Understanding Study of Silicate Based Gel Formed during the Setting Ceramic Materials
Consolidation of cementitious and geopolymeric materials involves silicate-based gel formation. This in situ mechanism is difficult to identify because it occurs in a complex and developing system representing only a minority phase. A study based on the behaviour of acidified sodium silicate solutions in alkaline medium, was therefore initiated in order to define the conditions of irreversible setting. A concentrated sodium silicate solution ([Si]=7 mol/l, pH=11.56, Si/Na=1.71) was used as starting solution. 29Si NMR spectroscopy, SAXS and elementary chemical analyses (ICP-AES) were used to characterize the various solutions. Acidification of initial solution, leads in a range of relatively low pH and silicon concentration to various gels formation: (i) reversible transparent gels made up of aggregates of particles (Si7O18H4Na4) and which do not change over time, (ii) soluble white gels that lead to gradual formation of a soluble solid consisting of colloid composition of NaSi1.87O4.24, (iii) “irreversible” gels which provide a syneresis phenomenon leading to formation of a strongly consolidated solid made up of soluble phase rich in sodium similar to white gels (NaSi1.87O4.24) and an insoluble phase type silica of composition NaSi12.66O25.82.
Pietro VINCENZINI and Cristina LEONELLI
M. T. Tognonvi et al., "Understanding Study of Silicate Based Gel Formed during the Setting Ceramic Materials", Advances in Science and Technology, Vol. 69, pp. 51-56, 2010