Clustering kinetics in aluminium-silver alloys

Resistometric studies of isochronal and isothermal annealing of an Al-0.64 at.% Ag alloy have given a value of 0.13 ± 0.02 eV for the silver-vacancy binding energy and 0.55 ± 0.03 eV for the migration energy of solute atoms.

Electrochemical studies of copper-aluminum-silver alloys in 0.5 M H2SO4

The electrochemical behavior in 0.5 M H2SO4 at 25 degreesC of a Cu-Al(9.3 wt%)-Ag(4.7 wt%) alloy submitted to different heat treatments and an annealed Cu- Al(9.7 wt%)-Ag(34.2 wt%) were studied by means of open circuit potential (E-mix) measurements, potentiodynamic polarizations and cyclic voltammetry. SEM and EDX microanalysis were used to examine the changes caused by the electrochemical perturbations. The steady state potentials observed for the studied samples were correlated in terms of the phases present in the alloys surface. The resulting E/I potentiodynamic profiles were explained in terms of the potentiodynamic behavior of pure copper and pure silver. The presence of aluminum decreased the extent of copper oxidation. In the apparent Tafel potential region, two anodic Tafel slopes were obtained: 40 mV dec(-1) in the low potential region and 130 mV dec(-1) in the high potential region, which were related with the electrochemical processes involving copper oxidation. (C) 2001 Elsevier B.V. Ltd. All rights reserved.

Electrochemical studies of copper, copper-aluminium and copper-aluminium-silver alloys: Impedance results in 0.5M NaCl

The electrochemical behaviour of Cu, Cu-Al and Cu-Al-Ag alloys in aqueous solutions of NaCl (0.5 M, pH = 3.00) was studied by means of voltammetric methods and electrochemical impedance spectroscopy. The surfaces were examined by SEM and EDX analysis. Cu-Al-Ag alloy shows a potentiodynamic behaviour similar to that of the pure copper electrode while the Cu-Al alloy presents some minor differences. In the active dissolution region the electrodes suffer pitting corrosion and in the other potential regions there are the formation of a passivant film with composition depending on the potential. The impedance responses of the electrodes are discussed. An electrodissolution mechanism is proposed and the effect of the alloying elements upon the impedance response and polarisation curves is explained. The main effects are due to the production of copper and silver chlorides and aluminium oxides/ hydroxides at the corroding interface. The addition of Al or (Al + Ag) increases the corrosion resistance of pure copper. © 1995.

Surface enrichment in gold/silver alloys: effects of temperature studied by atom probe tomography

Bimetallic alloys are increasingly used in heterogeneous catalysis. This interest is explained by the emergence of new features that are absent in the parent single metals. Synergistic effects between the two combined elements create a more efficient catalyst. One of the most challenging aspect of multicomponent materials in catalysis is the ability to fine-tune the catalytic properties of an alloy by controlling the nature and composition of the surface [1]. For example, the gold/silver alloy combines a high activity and a large selectivity for a broad range of oxidation reaction.It is well established that the surface composition of alloys may deviate from that of the bulk phase. Surface enrichment has also important consequences in some applications of heterogeneous catalysis. In some cases, the thermal and chemical treatments can lead to opposite trends regarding the nature of the metal prone to surface enrichment. Using atom probe tomography we aim to link the physicochemical conditions the composition of the very first atomic layers of bimetallic catalysts and eventually to fine-tune the catalytic features of the latter.

Age Hardening of Silver-Platinum Alloys

The alloy system selected for study was the binary alloy of platinum and silver. An examination of the various silver alloy diagrams revealed that of several possible alloys, the silver platinum was the most suit­able with regard to solubility.

Martensite aging kinetics in the Cu-10 wt.%Al and Cu-10 wt.%Al-10 wt.%Ag alloys

The martensite aging kinetics in the Cu-10 wt.%Al and Cu-10 wt.%Al-10 wt.%Ag alloys was studied using microhardness measurements, classical differential thermal analysis (DTA), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and in-situ high-temperature X-ray diffractometry (XRD). The results for the Cu-10%Al alloy indicated a process dominated by the martensite ordering assisted by migration of quenched-in vacancies and followed by the consumption of the α phase. For the Cu-10%Al-10%Ag alloy the dominant process is the consumption of the α phase associated with a decrease in the ordering degree of the martensitic phase. © 2007 Springer Science+Business Media, LLC.

Use of conventional electrochemical techniques to produce crystalline FeRh alloys induced by Ag seed layer

By combining galvanic displacement and electrodeposition techniques, an ordered Fe20Rh80 structure deposited onto brass was investigated by X-ray diffractometry, Mössbauer spectroscopy and magnetization measurements. Mössbauer and X-ray diffraction analyses suggest that the Fe-Rh alloy directly electrodeposited onto brass displays a nanocrystalline state while a similar alloy deposited onto Ag/brass shows a faced centered cubic-like structure, with dendrites-like features. These results directly indicate that the presence of Ag seed layer is responsible for the Fe-Rh alloy crystallization process. In addition, room temperature Mössbauer data indicate firstly paramagnetic states for two Fe-species. In the dominant Fe-species (major fraction of the Mössbauer spectra), Fe atoms are situated at a cubic environment and it can be attributed to the γ-Fe20Rh80 alloy based on their hyperfine parameters. In the second species, Fe atoms are placed in a non-local symmetry, which can be related to Fe atoms at the grain boundaries or/and Fe small clusters. These Fe-clusters are in superparamagnetic state at room temperature, but they may be ordered below 45 K, as suggested by magnetization data. © 2013 Elsevier B.V. All rights reserved.

