Greater Current Density Research Articles

Laboratory and field evidence in support of the electrogeochemically enhanced migration of ions through glaciolacustrine sediment

Ionic aureoles, overlying or contiguous to massive sulphide occurrences, are postulated to have been emplaced as a result of natural galvanic forces. The occurrences of these galvanic forces, most commonly referred to as the self-potential or spontaneous polarization phenomena, are well documented, but ionic migration in response to these electrical forces remained to be proven conclusively. The purpose of this study was to attempt to document ionic migration attributable solely to electrogeochemical transport. Pleistocene glaciolacustrine sediments rich in clay-size particles was the geological substrate chosen to minimize migration processes other than those of electrogeochemical transport. Laboratory experiments which simulated a field situation and utilized the radioisotope 65Zn as a tracer, revealed a readily detectable diffusion of Zn 2+ into glaciolacustrine clay; the distance of penetration of the Zn 2+ being significantly increased by the application of a DC electrical potential, similar in magnitude to a natural self-potential. The rate of diffusion was greatest around the margins of the cathodic electrode located at the base of the clay layers; the areas shown to have the greatest current density. The resulting pattern of Zn penetration into the clay, when viewed in a vertical section, showed a double peaked increase in Zn concentration on either side, and a distinct decrease in Zn penetration directly above this cathode. Extrapolation of the average diffusion coefficient found for Zn 2+ ( D 0 = 6.3 × 10 −9cm s −1) to other ions commonly associated with base metal deposits, revealed that only H + could be expected to move through appreciable thicknesses (>20 m) of clay in the 8000 years since sediment deposition. The hypothesis that H + would diffuse through varved clay, and that the resulting pattern would be predictably modified by a self-potential field generated by an oxidizing sulphide body, was tested over the Magusi River volcanogenic massive sulphide deposit near Noranda, Quebec. The organic soil horizon (H) and top of the clay soil layer (C) were sampled and analyzed for conductivity, pH, and other major and minor elements. The mineral horizon revealed distinct changes in conductivity, pH, Ca, Mg, and Fe above the contacts of the hanging wall and footwall of the sulphide horizon, thus producing a double-peaked “rabbit-ear” anomalous pattern. The H soil horizon, when corrections for variable “total” element and carbon concentrations were applied, showed clear anomalies in Fe and other pH sensitive elements. A ratio of EDTA Fe/TOTAL Fe to total organic carbon revealed the best “rabbit-ear” anomaly above the sulphide horizoon. The use of organic horizon geochemistry as a method of evaluating EM conductors overlain by water-saturated lacustrine sediments is recommended.

(B) Electrometallurgy: electrowinning and refining

Since the previous review in this series,l there have been major external influences on research and industrial practice in the extraction of metals. First, environmental pressure, principally in the USA and other developed countries, forced severe limitations on waste-gas emissions, particularly affecting S02 from sulphide ore smelters. Initially this provoked renewed enthusiasm in and economic reassessment of alternative’clean’ processes, especially those involving electrocheical and solution chemical reactions. However, following the sharp rise in oil prices in 1973, electricity became somewhat less attractive as a reducing agent. Consequently, in some cases, a temporary relaxation in pollution control has been permitted, but emphasis has clearly been placed on higher current efficiency at greater current densities in the operation of electrolytic cells. More recently still, world-wide inflation has made capital investment in unproven or prototype processes much less attractive. Thus, to attain higher current efficiencies and current densities, greater attention has been directed towards electrolytic cell design2,3 and operation. 4,5 It is to be hoped that packed- bed electrochemical reactors of bipolar (with or without fluidization), carbon fibre,6 and other configurations, given adequate financial support, will fulfil their initial promise in achieving these goals.

Auxiliary Phase Design for Capacitor Start Motors

A procedure is described for calculation of an auxiliary phase for a single-phase capacitor start motor. The size of wire, the number of turns, and the size of capacitor are determined to meet five restraints. These restraints are: required locked rotor torque, maximum allowable capacitor volts, maximum allowable locked rotor current, greatest current density in the auxiliary winding, and largest slot fullness that is permitted. A trial winding is calculated using estimated number of turns, a trial wire size, and a trial capacitor. The characteristic impedances are determined as a function of winding ratio, wire size, and capacitor size. For each wire size and capacitor, an auxiliary winding is determined which will meet the restraints if it is possible. The method is arranged to facilitate digital computer programming. The logical flow is such that the program will arrive at the best auxiliary or determine that no satisfactory design exists.

