Preparation of ceramic foams from metakaolin-based geopolymer gels

J. L. Bell, Waltraud M Kriven

Research output: Chapter in Book/Report/Conference proceedingConference contribution


The average pore diameter of hardened K2O·Al 2O3·4SiO2·11H2O gcopolymer gel was measured by standard porosimetry techniques and determined to be extremely small (6.8 nm in diameter). On heating the geopolymer, significant capillary pressure (> 21 MPa) was expected due to vaporization of water from small pores. These capillary forces were enough to cause cracking and failure of monolithic geopolymer bodies. To avoid this problem, foaming agents, including spherical Al powder and hydrogen peroxide, were added to the geopolymer paste to engineer controlled porosity into the material and to shorten the diffusion distance for entrapped water to leave the samples. In order to control the internal pressure, the mixed pastes were cast into sealed metal dies and cured at elevated temperatures. Armoloy®coating on steel dies was found to be effective at improving the mold life and preventing geopolymer from sticking to the mold after curing. Foamed samples made using 0.5 and 1.5 wt% H2O2 and curing at 200°C for 7 h, had good machinability and high compressive strengths (44-77 MPa), but did not produce crack-free ceramics on heating. Mercury intrusion porosimetry and SEM results suggested that these samples did not obtain a percolating network of porosity due to hydrogen peroxide addition. Samples made using 60 wt% spherical Al as a foaming agent had pores of irregular shape with a larger pore size distribution, and were successfully converted to crack-free ceramics on heating. The Al foamed samples appeared to have attained a percolating pore network and exhibited minimal shrinkage on heating.

Original languageEnglish (US)
Title of host publicationDevelopments in Strategic Materials, Proceedings - A Collection of Papers Presented at the 32nd International Conference on Advanced Ceramics and Composites
Number of pages16
StatePublished - Mar 27 2009
EventDevelopments in Strategic Materials - 32nd International Conference on Advanced Ceramics and Composites - Daytona Beach, FL, United States
Duration: Jan 27 2008Feb 1 2008

Publication series

NameCeramic Engineering and Science Proceedings
ISSN (Print)0196-6219


OtherDevelopments in Strategic Materials - 32nd International Conference on Advanced Ceramics and Composites
Country/TerritoryUnited States
CityDaytona Beach, FL

ASJC Scopus subject areas

  • Ceramics and Composites
  • Materials Chemistry


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