Page 99 - Visions of the Future Chemistry and Life Science

88 P. W. MAY

or ‘ballas’ diamond, and may be considered to be an aggregate of diamond
nanocrystals and disordered graphite. Although this type of film might be
considered inferior to the more crystalline and therefore better quality
diamond films, it still possesses many of the desirable properties of
diamond while being much smoother and considerably faster to deposit.
Thus, by the simple expedient of changing the growth conditions, films
can be deposited with properties ranging from almost graphitic to essen-
tially those of natural diamond. This allows the quality, appearance and
properties of a diamond film, as well as its growth rate and cost, to be easily
tailored to suit particular applications. With the advent of high power
microwave deposition systems, it is now possible to produce CVD
diamond films over areas up to 8 inches in diameter and of thicknesses
exceeding 1mm (see Figure 5.6).

5.8 Applications

The applications for which CVD diamond films can be used are closely
related to the various extreme physical properties it exhibits. Some of these
applications are already beginning to find their way into the marketplace;
however, some, including some of the more sophisticated electronic appli-
cations, are still a number of years away. Until recently, the main issue pre-
venting the wide-scale use of CVD diamond has been economic – the
coatings were simply too expensive compared to existing alternatives.
However, as higher power deposition reactors become standard, the cost
for 1 carat (0.2 g) of CVD diamond fell below US$1 in the year 2000, making
the use of CVD diamond much more economically viable, and finally
allowing engineers the opportunity to exploit its vast array of outstanding
properties in a wide variety of different applications.

5.8.1 Cutting tools
The extreme hardness of diamond, coupled to its wear resistance, makes it
an ideal candidate for use in cutting tools for machining non-ferrous
metals, plastics, chip-board and composite materials. Indeed, industrial
diamond has been used for this purpose since the 1960s, and remains a
lucrative commercial process today. This involves either gluing the
diamond grit to a suitable tool (saw blades, lathe tools, drill bits), or con-
solidating the diamond grit with a suitable binder phase (e.g. cobalt or
silicon carbide) to make a hard, tough and durable composite. CVD