Influence of Particle Size on Physicochemical Properties of Pharmaceutical Powders. I. On Fluidity of Sodium Borate and Boric Acid Powders. (1).

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Angles of repose and sliding angles of sodium borate and boric acid powders are investigated by four methods. These angles gradually increase with decrease of particle size by any method, and critical diameters are found to be 160μ for sodium borate and 110μ for boric acid powders. The relation between angle (α) and particle diameter (D) is represented as follows. D≤D_c tan α=A₁ exp (-B₁D) D≥D_c tan α=A₁'exp (-B₁'D) A₁>A₁' B₁>B₁'>0 It is concluded that the cohesive force between particles of powders is negligibly small in the region of particle diameter larger than the critical size, and the cohesive force remarkably influences the angle at smaller diameters. The following relation is found between C/Mg and D, in the case of sodium borate powders. C/Mg=0.81 exp (-147 D)