Mixed-alkali effect in aqueous silicate solutions

Abstract

The fluidity (4) and the conductivity ( 0 ) of strongly supercooled solutions of sodium and potassium metasilicate and their mixtures, of general formula xK2SiO3-(l-x)NazSiO3-7Hz0, have been measured to -70 "C. The Arrhenius plots were curved, and both 4 and u data were fitted to the equation 4 (or a) = A exp[-B/(T -To)], where To is a "zero mobility temperature" obtained by an iterative least-squares method. The viscosity data were measured over nine orders of magnitude and were well described for all solutions by this three-parameter equation. When the conductivity was plotted as a function of composition at constant fluidity, a conductance minimum was found at low temperatures which was identified as the appearance of the "mixed-alkali" effect. The results offer quantitative support for the idea that the mixed-alkali effect is only found when the structural relaxation time, ( 7g), is much longer ( N 100 times) than the conductivity relaxation time, ( 7 c ) .

Mixed alkali effect in 0.2[xKNO3 + (1 − x)NaNO3] + 0.8glycerol systems

“…A relatively high Toy value has been obtained for the present system. Similarly a high value for To was observed by Sangma et al (9) and Ingram et al (13) while investigating MAE in ternary systems. On the other hand, similar high value for To was also found for binary hydrate melts (15)(16)(17).…”

“…4.09H2O system failed to observe MAE in conductivity in the temperature range -5 to 70°C. But Ingram et al (13) observed deviation in viscosity and conductivity while studying xK,SiO, + (1 -x)Na,Si03 + 7H20 systems in the temperature range -70 to 20°C. The observed shallow minima in conductivity and viscosity isotherms was considered an evidence for the onset of MAE.…”

Structural characterization of geomaterial foams — Thermal behavior

“…This change is probably also due to the difference in water content in each sample (Table 1). An increase in water content leads to a decrease of viscosity due to the dilution effect [24], making pore coalescence possible in a viscoelastic medium and leading to some differences in the dissolution mechanisms of raw materials responsible of the multi-porosity.…”

Role of alkaline cations and water content on geomaterial foams: Monitoring during formation

“…Indeed, silicate solutions have a very complex structure, which can contain dimers, linear trimers, cyclic tetramers, among others, and their properties will depend strongly on the alkaline element used. The most striking difference between sodium silicate solution and potassium silicate solution is the disparity in their respective viscosities [11], which may be due to the differing extents of hydration of Na + and K + . This reflects the small concentration of free water in the sodium silicate solution as compared to that in the potassium silicate solution.…”