Gregory Alan Hope

Raman microprobe mineral identification

Raman spectroscopy and associated imaging techniques are generally non-destructive, and can be used to identify a wide range of minerals and gemstones. Raman is a sensitive technique which requires minimal sample preparation and can be used on massive specimens from lump ore to fine powders and liquids. Since glass and water are weak Raman scatterers, spectra from minerals can be obtained from samples in air, through glass, and/or immersed in water. Examples of the application of Raman spectroscopy to minerals of importance in mineral processing are discussed. These include: detection of minerals of light elements such as carbon and fluorine; distinguishing between polymorphs such as those of iron sulfides; characterizing sulfides containing minor elements such as iron in sphalerite; and the identification of silicate, oxide, and carbonate gangue minerals. The Raman microprobe also permits Raman imaging and mapping of surfaces and inclusions. Imaging of diamond is presented as an example of this technique.

SERS study of the interaction of thiourea with a copper electrode in sulphuric acid solution

The electrochemical interaction of thiourea with a copper electrode in sulphuric acid solution was investigated using Fourier transform Raman and in situ surface-enhanced Raman scattering (SERS) spectroscopy. SERS spectra of thiourea at a copper electrode were obtained in solutions containing greater than 5 ppm thiourea; the spectra obtained were consistent with adsorption of the molecule on the copper electrode via the sulphur atom. The SERS spectra provide evidence of complex formation involving thiourea and sulphate species at the electrode surface.

A SERS spectroelectrochemical investigation of the interaction of 2-mercaptobenzothiazole with copper, silver and gold surfaces

The interaction of the sulfide mineral flotation collector, 2-mercaptobenzothiazole, with silver, copper and gold surfaces has been investigated by surface enhanced Raman scattering (SERS) spectroscopy. 2-mercaptobenzothiazole, the copper, silver and gold compounds of this species, and the dithiolate, 2,2′-dithiobis(benzothiazole) were characterised by 13C NMR and Raman spectroscopy to provide a basis for identifying surface species. SERS investigations showed that, at pH 4.6 where the solution species is in the protonated form, and at 9.2, where it is present as the ion, adsorption on each metal occurs over a wide potential range. Attachment of the organic compound occurs through bonding between the exocyclic sulfur atom and metal atoms in the surface. X-ray photoelectron spectroscopy confirmed that the adsorbed layer was of monolayer thickness. Adsorption of the protonated 2-mercaptobenzothiazole occurs on copper at pH 4.6 at potentials below that at which charge transfer adsorption commences.

An electrochemical and sers study of the effect of 1-[N,N-bis-(hydroxyethyl)aminomethyl]-benzotriazole on the acid corrosion and dezincification of 60/40 brass

Abstract The effect of 1-[N,N-bis-(hydroxyethyl)aminomethyl]-benzotriazole (BTLY) on the corrosion and dezincification of a 60/40 brass in aqueous H 2 SO 4 at 30 °C has been investigated by means of solution analysis, potentiodynamic and surface enhanced Raman scattering (SERS) techniques. Overall inhibition (for copper and zinc dissolution) increased with increasing concentration to a maximum (63.1 %) at the 5 × 10 −4 M level. This was comparable to that observed for benzotriazole (BTAH) under the same conditions. Solution analysis indicates that BTLY is ineffective in preventing dezincification. Polarization studies show that BTLY acts initially to suppress the cathodic and anodic corrosion reactions. The SERS spectra suggest that the adsorption with copper in the brass occurs through nitrogen in the azole ring of the protonated molecule BTLYH.

A SERS study of SO2−4Cl− ion adsorption at a copper electrode in-situ

The adsorption of chloride and sulfate ions at a copper electrode in sulfuric acid solution has been investigated in-situ by SERS spectroscopy as a function of solution chloride concentration and electrode potential. In solutions containing low concentrations (less than 10 ppm) of chloride, the adsorption of sulfate and chloride species at the copper electrode is potential dependent. At low cathodic overpotentials, chloride is the predominant adsorbed species, while at high cathodic overpotentials, chloride is displaced by SO2−4 ions as the adsorbed species at the electrode surface. In electrolytes containing greater than 20 ppm chloride, the halide ion is the predominant adsorbed species over the entire potential range investigated. However, the presence of spectral bands associated with adsorbed SO2−4 ions are still evident, thus implying the presence of sulfate as a secondary adsorbed species.

