Crystalline calcium sulfate dihydrate and process for making same
AssigneeSouthern California Edison Company
InventorRichard B. Rolfe
Life of this patent
Estimating the term…
Abstract
By the process of the invention a unique crystalline calcium sulfate dihydrate product is precipitated from an aqueous solution of calcium sulfate and a combination of molecularly dehydrated inorganic phosphates. Also within the scope of the invention is a wallboard manufacturing process and a gypsum wallboard which comprises the gypsum of the invention.
Claims23
The process for the continuous precipitation of crystalline calcium sulfate dihydrate product comprising the step of continuously precipitating calcium sulfate dihydrate crystals from an aqueous mixture by reacting in said mixture a source of calcium ions and a source of sulfate ions in the presence of from about 0.5 to about 10,000 parts per million by weight of the mixture of an additive comprising a combination of molecularly dehydrated phosphates having the empirical formula:
- ##STR2## wherein n is from 3 to 14, the polymers having n equal to 12 to 14 comprise at least about 75% of the total polymeric species and the polymers having n equal to 3-4 comprise at least about 15% of the total polymeric species.
The process for the precipitation of a crystalline calcium sulfate dihydrate product comprising the steps of:
- (a) feeding an aqueous mixture of at least one calcium sulfate precursor to a reaction chamber;
- (b) chemically converting said precursor to calcium sulfate in said chamber;
- and
- (c) forming, in the presence of from about 0.5 to about 10,000 parts per million by weight of the mixture of an additive comprising a combination of molecularly dehydrated phosphates having the empirical formula:
- ##STR3## wherein n is from 3 to 14, the polymers having n equal to 12 to 14 comprise at least about 75% of the total polymeric species and the polymers having n equal to 3-4 comprise at least about 15% of the total polymeric species, a precipitate comprising calcium sulfate dihydrate crystals formed from the calcium sulfate reaction product of step b.
Dependencies are inferred from the claim text.