Granules and process for their production

1. Granules, comprising:

silica sand; and

aluminum oxide;

wherein:

when the granules are dried to a water content at most 2 mass % are subjected to screening using a sieve having 1 mm openings, a first volume cumulative median diameter D50(c) in a first particle size distribution curve of particles that pass through the sieve is from 350 to 1,000 μm;

in a second particle size distribution curve of water-insoluble components of the granules, a proportion of particles exceeding 50 μm in diameter is at most 6 vol %;

in the second particle size distribution curve of water-insoluble components of the granules, a 90% volume cumulative particle diameter D90(b2) from a smaller particle size side is at most 45 μm; and

a ratio of D90(b2) to a 50% volume cumulative particle diameter D50(b1) from the smaller particle size in the second particle size distribution curve of water-insoluble components of the granules, D90(b2)/D50(b1), is at most 1.9.

2. The granules according to claim 1 , wherein a filling rate of the granules is at least 75% as measured by mercury intrusion technique.

3. The granules according to claim 1 , wherein a bulk density of the granules is at least 1.1 g/ml.

4. A process for producing granules, comprising:

mixing at least silica sand and aluminum oxide to obtain a glass raw material mixture; and

granulating, without pulverizing, the glass raw material mixture;

wherein:

when the granules are dried to a water content at most 2 mass % and are subjected to screening using a sieve having 1 mm openings, a first volume cumulative median diameter D50(c) in a first particle size distribution curve of particles that pass through the sieve is from 350 to 1,000 μm;

in a second particle size distribution curve of water-insoluble components of the granules, a proportion of particles exceeding 50 μm in diameter is at most 6 vol %;

in the second particle size distribution curve of water-insoluble components of the granules, a 90% volume cumulative particle diameter D90(b2) from a smaller particle size side is at most 45 μm; and

a ratio of D90(b2) to a 50% volume cumulative particle diameter D50(b1) from the smaller particle size in the second particle size distribution curve of water-insoluble components of the granules, D90(b2)/D50(b1), is at most 1.9.

5. The process for producing granules according to claim 4 , wherein granulating the glass raw material mixture comprises performing a tumbling granulation method.

6. A method for producing a glass product, comprising:

producing granules by the process according to claim 4 ; and

melting the granules to form molten glass; and

forming a glass product from the molten glass.

7. The method for producing a glass product according to claim 6 , wherein the glass product comprises:

50 to 60 mass % SiO 2 ;

15 to 20 mass % Al 2 O 3 ;

6 to 10 mass % B 2 O 3 ;

2 to 6 mass CaO;

1 to 5 mass % MgO;

0.01 to 0.1 mass % Fe 2 O 3 ; and

5 to 10 mass % SrO.

8. The method for producing a glass product according to claim 7 , wherein the glass raw material mixture comprises, as water-insoluble components:

65 to 75 vol % of silica sand (SiO 2 ) having a D50 of 1 to 30 μm;

7 to 15 vol % of aluminum oxide having a D50 of 1 to 7 μm;

0.1 to 10 vol % of magnesium hydroxide having a D50 of 3 to 11 μm;

5 to 15 vol % of dolomite having a D50 of 5 to 20 μm;

3 to 15 vol % of strontium carbonate having a D50 of 2 to 10 μm;

0.1 to 2 vol % of fluorite (CaF 2 ) having a D50 of 5 to 30 μm; and

0.001 to 0.1 vol % of iron oxide (Fe 2 O 3 ) having a D50 of 5 to 50 μm.

9. The granules according to claim 1 , wherein the ratio of D90(b2) to D50(b1), D90(b2)/D50(b1), is at most 1.8.

10. The process according to claim 4 , wherein the ratio of D90(b2) to D50(b1), D90(b2)/D50(b1), is at most 1.8.