Thermal expansion behavior, microhardness and electrochemical corrosion resistance properties of Au_(52)Cu_(27)Ag_(17-x)(NiZn_(0.5))_x alloys

The thermal expansion behavior, microhardness and electrochemical corrosion resistance of Au52Cu27Ag17-x（NiZn0.5）x （x=0,6 and 12） alloys were investigated by dilatometer （DIL）, microhardness tester, electrochemical workstation, X-ray diffractometer（XRD）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM） and X-ray photoelectron spectroscopy （XPS）.With increasing x, the relative length expansion and DIL maximum temperature Tl m （i.e., thermal stability） of the alloys increase inthermal expansion measurements, which can be explained by the change of the atomic binding energy, mismatch entropy togetherwith phase transformation. With the increase of x, the microhardness can be improved, but the corrosion resistance decreases; inaddition, the anodic peak current densities of polarization curves decrease, which are related closely with the solid solution degreeand dissolution of Ag, Ni and Zn alloying elements in Cl^- -containing solution.

Nickel release rate of 18KW gold alloy for ornaments

Nickel is widely used as a bleaching element in white gold alloys, but it is a potential allergen. In this paper, a popular 18 KW gold alloy, often called ＂safe nickel,＂ was chosen as the experimental material; its nickel release rates under six different processing conditions were evaluated according to the EN1811 standard. The results reveal that both the surface processing method and heat treatment technology significantly affect the nickel release rate. A coarse surface releases more nickel ions than a smooth surface. The sample normalized at 700 ~C in the single region has a lower nickel release rate than the one treated at 550 ~C in the two-phase phase region, while high temperature normalizing at 800 ~C will accelerate it. All the measured nickel release rates of the experimental material under various processing conditions exceed the permitted threshold value in the Nickel Directive, which indicates that there exists the potential risk of nickel- induced allergy when it is used to make jewelries, espe- cially for piercing types.

Studies on Determination of Ge in Au Alloys by Potassium Iodate Potentiometric Titration Method

The paper presents a new method of determining Ge in gold alloys by potassium iodate potentiometric titration rather than by traditional distillation separation. The influences of conditions such as the reduction acidity, dosage of sodium hypophosphite and reduction time on the determination of Ge were studied. Comparison was made between the influences of end-point indication for potential method and starch method on accruracy and precision of the analysed results, stability and sensitivity of end-point, selectivity of method and so on. The possibility of reaction in an electrochemical way was discussed. Ge in the alloys such as AuGe 12 , AuGeNi 12 2 , AuAgGe 18.8 12.5 and AuAgGeNi 43.8 6 0.2 was measured, respectively, with the relative standard deviation of 0.10%~0.31% and the recoveries of added standard Ge in sample of 99.40%～100.40% when the reduction acidity was 0.40~0.80 mol/L HCl and 3.3 mol/L H 3 PO 4, 15 g sodium hypophosphite and reduction time 40 min. The new method presented is high accuracy and precision in results, good stability and sensibility in end point, easy operation and strong selectivity of determination. When it is applied to analyse actual samples, satisfactory results are achieved.

Amplified Detection of Iron Ion Based on Plasmon Enhanced Fluorescence and Subsequently Fluorescence Quenching

A facile and rapid approach for detecting low concentration of iron ion(Fe3+) with improved sensitivity was developed on the basis of plasmon enhanced fluorescence and subsequently amplified fluorescence quenching.Au1Ag4@Si O2 nanoparticles were synthesized and dispersed into fluorescein isothiocyanate(FITC) solution. The fluorescence of the FITC solution was improved due to plasmon enhanced fluorescence. However, efficient fluorescence quenching of the FITC/Au1Ag4@Si O2 solution was subsequently achieved when Fe3+, with a concentration ranging from17 n M to 3.4 l M, was added into the FITC/Au1Ag4@Si O2 solution, whereas almost no fluorescence quenching was observed for pure FITC solution under the same condition. FITC/Au1Ag4@Si O2 solution shows a better sensitivity for detecting low concentration of Fe3+compared to pure FITC solution. The quantized limit of detection toward Fe3+was improved from 4.6 l M for pure FITC solution to 20 n M for FITC/Au1Ag4@Si O2 solution.

New Asymmetric Model for Predicting Ternary Thermodynamic Properties

The prediction of the thermodynamic properties of ternary systems from the properties of their sub-binary systems is of great importance to phase diagram calculations. In the present study, a new asymmetric model which has more clear physical significance has been developed for evaluating the ternary thermodynamic properties from its three binary components. The model is considered to be rigorous in the case where the pseudobinary systems of fixed X2/X3 are regular are regular solution. The application of new model to the prediction of ternary enthalpies of mixing for Bi-Ga-Sn, Au-Ag-Sn and NaCl-KCl-CaCl2 systems shows that the calculated results by new model are closer to experimental data than those by Toop's model.

