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Salt nanowire surprise
Royal Society of Chemistry ^ | 26 May 2009 | Phillip Broadwith

Posted on 05/26/2009 9:54:43 PM PDT by neverdem

Common table salt - normally a brittle crystalline material - can be pulled into nanowires that will extend by more than twice their own length without breaking, US researchers have found.

Nathan Moore and his team at Sandia National Laboratories in Albuquerque, New Mexico, were investigating water adsorption onto salt crystals using an interfacial force microscope (IFM) to probe the salt surface when they stumbled upon their discovery.

'When we poked the salt surface, we saw some unusual force behaviour [between the tip of the microscope probe and the surface]. It seemed crazy at the time, but we thought: "could we be making nanowires?" - of course, seeing is believing, so we put salt in the [transmission electron microscope] and there we saw the nanowires!' (see video at bottom of page)

Time-lapsed transmission electron microscope images showing superelongation of a nanowire © Nano Letters

Surprisingly, the salt not only becomes ductile (i.e. able to be pulled into wires), but the wires are also superplastic - they can be extended by more than their own length before breaking. This unusual property is more normally associated with metals and certain ceramics, rather than ionic crystals like salt. The wires can also be compressed back into the crystal, but do tend to bend and buckle.

Part of the cause of this unusual superplasticity could be down to the microscope itself - the beam of electrons from the probe tip, which is used to form the image, can break up the surface of large salt crystals into tiny grains. This allows rapid diffusion of atoms along the grain boundaries, allowing the wires to deform rather than break.

Bombarding salt with the microscope electron beam can also displace chloride ions from the crystal lattice and cause electrons to recombine with sodium ions to form metallic sodium. 'Elemental analysis of the nanowires shows that the composition is predominantly sodium chloride,' says Moore, but there is a reduction in the proportion of chloride. This means that metallic sodium - which has less directional bonding and can also conduct, so could help dissipate charge from the electron beam - could be further improving the superplastic properties of the nanowires.

To see how much of an effect the electron beam has on the growth of the wires, the team tried pulling one out with the beam turned off, turning it back on to get a quick image every so often. They still saw massive elongation of the nanowire, although nowhere near as much as with the beam on, and the wire did eventually break. 'It's very clear the electron beam enhances the superplasticity,' comments Moore, 'but we don't know yet whether or not the electron beam is required to start the wire off.'

'Plasticity [of salt] on this scale is very interesting and also quite surprising,' says Florian Banhart, from the Institute for Physics and Chemistry of Materials (IPCMS) in Strasbourg, France. 'Atomic diffusion is quite a likely explanation for this behaviour as there will be a strong charging effect under the beam, which could create defects in the structure, so diffusion would be enhanced. What is quite convincing is that they see a difference between the situation with and without the electron beam.'

Moore thinks that the possibility of forming nanowires on salt surfaces could have implications in understanding the properties of geological salt deposits and sea salt aerosols, and perhaps help improve understanding about the role salt plays in cloud nucleation and smog formation. 'The fundamental aspects of this are very interesting - you have to wonder if, for example, sea salt particles in the atmosphere are doing the same thing when they collide - are they forming nanowires?'

ReferencesNW Moore et al, Nano Letters, 2009. DOI:10.1021/nl9004805

TOPICS: News/Current Events; Technical
KEYWORDS: nacl; nanotechnology; nanowire; plasticity; salt; science
Short Youtube video at the source
1 posted on 05/26/2009 9:54:43 PM PDT by neverdem
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To: neverdem

Now to try it with potatoes.

2 posted on 05/26/2009 10:07:22 PM PDT by kenth
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To: neverdem

I wonder if this will be like POST-IT NOTES???

Accidental discovery.

3 posted on 05/26/2009 10:07:45 PM PDT by UCANSEE2 (The Last Boy Scout)
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To: neverdem
Key phrase:

'It's very clear the electron beam enhances the superplasticity,'

I'm curious whether time does the same thing, via simple entropic processes.

4 posted on 05/26/2009 10:09:37 PM PDT by Gondring (Paul Revere would have been flamed as a naysayer troll and told to go back to Boston.)
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To: El Gato; Ernest_at_the_Beach; Robert A. Cook, PE; lepton; LadyDoc; jb6; tiamat; PGalt; Dianna; ...
Resolve A DOI Name Save that address.

Attention Diabetics - New to the fold

What is Juvenile diabetes (Sotomayor has had it since age 8)

FReepmail me if you want on or off my health and science ping list.

5 posted on 05/26/2009 10:36:46 PM PDT by neverdem (Xin loi minh oi)
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To: Gondring

I’m curious whether time does the same thing, via simple entropic processes.

If you’ve ever been bored out of your gourd you would know that time is elastic as it seems to stretch on forever. ;^)

6 posted on 05/27/2009 4:19:22 AM PDT by saganite (What would Sully do?)
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To: neverdem

What is a DOI Name?

7 posted on 05/27/2009 4:29:08 AM PDT by fanfan (Why did they bury Barry's past?)
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To: neverdem; DollyCali

This has to be one of the most outrageously surprising scientific discoveries of my lifetime, and such a “simple” venue! I’ve been involved in chemistry, materials science (including work with electron microscopy) and physics throughout my life, and there is no way that I would have guessed that behavior such as this is lurking within simple, non-doped NaCl. I grant that the local ionization the microscope endues on the crystal might affect Na and Cl in ways that are unexpected. However, be able to draw a filament out of the solid which proves to be essentially NaCl is simply breathtaking to me!

8 posted on 05/28/2009 1:17:04 PM PDT by AFPhys ((.Praying for President Bush, our troops, their families, and all my American neighbors..))
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