Patent ID: 7303601

Claim:
A polishing composition for memory hard disk having a pH of from 1 to 4.5 comprising water and an abrasive consisting essentially of silica particles, in which a relationship of a particle size (R) in nm at a range of from 40 to 45 nm and a cumulative volume frequency % (V) in a graph of particle size-cumulative volume frequency obtained by plotting a cumulative volume frequency (%) of the silica particles counted from a small particle size side satisfy the relationship where the cumulative volume frequency (V) in % is determined to be equal to or greater than the sum of the particle size (R) in nm plus 50, wherein the silica particles have a particle size distribution wherein silica particles having a size of from 10 to less than 40 nm are present in said composition, and wherein the particle size is determined by observation with a transmission electron microscope (TEM).