Sound and heat insulation materials from fly ash
Taking advantage of the fly ash waste, the authors of the Ho Chi Minh City Polytechnic University created a composite airgel and soundproofing material that can be manufactured on an industrial scale.
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Fly ash has not been thoroughly treated, caused environmental pollution. Photo: Internet
Fly ash is fine-grained flue gas dust obtained from coal combustion in boilers of thermal power plants, rotary kilns of cement plants, blast furnaces of metallurgical plants, and tunnel kilns of factories production of building materials, etc. The composition of fly ash usually contains silicon oxide, aluminum oxide, calcium oxide, iron oxide, magnesium oxide, sulfur oxide, etc. Currently, there are not many methods of thorough treatment, so fly ash pollutes the environment and affects human health.
Aerogel is defined as a dry gel system (no solvent in the gel system) with a large number of voids in the structure, with a very light weight, so the airgel is also known by the name "ice smoke" or "solid smoke". There have been studies in water synthesizing airgel from silica extracted and recovered from fly ash by traditional sol-gel method.
However, the synthesis process is complicated, using many unfriendly chemicals for pretreatment of fly ash, synthesizing aerogels, or using expensive solvents and chemicals. In addition, the specifications of materials made from fly ash are still not suitable for practice, such as higher thermal conductivity than traditional insulation. Most of the studies are only at the laboratory scale.
Face with that fact, the authors of Ho Chi Minh City University of Science and Technology carried out the project "Developing technologies to produce composite airgel materials from fly ash, oriented to be applied as ultra-lightweight, soundproof, and heat-insulating materials."
Raw fly ash was collected by the authors from Duyen Hai 1 Thermal Power Plant, then processed into smaller particles (0.5 - 2 µm), most of which are spherical in shape. The team used freeze-drying technology, solvents, and non-toxic binders to synthesize the airgel. Airgels synthesized directly from fly ash have super light (0.072 - 0.093 g/cm3), high porosity (94.94 - 95.78%) and good compressive strength (67.73 - 254.75 kPa). This material is further mixed with recycled PET (rPET) plastic fibers, with a diameter of 30 µm and a length of 64 mm to produce composite airgel materials (FA airgel).
Laboratory tests show that FA airgel material has super lightness (0.026-0.062 g/cm3), porosity (96.59-98.42%), good insulation (0.034-0.039 W/mK), sound absorption coefficient from 0.40 - 1.0 in the frequency range from 1,400 - 6,000Hz. The FA airgel sheet has uniform thermal insulation properties at all points on the sheet, with an average thermal conductivity of 0.036W/mK.
According to Assoc. Prof. Dr. Le Thi Kim Phung, Project Manager, FA aerogel has good compressive capacity 3 times better than bagasse airgel (88 kPa), 1.5 times higher than silica-cellulose aerogel (169 kPa). In addition, the production cost of FA airgel is very low, estimated at only 59,000 VND/m2. Meanwhile, the cost of some commercial insulation products, such as Chinese airgel costs from 250 to 430 thousand VND/m2, Aspen Aerogel products (USA) cost about 3 million VND/m2,...
The research project has been accepted by Ho Chi Minh City Department of Science and Technology and the authors are ready to transfer technology to businesses.
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