Alpha-alumina in the form of spherical non-aggregated particles having a narrow size distribution and sizes below 2 microns and process for preparing same

摘要

Alpha-alumina consisting essentially of solid, spherical, non- aggregated particles, having a diameter from 0.06 to 2 m, a polydispersion index below 2.0, a total porosity below 0.3 cc/g, a specific surface area from 0.7 to 80 m.sup.2 /g, and an apparent density of the particles from 3.20 to 3.94 g/cm.sup.3. The alpha-alumina is prepared by a process consisting, in that an alpha-alumina precursor, having a water content from 2 to 33% by weight, at starting temperatures ranging from room temperature to 850 C., and consisting essentially of solid spherical, non-aggregated particles, having a particle diameter from 0.07 to 2.3 m and a polydispersion index of . ltoreq.2.0, is subjected to a heat-treatment at temperatures ranging from 1130 to 1700 C., said precursor being instantaneously brought from the starting temperature to the treatment temperature, and by carrying out the treatment during times, as generally indicated in the accompanying FIG. 1 between straight lines (a) and (b), which are sufficient to convert the precursor to phase alpha, but not such as to cause breakages and/or aggregations; the resulting product being then brought again to room temperature by means of a non-instantaneous cooling of the order of at least 10 seconds.