New particle size measurement technique uses air permeability for greater precision
August 22, 2017
The Subsieve AutoSizer (Courtesy Micromeritics Instrument Corporation)
Micromeritics Instrument Corporation’s Particulate Systems Division, Norcoss, Georgia, USA, has announced a new instrument for the more precise estimation of the average particle size of powders. The new instrument uses an air permeability technique previously popularised by the Fisher Sub-Sieve Sizer, which is no longer available.
The Subsieve AutoSizer (SAS) measures the specific surface area of a powder by passing air through a packed powder bed and determining the pressure of the transmitted air by means of calibrated and traceable digital pressure transducers (also used for setting the packing force and input pressure) instead of the water-filled manometer standpipe (or bubble-rate pressure estimate, in the case input pressure) used in older methods. The specific surface area is then easily converted by the instrument to an equivalent spherical particle diameter using geometric and density considerations.
For over fifty years, the refractory metals, ceramics, lighting, other phosphors and pharmaceutical industries have relied on air permeability measurements to estimate the particle size of their materials. Some of these methods offer very imprecise results, leading to a large degree of rework and confusion in those industries. Because of its accurate and precise measurement of pressure by means of pressure transducers, the SAS reportedly provides much greater precision than traditional methods, allowing for appropriate particle size specifications to be set for both process and quality control, and for outgoing powder material specifications. The new instrument thus offers a fast and easily-obtained estimate of particle size in order to meet those specifications.
Several international standard test methods have been developed for use with the SAS, including ASTM Standard Test Methods B330 (for metals), C721 (for some ceramic materials) and E2980 (a general standard for particle size measurement of a wide range of materials). ISO Standard 10070, a general standard test method for this type of particle size measurement, is currently being revised for use with the SAS.
