November 1, 2005

Diamond coating shows promise

By using diamonds to help coat plastics and metals, engineers may soon bring this new technology to aerospace, engineering, and medical applications.

Engineers can coat medical implants and engineering components with a diamond-like carbon (DLC) material to make them harder wearing, reduce friction between components, and provide lightweight corrosion protection, said Professor Joe Franks of Brunel University in West London at the Novel Applications of Surface Modification conference.

DLCs, unlike diamond and other coating materials, can deposit on a surface without having to heat the component to several hundred degrees, Franks said. This means engineers can coat plastics, as well as metals and ceramics, with DLCs.

The Brunel team developed new DLC coatings for mechanical and biomedical applications. Mechanical applications include new coatings for drill bits and abrasive materials, non-clogging tungsten carbide milling inserts for engineering applications, and more efficient, lower friction, automotive components that are more fuel efficient.

DLC coatings are also biocompatible and unlike other types of coating don't trigger the coagulation of blood. Franks reported they have already provided surgeons at the Royal National Orthopaedic Hospital (RNOH) with DLC-coated knee implants for patients allergic to the metal used.

Researchers first discovered DLC in 1971 in a vacuum chamber using a technical and costly method that involved spraying charged carbon atoms at the surface they wanted to coat. Franks and his colleagues have developed a more effective method known as plasma-assisted chemical vapor deposition. The component that will undergo coating mounts in a vacuum chamber on an electrode connected to a high-energy radio wave transmitter. A hydrocarbon gas, such as methane or natural gas, pumps into the chamber, and the radio waves tear apart the hydrocarbon molecules and strip off the electrons from its carbon atoms to produce positive carbon ions. These ions attract to the negatively charged component to produce the coating.