Abstract: 2014 The valence state of cerium in CeCo5, CeNi5, CeCu5 and the pseudo-binary Ce(Ni1-xCux)5 compounds has been studied by means of measurements of lattice parameters, magnetic properties and X-ray absorption. Whereas the lattice parameters of CeCu5 correspond to a Ce3+ valence state, X-ray absorption experiments show that, in CeCo5 and CeNi5, Ce has the same valence state, close to 4 +, as in the insulator CeO2. Stoichiometry deviations in the RCo5 compounds (R = rare earth) can be correlated with the difference in the anomalies of the 03B1 lattice parameter of Ce compounds in the RCo5 and RNi5 series. In Ce(Ni0.1Cu0.9)5, Ce is in the 3+ state and the thermal variation of the susceptibility is characteristic of crystal field effects in the Ce3+ ion. In contrast the susceptibility of CeNi5 is one order of magnitude smaller and almost isotropic; as in YNi5, it arises mainly from the Ni 3d electrons which are close to the onset of ferromagnetism. In the Ce(Ni1-xCux)5 compounds, the Ce valence state decreases linearly with x up to x = 0.3 and more rapidly for higher copper concentrations. The evolution of the Ce valence state is discussed in terms of the band structure of the different compounds, especially the relative position of the Fermi level and the 4f1 state. J. Physique 43 (1982) 173-180 JANVIER 1982,

Abstract: Fine-grained powder of the mixed oxide (CeO2)0.9(Gd2O3)0.1, which is an ionic conductor for oxygen ions, was prepared by coprecipitation of the corresponding oxalates followed by calcination. The powder was used to prepare pellets sintered at a relatively low temperature of 1000°C compared with the usual sintering temperature of 1700° to 1800°C. The size of the powder grains was determined from BET surface area (SBET) measurements. The effect of precipitation conditions and calcination temperature on Sbet was examined. The largest surface area measured was 88 m2/g. Decomposition of the oxalate powder was followed using an optical dilatometer. The decomposition was indicated by a large shrinkage and it was completed below 300°C (for a heating rate of 3.3°C/min). The formation of the oxide was verified by X–ray diffraction analysis. It shows that the product of decomposition is the oxide and that decomposition can be carried to completion at 250°C if the heating lasts for 1 h. The pellets had a density of 83% of theoretical, small grains (0.5 μm), and a conductivity which, at 900°C, is two–thirds of the conductivity of dense samples obtained from the same raw material, but calcined and fired at much higher temperatures.

Abstract: We analysed the valence band and the 3d and 4d core levels of LaH x ( x = 0, 2.2, 2.9) and CeH x ( x = 0, 2.1, 2.9) using X-ray photoelectron spectroscopy. A hydrogen-induced band around 5 eV is observed in all the hydrides. The density of states at E F is considerably reduced in the dihydrides and vanishes completely in the trihydrides in agreement with the transition from metallic to non-metallic behaviour. The cerium 4f level appears at 2 eV and is separated from the hydrogen-induced band for both cerium hydrides. The character and occupancy of the 4f levels of cerium is almost conserved in the hydrides as is confirmed by measurements of the magnetic susceptibility. The 3d core levels are shifted by 1.3 eV (LaH 2.2 ), 2.9 eV (LaH 2.9 ), 1.9 eV (CeH 2.1 ) and 2.1 eV (CeH 2.9 ) and exhibit intense satellites on the low binding energy side.

Abstract: Pressure-composition isotherms for La1−xRexNi5-H systems (x = 0-≈ 1; Re  Ce, Pr, Nd and Sm) were measured. These rare earth metals are constituents of misch metal (Mm), and the change in the equilibrium pressure of hydrogen in the MmNi5H system depends on the presence of these constituents. Samarium and cerium were found to be characteristic of elements which produce a marked increase in the equilibrium pressure of hydrogen.

Abstract: Infrared and Zeeman infrared measurements of the tetragonal symmetry cerium fluoride ion and neodymium fluoride ion charge compensation sites in calcium and strontium fluoride are reported. The neodymium results are supplemented by optical absorption and fluorescence measurements. Crystal field analyses successfully account for the observed 2F72/(4f1) and 4I92/, 4I112/(4f3) multiplet crystal field splittings and for the measured Zeeman splitting values.

Abstract: This paper describes the absorption and fluorescence spectra of silica glasses doped with titanium, europium and cerium, and also describes the effects of the melting process and atmosphere used in the heat-treatment on the various ionic valence and spectral properties.

