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Electrochemical

Naomi Johns Waltheof School, Sheffield

Introducing electrochemical Anodising acid and are eaten away. Protected areas metalworking into school allows There is a natural oxide film which remain untouched and so surface children to use in a creative forms on the surface of decoration can be produced. fashion. When designing small scale when it is exposed to the atmosphere. The corrosive action of the acid is decorative metalwork projects, thought This film protects the metal giving it called the 'bite' and the acid-proof can be given to the various different resistance to corrosion. The process of material used for stopping out various ways of creating , texture and the anodising increases the thickness of the areas, the 'resist'. Nail polish, wax and use of colour. Because these techniques oxide film and so increases the stopping out varnish are examples of can be used in any workshop area and protection of the . The film is suitable resists. Once applied, the resist don't have to take place in a porous and so can be dyed using either should be left to dry out thoroughly metalworking environment, they may be the recommended dyes or Dylon fabric before being submerged in the acid bath. a useful step in moving away from the dyes. The results will differ depending Any chips or gaps in the resist will also idea that working with metal is on the dye used. The purer the be eaten away so it is important to check synonymous with heavy machinery and aluminium, the better the results tend to that the cover is a good one. oily white coats! It is also relevant that be. As a general rule, extruded As the metal is etched, tiny bubbles some electrochemical processes such as aluminium is purer and so better results stick to the surface and prevent the acid afford a useful insight will be achieved with this rather than from making good contact. These into important industrial technology. sheet material. bubbles need to be dispersed by stroking The amount of space required is The process of anodising is carried the with a feather or by using minimal although some time is out in a tank containing a solution an agitator. The work should be necessary to set up the equipment and of around 10% sulphuric acid, 90070 removed from time to time to check make up the chemical solutions. If an water. Tap water can be used though progress. Once sufficient depth has been area of the workshop is set aside for distilled water is recommended. An etched, the stopping out medium can be such purposes and the equipment is approved power supply of between dissolved using turps or thinners. readily available for use, then these 12-22 volts is needed. The bath is set up For or a solution processes can be easily incorporated into with the article being anodised of 1 part ferric chloride to 1 part water many existing projects, making them the anode and the plate the cathode. can be used. When etching aluminium more exciting and varied. Any such area Once the circuit has been connected, the the solution is weaker, usually I part definitely needs to be next to a sink process takes between 20-30 minutes. If ferric chloride to 3 parts water - which because of the chemicals and acids a deep colour is required, the film etches quicker if the solution is heated. which will need to be rinsed from the should be allowed to increase in When making up a solution, acid should work. thickness for about 40 minutes. always be added to water to prevent a Prior to introducing one or more of The aluminium should be suspended dangerous reaction. the following techniques into the CDT in the tank using aluminium wire as the curriculum, teachers may wish to acid will react with other . Wax Electroplating and electroforming experiment themselves and find out the can be used as an effective stopping out Electroplating is a method of coating a potential of the processes. Results are agent for areas where no oxide coating is conductive surface with a thin layer of easy to achieve, but a little required. Hydrogen gas is emitted metal. Electroforming is similar but the experimentation will be crucial if good during this operation and so work time involved is greater, the idea being to and predictable results are to be should be carried out in a well ventilated build up a thicker layer of metal. This is obtained. room. It is advisable to put some sort of done by onto a model or This is not intended to be a detailed cover over the tank as the solution may which is made from either a guicie but a brief look at four techniques spray out slightly. conductive material or a non-conductive which could be used successfully with The stages of the operation are as material which has been treated to make both lower and upper school pupils. In follows: it conductive. some instances, extra information may 1. degrease the aluminium When a direct current is passed be deemed necessary and some 2. rinse in cold water through an appropriate electrolyte references are given at the end of the 3. ariodi~,e between two metal plates or partially article. 4. rinse in cold water conductive materials - one connected CHILDREN NEED TO BE WELL 5. dye in warm (60°C) dye. The colour to the positive side and one to the INSTRUCTED IN THE SAFE USE OF is altered by changing the negative side of a power supply - ANY CHEMICALS. GOGGLES AND concentration of the dye solution, charged metal particles (ions) are RUBBER GLOVES SHOULD not by increasing the immersion released into the solution migrating ALWAYS BE WORN AND WORK time. The metal should be boiled in from positive to negative. The cathode is SHOULD BE CARRIED OUT IN A the dye solution for about 5 minutes made the workpiece and so through this WELL VENTILATED AREA TO to seal the colour. process receives a film of metal. SAFEGUARD AGAINST ANY Most of the information available FUMES THAT ARE GIVEN OFF. IF Etching about electroplating and electro forming IN DOUBT, ASK AN EXPERT. Etching is a metalworking technique is largely related to industry and is very where areas of metal are exposed to an detailed. This sort of detail is Right: This copper decoration wasgrown onto a wax model.

