Role of surfactants on the synthesis of impure kaolin-based alkali-activated, low-temperature porous ceramics

Abstract

Porous ceramics were generated by direct foaming the alkali-activated unprocessed kaolin (impure kaolin, iK) with the addition of hydrogen peroxide (H2O2) and calcining at a low temperature of 400 ​°C. Hydrogen peroxide, a blowing agent, decomposes producing oxygen gas bubbles forming the porous structure in the fresh alkali-activated iK paste. In the present study, three different molarity of alkali activator (5, 10, or 15 ​M NaOH) were employed. The dosage of blowing agent (H2O2) was varied between 0 and 2% with a constant dosage of 0.5% (wt. of binder) of surfactant. The gas bubbles in fresh-state geopolymer slurry are unstable with a tendency to coalesce. In such cases, surfactants are introduced to improve the stability of the gas-liquid interface. Two different surfactants: non-ionic and cationic ones were used to study the properties of alkali-activated porous material. Fresh properties such as viscosity, yield stress, foaming rate, and fresh density were compared between reference iK samples without surfactants and those with surfactants. The mechanical and microstructural properties of alkali-activated (AA) low-temperature porous iK ceramics were determined after calcination. Pore structures were characterized with electron microscope to understand the interaction of different parameters during fresh/hardened state and their relevance with the changes in the mechanical properties. Surfactants, irrespective of the type, highly influenced the fresh properties of the AA-iK samples, which in turn reflected on the compressive strength of the porous ceramics.

Keywords

• Surfactant
• Kaolin clay
• Alkali activation
• Rheology
• Porous ceramics
• Strength