0211infochem this one - rsc

The discovery last November of an alien planet in the Milky Way will provide scientists and astronomers with a wealth of new information.

We have known about planets orbiting stars other than the Sun for some time. What is special about this alien planet is that it is the first one we have detected that has come from another galaxy.

The Milky Way’s gravity pulled in the planet and now we have the chance to compare it and the star with the younger, indigenous stars and planets closer to home.

Star HIP 13044 has a very different composition to that of our Sun, which contains mostly hydrogen and helium with significant amounts of oxygen, carbon and iron.

If a star in the Milky Way has more of these heavier elements, it is statistically more likely to have orbiting planets. Until now, the theory has been that the star and its planets coalesce from whatever material is in that area of space. If the material is rich in heavier elements, there is a greater chance of some being left over to form planets.

HIP 13044 contains very little of the heavier elements, destroying the theory that stars like it have no planets. Assuming that the alien planet formed from the same material as its star, it should be quite different from any planet we have found before.

How can stars be so varied?The two lightest elements, hydrogen and helium, were the first to be formed in the Universe. Older stars were made of

just these two elements. As stars died they became supernovae. The immense energy involved fused these atoms into heavier elements such as oxygen, carbon and iron, which then became part of newer stars.

The chemistry of the starsStellar chemistry bears little resemblance to chemical processes on Earth. The temperatures and pressures inside stars change the ground rules regarding chemical bonds. However, we know what is in a star because of the electromagnetic spectrum we detect coming from it.

Chemists catalogued spectral lines of the elements in the early 19th century by heating materials until they glowed and using a spectroscope to examine the light emitted. This helped astronomers to decode stellar spectra and it remains the method for assessing the make-up of stars.

We have come a long way since chemists discovered that each element emits its own distinctive spectrum when heated. That research was not done in order to study the stars, nor for any other application, yet spectroscopy has developed and now it is used in areas as diverse as medicine, forensics and manufacturing.

In times of austerity we should not forget that scientific research forms the basis of our future economy. Atoms are invisibly small and the distance to HIP 13044 is incomprehensibly large. Chemistry bridges the gap.

Helen Sharman leads the nanoanalysis group at the National Physical Laboratory and was Britain’s first astronaut in 1991. This article was originally published at www.thereaction.net.

ISSUE 127 | MARCH 2011

Acting editor Laura Howes

Assistant editor David Sait

Design and layout Scott Ollington

PublisherBibiana Campos-Seijo

InfoChem is a supplement to Education in Chemistry and is published six times a year by the Royal Society of Chemistry,Thomas Graham House,Cambridge, CB4 0WF. 01223 [email protected] www.rsc.org/infochem

© Royal Society of Chemistry, 2011 ISSN: 1752-0533

Rare earths Bottom of the table, top of the league

On-screen chemistryPoisoning gangsters with phosphine gas

A day in the lifeMetallurgy and corrosion at TWI in Cambridge

Backyard chemistryProf Hal shows us how to make snow from nappies

Plus…Prize puzzles

InfoChemES

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An artist’s impression of the first planet of extragalactic origin

www.rsc.org/infochemRegistered Charity Number 207890

Alien planets In this issue

0211INFOCHEM_This One.indd 1 01/03/2011 08:44:52

Rare earth elements

They sit at the bottom of the periodic table like they don’t belong, but elements like neodymium, europium and terbium are vital ingredients in many gadgets and ‘green’ technologies. Tom Westgate finds out how the chemistry of the rare earth elements makes them so versatile and valuable.

The rare earth elements (REEs) play a central role in many of the technologies and gadgets that we take for granted. Your hard drive uses a magnet containing neodymium to access data and your LCD TV or monitor probably relies on terbium and europium to generate its vivid colours. In the near future, all these may be powered by electricity generated by a neodymium-based magnet spinning in a wind turbine.

