x Abu Dhabi, UAETuesday 25 July 2017

Why gold is out of this world, and fake diamonds can look real

Mankind has long been drawn by the lustre of gold and the sparkle of diamonds, but only recently have scientists been able to establish the extraordinary genesis of the precious metal and create in a laboratory diamonds that look like the real thing.

Gold and diamonds are staples of legends and tokens of love that have never lost their attraction.

Yet in terms of chemistry, they are nothing more than ho-hum collections of electrons, protons and neutrons. What makes them special is their extraordinary birthplaces, which, in the case of gold, is literally out of this world.

And this year we have seen major breakthroughs in the science of their creation that could change our perceptions of their true worth.

The high price of gold and diamonds is an economic reflection of a scientific fact: that the conditions in which they were formed are pretty unusual.

Contrary to common belief, gold and carbon - atoms of which form the raw material of diamonds - were not created in the cosmic Big Bang 14 billion years ago.

Indeed, only atoms of the two simplest elements, hydrogen and helium, were formed then, the universe expanding and cooling too fast to create anything more complex.

Everything we see around us owes its origins to nuclear reactions inside colossal, long-dead stars that died in supernova explosions, which then scattered their atomic spawn into the abyss of space.

Precisely how different types of atom were formed has been the subject of study for decades. But only recently has the astonishing truth about the origins of gold begun to emerge.

Scientists have long known that the heavier the atoms, the harder they are to create. Creating atoms heavier than iron is a real challenge, requiring intense pressure and temperature to create stable nuclei faster than their constituents can break apart.

In the case of really heavy elements such as gold, astrophysicists believed only the exploding cores of giant stars could provide the right conditions.

But there was a problem. Calculations showed that if that were true, gold would be far more common than it is. This suggested that it was formed somewhere even more exotic than in the heart of a supernova.

Earlier this year, scientists in Europe claimed to have found a suitable birthplace: the collision of two neutron stars.

These bizarre objects are the remnants of supernova explosions, and are incredibly dense, typically cramming the mass of two sun-like stars into a ball just 20-30 kilometres across. Some neutron stars end up in orbit around each other, slowly spiralling towards each other until they merge to form a black hole.

On the way, unimaginable pressures and temperatures are generated - and according to the new research, these are perfect for creating heavy atoms such as gold.

Researchers at the Free University of Brussels and the Max Planck Institute of Astrophysics, in Garching, Germany, reached their conclusions using computer simulations of the collision of two neutron stars.

As well as revealing the existence of suitable temperatures and pressures, the simulations showed that the cataclysm spews out heavy elements in quantities similar to those actually observed.

Based on estimates of the frequency of such collisions, the team believes these events may even be the prime source of such heavy elements. Astronomers are now on the look-out for neutron-star collisions showing signs of generating heavy elements. If they succeed, it will give us a whole new view of gold as the lustrous legacy of the birth of a black hole.

The image of diamonds may be about to have a makeover too, following another recent breakthrough. Natural diamonds are created deep in the heat and pressure that prevail in the Earth's mantle, hundreds of kilometres below our feet. These conditions compel carbon atoms to arrange themselves into a structure of unsurpassed strength, resulting in the cold, hard crystals we call diamonds.

Yet, while extraordinary, the conditions needed to form diamonds are not inconceivable, prompting Victorian scientists to have a shot at recreating them in the laboratory.

It proved much harder than anyone imagined. Not until 1955 did a team at General Electric in Schenectady, New York State, make headlines worldwide by announcing the creation of the first artificial diamonds, using a combination of 70,000 atmospheres pressure and temperatures exceeding 1,200°C.

But the end result was less than impressive: dull, dark specks fit only for industrial use. At the time, the team estimated it would be decades before gem-quality diamonds could be made.

Now their prediction has been proved right - though using a technique far removed from their own brute-force approach.

For some years, researchers at the Gemesis Corporation in Florida have been working on the creation of carat-sized, gem-quality diamonds in the laboratory using chemical vapour deposition (CVD).

Instead of crushing and heating carbon atoms into submission, CVD uses carbon atoms extracted from a gas such as methane to build up a diamond layer by layer inside a vacuum chamber.

Now, after a decade of research and development, Gemesis has begun marketing CVD-created diamonds. And, according to a report by the Gemological Institute of America, they are truly impressive, with only sophisticated laboratory tests capable of revealing their true origin. To look at, they have all the brilliance, sparkle and "fire" of very high quality natural diamonds.

Will they catch on? They certainly are not the choice of cheapskates: a decent-sized one-carat laboratory diamond created using the CVD method still carries a price tag of several thousand dollars.

In the end, those who can afford those prices may decide to pay the premium needed to buy a natural diamond. Which would be a shame, for if set in gold, it is clear the result would represent the union of human ingenuity and cosmic power.

 

Robert Matthews is Visiting Reader in Science at Aston University, Birmingham, England