New injection moulding technique allows glass to be cast in any shape

Fused silica glass offers numerous benefits as a material, but manufacturers often avoid using it because of the high temperatures required. However, researchers in Germany have now produced high quality glassware at far lower temperatures using injection moulding. Their technique could potentially have significant technical, economic and environmental benefits.

Silica glass is one of the oldest materials known, produced simply by heating grains of silicon dioxide until they melt. It has remarkable chemical stability, optical clarity and durability. In the 20th and 21st centuries, however, manufacturers have increasingly used polymer-based products, which often have inferior properties and have become notorious environmental contaminants. One reason is that many polymers can easily be shaped by injection moulding – heating the material until it softens before injecting it into a pre-formed mould. This usually occurs at 200–250˚C. By contrast, silica glass melts at around 2000˚C. Aside from the enormous energy demands ‘there are not too many mould materials that can sustain these temperatures’, explains Frederik Kotz of the University of Freiburg in Germany.

Everyday glassware usually contains additional chemicals. ‘We add soda, calcium – a lot of stuff like that – to reduce the melting temperature,’ says Kotz. ‘But it also affects properties like thermal stability, chemical stability.’ In precision glass manufacturing techniques, pure silica glass is generally produced at ultrahigh temperatures before being etched with hazardous chemicals such as hydrofluoric acid and flame polished to produce the desired shapes – although ultra-pure silica glass for optical fibres, for example, is usually produced by chemical vapour deposition.

A potential alternative is powder injection moulding: a technique first developed in the 1950s and used today to produce billions of pounds worth of everyday goods ranging from metal spanners to ceramic sinks. Solid particles suspended in a liquid binder are injection moulded into the desired shape and allowed to set. The resulting object is then placed into an oven, causing the binder to evaporate and the particles to fuse together – a process called sintering. Several research groups had previously attempted to produce glassware this way, but with limited success. ‘You normally get a white piece of glass – it’s more a ceramic,’ says Kotz.

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