By MALCOLM W. BROWNE
By unintentionally substituting the wrong gas for one they intended to use
for hardening tools, workers at a small metallurgical company have
accidentally hit upon a potentially valuable method for coating objects with a
hard diamond film.
Specialists trying to learn why and how the method works warn that it has yet
to prove its worth in industrial processing. But if the new diamond-coating
technique proves to be as cheap, fast and effective as its inventors say, it
may revolutionize the manufacture of machine tools, automobile engines, ships,
beverage cans and much more, materials experts say.
Although the discovery was made two years ago, it has not been reported in
scientific journals, and information about it has spread mainly by word of
mouth. Nevertheless, it has spurred excitement among potential users,
including the armed forces and the automotive and packaging industries.
The discoverer of the new method is Pravin Mistry, a 43-year-old British
metallurgist who founded a small, privately owned engineering company, QQC
Inc., in Dearborn, Mich., as an affiliate of Turchin Inc., a maker of machine
tools. Mistry's company specializes in applying coatings to industrial objects
slotto impart desirable properties.
"This is an interesting instance of technology leading science," said Dr.
Rustum Roy, who heads the Diamond and Related Materials Center at Pennsylvania
State University. "There is no question that this fellow is coating all kinds
of things with diamond, and doing it astonishingly rapidly and well, under
conditions that no scientists imagined would work."
Part of Mistry's method involves four powerful and finely tuned laser beams,
which interact as they scan the surface of an object as it is coated.
As Mistry explains it, the scanning takes place in a gaseous environment, and
the intense heat at the spot where the lasers converge breaks up some of the
gas into an electrically charged plasma. The lasers also vaporize a very thin
layer of the object being coated.
Roy, who is investigating the process at Penn State, believes that chemical
reactions occur between the surface of the object and the ionized atoms of the
gas, forming an ultrastrong bond. By continuing to deposit atoms from the hot
gas on the coated object, the thickness of the coating can be rapidly
increased to thicknesses up to a half inch, Mistry said.
"This technique might be used to produce many different kinds of coating
besides diamond, and it could be engineered for special requirements," Roy
said. "It takes only a minute or so to apply one kind of coating, and you
could use several coatings on the same object. For example, you might want to
coat part of a gear to harden it and another part of the gear for corrosion
resistance."
In 1994, Mistry's group made its discovery while using this interacting laser
technique to apply a coating of hard titanium diboride to the surface of an
aluminum object. An error in their procedure set the stage for a surprise that
may prove to be immensely profitable for all concerned: someone accidentally
substituted carbon dioxide for the nitrogen gas used in the process. A dense
coating formed rapidly, but it did not consist of the intended titanium
diboride. It turned out to be diamond.
News of the discovery spread rapidly among materials experts, who were amazed
that Mistry's technique for coating objects with diamond films was reportedly
1,000 times faster than existing diamond-coating techniques. Moreover, the
Mistry process promised to form particularly strong bonds between the coating
and the metal objects to which it was applied, a vital requirement for
hardened machine tools.
The U.S. Navy, Army and Air Force, and the Defense Department's Advanced
Research Projects Agency, as well as automotive companies, are following
developments with interest.
"I have seen objects coated using Mr. Mistry's process, and I can verify that
the coating is diamond," said Dr. Robert Pohanka, director of materials
research at the Office of Naval Research in Arlington, Va. "I have visited the
plant and seen the equipment.
"The key issue will be cost," he said. "Can you make things at reasonable
cost using this technique? How large an object can be coated? How strong is
the bonding between the object and the coating? These questions all must be
answered."
Mistry said in interviews that the technique was in its infancy, but that all
indications suggested that the coating was cheap and could be applied in
closely controlled shapes and thicknesses, with excellent adhesion to objects.
If the Mistry process lives up to expectations, Pohanka said, it could be
used to apply hard coatings to gears and bearings, to cover pumps and other
machinery with corrosion-resistant coatings, to protect the windows of combat
vehicles from scratching and erosion, and to harden engine components to
reduce wear.
Roy, whose research group has undertaken an investigation of the scientific
basis of the Mistry process, believes it could be used almost like a paint
brush to apply coatings of diamond or other special materials.
"Mr. Mistry's equipment is operated by robots under computer control," he
said, "and since the method is so flexible, it might some day be possible to
coat an entire ship's hull with a film made of diamond or some other
protective material."
Mistry has applied for more than 30 patents covering various aspects of his
invention, and several have already received approval, he said. He predicts
that his method will find widespread application in special tools and dies
that can machine aluminum and other metals without requiring a liquid coolant.
Coolants, which remove heat from objects being machined, pose environmental
problems. Scrubbing every trace of coolant from a metal object is expensive,
particularly when the object is an aluminum beverage can that must be
absolutely clean.
