Rare earth glass-polishing compositions of improved homogeneity and reproducibility are prepared by (a) simultaneously continuously admixing a cerium salt solution, a basic solution and a solution of at least one acid and/or one salt, the anion or anions of which being adopted to form insoluble rare earth compounds, the number of equivalents of base being equal to or greater than the number of equivalents of cerium, and the pH of the reaction medium being greater than about 6; (b) filtering the precipitate which reuslts from the reaction medium; (c) drying said recovered precipitate; and (d) calcining said dried precipitate.
Morphologically improved cerium oxide particulates useful, e.g., as catalysts/catalyst supports, and having a B.E.T. specific surface of at least 85.+-.5 m.sup.2 /g, measured at a temperature ranging from 350.degree. C. to 450.degree. C., are prepared by hydrolyzing an aqueous solution of a cerium (IV) salt in an acidic medium, filtering the precipitate of hydrolysis which results, washing and optionally drying said precipitate, and then calcining same.
Morphologically improved cerium oxide particulates having low sulfur content, useful, e.g., as catalysts/catalyst supports, and having a B.E.T. specific surface of at least 85.+-.5 m.sup.2 /g, measured at a temperature ranging from 350.degree. C. to 500.degree. C., are prepared by reacting an aqueous solution of cerium (IV) salt with an aqueous solution of sulfate ions to precipitate a basic ceric sulfate, filtering the precipitate which results, washing and optionally drying said precipitate, and then calcining same.
Glass polishing compositions, advantageously recycled into glassmaking formulations, are comprised of suspension of particulate ceric oxide and at least one colorless oxide of a lanthanide or yttrium rare earth, preferably an oxide of lanthanum, samarium, europium, gadolinium, dysprosium, thulium, ytterbium, lutecium, yttrium, or mixtures thereof.
A mixed light rare earth compound which has been obtained by chemically removing medium-to-heavy rare earth elements, Nd and impurities other than rare earth elements from an ore containing rare earth elements is fired at 500 to 1100.degree. C. to yield a mixed rare earth oxide. A cerium-based rare earth oxy-fluoride is added to the mixed rare earth oxide to obtain a mixture. The mixture is subjected to wet-pulverization, drying, firing, disintegration and classification to thereby yield a cerium-containing abrasive.
An improved process for the preparation of monodispersed spherical colloidal particles from rare earth salts is disclosed. These colloidal particles are obtained in this process by homogeneous precipitation techniques involving the forced hydrolysis of rare earth salts in aqueous media. More specifically, this process initially involves the formation of hydrolyzed cations which are precursors or intermediate to precipitation of the desired colloidal particle. The objective in the formation of this precursor species is to reach critical supersaturation concentration of this particle forming species so that only one burst of nuclei occurs. Colloidal particle formation is then effected by diffusion of solutes onto the existing nuclei. The improvements of this process reside, in part, in the ability to control the kinetics of formation of this intermediate species. Such control permits the formation of colloidal dispersions having very narrow particle size distribution. The colloidal dispersions of these particles are also quite stable. The rare earth colloidal particles prepared by this process are useful in both industrial and biologic environments.
