Robert Walker

The morphology and properties of electrodeposited copper powder

Abstract Copper powder was produced by electrodeposition from an electrolyte containing copper sulphate and sulphuric acid. The effect of varying the current density, the solution temperature and agitation as well as the addition of different chemicals was investigated on the size, shape and properties of the powder and the energy consumed. The best conditions were found to be a low current density, a high bath temperature, solution agitation and a low concentration of copper sulphate. The addition of sodium sulphate, cupric chloride and benzotriazole was beneficial and reduced the energy consumption.

High throw copper sulphate bath with chlorides

Abstract The throwing power of the plating solution was shown to improve with a decrease in the concentration of the copper sulphate and an increase in the concentration of sulphuric acid. With a low copper sulphate content, however, the cathodic current efficiency fell, hydrogen evolution occured and powdery deposits formed. Good results could be obtained with about 60 (g CuSO 4 ) l -1 and 150 (g H 2 SO 4 ) l -1 . The presence of sodium chloride in the bath affected the surface appearance, structure, microhardness and internal stress. An addition of about 50 (mg Cl - ) l -1 seemed to be the optimum and permitted an increase in the maximum microhardness but did not raise the internal stress.

Determination of the nernst diffusion layer thickness in the hydroson agitation tank

Abstract The thickness of the Nernst diffusion layer in the hydroson tank is calculated from the limiting current density for zinc electrodeposition from the sodium zincate bath. The value is determined using a modified form of the equation for a rotating cylindrical cathode and also from the Vielstich equation for turbulent flow across a plane surface. Another estimation of the thickness is calculated from the change in the pH measured at a cathode-electrolyte interface which involves the precipitation of magnesium hydroxide detected by electron spectroscopy for chemical analysis. From this work the thickness of the diffusion layer in the Hydroson tank at the focal point between two jets is considered to be 13.5 μm at the corresponding flow rate of 1.16 m s -1 .

Determination of the flow rate in the hydroson cleaning system

Abstract In this paper the values of the rate of flow of aqueous solution in the Hydroson system as determined by a physical technique and by an electrochemical method are compared. A brief description is given of the Hydroson system and its use in the cleaning of surfaces and the electrodeposition of zinc. The effect of agitation of the plating bath is also covered. Zinc was deposited from an alkaline zincate solution onto stationary steel cathodes in the form of a flat sheet in the Hydroson tank and onto a cylindrical rod which was rotated at different speeds in a static solution. The surface appearance and hardness of the different deposits were compared and deposits from the Hydroson system were found to be similar to those obtained with a rotation speed of 1500–3000 rev min-1. The flow rate through the Hydroson jets was measured and this was similar to the value calculated from the limiting current density for the cylindrical cathode rotating at 356 rad s-1.

CONTAMINATION OF POTABLE WATER BY CORROSION OF TIN-LEAD SOLDERED JOINTS

This work was undertaken as part of a contract from the Department of the Environment to investigate the potential of materials used in plumbing systems to contaminate the supply. Particular attention was paid to soldered joints as these will constitute the major source of lead contamination in the future. This report describes a galvanic corrosion cell for measuring corrosion rates of solder in potable waters and the work to establish that its corrosion behaviour reflected that of an authentic soldered joint. The work has established that more than a quantitative difference exists between the galvanically mediated corrosion of lead and that of the freely corroding metal. Qualitative differences also occur that are of significance to the Water Industrys treatment approach to reduce lead contamination problems. The test cell was used to investigate the effect of various water quality parameters on corrosion rates. The parameters found to stimulate corrosion were low pH and high chloride and nitrate concentrations. Sulphate, silicate and zinc were all found to reduce corrosion. Zinc was discovered to be an inhibitor from an investigation into the effect of flux residues. The material used contained zinc chloride as the active ingredient. Carbonate hardness and orthophosphate were both found to be without effect on corrosion rates. This was surprising, especially as the latter is successfully used to overcome contamination problems from lead pipe. Using the corrosion rates measured in this work, attempts were made to quantify the contamination risk from soldered joints. The general conclusion was that only by limiting the area of solder exposed in the bore of the tube could a significant long term problem be avoided. As this depends upon the individual skill of the person making the joint, the only sure way of avoiding contamination is to specify lead free solders.

Electrodeposition from hydrosonically agitated solutions

Abstract In this paper the publications describing the concept and action of the Hydroson system together with the current applications to industrial practice are reviewed. A description is given of the research carried out at the University of Surrey on cleaning and electrodeposition in order to elucidate the mechanisms involved in hydrosonic agitation. It is concluded that the action is not produced by cavitation, so that it differs from ultrasound, but is due to the impingement of high pressure jets of liquid at immersed surfaces. The flow rate at the focal point of two jets is shown to be 1.79m s−1. The thickness of the electrolytic double layer is reduced to 13.5 μm compared with 29 μm in a stirred solution. The combination of these two effects is to accelerate the cleaning processes and to reduce the concentration polarization during electrodeposition so permitting the use of higher current densities.

High-velocity oxygen fuel spray coatings for reclamation

Abstract These coatings are produced by a spray of molten powder in a system which has recently been developed utilizing a high-velocity fuel mixture of oxygen-propylene or oxygen-hydrogen. These gases are ejected at high speed from a nozzle and then ignited externally to form a flame which envelops the spray material. A high-velocity flame of compressed air carries the molten powder to a specially prepared surface where it solidifies to form a very dense coating of high bond strength and low porosity. The composition of the coating can be varied and depends upon that of the powder, the most commonly used for reclamation being based on either iron or nickel or tungsten carbide. During coating, the substrate temperature is held below 423 K so the process is considered ‘cold’. The spray coatings have good adhesion with low porosity. The high hardness and cost competetiveness means that they are beginning to replace electrodeposited nickel and chromium which have long been used for the repair of engineering components.

MANUFACTURE AND CORROSION OF LEAD SHOT FROM THE FLAGSHIP MARY ROSE

Abstract The corrosion resistance of lead-iron shot was found to depend upon the method of manufacture. Shot in which the lead had been wrapped around a sphere of cast iron suffered relatively little corrosion. Those made by casting molten lead into a mould containing a cube of wrought iron corroded where the corners of the iron were exposed to the seawater, that is, bimetallic corrosion occurred. The lead corroded to give a complex mixture of compounds which formed a protective layer. The iron had corroded badly and the metal exposed on cross-sectioning suffered from filiform corrosion. Hence it is essential to protect any remaining iron from the aggressive attack of chloride ions and moisture.

Hydroson Cleaning of Surfaces

Hydroson generators produce sonic waves in solutions, and the system can be fitted to a tank to clean immersed, contaminated articles. It was patented(1) in 1973 and then developed and transferred to the new company Nickerson Ultrason Ltd. in 1976. It is now widely used with over 150 installations employed in Europe, Japan, South Africa, and the USA.