Alpha-type calcium sulfate hemihydrate compositions
Disclosed is an improved alpha-type calcium sulfate hemihydrate. Methods of producing an improved powdered calcium sulfate hemihydrate (CaSO 4 .½H 2 O) [alpha-type] compound are disclosed, at least one method including forming calcium sulfate dihydrate (CaSO 4 .2H 2 O) into a briquette, calcining the briquette to transform the calcium sulfate dihydrate to calcium sulfate hemihydrate [alpha-type], drying the calcium sulfate hemihydrate [alpha-type] briquette, and optionally grinding the briquette. Also disclosed are methods of producing an improved gypsum plaster including producing the disclosed powdered calcium sulfate hemihydrate [alpha-type] and mixing the powdered calcium sulfate hemihydrate [alpha-type] with water.
1. A ground alpha-hemihydrate made from a process comprising
forming calcium sulfate dihydrate into a briquette having physically bound water in a range from about 15% to 21% by weight of the calcium sulfate dihydrate briquette, wherein forming calcium sulfate dihydrate into a briquette includes providing a pressure of formation greater than 14 megapascal to produce a substantially uncracked briquette that will remain substantially uncracked during calcination;
adding free water to the calcium sulfate dihydrate briquette, wherein the free water is just greater than 0% up to about 12% by weight of the calcium sulfate dihydrate briquette;
calcining the briquette;
transforming the calcium sulfate dihydrate briquette to an alpha calcium sulfate hemihydrate briquette; and
drying the alpha calcium sulfate hemihydrate briquette.
2. A product produced from a mixture comprising:
ground alpha-calcium sulfate hemihydrate made from the process of claim 1 and water.
3. The product of claim 2 , further comprising at least one of sand and fly ash.
4. An alpha calcium sulfate hemihydrate of claim 1 comprising:
crystals of the alpha-calcium sulfate hemihydrate that have grown together to form clusters of the crystals;
wherein the clusters of the crystals of alpha calcium sulfate hemihydrate have a smaller amount of pore volume between the clusters, when compared to the pore volume of alpha calcium sulfate hemihydrate crystals formed from dihydrate briquettes with about 0% to 12% moisture concentration.
5. The alpha calcium sulfate hemihydrate of claim 4 , wherein the clusters of crystals may be ground to produce blocky crystals of alpha-hemihydrate.
6. The alpha calcium sulfate hemihydrate of claim 5 , wherein the ground alpha-hemihydrate has a bimodal particle size distribution.
7. The alpha calcium sulfate hemihydrate of claim 4 , wherein the substantially reduced pore volume comprises a pore volume of about 30 to 50% of the volume of the crystals.
8. The alpha calcium sulfate hemihydrate of claim 4 , wherein the reduced pore volume comprises a pore volume of about 40 to 50% of the volume of the crystals.
9. A dry, ground alpha calcium sulfate hemihydrate of claim 1 converted from a calcined calcium sulfate dihydrate briquette; wherein the dry, ground alpha calcium sulfate hemihydrate has a water demand of less than 50 milliliters per 100 grams of dry, ground alpha calcium sulfate hemihydrate.
10. The alpha calcium sulfate hemihydrate of claim 9 , wherein the alpha calcium sulfate hemihydrate is formed from gypsum obtained as a byproduct from at least one of the following processes: desulfurization of flue gases, production of titanium dioxide, or production of phosphate fertilizers.
11. The alpha hemihydrate of claim 1 , wherein the pressure used to form the calcium sulfate dihydrate briquette ranges from about 100 to 200 MPa.