What is the difference between brown fused alumina #60 and #80 ? Is it just the difference in particle size?

#60 mesh is a sand grit with a size of 0.3-0.15 mm. Brown Fused Alumina  grades are judged based on the Al2O3 content. Those with Al2O3 content of more than 95% are called first-grade BFA, they also mention other components such as SiO2, Fe2O3, TiO2. Usually second-grade Al2O3 content of is above 80%, third grade Al2O3 content of is below80%. The color of the first grade is all brown, and the second grade and third grade is not so good as first grade.

There are 2 density kinds of Brown Fused Alumina, Bulk Density and True Density.

Bulk Density ranges from 1.40-1.99 g/cm³. Abrasives  bulk density is related to the grit size, particle size composition, abrasives variety, grit shape and other factors. Generally speaking, coarse grit abrasives have a higher bulk density than finegrit abrasives. The bulk density of mixed grit size abrasives is higher than a single grit size bulk density.

True density is 3.95 ~ 4.0 g/cm³. The true density of the abrasive refers to the mass of the abrasive contained in a unit volume (excluding the volume with open pores).