Porous geopolymers: Processing routes and properties

Abstract

Cellular ceramics constitute a specific class of materials containing a high level of porosity, greater than 60 vol%, which are characterized by the presence of three-dimensionally arranged open and/or closed cells. Because of their structure, cellular ceramics exhibit a unique combination of properties such as low density, low thermal conductivity, low thermal mass, high permeability, high thermal shock resistance and high specific surface area, making them essential for various engineering application. Nowadays, porous geopolymers have been the focus of promising research in the field of porous inorganic materials because of their unique combination of good thermal stability and excellent mechanical properties. An interesting technological feature is that their solidification kinetics is easily adjustable and thanks to ceramic-like structure they have significant structural stability at elevated temperatures. The processing methods used for the fabrication of porous geopolymers can be divided into various approaches. Many methods have been explored to synthesize reproducible porous sponges or foams from geopolymer systems, such as gaseous method, rapid solidification, foaming, freeze-casting and/or combination of them. Concerning the macro/micro-structure of cells, the processing can be strongly influenced by various characteristics as a chemical composition, rheological behaviour of the slurries, kinetics of pore formation and hardening behaviour. This study presents methods of processing and manufacturing approaches with respect to types of porous materials and experimental results in this field.