Alpha plutonium – a rebel element

What does it look like?

The crystal structure of alpha plutonium, image generated by the VESTA (Visualisation for Electronic and STructual analysis) software http://jp-minerals.org/vesta/en/.

The crystal structure of alpha plutonium, image generated by the VESTA (Visualisation for Electronic and STructual analysis) software http://jp-minerals.org/vesta/en/.

What is it?

Over the year we’ve introduced the crystal structure of a number of elements. Most of them take up very simple crystal structures, those that you can also form by pouring ping pong balls into a box. Atoms of materials like gold, krypton and even curium pack like this.

We’ve also introduced elements that don’t conform to the ‘simple crystal structure’ rules at room temperature – the elemental rebels so to speak. These are the elements where the atoms are awkward – they need to be *that* bit further away from each other.

The latest of these ‘rebel’ element is plutonium. This element, actually has seven allotropes, with a face centred cubic phase (known as the delta-phase) stable at just above room temperature, 310 K. Below this it forms a crystal structure known as it’s alpha-phase, which is monoclinic, a low symmetry structure that has low thermal conductivity and is quite brittle. Not great for use in reactors.

We’ve actually learnt how to tame the plutonium crystal structure somewhat. Alloy plutonium with a little bit of gallium, aluminium, americium, scandium or cerium and it forms into a gold-like face-centred cubic structure that isn’t brittle and conducts heat much better.

Where did the structure come from?

The structure of alpha plutonium was discovered by Zachariasen, and Ellinger 1963. It’s #9008587 in the Crystallography Open Database.

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A failed campaign – alpha and beta tin

What does it look like?

'White' or beta tin the structure of tin at room temperature Image generated by the VESTA (Visualisation for Electronic and STructual analysis) software http://jp-minerals.org/vesta/en/

‘White’ or beta tin the structure of tin at room temperature Image generated by the VESTA (Visualisation for Electronic and STructual analysis) software http://jp-minerals.org/vesta/en/

'Grey' or alpha tin the structure of tin at temperatures below -40oC Image generated by the VESTA (Visualisation for Electronic and STructual analysis) software http://jp-minerals.org/vesta/en/

‘Grey’ or alpha tin the structure of tin at temperatures below -40oC Image generated by the VESTA (Visualisation for Electronic and STructual analysis) software http://jp-minerals.org/vesta/en/

What is it?

When Napoleon’s armies marched towards Russia in June 1812, they were freshly kitted out with new uniforms, weapons and provisions, full of confidence in their future success in conquering to the East.  Yet later that year, the bedraggled remains of this army limped back to France, heavily defeated.  There were many reasons why Napoleon’s army failed in their conquest, but a quirk of crystal structure can’t have helped.  The uniforms of the Napoleonic army were held together by tin buttons, but in the protracted cold temperatures of the Russian winter these buttons started to crumble.  The reason?  What is often referred to as ‘tin pest’.

 

Tin pest is in fact a change of crystal structure of the tin itself.  When temperatures drop towards -40°C the metallic ‘white tin’, known also as beta-tin – will change to ‘grey tin’ or alpha tin.  The atoms within the alpha tin are co-ordinated, like carbon in diamond, to four other tin atoms making the material brittle.  As the French army strove through the Russian winter and temperatures dropped, so their buttons would have started to crumble. 

Where did the structure come from?

The structures of alpha and beta tin were determined by both structures can be found in the Open Crystallography database # 9008568 and # 9008570

A celebration of x-rays – Roentgenium

Roentgen's X-ray image of his wife, Anna's, hand. On seeing this she exclaimed 'I have seen my death'

Roentgen’s X-ray image of his wife, Anna’s, hand. On seeing this she exclaimed ‘I have seen my death’

On this day, 169 years ago the man who was to receive the very first Nobel prize in physics was born. Wilhelm Conrad Röntgen, was working with a cathode ray tube when he made his discovery. He had shielded most of the tube, and found that when it was on it still caused a fluorescent effect on a plate covered with barium platinocyanide even two meters away. He named these invisible waves, X-rays, indicating the unknown nature of them at the time. Roentgen, who is largely recognised as the father of diagnostic radiology, refused to take out any patents on is discoveries, and donated the money his receive from his Nobel prize to his university.

In 2004, it was decided to name element 111 after Röntgen. This element had first been discovered in Germany in 1994 and its most stable isotope (Röntgenium 272) has a half-life of only 26 seconds. Writing about the crystal structure of Röntgenium is a little different to the others we’ve posted about, as there’s never been enough of the material made to actually determine its crystal structure! It’s predicted to have a body centred cubic structure, which is (as it sounds) a cubic structure of atoms with one atoms sitting in the middle of these. There are a number of other elements that take up this structure, such as the alkali metals Lithium, Sodium and Potassium. Here we’ve pictured Potassium, which is #9008539 in the open crystallography database.

Image generated by the VESTA (Visualisation for Electronic and STructual analysis) software http://jp-minerals.org/vesta/en/

Image generated by the VESTA (Visualisation for Electronic and STructual analysis) software http://jp-minerals.org/vesta/en/

But mainly we wanted to say thanks to Röntgen for discovering X-rays and making the science of diffraction and crystallography possible.

GOLD! The crystal structure of success.

What does it look like?

Image generated by the VESTA (Visualisation for Electronic and STructual analysis) software http://jp-minerals.org/vesta/en/

Image generated by the VESTA (Visualisation for Electronic and STructual analysis) software http://jp-minerals.org/vesta/en/

What is it?

It’s coveted by many, yet owned by very few but on a crystal structure level gold is actually very similar to quite a few other metals.  At this level the gold atoms can nearly be thought of as spheres.  The structure of gold can be described as cubic close packed – or face centred cubic.  Each edge of the cube is 4.07 Å long.  You can see from the image above that the basic building block of the structure, with an atom of gold at each corner and sitting in the middle of each face.  This is one of the most efficient ways that spheres can pack together, using 74 % of the space.   Other metals that form the same crystal structure are Platinum, Lead, Nickel and copper.

Gold is the ultimate play-doh.  It’s relatively soft but is also very very malleable, a 1 gram amount can be beaten into a one meter square sheet.  Gold’s softness is one of the reasons why it can collect in fluvial beds to form beautiful flowing nuggets.  This relationship with water means that gold can even get sucked up into leaves of eucalyptus trees.  Australian scientists last year showed that trees in gold mining areas can suck up gold into their leaves, which means checking the leaves could be a cheaper way to hunt for the gold below.

Where did the structure come from?

Though it was pretty well known that the structure of gold was face centred cubic, a paper by Jette and Foote determined very accurately the length of the cubic for a number of materials – including gold.  This was very important work, because of the use of Gold and similarly unreactive metals as standards in lots of experiments.     This crystal structure is #9012430 in the open crystallography database.