Bottom of the table, top of the leagueREEs are a group of metals that includes the lanthanides (lanthanum to lutetium), plus scandium and yttrium. The lanthanides are in the f-block, on the bottom of the periodic table, because they all have valence electrons in 4f-obitals. ‘The important thing to know about f-electrons is that they don’t take part in bonding’ says Helen Aspinall, a lanthanide chemist at Liverpool University. These non-bonding electrons, buried deep within the atom and shielded by 4d and 5p electrons, are what give the lanthanides such interesting properties, from light emission to magnetism.

The REE’s optical properties are used to prevent forgery. Appropriately, europium is used to tell genuine Euro banknotes apart from counterfeits. Complexes of europium are added to the notes and emit red or green light under a UV lamp. The f-electrons of Eu3+ are free to absorb energy from UV light by moving temporarily to a higher energy level, before emitting energy as light as they return to their original state.

This light-emitting ability of ‘excited’ f-electrons is the reason REEs are also found in lasers, energy-saving light bulbs, and display screens.

Rare-earth elements are not really very rare. They are as common in the Earth’s crust as tin, lead and zinc. They were named ‘rare earths’ when they were discovered in the 19th century because they were found in scarce minerals.

Periodic table

What’s so rare about them?

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Magnetic attractionThe main reason that lanthanides are so valuable, however, is their magnetism. All lanthanides have at least one unpaired electron and because an unpaired electron has its own magnetic field, it acts like a little bar magnet. Gadolinium, with its seven unpaired electrons, or half filled f-shell, has some ‘pretty impressive magnetic properties,’ says Aspinall, because seven is the most unpaired electrons you can have on a metal. Gd3+ complexes are sometimes given to patients before a MRI scan, to boost the magnetic resonance signal and make a clearer image.

On their own, REEs are magnetic only below room temperature. But, when you combine them in an alloy with transition metals like iron or cobalt you get the best of both worlds: a permanent magnet that remains strongly magnetic at higher temperatures.

Lanthanide-based magnets, like the NdFeB magnets in hard drives and wind turbines, are prized because they cannot be demagnetised. This is because of the shape of the lanthanide atoms, which relates to the irregular shapes of the metal’s f-orbitals. ‘Neodymium atoms are shaped like smarties, and samarium atoms like jelly beans’, says Allan Walton, a research fellow in metallurgy and materials at the University of Birmingham. Packed in with other atoms in a crystal, these oddly-shaped atoms all line up in the same direction, and are unable to rotate and so their magnetic field is permanently locked in place.

Making magnetsThe chemistry of making a magnetic RE alloy is ‘surprisingly simple’, according to Dave Murphy of Less Common Metals Ltd in Birkenhead: ‘The principle is equivalent to putting sugar into tea.’

At Less Common Metals, the ‘tea’ is molten iron and boron, at about 1300°C. Murphy adds solid neodymium, which dissolves into the molten mixture and the mixture is then poured into a cast and cooled until it solidifies. Ideally all the Fe, B and Nd atoms should be randomly distributed in the final magnetic crystal, so the mixture is cooled as quickly as possible to freeze the atoms in place as they randomly move through the liquid. If the cooling is too slow, iron atoms clump together as the mixture solidifies, making a weaker magnet.

Supply and demandAs high-tech applications of REEs become more common, the metals become more and more valuable. 97 per cent of the world’s REEs are mined in China and in 2010 the Chinese government decided to cut the amount of REEs it exports (see InfoChem 126). Because of this, the price of REEs is rising sharply and the rest of the world is desperately seeking new sources.

Could chemistry help to make the most of the world’s precious REE supplies? Animesh Jha and his team of materials scientists at Leeds University believe so. Working to develop more efficient and environmentally friendly methods for processing titanium dioxide-

containing minerals, by chance they found that they could use simple chemistry to turn an almost worthless source of titanium into a potentially valuable source of REE ores.

Titanium-rich minerals are usually mixtures of TiO2 and FeO3, but lanthanide oxides are often trapped inside the minerals. These ‘impurities’ make the minerals a less-valuable source of TiO2, but Jha recognised their presence as ‘nature’s gift to humans.’

Helen Aspinall shows us there are ‘quite a few useful properties of the rare earth elements that can be exploited in some exotic chemistry.’

