Montedison S.p.a.

Paolo Cortesi

Gianni Donati

Giuseppe Saggese

Antonio Gennaro

Emiliano M Ceresa

Alpha-alumina consisting essentially of solid, spherical, non-aggregated particles, having a diameter from 0.06 to 2 .mu.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.degree. C., and consisting essentially of solid spherical, non-aggregated particles, having a particle diameter from 0.07 to 2.3 .mu.m and a polydispersion index of .ltoreq.2.0, is subjected to a heat-treatment at temperatures ranging from 1130.degree. to 1700.degree. 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.

Alpha-alumina in the form of spherical non-aggregated particles having a

Apparatus for preparing spherical, submicronic, monodispersed, and non-agglomerated particles of metal oxides by reacing with steam a gaseous stream containing an aerosol of liquid particles of a hydrolyzable metal compound. The apparatus is characterized in that into a duct, in which an inert gas stream containing vapors of a hydrolyzable metal compound flows, there is fed through a nozzle a cold inert gas stream, the temperatures and flows of the two gaseous streams being such as to establish in the duct a temperature lower than the condensation temperature of the metal compound; the mixed gaseous streams having a turbulent flow in the duct, with a Reynolds number equal to or higher than 1800. At the duct outlet, the aerosol of metal compound liquid particles, which has formed in the duct, is caused to react with steam, wherefore solid particles of hydrated metal oxide form, which are subsequently calcined to the oxide.

Apparatus for preparing monodispersed, spherical, non-agglomerated metal

Spherical, submicronic, monodispersed, and non-agglomerated particles of metal oxides by reacting with steam a gaseous stream containing an aerosol of liquid particles of a hydrolyzable metal compound. Into a duct, in which an inert gas stream containing vapors of a hydrolyzable metal compound flows, there is fed through a nozzle a cold inert gas stream, the temperatures and flows of the two gaseous streams being such as to establish in the duct a temperature lower than the condensation temperature of the metal compound; the mixed gaseous streams having a turbulent flow in the duct, with a Reynolds number equal to or higher than 1800. At the duct outlet, the aerosol of metal compound liquid particles, which has formed in the duct, is caused to react with steam, wherefore solid particles of hydrated metal oxide form, which are subsequently calcined to the oxide.

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Chivasso, Italy

Paolo Cortesi