Humus increases the surface tension of water and the mutual repulsion of the clay particles. The fluidization behaviour of clays cannot be judged only on their humus content. Clays with a low content of sodium and humus are difficult to fluidize.
The thickening of clay slips due to excess alkali is caused by the penetration of the Helmholtz double layer by alkali ions. Their positive charges partly neutralise the negative charges on the clay particles and diminishes their mutual repulsion which is the pre-requisite property of fluidization.
Thickening of clay slips on standing is a general absorbed property on all ceramic industries.
to be contd……
