Kinetics and mechanism of electroless copper deposition at moderate-to-high copper ion and low-to-moderate formaldehyde concentrations

Studies were carried out to establish the effect of moderate-to-high copper ion and low-to-moderate formaldehyde concentrations on electroless deposition of copper. The individual half-cell polarization curves were generated from a steady-state two-compartment cell as well as from potentiostatic measurements. The anodic and cathodic plots were superimposed on one another to get the mixed potential (E _m) and mixed current(i _m). Actual deposition rates were measured gravimetrically. At very low [HCHO] levels, E _m was found to lie in the cathodic linear region and no copper deposition took place. Above a certain level of [HCHO], the E _m and i _m values were found to shift to a position in the cathodic Tafel region, resulting in a smooth deposit on the substrate surface. A kinetic expression, derived employing the Butler-Volumer equation, matched well with the experimental findings.     

Kinetics and mechanism of corrosion of laboratory hot briquetted iron

While considerable work has been reported in the literature on the corrosion behavior and products of direct reduced iron and sponge iron, very little has been published on hot briquetted iron (HBI). The present article reports the kinetics and mechanism of HBI corrosion. As corrosion is an electrochemical process, measurements using electrochemical techniques have been made and these are compared to data gained by measuring mass changes in the briquettes over time. Similar trends were seen in data from both techniques, and the corrosion extent predicted by electrochemical measurements in saline solution was very close to the mass gain result obtained. Kinetic analysis of the data from mass gain over time trials was conducted. The activation energy for corrosion at temperatures between 25 °C and 80 °C has been calculated. The values of activation energy obtained indicate that corrosion was predominantly controlled by diffusion of oxygen in the liquid state. The internal structure of the briquettes was observed by microscopy both before and after corrosion in distilled water.     

Direct electrowinning of lead from galena concentrate anodes

The results of an investigation of the electrowinning of lead directly from a galena concentrate compact anode employing an acetate bath as the electrolyte are reported. The effects of graphite content in the compact electrode, bath composition, time of electrolysis, temperature of the bath, current density and compaction pressure were studied on a laboratory scale to optimize operating conditions. An electrode containing 6.25% graphite, compacted at 238 MN m^?2 for 5 min, resulted in 70% current efficiency for the dissolution of lead according to the reaction PbS → Pb²⁺ S⁰ + 2e in a bath of ammonium acetate (0.5 M), acetic acid (0.35 M) and lead acetate (0.1 M) when electrolysed at 333 K with a current density of 110.5 A m^?2. The results have formed the basis of a pilot plant design.     

Preparation and characterization of molybdenum trioxide from spent hydrodesulfurization catalyst

An approach to produce molybdenum trioxide from spent hydrodesulfurization (HDS) catalyst, obtained from a petroleum refinery, is presented here. The spent catalyst was devolatilized at 600 °C so as to make it free from oils, organics and other volatile species. It was then roasted with sodium carbonate at a temperature of 850 °C for 30 min. The leaching efficiency for 20% soda roasted sample at 10% pulp density was 99.8%. From the solution molybdenum was precipitated out as ammonium molybdate at pH 1.0 with HCl and ammonium chloride. This ammonium molybdate was calcined at 750 °C to get MoO₃. The product was characterized by XRD. Its purity was determined titrimetrically and by ICP-AES.     

Galvanic interaction between chalcopyrite and manganese dioxide in sulfuric acid medium

Dissolution of chalcopyrite and managanese dioxide minerals in the presence of each other in sulfuric acid medium was studied using compact disc electrodes of the minerals under various H₂SO₄ concentrations (0.05 to 0.5 M). [H⁺] had a positive effect on the reaction rate. Strong galvanic interaction was observed to take place between chalcopyrite and manganese dioxide, the galvanic interaction predominating over the individual dissolution (self-corrosion) rates. Evans diagrams constructed from polarization curves of the two minerals were helpful in interpreting the leaching data. The electrochemical nature of the dissolution reaction was analyzed through application of the Butler-Volmer equation and was confirmed from polarization measurements conducted with the respective mineral electrodes.     

Hydrogen Plasma Smelting Reduction of Fe2O3

Metallurgical and Materials Transactions B - The paper reports successful smelting reduction of iron ore (hematite) in thermal hydrogen plasma. A specially designed reactor with water cooled copper...     

Kinetics and mechanism of MnO2 dissolution in H2SO4 in the presence of pyrite

This paper describes a study of the kinetics and mechanism of MnO2 dissolution in H2SO4 in the presence of pyrite through leaching and electrochemical parameters. Manganese(iv) was found to dissolve mainly through reduction by the ferrous ion generated during oxidation of pyrite by the ferric ion. The oxidation which is slower and rate controlling may proceed through two different reactions, one producing S0 and the other SO42–. Manganese dissolution runs at the same rate as that of pyrite oxidation by maintaining ferrous ion concentration at a much lower level than that of ferric. Kinetic equations based on corrosion coupling principles are developed to explain the observed leaching behaviour.     

Stress distribution due to an external crack opened by two rigid inclusions

Dislocation layers have been exploited to determine stress distribution in the neighbourhood of an external crack opened by two symmetric rigid inclusions.     

Electrochemical Phenomena in MnO2-FeS2 Leaching in Dilute HCl. Part 1: Theoretical Derivation of Rate Equations Under Various Limiting Conditions

Abstract

The paper presents a theoretical analysis of MnO₂-FeS₂ dissolution in acidic media. It is assumed that MnO₂ and FeS₂ dissolve through the operations of MnO₂/Fe₂+ and FeS₂/Fe₃+ corrosion couples. At the mixed potential Em, the half cell reactions establish kinetic equilibria to satisfy charge balance. Kinetic expressions for the mixed potential, E _m and the mixed current, i _m are derived based on the position of E _m on different segments of the hypothetical polarization curves. Finally, the mechanism by which the rates of reactions of the two couples balance each other is discussed. © 1998 Canadian Institute of Mining and Metallurgy. Published by Elsevier Science Ltd. All rights reserved.

Résumé

Le document présente une analyse theorique de la dissolution du MnO₂-FeS₂ en milieux acides. On assume que MnO₂ et FeS₂ se dissolvent par operation des couples de corrosion MnO₂/Fe²⁺ et FeS₂/Fe₃+. Au potentiel de melange E _m les reactions de la demi-cellule etablissent des equilibres cinetiques pour satisfaire a la balance de charge. Les expressions cinetiques du potentiel de melange, E _m et du courant de melange, i _m, sont derivees en se basant sur la position de E _m, sur differents segments des courbes hypothetiques de polarisation. Finalement, on discute du mecanisme par lequelles taux des réactions des deux couples se balancent entre eux. © 1998 Canadian Institute of Mining and Metallurgy. Published by Elsevier Science Ltd. All rights reserved.     

Preparation of titanium metal by electrochemical reduction of titanium dioxide

Preparation of titanium metal by direct electrolytic reduction of TiO₂ in molten CaCl₂ bath was studied using sintered TiO₂ pellets as cathode. The process was carried out at 950°C under normal atmosphere without using any inert gas. Titanium was obtained in the form of powder/compact product depending on the method of preparation of the pellets and the reaction conditions. The product was characterized by XRD, SEM and EPMA. The purity of the product was >99% as evidenced from EPMA analysis.