Abstract: Sharp resonances in the photon-stimulated desorption (PSD) of ions from oxidized cerium using photon energies near the Ce $4d$ edge are reported. These resonances are due to autoionization from excited states arising from interaction of the Ce $4d$ and $4f$ levels. PSD spectra taken near the Ce $5p$ edge and valence photoemission studies near the Ce $4d$ edge allow examination of resonant-state decay channels leading to ion desorption. Comparison with optical-absorption data show the utility of PSD as a local probe for the determination of surface valency.

Abstract: The effect of rare earth dopants on the large bandgap semiconductors, barium titanate and lithium niobate, in the photoassisted reduction of carbon dioxide was studied in aqueous suspensions, by illumination with high pressure mercury lamps. The yields of the reduction products formic acid and formaldehyde was enhanced by the presence of low concentrations of the oxides of europium, neodymium, samarium and cerium in the above semiconductors. The optical properties of the materials were studied by diffuse reflectance spectroscopy.

Abstract: The effect of cerium addition on the VIM refining process of oxygen, sulfur, and nitrogen in a nickel-chromium alloy and the Udimet 901 iron-nickel-base superalloy is presented. It was found that cerium reduces sulfur and oxygen content effectively through the formation of cerium oxides, sulfides, and oxysulfides but did not reduce the already low nitrogen content. The kinetics of oxygen and sulfur depletion in the VIM heats follow the first order reaction rate theory and the proposed mechanism is that of the drift of inclusions to crucible skulls. The maximum addition of cerium to iron-nickel-base alloys is limited by segregation effects that lead to hot shortness.

Abstract: A process for preparing a catalyst for cleaning exhaust gases comprising a refractory carrier composed mainly of alumina and having deposited thereon, iron oxide, cerium oxide and at least one noble metal element, which comprises impregnating said carrier with (a) an aqueous solution A prepared by adding aqueous ammonia to an aqueous solution containing a water-soluble iron salt as a material for iron and a cerium salt of an organic acid as a material for cerium to adjust the pH of the aqueous solution to 6.0-9.0, and optionally adding an ammonium salt of an organic acid, and (b) an aqueous solution B containing a compound of the noble metal element.

Abstract: The nitration of benzene and a number of alkylbenzenes by cerium(IV) ammonium nitrate in acetonitrile shows the same intra- and inter-molecular selectivity as nitration with nitric acid under the same conditions but the extent of the other products formed in the two sets of reactions is very different. Nitration, by cerium(IV) ammonium nitrate (but not side-chain substitution) is suppressed by the addition of water. The results suggest that these nitration reactions by cerium(IV) ammonium nitrate occur through the intermediate formation of a nitronium ion from the cerium(IV) complex but the order with respect to the aromatic compound shows that this nitronium ion must then be formed in the presence of the aromatic substrate as a ‘ spectator’. The relative reactivities with respect to benzene in the nitration of anisole and naphthalene are much greater than those observed in nitration by nitric acid and, with both, the isomer proportions are also anomalous.

Abstract: A predominant glow peak at 226+or-3K in calcium sulphide, reported here, is thought to be due to sulphur vacancies acting as electron traps. In all, there are four predominant glow peaks in pure and cerium-activated CaS, two of which have been previously reported by the authors. These exhibit a significant behaviour which has been analysed to reveal the presence of hole traps as well as deep electron traps due to intrinsic point defects in CaS. Cerium has been used primarily to enhance thermoluminescence emission of CaS. However, in view of the fact that the role of cerium in producing compensating defects in CaS is still highly controversial, its role in the present work has been examined.

Abstract: The new compound Ce5B2C6 was prepared by melting cerium, boron and carbon in a high frequency furnace on a water-cooled copper hearth; the inert atmosphere was purified argon. The lattice parameters of the tetragonal cell were found to be a = 8.418(3) A and c = 12.077(4) A . The structure was determined from single-crystal counter data by Patterson and Fourier methods and refined to R = 0.052 for 640 unique structure factors. The space group is P4 (C41), Z = 4. It represents a new structural type which can be derived from the CaC2- and Sc15C19-type structures by filling the (distorted) octahedral voids alternately with carbon atoms and carbon pairs. Boron atoms are needed to stabilize the structure.

