An engineer's best friend

Diamond coatings are becoming more common - you can even buy diamond film-coated razor blades at your local chemist.

These coatings aren't as hardwearing as a real, engineering-quality diamond film on steel, which would be useful for wear-resistant tools and process equipment parts.

These films are very hard to achieve: the carbon atoms have to be deposited onto the surface, and to adhere properly, the first atoms must penetrate the surface. On some types of steel, this just doesn't happen. The carbon atoms form iron carbides within the metal surface, and this isn't a good substrate to grow diamond crystals. Graphite tends to form instead.

A Dutch chemist, Ivan Buijnsters, believes he has found a solution to the problem - an extra layer, between the steel and the diamond, to act as both an adhesive and a substrate. He used a deposition method to build up the diamond film, allowing a stream of methane diluted in hydrogen to flow over a stainless steel sample, heated to 600 degrees C, and dissociating the methane on a hot wire just above the metal surface.

He achieved his best results when the steel had been precoated with a film of boron. This adheres well to the steel surface, and encourages the growth of diamond crystals (see picture).

Moreover, it ensures that the surface of the steel and the diamond film contract at roughly the same rate as they cool, which prevents the coating from flaking away from the surface.