from R&D Innovator Volume 2, Number 19
Discovering a Material That's
Harder Than Diamond
Wentorf is Distinguished Research Professor of Chemical
Engineering at Rensselaer Polytechnic Institute.
He is a member of the National Academy of Engineering, has
been granted 44 U.S. patents, and has received the Ipatieff Prize
from the American Chemical Society.
scene is General Electric Research and Development Center.
The year is 1957, about two years after we had learned to
make diamonds from graphite at very high pressures (50,000 atm.)
and temperatures (about 1,500 ˚C) using molten transition
metals as catalysts. We
had this marvelous high-pressure equipment, which gave us unique
opportunities to explore conditions heretofore unavailable in
our success with diamonds had given us a breathing space from
funding problems, as well as improved equipment.
So we were unusually free to explore.
boss, Tony Nerad, was a remarkable leader.
One of his maxims was that if you weren’t having a good
time, it was your own fault.
(Only later did I begin to understand the profundity of
this simple statement.) He
also felt that working scientists should be shielded as much as
possible from bureaucratic concerns.
Tony visited each of his more than 20 scientists once a
week and spent at least a half an hour chatting about their work.
He often boned up on a particular subject before these
visits so he could contribute to the discussion—or could find
ammunition that would shock us into seeing things in a new way.
His insights were often remarkable, and he was a reliable
source of encouragement in the face of difficulties.
When you dealt with Tony, you were dealing with intuition
in big batches.
New Diamond-Like Material
and I started talking about the analogies between carbon and boron
nitride, and whether a diamond-like form of boron nitride would
form at extreme pressures and temperatures. We got a pound of fairly pure boron nitride powder, but
nothing I tried seemed to do anything to it.
one is on new ground, the only way to discover the ground rules is
to try many things. Of
course, one is guided by basic principles, but the main idea is to
make mistakes as fast as possible, and never to repeat a mistake.
I find that a brief (15-30 minutes) meditation can clear my
mind and give me the freshness I need to choose and hold several
things in awareness simultaneously and compare them.
This solitude also gives me the sensitivity to become aware
of and pull in the new considerations which float around the
periphery of consciousness, and connect them to the problem at
hand. When I am
tired, these happy things simply do not happen.
I might add that Tony recognized the importance of a calm,
clear mind, and did his part in helping us attain it.
to that point I had been trying to change the boron nitride by the
seemingly logical approach of trying materials which were known to
have catalytic powers for something or other. Such materials would include many of the transition metals,
but would not include magnesium, which was regarded as a simple
salt-former and which had no effects to speak of in diamond
having failed, I became more open-minded, and so one day, as part
of the “make the maximum number of mistakes” approach, I put a
bit of magnesium wire in the soft boron nitride and gave it the
high-pressure, high-temperature treatment.
While dissecting the specimen under the microscope, I saw
some dark particles adhering to the remains of the magnesium wire.
These particles could scratch a polished block of sintered
boron carbide, something that only diamond was known to do. Clearly, this was an interesting synthesis.
smelled ammonia, which implied that magnesium nitride was present
and reacting with moisture in the air.
When I put the specimen into dilute HCl as the first
cleanup step, I smelled traces of boron hydrides, suggesting the
presence of magnesium borides.
So evidently the magnesium had at least reacted with boron
nitride, which was encouraging.
we used freshly made magnesium nitride instead of the magnesium
wire, the hard particles were white or colorless and had a cubic
crystal structure. Soon
I found that these cubic boron nitride particles were relatively
fireproof and could scratch
was interested—and ready to follow up.
a few months, we developed fairly effective procedures for
synthesizing cubic boron nitride, which we named “Borazon.”
The effective catalysts were, generally speaking, the
alkali and alkaline earth nitrides which, when molten at high
pressure, are powerful solvents for boron nitride. How obvious it seems in retrospect: “like dissolves like”—one nitride dissolves another!
The department which synthesized commercial diamonds made
some test batches, and tried it as an abrasive.
Borazon wasn't cost-effective for many applications.
For a few years, it was an invention without an
we found that cubic boron nitride was excellent for grinding hard
steels and nickel-based alloys, for which diamond isn't
reason lay in its relative chemical inertness towards iron, nickel
and cobalt, even at the high temperatures found at the interface
between the abrasive and the metal.
This has led to a multi-million dollar industrial
technology, using machines especially built for cubic boron
nitride, to manufacture high-precision steel and other alloy parts
and to sharpen high-speed steel tools.
attention then turned back to diamond for a few years, as we
sporadically sought methods for growing large, high quality
crystals (“gems”). Eventually,
in 1979, we succeeded. The
essentials of this method—namely to allow diamond to dissolve in
a hot portion of a liquid metal melt at high pressures and grow
slowly on a cooler seed—were discovered while trying to answer
certain puzzling questions about diamond growth.
Then, as a by-product of those studies, we unexpectedly
found effective ways to sinter diamond powder into extremely hard,
tough cutting tools and wire-drawing dies.
They have been an outstanding industrial success.
success with diamonds suggested that sintered cubic boron nitride
tools might be useful. As
in the original boron nitride synthesis, the experience with
diamond was only slightly helpful—the chemistry of boron nitride
is different. I had a
hunch that a thin film of boron oxide on the crystals interferes
with their bonding together, and I knew that aluminum was potent
enough to reduce boron oxide—but how to add just the right
amount of aluminum in the proper form took more than a year to
work out. This search
was greatly accelerated by colleagues who devised rapid,
significant tests to evaluate our experimental products.
It was a happy time.
Observations on Exploratory Work
takes time for me to grow used to new concepts and be able to work
with them. It takes
days for a solution to a problem to form in my mind and be
recognized, it seems almost obvious.
And then it takes days for me to realize that my first
solution may not have been the best one.
There seem to be no rules or algorithms for solving many
scientific or technical problems—the solution instead embodies
entirely new concepts or views which seem to be hidden until
discovered, so that a direct frontal attack on the problem is a
waste of time.
years of trying to solve problems, it becomes habit-forming, and I
make up problems of various kinds to solve for the fun of it.
I suppose many artists do the same thing; I have always
felt a certain mutual bond when I talk with artists, most of whom
are continually trying to solve a problem for the first time.