Highly porous mullite ceramics from engineered alkali activated suspensions

Abstract

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 c-Al 2 O 3 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°C, for 1 hour. Preliminary results concerning the extension of the concept to mullite three-dimensional scaffolds are presented as well.

Bioactive Glass-Ceramic Foam Scaffolds from ‘Inorganic Gel Casting’ and Sinter-Crystallization

“…As previously observed [ 21 ], the partial gelation of glass slurries, upon alkaline activation, leads to a marked pseudoplastic behavior, in analogy with what happens with more common ‘inorganic polymers’ (including geopolymers). Air bubbles, incorporated by intensive mechanical stirring (aided by the surfactant), at high shear rates and low viscosity, remain trapped when stirring stops, at low shear rate and high viscosity [ 24 ]. In the present investigation, there was an increase of 100–150% in the volume of slurries, passing from the alkali activation step to the hardened state.…”

A Review on Synthesis of Mullite Ceramics from Industrial Wastes

“…Due to its rare existence in nature, all the mullite ceramics used in industry are man-made. Much research has been done to prepare mullite ceramics using different precursors, starting either from industrial/laboratory grade chemical [3] or naturally occurring aluminosilicate minerals [4]. However, the cost of these starting materials is expensive, which are synthesized or mined beforehand.…”

Synthesis of SiAlON‐type compounds by carbothermal reduction and nitridation of nanoparticulate geopolymers

“…After an ion-exchange process by chemical treatment, in situ refractory phases (e.g., mullite or SiAlON) can be obtained on heating the component to high temperatures while retaining the same shape. 26 This study, which is the third of our systematic studies, focused on the synthesis of SiAlON by carbothermal reduction and nitridation of geopolymers. After defining a suitable starting composition such as…”