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Diamonds are the hardest naturally occurring minerals known to man.
Even so, scientists are working to make them even tougher, in order to
use the sparkling gems as tools for cutting.
Now, a team of researchers, led by Yongjun Tian and Quan Huang at Yanshan University in China, has created synthetic diamonds that are harder, meaning they are less prone to deformation and breaking, than both natural and other man-made diamonds.
To create these tougher-than-steel diamonds, the researchers used tiny particles of carbon,
layered like onions, and subjected them to high temperatures and
pressures. The resulting diamonds had a unique structure that makes them
more resistant to pressure and allows them to tolerate more heat before
they oxidize and turn to either gas (carbon dioxide and monoxide) or
ordinary carbon, losing many of their unique diamond properties. [In Photos: 13 Mysterious & Cursed Gemstones]
First, a bit about diamonds: Gem-quality diamonds
are single crystals, and they are quite hard. But artificial diamonds
used on tools are harder still. That's because they are polycrystalline
diamonds, or aggregates of diamond grains called domains, that measure a
few micrometers or nanometers across. The grains help to prevent the
diamond from breaking, as the boundaries act like small walls that keep
chunks of diamond in place. The smaller the domains are, the stronger
the diamond.
Tian's team used the onionlike carbon nanoparticles to make diamonds
with domains that are a few nanometers in size and are mirror images of
each other. Such "nanotwinned" crystals are much harder than ordinary
diamonds, by a factor of two.
The team tested the artificial diamond's hardness
by pressing a pyramid-shaped piece of diamond into the nanotwinned
diamond. Tian's group made a small indentation in their artificial
diamond, applying pressures equivalent to nearly 200 gigapascals (GPa) —
about 1.9 million atmospheres. An ordinary natural diamond would crush
under just half that pressure.
The team also tested how hot the nanotwinned diamond could get before
oxidizing. In two different tests, they found that the ordinary diamond
began to oxidize at about 1,418 and 1,481 degrees Fahrenheit (770 and
805 degrees Celsius), depending on the testing method. The nanotwinned
diamonds didn't oxidize until they reached 1,796 or 1,932 F (980 or
1,056C).
But not everyone is convinced by these results. Natalia Dubrovinskaia, a
professor of material physics at the University of Bayreuth in Germany,
said she doesn't trust the pressure tests. If what Tian's group is
reporting is true, the indenter should have broken, because the material
of the indenting tool is not as hard as the nanotwinned diamond, she
told Live Science in an email.
Tian disagreed with Dubrovinskaia's assessment of the indenter. He said
that it is possible to measure pressure on the nanotwinned diamond
because the indenter was pushed from a vertical position and the amount
of shearing force on it wasn't enough to damage it.
Tian and Dubrovinskaia have "sparred" before; last year, the Yanshan
lab said it demonstrated a similar phenomenon, making a form of
ultrahard cubic boron nitride. At the time, Dubrovinskaia voiced similar
concerns.
Tian, meanwhile, stands by his work. "Indentation hardness of any
material can be measured reliably using [a] diamond indenter when the
indenter axis is exactly perpendicular to the smooth surface of [the]
tested sample," he said.
Another scientist, Ho-Kwang Mao, of Argonne National Laboratory in
Illinois, thinks Tian's work is valid; he noted that an indenter could
reliably measure the hardness of materials much harder than itself.
In addition, the novel part of the work is that such a hard material
has been created in a way that can be readily reproduced. "They created a
bulk material," Mao said. "They succeeded in making this and making it
harder than diamond — that's novel."
The new study is detailed in the June 12 issue of the journal Nature.
Ancient zircon crystals,
discovered in Australia in 2001, have now been proved to be our planet’s oldest
known substance. The 4.4 billion-year-old gem offers clues that Earth could have
become habitable much earlier than previously believed.
Aside from being just a
cool fact to know, this recent discovery (available in the journal, Nature
Geoscience) gives scientists at the University of Wisconsin a new
insight into our planet’s infancy.
There are now grounds to suggest
that Earth cooled down much sooner, and that life appeared way before many
scientists had thought.
"We have no evidence
that life existed then. We have no evidence that it didn't,” Wisconsin
geoscience professor and report lead, Professor John Valley, told Reuters. “But
there is no reason why life could not have existed on Earth 4.3 billion years
ago," he added.
The oldest fossil records of life
are stromatolites produced by an archaic form of bacteria from about 3.4 billion
years ago.
Scientists believe that thanks to
low enough temperatures, Earth had a hydrosphere and possibly early life even
before 4.3 billion years ago. In fact, there is even a theory of a "cool
early Earth.” Professor Valley says their
discovery really strengthens this notion. “The study reinforces
our conclusion that Earth had a hydrosphere before 4.3 billion years ago, and
possibly life not long after,” John
Valley is quoted as saying in the press-release. Our planet formed as a ball of
molten rock 4.54 billion years old. The first 500 million years of Earth have
been dubbed Hadean, after the ancient Greek god of the underworld, or hell-like,
because scientists believed that it was covered with lava and subsurface magma,
making it an absolutely inhospitable place.
Valley’s discovery undermines
this idea.
This 4.4 billion-year-old zircon
crystal proves that the Earth cooled from a ball of magma and formed continents
much earlier.
He and his team confirmed that
our planet first developed a crust just 160 million years after the formation of
our solar system.
“Our samples formed
after the magma oceans cooled and prove that these events were very
early,” he wrote.
But his team still has no answer
to the main question: "One of the things that we're really interested in is:
when did the Earth first become habitable for life? When did it cool off enough
that life might have emerged?" Professor Valley said.
So, how did the University of
Wisconsin scientists make their breakthrough findings?
They used two different
age-determining techniques on the tiny zircon crystal, as small as 200 by 400
microns, about twice the diameter of a human hair, extracted from a rock outcrop
in the Jack Hills region, Western Australia, in 2001.
But first they used a
widely-accepted dating technique based on determining the radioactive decay of
uranium to lead in a mineral sample.
Valley and his colleagues then
looked at lead atoms in zircon using a new technique called atom-probe
tomography in conjunction with secondary ion mass spectrometry. It helped them
identify individual atoms of lead in the crystal and then determine the age and
thermal history of zircon by estimating the mass of lead atoms.
And so it was confirmed that the
zircon is indeed 4.4 billion years old.
