Rheological Characterization of Suspension and Gel Prepared from Colloidal Silica for Sealed Lead-Acid Batteries by Small Amplitude Dynamic Oscillation Measurement

Abstract

Gelation behaviors of silica suspensions, prepared from 6 grades of commercial colloidal silica (Ludox® series) and sulfuric acid, were investigated rheologically by a small amplitude dynamic oscillation measurement method in which storage and loss moduli were monitored with time. To date, the gel strength of silica suspension/gel in sulfuric acid and its progress with time have not been properly defined, because of their complex rheological behavior such as their weak structure. For the purpose of a quantitative investigation, the time evolution of the storage modulus was measured for the representation of gel strength and its progress related to fluidity decline with time for application to battery manufacture.A suspension prepared from small-sized silica particles showed high gel strength and accelerated gelation. It was demonstrated that the total surface area in a unit volume of suspension determines the gelation behavior, regardless of particle size in different grades of silica. This implies that high gel strength can be achieved with low content of silica of small particle size.It was also found that deionized colloidal silica enhances gel strength. This means that sodium ions in the Ludox®, which play a stabilizing role, should be removed in order to form a strong gel. A positively charged surface and chloride stabilizing ions are not suitable for gelled electrolyte, since they accelerate gelation but do not enhance gel strength.In conclusion, colloidal silica particles of small size and negative surface charge without stabilizing ions should be used for achieving high gel strength in application to batteries.