K₂O-Metakaolin-Based Geopolymer Foams: Production, Porosity Characterization and Permeability Test

Area of Science:

• Materials Science
• Chemical Engineering
• Ceramic Engineering

Background:

• Geopolymers offer a sustainable alternative to traditional binders.
• Controlling porosity in geopolymer materials is crucial for tailoring their properties.
• Direct foaming is a promising technique for creating lightweight, porous structures.

Purpose of the Study:

• To produce near-net shaped geopolymer foams with varying porosity using direct foaming.
• To investigate the effect of different blowing agents (hydrogen peroxide and metallic silicon) on foam characteristics.
• To evaluate the gas permeability of the synthesized geopolymer foams.

Main Methods:

• Four geopolymer foam formulations were prepared using a metakaolin-based geopolymer.
• Direct foaming was employed with varying amounts of hydrogen peroxide (H2O2) and metallic silicon as blowing agents.
• Foams were characterized for bulk density, total porosity, accessible porosity, specific surface area, and gas permeability (Darcian and non-Darcian).

Main Results:

• Foams exhibited bulk densities from 0.34 to 0.66 g cm⁻³, total porosity from 70% to 84%, and specific surface area from 47 to 94 m² g⁻¹.
• Foams produced with H2O2 showed significantly higher gas permeability coefficients (k1 and k2) compared to those made with metallic silicon.
• A strong correlation was observed between pore structure, processing methods, and gas permeability.

Conclusions:

• Direct foaming allows for the controlled production of geopolymer foams with tunable porosity.
• The choice of blowing agent critically influences the pore structure and resulting gas permeability.
• The synthesized geopolymer foams demonstrate performance comparable to other porous materials, suggesting broad application potential.