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Last Updated: Thursday, 15 June 2006, 11:16 GMT 12:16 UK
Dry ice creates toughened glass
Glass skyscraper
Silicon is easily converted into glass
A form of solid carbon dioxide that could be used to make ultra-hard glass or coatings for microelectronic devices has been discovered.

The material, named amorphous carbonia, was created by an Italian led team.

The scientists told the journal Nature that the material was always thought to be possible but, until now, had never been created in the lab.

It was made by squeezing dry ice, a form of carbon dioxide used to create smoke in stage shows, at huge pressure.

Scientists are interested in the new material because of the potential applications. Also, they believe it could give them clues to the processes that happen in the centre of huge gas giant planets such as Jupiter.

Unusual properties

All chemical elements can be classified in the periodic table, which groups elements with similar properties.

Carbon is part of the group IV (now more properly named group 14) elements that also includes silicon, germanium, tin and lead.

However, unlike these other elements that form solids when they react with oxygen at normal atmospheric pressure, carbon forms the gases carbon monoxide and carbon dioxide.

This happens because carbon atoms are lighter than other elements in the group.

Carbonia-based minerals and glasses could give rise to useful technological materials
Professor Paul McMillan, University College London
When silicon reacts with oxygen it forms silica, known as the mineral quartz, which is commonly used to make glass.

Germanium reacts similarly and is often used to produce a glass material for lenses and fibre optic cables.

Both of these glasses are formed of a disorderly network of atoms.

But when carbon reacts at room temperature and pressure it does not form a network. Instead, carbon atoms join with oxygen atoms to form discrete molecules and therefore gases.

Carbon dioxide can be formed into a solid, such as dry ice, by cooling and squeezing. However, even in this solid form, the molecules resist linking up with their neighbours and remain as discrete units.

Simulations, though, had suggested that given the right conditions these molecules could be persuaded to join hands and form glass-like materials.

Extreme pressure

Recently, scientists in California coaxed carbon dioxide molecules to form a solid network by applying extreme pressure at high temperatures.

Their discovery could lead to a way of storing or disposing of carbon dioxide gas, a major contributor to global warming, deep in the Earth's interior.

The new material could give insights into the interior of gas planets
To create the glassy amorphous carbonia, the team led by Professors Mario Santoro and Federico Gorelli of the University of Florence heated solid carbon dioxide between diamond teeth at pressures over 400,000 times greater than atmospheric pressure.

The material was then cooled to room temperature to form the glass.

Atomic analysis of the material confirmed the glass had a similar structure to silica, but is thought to be much harder and stiffer, like diamond.

When the material is depressurised, it returns to a solid formed of discrete molecules.

The next stage of the research is to work out how to make the glass stable at room temperature and pressure.

"Carbonia-based minerals and glasses could give rise to useful technological materials, if we can recover them to ambient conditions," commented Professor Paul McMillan, of University College London, in an accompanying article in Nature.

Applications could include ultra-tough glass or protective coatings for micro electronics.

However, in the first instance, it will give planetary scientists insights into what happens in the interior of huge planets known as gas giants.

"These findings will also help set the rules for understanding structure, bonding and thermodynamic properties as we move our experiments into the high pressure, high temperature conditions mimicking those deep inside planetary interiors," wrote Professor McMillan.

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