Similar to transition metals, lanthanides form coordination complexes, but the changes in chemical properties across the lanthanide series are much more subtle, compared with their d-block neighbours. All lanthanides are most stable in the +3 oxidation state. Some (like europium and samarium) can exist in +2, but these compounds tend to be reducing agents, giving up electrons as they return to the more stable +3 state.

Rare-earth elements have quite large ionic radii, which means they can form stable structures with coordination numbers up to 12. This is useful for catalysis where reagents from the catalysed reaction need to be accommodated in the catalyst complex. Aspinall singles out Cerium as a good example. As well as stabilising high coordination number complexes, Ce can exist in both the +4 and +3 oxidation states, opening up some very useful redox chemistry: Ce(IV) complexes can oxidise a range of organic substrates, then cycle back from +3 to +4 and do it again.

REE complexes can also act as Lewis acid catalysts in reactions like the Friedel-Crafts alkylation of aromatic rings The range of ionic radii means you can choose whichever lanthanide is the best size match for the reagents in the catalysed reaction.

Your LCD TV or monitor probably relies on terbium and europium to generate its vivid colours

Exotic chemistry

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InfoChem 3


Polyethylene glycol, PEG, is a polymer made up of many ethylene glycol units strung together in a chain. It has a huge number of uses and can be found throughout our daily life.

PEG molecules can be of any length desired, depending on how many repeating units are in each chain. Short chains of low molecular weight are colourless, viscous, liquids and long chains of high molecular weight are white, waxy, solids. Typically PEG is highly soluble in water, odourless and non-toxic.

In pharmaceuticals, PEG is often used to improve the characteristics of a particular drug. To make a molecule more water soluble, PEG is attached to it using a process known as pegylation. In addition, the increased size of the drug will slow the rate at which it is removed from the body by the kidneys, reducing the frequency of dose that needs to

be given to a patient. As an example, Hepatitis B and C can be treated with pegylated drugs.

In the lab, scientists are investigating PEG, either dissolved in water or neat, as a green alternative to the usual laboratory solvents. Compared to normal solvents, PEG is cheaper, less flammable and less toxic.

PEG is also used by archaeologists to displace water. This helps preserve wooden ships so that the timbers maintain their shape and structure as they dry. PEG is one of the polymers used in the preservation of the 3rd century terracotta army discovered in 1974 in Lintong, China.

Closer to home, PEG is found in many bathroom products, such as toothpaste and shower gel, where it acts as a thickener or dispersant for other substances. It is the base material and binding agent in many cosmetics.

You will also find it in household soaps, cleaners, and adhesives; as a softening agent to alter the texture of fabrics; in the ink of inkjet printers, food packaging and even in processed food to improve its texture or as an emulsifier.

Such is the extent to which PEG pervades our society, it’s unlikely a day will pass where you won’t use it, apply it, or consume it.

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Metal oxides of some rare earth elements

Jha’s team heated a mixture of the TiO2-containing mineral and an alkali such as sodium bicarbonate to around 800°C. This oxidised the TiO2 and FeO3, forming sodium titanate and sodium ferrate (Na2TiO3 and Na2FeO4) but the lanthanide oxides did not react. When the mixture was added to water, the Na2TiO3 and lanthanide oxides remained insoluble but the Na2FeO4 was hydrolysed and dissolved, breaking up the mineral lattice and freeing the small particles of REE oxides trapped inside. By chance, REE particles float in water while Na2TiO3 sinks so they can be easily skimmed off the surface of the water.

Jha suspected the REEs could be extracted from the minerals, but ‘we were not expecting it to come out so simply’, he says. As well as exploiting a neglected source of REEs, he believes the process offers a greener way to process the REE ores that are mined in China and elsewhere.

Reduce, reuse, recycleAnother way to make the most of existing REE supplies is by recycling, but melting down a NdFeB magnet, for example, takes too much energy to be economical. Because of this, says Allan Walton ‘there are so many magnets out there being scrapped and we’re not sure where they’re going,’ But Walton and his colleagues at Birmingham, including Andy Williams, have taken a step towards solving this problem.

