Among the characteristics that help differentiate one grade of aluminum from
the next are median particle size, aspect ratio, particle size distribution,
particle geometry, and surface chemistry.
Median Particle Size
The median particle size is usually measured in microns and is an indication of
the average cross sectional length of the aluminum pigment. The particle size
value is usually expressed as the D(50%) and represents the size at which 50%
of the flakes in the distribution are larger and 50% smaller. Generally speaking
larger particle size grades are brighter, more reflective and have more sparkle
than those with smaller particle sizes.
Aspect Ratio
The aspect ratio is determined by dividing the cross sectional thickness (T)
into the cross sectional length (D). Aspect ratios of from 100 to over 1000 are
typical of most milled aluminum pigments. Aluminum pigment grades with higher
aspect ratio values will typically have greater surface area and therefore
better coverage or hiding power. The actual hiding power of an
individual aluminum pigment grade is also greatly influenced by its particle
size distribution.
Particle Size Distribution
Particle size distribution range is a measure of the difference between the
size of the largest and the smallest flakes of any particular grade. The
particle size distribution is characteristic of any single grade but can vary
greatly from one grade to another. In general aluminum pigments with broad
distribution ranges have greater hiding power and coverage but do not produce
clean colors when used in combination with chromatic pigments. On the other
hand, aluminum pigment grades with narrow distribution ranges are capable of
producing cleaner colors when used with transparent pigments or dyes, but
require higher loading levels to build opacity.
