Silver Enrichment Research Articles

Alloying and surface composition of model Pd–Ag films synthesized by electroless deposition

PdAg model films and real composite membranes were prepared by sequential electroless deposition on top of porous stainless steel supports. Their surface properties were investigated by X-ray photoelectron spectroscopy (XPS), Angle resolved XPS and sputtering depth profile. It was shown that the surface of the alloy was strongly enriched in silver after the annealing treatment up to 500 °C on hydrogen stream. A relationship between the Ag 3d5/2 core-level binding energy shift and the silver surface composition was observed from the XPS data obtained with the model samples. The surface composition of real membranes after both hydrogen permeation and reaction experiments showed silver enrichment, in agreement with the data obtained from the model sample.

Microstructure development in Al-Cu-Ag-Mg quaternary alloy

The solidification behaviour of multi-component and multi-phase systems has been largely investigated in binary and ternary alloys. In the present study, a quaternary model system is proposed based on the well known Al-Cu-Ag and Al-Cu-Mg ternary eutectic alloys. The quaternary eutectic composition and temperature were determined by EDS (Energy Dispersive Spectrometry) and DSC (Differential Scanning Calorimetry) analysis, respectively. The microstructure was then characterised by SEM (Scanning Electron Microscope). In the DSC experiments, two types of quaternary eutectics were determined according to their phase composition. For each type of eutectic, various microstructures were observed, which result in different eutectic compositions. Only one of the determined eutectic compositions was further studied by the controlled growth technique in a vertical Bridgeman type furnace. In the initial part of the directionally solidified sample, competing growth between two-phase dendrites and three-phase eutectics was obtained, which was later transformed to competing growth between three-phase and four-phase eutectics. Moreover, silver enrichment was measured at the solidification front, which is possibly caused by Ag sedimentation due to gravity and Ag rejection from dendritic and three-phase eutectic growth, and its accumulation at the solidification front.

Effect of atmospheres on tribological property of plasma-sprayed NiCr–Ag composite coating

NiCr–Ag composite solid lubricant coating was deposited on stainless steel by atmospheric plasma spray. The microhardness, phase composition and microstructure of as-sprayed coating were characterized. Meanwhile, the friction and wear behaviour of as-sprayed coating sliding against ceramic (Si3N4) ball in air, argon and oxygen were evaluated using a ball-on-disc friction and wear test rig. It was found that when sliding against Si3N4 in oxygen, the composite coating underwent severe oxidative wear and splat delamination, showing the highest friction coefficient and wear rate. When sliding against Si3N4 in argon, the composite coating had the lowest friction coefficient and wear rate; and in this case, no crack and splat delamination could be observed on the worn surface because of the elimination of oxidation of the coating and enrichment of solid lubricant silver on sliding surface in inert atmosphere. In addition, the friction coefficients of the as-sprayed coating in all three atmospheres decreased with the increase of sliding speed or load.

Distribution and Enrichment of Silver and Cadmium in Coastal Sediments from Bahía Todos Santos, Baja California, México

Silver, cadmium and iron were studied in sediment from Bahia Todos Santos, Baja California, México during 2004. Results showed that the spatial distributions of these metals were very similar to that of organic carbon and fine grain size, with values increasing from the inner to the outer parts of the bay. High concentrations and enrichments of silver (0.051-0.071 μg g⁻¹ dry weight) and cadmium (1.9 μg g⁻¹ dry weight) in Bahía Todos Santos were associated to harbor dredging activities and to coastal upwelling, respectively. However, the distribution of silver and cadmium in most of the study area is controlled by grain size and organic carbon content.

Enrichment and separation of silver from waste solutions by metal ion imprinted membrane

Using blends of chitosan and polyvinyl alcohol as film-forming materials, the metal ion imprinted membrane was prepared with silver ions as template (Ag(I)-IIM). The DSC curve shows that the membrane does not exhibit the heat resistance very well but the favorable compatibility. FT-IR analysis implies that the coordinating atoms may be N atom of –NH 2 in chitosan and O atom of –OH in polyvinyl alcohol. The results on the experiment of competitive adsorption indicate that Ag(I)-IIM has the ability of specificity and recognition to Ag(I). The large adsorption capacity for Ag(I) indicates that Ag(I)-IIM can be used in silver enrichment and separation from waste solutions as an effective material.

