Microspheres and retroreflective articles. In one embodiment, the microspheres comprise at least 30 wt. % alumina, at least 35 wt. % zirconia, and silica. In another embodiment, the microspheres comprise at least 30 wt. % alumina, at least 30 wt. % zirconia, and silica; wherein the wt. % zirconia is greater than the wt. % alumina.

Microspheres and retroreflective articles. In one embodiment, the microspheres comprise at least 30 wt. % alumina, at least 35 wt. % zirconia, and silica. In another embodiment, the microspheres comprise at least 30 wt. % alumina, at least 30 wt. % zirconia, and silica; wherein the wt. % zirconia is greater than the wt. % alumina.

Microspheres and retroreflective articles are described. In one embodiment, the microspheres comprise at least 40 wt. % alumina, at least 35 wt. % zirconia, and silica. In another embodiment, the microspheres comprise at least 80, 85, or 90 wt. % of a combination of alumina, zirconia, and silica and the microspheres have a density of at least 3.

Microspheres and retroreflective articles are described. In one embodiment, the microspheres comprise at least 40 wt. % alumina, at least 35 wt. % zirconia, and silica. In another embodiment, the microspheres comprise at least 80, 85, or 90 wt. % of a combination of alumina, zirconia, and silica and the microspheres have a density of at least 3.

A method of forming a titania-coated inorganic particle comprising the steps of: (a) agitating a mixture of inorganic particle and organic solvent; (b) adding titania precursor dropwise into the mixture of step (a) under agitation; and (c) adding catalyst to the mixture of step (b) thereby converting said titania precursor to titania which then forms a coating on said inorganic particle; wherein steps (a) to (c) are performed at neutral pH and ambient temperature.

A method of forming a titania-coated inorganic particle comprising the steps of: (a) agitating a mixture of inorganic particle and organic solvent; (b) adding titania precursor dropwise into the mixture of step (a) under agitation; and (c) adding catalyst to the mixture of step (b) thereby converting said titania precursor to titania which then forms a coating on said inorganic particle; wherein steps (a) to (c) are performed at neutral pH and ambient temperature.