Walton pumps high-pressure hydrogen into the crystal structure of the alloy, forcing the metal ions apart and making the magnet swell and crack. Gradually, this breaks the magnetic block down to a powder, which can be simply poured out from a hard drive – much quicker than dismantling it to remove the magnet.

Although the powder is no longer magnetic, the process is reversible. ‘If you heat and press the powder in a vacuum you can get the hydrogen out again,’ Walton explains, and squeezing out the hydrogen atoms reforms the block and restores the magnetism.

The REEs’ affinity for hydrogen is useful in another important green technology. Electric cars rely on hydrogen to power their fuel cells, but need a safe and reliable way to store the highly explosive gas. Alloys like LaNi5H6.6H20 could be the answer for hydrogen storage as the hydrogen is incorporated into the metal bonding – just like in the powder formed by Walton and Williams’ process. To get the hydrogen out, you simply heat up the alloy and best of all, says Dave Murphy, ‘the alloy is completely safe. You can fire a bullet through it.’ Once all the hydrogen is used, the alloy can be ‘refilled’ by pumping hydrogen back in.

Magnifi cent moleculesDavid Sait, assistant editor, highlights one of his favourite molecules. In this issue: polyethylene glycol

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On-screen chemistry

Breaking Bad - poisoning gangsters with phosphine gasIn Breaking Bad 1 Walter White, a down-on-his-luck high school chemistry teacher, finds out he has terminal cancer. His family is struggling to pay the bills so he decides to turn his chemistry creativity towards making illegal drugs. He joins up with Jesse, a local drug dealer, cooking up methamphetamine, known on the streets as ‘meth’ or ‘crystal meth’.

Almost at once things go badly wrong when two rival gangsters threaten to kill them. Bargaining for his life Walter takes them into the lab promising to show them how to make top-grade meth.

Thinking on his feet he starts the process but manages to contrive a reaction to produce poisonous gas to kill the gangsters. He heats up a pan of water and when it’s boiling throws in a bottle of red phosphorus. A shower of sparks causes enough confusion for White to escape outside where he holds the door shut trapping the two gangsters in the fumes and poisonous gases.

Later Walter explains to Jesse “red phosphorus in the presence of moisture and accelerated by heat yields phosphorus hydride … phosphine gas … one good whiff and ...”.

It’s a clever way of getting out of a tight spot but is the chemistry correct?

Not all phosphorus is the samePhosphorus does indeed react with water vapour to produce phosphine (PH3), a colourless, flammable and toxic gas (b.p. -87°C, dangerous level ca. 50 ppm in air). However the standard industrial reaction requires white phosphorus, rather than red, and concentrated sodium hydroxide:

P4 + 3NaOH + 3H2O → 3NaH2PO2 + PH3

Phosphine gas is reported to be a dangerous by-product in the illicit production of ‘meth’ so this may be where the idea came from in the programme.

Red and white phosphorus are allotropes, with white phosphorus existing as P4 molecules and red phosphorus as an amorphous network. White is much more reactive than red phosphorus and can be heated to make the red allotrope, which can then be purified with hot water. Heated red phosphorus can react with hydrogen to make PH3 but Walter only has steam.

As it’s definitely red phosphorus that Walter is using the chemistry is not looking too good. He did heat the pan over a camping gas stove and so the sparks could have been some of the phosphorus burning in the flame (red P burns above 260°C in air) but simply adding red phosphorus to a frying pan of steaming boiling water would not produce the clouds of phosphine gas we see in the programme.

Not your average school chemistry lesson …

Jonathan Hare explains...

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Reference1. Breaking Bad, Sony Pictures

Television, 2008, http://bit.ly/an4aAn

InfoChem 5


Nasa astronauts wear a ‘Maximum Absorption Garment’, a nappy, when on extravehicular activity (a spacewalk).

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Introduction Nappies are designed to absorb large amounts of liquid in order to keep the liquid away from the baby’s skin and so prevent nappy rash. They do this by using sodium polyacrylate; a polymer which has the ability to absorb many times its own weight of water.

