Rare Earth Application in Sealing Anodized Al-Based Metal Matrix Composites

A new method for corrosion protection of Al-based metal matrix composites (MMC) was developed using two-step process, which involves anodizing in H2SO4 solution and sealing in rare earth solution. Corrosion resistance of the treated surface was evaluated with polarization curves. The results showed that the effect of the protection using rare earth sealing is equivalent to that using chromate sealing for Al6061/SiCp. The rare earth metal salt can be an alternative to the toxic chromate for sealing anodized Al MMC.

Catalytic Synthesis of Tert-Butyl Acetate by Nd_2O_3/Al_2O_3-Nd_2O_3/ZnO

Nd2O3 was used to support Al2O3 and ZnO to prepare a supported solid base catalyst and investigate the effect of catalyst and reaction conditions on the synthesis of tert-butyl acetate. The composited oxide of Nd2O3/Al2O3-Nd2O3/ZnO exhibited excellent catalytic activity for the synthsis of tert-butyl acetate. The molar ratio of tert-butanol to acetic anhydride is 3∶1, the catalyst in total amount of reactant nearly 0.5%, and reaction time 6 h. With the above conditions, yield of the reaction could reach to 65%. The structure of product were verified by the FT-IR, Element analysis, and MS, which proved that the product was tert-butyl acetate.

Surface composition change of chlorine-doped catalyst Ni(Clx)/CeO2 in methanation reaction

The oxide sample NiO/CeO_2 with feed atomic ratio of Ni/Ce at 40%, prepared by co-precipitation method and calcination at 500 oC for 2 h, was impregnated by aqueous solution of NH_4Cl to dope chlorine ions. After the impregnated samples were dried and calcined at 400 oC for 2 h, the calcined samples NiO（Cl_x）/CeO_2（x=0.1–0.5） were characterized by means of X-ray diffraction（XRD） and temperature programmed reduction（TPR） techniques. It was comfirmed that the doped chlorine ions hindered reduction of Ni^（2＋） ions in the calcined samples, and suppressed adsorption of CO_2 and CO on the reduced sample Ni（Cl_（0.3））/CeO_2. The reduced samples Ni（Cl_x）/CeO_2（x=0.0–0.5） were used as catalysts for selective methanation of CO in H_2-rich gas. When chlorine ions were doped at the feed atomic ratio of Cl/Ce（x） equal to 0.3–0.5, CO in the H_2-rich gas could be removed to below 10 ppm with a high selectivity more than 50% in a wide reaction temperature range of 220–280 oC. However, the selectivity of CO methanation decreased with reaction time in the durability tests over the catalyst Ni（Cl_（0.3））/CeO_2 at the reaction temperature of 260 oC and even at 220 oC. The lowering of the selectivity was found to be related with the surface composition change of the catalyst in the catalytic reaction.

Effect of La_2O_3 on electrical friction and wear properties of Cu-graphite composites

Sliding friction and wear experiments using Cu-La2O3-graphite composites against Cu-5 wt.%Ag alloy ring were conducted at a constant sliding speed of 10 m/s, a current density of 10 A/cm2 and a load of 2.5 N/cm2. These composites with different La2O3 and graphite contents were fabricated by hot-pressing. Physical and mechanical properties of the composites were examined. Morphologies of the worn surface of composites were observed using optical microscopy. X-ray photoelectron spectroscopy spectra were used to study compositions of the lubricating film. The results showed that with the increasing addition of La2O3, hardness, flexural strength and electrical resistivity increased, but the relative density dropped. The friction coefficient increased with the increasing addition of La2O3. Composite containing 3 vol.% of La2O3 and 37 vol.% of graphite showed the best wear resistance. The main wear mechanisms of composites were abrasive wear, oxidative wear and adhesive wear.

Effect of LaFeO_3 on hydrogenation/dehydrogenation properties of MgH_2

LaFeO3 was used to improve the hydrogen storage properties of Mg H2. The Mg H2＋20 wt.%La Fe O3 composite was prepared by ball milling method. The composite could absorb 3.417 wt.% of hydrogen within 21 min at 423 K while Mg H2 only uptaked 0.977 wt.% hydrogen under the same conditions. The composite also released 3.894 wt.% of hydrogen at 623 K, which was almost twice more than Mg H2. The TPD measurement showed that the onset dissociation temperature of the composite was 570 K, 80 K lower than the Mg H2. Based on the Kissinger plot analysis of the composite, the activation energy E des was estimated to be 86.69 k J/mol, which was 36 k J/mol lower than Mg H2. The XRD and SEM results demonstrated that highly dispersed La Fe O3 could be presented in Mg H2, benefiting the reduction of particle size and also acting as an inhibitor to keep the particles from clustering during the ball-milled process.

Preparation and characterization of LSO-SDC composite electrolytes

The properties of LSO-SDC composite electrolytes prepared by the mixed powder with different LSO/SDC mass ratios were studied. The apatite-type lanthanum silicates La10Si6O27（LSO） and Sm0.2Ce0.8O1.9（SDC） were synthesized via sol-gel process and glycine-nitrate process（GNP）, respectively. The phase structure, microstructure, relative density, thermal expansion properties and oxygen ion conductivity of the samples were investigated by means of techniques such as X-ray diffraction（XRD）, scanning electron microscopy（SEM）, Archimedes method, dilatometer, and AC impedance spectroscopy. The results showed that SDC addition to the samples could enhance the density of the samples. However, the LSO-SDC composite electrolyte sintered at 1550 oC was over sintering when the SDC content was 50 wt.%. At the lower content of SDC（0–10 wt.%）, the decrease of conductivity was predominantly attributed to the reducing concentration of carriers. However, the conductivities of the composite electrolytes increased with the increasing SDC content（10 wt.%–40 wt.%） because of the enhanced percolation of highly conductive SDC component in the microstructure of composite electrolytes. In addition,the dependence of conductivity on p（O2） showed that LSO-SDC composite electrolytes were stable in the examined range of p（O2）.