Influence of CO2-Ar Mixtures as Shielding Gas on Laser Welding of Al-Mg Alloys

In this study, AA5083 samples were butt welded under a conduction regime with high-power diode laser (HPDL). Various mixtures composed of Ar and CO2 were used as a shielding gas. The influence of the shielding gas composition on the microstructure and on the properties of laser welds was analyzed. The weld beads were deeply characterized by metallographic/micro- structural studies, X-ray diffraction (XRD), X-ray energy dispersive spectrometry (X-EDS) chemical analyses, X-ray photoelectron spectra (XPS), microhardness, and tensile strength. The corrosion resistance of laser-remelted surfaces with different CO2/Ar ratios was also estimated by means of electrochemical tests. The addition of CO2 to the shielding gas results in a better weld penetration and oxidizes the weld pool surface. This addition also promotes the migration of Mg toward the surface of weld beads and induces the formation of magnesium aluminates spinel on the welds. The best corrosion resistance result is achieved with 20 pct CO2. The overall results indicate that the addition of small percentage of CO2 to Ar leads to improvements of the mechanical and corrosion properties of the aluminum welds

Formation and characterization of nanotubes of La(OH)3 obtained using porous alumina membranes

An electrodeposition process is used to synthesize nanotubes of a lanthanum-containing phase, employing porous alumina membranes as templates. This method should lead to the formation of La(OH)3 nanowires, according to the previous results presented by Bocchetta et al (2007 Electrochem. Commun. 9 683–8), which can be decomposed to La2O3, as the latter shows more interest for different applications. The results obtained by means of different electron microscopy techniques indicate that this method leads to the formation of nanotubes of about 200 nm in diameter and 30–40 μm in length, instead of the nanowires proposed in the literature. Additionally, the chemical characterization demonstrates that the material synthesized is composed of lanthanum hydroxycarbonate. The presence of carbonates is found to be crucial in determining the conditions for the preparation of La2O3 from the nanotubes here obtaine

Can Ultrasound or pH Influence Pd Distribution on the Surface of HAP to Improve Its Catalytic Properties in the Dry Reforming of Methane?

The influence of ultrasound and different pH pre-treatments during the metal doping/modification of a hydroxyapatite (HAP) support is investigated. HAP is first synthesised via a hard-template synthetic route using carbon nanorods followed by their full physiochemical characterisation. The HAP was found to be crystalline and comprised a mesoporous structure as observed via XRD and nitrogen adsorption with a BET surface area of 97.57 (±1.16) m2 g−1. Ultrasound-assisted ion exchange (IE) and incipient wetness impregnation (IW) methodologies were employed to decorate the surface of HAP with Pd0 and are compared to previous procedures. The influence of pH upon the distribution of Pd0 throughout the samples during the doping process is also studied. All the prepared samples were evaluated for their catalytic activity towards dry reforming of methane (DRM) and the reaction was monitored via a thermal conductivity detector, coupled with gas chromatography (GC-TCD). It was found that ultrasound-assisted IE significantly accelerated the process from 3 days to 3 h and with the Pd0 metal remaining highly distributed upon the HAP with minor changes in catalytic conversions. Moreover, the ultrasound-assisted IW method successfully improved the Pd0 distribution and catalytic performance. On the other hand, the dispersion of the metal was unaffected after pH treatments in IE with no catalytic improvements observed, in contrast to IW, where considerable increase in metal distribution and subsequently catalytic performance was observed

Mechanical, pH and Thermal Stability of Mesoporous Hydroxyapatite

The stability of mesoporous hydroxyapatite (HAP) powder was studied following treatments of ultrasound, pH and heating. HAP was found to be mechanically stable up to (and including) 1 h continuous ultrasonic treatment in water. The HAP structure was also stable to pH, evidenced by practically identical XRD and FTIR spectra over the pH range 2–12. The surface area increased progressively with increasing acidity, reaching a maximum of 121.9 m 2 g −1 at pH 2, while alkaline conditions decreased the surface area to a minimum of 55.4 m 2 g −1 at pH 12. Heating in air had a significant influence on the structural and morphological properties of HAP, which underwent dehydroxylation to form oxyhydroxyapatite (OHAP) at temperatures ≥ 650 °C, and β-tricalcium phosphate (β-TCP) ≥750 °C. The surface area decreased at elevated temperatures due to agglomeration of HAP crystals by sintering, which was associated with an increased particle size

