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The cloim thot grophene is 200 timesstronger thon steel is widely repeoted, Universityof Combridge Professor Horry Bhodeshio set the

record stroight of o London Moteriols Society lectureheld ot the Royol School of Mines.-JQmes Perkins reports,

O teel experl. Harry Bhadeshia is f lattered that

\ t t ' r . material he has spent his professional l i fe\- / researching is held in such a high regard that i t isthe substance against which everything else is measured.But the c la im that graphene is '100 [or 200, or 300) t imesstronger than steel is 'absolute rubbish' , according to theUniversi ty of Cambridge metal lurgist . The claim, whichstems from research conducted in 2008, is repeated odnouseum in reportage of graphene, encouraged by manyuniversitv media departments.

This comparison is based on shaky foundat ions and,as Bhadeshia says, design involves a combination ofparameters depending on the appl icat ion. ' l t is nonsenseto ta lk about the dimension of a new mater ia l on thebasis of just one property. A design problem is notinterest ing at a l l unless there are many solut ions for thesame parameters. l f you are talking just about strength, i tis a very boring problem to work on. '

M*w sfr*ng is grmphene?In 2008, researchers from the engineering departmentat Columbia University, USA conducted the f irst strengthtest on graphene and published the results in Sclencein a paper called Meosurement of the Elostic Propertiesond lntrinsic Strength of Monoloyer Grophene.Iheteam placed pr ist ine graphene f lakes over smal l c i rcularholes etched in si l icon and tested their strength usingnanoindentat ion, which involved pushing on the centreof each f lake with a diamond-t ipped atomic forcemicroscope with a radius of 20nm. The studies foundthat the in l - r insic strengl .h of the mal.er ia l was 130GPa.In a quote publ ished with the associated press release,Professor James Hone said. '0ur research establ ishesgraphene as the strongest material ever measured, some200 t imes stronger than structural steel. 'The same team,in a 201 3 Sclence paper t i t led High-Strenglh Chemicol-Vopor-Deposited Grophene and Groin Boundories, againused nanoindentation to prove CVD-grown graphene hada tensi le strenqth of 11 BGPa.

A paper publ ished in Nonosco/e in August 201 5,Nonoindentotion connot occurotelY predict the tensilestrength of grophene or other 2D moteriols, casts somedoubt on whether the results from this method areaccurate but, even using the measurements from 2008and 2013, Bhadeshia shot down the claim that grapheneis 200 t imes stronger than steel.

The stcel eernpsriso,"lBy comparing the strength of graphene to A36 structural steel, for example, which hasan ult imate tensi le strength of 400MPa, graphene is 325 t imes stronger than steel, butBhadeshia explained that comparisons such as this are not acurate.

A fairer test would be against the i ron whisker Brenner grew in 1956, in which he foundan ult imate tensi le strength of 13GPa. ln theory, Bhadeshia said, i t should be possible toachieve an ult imate tensi le strength of 21 GPa in an ideal crystal of iron. 'Divide 1 30 by 21and that is only 6.19 t imes the strength ofsteel, not 100 t imes the strength ofsteel. 0fcourse, this is the intr insic strength of graphene, which means i f I make i t bigger than onemicrometre, i t is going to col lapse. Steel I can make very, very big. '

Likc for !ikcTo compare the strength of a nanomater ia l wi th another that has proved i tsel f as oneof the most useful bulk mater ia ls created bY the human race is unfair on a number offro nts.

As Bhadeshia explained, 'The thing to not ice is the strength col lapses when you scalethe part icle by micrometers, and even nanometers" As soon as you scale the part icle up,the strength col lapses, and that is because the probabil i ty of f inding a defect in a sampleincreases as the part icle size is larger. This was a very well establ ished fact in 1956.'

0ther stresses a mater ia l needs to stand up to include fat igue, compression,torsion in phase, axial loading and centr ipetal forces. l t a lso needs to fa i l in a safe, andpredictable way- 'Anyone who tel ls you that they have created a new material becausei t is very strong is real ly ta lk ing nonsense and we shouldn' t be saying this k ind of th ingto students, ' said Bhadeshia

Grophene is still grestJust because the claim of graphene's strength is dubious, does not mean i t is not animpressive material with fantastic propert ies. Bhadeshia said, ' l am 1000/o sure we shouldwork on i t and i t should be heavi ly funded for research. To claim things that are not trueis what I am against . '

The University of Manchester is a proponent of the 200-t imes stronger thansteef claim and Moteriols World approached the university for comment.

lThe strength of a material is determined by how f irmly two atoms arebound together. Carbon atoms have a high level of electr ical attract ionwhich gives graphene i ts strength, 'a spokesman said.

'The University of Manchester has described graphene as 20o t imesstronger than steel based on the intr insic propert ies of mono-layer single-crystals rather than their performance in devices or composite materials, '

What do you think about the comparison of graphene's strength compared to stee l?Email materials.world@iom3.org, or tweet us @materialsworld

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WelcomeDuring the press cycle of this nanotechnology-themed issue of Moteriols world, Iat tended a lecture by steel expert Sir Harry Bhadeshia at the Royal school of Minesin London, organised by the London Materials Society, t i t led Hundred t imes strongerthon steel.John ol iver would have been proud of the way the cambridge Professortook down the claims made about graphene's strength compared to steel ( read thestory on page 20). The lecture was a t imely reminder of the care that needs to be takenwhen report ing on nanotechnology. The potent ia l in th is area of mater ia ls science isincredible, wi thout exaggerat ion. As Bhadeshia said, ' l am 1000i0 sure we should workon [graphene], and i t should be heavi ly funded research, but c la iming things that arenot t rue is what I am against ' " l t is easy for the average person to get exci ted aboutsomething being 100 t imes stronger than steel , and i t makes a great headl ine, whichcould be why this is being propagated by some universi t ies. But is misleading the publ icthe r ight th ing to do? The concept of graphene is hard enough to understand withoutconfusing people by making erroneous comparisons. I would l ike to th ink th is issueof Moteriols lzVorld del ivers a sober analysis of nanoscience, covering applications asdiverse as water f i l t rat ion membranes (page 3a), funct ional ised plast ic addi t ives andconduct ive inks (page 3B) and in heal thcare technology (page a2). 0n page 15, SimonFrost wr i tes about the potent ia l for strengthening metals by stretching them at thenanoscale. Director of the Cambridge Graphene Centre, Professor Andrea Ferrar i , a lsosatdown withMoter iotsworld,ahead of del iver ingtheinaugural cafeNanolecture,to ta lk about graphene. To view the interview, v is i t app.mater ia lsworld.org. Final ly,our coverage of the UK steel industry cr is is in the November issue generated the mostfeedback from our readers that I have seen in my t ime at th is magazine, so thank you toal l those who took the t ime to wr i te in. we value your thoughts and opinions on whataooears in Moteriols World.

Fred Starr recol lects thefirst t ime he was l iedto about nuclear Powerand the corrosion thataffected the Magnoxplants, on page 31.

Front cover: Si l icon wafer. Shutterstock.

Electroforming is aprocess that has goneunrecognised, says TonyHart on page 32, desPiteits use increasing overthe past 100 years.

Mines are susceptible tovarious forms of theftand fraud.0n page 44,Guy Richards exploresthe various threats andcou ntermeasu res.

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