High-porosity geopolymer foams with tailored porosity for thermal insulation and wastewater treatment
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Hamada Elsayed Department of Industrial Engineering, University of Padova, 35131 Padova, Italy; and Ceramics Department, National Research Centre, 12622 Cairo, Egypt
Alessandro Zaggia and Lino Conte Department of Industrial Engineering, University of Padova, 35131 Padova, Italy
Hongqiang Li College of Civil Engineering, Hunan University, 410082 Changsha, China
Paolo Colombo Department of Industrial Engineering, University of Padova, Padova, Italy; and Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802, USA (Received 19 December 2016; accepted 24 March 2017)
High-porosity metakaolin-based geopolymer foams (GFs) were fabricated by a gelcasting technique using hydrogen peroxide (foaming agent) in combination with Tween 80 (surfactant). Slurries processed in optimized conditions enabled to fabricate potassium based GFs with a total porosity in the range of ;67 to ;86 vol% (;62 to ;84 vol% open), thermal conductivity from ;0.289 to ;0.091 W/mK, and possessing a compressive strength from ;0.3 to ;9.4 MPa. Moreover, factors that influence the compressive strength, the porosity, the thermal conductivity, and the cell size distribution were investigated. The results showed that the cell size and size distribution can be controlled by adding different content of surfactant and foaming agent. The foamed geopolymer can also be used as adsorbents for the removal of copper and ammonium ions from wastewater. The foams, due to their low thermal conductivity, could also be used for thermal insulation. It was also possible to produce geopolymer formulations that could be printed using additive manufacturing technology (Direct Ink writing), which enabled to produce components with nonstochastic porosity.
I. INTRODUCTION 1,2
In the 1970s, Davidovits reported on geopolymers as semicrystalline three-dimensional aluminosilicate materials, which can be formed from aluminosilicate sources (metakaolin, fly ash, or slag) mixed with an aqueous solution containing reactive ingredients (potassium hydroxide, phosphoric acid, or sodium silicate).1,3 Today, GFs have been widely investigated because of their unique combination of low thermal conductivity associated with good mechanical properties and excellent high temperature stability,3–7 environmentally friendly nature, simple fabrication, and the fact that they do not require high temperature sintering.8 They have been used as membrane and membrane supports,9,10 adsorbents and filters,11–14 catalysts,15,16 and building materials.4,17,18 Generally, aluminum6,19,20 and silicon18,21–24 Contributing Editor: Eugene Medvedovski a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2017.127
powders have been used as pore foaming agent for the fabrication of foamed geopolymers, but the redox reactions are intense (making it difficult to control the generated cell size and total porosity) due to the high alkalinity of the system,1 and the cells formed by this foaming route are typically closed, thereby li
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