Numerical modeling and experimental investigation of heat transfer and fluid flow during laser welding of AA 5083 aluminium

Paper presented at the 7th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Turkey, 19-21 July, 2010.ksb201

Ceria-supported Au-CuO and Au-Co3O4 catalysts for CO oxidation: An O-18/O-16 isotopic exchange study

International audienceIn this work isotopic exchange of O-18(2) with O-16 and oxidation of (CO)-O-16 were investigated at 130 degrees C on ceria-supported Au-CuO and Au-Co3O4 catalysts. Oxygen storage capacity (OSC) was measured at 400 degrees C to check the influence of the metals in the catalysts, resulting in an enhancement of OSC for gold-containing catalysts compared to monometallic catalysts. The reactivity of surface oxygen atoms and the oxygen availability from the samples were studied by two isothermal experiments, both feeding (CO)-O-16 (anaerobic oxidation (CO)-O-16/Ar and aerobic oxidation (CO)-O-16/O-2) to the O-18 pre-exchanged samples. Exchange leads to (CO)-O-18 formation and oxidation leads to (CO2)-O-16, (COO)-O-16-O-18 and (CO2)-O-18 formation. In anaerobic conditions the predominant reaction at the beginning is the exchange: a rapid exchange of (CO)-O-16 with the surface can be observed for all the samples except for CoCe that inhibits the exchange and the CO oxidation. In aerobic conditions, the predominant reaction is CO oxidation with the rapid increase of (CO2)-O-16 due to the relatively high O-16 coverage in reaction as a result of the (CO)-O-16 exchange and from exchange between O-18 surface species and O-16 bulk atoms. At 130 degrees C, bare ceria shows null activity in both aerobic and anaerobic oxidation

Role of surface vanadium oxide coverage support on titania for the simultaneous removal of o-dichlorobenzene and NOx from waste incinerator flue gas

The catalytic activity of VOx species supported on TiO2 was investigated in the simultaneous destruction of NO and 1,2-dichlorobenzene (o-DCB), as typical pollutants molecules in the off-gases from municipal waste incinerator (MWI) plants. Catalysts with different vanadium loading were prepared in order to obtain different VOx species and characterized by ICP-AES, XPS, N2 adsorption at −196 °C, XRD, H2-TPR, Raman and UV–vis–NIR DRS spectroscopy. The characterization results show that molecularly dispersed isolated and polymeric vanadia species form below the dispersion limit loading (“monolayer coverage”), while crystalline species form above it. We used moderate HNO3 treatment to partially leach vanadium oxide species, creating a series of catalysts with variable vanadia loading. The catalytic activity of the VOx/TiO2 catalyst shows that it is able to catalyze the destruction of both pollutants, although higher temperature is required for o-DCB oxidation than for NO reduction. Surface vanadia coverage has a clear effect on TOF and activation energy values, which underline that isolated vanadia species are more efficient for o-DCB oxidation, while the polymeric ones are more efficient for NO reduction.This research was funded by Basque Government though the Grant to Consolidated Research Groups (GIC-07/67-JT-450-07) and the SAIOTEK program (S-PE11UN074), by University of the Basque Country UPV/EHU through the UFI (UFI 11/39) and the Grant for the acquisition and renovation of scientific infrastructure (INF12/37) and by the Spanish Ministry of Economy and Competitiveness (CTM2012-31576). One of the authors (MGV) acknowledges also the Basque Government for the PhD Research Grant (BFI-2011-238).Peer Reviewe