Polishing composition for magnetic disk substrate

Abstract

Embodiments provide a polishing composition for a magnetic disk substrate, the polishing composition containing colloidal silica, at least one of a phosphorus-containing inorganic acid and a phosphorous-containing organic acid, and water. According to at least one embodiment, the colloidal silica in the polishing composition has an average particle diameter (D50) in the range of 5 to 50 nm observed by a transmission electron microscope. In measuring a volume-based particle size distribution of the colloidal silica by dynamic light scattering, when the particle size distribution is measured by adjusting a concentration of colloidal silica particles to be 0.25 mass %, the colloidal silica contains 10 vol % or less of colloidal silica particles larger than 50 nm. The polishing composition has 1 to 50 mass % of the colloidal silica, and the pH (25° C.) in the range of 0.1 to 4.0. The colloidal silica is stabilized by sodium or ammonium.

Dependencies are inferred from the claim text.