Standardization News

A large and diverse set of manufactured materials are in powdered form at one stage or another. No matter what the material is, from cement to metered dose inhaler ingredients, product performance is related to particle size distribution.

"The strength of concrete is related to the fineness of the cement powder used, but the danger with very fine grades is excessive heating on setting," says ASTM member Alan F. Rawle, Ph.D., applications manager, Malvern Instruments Inc. "The particle size distribution of the materials in a metered dose inhaler controls the entry of particles to the lungs and thus has an effect on the efficacy of the treatment."

A proposed new ASTM International standard, WK45240, Test Methods for the Particle Size Distribution Measurement of Powdered Materials by Wet and Dry Laser Diffraction, will set out a general approach to measuring powders, suspensions or slurries using the appropriate wet or dry methodology.

Rawle notes that anything in powdered, suspension, spray or emulsion form is potentially measurable by laser diffraction and will be covered by WK45240. Applications in which particle size distribution is used to control final performance include:

"WK45240 will provide practical guidance on sampling, dispersion, verification and correct use of optical constants," says Rawle.

Important factors being considered in the development of the standard include the degree of precision required for a measurement, the top end size of the material, density of the sample and most importantly, the relation of the product performance to the measured numbers.

WK45240 is being developed by Subcommittee E29.02 on Non-Sieving Methods, part of ASTM International Committee E29 on Particle and Spray Characterization.

CONTACT Technical Information: Alan F. Rawle, Ph.D., Malvern Instruments • Westborough, Mass. • Phone: 508-768-6434 | ASTM Staff: Katerina Koperna • Phone: 610-832-9728 | Upcoming Meeting: Oct. 6-7 • October Committee Week • New Orleans, La.