Kinetics of martensitic phase decomposition in the Cu-10wt.%Al alloy with Ag additions

The study of the kinetics of martensitic phase decomposition in the Cu-10wt.%Al alloy with Ag additions showed that the presence of Ag retarded the eutectoid decomposition reaction and enhanced martensite stabilization. This stabilization effect was attributed to Ag atoms redistribution as structure defects, increase in the numbers of Cu-Al pairs due to Ag-Al interaction and the Al atoms redistribution around one Cu atom at the sub-lattice of the martensitic crystal. © 2008 Trans Tech Publications.

Effect of Ag addition on phase transitions of the Cu-22.26 at.%Al-9.93 at.%Mn alloy

The phase transitions that occur in the Cu-22.26 at.%Al-9.93 at.%Mn and Cu-22.49 at.%Al-10.01 at.%Mn-1.53 at.%Ag alloys after slow cooling were studied using differential scanning calorimetry at different heating rates, microhardness changes with temperature, magnetization changes with temperature, scanning electron microscopy and energy dispersion X-ray spectroscopy. The results indicated that the presence of Ag does not modify the transition sequence of Cu-Al-Mn alloy, introduces a new transition due to the (Ag-Cu)-rich precipitates dissolution at about 800 K, and changes the mechanism of DO 3 phase dissolution. This mechanistic change was analyzed and a sequence of phase transitions was proposed for the reaction. © 2013 Elsevier B.V.

Caratterizzazione di membrane inorganiche per la separazione di idrogeno da gas di reforming

The work of this thesis has been focused on the characterisation of inorganic membranes for the hydrogen purification from steam reforming gas. Composite membranes based on porous inorganic supports coated with palladium silver alloys and ceramic membranes have been analysed. A brief resume of theoretical laws governing transport of gases through dense and porous inorganic membranes and an overview on different methods to prepare inorganic membranes has been also reported. A description of the experimental apparatus used for the characterisation of gas permeability properties has been reported. The device used permits to evaluate transport properties in a wide range of temperatures (till 500°C) and pressures (till 15 bar). Data obtained from experimental campaigns reveal a good agreement with Sievert law for hydrogen transport through dense palladium based membranes while different transport mechanisms, such as Knudsen diffusion and Hagen-Poiseuille flow, have been observed for porous membranes and for palladium silver alloy ones with pinholes in the metal layer. Mixtures permeation experiments reveal also concentration polarisation phenomena and hydrogen permeability reduction due to carbon monoxide adsorption on metal surface.

Desenvolvimento de eletrocatalisadores de PdM (M= Ni, Cu, Ag) para reação de redução de oxigênio em meio básico na ausência e presença de álcool

Tese (Doutorado em Tecnologia Nuclear)

Processing maps for hot working of Cu-Ni-Zn alloys. Part I - Alpha-nickel silver

The constitutive behaviour of agr — nickel silver in the temperature range 700–950 °C and strain rate range 0.001–100 s–1 was characterized with the help of a processing map generated on the basis of the principles of the ldquodynamic materials modelrdquo of Prasadet al Using the flow stress data, processing maps showing the variation of the efficiency of power dissipation (given by 2m/(m+1) wherem is the strain-rate sensitivity) with temperature and strain rate were obtained, agr-nickel silver exhibits a single domain at temperatures greater than 750 °C and at strain rates lower than 1s–1, with a maximum efficiency of 38% occurring at about 950 °C and at a strain rate of 0.1 s–1. In the domain the material undergoes dynamic recrystallization (DRX). On the basis of a model, it is shown that the DRX is controlled by the rate of interface formation (nucleation) which depends on the diffusion-controlled process of thermal recovery by climb. At high strain rates (10 and 100s–1) the material undergoes microstructural instabilities, the manifestations of which are in the form of adiabatic shear bands and strain markings.

Processing maps for hot working of Cu-Ni-Zn alloys Part II Alpha-Beta nickel silver

The constitutive behaviour of agr-beta nickel silver in the temperature range 600�850 °C and strainrate range 0.001�100s�1 was characterized with the help of a processing map generated on the principles of the dynamic materials model. On the basis of the flow-stress data, processing maps showing the variation of the efficiency of power dissipation (given by [2m/(m+1)], wherem is the strain-rate sensitivity) with temperature and strain rate were obtained, agr-beta nickel silver exhibits a single domain at temperatures greater than 700 °C and at strain rates lower than 1 s�1 with a maximum efficiency of power dissipation of about 42% occurring at about 850 °C and at 0.1 s�1. In the domain, the agr phase undergoes dynamic recrystallization and controls the deformation of the alloy, while the beta phase deforms superplastically. Optimum conditions for the processing of agr-beta nickel silver are 850 °C and 0.1 s�1. The material undergoes unstable flow at strain rates of 10 and 100 s�1 and in the temperature range 600�750 °C, manifestated in the form of adiabatic shear bands.