THE PERMEABILITY AND ELUTRIATION METHODS FOR DETERMINING THE SPECIFIC SURFACE OF DRY CHEMICAL FIRE-EXTINGUISHING POWDERS

The air permeability (Blaine) method gives a direct measure of the total surface of a powder sample. The air elutriation (Roller) method gives the distribution of particle diameters in a sample, from which the surface can be found by numerical or graphical integration. Measurements of the specific surface by the permeability method of powders ranging from approximately 2600 to 5900 sq.cm./g. were reproducible to within plus or minus 1.5% when the test was carried out in a preferred manner. The air elutriation method proved to be very sensitive to the relative humidity of the operating air when used with the same powder as used in the permeability method. In some instances, separating with dry air gave values of specific surface nearly double those obtained using moist air. In view of this sensitivity to operating conditions, as well as the much greater time required for each determination, the elutriation method appeared to be unsuitable for characterizing dry chemical powder extinguishants. (Author)