Abstract: A form of calcium carbonate having a blocky rhombohedral crystal structure and properties including a surface area of from about 3 to about 15 m.sup.2 g, an average discrete particle size of from about 0.2 to about 0.9 micron, wherein the discrete particles have an aspect ratio less than about, 2:1 and a particle size distribution such that at least about 60 weight percent of the particles have a size within 50 percent of the equivalent discrete particle spherical diameter, suitable for use as a filler material in papermaking to improve the optical properties of the resulting paper, is disclosed. An accelerated heat-aging process, including embodiments thereof which utilize hydrothermal techniques, for rapidly producing this form of calcium carbonate, and a related form of calcium carbonate having a hexagonal prismatic crystal structure and the same properties, in large quantities to meet the demand of the papermaking industry, as well as a method for using these materials in papermaking, are also disclosed.

Abstract: A form of calcium carbonate having a blocky[-six-sided] rhombohedral crystal [habit ] structure and [a morphology, with] properties including a surface area of from about 3 to about 15 m.sup.2 /g, an average discrete particle size of from about 0.2 to about 0.9 micron, wherein the discrete particles have an aspect ratio less than 2, and a particle size distribution such that at least about 60 weight percent of the particles have a size within 50 percent of the equivalent discrete particle spherical diameter, suitable for use as a filler material in papermaking to improve the optical properties of the resulting paper, is disclosed.

Abstract: A form of calcium carbonate having a blocky rhombohedral crystal structure and properties including a surface area of from about 3 to about 15 m.sup.2 /g, an average discrete particle size of from about 0.2 to about 0.9 micron, wherein the discrete particles have an aspect ratio less than about 2:1, and a particle size distribution such that at least about 60 weight percent of the particles have a size within 50 percent of the equivalent discrete particle spherical diameter, suitable for use as a filler material in papermaking to improve the optical properties of the resulting paper, is disclosed. An accelerated heat-aging process, including embodiments thereof which utilize hydrothermal techniques, for rapidly producing this form of calcium carbonate, and a related form of calcium carbonate having a hexagonal prismatic crystal structure and the same properties, in large quantities to meet the demand of the papermaking industry, as well as a method for using these materials in papermaking, are also disclosed.

Abstract: A form of calcium carbonate having a blocky rhombohedral crystal structure and properties including a surface area of from about 3 to about 15 m.sup.2 /g, an average discrete particle size of from about 0.2 to about 0.9 micron, wherein the discrete particles have an aspect ratio less than about 2:1, and a particle size distribution such that at least about 60 weight percent of the particles have a size within 50 percent of the equivalent discrete particle spherical diameter, suitable for use as a filler material in papermaking to improve the optical properties of the resulting paper, is disclosed. An accelerated heat-aging process, including embodiments thereof which utilize hydrothermal techniques, for rapidly producing this form of calcium carbonate, and a related form of calcium carbonate having a hexagonal prismatic crystal structure and the same properties, in large quantities to meet the demand of the papermaking industry, as well as a method for using these materials in papermaking, are also disclosed.

Abstract: A form of calcium carbonate, acid-stabilized by the addition to finely divided calcium carbonate of one of a calcium- chelating agent and a conjugate base, such as sodium hexametaphosphate, followed by the addition of a weak acid, such as phosphoric acid, is disclosed. A process for producing this material, and a method for its use in the making of neutral to acidic paper in order to improve the optical properties of the paper are also disclosed.

Abstract: A form of calcium carbonate, acid-stabilized by the addition to finely divided calcium carbonate of one of a calcium- chelating agent and a conjugate base, such as sodium hexametaphosphate, followed by the addition of a weak acid, such as phosphoric acid, is disclosed. A process for producing this material, and a method for its use in the making of neutral to acidic paper in order to improve the optical properties of the paper are also disclosed.

Abstract: This invention relates to a process for the preparation of high surface area rhenium sulfide hydrodesulfurization catalysts and to a process of using such catalysts for hydrotreating, particularly hydrodesulfurizing heavy hydrocarbons. The catalyst may be supported during use. They are preferably made using an aqueous procedure for forming the solid ReS.sub.2+s precursor. The precursor is then heated for a period of time in substantially pure H.sub.2 S.