Metals cerium

Cerium metal has unique soHd-state properties and is the only material known to have a soHd—soHd critical point. Three aHotropes, a, P, y, are stable at or close to ambient conditions and have complex stmctural interrelationships. 

Zennetall, n. cerium metal, zermilrben, v.t. crush wear down rot (as fabrics). 

The diastereoselectivity of the reaction may be rationalized by assuming a chelation model, which has been developed in the addition of Grignard reagents to enantiomerically pure a-keto acetals7,8. Cerium metal is fixed by chelation between the N-atom, the methoxy O-atom and one of the acetal O-atoms leading to a rigid structure in the transition state of the reaction (see below). Hence, nucleophilic attack from the Si-face of the C-N double bond is favored4. 

E. S. Shedd, J. D. Merchaw and T. A. Henrie, Continous Electrowinning of Cerium Metal from Cerium Oxides, U. S. Bureau of Mines, Rept. Invst. No. 6362,1964. 

Cerium(lll) chloride is used to prepare cerium metal and other cerium salts. It also is used as a catalyst in olefin polymerization, and in incandescent gas mantles. 

Mediated electrochemical oxidation (MEO) is an ex situ treatment technology that uses electricity, acid, and a metal catalyst to destroy organic wastes at low temperatures and pressures. The proprietary CerOx Corporation MEO configuration uses cerium metal as a catalyst to oxidize organic waste into carbon dioxide and water. The process occurs in an acidic solution, typically nitric acid. The first step involves the generation of an oxidant at the anode, followed by the reduction of water or another chemical species at the cathode. This technology serves as a nonthermal alternative to incineration. 

The Mott-like transition, a central concept for the description of the actinide metal series, causes the sudden increase of the atomic volumes, encountered when between Pu and Am (Fig. 3). All other properties indicate the onset of a 5f localized behaviour at Am (see Part V) the 5 f pressure, which had contained to smaller values the equilibrium interactinide distance, suddenly gives in, with the withdrawal of the 5f s within the atomic core. The occurrence of such a transition within a series characterized by an unsaturated shell, is a unique phenomenon of the actinide series. In lanthanides, it does not occur except perhaps under pressure in cerium metal the approaching of cerium atoms induces suddenly the itineracy of 4f orbitals and a sudden volume collapse - see Chap. C. Neither it occurs in d-transition metal series, where the atomic volumes have an almost parabolic behaviour when plotted vs. Z (see Fig. 3 and Chap. C). The current... 

Mischmetal is produced commercially by electrolysis, The usual starting ingredient is the dehydrated rare earth chloride produced from monazite or bastnasite. The mixed rare earth chloride is fused in an iron, graphite, or ceramic crucible with the aid of electrolyte mixtures made up of potassium, barium, sodium, or calcium chlorides. Carbon anodes are immersed in the molten salt. As direct current flows through the cell, molten mischmetal huilcls up in the bottom of the crucible. This method is also used to prepare lanthanum and cerium metals. 

The principle of the method can be seen by referring to Fig. 23, which is a partial phase diagram of the cerium hydrogen system. Molten cerium metal is placed within a thermal gradient such that the lowest temperature is above the peritectic temperature (ca. 1010°C., from the diagram), and hydrogen is slowly dissolved in... 

Cerium metal in the form of small rectangular billets approximately 5 X X 2 in. is used in this preparation. The surfaces of the billets are filed down under a bath of mineral oil to ensure removal of any oxide layer. Caution is advised as the metal may be pyrophoric. The billets are rinsed in carbon tetrachloride to remove the mineral oil and are then transferred to the vacuum glove box. All subsequent handling of the metal is done in the vacuum glove box in a high-purity argon or helium gas environment. 

A sample of cerium metal (approximately 15 g.), previously cleaned and weighed, is placed in a V-shaped tungsten boat. The boat is positioned inside a 26-mm.-o.d., heavy-wall, silica reaction tube, and a curved shield of tungsten foil is placed over the boat to prevent the possibility of silica flakes (formed by reaction with cerium vapor) from falling into the melt. The silica reaction tube is transferred anaerobically from the glove box and installed on the vacuum and gas-handling system. 

