Liquid gold?

Electroplating, the key to reducing corrosion, is hazardous and inefficient. Now there’s a coatings technique that is claimed to be environmentally friendly and cost effective. Christopher Sell reports.

Researchers at the University of Leicester have developed a technique for treating metals which could have environmental and economic benefits for a wide range of industries, including aerospace and automotive.

Developed through spin-out company Scionix — the world’s largest manufacturer of ionic liquids — ionic liquid technology is claimed to be a sustainable, environmentally-friendly method of electroplating chromium and other metals.

Ionic liquids, essentially salts that are fluid at room temperature, are able to dissolve many different organic and inorganic materials, including the trivalent form of chromium, which, owing to its relatively low toxicity, is attractive for electroplating operations.

According to the DTI, metal corrosion costs developed countries an annual three to five per cent of their GNP. In the UK this amounts to approximately £40bn. Electroplating is a key technology in reducing corrosion and one of the most widely-applied coating processes in the industrial world. providing a high resistance to corrosion and producing a tough, low-friction surface, it plays a key role in civil and military aerospace, industrial hydraulics and the automotive and maritime industries.

Despite this, electroplating has changed little over the years. It is inefficient and uses mineral acids that are hazardous and polluting. Scionix research director Dr Andy Abbott explained that the process uses acid-based electrolytes containing hexavalent chromium, whose toxicity and carcinogenic properties means recent legislation such as the EU End-of-Life Vehicle Directive is restricting its use. In contrast, ionic liquids are non-volatile, and avoid the production of toxic chromic acid vapours and large amounts of hydrogen.

As well as its environmental benefits, Abbott said that his technology also uses far less energy than existing processes. ‘Liquid coating gives us up to 90 per cent efficiency, while general plating techniques offer up to 20 per cent,’ he said. ‘There are many process benefits — for instance, good corrosion resistance and the fact that there is no need to pre-treat surfaces before putting the material down. It is cutting out several phases of production.’

Abbott is also looking into using the technology to improve resistance in metals through electropolishing, which is another effective way of increasing corrosion resistance. Electropolishing components also decreases wear and increases lubricity in engines, thereby eliminating a major cause of engine wear.

As in electroplating, current processes employ harsh acids which are corrosive and must be neutralised before disposal. Scionix has developed alternative electropolishing technology using ionic liquids based on choline chloride, which are said to be more efficient, provide improved surface resistance and reduce environmental impact.

‘In general we are targeting the production industry — the people who make the metal deposits and those companies who would normally process materials,’ explained Abbott. He said that such companies typically coat for a variety of industries, mostly aerospace, automotive and other engineering, which involves anti-corrosion.

It is hoped that the first industrial-scale processes will be in operation within five years. At present, wear-resistant, low-friction coatings suitable for hydraulic systems are being tested for the aerospace industry by UK engineering group Smiths Industries.