Abstract: Embodiments provide a polishing composition for a magnetic disk substrate, the polishing composition containing colloidal silica, at least one of a phosphorus-containing inorganic acid and a phosphorous-containing organic acid, and water. According to at least one embodiment, the colloidal silica in the polishing composition has an average particle diameter (D50) in the range of 5 to 50 nm observed by a transmission electron microscope. In measuring a volume-based particle size distribution of the colloidal silica by dynamic light scattering, when the particle size distribution is measured by adjusting a concentration of colloidal silica particles to be 0.25 mass %, the colloidal silica contains 10 vol % or less of colloidal silica particles larger than 50 nm. The polishing composition has 1 to 50 mass % of the colloidal silica, and the pH (25° C.) in the range of 0.1 to 4.0. The colloidal silica is stabilized by sodium or ammonium.

Abstract: Embodiments provide a polishing composition for a magnetic disc substrate including colloidal silica, a phosphorus-containing compound, a water-soluble polymer compound, and water. According to at least one embodiment, the water-soluble polymer compound is a copolymer having a structural unit derived from an unsaturated aliphatic carboxylic acid and a structural unit derived from an unsaturated amide.

Abstract: Embodiments relate to a polishing composition for a magnetic disk substrate, where the polishing composition contains colloidal silica, a water-soluble polymer compound, and water. According to at least one embodiment, the water-soluble polymer compound has a weight average molecular weight of 20,000 to 10,000,000 and a concentration of 0.0001 to 2.0% by mass.

Abstract: Embodiments of the subject application provide a polishing composition for a magnetic disk substrate, whereby the polishing composition contains colloidal silica, at least one of a phosphorus-containing inorganic acid and an organic acid, and water. According to at least one embodiment, the colloidal silica in the polishing composition has an average particle diameter (D50) in the range of 5 to 50 nm observed by a transmission electron microscope. In measuring a volume-based particle size distribution of the colloidal silica by dynamic light scattering, when the particle size distribution is measured by adjusting a concentration of colloidal silica particles to be 0.25 mass %, the colloidal silica contains 10 vol % or less of colloidal silica particles larger than 50 nm. According to at least one embodiment, the polishing composition has 1 to 50 mass % of the colloidal silica, and the polishing composition has the pH (25° C.) in the range of 0.1 to 4.0.

Abstract: Embodiments relate to a polishing composition for a magnetic disk substrate, where the polishing composition contains colloidal silica, a water-soluble polymer compound, and water. According to at least one embodiment, the water-soluble polymer compound has a weight average molecular weight of 20,000 to 10,000,000 and a concentration of 0.0001 to 2.0% by mass.

Abstract: Embodiments provide a polishing composition for a magnetic disc substrate including colloidal silica, a phosphorus-containing compound, a water-soluble polymer compound, and water. According to at least one embodiment, the water-soluble polymer compound is a copolymer having a structural unit derived from an unsaturated aliphatic carboxylic acid and a structural unit derived from an unsaturated amide.

Abstract: A production method for natural gas according to the invention includes a step of adiabatically compressing a raw natural gas containing helium gas, a step of separating the helium gas from the raw natural gas by passing the adiabatically-compressed raw natural gas through a separation membrane unit, a step of conveying the raw natural gas from which the helium gas has been separated to a terminal through a pipe line, and a step of pressing the helium gas separated from the raw natural gas into an underground storage formation.

Abstract: A production method for natural gas according to the invention includes a step of adiabatically compressing a raw natural gas containing helium gas, a step of separating the helium gas from the raw natural gas by passing the adiabatically-compressed raw natural gas through a separation membrane unit, a step of conveying the raw natural gas from which the helium gas has been separated to a terminal through a pipe line, and a step of pressing the helium gas separated from the raw natural gas into an underground storage formation.

Abstract: A polishing composition of abrasive grains, a phosphorus-containing inorganic acid or salt thereof and another inorganic acid or salt thereof contained in an aqueous medium is used for the polishing of magnetic disk substrates or the like.