarily on the anions or corresponding salts rather than on the effect of the rare earth metals ceriumoxalate as treatmoit for seasickness and Nd-isonikotinate as treatment for thromboses. 

Industrial Applications of Pure Rare Earth Metals and Related Alloys... 

By contrast, the industrial user must view any raw material purchase in terms of its cost effectiveness and in the case of rare earth metals this frequently requires the adoption of low purity specifications. Therefore, in the context of the industrial applications to which reference will be made, the term pure will be taken to include all metals having a purity of not less than 95% - the balance being predominately other rare earths. But before considering the applications in detail it is perhaps of value to have some appreciation of the size of the market for these metals. 

Of those factors that have proved a disincentive to the wider application of the metals perhaps none has proved more formidable than cost. Unquestionably some rare earth metals are expensive when compared with many of the more common metals but then others, such as the commercial grades of lanthanum and cerium produced by electrolytic methods, are relatively inexpensive. Unfortunately, for most rare earth metals one must use a metallothermic reduction process that is inherently costly to operate. However, while there is a wide variation in the price of the various metals, from 50 - 7,000 per lb., the overall picture is one of relative price stability when judged against the movements of many other metals. To some extent this stability has been born out of the need to encourage potential users to adopt a particular metal in the face of a competitive product while in other cases it reflects more the economy of scale that has been possible once production has passed a given level. 

In conclusion, it is particularly reassuring to know that research involving rare earth metals and related alloys is as active today as at any time during the past ten years. Additionally, many of the industrial applications to which reference has been made are at a relatively early stage in their development. Taken together these factors must point to an exciting future for rare earth metals. 

The source of luielium to date has been the processing of the other heavy rare-earth metals. Because of very limited availability, little research Was conducted on lutetium until the mid-1960s Most of these studies now are concentrating on prospective uses in phosphors, semiconductor, and other electronic circuitry components. A lulclium dilhalocvaninc complex has received much consideration recently for application in large, thin screens for television projection. 

Carboxylic acids represent a group of readily available and relatively inexpensive extractants. They have found rather limited application in commercial processes, however, probably on account of their generally low selectivity and poor pH functionality. Nevertheless, they have been used for the separation of copper from nickel,37 the removal of iron from the rare-earth metals,38 separations among yttrium and the rare earths,39 the recovery of indium40 and gallium,41 the removal of... 

The use of organophosphorus acids, such as di(2-ethylhexyl)phosphoric acid (D2EHPA di(2-ethylhexyl) monohydrogen phosphate 2 R = C4H9CH(Et)CH2), is now well established in the recovery of base metals. This reagent has found commercial application in the separation of cobalt from nickel,67 68 the separation of zinc from impurities such as copper and cadmium,69 the recovery of uranium,68 beryllium70 and vanadium,71 and in separations involving yttrium and the rare-earth metals.72 73... 

The use of solvating extractants in the recovery of gold and platinum-group metals (PGM) was described in the previous section. These extractants have also found some specialized applications in the extractive metallurgy of base metals. For example, they have been used in the recovery of uranium, the separation of zirconium and hafnium, the separation of niobium and tantalum, the removal of iron from solutions of cobalt and nickel chlorides, and in the separation of the rare-earth metals from one another. 

At the beginning of the twentieth century, the incandescent mande, utilizing the candoluminescence of a mixture of thorium (95% weight) and cerium oxides was developed. The pyrophoricity of rare-earth metals led to the invention of the lighter flint made through the alloying of iron and mischmetal. Since that time, numerous other applications have developed to coincide with the availability of the rare-earth compounds on an industrial scale and having a controlled purity. 

A lean NOx trap (LNT) (or NOx adsorber) is similar to a three-way catalyst. However, part of the catalyst contains some sorbent components which can store NOx. Unlike catalysts, which involve continuous conversion, a trap stores NO and (primarily) N02 under lean exhaust conditions and releases and catalytically reduces them to nitrogen under rich conditions. The shift from lean to rich combustion, and vice versa, is achieved by a dedicated fuel control strategy. Typical sorbents include barium and rare earth metals (e.g. yttrium). An LNT does not require a separate reagent (urea) for NOx reduction and hence has an advantage over SCR. However, the urea infrastructure has now developed in Europe and USA, and SCR has become the system of choice for diesel vehicles because of its easier control and better long-term performance compared with LNT. NOx adsorbers have, however, found application in GDI engines where lower NOx-reduction efficiencies are required, and the switch between the lean and rich modes for regeneration is easier to achieve. 

The excellent insulating and dielectric properties of BN combined with the high thermal conductivity make this material suitable for a huge variety of applications in the electronic industry [142]. BN is used as substrate for semiconductor parts, as windows in microwave apparatus, as insulator layers for MISFET semiconductors, for optical and magneto-optical recording media, and for optical disc memories. BN is often used as a boron dopant source for semiconductors. Electrochemical applications include the use as a carrier material for catalysts in fuel cells, electrodes in molten salt fuel cells, seals in batteries, and BN coated membranes in electrolysis cells for manufacture of rare earth metals [143-145]. 

According to Ref. 32, there is no formation of free phthalocyanine in the system "z-BuOII CII3ONa ( -Bu)4NBr o-phthalonitrile without the application of electrolysis at about 100°C (Example 11), unlike some other solvents where both chemical and electrochemical formation of phthalocyanine could take place. So, this solvent was chosen by the authors of Ref. 33 in order to synchronize metal anode dissolution with the formation of free phthalocyanine on the cathode surface and to avoid obtaining a mixture of metal-free phthalocyanine-lanthanide phthalocyanine. Unlike conventional chemical methods of preparing rare-earth metal phthalocyanines [63,85,86], where the syntheses are carried out at 170-290°C, it is possible to decrease the reaction temperature to about 100°C. 

Classical Friedel-Crafts catalysts such as BF3 etherate or Bronstedt acids, which are applied in stoichiometric amounts or even in excess, still have their value, because they are relatively inexpensive yet powerful catalysts for C-H transformation at arenes and, most importantly, they are often successful when modern catalysts fail. Gold(III) chloride, at less than 1 %, has impressive reactivity under very moderate reaction conditions and its selectivity is exceptionally good. Friedel-Crafts type reactions with this catalyst are, however, restricted to very electron-rich arenes. Further studies should concentrate on increasing the electrophilicity of gold catalysts. New catalysts have emerged, for instance based on ruthenium and rhenium, which promise broad applicability based on alternative mechanisms. Catalysts based on rare earth metals are discussed in the next chapter. 

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