Silver surface enrichment controlled by simultaneous RBS for reliable PIXE analysis of ancient coins

Evidence of silver surface enrichment of ancient silver–copper coins has been pointed out in the past years. Surface enrichment can be fortuitous or intentional. In this paper, we have investigated the cleaning procedures usually performed after excavation or in museums. We have shown that chemicals or commercial products routinely used dissolve preferentially the copper phase and consequently contribute to the silver surface enrichment. As a result, surface analyses such as PIXE or XRF can be strongly affected by this effect. By using simultaneously RBS and PIXE, it is possible to check through the silver surface enrichment and then select the reliable measurements, characteristic of the bulk composition. Results on coins recently discovered and mechanically or chemically cleaned are presented.

Non-destructive analysis of silver selenide films obtained by Pulsed Laser Deposition (PLD) with Micro-XRF

Thin films of silver selenide with varying composition have been deposited on magnesium oxide substrates with pulsed laser deposition and were investigated via micro-XRF. A calibration procedure was designed to determine the absolute thicknesses of the films. The lateral homogeneity was investigated by elemental mapping, thus delivering information about the deposition process. Wet chemical analysis was performed on the dissolved layers with ICP-OES and ICP-MS to determine the stoichiometry of the Ag x Se y . The results suggest a correlation between the composition of the layers and their thicknesses by showing a silver enrichment for thinner layers.

Copper, gold and silver enrichment in ore mylonites within massive sulphide orebodies at Hongtoushan VHMS deposit, N.E. China

The Hongtoushan Archaean Cu–Zn Volcanic-hosted Massive Sulphide (VHMS) deposit occurs in the Hunbei granite–greenstone terrane, Liaoning Province of NE China. The ores were metamorphosed (3.0–2.8 Ga) to upper amphibolite facies at temperatures between 600 and 650 °C, and underwent three phases of deformation. The deformation has transposed the stratiform orebodies into a Y-shaped configuration. Ore minerals in the deposit were originally composed of pyrite, pyrrhotite, chalcopyrite and sphalerite. Prograde metamorphism obliterated almost all the sedimentary textures in the ores, and the present ore textures were formed substantially during peak and post-peak metamorphism. Intensive remobilisations have occurred in the Hongtoushan deposit at various scales. There are more than 30 oreshoots inside the main massive sulphide orebodies. The oreshoots range from 2 to 30 m in length, 0.1 to 1.5 m in width, and 2 to 30 m in depth extension. Most run parallel or sub-parallel to the strike of the massive sulphide ore layers with only a few being developed in metamorphic rocks in the immediate vicinity of the sulphide orebodies. Almost all the sulphide and gangue minerals in the oreshoots have been affected by intense shearing. Pyrite is characterised by cataclastic flow; pyrrhotite, chalcopyrite and sphalerite exhibit strong plasticity. Hydrothermal alteration minerals in the oreshoots are dominated by deformation-free hornblende, actinolite, epidote, clinozoisite, biotite, muscovite, albite, carbonate and quartz. Cu, Au and Ag in the ore mylonites average 11 wt.%, 1.74 and 235 g/t, respectively. Compared to the massive sulphide ores, these oreshoots show remarkable enrichment of these elements with enrichment coefficients of 5.3, 5.0 and 4.6, respectively. We draw the conclusion that these oreshoots are actually ore mylonites overprinted by late-stage fluids. The presence of annealing textures in pyrrhotite and the absence in pyrite suggest that formation and succeeding annealing of the ore mylonite took place over the temperature range from 550 to 450 °C. Such a temperature range, combined with the geology and mineralogy, indicates that these ore mylonites and the derivative oreshoots were formed during upper-greenschist-facies retrograde metamorphism. Similarity of the ore mylonites to the massive ores in metal varieties and lead isotope ages suggest that Cu, Au and Ag of the overprinting fluids on the ore mylonites were derived mainly from the nearby massive sulphide ores. However, lead isotope compositions of the ore mylonites also suggest that an external source, such as the metamorphic host rocks, has also contributed to their metal budget.