Abstract: A method for preparing a divalent-europium-activated calcium sulfide phosphor comprising reacting a molten mixture consisting essentially of alkaline-earth-metal chloride and europium chloride with gaseous carbon disulfide at temperatures between 850° and 1200° C. for 1 to 6 hours. The molten mixture may include activator proportions of cerium and/or alkali metal cations. Minor proportions of calcium may be replaced with one or more other alkaline-earth-metal cations.

Abstract: The redox catalytic properties of ruthenium dioxide hydrate (RuO2·xH2O) were studied using a test system of Ce4+ in 0.5 mol dm–3H2SO4. In powder form RuO2·xH2O appeared a poor redox catalyst unless bound to an inert support, such as titanium dioxide (TiO2). This was attributed to the production of ruthenium tetraoxide (RuO4), which was observed with RuO2·xH2O and a RuO2·xH2O–TiO2 mixture but not with a TiO2-bound RuO2 catalyst. In the absence of a catalyst, or when TiO2 or Al2O3 were used, no decay of the Ce4+ was observed (t > 200 h).

Abstract: Benzene, alkylbenzenes, and phenolic ethers react with cerium(IV) ammonium nitrate in acetonitrile to give nitrocompounds and (if α-hydrogen atoms are present) also the products of side-chain substitution. With many substrates, the major products of side-chain substitution are benzyl nitrates but compounds which can give rise to particularly stable benzyl cations give mainly products from reaction with the solvent. Relative rates of side-chain substitution have been determined by the competition method: the results indicate reaction via a radical cation and the isotope effect kH/kD= 2.3 observed in reactions with [2H10]-p-xylene suggests that proton loss from this radical cation is, at least partly, rate-determining.

Abstract: A catalytic system and process for producing mixtures of methanol and higher alcohols from synthesis gas, the catalytic system comprising zinc, chromium, copper, one or more alkaline metals, and possibly one or more metals chosen from molybdenum, manganese, lanthanum, cerium, aluminum, titanium and vanadium, either all or only part of said elements being chemically bonded to oxygen and/or together.

Abstract: The crystal structures of the title compounds have been determined from diffractometer data. The crystals of the cerium compound are tetragonal, space group P4222 with four molecules in the unit cell of dimensions a= 11.461(2), c= 33.479(6)A(R= 0.060). The thulium analogue is orthorhombic, space group Pca21 with four molecules in the unit cell of dimensions a= 19.899(3), b= 11.451(2), c= 19.051(2)A(R= 0.037). In both compounds the lanthanide ion is co-ordinated to eight sulphur atoms with average Ln–S distances of 2.991 A(Ce) and 2.870 A(Tm). The co-ordination polyhedra are D2d, dodecahedra (mmmm isomer) distorted towards the D2 square antiprism, the cerium compound having two independent molecules in the unit cell, both with 222 crystallographic symmetry. Despite the difference in crystallography between the Ce and Tm compounds, the molecular structures are quite similar in the solid state. However, in solution this is not the case as shown by paramagnetic n.m.r. data. The 31P dipolar shifts are shown to be in accord with a change from dodecahedral to square-antiprismatic geometry when Ln = Dy.

Abstract: Systematic series of two CaMg-aluminosilicate glasses containing both cerium and uranium simultaneously in various molar ratios have been prepared at 1500°C as a function of imposed oxygen fugacity in order to investigate adjustments via internal redox reactions in the separate cerium and uranium redox equilibria. Cerium does not affect the stability region of U(IV) in the glass. The net internal redox reaction, U(V)+Ce(IV)→U(VI)+Ce(III), does occur but not to completion. Species such as Ce(III)OU(IV) might be viable associates in the microstructure of the uranium-cerium aluminosilicate glasses.

Abstract: PURPOSE:To prepare the titled resin composition having excellent thermal stability, colorability, transparency, processability, etc, by adding a specific organic rare earth metal compound to a vinyl chloride resin CONSTITUTION:100ptswt of a vinyl chloride resin is incorporated with 01- 100ptswt, pref 20-50ptswt of an organic rare earth metal compound of formula (R, R' and R'' are 1-18C saturated, unsaturated or aromatic hydrocarbon group or alkoxyalkyl; M is rare earth element composed mainly of cerium and lanthanum; Z is residue of saturated, unsaturated or aromatic dibasic acid) Said metal compound is pref an organic lanthanum compound, and the effect is kept at a high level even at a low lanthanum content Addition of a fatty acid zinc salt, esp an organic phosphite ester and an epoxidized oil in combination, exhibits a remarkable synergistic effect