Spherical corundum particles, based on fused aluminum oxide and a method for producing said particles
View Patent ↗A method is provided for manufacturing spherical corundum grains having a bulk density between 1.5 kg/L and 2.5 kg/L, with aluminum oxide being melted in an electric arc furnace with the addition of 0.1 to 1% quartz sand, the melt being poured in a pouring quantity of less than 100 kg/min, and the pouring stream being blown using compressed air at a pressure between 3 to 10 bar.
1. Spherical corundum grains based on fused aluminum oxide, having a spherical diameter between 0.001 and 5 mm, a maximum sodium oxide content of 0.5% by weight, and a maximum titanium oxide content of 0.5% by weight, characterized in that the spherical corundum grains have a bulk density between 1.5 kg/L and 2.5 kg/L.
2. Spherical corundum grains according to claim 1 , characterized in that the spherical corundum grains have a specific surface (BET) between 0.005 and 0.05 m 2 /g.
3. Spherical corundum grains according to claim 1 , characterized in that the spherical corundum grains have a grain fracture strength (Vollstädt) of ≧20 N.
4. Spherical corundum grains according to claim 1 , characterized in that the spherical corundum grains have a pore volume, measured using digital image analysis, of less than 50%.
5. Spherical corundum grains according to claim 1 , characterized in that for the spherical corundum grains the relative pore volume of micropores smaller than 3 μm is greater than 5%, relative to a total pore volume of 30-40%.
6. Method for manufacturing spherical corundum grains according to claim 1 , comprising the steps of:
a) melting aluminum oxide in an electric arc furnace with the addition of 0.1 to 1%, preferably 0.2 to 0.6%, quartz sand relative to the total weight of the starting materials,
b) pouring the melt in a stream at a pouring rate of less than 100 kg/min, and
c) directing a flow of compressed air at a pressure between 3 and 10 bar at the poured stream,
characterized in that the melt is carried out under oxidizing conditions.
7. Spherical corundum grains according to claim 3 , wherein the spherical corundum grains have a grain fracture strength (Vollstädt) of ≧40 N.
8. Spherical corundum grains according to claim 4 , wherein the spherical corundum grains have a pore volume, measured using digital image analysis, of less than 40%.
9. Spherical corundum grains according to claim 8 , wherein the spherical corundum grains have a pore volume, measured using digital image analysis, of less than 30%.
10. Spherical corundum gains according to claim 5 , wherein for the spherical corundum grains the relative pore volume of micropores smaller than 3 μm is greater than 15%, relative to a total pore volume of 30-40%.
11. The spherical corundum grains according to claim 1 , wherein the spherical corundum grains have a pore volume, measured using digital image analysis, between 25% and 50%.