An investigation of extreme silver enrichment at tennantite surfaces exposed to alkaline solutions: an XPS-based study

AbstractExtreme silver enrichment at the surface of the complex sulphide, tennantite (ideal formula: Cu12As4S13), occurs following exposure to alkaline solutions, and involves the development of an Ag-rich sulphide surface species. The tennantite has a low bulk Ag content of 0.3 at.%, and a percentage surface enrichment of Ag is thirty-six times that of the bulk. The techniques of X-ray photoelectron spectroscopy (XPS) and reflection extended X-ray absorption fine structure spectroscopy show the new phase to be a Ag sulphide species compositionally similar to cupriferous proustite ((Cu,Ag)3AsS3). Solution experiments and XPS depth profiling show that the surface is most depleted in Cu and Zn, and enriched in Ag compared to the bulk tennantite. Selective dissolution and reprecipitation at the tennantite surface cannot explain the enrichment of Ag relative to the bulk. Migration must have occurred and could have been driven by the leaching out of Cu which produces a metal-depleted surface, coupled to the relative incompatibility of Ag in the tennantite lattice. To account for the extreme enrichment at the surface, Ag must have diffused from depths of up to 9 nm, probably via structural weaknesses and vacancies in the tennantite lattice.

Geology and Genesis of the Multistage High-Sulfidation Epithermal Pascua Au-Ag-Cu Deposit, Chile and Argentina

The giant Pascua epithermal Au-Ag-Cu deposit is located in the El Indio belt of north-central Chile and Argentina and was the product of a high-sulfidation hydrothermal system. The host rocks consist mainly of Triassic granite and heterolithic Miocene breccia pipes. Granitic rocks host ~60 percent of the mineralization (or >80% if granitic breccia fragments are included) but were not the cause of hydrothermal activity. The economic mineralization forms a large orebody centered on Brecha Central, the largest of the breccia pipes, and several smaller satellite bodies that are separated by zones of subeconomic mineralization. Hydrothermal activity produced two main stages of advanced argillic and vuggy silica alteration. These were separated by an intermediate stage of argillic alteration, silicification and hypogene jarosite, which occurred penecontemporaneously with the emplacement of Brecha Central. Main-stage Au-Ag-Cu mineralization occurred toward the end of the second stage of alteration and involved precipitation of native gold with pyrite and enargite and incorporation of Au in the structure of these minerals. Four types of mineralization are recognized based on the occurrence of economic concentrations of Au in rocks containing significant amounts of the following minerals: (1) alunite, pyrite, and enargite; (2) pyrite; (3) pyrite and szomolnokite; and (4) native gold. Main-stage gold mineralization was followed by a sulfate stage represented by barite and anglesite at lower elevations and barite, anglesite, plus primary szomolnokite, the first reported occurrence of this phase as a hydrothermal ore mineral, at higher elevations. Late-stage silver mineralization, characterized by the occurrence of microscopic Cl-, I-, and Hg-bearing phases in voids and fractures, enriched the upper parts of the deposit, forming an extensive subhorizontal zone that overprints previous alteration and mineralization. Advanced argillic alteration and high-sulfidation mineralization at Pascua are interpreted to have resulted from a high-level hydrothermal system developed above a porphyry stock located in Argentina. Extensive vuggy silica and advanced argillic alteration reflect interaction of the wall rocks with acidic magmatic vapors. Gold, copper, and arsenic are interpreted to have been transported by these vapors and to have deposited as a result of their cooling and subsequent condensation. Ore-forming hydrothermal activity terminated with silver enrichment in response to the condensation of residual magmatic vapors during the waning stages of the system.

