The PL "violet shift" of cerium dioxide on silicon

CeO2 thin film was fabricated by dual ion beam epitaxial technique. The phenomenon of PL violet shift at room temperature was observed, and the distance of shift was about 65 nm. After the analysis of crystal structure and valence in the compound were carried out by XRD and XPS technique, it was concluded that the PL shift was related with valence of cerium ion in the oxides. When the valence of cerium ion varied front tetravalence to trivalence, the PL peak position would move from blue region to violet region and the phenomenon of "violet shift" was observed.

CERIUM SILICIDE FORMATION IN THIN CE SI MULTILAYER FILMS

Alternating layers of Si(200 angstrom thick) and Ce(200 angstrom thick) up to 26 layers altogether were deposited by electron evaporation under ultrahigh vacuum conditions on Si(100) substrate held at 150-degrees-C. Isothermal, rapid thermal annealing has been used to react these Ce-Si multilayer films. A variety of analytical techniques has been used to study these multilayer films after annealing, and among these are Auger electron spectroscopy, Rutherford backscattering, X-ray diffraction, and high resolution transmission electron microscopy. Intermixing of these thin Ce-Si multilayer films has occurred at temperatures as low as 150-degrees-C for 2 h, when annealed. Increasing the annealing temperature from 150 to 400-degrees-C for 1 h, CeSi2 forms gradually and the completion of reaction occurs at approximately 300-400-degrees-C. During the formation of CeSi2 from 150-400-degrees-C, there is some evidence for small grains in the selected area diffraction patterns, indicating that CeSi2 crystallites were present in some regions. However, we have no conclusive evidence for the formation of epitaxial CeSi2 layers, only polycrystals were formed when reacted in the solid phase even after rapid thermal anneal at 900-degrees-C for 10 s. The formation mechanism has also been discussed in combining the results of the La-Si system.

Effects of cerium on the microstructure and mechanical properties of Mg–20Zn–8Al alloy

Mg-20Zn-8Al-xCe(x=0-2 wt.%) alloys were prepared by metal mould casting method, the effects of Ce on the microstructure and mechanical properties of the alloys were investigated. The results showed that the dendrite as well as gram size were refined by the addition of Ce, and the best refinement was obtained in 1.39% Ce containing alloy.

Phase stability and thermophysical properties of neodymium cerium composite oxide

Nd2CexO3+2x (x = 2.25, 2.5, 2.75, 3.0) were synthesized by solid-state reaction, and their phase stabilities and thermophysical properties were investigated. The X-ray diffraction (XRD) results indicated that Nd2CexO3+2x with fluorite structure were stable after long-term annealing at 1673 K. They have higher thermal expansion coefficients (TECs) than yttria-stabilized zirconia (YSZ) which is the typical thermal barrier coating (TBC) material, especially the thermal expansion as a function of temperature is parallel to that of the nickel-based superalloy.

Synergistic extraction and recovery of Cerium(IV) and Fluorin from sulfuric solutions with Cyanex 923 and di-2-ethylhexyl phosphoric acid

Synergistic extraction and recovery of Cerium(IV) (Ce(IV)) and Fluorin (F) from sulfuric solutions using mixture of Cyanex 923 and di-2-ethylhexyl phosphoric acid (D2EHPA) in n-heptane have been carried out. in order to investigate the synergistic extraction of Cyanex 923 + D2EHPA, extraction Ce(IV), F, Ce(III) and Ce-F mixture solution using D2EHPA or Cyanex 923 as extractant alone were studied firstly, and then Synergistic extraction of Ce(IV), F and Ce(IV)-F mixture solution with D2EHPA + Cyanex 923 were carried out. The largest synergistic coefficient of Ce(IV) is obtained at the mole fraction X-Cyanex (923) = 0.8. The synergistic enhancement coefficients (R-max) obtained for Ce(IV) are 23.12 in Ce(IV) solution, and in Ce-F mixed solution R-max for Ce(IV) and F are 2.24 and 3.25 respectively.

The separation of Cerium(IV) from nitric acid solutions containing Thorium(IV) and Lanthanides(III) using pure [C(8)mim]PF6 as extracting phase

The extraction behavior of Ce(IV) along with Th(IV) and Ln(III) (Ln = Ce, Gd, Yb) nitrate by pure ionic liquid, [C(8)mim]PF6, was investigated. [C(8)mim]PF6 alone showed good extraction ability for Ce(IV), while it was slight for Th(IV) and negligible for Ln(III). The extraction behavior of Ce(IV) by [C(8)mim]PF6 was particularly studied, and the most probable extraction mechanism proposed was the anion exchange mechanism. Moreover, the stripping of Ce(IV) from IL phase was also investigated. The Ce(IV) in IL phase can be quantitatively recovered by water.

Thermal barrier coating of lanthanum-zirconium-cerium composite oxide made by electron beam-physical vapor deposition

Lanthanum-zirconium-cerium composite oxide (La-2(Zr0.7Ce0.3)(2)O-7, LZ7C3) as a candidate material for thermal barrier coatings (TBCs) was prepared by electron beam-physical vapor deposition (EB-PVD). The composition, crystal structure, thermophysical properties, surface and cross-sectional morphologies and cyclic oxidation behavior of the LZ7C3 coating were studied. The results indicated that LZ7C3 has a high phase stability between 298 K and 1573 K, and its linear thermal expansion coefficient (TEC) is similar to that of zirconia containing 8 wt% yttria (8YSZ). The thermal conductivity of LZ7C3 is 0.87 W m(-1) K-1 at 1273 K, which is almost 60% lower than that of 8YSZ. The deviation of coating composition from the ingot can be overcome by the addition of excess CeO2 and ZrO2 during ingot preparation or by adjusting the process parameters.

Extraction and recovery of cerium(IV) along with fluorine(I) from bastnasite leaching liquor by DEHEHP in [C(8)mim]PF6

BACKGROUND: Ionic liquids (ILs) as environmentally benign solvents have been widely studied in the application of solvent extraction. However, few applications have been successfully industrialized because of the difficult stripping of metal ions or the loss of components of the ILs. More work needs to be done to investigate the extraction behaviour of IL-based extraction systems. In this work, the extraction behaviour of Ce(IV), Th(IV) and some trivalent rare earth (RE) nitrates by di(2-ethylhexyl) 2-ethylhexylphosphonate (DEHEHP) in the IL, 1-methyl-3-octylimidazolium hexafluorophosphate ([C(8)mim]PF6), was investigated and compared with that in the n-heptane system. In particular, the effect of F(I) on the extraction mechanism for Ce(IV) and its separation from Th(IV) was investigated. Otherwise, the recovery efficiency of Ce(IV) and F(I) from a practical bastnasite leach liquor was examined using IL based extraction.