Mantle oxidation

Material barriers Contours of land Immiscible substances (lipids) in membranes Earth s mantle (oxides)... 

Mass fractions of cores (metallic iron) versus concentrations of FeO in mantles (oxidized iron) in the terrestrial planets and asteroid Vesta. After Righter et al. (2006). 

Wood B. J. and Virgo D. (1989) Upper mantle oxidation state ferric iron contents of Iherzolite spinels by Fe Mossbauer spectroscopy and resultant oxygen fugacities. Geochim. Cosmochim. Acta 53, 1277-1291. 

Wood B. J., Bryndzia L. T., and Johnson K. E. (1990) Mantle oxidation state and its relationship to tectonic environment and fluid speciation. Science 248, 337-345. 

Cerium is a component of misch metal, which is extensively used in the manufacture of pyrophoric alloys for cigarette lighters. While cerium is not radioactive, the impure commercial grade may contain traces of thorium, which is radioactive. The oxide is an important constituent of incandescent gas mantles and is emerging as a hydrocarbon catalyst in self cleaning ovens. In this application it can be incorporated into oven walls to prevent the collection of cooking residues. 

At the beginning of the twentieth century, the incandescent mantle, utilising 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 appHcations have developed to coincide with the availabiUty of the rare-earth compounds on an industrial scale and having a controlled purity. 

The way to think of them all is as Si04 tetrahedra (or, in polymer terms, monomers) linked to each other either directly or via a metal ion (M) link. When silica is combined with metal oxides like MgO, CaO or AI2O3 such that the ratio MO/SiOj is 2/1 or greater, then the resulting silicate is made up of separated Si04 monomers (Fig. 16.4a) linked by the MO molecules. (Olivene, the dominant material in the Earth s upper mantle, is a silicate of this type.)... 

The minerals on which the work was performed during the nineteenth century were indeed rare, and the materials isolated were of no interest outside the laboratory. By 1891, however, the Austrian chemist C. A. von Welsbach had perfected the thoria gas mantle to improve the low luminosity of the coal-gas flames then used for lighting. Woven cotton or artificial silk of the required shape was soaked in an aqueous solution of the nitrates of appropriate metals and the fibre then burned off and the nitrates converted to oxides. A mixture of 99% ThOz and 1% CeOz was used and has not since been bettered. CeOz catalyses the combustion of the gas and apparently, because of the poor thermal conductivity of the ThOz, particles of CeOz become hotter and so brighter than would otherwise be possible. The commercial success of the gas mantle was immense and produced a worldwide search for thorium. Its major ore is monazite, which rarely contains more than 12% ThOz but about 45% LnzOz. Not only did the search reveal that thorium, and hence the lanthanides, are more plentiful than had previously been thought, but the extraction of the thorium produced large amounts of lanthanides for which there was at first little use. 

Phenylquinoline 1-oxide (10.0 g, 45.2 mmol) in acetone (1.25 L) was irradiated for 12 h with a Hanovia Q-700 medium-pressure Hg lamp, equipped with a Pyrex cooling mantle placed in the center of the reaction vessel, when TLC showed the absence of starting material. The solution was evaporated in vacuo and the residue was extracted with boiling hexane. The extract was evaporated under reduced pressure and the residue was crystallized (pentane) yield 9.0 g (90%) mp 65-66 C. 

From a geochemical viewpoint, U is an incompatible lithophile and refractory element. U exists in three distinct oxidation states in nature (Galas 1979) but the most common are ([Rn] 5f ) and ([Rn]). The most reduced form (metal) is never found in natural environments. At the surface of the earth, U is dominantly in the form. However, in a reducing environment, it will be in the state where it is insoluble and therefore generally far less mobile than U(VI). In the mantle, U is thought to occur in the... 

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