Sodium polyacrylate (sometimes called ‘waterlock’) has the chemical formula -[-CH2-CH(COONa)-]n- and is used in products such as detergents, coatings, thickening agents, fake snow and of course nappies. It has the ability to absorb as much as 200 to 300 times its own mass in water.

Materials You will need: disposable nappies (several types); zip-lock bags; scissors; plastic cup; water; newspaper; salt; spoon.

Backyard chemistry

In this issue: making snow from nappies

MethodPlace a new nappy onto the newspaper. Carefully cut through the inside lining and remove all of the cotton-like padding material. Put the padding into a clean zip-lock bag. Sweep any spilled crystals onto the paper and pour into the bag with the nappy padding.

Blow a little air into the bag to make it puff up, then lock it. Shake the bag to separate the crystals from the nappy padding and carefully remove the padding from the bag. The white powder left at the bottom of in the bag is the sodium polyacrylate; this is what you will use for the experiment. If you don’t see crystals the absorbent is intercalated within the padding; use strips of the material instead.

Pour the sodium polyacrylate into a plastic cup and fill the cup to about a third of its depth with water. Mix with the spoon until the mixture begins to thicken and the water/sodium polyacrylate has turned into a snow-like material, which will feel dry to the touch. You can even turn the cup upside-

down and the snow should stay should stay inside.

Once you have finished examining the water-bound polymer, add a teaspoon of salt to the polyacrylate snow and stir. The snow should ‘dissolve’.

You can also measure the volume of water that one nappy absorbs by slowly adding water to it – try to see if different brands of nappy absorb the same amount of water – are the more expensive brands better value for money?

ExplanationSodium polyacrylate is a superabsorbent polymer, a long chain of repeating monomers that expand when they come in contact with water. The water is drawn into and held by the polymer molecules which effectively act like giant sponges. For this reason nappies mustn’t be disposed of down the toilet since they will block it as they swell up. The padding is used spread the liquid by capillary action so that the liquid is distributed within the body of the nappy.

The snow ‘dissolved’ when the salt was added because salt interferes with the binding between the water and the sodium polyacrylate.

Care should be taken with scissors.

All liquids should be discarded in the sink after use.

Based on an idea originally seen in Steve Spangler Science

Did you know?

Health & Safety

Prof Hal Sosabowski presents experiments you can do on your own

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Introduction Introduction

MethodPlace a new nappy onto the newspaper. Carefully cut through the inside lining and remove all of the cotton-like padding material. Put the padding into a clean zip-lock bag. Sweep any spilled crystals onto the paper and pour into the bag with the nappy padding.

Blow a little air into the bag to make it puff up, then lock it. Shake the bag to separate the crystals from the nappy padding and carefully remove the padding from the bag. The white powder left at the bottom of in the bag is the sodium polyacrylate; this

down and the snow should stay should stay inside.

6 InfoChem


2008–present, project leader at The Welding Institute

2004–2008, PhD in Materials Science and Metallurgy from the University of Cambridge

2000–2004, MSci in Natural Sciences (with a chemistry and materials specialism) from the University of Cambridge

1998–2000, Mathematics, Further Mathematics, Physics, Chemistry and Economics & Business Studies A-levels at St. Clement Dane’s School, Chorleywood

Backyard chemistryTW

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Investigations Roger joined TWI’s graduate scheme after doing a PhD but a doctorate is not necessary for the scheme. Graduates generally join either as technicians, with a focus on laboratory work, or as project leaderslike Roger.

Roger works in the metallurgy, corrosion and surfacing technology group. It is part of his job to investigate why a customer’s welded steel joint failed or how and why a sample corroded.

His team often work for the oil and gas industry - investigating metals, polymers and ceramics in saltwater or hydrogen sulfide environments. This involves studying the underlying microstructure of the metal using optical or electron microscopy, x-ray diffraction and a variety of mechanical tests and so Roger’s chemistry background is vital.

Roger is also responsible for managing the heat treatment facility at TWI. During the year, 50-60 people may need this equipment to analyse and treat samples at temperatures up to 1500oC. It’s Roger’s job to allocate time to the furnaces and ensure that the equipment is accurately calibrated.

