PARTICLE SHAPE AND DIFFERENTIAL SHRINKAGE OF STEATITE TALC BODIES *

An attempt has been made to correlate the differential shrinkage of fired steatite pieces with the particle shape of the raw talc used in their manufacture. Various talcs of widely varying particle shape were used in making the steatite test pieces. It was found that the more irregular in shape the talc particles, the greater the differential shrinkage. A method is given for assigning arithmetical values to various particle shapes depending on their deviation from sphericity, this arithmetical value being known as specific shape factor. A direct relationship was found to exist between the differential shrinkage of a talc and its specific shape factor. As the talc particles became more irregular in shape, the “specific shape factor” value increased and the differential shrinkage was found to increase. The proper selection of the talc td be used and blends of various talcs were found to be helpful in the control of differential shrinkage.