Scientists Discover Material Harder Than Diamond
February 12, 2009 By Lisa Zyga
A diamond ring. Scientists have calculated that wurtzite boron nitride and lonsdaleite (hexagonal diamond) both have greater indentation strengths than diamond. Source: English Wikipedia.
(PhysOrg.com) -- Currently, diamond is regarded to be the hardest known material in the world. But by considering large compressive pressures under indenters, scientists have calculated that a material called wurtzite boron nitride (w-BN) has a greater indentation strength than diamond. The scientists also calculated that another material, lonsdaleite (also called hexagonal diamond, since it’s made of carbon and is similar to diamond), is even stronger than w-BN and 58 percent stronger than diamond, setting a new record.
This analysis marks the first case where a material exceeds diamond in strength under the same loading conditions, explain the study’s authors, who are from Shanghai Jiao Tong University and the University of Nevada, Las Vegas. The study is published in a recent issue of Physical Review Letters.
“The new finding from our results is that large normal compressive pressures under indenters can transform certain materials (such as w-BN and lonsdaleite) into new superhard structures that are harder than diamond,” coauthor Changfeng Chen from the University of Nevada, Las Vegas, told PhysOrg.com. “This is a new mechanism that can be used to design new superhard materials.”
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The scientists explain that the superior strength of w-BN and lonsdaleite is due to the materials’ structural reaction to compression. Normal compressive pressures under indenters cause the materials to undergo a structural phase transformation into stronger structures, conserving volume by flipping their atomic bonds. The scientists explain that w-BN and lonsdaleite have subtle differences in the directional arrangements of their bonds compared with diamond, which is responsible for their unique structural reaction.
Under large compressive pressures, w-BN increases its strength by 78 percent compared with its strength before bond-flipping. The scientists calculated that w-BN reaches an indentation strength of 114 GPa (billions of pascals), well beyond diamond’s 97 GPa under the same indentation conditions. In the case of lonsdaleite, the same compression mechanism also caused bond-flipping, yielding an indentation strength of 152 GPa, which is 58 percent higher than the corresponding value of diamond.
“Lonsdaleite is even stronger than w-BN because lonsdaleite is made of carbon atoms and w-BN consists of boron and nitrogen atoms,” Chen explained. “The carbon-carbon bonds in lonsdaleite are stronger than boron-nitrogen bonds in w-BN. This is also why diamond (with a cubic structure) is stronger than cubic boron nitride (c-BN).”
Until recently, normal compressive pressures under indenters have not been included in the calculations of ideal shear strengths of crystals from first principles, but latest developments have enabled researchers to consider their effects, resulting in surprising discoveries like the one shown here. Still, experimenting with w-BN and lonsdaleite will be challenging, since both materials are difficult to synthesize in large quantities. However, another recent study has taken a promising approach to producing nanocomposites of w-BN and c-BN, which may also provide a way to synthesize nanocomposites containing lonsdaleite and diamond.
In addition, by showing the underlying atomistic mechanism that can strengthen some materials, this work may provide new approaches for designing superhard materials. As Chen explained, superhard materials that exhibit other superior properties are highly desirable for applications in many fields of science and technology.
“High hardness is only one important characteristic of superhard materials,” Chen said. “Thermal stability is another key factor since many superhard materials need to withstand extreme high-temperature environments as cutting and drilling tools and as wear, fatigue and corrosion resistant coatings in applications ranging from micro- and nano-electronics to space technology. For all carbon-based superhard materials, including diamond, their carbon atoms will react with oxygen atoms at high temperatures (at around 600°C) and become unstable. So designing new, thermally more stable superhard materials is crucial for high-temperature applications. Moreover, since most common superhard materials, such as diamond and cubic-BN, are semiconductors, it is highly desirable to design superhard materials that are conductors or superconductors. In addition, superhard magnetic materials are key components in various recording devices.”
More information: Pan, Zicheng; Sun, Hong; Zhang, Yi; and Chen, Changfeng. “Harder than Diamond: Superior Indentation Strength of Wurtzite BN and Lonsdaleite.” Physical Review Letters 102, 055503 (2009).
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3 hours ago
(for reference, check Wikipedia entry on graphene, under "Mechanical properties")
There are different kinds of properties that slopily may be refered to as hardness; tensile strength, elastic modulus, indentation hardness, scratch hardness and so on.
Well, not exactly true. Diamonds made from high pressure have these properties, but diamonds made from chemical vapor deposition (CVD) are actually very high quality. Probably in the next 10 years we will see a huge trend in man-made diamonds...
True, but if you are not worried about depreciation of the relationship, then try getting your loved one an artificial diamond (and then tell her the truth - heck she'll find out eventually).
While some women are OK with that, most will think that "artificial" is what you think of the relationship and , well you can guess what'll happen next :-).
The DeBeers have hypnotized a good % of the world's population of women (well, the affluent and semi-affluent anyhow :-))
It was not known if said scientist survived the experiment though.
("You did WHAT???????" "But it was for the sake of science, dear...")
http://pubs.acs.o...nds.html
THE MANY FACETS OF MAN-MADE DIAMONDS
Synthetic diamond makers are targeting the gem market first, but their product could transform many other industries, too
P.S.: If you tell your wife/girlfriend, make sure you don't call it Man Made - you'll be adding sexism to injury (said injury probably to yourself).
Not to mention toughness, fracture resistance,
I tried my best to convince her of the fantastic benefits of synthetic diamonds, but she opted for a real one even though it was flawed.
Fake diamonds may very well INCREASE the price of real diamonds for jewelry's sake simply because of their natural origin.
BTW, the moissanite is near diamond on the hardness scale, and in my opinion a little prettier than a diamond - it has a higher refractive index (i.e. it's sparklier). It does have a very slight yellow tinge though. Jewelers can't even tell the difference between the two without a special device made specifically to distinguish between silicon carbide and diamond.
I much prefer the rarer stones, a Burmese Ruby, for example. My new favorite was Tanzanite until the stupid war and they were used to support terrorist groups.
There are rainbows of colored gemstones. What's s hot about one that can scratch glass? It's all hype. I don't buy them unless they happen to be accent stones on a piece I want.
So new stuff that is harder, is it considered man-made? Is it a single substance, like the carbon of a diamond? Unless it can say NO to the first and YES to the second questions, then it's not so miaculous, is it?
crystal lattice links:
http://en.wikiped..._lattice
rotate from various perspectives:
http://cst-www.nr.../a4.html (diamond)
http://cst-www.nr...a_f.html (hexagonal -moss.)
Here are some interesting links about moissanite:
http://www.galler...sani.htm (the compound/mineral)
http://www.moissanite.com/ (jewelry)
Scientists have known about and grown quasicrystals for the past decade if not two decades.
Everyone knows that quasicrystals are 11 times harder than diamond and are most effectively grown in zero gravity.
Why do you think all the space shuttle launches?
To add on more to the space station which hasn't grown?
THINK......
Ok maybe Verbz is off base or joking (I draw the line at personal attacks). However when you look at big gov's history it is littered with precedences e.g. nuclear testing on civilians/military, biowarfare test on NY metro, parallel military Apollo program, CIA running its own show without any congressional oversight. You can't blame people for crying wolf when the wolf has visited regularly!