Membrane Separators for Electrochemical Energy Storage Technologies

Abstract

Three types of aqueous sodium silicate solutions characterized by molarSiO2:Na2O ratios of 2.2, 3.3, and 3.9 were investigated by dynamiclight scattering and viscosity measurements. The solutions wereprepared by diluting concentrated commercial products to SiO2 contentbetween 0.5 and 15 wt%. Dynamic light scattering (DLS) was used forthe investigation of size distributions of colloids immediately afterdilution. At least three size classes of colloidal particles weredetected, which exist in parallel in the solutions. The respectiveradii are 0.4 to 0.6 nm, 2.5 to 13 nm, and 75 to 85 nm. The largercolloids dominate the mass distribution, whereas the smaller colloidscontrol the surface area of the colloidal fraction. Material propertiessuch as pH, viscosity, refractive index, and density were measured as afunction of dilution. The evaluation of the viscosity data indicatedthat the colloids have a lower density than dense amorphous silica.Aging effects could be suppressed by measuring within 1 h afterdilution. (C) 2003 Elsevier Inc. All rights reserved.