Diamond-coated tools, Mistry said, aid the "dry machining" of aluminum engine
blocks, beverage cans and many other things. In conventional machining, the
object being shaped heats up, but in dry machining, most of the heat is
carried away by chips and filings that fly off, leaving the object being
machined relatively cool. But to work, the tool must be extremely hard, and
diamond coating is a way to achieve the necessary hardness.
For more than a decade, toolmakers and other manufacturers have experimented
with diamond coatings applied to objects by a process known as chemical vapor
deposition, or CVD. Ordinarily, the object to be coated is placed in a chamber
containing a high-pressure, high-temperature mixture of methane, or some
other carbon-based gas, and hydrogen. The gases are heated by hot filaments or
radio waves, breaking up the methane into its constituent carbon and hydrogen
atoms. The electrically charged carbon atoms settle on the object to be
coated, many of them arranging themselves as crystalline diamond, rather than
as graphite, another crystalline form of carbon.
The chemical vapor method is simple and cheap in comparison with the
high-pressure technique used since the 1950s to make synthetic diamonds. In
the last decade, many companies have experimented with carbon-vapor diamond
films as scratchproof coatings for sunglasses, ultrahard sheaths for steel
machine tools, heat-conducting radiators for electronic chips, flat-panel
video displays and rigid resonators used in loudspeakers to improve
high-frequency sound.
Some of these films have consisted mostly of diamond, while other coatings,
called "diamondlike," consist largely of graphite with some diamond crystals
mixed in. But though dozens of companies manufacture carbon-vapor diamond
coatings for a large range of products, their success has been spotty and the
technology has progressed much more slowly than innovators had hoped.
One reason, according to Dr. William F. Banholzer, manager of engineering for
the General Electric Co.'s Superabrasive program, was that many "diamondlike"
films lacked the strength and adhesion to harden tools effectively. They
tended to flake away from metal.
"The chemical vapor deposition technique was terribly hyped," Banholzer said,
"and these days, most large companies are canceling their CVD programs."
Another factor that has worked against the development of synthetic diamond
materials is a precipitous decline during the last five years in world prices
for industrial diamonds. The cheapest industrial diamond abrasive, called
"loose chip abrasive," is made in enormous quantities by China using a
high-pressure, high-temperature method, and these diamonds are sold for as
little as 20 cents per carat.
"Mind you," Banholzer said, "I don't want to put down or discourage Mr.
Mistry or others working in this field, but we have yet to see how much his
technique is really worth in commercial terms. Cost, performance, adhesion and
ease of production all need to be evaluated."
In pure, crystalline form, most carbon is graphite, which consists of
molecular sheets of elemental carbon atoms linked together into planes and
arranged in a pattern something like that of chicken wire. Graphite is a
slippery, black substance used as a lubricant and for making pencil lead,
among other things.
But when subjected to enormous pressure, the spaces between carbon atoms in
graphite are compressed, forcing the atoms to rearrange themselves into
compact eight-sided crystals -- crystals of diamond.
Most natural diamond crystals are black mixtures of diamond and graphite, and
are used as abrasives. But occasionally diamond takes the form of pure
crystals, transparent gems.
Natural diamonds are believed to have been created by the great pressures and
high temperatures that prevail deep in the earth's crust and mantle. Whether
natural or synthetic, diamond has properties unique among all other known
substances; diamond is the hardest known material, it has the highest
refractive index (a measure of the degree to which a material bends light),
and it conducts heat faster than anything else, faster even than copper.
Diamond can also act as a semiconductor, and it has been proposed as a base
material for electronic chips, replacing silicon.
Although there are several claimants to having synthesized the first
diamonds, it was General Electric that manufactured the first large gem
quality diamonds, and the company still makes them.
In the early 1950s, GE engineers built a gigantic press that mimicked the
natural diamond-forming process by subjecting graphite to huge pressures and
temperatures. The technique, while very expensive, produced gem diamonds of
high quality and large size.
But to GE, "gems are not a business; they are an aspect of sociology,"
Banholzer said. "Wives don't seem to accept the idea that a synthetic gem
diamond is the same in substance and quality as a natural diamond. The price
for synthetic and natural gem diamonds is about the same -- around $2,000 a
carat. But gems will never be a big market for us."
To manufacturers, however, a securely bonded diamond coating that is able to
extend the life of a drill or die or saw or axle by thousands of times would
be worth its weight in gold. Such a coating may at last be within reach.
Mistry has applied for more than 30 patents covering various aspects of his
invention, and several have already received approval, he said. He predicts
that his method will find widespread application in special tools and dies
that can machine aluminum and other metals without requiring a liquid coolant.
