Earth oxidation

Historically an earth was a non-metallic substance, nearly insoluble in water and unchanged on heating. The alkaline earth oxides, e.g. CaO, have an alkaline reaction in addition to being clearly earths . 

Within the periodic Hartree-Fock approach it is possible to incorporate many of the variants that we have discussed, such as LFHF or RHF. Density functional theory can also be used. I his makes it possible to compare the results obtained from these variants. Whilst density functional theory is more widely used for solid-state applications, there are certain types of problem that are currently more amenable to the Hartree-Fock method. Of particular ii. Icvance here are systems containing unpaired electrons, two recent examples being the clci tronic and magnetic properties of nickel oxide and alkaline earth oxides doped with alkali metal ions (Li in CaO) [Dovesi et al. 2000]. 

Another sol—gel abrasive, produced by seeding with a-ferric oxide or its precursors, has been patented (30). A magnesium-modified version of this abrasive, also called Cubitron, is being produced as a replacement for the earlier type. Yttria [1314-36-91-vnc>A V eA sol—gel abrasives have also been patented (31), as well as rare earth oxide modified materials (32). These abrasives are all produced by 3M Corporation they have performed very well ia various applications such as ia coated abrasives for grinding stainless steel and exotic alloys. 

The lanthanides, distributed widely in low concentrations throughout the earth s cmst (2), are found as mixtures in many massive rock formations, eg, basalts, granites, gneisses, shales, and siUcate rocks, where they are present in quantities of 10—300 ppm. Lanthanides also occur in some 160 discrete minerals, most of them rare, but in which the rare-earth (RE) content, expressed as oxide, can be as high as 60% rare-earth oxide (REO). Lanthanides do not occur in nature in the elemental state and do not occur in minerals as individual elements, but as mixtures. 

Table 6. Rare-Earth Oxide Distribution in Mineral and Clay Sources, wt ...

A large deposit of loparite occurs ia the Kola Peninsula, Russia. The production of REO reaches 6500 t/yr. Loparite contains over 30% of rare-earth oxides from the cerium group. In addition, loparite contains up to 40% titanium oxide and up to 12% niobium and tantalum oxides. 

Another characteristic of the solvent extraction system is the high solute concentration in both aqueous and organic phases, which influences greatly the size of the required installation. Concentrations of rare-earth oxides (REO) higher than 100 g/L are often reached in both phases. The process therefore requires only relatively small equipment. 

Re OPe . The final step in the chemical processing of rare earths depends on the intended use of the product. Rare-earth chlorides, usually electrolytically reduced to the metallic form for use in metallurgy, are obtained by crystallisation of aqueous chloride solutions. Rare-earth fluorides, used for electrolytic or metaHothermic reduction, are obtained by precipitation with hydrofluoric acid. Rare-earth oxides are obtained by firing hydroxides, carbonates or oxalates, first precipitated from the aqueous solution, at 900°C. 

Direct attack by hot 70—80 wt % hydrofluoric acid, sometimes with nitric acid (qv), is effective for processiag columbites and tantalo-columbites. Yields are >90 wt%. This method, used in the first commercial separation of tantalum and niobium, is used commercially as a lead-in to solvent extraction procedures. The method is not suited to direct processiag of pyrochlores because of the large alkaU and alkaline-earth oxide content therein, ie, ca 30 wt %, and the corresponding high consumption of acid. 

Heterogeneous Catalytic Polymerization. The preparation of polymers of ethylene oxide with molecular weights greater than 100,000 was first reported in 1933. The polymer was produced by placing ethylene oxide in contact with an alkaline-earth oxide for extended periods (61). In the 1950s, the low yield and low polymerization rates of the eady work were improved upon by the use of alkaline-earth carbonates as the catalysts (62). 

Fused basic salts and basic oxides react with vitreous siUca at elevated temperatures. Reaction with alkaline-earth oxides takes place at approximately 900°C. Hahdes tend to dissolve vitreous siUca at high temperatures fluorides are the most reactive (95). Dry halogen gases do not react with vitreous siUca below 300°C. Hydrogen fluoride, however, readily attacks vitreous siUca. 

