MATERIALS PROCESSING
Processing glass like a polymer
Andy Pye discovers a novel forming technology producing quartz glass that can be CNC machined P
ure quartz glass is highly transparent and resistant to thermal, physical and chemical impacts. These are optimum prerequisites for use in optics, data technology or medical engineering. For efficient, high-
quality machining, however, adequate processing is lacking. Now, scientists of Karlsruhe Institute of Technology (KIT) in Germany have developed a forming technology to structure quartz glass like a polymer. Glass particles of 40nm are mixed with a liquid
polymer, then the mix is formed like a sponge cake, and hardened to a solid by heating or light exposure. The resulting solid consists of glass particles in a matrix at a ratio of 60-40 per cent volume. The polymers act like a bonding agent that retains the glass particles at the right locations and, hence, maintains the shape. This so-called “glassomer” can be milled, turned, laser-machined or processed in CNC machines just like a conventional polymer. “It has always been a big challenge to combine
highly pure quartz glass and its excellent properties with a simple structuring technology,” says Dr Bastian Rapp, head of the NeptunLab interdisciplinary research group of the KIT Institute of Microstructure Technology (IMT). “Instead of
28 /// Environmental Engineering /// June 2018
❱❱ Just as with a conventional polymer, “glassomer” can be milled, turned, lasered or processed in CNC machines
heating glass up to 800°C for forming or structuring parts of glass blocks by laser processing or etching, we start with the smallest glass particles. The entire range of polymer forming technologies is now opened for glass.” For fabricating high-performance lenses that are
used, for example, in smartphones, glassomer rod is produced, from which the lenses are cut. For highly pure quartz glass, the polymers in the composite must be removed. To do so, the lenses are heated in a furnace at 500-600°C and the polymer is burned out to carbon dioxide. To close the resulting gaps in the material, the lenses are sintered at 1,300°C. During this process, the remaining glass particles are densified to pore-free glass. This forming technology enables production of
highly pure glass materials for any applications, for which only polymers have been suited so far. This opens up new opportunities for the glass processing industry as well as for the optical industry, microelectronics, biotechnology and medical engineering. “The process is suited for mass production. Quartz
glass is much cheaper, more sustainable and more energy-efficient than special polymers,” Rapp explains. EE
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