Raja Kishore Paramguru

Kinetics and Mechanism of Electroless Deposition of Copper

This paper describes investigations on the role of electrolyte composition on the mechanism of the electroless copper deposition process. Both potentiostatic and galvanostatic polarization curves as well as steady-state plots are used in these investigations. Actual deposition rates are also measured through gravimetrically determined weight gain for comparison. The observation indicates that the two-compartment cell gives the mixed potential, E{sub m}, values closer to that of the actual plating, whereas the deposition rate determined from the mixed current, i{sub m}, value is lower than that of the actual one. The mechanism of electroless copper deposition changes from anodic to cathodic control as well as from diffusion to activation control depending on the concentration of Cu{sup ++} and HCHO. The mechanism in each case could be determined through the application of the Butler-Volmer equation to the half-cell reactions depending on the position of E{sub m} in the polarization plots of the individual half-cell reactions.

Reduction of Oxide Minerals by Hydrogen Plasma: An Overview

Abstract Carbothermic reduction of oxide minerals is one of the major routes to obtain the correspondingxa0metals. This process produces a lot of CO2, which is responsible for greenhouse effect. Alternatively, hydrogen plasma containing hydrogen in atomic, ionic, and excited states can reduce almost every metal oxide even at lower temperatures. Besides this advantage, plasma processing also offers kinetic advantages. Further, hydrogen-water cycle does not pose any environmental problems. However, reduction of metal oxidesxa0in hydrogen plasma is not so straightforward—there are issues relating to introduction of material into the plasma zone, residence time, reverse reaction, and scale-up that must be resolved—yet, it holds the key to future environmental challenges particularly with respect to CO2 emission. This paper provides an overview of reduction of oxide minerals by hydrogen plasma. The influences of various reaction conditions particularly with respect to reduction of oxides are discussed and some aspects of both thermal and non-thermal cold plasma linking oxidative as well as dissociative reduction are presented.

Formation of Calcium Titanate During Electroreduction of TiO2 in Molten CaCl2 Bath

The direct electrochemical reduction of a TiO2 cathode in a molten CaCl2 bath to produce titanium metal invariably results in the formation of CaTiO3 as an intermediate product. To obtain even more insight into the formation of CaTiO3, experiments are performed in open-circuit conditions as well as at a cell voltage of 2xa0V for different time periods. In this study, we examine the conversion of TiO2 to CaTiO3 in the molten CaCl2 bath. Prolonged electrolysis experiments are conducted and the newly transformed phases are analyzed using X-ray diffraction (XRD). The formation of CaTiO3 and its subsequent transformation to different species during reduction is discussed. An approach for preparing CaTiO3 chemically by treating the TiO2 electrode in CaCl2 bath and subsequently reducing it by electrochemical means to produce titanium metal has been proposed.

Direct reduction of iron in low temperature hydrogen plasma

Abstract This paper describes the effects of various parameters on the reduction of hematite in the presence of microwave assisted non-thermal hydrogen plasma. The parameters include microwave power, hydrogen flowrate, pressure, microwave power density and temperature. It has been shown that hydrogen flowrate, pressure and microwave power are interrelated to effect the microwave power density that controls the plasma temperature. The experimental conditions encounter three temperatures: surrounding the sample, associated with the plasma and at the plasma/substrate interface. It has been deduced that the third one is the most effective in determining the rate of the reaction, and in the present case, activation energy of 20 kJ mol−1 is reported.

Preliminary investigation into direct reduction of iron in low temperature hydrogen plasma

Abstract There has been an increasing interest in reduction of iron ore by hydrogen. This study deals with the reduction of haematite in a microwave assisted non-thermal hydrogen plasma. The plasma is composed of excited hydrogen molecules, hydrogen atoms, and ionic hydrogen among other gaseous species. The reduction in hydrogen plasma occurred even at temperatures as low as 573 K. In contrast, the same could not be achieved by merely introducing hydrogen gas to the reducing environment without creating the plasma. It is only ∼1073 K that the extent of reduction by gaseous means is comparable to that of reduction by hydrogen plasma. Based on the experiments, as well as the data available from literature, it was deduced that the reduction of haematite at a low temperature in hydrogen plasma could have been due to the contribution of vibrationally excited hydrogen molecules to the reduction process.

The recovery of vanadium from spent catalyst: a case study

Abstract Recovery of vanadium from spent industrial catalysts is being widely practiced worldwide, as the material is available in large quantities with appreciable vanadium content. However, due to diversity in characteristics, many of these spent catalysts do not respond to the already established extraction methods, and separate studies are necessary to deal with specific cases. This article describes a process for vanadium recovery from a typical spent catalyst of ∼2·5%V2O5 content. The material was first water leached at room temperature in the presence of Na2SO3, whereby >99% of vanadium was brought into the solution. After solid–liquid separation, the pH of the solution was raised to 8·5, with the addition of NaOH resulting in a precipitate, which, after drying, contained ∼25%V2O5. Roasting the solid with Na2CO3 at 700°C for 30u2005min followed by water leaching yielded a concentrated vanadium bearing solution from which vanadium was separated as ammonium vanadate by adding NH4Cl. The ammonium vanadate product after heating in air contained 92·6%V2O5. Various parameters during Na2SO3 leaching of spent catalyst were studied. Na2CO3 roasting of the vanadium enriched product and ammonium vanadate precipitation were optimised.

A Fundamental Investigation of Electrochemical Preparation of Battery Grade Nickel Hydroxide

Electrochemical studies on nickel hydroxide have shown that three reduction reactions take place simultaneously at the cathode to reduce nitrate to nitrite, nitrite to ammonium ion and nitrate to ammonium ion. All the three reactions produce hydroxyl ion which raise pH to a level favorable to precipitate Ni(OH)2. Current density, which regulates flow of OH- supply, has prominent effect on the process and products. It determines whether α- or β-Ni(OH)2 would be precipitated and has a direct relationship with size and structure of the product and also with the associated water molecules. Replacement of Ti anode with consumable Ni sheet remarkably improves current efficiency (production rate) and decreases power consumption.

Effect of Cell Voltage and Temperature during Electrolytic Reduction ofTiO2

The properly dried CaCl2 salt is melted to the required temperature of electrolysis. Electrolysis of TiO2 electrode has been carried out at two different bath temperatures of 900 and 950°C keeping a constant cell voltage of 3 V. Also the electrolysis of TiO2 electrode is carried out at three different cell voltages of 2.8, 3.0 and 3.3 V at a bath temperature of 950°C. The current-time plot is drawn for each experiment. The resulting products after electrolysis are characterized by XRD and SEM. The effects of bath temperature and cell voltage of electrolysis on reduction process as well as on the characteristics of reduced products are studied.

Electrochemical Studies on Cathodic Reduction of Titanium Dioxide in Molten Calcium Chloride

Abstract The polarization studies have been performed on the electrochemical reduction of TiO2 in a molten CaCl2 bath at 950°C. The cathodic and anodic plots have been drawn by taking TiO2 pellet as cathode and graphite rod as anode, respectively. The cathodic and anodic over-potentials at various cell voltages have been measured. Prolonged electrolysis has been carried out at a cell voltage of 3 V and the resultant products have been analyzed by X-ray Diffraction to find out the reaction pathway through which TiO2 is reduced to titanium. The results indicate that the electrochemical reduction of TiO2 to titanium proceeds through a multi-step reduction process.