Fundamental Study of Clay: Vii, Effect of Particle Size on Properties of Casting Slips*

A bstratct Binary and ternary mixtures were made of 0.2‐ to 0.4‐μ and 0.8‐ to 1.6‐μ size purified fractions of clay and of 16‐ to 44‐μ size purified flint. Specific gravity, deflocculation point, and hydrogen‐ion concentration determinations were made on each composition to obtain the same apparent viscosity. Small cylinders were prepared by solid casting, and the shrinkage, porosity, and modulus of rupture of the dried specimens were measured. The general conclusions are as follows: (1) The packing of particles and the ratio of the plastic to the nonplastic components affect all slip properties; (2) the best combination of properties for casting slips was obtained at the composition corresponding to the closest packed system; (3) the casting time and drying shrinkage, both very small for bodies containing 20 to 25% of clay, increase together with the fine component; (4) the porosity of the dried casts is greatly affected by the particle‐size distribution of the batch; (5) the minimum porosity of 28.5% obtained in this work is much lower than that of the standard sanitary body, which has a porosity of 35.5%; and (6) the particle‐size control of casting slips not only will provide uniformity of the products but will also permit the desired variations in the properties of casting slips and cast bodies.