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Salt melt processing of nanofibres

Doublewalled carbon nanotube - interactive version required Flash.

Carbon nanotubes (‘bucky tubes’ or nanofibres) are scarcely out of the scientific news these days, with claims of applications as diverse as plastic computers and indium-free touch screens for your iPhone (other touch screen devices are available!). While they have great potential, this can only be realised if they can be prepared reliably and in quantity. Unfortunately, most techniques yield carbon nano-tubes in miserably low yields. One of the high yield techniques, uses Catalytic Chemical Vapour Deposition (CCVD). In this, tiny molten drops of nickel serve as condensation nuclei for the carbon nanotube. While efficient, the product is contaminated with nickel, which is included within the carbon tubes, and extremely difficult to remove.

So, lots of carbon fibres, but of poor quality…

So what researchers at Nanofolio have done is work out a technique for cleaning up the tubes we can make. The technique is called salt melt processing, and involves soaking the carbon nano-tubes in a bath of molten salt – in an argon atmosphere to stop them catching fire! At 950DEG C, the molten salt breaks pen the ends of the nanotubes, liberating the nickel, which (after cooling) can be dissolved with dilute mineral acid and re-cycled.

This work is of critical importance to a wide range of nanotechnology applications, but it doesn’t lend itself easily to developing a feature, as we have done with earlier Nanofolio research (see all of our nanotechnology research features for Nanofolio). Here we simply don’t have a mechanism we can elucidate with moving interactive models. The work still deserves to stand out, however…

Initially we thought we’d have to prepare general art-work based on idealised carbon nano-tubes of the sort that usually illustrate work in this area (see, for example Wikipedia). These things are ubiquitous, however, and don’t address our story. When we reviewed the publications on the topic, however, we realised that we had some good scanning electron micrographs (SEM’s) following the processing history.

SEM’s are beautiful, but very common in the scientific literature, so we wanted to do something to make them stand out a bit. Fortunately, the final processed product has a uniform electrical conductivity, and this means that it has a nice even illumination under the electron gun – the tube appears at a uniform brightness, dependent only upon the distance from the electron gun in the microscope.

In short, we could extract depth information from the SEM using a standard graphics package. This allowed us to prepare contoured images, and using the simple ‘pop-up 3D’ technique we’ve reported previously we could get workable 3D images. Given that we could extract depth information automatically, we were able to illustrate this feature with three 3D images – a bit of a first (you’ll se very few sites sporting more than one 3D image – and that usually on the home page for impact!)

Processing carbon nanofibres on the Nanofolio website