A typical dayRoger is involved with many different projects simultaneously so his day will include a variety of activities. He has to be organised to manage his time and juggle different projects with different deadlines.

For shorter projects that are a few weeks long, Roger will manage the whole process from start to finish. He will do perhaps 10 per cent of the laboratory work himself and delegate the rest to colleagues with specialist training. With these projects the job is not just to see why something failed but also to work out how to prevent the same problem in the future. It’s Roger’s job to report these findings back to the client.

Larger projects can last from three months to two years or more, and might involve the manufacture and testing of new equipment for a customer’s project. On such large projects, Roger is part of a team including managers, technicians and support staff. Although he wouldn’t do all the work Roger would be involved at all levels, coordinating testing, analysing data and liaising with customers.

TWI also has an active internal research programme, conducting blue-sky research and studying interesting industrial phenomena. For this, Roger searches the literature and does experiments just like when he was doing his PhD. Past TWI research has led to many industrial breakthroughs, like the invention of Friction Stir Welding, which was used to make space shuttle fuel tanks.

The spice of lifeRoger says that every week he learns something new or encounters a new challenge. It is this, together with the daily mix of research, lab work, project management and working with clients, that he enjoys most about his role.

Project leader at TWIRoger Barnett has been working at TWI in Cambridge as a project leader since 2008. He talks to David Sait about his typical day.

A Day in the life of

Roger BarnettPathway to success

You can download InfoChem at www.rsc.org/infochem

and copy it for use within schools

TWI

InfoChem 7


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Students are invited to solve Benchtalk’s Find the element puzzle, contributed by Simon Cotton. Your task is to complete the grid by identifying the eight elements using the clues below. All the clues & answers are related to the lanthanides.

1. This element is used to make the most widely used magnetic resonance imaging (MRI) contrast agents.

2. Named after a continent, this element forms red phosphors traditionally used in colour TVs.

3. This element is not a lanthanide, but is chemically very similar, so it occurs in all their ores.

4. A village in Sweden that gives its name to four elements discovered there, including three lanthanides.

5. This is the only lanthanide that has no stable isotopes.

6. This lanthanide forms pink compounds and is used to make pink glass, as well as fi bre amplifi ers for communications.

7. This lanthanide is named after an asteroid; its oxide is used in catalytic converters and also in self-cleaning ovens.

8. When combined with iron and boron, this element makes the strongest permanent magnets known.

If you have completed this correctly, in 9 down you will have the element which is the last stable lanthanide to be discovered, in 1907, taking its name from the Latin for Paris.

Please send you answers to: the editor, Education in Chemistry, the Royal Society of Chemistry, Thomas Graham House, Cambridge CB4 0WF, to arrive no later than Wednesday 30 March. First out of the editor’s hat to have correctly completed the grid will receive a £30 Amazon gift voucher.

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Find the element no. 17 solutions and winnerThe winner was Jihad Daba from Saint David’s Catholic College, Cardiff .

Puzzles£50 at Amazon to be won

ANABOLIC STEROIDSANDROSTENEDIONEBODYBILE ACIDSCONJUGATIONDETECTING STEROIDSDIANABOLDRUGEXCRETEDFAECESFAMILY OF MOLECULESHORMONESHYDROGEN

HYDROXYLATIONINACTIVE EPIMERLIFELIVERLIVER DAMAGEMALE TESTESMASS SPECTROMETRYMOLECULEMUSCLEMUSCLE MASSORALLYOXIDISEDREDUCTION

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F L U O R I N EMonth Prize Wordsearch No. 54 winnerThe winner was Veronica Sula from Milton Keynes. The 7-letter word was PROTEIN.

Prize wordsearch no. 55Students are invited to fi nd the 31 words/expressions associated with steroids hidden in this grid, contributed by Bert Neary. Words read in any direction, but are always in a straight line. Some letters may be used more than once. When all the words are found, the unused letters, read in order, will spell a further 8-letter word. Please send your answers to the editor at the usual address to arrive no later than Wednesday 30 March. First correct answer out of the editor’s hat will receive a £20 Amazon gift voucher.

Find the element No. 18

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