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The anodic behavior of copper, wrought 90-10 copper-nickel, and nickel aluminum bronze in chloride media have been examined using a rotating disc electrode (RDE) at Reynolds numbers of 80 ...

Corrosion rates of mild steel, AISI 316 stainless steel and hot-dipped galvanised steel in contact with preservative-treated Pinus radiata have been determined using four distinct accelerated (49 ± 1 °C) and non-accelerated (21 ± 2 °C) weight loss methodologies. The data were measured as a function of timber moisture content and copper concentration over periods of exposure ranging from 2 weeks to 14 months. The results show that the corrosion resistance of the stainless steel was not influenced by classification or magnitude of preservative loading. Corrosion rates of this material were multiple orders of magnitude lower than those of the mild and galvanised steels. In most instances, corrosion rates of hot-dipped galvanised layers in contact with alkaline copper quaternary-treated timbers were up to a factor of 10 times, or greater, than those measured for copper–chrome–arsenate treatments. A direct negative influence of copper ion concentration on the corrosion resistance of mild steel was also observed for each preservative type.

The anodic, chloride ion-facilitated dissolution of copper, wrought 90-10 copper-nickel, and wrought nickel aluminum bronze, in controlled aqueous chloride electrolytes, has been examined ...

The passivation characteristics of sulfuric acid cleaned mild steel in spent Bayer liquor (pH 14.4 and 160 °C) are examined using a high pressure nickel flow loop. An entrained atmosphere of 99.90% v/v oxygen gas is incorporated as an experimental variable along with Reynolds number (141,700 and 50,950) and intensity of fluid flow disturbance. State of passivation has been defined using criteria derived from transient polarisation resistance measurements and large-scale polarisation, linear sweep voltammetry. In the majority of cases, oxygenation introduces instantaneous passivation of the mild steel on contact with the Bayer liquor. In comparison to de-oxygenated and aerated electrolytes, this rapid rate of passivation can lead to up to an order of magnitude reduction in the quantity of charge associated with metal dissolution over 20 h. Although relative rates of corrosion when passive are low and largely independent of the level of flow disturbance, dissolution rates when passive are somewhat larger at the higher Reynolds number.

The cases of a sudden pipe expansion and a sudden pipe contraction are simulated within a flow loop-based test section designed to approximate disturbed conduit flow. Mass transfer rates to patch electrodes at selected positions within the test section have been measured using a limiting current methodology applied to oxygen reduction at copper in 3.5% wt./vol. NaCl. Using both large-scale polarisation linear sweep voltammetry and a potential step current transient technique with hydrodynamic steps, absolute and relative rates of oxygen mass transfer have been examined as a function of Reynolds number and location within the test section. The highest rates of oxygen transfer were observed both within the high velocity area of the test section and close to known regions of flow disturbance. Under the flow conditions used, patch electrode mass transfer relates to wall shear stress, which allowed areas of high mean and high fluctuating wall shear stress to be identified.

The flow-enhanced corrosion of mild steel has been examined in high-temperature spent Bayer liquor as a function of Reynolds number, fluid flow disturbance, and electrolyte aeration. ne electrochemical characteristics of the steel in this electrolyte was derived using a high-pressure nickel flow loop at 160 degrees C (total gauge pressure = 0. 7 MPa to 0.9 MPa). The influence of both a sudden pipe expansion and a pipe contraction on both corrosion rate and polarization behavior was quantified. Considering the mechanism of the corrosion reaction, electrolyte mass transfer did not directly control the electrochemical rates of either the cathodic or anodic currents at the corrosion potential. It is concluded that chemical modification and/or dissolution/erosion of passivating layers may have a strong influence over the metal loss of the steel observed in some alumina plants. Aeration of the liquor was found to be a significant factor regarding passivation rates and the corrosion characteristics of acid-treated steel, and it caused an overall increase in the rate of active and. passive steel dissolution relative to the deoxygenated state for all but one electrode. However, the time to passivation was relatively low at high fluid velocities (Re congruent to 141,500), which led to a 27016 to 509,6 reduction in metal loss over a caustic exposure time of 19 h. At low velocities (Re congruent to 50,900), time to passivation in the aerated liquor was also lowered, but not to the same order as that observed in the high-velocity area. Therefore, as a result of elevated reaction rates in the presence of oxygen, total corrosive losses over this short operating period were up to 37%, higher than that of the deoxygenated electrolyte. The results were essentially independent of the level off low disturbance.