inappropriate if the techniques are to be used in school workshops. Copper plating is the most suitable because the necessary materials are readily available and because good results are easy to achieve. The copper plating solution (electrolyte) is made up as follows: 2 Y2 litres water 30 grammes alum powder 550 grammes copper sulphate 65 grammes sulphuric acid The anode is a copper sheet and the cathode is the workpiece. A variable direct current supply of between 2-12 volts is required. This could be a number of HP2 battery cells placed in series or an approved power pack of the type often found in schools. The simplest application of the plating technique and a good one to test if the operation is working satisfactorily, is to plate copper onto brass sheet, areas of which have been stopped out with varnish to make them non-eonductive and therefore Electroformmg, where an article may Any surface colouring will rub off in unable to plate. In this fashion surface have to stay immersed in a tank for up to time if the piece is to be handled decoration can be developed. The 6 hours, is not a process which can be regularly, therefore any colouring in plating process should be carried out as used throughout a lower school group recessed areas is going to be more follows: but may provide interesting ideas for permanent. For this reason, the 1. clean the brass with metal polish work with smaller upper school groups colouring of metals compliments the 2. stop out the areas which are to and GCSE candidates. Lower school effects achieved through electro forming remain brass work may be more limited to simpler and etching. 3. connect the workpiece into the plating techniques but even within these The four processes outlined above can circuit (by means of a crocodile clip confines interesting and be used together in a number of or metal ) and suspend in the decorative can be developed. interesting ways. Colouring aluminium electrolyte by anodising can be made more varied if 4. remove after a few seconds to check Metal colouring the surfaces are textured first by etching that plating is taking place Metals have been chemically coloured and electro formed copper can be 5. leave to plate until required throughout history and a recent revival coloured using a chemical recipe. thickness has grown of interest has been partly due to the Because the results are rarely 6. rinse in cold water and clean off Hughes and Rowe 1984 exhibition and predictable, the introduction of varnish. the subsequent Council electrochemical metalworking into COT A non-conductive surface such as publication. The book is full of recipes will help children to work in an acrylic sheet can be made conductive by and techniques many of which are exploratory fashion. Often the applying conductive paint. A copper suitable for use with copper and brass. unintended 'mistakes' will be as layer can then be grown onto the plastic. There are many colour plates which interesting as the original idea. Most materials can be treated to make show the range of exciting results which them conductive and can then be used as can be achieved. Recipes for interesting For further information: a mould on which to grow a copper mottled effects, green, black and many The British Anodising Association, coating. This can either be left as a other colours can be found which use Broadway House, Calthorpe Road, Five permanent decoration on the surface or harmless chemicals and so would be Ways, B15 ITN. Tel: 021 can be peeled away from the material on ideal for COT projects. The colouring is 4550311 which it was grown. Wax can be used to carried out by using a variety of The Colouring, Bronzing and make 3 dimensional moulds if graphite methods some of which involve leaving Patination of Metals, Hughes and Rowe, powder is melted into it to make it the workpiece in sawdust which has been The Crafts Council, 1984. conductive. The graphite powder should dampened with chemical solution for a Electroplating and Electroforming on also be dusted over the surface to few days, other results can be achieved a Small Scale, send an SAE (A4) and £2 improve conductivity. Once a sufficient more immediately by applying the postal order or cheque made payable to thickness of copper shell has developed, solution to a heated metal surface. N. Johns to WaltheofSchool, the wax can be melted out. Beaumont Close, Sheffield, S2.