Coolants, which remove heat from objects being machined, pose environmental
problems. Scrubbing every trace of coolant from a metal object is expensive,
particularly when the object is an aluminum beverage can that must be
absolutely clean.
Diamond-coated tools, Mistry said, aid the "dry machining" of aluminum engine
blocks, beverage cans and many other things. In conventional machining, the
object being shaped heats up, but in dry machining, most of the heat is
carried away by chips and filings that fly off, leaving the object being
machined relatively cool. But to work, the tool must be extremely hard, and
diamond coating is a way to achieve the necessary hardness.
For more than a decade, toolmakers and other manufacturers have experimented
with diamond coatings applied to objects by a process known as chemical vapor
deposition, or CVD. Ordinarily, the object to be coated is placed in a chamber
containing a high-pressure, high-temperature mixture of methane, or some
other carbon-based gas, and hydrogen. The gases are heated by hot filaments or
radio waves, breaking up the methane into its constituent carbon and hydrogen
atoms. The electrically charged carbon atoms settle on the object to be
coated, many of them arranging themselves as crystalline diamond, rather than
as graphite, another crystalline form of carbon.
The chemical vapor method is simple and cheap in comparison with the
high-pressure technique used since the 1950s to make synthetic diamonds. In
the last decade, many companies have experimented with carbon-vapor diamond
films as scratchproof coatings for sunglasses, ultrahard sheaths for steel
machine tools, heat-conducting radiators for electronic chips, flat-panel
video displays and rigid resonators used in loudspeakers to improve
high-frequency sound.
Some of these films have consisted mostly of diamond, while other coatings,
called "diamondlike," consist largely of graphite with some diamond crystals
mixed in. But though dozens of companies manufacture carbon-vapor diamond
coatings for a large range of products, their success has been spotty and the
technology has progressed much more slowly than innovators had hoped.
One reason, according to Dr. William F. Banholzer, manager of engineering for
the General Electric Co.'s Superabrasive program, was that many "diamondlike"
films lacked the strength and adhesion to harden tools effectively. They
tended to flake away from metal.
"The chemical vapor deposition technique was terribly hyped," Banholzer said,
"and these days, most large companies are canceling their CVD programs."
Another factor that has worked against the development of synthetic diamond
materials is a precipitous decline during the last five years in world prices
for industrial diamonds. The cheapest industrial diamond abrasive, called
"loose chip abrasive," is made in enormous quantities by China using a
high-pressure, high-temperature method, and these diamonds are sold for as
little as 20 cents per carat.
"Mind you," Banholzer said, "I don't want to put down or discourage Mr.
Mistry or others working in this field, but we have yet to see how much his
technique is really worth in commercial terms. Cost, performance, adhesion and
ease of production all need to be evaluated."
In pure, crystalline form, most carbon is graphite, which consists of
molecular sheets of elemental carbon atoms linked together into planes and
arranged in a pattern something like that of chicken wire. Graphite is a
slippery, black substance used as a lubricant and for making pencil lead,
among other things.
But when subjected to enormous pressure, the spaces between carbon atoms in
graphite are compressed, forcing the atoms to rearrange themselves into
compact eight-sided crystals -- crystals of diamond.
Most natural diamond crystals are black mixtures of diamond and graphite, and
are used as abrasives. But occasionally diamond takes the form of pure
crystals, transparent gems.
Natural diamonds are believed to have been created by the great pressures and
high temperatures that prevail deep in the earth's crust and mantle. Whether
natural or synthetic, diamond has properties unique among all other known
substances; diamond is the hardest known material, it has the highest
refractive index (a measure of the degree to which a material bends light),
and it conducts heat faster than anything else, faster even than copper.
Diamond can also act as a semiconductor, and it has been proposed as a base
material for electronic chips, replacing silicon.
Although there are several claimants to having synthesized the first
diamonds, it was General Electric that manufactured the first large gem
quality diamonds, and the company still makes them.
In the early 1950s, GE engineers built a gigantic press that mimicked the
natural diamond-forming process by subjecting graphite to huge pressures and
temperatures. The technique, while very expensive, produced gem diamonds of
high quality and large size.
But to GE, "gems are not a business; they are an aspect of sociology,"
Banholzer said. "Wives don't seem to accept the idea that a synthetic gem
diamond is the same in substance and quality as a natural diamond. The price
for synthetic and natural gem diamonds is about the same -- around $2,000 a
carat. But gems will never be a big market for us."
To manufacturers, however, a securely bonded diamond coating that is able to
extend the life of a drill or die or saw or axle by thousands of times would
be worth its weight in gold. Such a coating may at last be within reach.