Fraction Of Ce Research Articles

Pinning of Austenite Grain Boundary of Fe-0.09 to 0.53mass% C-0.02mass%P Alloys by Primary Inclusions of Ce2O3 and CeS.

The effect of the deoxidation and desulfurization products of Ce 2 O 3 (the mean planar diameter, đ A =1.6 to 2.1 μm) and CeS (đ A =2.2 to 2.8 μm) particles on the austenite grain growth was studied in Fe-0.20 (0.09 and 0.53) mass%C-0.02 mass%P alloys. The melts at 1 873 K were continuously cooled to 1 673, 1 573 and 1 473 K and then were held for 0 to 180 min in the austenite single phase region. Grain growth in the presence of particles was strongly inhibited by the pinning effect and the mean grain size was independent of the carbon content for a given holding time, holding temperature, and volume fraction of Ce 2 O 3 particles (f V =0.08 to 0.12%). The planar limiting grain diameter, D A , obtained at holding times of more than 60min, was found to be significantly smaller than that predicted from the Zener relation, and the deviation from this relation increased with increasing the đ A /f V value. The fraction of particles at the grain boundaries, Φ A =0.07 to 0.23, was about 20 to 60 times higher than that estimated from the random distribution from the Zener limit. Based on these values for Φ A , the limiting grain size was discussed as a function of f V value, and the present results for Ce 2 O 3 and CeS particles were compared with those obtained for the MgO and ZrO 2 particles in Fe-0.20 mass%C-0.02 mass%P and Fe-10 mass%Ni alloys.

Lanthanide ions for the hydrolysis of 5′-mononucleotides and 3′-mononucleotides

Cleavage of adenosine-5′-monophosphate (5′-AMP), guanosine-5′-monophosphate (5′-GMP), adenosine-3′-monophosphate (3′-AMP) and guanosine-3′-monophosphate (3′-GMP) by lanthanides was investigated by NMR and the method of measuring the liberated phosphates. Rapid cleavage of both 5′-mononucleotides and 3′-mononucleotides by Ce III and Ce IV under air at pH 9 and 37°C was observed. Other lanthanides showed less efficiency for hydrolyzing 5′-mononucleotides but 3′-mononucleotides were catalyzed by a range of lanthanide ions. The mechanism for hydrolyzing 3′-mononucleotides by lanthanides was investigated. The notable difference in reactivity between Ce III and the other lanthanide ions under air was further studied showing that the cleavage is enhanced with increasing molar fraction of Ce IV. The fast cleavage of mononucleotides by Ce III under air at pH 9 is ascribed to the resultant Ce IV in the reaction mixture.

A Study of the Structure and the Morphology of Oxide Films on Amorphous Al‐Fe‐Ce Alloys by XPS and SEM

Aluminum‐based metallic glasses are of technological importance due to their high strength, low density, and anticipated high resistance to corrosion. We report on the corrosion characteristics of melt‐spun ribbons of . The amorphous alloys showed excellent corrosion properties in aqueous . We have also examined the composition, structure, and morphology of the native and passive oxide films using scanning electron microscopy (SEM), x‐ray photoelectron spectroscopy (XPS), and angle‐resolved XPS. We show that the composition of the native oxide film is that of . The thickness of the native oxide is estimated from angle‐resolved XPS data to be about 1.6 to 3.1 nm (i.e., nanometer). Passive films were formed in 0.9 weight percent (0.15M) solution by potentiostating below the pitting potential for 30 and 60 min. The passive oxide films contain oxidized Al, Fe, and Ce. The chemistry of Al in the passive oxide films is also that of . Iron appears to be present in the passive film as and and/or with varying mole fractions depending on alloy composition. Cerium in the passive film appears to be present in the +3 oxidation state as or . A small fraction of Ce in the passive film of is present in the +4 oxidation states as .

Redox properties of cerium‐exchanged Y‐zeolites

AbstractThe oxidation of cerium(III)‐exchanged zeolite NaY (exchange level 24‐91%) with aqueous hydrogen peroxide and oxygen has been studied. The fraction of Ce(IV) produced decreases with increasing Ce content of the zeolites. Hydrogen peroxide is catalytically decomposed by the Ce(III)/Ce(IV) redox couple with formation of an equilibrium level of a Ce(IV) hydroxide species. Oxidation with oxygen at temperatures higher than 400 K yields an oxycerium(IV) complex. The latter NaCe(IV)Y zeolite effects oxidative glycol cleavage of 2,3‐dimethyl‐2,3‐butanediol to acetone. Activation in oxygen restored its oxidizing capacity. Thus, the oxygen‐activated NaCe(IV)Y zeolite is a regenerable glycol‐cleaving oxidant. The H2O2‐oxidized NaCe(IV)Y is not active in glycol‐cleavage oxidiation.