Abstract: The present application relates to optically active elements and the methods of making these elements. The optically active elements include multiple layers of optically active beads positioned adjacent to a core particle. The methods of making these optically active elements involve applying multiple layers of optically active beads around a core particle. At least some of the optically active elements exhibit increased durability and/or performance due to the inclusion of multiple layers of optically active beads.

Abstract: The present disclosure relates to microspheres (i.e., beads) having a high index of refraction. The disclosure also relates to retroreflective articles, and in particular pavement markings, comprising such microspheres.

Abstract: The present disclosure relates to microspheres (i.e., beads) having a high index of refraction. The disclosure also relates to retroreflective articles, and in particular pavement markings, comprising such microspheres.

Abstract: The present invention relates to microspheres (i.e., beads) having a high index of refraction. The invention also relates to retroreflective articles, and in particular pavement markings, comprising such microspheres.

Abstract: Procedure for making Al.sub.2 O.sub.3 spheroids, 600 micrometers in diameter or less, utilizes an AlOOH sol containing 0.25% weight percent MgO (in the form of Mg(NO.sub.3).sub.2 .multidot.6H.sub.2 O) and HNO.sub.3. The sol is dispersed into droplets in a particle forming fluid (e.g., 2-ethylhexanol) where gelling occurs. The gelled spheroids are collected, dried and pre-fired in air at temperatures less than 1,200.degree. C. for up to about 12 hours. The dried and prefired beads are fired in a 2-step process at temperatures of about 1,850-1,950.degree. C. in the following sequence:a first dry oxygen firing for about ten minutes, followed by a wet hydrogen firing for up to 350 minutes. Reasonably transparent microspheres having crystallites in the range of 5-100 micrometers are obtained with little intergranular porosity, and their density is estimated to be near theoretical.