Cerium/ions/salts

Cero-. ceroua, cerium(III). -ion, n. ceroua ion, eerium(III) ion. -salz, n. eerous salt, cerium (III) salt, -sulfat, n. ceroua sulfate, cerium(III) sulfate. 

At this stage reference may be made to potential mediators, i.e. substances which undergo reversible oxidation-reduction and reach equilibrium rapidly. If we have a mixture of two ions, say M2+ and M +, which reaches equilibrium slowly with an inert electrode, and a very small quantity of cerium(IV) salt is added, then the reaction ... 

The oxidation of an anthracene suspension in sulfuric acid conducted in the presence of cerium salts can serve as an example of mediated oxidation. In the bulk solution the Ce" ions chemically oxidize anthracene to anthraquinone. The resulting Ce ions are then reoxided at the anode to Ce". Thus, the net result of the electrochemical reaction is the oxidation of anthracene, even though the electrochemical steps themselves involve only cerium ions, not anthracene. Since the cerium ions are regenerated continuously, a small amount will suffice to oxidize large amounts of anthracene. 

A perspective method for the production of HCP was proposed by Labarre et al 92-94) [t invo]ves radical graft-copolymerization of methyl methacrylate onto heparin effected by cerium salts (Ce4+). As well as other hydroxyl-containing polymers, heparin may react with cerium ions producing free radicals which may initiate graft-copolymerization of unsaturated compounds ... 

The interaction of arenes or alkylarenes, ArCH2R, with some oxidants, Ox, [27] for example, with cerium(IV) salts [27c] or photoactivated quinones [27d], gives rise to the formation of the ion-radical pair ... 

Boris Pavlovich Belousov (1893-1970) looked for an inorganic analogue of the biochemical Krebs cycle. The investigations began in 1950 in a Soviet secret military institute. Belousov studied mixtures of potassium bromate with citric acid, and a small admixture of a catalyst a salt of cerium ions. He expected a monotonic transformation of the yellow Ce + ions into the colourless Ce +. Instead, he found oscillcilions of the colour of the solvent (colourless-yellow-colourless-... etc., also called by Russians vodka-cognac-vodka-... 

A few of the lanthanides exhibit broad, rather intense bands which can be identified with Ap Ap 5d transitions. Freed made this identification in 1931 of the bands at 33,700, 39,600, 41,700, 45,100, and 47,400 cm of cerium(III) salts containing Ce(H20)9+. Since gaseous Ce + has the levels 5i at 49,737 and 52,226 cm (with the J values 3/2 and 5/2), while Ce(III) anion complexes have the Laporte-allowed 4/ 5d bands at lower wave numbers than the aquo ion, we have the same evolution as... 

The maximum rate of electrochemical regeneration of cerium(IV) is obtained with the concentration of cerium(III) at saturation level. When the cerium(III) ion does not interfere with the cerium(IV)-mediated reaction, it is advisable to add more cerium(III) salts to the reaction mixture than the amount that can be oxidized to cerium(IV). The concentration of cerium(IV) that can be reached it limited by the solubility of cerium(IV) in the reaction solvent, and the cerium(IV) solubility is often lower than the cerium(III) solubility. Tzedakis and Savall (1992) showed that the concentration of cerium(III) has no significant influence on the oxidation of 4-methoxytoluene to 4-methoxybenzaldehyde. 

Cerium(IV) ions are widely used as initiators for radical polymerizations of vinyl monomers (acrylamide, acrylonitrile, methyl methacrylate, vinyl acetate,. ..). In order to act as an initiator, a reductant has to be added to the solutions containing the monomer and a cerium(IV) salt. Free radicals are produced by the oxidation of the reductant by cerium(IV) and these free radicals can initiate the polymerization reaction. Table 3 gives an overview of the different... 

