Abstract: The present invention provides bead-like hollow particles and an easy and convenient method for producing the same, and a friction material using the bead-like hollow particles. The particles are bead-like hollow particles comprising odd-shaped particles composed of a metal oxide as a main component and having at least one of a through hole and non-through hole in a surface; the method is a producing method for the bead-like hollow particles, which comprises spraying and drying a suspension of a particulate biological material and a particulate metal oxide by a two-fluid nozzle spray dryer to obtain a powder composed of the particulate biological material as a core and a layer of the particulate metal oxide as a shell, and heating the obtained powder; and the friction material is a friction material using the hollow particles.

Abstract: A friction material is provided with a matrix fiber, a binder, and a filler. The friction material contains a stabilized zirconia having a lattice constant in a range from 99.93 to 99.95% as compared with a lattice constant of a single crystal of stabilized zirconia. The lattice constant scarcely changes, since the stabilized zirconia contained in the friction material undergoes less introduction of distortions when used under severe conditions. Accordingly, the stable friction characteristic with less change of the friction coefficient in the initial stage of using the brake can be obtained.