Experiences in the development of magnesium cell technology at Central Electrochemical Research Institute, Karaikudi

Research activities on the preparation of magnesium metal by molten salt electrolytic process were initiated in CECRI as early as in 1958. CECRI started its experiments on a bench scale level and further developed into pilot plant scale and finally to the scale of semicommercial unit. Various types of electrolytic cells were developed at CECRI which include externally heated cells with different design modifications, modular cells, bipolar/multipolar cells and new modified monopolar ceUs. The primary aim of each development was aimed at high current efficiencies energy efficiencies and space time yields. Various types of raw materials like magnesite, sea bitterns, and byproduct MgCl2 from ZrrTi plants etc. were utilised during the investigations. These studies were carried out with financial grants from Govt. of Tamil Nadu, CSIR, DRDO and Nuclear Fuel Complex. The paper illustrates the design and operational features of different electrolytic cells with consequent gradual decrease in specific energy consumption for magnesium production and increased space time yields with improvement in cell design and operational parameters

Leptonic and Semileptonic Decays of Charm and Bottom Hadrons

We review the experimental measurements and theoretical descriptions of leptonic and semileptonic decays of particles containing a single heavy quark, either charm or bottom. Measurements of bottom semileptonic decays are used to determine the magnitudes of two fundamental parameters of the standard model, the Cabibbo-Kobayashi-Maskawa matrix elements $V_{cb}$ and $V_{ub}$. These parameters are connected with the physics of quark flavor and mass, and they have important implications for the breakdown of CP symmetry. To extract precise values of $|V_{cb}|$ and $|V_{ub}|$ from measurements, however, requires a good understanding of the decay dynamics. Measurements of both charm and bottom decay distributions provide information on the interactions governing these processes. The underlying weak transition in each case is relatively simple, but the strong interactions that bind the quarks into hadrons introduce complications. We also discuss new theoretical approaches, especially heavy-quark effective theory and lattice QCD, which are providing insights and predictions now being tested by experiment. An international effort at many laboratories will rapidly advance knowledge of this physics during the next decade.Comment: This review article will be published in Reviews of Modern Physics in the fall, 1995. This file contains only the abstract and the table of contents. The full 168-page document including 47 figures is available at http://charm.physics.ucsb.edu/papers/slrevtex.p

Limits on the production of scalar leptoquarks from Z (0) decays at LEP

A search has been made for pairs and for single production of scalar leptoquarks of the first and second generations using a data sample of 392000 Z0 decays from the DELPHI detector at LEP 1. No signal was found and limits on the leptoquark mass, production cross section and branching ratio were set. A mass limit at 95% confidence level of 45.5 GeV/c2 was obtained for leptoquark pair production. The search for the production of a single leptoquark probed the mass region above this limit and its results exclude first and second generation leptoquarks D0 with masses below 65 GeV/c2 and 73 GeV/c2 respectively, at 95% confidence level, assuming that the D0lq Yukawa coupling alpha(lambda) is equal to the electromagnetic one. An upper limit is also given on the coupling alpha(lambda) as a function of the leptoquark mass m(D0)

Combustion synthesis of ABO3 and AB2O4 compounds - an overview

Combustion synthesis has been accepted as a versatile method to synthesize new materials due to its simplicity. The method has been used to prepare numerous materials among which perovskites (ABO3) and spinels (AB2O4) occupy a prominent place. An attempt has been made in this overview to consolidate the recent works on combustion synthesis of these new materials. Various experimental conditions to synthesize the required products and different characterization tools used for unraveling the structural features are highlighted. Further the novelty and mathematical basis of preparative conditions for the synthesis employed by different researchers are also enumerated. This covers the salient features of synthesis, property evaluation and applications of simple as well as substituted perovskite and spinel compounds carried out recently. This will be useful to any researcher entering into this field of new materials worl

Anodes for aluminium production

Anodes used lor aluminium production play an important role in the electrolytic process. Though information about aluminium technology is available, the theoretical and practical aspects and modern trends in the nature of anodes are scattered. An attempt is made to consolidate the various particulars in order to present an overview of the present status of the anodes. An insight into the studies conducted for predicting the mechanism of anodic reactions and products has been made. Emphasis has been made on the development of 'inert-anodes', leading to pollution-free aluminium cells operating at higher energy efficiencie