Respiratory Effects from the Passage of Polarizing Currents Through the Medulla Oblongata.

In a series of experiments now extending over several years we have been attempting to investigate the site and functioning of the central respiratory mechanism by exposing the posterior portion of the floor of the fourth ventricle and studying the effects of local cooling of that region and the effects of the application of certain drugs to it. It was felt that additional information might be gained by studying the effects of the passage of polarizing currents through this part of the brain stem for it seemed likely that if too great current density was avoided, it might be possible in this way to produce temporary depression of function without causing irreparable tissue damage.Twenty experiments have been performed. In all these, dogs anesthetized either with morphine and urethane or with pentobarbital were used. As one electrode we used the instrument which had previously served as our applicator in the experiments on central cooling. The silver chloride plated silver tip of this electrode, triangular...

Polarity in Lethal Action of Electric Current

Electric currents have been shown to be capable of directing or determining the growth of certain organisms of simple symmetry., , The present is a report of experiments in which the application of direct electric current resulted in partial death of the organism; the effect being localized in a polar fashion. The results given below were obtained with the Bryophyte Conocephalus. Lunularia and Marchantia reacted similarly but not as definitely. The plants were cleaned. Most of the rhizoids and the apex and base were clipped off. Current was applied through an agar bed (usually containing nutrients) upon which the plants were placed in intimate contact. It was found that death occurred in that part of the plant which lay toward the anode. This effect was not due to the creeping of toxic materials from the electrodes as suitable precautions were taken. Also, successive rows throughout the experimental dish were similarly affected while the region toward the cathode remained alive in all plants. The extent of the dead region increased with greater current density; also with greater duration of exposure. Larger pieces were more susceptible than small, i. e., the percentage dead region/plant size was greater. No difference was detected in quantity of effect between plants oriented in opposite directions; that is, apex and base were equally susceptible when turned toward the anode. Regeneration did not, of course, occur toward the anode, but was not absent elsewhere. As a result new growths were more frequently seen on plants turned with apex toward the cathode. This report is based on 116 plants which were subjected to direct currents of approximately ½ to 6δ for a period of time up to 350 hours. The dead region comprised 5 to 63% of the length of the thallus. Large plants (about 6 cm. long) showed about 20% more injury than small ones (1 cm. or less) for the same duration and density of current.

Some recent developments of high-current arcs, with special reference to searchlights

With ordinary carbons (i.e. carbons free from any special salts or mixtures) an improved efficiency in terms of the flux of light per watt expended is obtained by running at higher current density.(2) It is not possible to run an ordinary carbon arc with any degree of smoothness, steadiness or silence at a greater current density than 0.15 ampere per sq. mm. of the cross-section of the positive carbon, but if the arc stream be acted upon by a system of external magnetic forces tending always to keep it central, a current density of 0.31 ampere per sq. mm. can be attained with smooth and silent operation.(3) A device for producing the necessary external forces is described.(4) The use of this “control” renders the soft ”core” generally to be found in positive carbons unnecessary and even disadvantageous.(5) Ordinary solid carbons of greater diameter than 20 mm. must be copper coated in order to carry current the rating of at the 0.31 ampere per sq. mm. without becoming red-hot along their entire length.(6) For arcs at from 80 to 300 amperes a cored copper-coated negative of such diameter that the current density is about 1 ampere per sq. mm. of its cross-section has been found most suitable.(7) Whilst the impregnation of carbons with salts or other mixtures does make for smoother running in some cases and lowers the potential difference required for a given current and arc length in all cases so far tried, yet the total flux of light received in searchlight beams from such arcs at working ranges is much less than that from a plain carbon arc at the same current and current density, both absolutely and per watt expended.(8) In view of the fact that the National Physical Laboratory tests with impregnated carbons showed that they were only very slightly inferior in intrinsic brilliance to ordinary carbons, the absolute importance of outdoor photometric tests over working ranges is emphasized. The methods adopted are described.(9) The potential difference per mm. of arc length is lower with these high-current arcs than with the comparatively low-current arcs.(10) The potential difference between the carbon holders for constant-current “controlled” arcs increases with the arc length up to a certain length, when it suddenly falls and then steadily increases again. Investigations of this have been done principally with 200-ampere arcs at lengths of from 20 mm. to 84 mm.The drop in pressure occurs at a shorter length with impregnated carbons than with plain carbons.