Nickel–aluminium bronze (NAB) alloys show good corrosion resistance under marine conditions. The corrosion behaviour of cast and wrought NAB alloys is illustrated in this work through a range of electrochemical techniques including open-circuit potentiometry with time, oxygen reduction voltammetry, NAB dissolution voltammetry, potential step (or flow step) current transients and linear polarisation resistance. The galvanic coupling of NAB to stainless steel or copper is examined by zero resistance ammetery. The importance of using controlled flow working electrodes is illustrated by the use of a rotating disc electrode, a rotating cylinder electrode and a bimetallic (NAB/copper–nickel) rotating cylinder electrode. In addition to controlling the hydrodynamics, such electrodes allow charge transfer data to separate from those of mass transport control under mixed kinetic control. Longer term seawater immersion trials on planar coupons coupled to titanium or cupronickel are also reported. The relative contributions of erosion and corrosion attack are considered using a wall-jet electrode and the corrosion characteristics of NAB are compared to those of copper and copper–nickel in chloride media.

A bimetallic rotating cylinder electrode (having individual electrode areas of 10 cm2 and rotating at 200–1400 rpm) has been used to examine the corrosion and protection characteristics of copper/nickel aluminium bronze and 90–10 copper–nickel/nickel aluminium bronze galvanic couples in filtered seawater at 25 °C. The flow-influenced electrochemistry of the systems was determined using zero resistance ammetry, corrosion potential measurements and a potential step current transient technique. In each case, the galvanic corrosion potential and corrosion rate displayed a Reynolds number dependency where mass transport control of the anodic dissolution reaction partially controlled the reaction rate. Bimetallic impressed current cathodic protection (ICCP) has also been demonstrated for a range of applied protection potentials and Reynolds numbers. A comparison has been made between the directly measured bimetallic ICCP current demand and that determined from independent, single-metal rotating cylinder electrode measurements. In this case, the mixed charge and mass transport controlled rate of oxygen reduction was examined.

The literature dealing with the electrochemical corrosion characteristics of unalloyed copper in aqueous chloride media is examined. The enormous quantity of polarisation and mixed/corrosion potential data that has been made available in the literature over the last 50 years has been compiled and discussed in a comprehensive review. For a wide range of electrode geometries, the importance of the chloride ion and the mass transport of anodic corrosion products on the corrosion behaviour of copper are made clear for both freshly polished and ‘filmed’ surfaces.

A high-resolution method has been developed for the determination of localized values of interfacial reaction rate and mass transfer coefficient in aqueous solution. Scanning electron microscopy has been successfully applied to this problem through the measurement of electroplated film thickness formed under limiting current conditions. The method involves the calculation of local values of reaction rate via Faraday's laws and subsequent conversion of the data to absolute values of mass transfer coefficient. The technique has been verified in an undisturbed, turbulent flow regime (rotating cylinder electrode) through the use of Sherwood group dimensionless analysis. The resulting relationship shows comparable accuracy relative to electrochemical measurements. Favourable comparison has also been made with the generally accepted rotating cylinder correlation of Eisenberg, Tobias and Wilke. Differential rates of mass transfer to a single surface under conditions of disturbed flow have also been examined at a high spatial resolution using the stepped rotating cylinder electrode geometry. In this case, reaction rates have been measured as a function of circumferential distance within a recirculation zone situated immediately downstream of a backward-facing step.

This paper deals with the application of the principles presently employed in the design of directional antennas for the Standard Broadcast band to the control of radiation from TV transmitting antennas in order that optimum use is made of the energy radiated from such antennas. Until very recently TV antennas were designed primarily to concentrate the radiated energy in the direction of the horizontal plane and the greater this concentration the more desirable the antenna. During the past year the engineering profession has realized the importance of determining the nature of the area to be served by a given antenna system and then designing the antenna to cover this area most effectively with the power available. The need for such design is shown by several examples of problems already solved by this method and the general method of attack on the problem is developed in some detail.

This paper describes the objectives, mechanical and electrical problems and solutions, and final performance of the multiple antenna system for television and FM broadcasting on the Empire State building in New York City. A specially built steel tower supports six individual antennas from which there are transmitted five picture carriers, five sound carriers, and three FM broadcasting carriers with completely satisfactory freedom from the effects of mutual coupling. The paper describes the planning, execution, and results of extensive preliminary field laboratory work during which much basic information on such systems was obtained through the use of full-scale model antennas.

In January, 1959, the Television Allocations Study Organization authorized its Committee on Directional Antennas to conduct field tests on directional TV antennas looking toward development of a means whereby the operational antenna pattern could be determined and to explore the effect of reflections and anomalous propagation on the degree of directivity actually obtained as compared with that calculated. Tests were subsequently carried out at WBZ-TV in Boston, Massachusetts, and at WKY-TV in Oklahoma City, Oklahoma, with special directional antenna systems possessing various degrees of directivity. Measurements were made at distances varying from a few miles from the transmitter to well over 100 miles from the transmitter. Within the limits imposed upon the tests by the choice of sites, nature of the terrain, and a limited period of observation, it was found that propagation conditions did not materially affect the directivity of the array, even at distances where the scatter fields were of appreciable magnitude. In the course of these measurements and tests, a procedure was developed whereby the operational antenna pattern could not only be determined, but also rechecked at suitable intervals thereafter.