This part of ISO 13318 covers methods for determining the particle size distributions of particulate materials, typically in the size range 0,1 µm to 5 µm, by centrifugal sedimentation in a liquid. NOTE This part of ISO 13318 may involve the use of hazardous materials operations and equipment. This part of ISO 13318 does not purport to address all the safety problems associated with its use. It is the responsibility of the user of this part of ISO 13318 to establish appropriate safety and health practices and to determine the applicability of the regulatory limitations prior to its use. The methods of determining the particle size distribution described in this part of ISO 13318 are applicable to slurries, particulate materials which can be dispersed in liquids and some emulsions. A positive density difference between the discrete and continuous phases is necessary, although centrifugal photosedimentation can be used for emulsions where the droplets are less dense than the liquid in which they are dispersed.