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“The Elementary Unknown Sea” CPS Talk 26.01.15

By zccasle, on 6 February 2015

Andrea

Andrea Sella braves the ‘Elementary Unknown Sea’. An account of the Rare Earth Elements, their place in our technological-cultural hearts and why they made the headlines in BBC news.

Prof. Sella is one to embrace historical context and the story of the Rare Earths begins in Sweden 1792 with Johan Gadolin who was given a rock. This is a long time before Mendeleevs Periodic Table, new elements were there for the taking and rocks would be a good place to start. However isolating such elements would prove to be a tricky task. For the Rare Earths this is made even more difficult by their analogous chemistry, dominated by the (III) oxidation state and similarity in size. Separating them would remain a problem right through to the 20th Century.

The Rare Earths start at Y and end at Lu, they are not so rare as of yet so their name rings of antiquated nomenclature. The chemists of the time made laborious and ingenious attempts to isolate new materials, in the case of the Lanthanides this could involve thousands of consecutive solvent extractions. In some cases they still didn’t isolate an element, Didymium was a compound masquerading as an element for about 40 years.

It was thanks to Carl Auer von Welsbach that the Rare Earths became incorporated into the technical demands of society. Firstly he solved the Didymium problem and showed that it consisted of the two elements Praseodymium and Neodymium. He then went onto illuminate Europe, literally, and this was thanks to another of the Lanthanides; Thorium. In the 1890’s the Thorium gas mantle first lit the streets of European capitals bringing with it the requirement of piped gas. For his contribution he is commemorated on a special addition Austrian 25€ coin. The gas mantles were phased out because Thorium is radioactive, but if you can dig out an old camping lamp you may just have some Thorium Dioxide in the mantle, so don’t eat it.

Those of us lucky enough to receive the core third year Inorganic Chemistry Lectures by Dr Jeremy Karl Cockcroft (another Rare earth enthusiast), were given full proof of the radioactive nature of old gas mantles, nothing is quite so unnerving as the gentle clicking of the Geiger counter.

What other strange uses may these rare earth’s have? Currency. Hopefully this is not too instructive, but modern Euro notes contain Europium in an ink which is used to mark their authenticity. This is due to its fluorescent properties that allow it to glow pink under UV light. So don’t eat Euro’s either, most heavy metals are toxic.

There’s no chance of anyone eating these, but rare earths are also used in catalytic converters, sweetening the deal with the combustion engine problem by making sure that only fully oxidised hydrocarbons are released into the atmosphere. Not great for the green house effect but very good for improving air quality. Specifically Cerium (IV) Oxide a highly stable, non toxic, high refractory material that provides a low energy oxidation of combustion by products such as carbon monoxide.

Finally, Erbium. I get the impression that this application will still be going when combustion engines have long been scrapped. Erbium compounds act as the solid state optical amplifiers for fibre optic data signals. The huge cables that carry the internet under the Atlantic etc. Do so with the help of Erbium. Such materials have lessened the energetic requirements of optical data transfer by removing the need to amplify the signals electronically and then resubmit optically, Erbium does the hard so we don’t have to.

The Rare Earths hit the headlines when the Chinese Government decide that they would limit the amount of rare earths that they would export. This move saw the price of rare earth stock rise very sharply and got the prospectors very excited. Economics 101. The US kicked up a fuss and the move was reversed and down came the price. It illustrates that a lot of industries got wobbly knees when it looked like they’d have to pay more for their Rare Earths.

So what was Andrea’s final thought? Yes we should all take care of ourselves… and each other, but we should also respect the materials; respect the fact that future generations will be grateful for forests instead of quarries and let’s be careful not to make the rare earths any rarer.

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