C (190-196) and by the thermal decomposition of the trifluoride at 800°C in air (191, 197, 198). The lanthanum compound itself may also be prepared by hydrolysis of the trifluoride (199) and by the reaction of the oxide with molten sodium fluoride (200). On treatment with CFCI3 (201), it is converted back to the trifluoride. The cerium analog has been prepared from Ce02 by reaction with CeF3 at 2750°C (202) or with CeF3 and cerium metal at 900°C in a nickel tube (203). The infrared spectra of these solids have been reported (204). 

Figure 2. The change in the energy of the center of the 4f bands tf and in the band widths Ff as a function of the electron dynamic effective mass m+- in Y-cerium metal. Energy in Rydberg units. For m+./m > 1 the state becomes almost atomic like, and the f bands for different J = L + S values do not overlap in energy, AE3l F...

In preparing fine particles of inorganic metal oxides, the hydrothermal method consists of three types of processes hydrothermal synthesis, hydrothermal oxidation, and hydrothermal crystallization. Hydrothermal synthesis is used to synthesize mixed oxides from their component oxides or hydroxides. The particles obtained are small, uniform crystallites of 0.3-200 jim in size and dispersed each other. Pressures, temperatures, and mineralizer concentrations control the size and morphology of the particles. In the hydrothermal oxidation method, fme oxide particles can be prepared from metals, alloys, and intermciallic compounds by oxidation with high temperature and pressure solvent, that is, the starting metals are changed into fine oxide powders directly. For example, the solvothermal oxidation of cerium metal in 2-mcthoxycthanol at 473-523 K yields ultrafine ceria particles (ca 2 nm). 

The most interesting result is the formation of a transparent colloidal solution of ceria with 2 nm particles. Cerium metal tips with the superficial layers of oxide are allowed to react in 2-methoxyethanol at 250 to 300°C, and removal of coarse ceria particles originating from the superficial layers yields the colloidal solution. Addition of water to the solution does not cause any change except dilution of the color of the solution, but addition of a drop of a solution of any kind of salt immediately causes precipitation of ceria particles. - The reaction mechanism is as follows The solvent slowly dissolves the superficial layers, and when the solvent reaches the metal, rapid reaction occurs, yielding an alkoxide solution. The concentration of the ceria precursor becomes so high that a burst of nucleation occurs, yielding the colloidal solution. The reaction of cerium acetylacetonate in the same solvent yields ceria particles but does not give a colloidal solution. 

Cerium metal and its compounds have a great variety of uses, many in the field of glass and ceramics. Cerium and its compounds are added to these materials to add color (yellow), remove unwanted color, make glass... 

Imamoto, T., Kusumoto, T., Tawarayama, Y., Sugiura, Y., Mita, T., Hatanaka, Y., Yokoyama, M. Carbon-carbon bond-forming reactions using cerium metal or organocerium(lll) reagents. J. Org. Chem. 1984, 49, 3904-3912. 

Use Incandescent gas mantles, spectrography, preparation of cerium metal, polymerization catalyst. 

Use In arc carbons to increase their brilliance preparation of cerium metal. 

Metallic structures of coordination number = 12 are incapable of increasing the coordination number. Application of pressure results in lattice contraction with simultaneous delocalization of electrons. For example in the cubic face centered cerium metal the intemuclear distances of 362 pm are contracted to 340 pm under pressure at 20 kbar 50). 

Catalysts, chemical Cerium salts Cerium metal Charcoal, activated Chlorosulfonic acid Chromates and bichromates Chromic acid Chromium compounds, inorganic Chromium salts Cobalt 60 (radioactive)... 

Cerium enolates may also be generated reductively in THF from oi-iodo or a-bromo esters in the presence of an aldehyde or ketone using cerium metal turnings and catalytic HgCk (or cerium amal-gam). This leads to a Reformatsky-type reaction (Volume 2, Chapter 1.7) producing the (3-hydroxy ester (47) as a mixture of diastereomers (equation 16). 

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