Uses of the rare earths

Unseparated elements, typically in the form of Mischmetal, which is an alloy of rare earth elements, typically approximately 50% cerium and 25% lanthanum with smaller amounts of neodymium atrd praseodymium, can be used for a variety 

5 General chemistry properties of rare earth eiements and compounds 

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Early in his life he left his children such a large inheritance that his son Karl was able to pursue his studies of chemistry in 1878 in Vienna with Professor lAjeSaen and in 1880 with Bunsen in Heidelberg without material worries. In the laboratory of Bunsen he was first introduced into the chemistry of the rare earth elements. Uhtil his death in 1929 he remained true to this field of work. The intensive involvement in spectroscopy with Bunsen also made him familiar with the problems of radiant li t v ch without doiibt was important for his later invention of Auer-Li t and with that the use of the rare earth elements. Further, he had an insight into the work of winning the rare earth metals from their salts through Bunsen, Hill rand and Norton A)o succeeded for the first time in 1875 to produce rare ecu h metals by electrolysis vhich later was further developed in Munich by Muthmann. Ihe concepts "pyrophor" and "pyrophoricity" originate from Auer von Welsbach. 

The third major invention for the use of the rare earth elements was the addition of rare earth fluoride as a wick in arc light carbons which, at that time, were used for a wide range of lighting purposes and later also for cinema production and for search lights. This use of rare earth compounds is based on the intensive arc light developed by Beck in Germany in 1910. 

The rare earths play three roles in the production of nodular iron. These roles are as a nodulizing element (or as the growth modifier) as a means of enhancing the nodule count (or nucleation) and, finally as controllers of deleterious elements. The use of the rare earths for each of these purposes will be described in detail in the following sections. 

Further, it was demonstrated that the introduction of cerium, as mischmetal, in proper amounts was effective in eliminating iron carbides which cause deterioration in physical properties (21). The elimination of iron carbides in thin sections by proper use of the rare earths represents a major contribution to the industry. Different researchers have agreed that there is an optimum percentage for this rare earths addition, which they reported as cerium only, from 0.01% to 0.02% cerium (from about 0.02% to 0.04% total rare earths) that provides this increase in nodule count and control of iron carbides when used in conjunction with magnesium nodulizers (see Figure 9). 

It should be recalled that the final step in the nodular iron treatment process is termed "post inoculation." The purpose of this procedure is to aid in the elimination of iron carbides and promote enhanced nucleation and proper growth of graphite spheroids. This is accomplished by the introduction of the element silicon (usually a ferrosilicon alloy) along with calcium and maybe some magnesium or rare earth. It has been demonstrated that the benefits of rare earth additions are not affected as a function of the time in the process that they are added (23). For example, the elimination of iron carbides by use of the rare earths is possible if the rare earths are introduced along with the primary nodulizer or with the post inocu-lant. In passing, it should be remarked that both the primary nodulizers and ferrosilicon inoculants contain about 1% calcium. 

This chemical reactivity is responsible for some uses of the rare earth metals, such... 

Our major purpose is to demonstrate how the rare earths, and the lanthanides in particular, have provided unique insights into geochemistry and cosmochemistry. Many of the examples which we will use will be drawn from those aspects which have received rather less attention in previous reviews. These include the use of the rare earths to elucidate both the evolution of the moon and the composition and evolution of the continental crust of the earth. We will, however, attempt to provide some comment on all areas of geochemistry and cosmochemistry where lanthanides have added significantly to our understanding. 

This review is concerned principally with the use of the rare earth elements as tracers of geological processes. We do not discuss, except in passing, the great advances which have resulted from the use in geochemistry and cosmochemistry of the radioactive decay of to Nd and Lu to " Hf. These topics each... 

A vast body of literature now exists on the use of the rare earth elements (principally the lanthanides) in terrestrial ingenous geochemistry. Much of this is summarised in work by Haskin (1979), Haskin and Paster (1979), Hanson (1980), Moller and Muecke (1984) and by Henderson (1984). Frey (1979) has reviewed all of... 

Subsequent treatment depends on the intended use of the rare earths. For some applications, particularly the older ones, it is not necessary to achieve a separation of the elements. For example, a mixture of the cerium group metals, called mischmetal, has been used for decades for lighter flints. Thus from a bastnasite or monazite ore base, which contains predominantly the cerium group elements, little further separation work is necessary. However, for basic research into the properties of the elements and their compounds and in applications involving increasingly sophisticated technology the availability of the individual elements in a high purity form is essential. 

The second part reviews published applications of CEF parametrization to the understanding of superconductivity. The use of the rare-earth f states as a local probe to monitor changes of the local charge distribution, and resulting models of clustering and percolative superconductivity, are discussed. Also discussed are s-f, f-f, and f-phonon interactions. Quantification of these interactions is important to the overall vmderstanding of these imusual complex oxides. 

Determined levels and associated uncertainties will not affect the intended use of the rare earth. 

Imanaka present, in the latter chapter, an account of the use of the rare earths to satisfy the growing demand for chemical sensors for a wide variety of substanees found in our environment that require monitoring. These include oxygen, fluorine, sulfur dioxide, earbon dioxide, moisture, alcohol, and nitric oxide. 

Table 10.1 Abundance, reserves, production and uses of the rare earths... 

The use of the rare earths as a geochemical tool began in the early I960 s with the development of techniques for their analysis by neutron activation, followed by methods of isotope dilution mass spectrometry. These techniques provided measurements of sufficient accuracy on common (but chemically complex) natural materials that the potential use of rare earth distributions could be recognized and put to use. Summaries of early work are given by Haskin and Frey (1966), Haskin et al. (1966a), and Herrmann (1968). 

The factors considered above demonstrate that in many respects the rare earth ions resemble the alkaline earth ions in their complex-forming tendencies more closely than they do the d-transition elements. Indeed one of the more recent uses of the rare earth ions is as a substitute for calcium in biological systems. 

Strong light absorption by the jS-diketonate ligands is an advantage for sensitizing the luminescence of lanthanide ions by the antenna effect, but this property limits the usefulness of the rare-earth jS-diketonate complexes as laser materials. In order to achieve uniform excitation of the solutions containing the rare-earth chelate at the concentration required for laser... 

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