Rare metals scarcity

Oxidative addition offers a direct method to cleave a covalent bond. Although a wide variety of bonds, such as C-1 and C-Br, are known to facilely undergo oxidative addition reactions to low-valent transition metal complexes, examples of oxidative addition of C—C single bonds are far more rare. The scarcity is in part associated with the thermodynamic stability of C—C bonds. Whereas oxidative addition of C-Br and C-I bonds to low-valent metals is thermodynamically favored in general, that of a C—C single bond is often thermodynamically disfavored. 

The Group 7 metals technetium and rhenium have not been applied to the problem of oxidation chemistry to the level of their Group 6 and Group 8 counterparts. This is understandable in light of their relative scarcity. Technetium is a synthetic element, recovered as a fission by-product from uranium.3 "Tc is radioactive (/3 decay, 0.3 MeV, tv2 = 2.14 X 10s years) and its use even in the laboratory requires the appropriate safety precautions. Rhenium is not plagued by either issue, yet it is still a relatively rare element, present at only an estimated 0.001 ppm in the Earth s crust. It is... 

Noble metal catalysts are highly active for the oxidation of carbon monoxide and therefore widely used in the control of automobile emissions. Numerous recent studies on noble metal-based three-way catalysts have revealed characteristics of good thermal stability and poison resistance(l). Incorporation of rare earth oxides as an additive in automotive catalysts has improved the dispersion and stability of precious metals present in the catalyst as active components(2). Monolith-supported noble-metal catalysts have also been developed(3). However, the disadvantages of noble metal catalysts such as relative scarcity, high cost and requirement of strict air/fuel ratio in three-way function have prompted attention to be focused on the development of non-noble metal alternatives. 

Unfortunately, the usefulness of this analysis of vibrational properties is limited by the scarcity of experimental data for metal clusters. Beyond dimers, experimental results are rare, and concern almost exclusively clusters in frozen matrices. 

The concentration of rare earth elements and other precious metals in our waste streams is often higher than in the ore. Ultimately, the scarcity of rare earth elements comes down to our own short-sightedness and the apparent low cost of business as usual—dig it up, use it, discard it. If we value modem society and want to build a better future, business as usual is no longer an option. We must treasure our rare resources. 

While cadmium yellow pigment was at first very rare due to the scarcity of the metal, it became more available to artists in the 1830s after cadmium started to be produced commercially in Upper Silesia (now Poland). A reference to cadmium sulfide is made in George Field s Practical Journal of 1809, where a yellow cadmium water color sample is discussed. Cadmium yellow was also exhibited by today s well known Artist Supply company, Winsor and Newton, at the important Crystal Palace exhibition of 1851, in England. 

While cadmium yellow pigment was at first very rare due to the scarcity of the metal, it became more available to artists in the 1830s after cadmium started to be produced commercially in Upper Silesia (now Poland). A reference to cadmium... 

Rare eartb metals (REM), wbicb include tbe 15 lantbanoids as well as yttrium and scandium, tend to occur in tbe same ore deposits and exhibit similar chemical properties. The term rare earth is misleading because it implies scarcity and high costs as impediments for the use of these metals. Indeed, the element concentrations in the continental crust (Figure 6.1) show that even the rarest lanthanoid thulium is far more common than some precious metals, e.g. silver and gold, and the most abundant lanthanoid cerium is even more common than copper. However, because of their geochemical properties, rare earth elements have very little tendency to become concentrated in exploitable ore deposits. Consequently, most of the world s supply of REM comes from only a handful of sources. It was the very scarcity of these minerals (previously called "earths") that led to the term "rare earth". The REM are also considered as non-toxic and generally not expensive. 

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