SoHd lubricants ate added to help control high friction characteristics in high speed or heavy-duty appHcations where high temperatures are generated. Molybdenum disulfide [1317-33-5] M0S2, may be used alone or in a complex compound formed by grinding with fine natural graphite, and zinc sulfide [1314-98-3] ZnS. Other compounds include calcium fluoride, cryoHte [15096-52-3] Na AlF, rare-earth oxides, and metal sulfides, eg, iron, antimony, or zinc (see LUBRICATION AND LUBRICANTS). 

The resistance of graphite to thermal shock, its stabiUty at high temperatures, and its resistance to corrosion permit its use as self-supporting vessels to contain reactions at elevated temperatures (800—1700°C), eg, self-supporting reaction vessels for the direct chlorination of metal and alkaline-earth oxides. The vulnerabiUty of cemented joints in these appHcations requires close tolerance ( 0.10 mm) machining, a feat easily accompHshed on graphite with conventional metal machining equipment. 

Other Rea.ctlons, The anhydride of neopentanoic acid, neopentanoyl anhydride [1538-75-6] can be made by the reaction of neopentanoic acid with acetic anhydride (25). The reaction of neopentanoic acid with acetone using various catalysts, such as titanium dioxide (26) or 2irconium oxide (27), gives 3,3-dimethyl-2-butanone [75-97-8] commonly referred to as pinacolone. Other routes to pinacolone include the reaction of pivaloyl chloride [3282-30-2] with Grignard reagents (28) and the condensation of neopentanoic acid with acetic acid using a rare-earth oxide catalyst (29). Amides of neopentanoic acid can be prepared direcdy from the acid, from the acid chloride, or from esters, using primary or secondary amines. 

Such behavior is observed with alkah and alkahne earth oxidations where the oxide volume is less than the metal volume and cracks develop in the product coat, permitting ready access for further reaction. 

Turning to non-metallic catalysts, photoluminescence studies of alkaline-earth oxides in dre near-ultra-violet region show excitation of electrons corresponding to duee types of surface sites for the oxide ions which dominate the surface sUmcture. These sites can be described as having different cation co-ordination, which is normally six in the bulk, depending on the surface location. Ions on a flat surface have a co-ordination number of 5 (denoted 5c), those on the edges 4 (4c), and dre kiirk sites have co-ordination number 3 (3c). The latter can be expected to have higher chemical reactivity than 4c and 5c sites, as was postulated for dre evaporation mechanism. 

An effect which is frequently encountered in oxide catalysts is that of promoters on the activity. An example of this is the small addition of lidrium oxide, Li20 which promotes, or increases, the catalytic activity of dre alkaline earth oxide BaO. Although little is known about the exact role of lithium on the surface structure of BaO, it would seem plausible that this effect is due to the introduction of more oxygen vacancies on the surface. This effect is well known in the chemistry of solid oxides. For example, the addition of lithium oxide to nickel oxide, in which a solid solution is formed, causes an increase in the concentration of dre major point defect which is the Ni + ion. Since the valency of dre cation in dre alkaline earth oxides can only take the value two the incorporation of lithium oxide in solid solution can only lead to oxygen vacaircy formation. Schematic equations for the two processes are... 

Rare earth oxides and phosphors Ceramics (AI2O3) and glasses Mining ores and rocks Superconductors and precursor materials Thin films... 

Refactory ceramic fibres or special purpose fibres, with the exception of those specified elsewhere in the Approved Supply List (man-made vitreous (silicate) fibres with random orientation with alkaline oxide and alkali earth oxide (Na20 + K2O + CaO + MgO + BaO) content less than or equal to 18% by weight)... 

Rare Earth. Increasing the amount of rare earth oxide (REO) on the zeolite decreases the octane (Figure 6-5). 

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