Phase Equilibria in System Pd-Au-Sn and Pd-Cu-Sn at 800℃ and 500℃

Alloys of Pd-Au-Sn and Pd-Cu-Sn systems were investigated using metallography,electron microprobe,X ray diffraction and DTA.Partial isothermal sections were plots at 800oС and 500oС.Ternary τ-phase having tetragonal structure has been established in each systems.The region of existence of phases in equilibrium with the solid solution based on palladium.

Electrochemical converting ethanol to hydrogen and acetic acid for large scale green hydrogen production

Electrochemical coupling hydrogen evolution with biomass reforming reaction(named electrochemical hydrogen and chemical cogeneration(EHCC)),which realizes green hydrogen production and chemical upgrading simultaneously,is a promising method to build a carbon-neutral society.Herein,we analyze the EHCC process by considering the market assessment.The ethanol to acetic acid and hydrogen approach is the most feasible for large-scale hydrogen production.We develop AuCu nanocatalysts,which can selectively oxidize ethanol to acetic acid(>97%)with high long-term activity.The isotopic and in-situ infrared experiments reveal that the promoted water dissociation step by alloying contributes to the enhanced activity of the partial oxidation reaction path.A flow-cell electrolyzer equipped with the AuCu anodic catalyst achieves the steady production of hydrogen and acetic acid simultaneously in both high selectivity(>90%),demonstrating the potential scalable application for green hydrogen production with low energy consumption and high profitability.

Concurrent catalytic removal of typical volatile organic compound mixtures over Au-Pd/α-MnO2 nanotubes

α-MnO2 nanotubes and their supported Au-Pd alloy nanocatalysts were prepared using hydrothermal and polyvinyl alcohol-protected reduction methods, respectively. Their catalytic activity for the oxidation of toluene/m-xylene, acetone/ethyl acetate, acetone/m-xylene and ethyl acetate/m-xylene mixtures was evaluated. It was found that the interaction between Au-Pd alloy nanoparticles and α-MnO2 nanotubes significantly improved the reactivity of lattice oxygen, and the 0.91 wt.% Au0.48 Pd/α-MnO2 nanotube catalyst outperformed the α-MnO2 nanotube catalyst in the oxidation of toluene, m-xylene, ethyl acetate and acetone. Over the0.91 wt.% Au0.48 Pd/α-MnO2 nanotube catalyst,（i） toluene oxidation was greatly inhibited in the toluene/m-xylene mixture, while m-xylene oxidation was not influenced;（ii） acetone and ethyl acetate oxidation suffered a minor impact in the acetone/ethyl acetate mixture; and（iii） m-xylene oxidation was enhanced whereas the oxidation of the oxygenated VOCs（volatile organic compounds） was suppressed in the acetone/m-xylene or ethyl acetate/m-xylene mixtures. The competitive adsorption of these typical VOCs on the catalyst surface induced an inhibitive effect on their oxidation, and increasing the temperature favored the oxidation of the VOCs. The mixed VOCs could be completely oxidized into CO2 and H2 O below 320°C at a space velocity of 40,000 m L/（g·hr）. The 0.91 wt.% Au0.48 Pd/α-MnO2 nanotube catalyst exhibited high catalytic stability as well as good tolerance to water vapor and CO2 in the oxidation of the VOC mixtures. Thus, the α-MnO2 nanotube-supported noble metal alloy catalysts hold promise for the efficient elimination of VOC mixtures.

Au-Pd/mesoporous Fe_2O_3:Highly active photocatalysts for the visible-light-driven degradation of acetone

Three-dimensionally ordered mesoporous Fe2O3（meso-Fe2O3） and its supported Au, Pd,and Au-Pd alloy（xA uP dy/meso-Fe2O3; x = 0.08–0.72 wt.%; Pd/Au molar ratio（y） = 1.48–1.85）photocatalysts have been prepared via the KIT-6-templating and polyvinyl alcohol-protected reduction routes, respectively. Physical properties of the samples were characterized, and their photocatalytic activities were evaluated for the photocatalytic oxidation of acetone in the presence of a small amount of H2O2 under visible-light illumination. It was found that the meso-Fe2O3 was rhombohedral in crystal structure. The as-obtained samples displayed a high surface area of 111.0–140.8 m^2/g and a bandgap energy of 1.98–2.12 eV. The Au, Pd and/or Au–Pd alloy nanoparticles（NPs） with a size of 3–4 nm were uniformly dispersed on the surface of the meso-Fe2O3 support. The 0.72 wt.% AuP d1.48/meso-Fe2O3 sample performed the best in the presence of 0.06 mol/L H2O2 aqueous solution, showing a 100% acetone conversion within4 hr of visible-light illumination. It was concluded that the good performance of 0.72 wt.%AuPd（1.48）/meso-Fe2O3 for photocatalytic acetone oxidation was associated with its ordered mesoporous structure, high adsorbed oxygen species concentration, plasmonic resonance effect between AuPd（1.48） NPs and meso-Fe2O3, and effective separation of the photogenerated charge carriers. In addition, the introduction of H2O2 and the involvement of the photo-Fenton process also played important roles in enhancing the photocatalytic activity of 0.72 wt.%AuPd（1.48）/meso-Fe2O3.