Kinetics of pore formation and resulting properties of lightweight inorganic polymers

Abstract

Inorganic polymer (IP) foams could be used as an alternative to commonly available cellular concretes. To do so, however, it is crucial to understand how the foaming kinetics and the final foam properties can be controlled and tailored to delivered the desired performance. The research reported in this article investigates the influence of the SiO 2 /Na 2 O ratio of the activating solution, addition time of foaming agent, and temperature, on the reaction kinetics and final properties of a porous IP. The IPs were formed by activating fayalite slag, a by-product of secondary copper production, with a sodium-silicate solution. Foaming was achieved by introducing metallic Al into the formulation, oxidizing it in the alkaline environment, liberating H 2 gas, and entrapping it. Reaction kinetics were assessed using isothermal calorimetry, rheology, and a dedicated setup to record the foaming. The mechanical and physical properties of the foam were assessed via compressive strength and water absorption measurements. Microstructural analysis was undertaken using electron microscopy and computed tomography. The results showed that by decreasing the SiO 2 /Na 2 O ratio and/or increasing the temperature, the reaction kinetics were accelerated. Regarding the properties, postponing the initiation of the foaming led to more uniform and smaller pores, resulting in an increased compressive strength-to-density ratio. K E Y W O R D Sinorganic polymers, kinetics, pore formation, porous materials

Impact of the solidification path of FeOx–SiO2 slags on the resultant inorganic polymers

“…In comparison with previous studies, the timing of the maximum of the exotherm is similar, taking into account the activating solution that was used. The absolute values of the cumulative heat of the three samples are comparable to other Fe‐rich slags …”

Mineralogy and glass content of Fe‐rich fayalite slag size fractions and their effect on alkali activation and leaching of heavy metals

“…This measurement of heat released by FF is consistent with other iron-rich slags activated with similar alkaline solutions, as reported in the literature. 32,39,40 In both paste samples, the reaction continues after 96 h, as by this point, the cumulative heat released is still increasing. The continuation of the reaction was found to induce microstructural evolution at the later ages.…”

Geopolymer foams: An overview of recent advancements

“…Henon et al observed higher and faster expansion when increasing temperature [101]. Denissen et al also reported that increasing temperature causes faster foaming [100]; however, the influence of temperature was dependent on the SiO 2 /Na 2 O: higher ratios led to greater expansion at higher temperatures, but when using a low SiO 2 /Na 2 O ratio, the highest volume expansion was achieved at 20-25 °C. This behaviour was attributed to the complex interaction between foaming kinetics, setting time and the physical properties of the paste.…”

“…Curing temperature [100,101] and activator concentration [102] can also be used to control foaming kinetics and setting time. Henon et al observed higher and faster expansion when increasing temperature [101].…”