by Paula Wood-Adams
Professor Jean-Luc Meunier of the Department of Chemical Engineering never imagined at the beginning of his career that he would one day be making diamonds. As a student he was fascinated with space physics, an interest that took him in 1975 from his native Quebec to the École Polytechnique Fédérale (EPFL) de Lausanne in Switzerland, where he obtained his Bachelor of Engineering in Physics.
"At that time the fashionable area of study at EPFL was solid state physics," says Meunier. "But I wanted to be different. I wanted to study something new and unusual." This desire to study the unusual led to his interest in plasma physics and, ultimately, to creating diamonds.
More than 99% of matter in the universe is in the form of plasma, and the understanding of space physics depends upon the understanding of plasma behaviour.
"Plasma is simply the fourth state of matter," explains Meunier. If a solid is heated it will eventually turn into a liquid which, when heated further, will become a gas. If more heat or energy is added, the gas becomes plasma." Unlike the characteristics of the other states of matter, the characteristics of plasma can vary over enormous ranges of magnitudes. For example, the density of a plasma can range from 1 particle per cubic meter under nearly vacuum conditions to 1025 (106 is 1 million) particles per cubic meter in the middle of a star. "Over this incredible range, we can describe plasma behaviour with the same basic laws. I find this fascinating," says Meunier.
After finishing his undergraduate degree, Meunier returned to Quebec to do graduate studies at the Institut National de la Recherche Scientifique in conjunction with Hydro-Québec. For his thesis research Meunier studied the erosion of metal surfaces caused by exposure to plasma.
During shutdowns of high power electrical systems, electric arcs are formed that release large amounts of energy and heat up the surrounding gas to plasma conditions. This plasma erodes any metal surfaces that it touches, causing severe damage to the equipment.
The object of his research was to find ways to reduce the damage. It was this work that sparked Meunier's current passion, the study of plasma-solid interfaces, and led eventually to the work he is now doing at McGill.
Meunier is using the awesome power of plasma to turn methane--the major constituent of natural gas--into diamonds. Diamond is a valuable material not only for its esthetic qualities, but also because of its unique physical properties. It has useful electrical and good optical properties, and is able to dissipate heat quickly. Diamond is also extremely hard, chemically inert and has a low friction factor. Two diamond surfaces rubbing together generate less friction than two oil covered metal surfaces.
Meunier and graduate student Jörg Oberste-Berghauss are developing a process to coat cutting tools such as drilling heads with diamond films. Diamond coatings slow down the normal wear and tear on these tools and allow them to be used much longer.
To produce diamond films, an induction plasma torch is used to supply heat. The plasma torch is generated by passing a high frequency alternating current through a metal coil that induces a magnetic field within the coil. A mixture of methane, hydrogen, and argon is injected into the center of the coil and a secondary electric current caused by the magnetic field heats the gas up to 10,000 degrees Celsius-plasma conditions.
A plasma flame shoots out of the end of the coil and heats the surface where the diamond is to be deposited. At this point the components of the gas are completely broken down into carbon, hydrogen and argon ions and atoms. The carbon atoms attach themselves to the surface in the unique crystalline structure of diamond, while the role of hydrogen is to prevent the formation of graphite. The resulting diamond films are very thin and virtually invisible but they increase the durability of the surface dramatically.
Meunier's ultimate objectives are to increase the size of the surface that can be coated and to be able to apply a uniform coating to complicated forms. "I want to develop a technique for spraying diamond films onto any imaginable shape of tool," he says.
To do this, the rate at which the diamond is deposited must be increased and the factors affecting the surface uniformity identified. Meunier says he and Oberste-Berghauss will examine in detail what is happening at the plasma-solid interface using a small probe.
"By placing the probe at different places within the plasma torch, we can study the spatial effects on the film's uniformity. Once these effects are understood, we'll look at other important variables such as temperature, and composition of the gas. Our work is really just beginning."