Particle size reduction achieved by turbomilling is much greater than when using jar mills, colloid mills, or ultrasonics. The operating variables found to influence kaolin comminution efficiency were type, size and shape of grinding media, the ratio of medium weight to clay weight, clay pulp density, degree of pulp dispersion, and the angular arrangement of the rotor and stator bars. The Bureau also investigated milling of other industrial minerals, including natural and synthetic mica, pyrophyllite, talc, marble, barite, sericite, and anthracite. The Bureau also investigated the use of the turbomill as a technique for the production of submicrometer ceramic powders including barium ferrite, calcite, dolomite, fluorspar, silica, and zirconia. Autogeneous turbomilling in which the milling medium and the material to be milled are of similar composition was used to produce high-purity, ultrafine powders. Additional studies included turbomilling of nonoxide ceramic materials. Use of polymer construction for parts of the mill aided in elimination of metal contaminants in the final milled product. Optimum milling efficiency for a-sic was obtained at 50 deg c in a slurry of ph 9.5 Using a sodium lignosulfonate as the dispersant. Eighty percent of a minus 100-plus 200-mesh a-sic was ground to less then 1 um in 4 h. Similar results were observed for si3n4 and tib2.