... Balls 1.Material:silicon nitride ceramic 2.Purpose:used in chemical industry 3.Best quality Silicon nitride ceramic balls1. 59% lighter ... hardness as 78.4. Smaller friction coefficient.5. Only 1/4 coefficient of thermal expansion of steel, can endure sharp ... chemical industry, metallurgical, medical, food, oil plant, electronic etc.Note: 1) black color as standard, gray color could be supplied upon ...