Gem of a solution

Diamonds aren't forever. Known as the hardest material in existence, diamond is, in fact, rather vulnerable stuff, subject to chemical attack on several fronts.

And while diamond has many uses in engineering, it is a hard material to work with; while it cuts through anything, keeping it in place in a cutting tool is not easy. However, a UK-based engineering coatings company now claims to be able to fix industrial diamonds in place and protect them from harmful environments without compromising their hardness.

Hardide, which is based near Oxford, specialises in ultra-hard coatings, particularly tungsten carbide. 'We mainly coat stainless steel, to protect it in arduous applications,' said technical director Yuri Zhuk. 'We've developed our own technique for applying the coating, where we form the crystalline tungsten carbide directly on the surface of the metal.'

This technique, a form of chemical vapour deposition (CVD) where tungsten hexafluoride is reacted with a carbon-containing gas, forms the basis of the diamond protection system. 'This isn't primarily to protect the diamond from wear,' Zhuk said. 'In fact, it's mainly to keep the diamond in the tool.'

One problem with diamond, Zhuk said, is that it's very hard to get anything to stick to it. Most drills or saws that use diamond as a cutting element use a metal matrix to grip the diamond mechanically, in the same way that diamonds are set in jewellery using a claw-like setting. But when the tool is in use, this matrix wears away and eventually the diamonds just drop out.

The tungsten carbide coating, applied in a similar way to the CVD process, forms a chemical bond to the carbon atoms in the diamond and bonds strongly to the metal body of cutting tools. In effect, Zhuk said, it acts as a glue between diamond and steel.

'We test the bond by pulling on the diamond and we've found that it's so strong that the diamond fractures before the bond breaks.'

The coating also protects the diamond from the steel. The iron component of steel is not diamond-friendly, Zhuk explained — it catalyses a reaction that eventually turns the diamond into soft graphite. With the tungsten carbide layer both binding the two materials together and forming an impermeable barrier between them, the tools last much longer.

The company has been granted a patent for the coating process and its application to diamond tools and hopes to exploit its discovery in the mining, oil and gas and construction markets.

According to Hardide chief executive Jim Murray-Smith, the global diamond tool market has estimated annual sales of $5bn (£2.6bn) 'and is based largely in the oil and gas sector, where we have a proven track record'. He added: 'Our plant in Houston, Texas opened on 1 September and is ideally located to capitalise on the potential of this coating in the US oil and gas market.'