Investigation of corrosion behaviour of magnesium in aqueous solutions

The paper present.. the corrosion data of ma~nesium metal in different aqueous solutions such as NHl~l, Naf and NaCl04 of concentrations ran~ing from 0.1 to 2.0 M. Pola.-isation and optical methods have been used to evaluate the cOITosion paraDlt'ters and surface properties. The dependence of the open circuit potential, cOlTosion potential, corrosion currt'nt and Tafel slopes on the nature and concentmtion of the electrolytes has been examined. Corrosion current increases linearly with concentration of the electrolyte in all the media. The findinJ!;s further infer the corrosivity of the anions decrease in the ordt'r as CI-> r > no:;. The naturt' of the corrosion products formed on the surface as well as lIlorphnlogical features of the specimt'll nhtained from XRD and SEM techniques are also discussed in this communicatioII

Stress relieving as a technique for improving the corrosion resistance of low alloy steels

The corrosion behaviour of a low alloy steel in 18% H2S04 solution, containing 1000 ppm chloride ion, after annealing and stress relieving is reported in this study. Annealing, followed by stress relieving at 400°C, appears to improve the corrosion resistance properties of this alloy

Removal of magnesium from aluminium scrap and aluminium-magnesium alloys

Most of the commercial grade aluminium and aluminium alloys containing varying percentages of magnesium (0.5 - 5.0%) are cheap raw materials for superpure aluminium by electrorefining. Since the presence of magnesium will consume the electrolyte of the refining bath and because of the possibility of magnesium depositing in the pure aluminium cathode, prior removal of magnesium is a necessity. Removal of magnesium by air-oxidation, chlorination, chemical treatment and electrolysis have been reported. A suitable fluoride based flux has been formulated and the results of the efficiency of magnesium removal has been discussed and compared with the other results

Galvano-gasometric studies of magnesium in aqueous solutions

The difference effect (∆) behaviour of magnesium is studied in Na2SO4, NaBr, MgSO4 and MgBr2 solutions up to 2.0 M concentration using galvano-gasometry set up. Comparison of the hydrogen gas evolution rates obtained from galvano-gasometry method and from the atomic absorption spectrophotometer (AAS) shows a lower value in the former. A transition from positive difference effect to negative difference effect in sodium salt solutions and its absence in magnesium salt solutions are observed during the study. The current density at which the transition occurred is termed as transition current density denoted by the symbol ~. The relationship of iτ with the nature and concentration of the electrolytes are also discussed in this communicatio

Evaluation of Mg2+-substituted NiFe2O4 as a green anode material

In recent years, the awareness of energy, environment and economy for the metallurgical industries, has necessitated the development of mixed oxide-based oxygen-evolving anode materials to avoid the emission of greenhouse gases, such as CO2, CO, and CF6, during electrolysis. In this regard, the noncarbon anode material Ni1 xMgxFe2O4 (x = 0.0, 0.3, 0.6, 0.9) has been prepared by nonconventional citrate gel process using metal nitrate salts as cation precursors and citric acid as a chelating agent. The X-ray analysis showed the existence of single-phase spinel structure with increase of lattice parameter and tetrahedral radius with increasing Mg2 + ion concentration, as against a decrease in density. The FT-IR spectra show the characteristic features of the synthesized ferrite compounds. The DC electrical conductivity increases with increasing temperature. It also increases with an increase of Mg2 + ion concentration and reaches a maximum value of 3.3 S cm� 1 at x = 0.6 at which, the activation energy for conduction is found to be minimum. The effect of the Mg2 + substitution on the electrocatalytic activity of the electrodes towards the oxygen evolution reaction (OER) is studied by using steady state potentiostatic polarization measurements in alkaline KOH solution. The Roughness factor (Rf) and the Double layer capacitance (Cdl) of the synthesized electrodes were measured by using Electrochemical Impedance Spectroscopy. The chemical stability of the Ni0.4Mg0.6Fe2O4 electrode, which is observed to possess optimum properties, was ascertained in a saturated cryolite–alumina melt at the 960 jC, the operating temperature of aluminium electrolysis