Silver surface enrichment of silver–copper alloys: a limitation for the analysis of ancient silver coins by surface techniques

Silver surface enrichment of silver–copper alloys: a limitation for the analysis of ancient silver coins by surface techniques

Silver surface enrichment of silver–copper alloys: a limitation for the analysis of ancient silver coins by surface techniques

The surface enrichment of archaeological silver–copper alloys has been recognized for many years. However, the origin of this enrichment is not well defined and many hypotheses have been put forward to account for this behaviour: segregation of the components during casting, deliberate thermal and/or chemical post-treatment, abrasion or corrosion. Among the hypotheses mentioned above, we have focused our study on the first step of coin manufacturing. Replications of silver–copper standards of various compositions ranging from 30% to 80% Ag, reflecting the composition of silver blanks, have been produced. Metallographic examination, PIXE and SEM–EDS have been used for the characterization of each sample. A model of the direct enrichment has been established. This model allows us to propose a relationship between the surface composition and the silver content of the core. Comparison with data of Roman coins from the Roman site of Châteaubleau (France) and from the literature and consequences for the analyses of ancient coins by surface methods are presented.

Trace enrichment and determination of silver by immobilized DDTC microcolumn and flow injection atomic absorption spectrometry

Flow injection (FI) system incorporating a microcolumn of immobilized diethyldithiocarbamate (DDTC) on surfactant-coated alumina was combined with atomic absorption spectrometry for on-line trace enrichment and determination of silver in different matrices. Silver was deposited on the microcolumn by processing a standard or solution of analyte at pH 3–4 on the column. Injection of 250μl of ethanol then served to elute the retained species to atomic absorption spectrometry (AAS). A sample volume of 20ml resulted in a pre-concentration factor of 125, and precision at the 20μgl−1 was 4% (R.S.D.). The procedure was applied to tap water, well water, rain water, sea water, radiology film, and lead concentrate samples. The accuracy was assessed through recovery experiments, independent analysis by furnace-AAS, and analysis of certified reference material.

Trace enrichment and determination of silver by immobilized DDTC microcolumn and flow injection atomic absorption spectrometry

Flow injection (FI) system incorporating a microcolumn of immobilized diethyldithiocarbamate (DDTC) on surfactant-coated alumina was combined with atomic absorption spectrometry for on-line trace enrichment and determination of silver in different matrices. Silver was deposited on the microcolumn by processing a standard or solution of analyte at pH 3–4 on the column. Injection of 250 μl of ethanol then served to elute the retained species to atomic absorption spectrometry (AAS). A sample volume of 20 ml resulted in a pre-concentration factor of 125, and precision at the 20 μg l −1 was 4% (R.S.D.). The procedure was applied to tap water, well water, rain water, sea water, radiology film, and lead concentrate samples. The accuracy was assessed through recovery experiments, independent analysis by furnace-AAS, and analysis of certified reference material.

Anomalous Enrichment of Silver in Organic Matter of the Songxi Shale‐hosted Ag‐Sb Deposit in Northeastern Guangdong

Abstract The silver contents of organic matter in the host rocks of the Songxi shale‐hosted Ag‐Sb deposit of northeastern Guangdong, South China, have been directly determined using the electron microprobe technique. The silver contents in two types of organic matter, marine vitrinite and solid bitumen, vary in the range from 100times10−6 to 350times10−6, which are from tens of times to thousands of times higher than those of the host rocks in the ore deposit. The average silver content of the organic matter is also several times higher than the pay grade of silver for commercial mining of the ore deposit. It is quite obvious that the organic matter of the host rocks in the ore district is characterized by an anomalous enrichment of silver. The results of this study indicate that the silver anomalies in the organic matter have been derived from both the host rocks and the silver‐bearing fluids of the Songxi black shale ore source. In the course of sedimentation and later hydrothermal reworking, organic matter was able to entrap the element silver from source rocks and silver‐bearing fluids through complexation and reduction, so that silver could be further enriched (or precipitated) in the solid bitumen. The quantitative assessment in this study suggests that the distribution of solid bitumens in the ore district may be considered an indication for mineral exploration.

