TRANSPARENT NON-VITREOUS ZIRCONIA MICROSPHERES Abstract of the Disclosure Solid, transparent, non-vitreous, zirconia and zirconia-silica ceramic microspheres, useful as lens elements in retroreflective pavement markings. The microspheres are characterized by: (a) containing at least one additive metal oxide selected from alumina, magnesia, yttria and mixtures thereof; (b) an index of refraction greater than 1.6; and (c) being virtually free of cracks. These microspheres are formed by a sol-gel technique of extractive gelation (extracting carboxylic acid away from zirconyl carboxylate) of a sol in liquid medium such as hot peanut oil. The microspheres of this ceramic composition have been made with relatively large diameters, (e.g.200-1000 micrometers) making them quite useful as lens elements in pavement marking sheet materials.

Transparent non-vitreous zirconia microspheres

Solid, transparent, non-vitreous, ceramic particles useful as lens elements in retroreflective pavement markings characterized by having: A. at least one metal oxide phase; and B. an average minimum dimension of more than 125 micrometers. These particles are formed by various sol gel techniques, one example of which is the chemical gelation of titania sols by first mixing with glacial acetic acid, then with ammonium acetate, followed by formation of microspheres in 2-ethylhexanol. Microspheres of this ceramic composition can have relatively large diameters (e.g. over 200-1000 micrometers) making them quite useful as retroreflective lens elements in pavement marking sheet materials.

Transparent non-vitreous ceramic particulate

There are three basic types of precursor solution used to form oxides and glasses through gellation: solutions of metallic salts, colloidal sols, and solutions of polymerizing species. Although an intermediate state in all three cases is called a gel, there are fundamental differences in the gelling mechanism and nature of the gel in these systems. In colloidal systems gelling is a result of electrolytic effects which also determine the interparticle distance at the gelling point, thus influencing the capability of the gel to remain monolithic during the transformation to an organic-free state. On the other hand, gelling in polymerized systems occurs as a result of polymerization by chemical reaction. The nature and kinetics of these reactions determine the properties of the gel and resultant inorganic polymer.

Colloidal versus polymer gels and monolithic transformation in glass-forming systems

Titania gel spheres by a new sol-gel process

Powder characteristics and microstructure of uranium dioxide and uranium dioxide-gadolinium oxide fuel

The sol-gel process was originally developed and applied at the Oak Ridge National Laboratory for preparation of high-density thoria-urania fragments and microspheres for nuclear reactor fuels. The application of the process for preparation of microspheres to sols of urania, urania-zirconia, and urania-carbon is reported in this paper. Relatively high-strength, spherical particles of UO2, UO2-ZrO2, and UC2 were prepared with diameters of 50-500 microns and densities of 80-100% of the theoretical densities.



Le procede dit sol-gel a ete originairement mis au point et utilise au Laboratoire national d'Oak Ridge pour la preparation de fragments et de microspheres de thorine et d'urane pour les combustibles des reacteurs nucleaires. On rapporte dans le present travail l'application du dit procede servant a la preparation de microspheres a des sols d'urane-zircone et d'urane-carbone. On a prepare des particules spheriques d'UO2, UO2-ZrO2 et UC2 qui possedaient une resistance relativement elevee, des diametres de 50-500 microns et des densites atteignant 80 a 100% des valeurs theoriques.

S. D. Clinton

Papers

Preparation of urania and urania--zirconia microspheres by a sol-gel process.