Abstract
Using a Green type viscometer the change of viscosity with time under constant shearing force was observed for the purpose of measureing the extent thixotropic break down of the clay suspensions.
The results may be summarized as follows:
(1) When the amount of electrolyte (sodium silicate) is less than 2 milli equivalents/100g clay the viscosity increase with time. The addition of a little more electrolyte, i.e. 3m. eq/100g clay., affects the progress in such a way that the viscosity decreases at the beginning until it reaches the minimum, from then gradually increases with time. With the addition of more than 5m. eq./100g clay the viscosity decreases linearly with time and the slip shows thixotropy.
(2) Clay slip containing NaO·SiO2 or NH4OH shows the thixotropic breakdown to a small extent, which increases remarkably by the additional of sodium carbonate (0, 25g/100g clay).
The authors have reached to the conclusion that a clay slip suitable for solid casting may be prepared by adding sodium silicate for decreasing the viscosity and also sodium carbonate in order to give the thixotropic property.