A new mechanism of formation of the silver-rim structure on primary gold grains

Gold minerals in the Baochun skarn-type gold deposit are Au-Ag alloys with Ag contents within the range of 15–35. 5 wt% and the minerals vary from 5μm to 50μm in size. As viewed from the electron microprobe images, most gold grains show silver rims with a high Ag content as compared with the core, ranging generally from 2 to 3μm in width. From dynamic calculations based on the mass action and mass balance constraints on the crystallization of native gold, it is considered that the enrichment of silver in the rim of gold minerals is due to gradual enrichment of silver in the ore-forming solutions with its evolution from the early to the late metallogenic stage.

Palladium–Silver Sol–Gel Catalysts for Selective Hydrodechlorination of 1,2-Dichloroethane into Ethylene: II. Surface Composition of Alloy Particles

The surface composition of alloy particles in Pd–Ag/SiO2 hydrodechlorination (HDC) sol–gel catalysts has been determined by combining three experimental techniques, carbon monoxide chemisorption, X-ray diffraction, and transmission electron microscopy. Values obtained through this method show a very marked silver enrichment of the surface, as expected: as a consequence of the important gap between palladium and silver surface energies. These values are in complete agreement with surface composition curves calculated in other studies by means of Auger electron spectroscopy and infrared spectroscopy. The influence of sample pretreatment temperature as well as the influence of carbon monoxide on surface composition are discussed.

Is the external beam PIXE method suitable for determining ancient silver artifact fineness?

In archeometry, the non-destructive characteristic of an analytical method is always very attractive. For most of techniques, besides the need of sampling, difficulties can originate from the shape and the size of the silver artifacts to be analyzed. The external PIXE method should be an answer to this problem but several questions are arising from the implementation of the technique to such a material. The aim of this paper is to specify the experimental procedure as to take into account several parameters, which could induce dramatic errors. Among them it can be pointed out the superficial enrichment in silver, arising from the dissolution of copper and copper oxide, the surface roughness effects, the great importance of the stability of the geometric conditions. The accuracy and the precision of the method are considered within the scope of the results obtained in ancient times by the cupellation with ashbone cupels. In addition, the process involved to obtain silver alloys has been studied in order to define its influence on the real fineness of the objects.

Atomic-scale structure and chemistry of ceramic/metal interfaces—I. Atomic structure of {222} MgO/Cu (Ag) interfaces

Ceramic/metal (C/M) {222} MgO/Cu (Ag) heterophase interfaces, prepared by internal oxidation, are studied by scanning transmission electron microscopy (STEM). The observed spacing between misfit dislocations (1.45 nm) in a 〈110〉 projection is in agreement with the prediction of Bollmann's geometric O-lattice theory and experimental values in the literature for {222} MgO/Cu interfaces. It is concluded that the {222} MgO/Cu (Ag) interfaces are semicoherent and contain a trigonal network of pure edge misfit dislocations parallel to 〈110〉-type directions, with an ( a/6)〈211〉-type Burgers vector. Misfit dislocations are also found in a standoff position at a distance of a single (111) spacing of the Cu (Ag) matrix. Extra intensity at the interface, in some angular dark-field images indicates silver segregation, in agreement with our atom-probe field-ion microscope results. On the metal side of the interface, extra intensity is observed in five atomic layers, which corresponds to a total silver enrichment of approximately 0.7 effective monolayers.

DETECTION OF NEAR‐SURFACE SILVER ENRICHMENT ON ROMAN IMPERIAL SILVER COINS BY X‐RAY SPECTRAL ANALYSIS*

A collection of 218 Roman imperial silver coins, covering three centuries, was analysed non‐destructively by two variants of X‐ray spectral analysis. Electron beam excitation and energy‐dispersive spectrometry was used for the analysis of the uppermost thin layer (3 μm) of each coin, while X‐ray tube excitation and wavelength‐dispersive spectrometry was applied for the analysis of thicker layers (30 μm), Ag and Cu as major constituents and 18 minor elements were determined quantitatively. Comparing the silver content of the obverse and the reverse of a coin, inhomogeneities could be identified. By comparison of the silver content of the upper thin and the thick surface layers, near‐surface silver enrichment could be detected. Inhomogeneities and enrichments increase in the second and more so in the third century. A large scatter of the silver content and silver enrichment for coins of the same emperor was attributed to varying abrasion of Ag‐enriched layers of the individual coins during decades of circulation.