The process involves first grinding the metal waste into a powder and mixing it with chemical crosslinkers. This mixture is then heated in the oven, frozen and freeze-dried to create the aerogel. In the Journal of Material Cycles and Waste Management, the NUS team describes how they transformed aluminium waste into aluminium hydroxide aerogels using a polyvinyl alcohol binding agent. The same principle can be applied using different metals with slight tweaks to the process, according to the researchers.
“Our approach is cheaper, does not produce any hazardous waste, consumes less energy and is more environmentally-friendly than conventional recycling methods for metal waste,” said research lead Associate Professor Duong Hai-Minh, from the NUS Department of Mechanical Engineering.
“The metal-based aerogels created using our unique fabrication technique have high thermal and mechanical stability. Hence, they are promising candidates for heat and sound insulation in harsh environments with high temperature or high mechanical impact. We are also exploring new uses for such aerogels, such as biomedical applications.”
The NUS team claims that a piece of metal-based aerogel that is 1 sqm in size and 1 cm thick costs just $7.90 to produce, which is around half the price of commercially available silica aerogel. As well as having potential for traditional aerogel applications such as insulation, the unique properties of the NUS metal aerogels open up a range of new possibilities, according to Assoc Prof Duong.
“Our aluminium aerogel is 30 times lighter and insulates heat 21 times better than conventional concrete,” he explained.
“When optical fibres are added during the mixing stage, we can create translucent aluminium aerogels which, as building materials, can improve natural lighting, reduce energy consumption for lighting and illuminate dark or windowless areas. Translucent concrete can also be used to construct sidewalks and speed bumps that light up at night to improve safety for pedestrians and road traffic.”
When coated with a chemical called methyltriethoxysilane (MTEOS), the aluminium aerogels can also repel water, becoming a self-cleaning construction material that allows dirt or debris to be washed away by rain.