Instability of SiO₂ Colloids and Sorption of Ca²⁺ Ions

Abstract

Abstract--SiO2 sols were made unstable by addition of Ca 2 + ions. The resulting states of instability were classified as gelation, flocculation, and precipitation by means of observation, by checking the Tyndall effects on the supernatant or suspending solution, as appropriate, and by measuring the apparent densities of flocculated mass. The concentrations of free Ca 2 § ions left in solution were measured by means of a Ca 2+ ion selective electrode. The amounts sorbed onto SiO2 particles were then calculated by material balance. It was found that while the amount sorbed dictates the limit of stability, the SiO2 concentration in the mixture is an important factor deciding the state of instability. Depending on the SiO2 concentration, there were two distinct flocs with the apparent floc density of 6 _+ 1 and 12 _+ 1 mg SiO2/ml.

Polymorphic Crystallization and Diversified Growth of CaCO3 in HPAM‐HABS‐Na2SiO3 Hybrid Solutions

“…Chan proved that 0.4% calcium ions could be absorbed by silica colloid grains. Consequently, there is no precipitation of calcium silicate produced in this system (Figure , A and B).…”

“…These growth positions are hindered in the direction perpendicular to this HPAM chain due to the hydrophobic domain that exists in polymer chains or micelles. Meanwhile, the viscosity of this system increases due to the formation of a polymer‐network connected by hydrogen bonding with HPAM, the network which can effectively interfere with the diffusion of Ca 2+ and CO 3 2− and then inhibited the growth of CaCO 3 . The electrostatic interactions of negatively charged ‐COO − on the HAPM chains of the network and the surface of silica colloid tend to repel each other.…”