Chemistry World – Can graphite treated merely with water become a superconductor at room temperature? This is the extraordinary claim made by scientists in Germany. Unsurprisingly, this has been met with scepticism – from measured to outright – by other experts in superconductivity.
Pablo Esquinazi and his team at the University of Leipzig say that they observed a ‘tantalising hint’ of superconductivity at room temperature in samples of graphite powder that had been mixed with water and dried overnight at 100oC. The researchers placed the material in a magnetic field and observed changes in the graphite’s magnetism – tracing a hysteresis loop – that are characteristic of a superconductor. Analysis showed that only a tiny fraction of the sample, around one part in 10,000, was producing the response.
Other experts are not convinced. ‘There is no physical evidence of superconductivity, by which I mean primarily there are no resistance measurements that show the material has become superconducting,’ says Mark Ellerby of University College London in the UK, who works on graphite-based superconductors. ‘Graphite is a very interesting material that has a lot of magnetic properties of its own and these are only alluded to. My feeling is that this is a highly suppositional paper that uses interpretation in a strongly philosophic nature, without providing physical evidence.’
Archie Campbell, emeritus professor at the University of Cambridge, UK, is equally sceptical. ‘They do the right thing in measuring the magnetisation as a function of field. This appears to show hysteresis but the loops at increasing amplitude of field do not correspond to those of a superconductor,’ he says. ‘Also, the critical current does not seem to change significantly between 5K and 300K which is highly improbable. The model they have is that there are a few superconducting grains, but the signal is only one in 104 of what you would expect from a solid superconductor so only 1 grain in 104 is superconducting. There is no reason for this in a simple homogeneous system such as this. I think it is an experimental artefact.’
On the disappearance of the signal when the sample is compressed, Ted Forgan of the University of Birmingham in the UK, says: ‘The authors give reasons why the signal should be smaller, but I am not convinced that it would go away completely on their model. Graphite is flaky, with a very large and anisotropic diamagnetism [the creation of a magnetic field in opposition to the externally applied field]. One could imagine changing diamagnetic signals from realignment of micron-sized graphite particles which would go away if the sample were compressed so the particles could not rotate.’ Forgan concludes: ‘So, not proven, but not disproved either and worth following up.’
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