Sulfur Enrichment Research Articles

Role of adsorbed sulphur in the dissolution and passivation of nickel and nickel-sulphur alloys

The influence of sulphur on the dissolution and passivation of nickel in acidic medium was investigated. The amounts of sulphur in the bulk and on the surface of the metal were measured by using 35S radiotracer. A possible influence of the crystallographic orientation of the metal on the phenomena under investigation could be revealed by using nickel single crystals. On pure nickel the highest rate of dissolution was observed on the (110) face, and the lowest rate on the (111) face. The residual current after passivation was lower on the (111) face, in relationship with the epitaxial feature of the oxide NiO formed. The presence of a monolayer of adsorbed sulphur on nickel increases the rate of dissolution in the active region and extends the active region towards more anodic potentials. The formation of the passive layer requires the partial desorption of the adsorbed sulphur. When sulphur was homogeneously dissolved in the bulk of the metal, the following experimental results were obtained: (1) There is a critical sulphur concentration above which the active-passive transition disappears. This concentration depends on the crystallographic orientation. The higher the rate of dissolution of a face, the lower the critical concentration. It is ranging from 30 to 50 × 10 -6 at a potential sweeping rate of 1 V/h. (2) The metal dissolution brings about a surface enrichment with sulphur, responsible for the inhibition of the passive layer formation. This enrichment is further developed beyond the monolayer coverage, until a thin film of nickel sulfide with a stationary thickness is formed. The metal dissolution takes place through this non-protective layer with a remarkably high current density. (3) Under certain conditions reported here a localised corrosion with epitaxial pits was observed on the low index faces. This corrosion is attributed to a preferential dissolution of the metal at the structural defects resulting in a sulphur enrichment that inhibits locally the formation of the passive layer. The formation of the passive layer NiO can also be inhibited when sulphur is no longer introduced into the metal but into the electrolyte, in the form of a soluble sulfide. In all studied cases the passivation of the metal can occur only if the sulphur concentration on the surface is below the monolayer coverage.

Grain Boundary Segregation of Sulfur, Nitrogen, and Carbon in α‐Iron

AbstractThe segregation of sulfur, nitrogen, and carbon at surfaces and grain boundaries of α‐iron was studied by Auger Electron Spectroscopy (AES). Specimens of pure iron, doped with nitrogen or carbon by equilibria with gas mixtures were introduced into the UHV‐chamber and fractured by impact at about −130°C. Enrichment of nitrogen, carbon, or sulfur was observed on the intergranular fracture surfaces. Displacement equilibria exist between nitrogen or carbon and sulfur, which was present in the bulk material only as a trace impurity. The presence of sulfur decreases the cohesion of the grain boundaries, so that mainly intergranular fracture occurs. Obviously nitrogen or carbon reinforce the cohesion of grain boundaries, so that transgranular fracture prevails.

Preparation of oxygen-18 enriched sulfur trioxide

Oxygen-18 enriched sulfur trioxide has been prepared by a simple and relatively inexpensive procedure. This has been occomplished by the addition of sulfur trioxide to oxygen-18 enriched water to form fuming sulfuric acid containing approximately 50 per cent dissolved sulfur trioxide. On distillation of this fuming sulfuric acid, the sulfur trioxide obtained was enriched in oxygen-18. It was isolated and analyzed as its dimethylformamide complex.

Grain boundary segregation and the grain size dependence of strength of nickel-sulfur alloys

Tensile, miorohardness and autoradiographic observations of Ni-S alloys containing <1 to 50 ppm S indicate that sulfur is strongly segregated to grain boundaries in nickel. For all but the most concentrated of these alloys the sulfur appears to be in solid solution. This non-equilibrium sulfur enrichment of the grain boundaries appears to occur via a solute-vacancy interaction mechanism. This segregation causes a local increase in microhardness and an unusual variation of the Petch slope k in the grain size dependence of the flow stress. The latter can be qualitatively rationalized by an extension of Li's model of dislocation generation from grain boundary ledges.

Effects of diabase dike intrusion on sulfide minerals at Manitouwadge, Ontario

A diabase dike intruding a Cu-Zn massive sulfide orebody has caused a migration of copper and sulfur in the orebody towards the dike, but neither element penetrated the glassy chilled margins of the dike. This resulted in the development of a chalcopyrite-rich zone along the contact and a much broader zone of sulfur enrichment within which pyrrhotite was firstly sulfur enriched and then converted to pyrite and where the iron content of sphalerite was decreased.

Der Schwefelgehalt in Knochen und Z�hnen rezenter und fossiler Organismen

The sulfur content of teeth and bones has been determined by a microprobe. Recent samples only contain about 0.05 weight percent of sulfur, independent of a marine or terrestrial origin of the organisms. The total sulfur of these samples is partly related to the organic matter and partly to SO 4 2− -ions replacing PO 4 3− -ions in the crystalline matter of the skeletons. In the living organisms this matter consists of octacalciumphosphatecarbonate (OCPC) (Hayek, 1967), which is transformed only to a small degree into apatite. During diagenesis the process of apatite-crystallisation proceeds, and more sulfate enters the lattice of the phosphate, which leads to an enrichment of sulfur up to about one percent by weight. There is no relation observed between the concentration of sulfur and the age of the organisms. Influences of the environment of diagenesis on different minor compounds entering the phosphates of bones and teeth in different state of composition have been evaluated. As a result the possibility of dating fossils by minor element analysis (F, Mn, SO 4 2− etc.) must be questioned. Differences between freshwater and marine invironment of deposition cannot be observed in the total sulfur of diagenetic phosphates.

A Study of the Proteins of the Wool Follicle

A study has been made of the incorporation at different levels in the developing fibre of 35S into the two main protein fractions of wool. The proteins have been studied as the S-carboxymethyl derivatives rather than as the oxidized derivatives previously investigated. The results obtained give further support for a mechanism of synthesis which involves two stages. However, the incorporation of some 35S into the low-sulphur fraction of the keratinized fibre only 24 hr after the injection of [35S]cystine is somewhat surprising and possible explanations for this have been considered. A detailed comparison has been made of the proteins extracted from the unkeratinized portions of wool roots by 8M urea with those which can be extracted from the keratinized residue with urea-thioglycollate. As might be expected the latter proteins were very similar to those isolated from wool itself. The group of urea-soluble, high-sulphur proteins was different in containing considerable amounts of protein lower in both molecular weight and sulphur content than the comparable fraction from the fully keratinized wool. The possibility is discussed that some of these urea-soluble, high-sulphur proteins may be precursors of those in the fully keratinized fibre, conversion taking place by a process of sulphur enrichment.

Proton Groups from theS33(d,p)S34Reaction

Natural and 25% enriched sulfur targets sandwiched between two silver layers were bombarded with deuterons accelerated in the MIT-ONR electrostatic accelerator to an energy of 6.0 MeV. Proton groups from the $d,p$ reactions were observed at angles 90, 50, and 20 degrees to the deuteron beam with a broad-range magnetic spectrograph. Twenty-three proton groups corresponding to levels in ${\mathrm{S}}^{34}$ were observed. The ground-state $Q$ value of the ${\mathrm{S}}^{33}(d,p){\mathrm{S}}^{34}$ reaction was measured as 9.193\ifmmode\pm\else\textpm\fi{}0.010 MeV.