THE EFFECT OF VARIOUS ADDITION AGENTS AND TREATMENTS ON THE GREEN STRENGTH OF MISSOURI REFRACTORY CLAYS1

Abstract

Tests were made with the plastic and semiflint fire clays of north central Missouri and the burley diaspore of south central Missouri. Aging plastic fire clay ten days produces about a 38% increase in modulus of rupture. Na2CO3 treatment produces about a 50% increase. Tannic acid which flocculates the colloids improved the modulus a good deal; an acid treatment after an alkali treatment, however, produced no added effect of importance. The effect of developing bacterial growth was marked, especially if aged for a considerable time. The addition of bentonite Collotone R increased the modulus almost 3 times. The maximum is reached with about 8% bentonite. The additive effect of dextrine in combination with bentonite is positive but of negligible consequence. Tennessee ball clay is without important positive effect in amounts up to 8%. Sodium silicate additions up to 8% gave negative results. With as little as 4% bentonite the modulus of rupture of flint clay is tripled. Aging of flint clay has an important positive effect. Effect of the bentonite can be obtained in the dry-press, stiff-mud, or soft-mud bodies, but it is greatest in the stiff-mud. Burley clay is less self-bonding than the flint and the effect of the bentonite was more marked even than in the case of flint. Four per cent bentonite increased the modulus of rupture to about 4 1/2 times its original modulus of rupture. The modulus of rupture of flintclay-bentonite mixtures might approach that of plastic fireclay-bentonite mixtures at high contents of bentonite, leading to the indication that in the case of these two clays the total colloidal content is the determining factor. With 3% bentonite the modulus of rupture of the flint is made equal to that of the plastic and straight, a result applicable to problems where the dissolving out of the bonding material in the refractory is a determining factor in service. The P.C.E. of the plastic fire clay drops 1 cone for 3% and 2 cones for 6% of bentonite addition.