Spherically shaped precipitated calcium carbonate, its preparation and use
AssigneePfizer Inc.
InventorDennis B. Vanderheiden
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Abstract
A precipitated calcite of substantially spherical morphology having an average spherical diameter of from 2 to 10 microns and a specific surface area of from 1 to 15 square meters per gram is prepared by introducing carbon dioxide gas into an aqueous slurry of calcium hydroxide containing dissolved polyphosphate in the amount of from 0.1 to 1.0 percent, calculated as grams of phosphorus per 100 grams of the calcite equivalent of the calcium hydroxide, the starting temperature of the carbonation being 15.degree. to 50.degree. C. The spherical calcite is particularly suitable for use in dull finish coated paper.
Claims9
A precipitated calcite having particles of substantially spherical morphology with an average spherical diameter of from about 2 to 10 microns, a particle size distribution such that at least about 50 weight percent of the particles lie within 50 percent of the average spherical diameter, a specific surface area of from about 1 to 15 square meters per gram, a void volume of from about 0.5 to 1.0 cubic centimeter per gram, and a plurality of up to about 5000 surface nodules per particle, the nodules having a height of from about 0.02 to 1.0 micron and an aspect ratio of less than about 2.
A process for preparing a precipitated calcite of substantially spherical morphology, which comprises passing gaseous carbon dioxide through an aqueous slurry of calcium hydroxide initially containing dissolved polyphosphate as sole additive in an amount of from about 0.1 to 1.0 percent, calculated as grams of phosphorus per 100 grams of the calcium carbonate equivalent of the calcium hydroxide, the introduction being started at a temperature of from about 15.degree. to 50.degree. C.
Dependencies are inferred from the claim text.