Highly porous geopolymers: effect of the processing route on the reached properties

The geopolymers (inorganic polymers formed basically of silicates) have attracted increasing attention from academia for several reasons, particularly because it is considered a sustainable material where industrial by-products (fly ash and blast furnace slag) can be used as raw material, and is based on a low energy cost process. Such materials find applications in virtually all industrial sectors, depending on the molar ratio Si:Al, responsible for its properties. Currently the application of large volumes of geopolymers is focused on replacement of Portland cement, a material with an extremely aggressive process of obtaining to the environment. However, due to their similar properties to the ceramic material and increase search for new applications, studies of porous geopolymers are also of great interest. Processing routes currently used to obtain porous geopolymers are based on the civil construction for the production of aerated concrete with closed porosity, limiting their application. Thus, the development of a new processing route to produce porous geopolymers, which permits the formation of a structure with open porosity, enabling the expansion in the applications of such material is essential. Two different routes are proposed based on porous ceramic processing routes with highly porous geopolymers results, with a homogeneous microstructure, and open cell porosity of up to about 85vol%, with physical properties that suggest they may be used as a substitute for low-cost highly porous ceramics for applications such as catalyst supports, filtration of hot gases, adsorption and insulating refractory furnaces

Highly porous mullite ceramics from engineered alkali activated suspensions

Air may be easily incorporated by vigorous mechanical stirring, with the help of surfactants, of activated geopolymer-yielding suspensions. The cellular structure is stabilized by the viscosity increase caused by curing reactions, configuring an inorganic gel casting. The present paper is aimed at extending this approach to mullite foams, obtained by the thermal treatment of engineered alkali activated suspensions. Green foams were first obtained by gel casting of a suspension for Na-geopolymer enriched with reactive -Al2O3 powders. Sodium was later extracted by ionic exchange with ammonium salts. In particular, the removal of Na+ ions was achieved by immersion in ammonium nitrate solution overnight, with retention of the cellular structure. Finally, the ion-exchanged foams were successfully converted into pure mullite foams by application of a firing treatment at 1300 degrees C, for 1hour. Preliminary results concerning the extension of the concept to mullite three-dimensional scaffolds are presented as well

Mechanical and thermal characterization of an epoxy foam as thermal layer insulation for a glass fiber reinforced polymer

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