Novel nanomaterials can be made using ancient casting technology, claim Chinese Scientists. 

Titanium carbide nanowires are important non-oxide ceramic materials that have high melting points, hardness and resistance to corrosion which have many applications including catalysis, microelectronics and hydrogen storage. Existing methods to synthesis them involve using other nanotubes as templates or reactions catalysed by nanoparticles but these give little control over the purity, shape, size, aspect ratio, crystal orientation and structure in the resulting nanowires. 

Now Zhonghu Zhang, Shandong University, China and colleagues have come up with a new method of producing titanium carbide nanowires using the far from new process of casting - where molten metal/alloys are injected or poured into a mould to form an object of desired shape.   

The group melted nickel pellets and titanium rods together in a graphite crucible and poured the melt into moulds to solidify. A small amount of carbon is present in the melt, originating from impurities in the source metal, and also picked up from the graphite crucibles so that the final cast alloy contains TiC nanowires within a dominant nickel-titanium matrix. The nanowires are isolated by electropolishing to dissolve the soluble NiTiC matrix and filtering to extract the un-dissolved TiC nanowires.

Changing the shape of the mould, adjusts the cooling rate of the casting, and controls the carbon content and size of the resulting TiC nanowires - the faster the sample cools the smaller the resulting nanowires. As casting is a bulk processing method it could be scaled up to produce TiC nanowires on an industrial scale, says Zhang. 

Mark Blamire, an expert in device Materials at the University of Cambridge, UK comments 'this is not a standard approach and relies on a subtle phase diagram. It is a good line to take for this particular nanostructure. Whether it can be generalised is the question.'

However, Zhang comments, 'the difficult part of the process is extracting the nanowires. We will think about how to do that in the future.' Future research will also investigate whether this casting method could be applied to produce nanowires of other transition metal carbides, oxides and nitrides.

Aileen Day

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