The Ce + ion is one of the most active catalysts for peptide hydrolysis. Its activity is much higher than that of the trivalent lanthanide ions and other transition metal ions. In particular, Ce + is far superior to other tetravalent ions like Zr" or Hf +. Yashiro et al. (1994) reported that dipeptides and tripeptides were efficiently hydrolyzed under neutral conditions by the y-cyclodextrin complex of cerium(IV). Komiyama and coworkers (Takarada et al., 2000) studied the catalytic hydrolysis of oligopeptides by cerium(IV) salts. The hydrolysis is fast, especially when the oligopeptides contain no metal-coordinating side-chains. The hydrolysis rates of the dipeptides, tripeptides and tetrapeptides is similar. The hydrolysis reaction was performed at pH 7 and 50 °C and under these conditions, the half-life of the amide bond was only a few hours. The authors found that ammonium hexanitratocerate(IV) is more active than other cerium(IV) compounds like ammonium cerium(IV) sulfate, cerium(IV) sulfate and cerium(IV) hydroxide. The lower reactivity of ammonium cerium(IV) sulfate is ascribed to the competitive inhibition by sulfate ions, while the low reactivity of cerium(IV) sulfate and cerium(IV) hydroxide can be explained by their poor solubility in water. However, in the reaction mixtures at the given reaction conditions, most of the cerium(IV) consists in a gel of cerium(IV) hydroxides. No oxidative cleavage has been observed. 

The first paper published by Hinton et al. (1984) describes the use of cerium chloride salts as aqueous inhibitors of corrosion for 7075-T6 aliuninum alloy in a O.IM solution of aerated sodimn chloride. Three years later, the same author published a study which stated that additions of small concentrations of rare earth salts (1000 ppm of LaCl3, YCI3, PrCl, NdCl, or CeCy, to a 0.1M NaCl solution induce a decrease in the corrosion rate of AA7075 (Amott et al., 1987). The best degree of inhibition was achieved with Ce ions (Fig. 3.1) when added as chloride compounds (Hinton et al., 1986), because of the formation of a compact film of cerium oxides and hydroxides (Amott et al., 1985). 

In a recent paper, Moutarlier et al. [15] have claimed that the use of cerium salts in sol-gel-based corrosion protection is limited due to the high solubility of the cerium ions. In all of the papers cited here, the authors limited themselves to the use of cerium chloride or cerium nitrate. In order to examine the influence of alternative anions, in the present study, cerium sulphate, cerium acetate hydrate (cerium Ac) and cerium acetylacetonate (cerium Acac) have been compared to cerium nitrate and cerium chloride. Additionally, attempts were made to limit the solubility of cerium chloride and cerium nitrate with the addition of acetylacetone to form complexes of the cerium ions. Table 10.1 gives the solubilities of the cerium compounds examined in this study. 

Impedance modulus Z (at 0.01 Hz) against the Immersion time In 3.5 wt.% sodium chloride solution for seven different cerium salt-doped coating systems measured by EIS. The concentration of cerium Ions In each coating was calculated to be 4 wt%... 

Cerium ions are very promising candidates for the replacement of toxic chromates. They provide dominant cathodic protection by forming an insoluble oxide on corrosion sites [14-17]. Cerium salts, especially the nitrates, have been used and studied extensively for corrosion protection. 

Cerium oxide has been deposited from electrolytic solution containing either cerium nitrate or cerium chloride salts. Using chloride salts poses a problem, in that the deposits tend to be amorphous and incorporate chloride ions into the films except under certain conditions. Creus et al. found that to deposit using cerium chloride salts required either an addition of H2O2 to the aqueous electrol3d e solution or use of a mixed water-ethyl alcohol solution [74]. Others also found that the base generation method could be used for the deposition from chloride salts when the plating solution contained a mixture of water and ethanol [70, 75,76]. 

Separation Processes. The product of ore digestion contains the rare earths in the same ratio as that in which they were originally present in the ore, with few exceptions, because of the similarity in chemical properties. The various processes for separating individual rare earth from naturally occurring rare-earth mixtures essentially utilize small differences in acidity resulting from the decrease in ionic radius from lanthanum to lutetium. The acidity differences influence the solubiUties of salts, the hydrolysis of cations, and the formation of complex species so as to allow separation by fractional crystallization, fractional precipitation, ion exchange, and solvent extraction. In addition, the existence of tetravalent and divalent species for cerium and europium, respectively, is useful because the chemical behavior of these ions is markedly different from that of the trivalent species. 

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