Theoretical Analysis on Tensile Strength of ZA22/Al2O3 Short Fiber Composite Added with Ce

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氧化铈粒度控制研究

以碳化铈为前驱体,通过对沉淀条件的控制及填加剂的使用,控制碳酸盐的粒度,在850℃条件下灼烧后一次性得到D 50=4～7μm理想粒度的氧化铈,并可实现连续的工业化生产.     

Lattice contraction of cerium hydrides from first-principles LDA + U calculations

Ce can be loaded with H forming complicated continuous solid solution and compounds, and causing remarkable electronic-structure changes. First-principles pseudopotential plane wave method with adding a Hubbard parameter U for considering the strong Coulomb correlation between localized 4f electron is employed to investigate the electronic and structural properties of stoichiometric and nonstoichiometric face-centered cubic (fcc) Ce hydrides (CeH_x, x = 2, 2.25, 2.5, 2.75 and 3, respectively.). The most remarkable result is the decreasing trend of the calculated lattice parameters with increasing H composition, which is resulted from the associated effects of the enhanced chemical bonding owing to the participation of Ce 5d electron and, the size effects owing to the small H atomic radius and the large volume of octahedral interstice thus in favor of reducing the atomic distance for the formation of chemical bonding between Ce and octahedral H atoms.     

Optical properties of translucent CaGa2S4:Ce films prepared by pulsed laser deposition

Translucent CaGa₂S₄:Ce thin films were prepared by pulsed laser deposition. Optical absorption associated with the 4f₁ (²F_5/2) to 5d₂ second-highest excited state transition of the Ce³⁺ ion was clearly observed at 3.60 eV as well as the 4f₁ (²F_5/2) to 5d₁ lowest excited state transition at 2.93 eV. Energy splitting of the 5d state by the crystal field is discussed in terms of a model of a square antiprism structure with D_4d symmetry.     

Heteroepitaxy of Ir films on silicon with a ceria/yttria stabilized zirconia buffer layer

Heteroepitaxial Ir films on Si(001) with a double ceria/yttria stabilized zirconia heteroepitaxial buffer layer were grown by magnetron sputtering. As-deposited CeO₂ films covered with {111} faceted pyramids resulted in iridium films with the [001] axis normal to the substrate plane. The buffered substrates annealed at 1115 °C have a smooth surface; Ir films on such substrates have the (111) orientation and consist of grains turned at 90° toward each other.     

Formation of subsurface crevices in aluminum alloy 2024-T3 during deposition of cerium-based conversion coatings

The processing variables that contributed to the formation of subsurface crevices under cerium-based conversion coatings on AA 2024-T3 were investigated. Focused ion beam milling revealed the presence of subsurface crevices underneath a small fraction (∼ 10%) of coated areas, typically in areas with large cracks through the coatings. A solution of sodium chloride and H₂O₂ etched AA 2024-T3 and produced features similar to subsurface crevices, which confirmed that crevices formed during deposition due to the composition of the coating solution. Using sodium nitrate in place of sodium chloride resulted in no etching of the substrate. Thus, coatings free of subsurface crevices could be produced by using cerium nitrate instead of cerium chloride in the coating solution. Electrodeposited coatings, even those deposited from solutions containing chloride ions and H₂O₂, were also free of subsurface crevices. As a result, subsurface crevices are not inherent to cerium-based conversion coatings, but rather were formed due to certain process parameters, specifically the presence of chloride ions and hydrogen peroxide in the coating solution.     

Cerium insertion in 316L passive film: Effect on conductivity and corrosion resistance performances of metallic bipolar plates for PEM fuel cell application

A surface treatment to modify passive film properties formed on 316L stainless steel has been designed for bipolar plate application in PEMFC systems. This one is based on cerium insertion from electrochemical technique. The effect of this element addition on the composition of the passive films was evaluated by X-ray photoelectron spectroscopy (XPS) and low energy ion spectroscopy (LEIS). Potentiodynamic and potentiostatic curves, and electrochemical impedance spectroscopy (EIS) were used for the characterisation of the corrosion protection in simulated PEMFC media. Interfacial contact resistance (ICR) was also evaluated. Results highlight an increase of the polarisation resistance of the cerium treated sample at ambient temperature, and a good corrosion resistance in anodic and cathodic simulated media. An important diminution of the IRC is obtained (80% with respect to the reference), which is attributed to the enhancement of the passive layer conductivity of the processed sample. Surface analyses show a great enrichment of cerium in first atomic layers of the films, which explains the better conductivity observed by an increase of charge carrier density in the passive film.     

Evolution of Al2O3 inclusions by cerium treatment in low carbon high manganese steel

The influence of cerium (Ce) treatment on the morphologies, size and distributions of Al2O3 inclu-sions in low carbon high manganese steel was investigated by OM, SEM-EDS and theoretical calcula-tion.The results showed that Ce can modify the morphologies and types of Al2O3 inclusions.After Ce treatment, the irregular Al2O3 inclusions were replaced by smaller and dispersive spherical cerium oxysulfides.The effects of treatment time and Ce content on the evolution of Al2O3 inclusions were examined.It indicated that Al2O3 inclusions were wrapped by rare earth inclusions to form a ring like shape Ce-enriched band around the inclusions.Model was established to elucidate the evolution mech-anism of Al2O3 inclusions.Evolution kinetics of inclusions was discussed qualitatively to analyze the velocity controlled step.It was found that diffusion of Ce3 + and Al3 + in solid inclusion core and the formed intermediate layer would be the limited step during the evolution process.     

Comparative study of activity of cerium oxide at thermal reduction temperatures of 1300–1550 °C for solar thermochemical two-step water-splitting cycle

Thermochemical two-step water-splitting using CeO₂ (cerium oxide) particles was studied to examine oxygen and hydrogen productivity and repeatability at thermal reduction (T-R) temperatures of 1300–1550 °C and water decomposition (W-D) temperatures of 400–1000 °C for the production of hydrogen from water using concentrated solar radiation as the energy source. The temperature dependency of oxygen and hydrogen productivity and the cyclic repeatability of CeO₂ are reported in this paper. The characteristic features of CeO₂ particles in the thermochemical two-step water-splitting cycle are compared with the well-known highly active reactive mediums of zirconia-supported Ni-ferrites (NiFe₂O₄/m-ZrO₂ and NiFe₂O₄/c-YSZ) and unsupported NiFe₂O₄.     

Effect of chilling and cerium addition on microstructure and cooling curve parameters of Al–14%Si alloy

Abstract

Al–14%Si alloys, with and without cerium, were cast at varying cooling rates by solidifying them in a crucible and against chills. The effect of melt treatment and chilling on microstructure and cooling curve parameters of the alloy was assessed. Ce treated alloys solidified in clay graphite crucible at a slow cooling rate showed refinement of primary silicon and the formation of Al–Si–Ce ternary intermetallic compound. The addition of Ce to the alloy solidified against chills resulted in simultaneous refinement and modification of primary and eutectic silicon. Nucleation temperatures of both primary and eutectic silicon decreased on addition of cerium. The formation of the intermetallic compound decreased with increase in cooling rate, leading to the modification of the eutectic silicon. The increase in the degree of modification of the eutectic Si was associated with the decrease in the volume fraction of the intermetallic compound formed.