Effect of alkali cation on irreversible gel formation in basic medium

This study is based on the understanding of the behavior of alkali silicates in a basic medium and aims to identify the mechanisms responsible for the formation of an irreversible gel and its consolidation. Commercial lithium, sodium and potassium silicate solutions were used to reveal the effect of the cation nature on the gelation process. Gels are obtained by acidifying alkaline silicate solutions with hydrochloric acid. A syneresis phenomenon during ripening that leads to the formation of a strongly consolidated solid has been observed. Whatever the cation, the gelation or syneresis mechanism would be similar. However, gelation time decreases and syneresis increases with the cation size. Gelation results from formation of small particles which grow in number and size and then gather to fill the available space. Ripening takes place through a dissolution/precipitation mechanism.

Research Highlights
► Gels are obtained by acidifying alkaline silicate solutions with hydrochloric acid.
► Gelation is promoted by increasing silicon concentration and by decreasing both pH value and cation size.
► Whatever the cation, the gelation or syneresis mechanism would be similar in alkaline solutions.
► Gelation results from the formation of small particles, which grow in number and size and then gather to fill the available space.
► Ripening takes place through a dissolution/reprecipitation mechanism. The latter decreases greatly with the cation size.