Spectroelectrochemical investigations of the interaction of ethyl xanthate with copper, silver and gold: II. SERS of xanthate adsorbed on silver and copper surfaces

Raman spectroscopy has been applied to the investigation of the interaction of ethyl xanthate with silver and copper surfaces. SERS spectra recorded in situ and on emersed electrodes have confirmed the conclusion of previous studies that ethyl xanthate is chemisorbed on these metals at potentials below the reversible value for the corresponding metalmetal ethyl xanthate couple without change in its molecular integrity. The stretching vibrations of the hydrocarbon groups in the xanthate molecule were found to be suppressed when SERS spectra were recorded in situ, but the corresponding rocking and deformation vibrations were unaffected. The hydrocarbon stretching vibrations were strong in the spectra from emersed electrodes. The difference between the spectra from surfaces in the two environments is discussed in terms of absorption of the signal by the overlaying water layer and the hydrophobic nature of chemisorbed xanthate.

Confirmation of thiourea/chloride ion coadsorption at a copper electrode by in situ SERS spectroscopy

The coadsorption of chloride with thiourea and sulfate ions at a copper electrode in sulfuric acid solution has been investigated in situ by SERS spectroscopy. The presence of the halide species in solution and subsequent adsorption at the copper electrode leads to enhancement of the SERS spectra for the adsorption of thiourea and sulfate ions at the copper electrode. The in situ SERS spectra indicate that the adsorption of chloride at the copper electrode is dependent upon electrode potential and solution chloride concentration. The coadsorption of chloride at the copper electrode in sulfuric acid electrolyte containing thiourea is particularly favoured at low potentials and is characterised by the presence of a distinct band at 300 cm−1 which is assigned primarily to a Cu-Cl vibration. However, this band contains secondary contributions from Cu-S and Cu-O vibrations arising from the coadsorption of thiourea and sulfate species at the copper electrode respectively.

An electrochemical and SERS study of the action of polyvinylpyrrolidone and polyethylenimine as inhibitors for copper in aerated H2SO4

Abstract The adsorption and inhibitive effects of polyvinylpyrrolidone (PVP) and polyethylenimine (PEI) on copper in 2 M H 2 SO 4 at 30 ° C have been investigated by means of weight loss, potentiodynamic and in situ surface-enhanced Raman scattering (SERS) techniques. Both polymers reduce the rate of the anodic (metal dissolution) and cathodic (O 2 reduction) corrosion reactions. At all concentrations studied, PVP was found to be the better inhibitor. The dependence of the adsorbate spectra on applied potential and pH was established. There was evidence for PVP adsorption through oxygen whilst PEI showed coordination through the nitrogen atom.

A Spectroelectrochemical Study of Surface Species Formed in the Gold/Thiosulfate System

Surface-enhanced Raman scattering (SERS) spectroscopy has been applied to identify species formed during gold leaching in thiosulfate media. Surface coverages of copper and sulfur for various thiosulfate dissolution systems were determined electrochemically and by X-ray photoelectron spectroscopy. A gold sulfide monolayer was shown to be formed slowly in the potential region where leaching occurs. At higher potentials, more sulfur is adsorbed but, rather than creating a multilayer, sulfur-sulfur linkages are formed with the sulfur atoms no longer being covalently bonded to gold. SERS spectra show the presence of polythionates on the gold surface in addition to gold sulfide and S°. At longer exposure times, thiosulfate is oxidized to elemental sulfur and sulfate, both products being identified by normal Raman spectroscopy from the leach solution. In typical thiosulfate/ ammonia/copper(II) leach solutions, copper is present on the surface of gold in addition to sulfur. In these situations, ammonia is coadsorbed.

Induced codeposition of Sm-Co amorphous films in urea melt and their magnetism

The electroreduction of Co(II) and Co(II) + Sm(III) in urea-acetamide-NaBr-MCl x melts were investigated by cyclic volatmme-try and chronoamperometry. The reduction of Co(II) is an irreversible process. Sm(III) cannot be reduced alone, but Sm-Co can be codeposited by induced deposition. The mechanism may involve a polynuclear complex containing Co(II) and Sm(III). An amorphous Sm-Co film comprised of nanoagglomerates has been synthesized. SEM shows that most of the agglomerates fall within a size range of 20-35 nm with a few agglomerates in the 50-90 nm range. The Sm content in the films varies from 7.9 to 79.16 wt % with the applied potential and the molar ratio of Sm(III)/Co(II) in melt. The film could be crystallized by heat-treatment at 900°C. Large crystal grains appeared after heat-treatment and their phase was confirmed as Sm 2 Co 1 7 . In addition, crystalline nanoparticles with the size of 10 nm were found on these large crystal grains. The magnetic properties of the Sm-Co films were determined using hysteresis loops, the coercive field H c of Sm (79.16 wt %)-Co amorphous film is 2300 Oe at 5 K; and the remanent magnetization M R and the saturation magnetization M S are 0.536 and 1.429 emu g - 1 , respectively.