Cerium Deposition Research Articles

Growth and oxidation of thin cerium films on polycrystalline platinum

Deposition of cerium on polycrystalline platinum ribbons has been studied by Auger electron spectroscopy. Our data indicate that intermixing or compound formation occurs during the deposition of Ce on Pt at room temperature. However, coadsorption of oxygen, at a low level, has been found to change the growth process, a pseudo layer-by-layer growth mechanism being then observed. The oxygen uptake has been followed on these various surfaces. It strongly decreases when a Pt-Ce compound is formed.

Gulliver among the atoms: Gillan, M. New Scientist (Apr 1993) 138 (1867), 34–37

Conversion treatments based on immersion in Cr(VI) aqueous solutions are key technologies that combine low cost, easy application and high performance. However, they are environmentally problematic due to their carcinogenity and genotoxicity. Among the potential alternatives, treatments based on rare-earth compounds have drawn attention due to the stability of their oxides and their environmental acceptability. Despite the amount of work published, there is not yet an industrially suitable alternative treatment for aircraft aluminium alloys that is able to provide the required corrosion protection. A common feature of these alloys is the high level of copper in their chemical composition. Although the presence of copper in an alloy may enhance cerium deposition, high copper content alloys (AA2024, AA7075) have proven the most difficult to protect with Ce conversion coatings.In the present work, a commercial 8090-T8 aluminium alloy containing 1.15 weight percent (wt.%) Cu was coated with a Ce conversion coating at room temperature from a Ce bath without prior pretreatment of the specimens. Polarisation curves revealed that the presence of a cerium conversion coating (CeCC) reduces by two orders of magnitude the corrosion rate of the AA8090 alloy in a sodium chloride solution. Impedance measurements exhibited capacitive behaviour for the CeCC up to 216 h, showing that the cerium layer protects the bare alloy in the aggressive solution.Electrochemical tests have therefore revealed that these conversion layers afford long-lasting protection; withstanding up to 168 h in Salt Spray test.

Cerium anomalies in lateritic profiles

The REE geochemistry and mineralogy have been studied in four lateritic profiles, one derived from a syenite (Akongo, SW Cameroon), the others being developed on a gneissic basement and located along a soil toposequence (Goyoum, E Cameroon). There is a fractionation between LREE and HREE in the lateritic samples during weathering, the weathered residual products being enriched in LREE (from La to Eu) and depleted in HREE (from Gd to Lu); sampled waters are enriched in HREE in relation to the syenite host-rock. A positive Ce-anomaly has been found systematically at the top of the saprolite, beneath a zone of iron oxide accumulation in the laterite. Up to 2000 ppm Ce may be present. In the Akongo profile, cerianite, CeO 2, is present as very fine coatings in non-ferruginous clayey domains. Primary REE-bearing accessory minerals are weathered at the bottom of the profile. Specifically, allanite and apatite are transformed into florencite and rhabdophane but these phases have no Ce-anomaly. All the data are interpreted as the result of the following processes: 1. (1) REE leaching in a reducing environment. 2. (2) oxidation of Ce 3+ to Ce 4+ in an oxidizing environment. 3. (3) deposition of cerium as cerianite whereas the other REE remain in solution.

Ultracytochemical localization of superoxide dismutase activity in rabbit alveolar macrophages: A comparative study using KO2 or xanthine-xanthine oxidase as O-2 generating system.

An attempt has been made to obtain evidence for the localization of superoxide dismutase (SOD) activity in rabbit alveolar macrophages (AMφ). SOD localization was investigated with two different superoxide (O-2)-generating systems, the potassium superoxide (KO2) and the xanthine-xanthine oxidase system. The hydrogen peroxide (H2O2) generation site, which indicates SOD activity, was electron cytochemically investigated by using the cerium method introduced by Briggs et al.In the KO2 system, the formation of cerium perhydroxide serves as an indication of SOD activity, and its presence was confirmed throughout the cytoplasm and mitochondria, but not in the nucleus and granules. Under the action of diethyldithiocarbamate and potassium cyanide, which act as Cu, Zn-SOD inhibitors, it was found that the cytoplasmic SOD activity was virtually completely suppressed, and that complete inhibition of SOD activity occurred in the presence of catalase (a scavenger of H2O2) or in the absence of KO2. In the xanthine-xanthine oxidase system, cerium deposits were observed in the cytoplasm, but rarely in the mitochondria. Occasionally some reaction product was seen in the nucleus and granules.From the results, it is concluded that KO2 system is an excellent method for investigation of the localization of SOD activity.

Use of the cerium chloride technique and energy dispersive X-ray microanalysis in plant peroxisome identification

Glycolate oxidase activity is demonstrated cytochemically with the CeCl3 technique in leaf peroxisomes ofNicotiana tabacum, Glycine max, Psychotria punctata and in unspecialized peroxisomes ofYucca torreyi roots. Reaction product deposition occurs throughout peroxisomal matrices, whereas nucleoid inclusion bodies, occurring in all four species, are cytochemically unreactive. We observed reactive and nonreactive microbodies within individual cells in these four plants despite prolonged incubation times and increased CeCl3 concentration. These results may reflect differences in glycolate oxidase content or peroxisomal differentiation within individual cells of a given tissue. We demonstrate substrate-independent cerium deposits in cell walls, cytoplasmic hoop-shaped structures and chloroplast thylakoids at extended incubation times or increased CeCl3 concentration, perhaps indicating the presence of endogenous H2O2. Elemental spectral analysis of electron-dense deposits with energy dispersive X-ray microanalysis using a STEM detects peaks generated from the L-series of cerium. SEM X-ray mapping for the Lα1 peak of cerium verifies peroxisomal localization of reaction product in thin sections.

Electron‐microscopic investigation of cerium–cotton cellulose reactions

AbstractCotton fibers were treated with an aqueous solution of ceric ammonium nitrate and examined with the electron microscope. The greatest deposition of cerium occurred in the primary wall due largely to the reaction with noncellulosic constituents in this area of the fiber. The use of ceric ions for an electron‐microscopic stain was found ineffective for producing the desired contrast in the cotton fiber.

The formation of surface films at the transition between mild and severe metallic wear : J. K. Lancaster, Proc. Roy. Soc., A 273 (1963) 466–483; 14 figs., 9 refs.

An electrochemical approach for the preparation of Mg-Li-Ce alloys by co-reduction of Mg, Li and Ce on a molybdenum electrode in KCl-LiCl-MgCl2-CeCl3 melts at 873 K was investigated. Cyclic voltammograms (CVs) and square wave voltammograms indicated that the underpotential deposition (UPD) of cerium on pre-deposited magnesium led to the formation of Mg-Ce alloys at electrode potentials around −1.87 V. The order of electrode reactions was as follows: discharge of Mg(II) to Mg-metal, UPD of Ce on the surface of pre-deposited Mg with formation of Mg-Ce alloys, discharge of Ce(III) to Ce-metal and after that the discharge of Li+ with the deposition of Mg-Li-Ce alloys, which was investigated by CVs, chronoamperometry, chronopotentiometry and open circuit chronopotentiometry. X-ray diffraction (XRD) illuminated that Mg-Li-Ce alloys with different phases were obtained via galvanostatic electrolysis by different current densities. The microstructures of Mg-Li-Ce alloys were characterized by optical microscopy (OM) and scanning electron microscopy (SEM), respectively. The analysis of energy dispersive spectrometry (EDS) showed that Ce existed at grain boundaries to restrain the grain growth. The compositions and the average grain sizes of Mg-Li-Ce alloys could be obtained controllably corresponding with the phase structures of the XRD patterns.