The fluidizing effect of alkalies on kaolins and other clays varies greatly from clay to clay. Some clay can be fluidized very well by small amounts of alkalies and some clays response is very low. The precipitate of humic acid added to a clay which was not responding with alkalies has responded well and by […]

Hydroxides have a more pronounced fluidizing effect than the equivalent amount of carbonates. And hence one at first sight prefers hydroxide for fluidizing clay slips. However it is not true in the practical situation. This is due to CaHCO3 or CaSO4 dissolved in the water of the slip and derived in part from the plaster […]

Neutralization takes time. Normally the ageing of plastic clay bodies requires 4 to 6 weeks to complete. Reaction equilibrium is set up between the clay and the soda solution. Part of the alkali of the soda mostly remains in the solution as Sodium Bicarbonate.
Fluidizing is better achieved with small amounts of sodium hydroxide than sodium […]

The fluidization of clay slips begins with neutralization of the acidic clay. This involves the following 4 stages:
1. Neutralization of H+ (substitution of H+ by Na+) H+ Ca2+ clay + Na2CO3 -> Na+ Ca2+ clay + NaHCO3
2. Cation exchange (substitution of Ca2+ in the double layer by Na+)
3. Anion Adsorption on the positively charged […]

In another type of test the mechanical strength measured is taken as a basis to measure the plasticity of the clay or clay body. In this process the clay wad is prepared in the form of cylinders emerging from a small extrusion press or by casting process in plaster moulds. The prepared cylinders are dried […]

In forming process where there is no great application of pressure a trail shaping on the wheel or rolling out with a hand roller at different water contents in the body can be used to find out the workability. A widely used apparatus in laboratory is the Pfefferkorn apparatus in which a cylinder of plastic […]

The workability of a body is mostly judged by industrial standards. However the process of shaping of clay is differs based on the method used in the forming process like hand pressing or mechanical pressing or throwing in a wheel etc. And hence the method of testing must be adapted to suit the particular working […]

On shaking the basin gently we can differentiate the clay preparations moved for which the water content was above a certain limit. The water content at which two halves could just be caused to contact was called by him as flow limit. In the second method the bodies were rolled out into threads at successively […]

It is very important for ceramics to find out the plasticity of clays with a numeric statement. However there are number of factors involved and their separate contributions are not known exactly. And hence there are lots of difficulties in the selection of a perfect method for the measurement of plasticity. There are accepted methods […]

Air in the ceramic plastic body is always considered to be important issue which reduces the plasticity and thus the workability. In making ceramic bodies practical use is made by passing the plastic body through a kneading machine or a vacuum pug mill. During kneading or wedging the air is removed from the body and […]