To provide hollow silica particles having a dense silica shell layer. A method for producing hollow silica particles, which comprises: adjusting the pH of an oil-in-water emulsion containing an aqueous phase, an oil phase and a surfactant to at most 3.0 and adding a first silica material to the oil-in-water emulsion, adding a second silica material to the emulsion having the first silica material added, at its pH of at least 8, in the presence of alkali metal ions, to obtain a hollow silica precursor dispersion, and obtaining a hollow silica precursor from the hollow silica precursor dispersion and obtaining hollow silica particles from the hollow silica precursor.

To provide hollow silica particles having a dense silica shell layer. A method for producing hollow silica particles, which comprises: adjusting the pH of an oil-in-water emulsion containing an aqueous phase, an oil phase and a surfactant to at most 3.0 and adding a first silica material to the oil-in-water emulsion, adding a second silica material to the emulsion having the first silica material added, at its pH of at least 8, in the presence of alkali metal ions, to obtain a hollow silica precursor dispersion, and obtaining a hollow silica precursor from the hollow silica precursor dispersion and obtaining hollow silica particles from the hollow silica precursor.

A process for preparing precipitated silica, is disclosed. The process includes preparing an aqueous solution of sodium silicate having a pH in a range of 10.6 to 10.8, simultaneously adding to said aqueous solution of sodium silicate, a sodium silicate solution, water and an acid in at least two phases to obtain a reaction mixture, wherein in an initial phase the sodium silicate solution, the water and the acid is added till the sodium ion concentration of the reaction mixture is in range of 0.13 normal to 0.57 normal and in a final phase the sodium silicate solution, the water and the acid is added till the sodium ion concentration of the reaction mixture is in a range of 0.3 to 0.9 normal; acidifying the reaction mixture with the acid to a pH in a range of 3 to 4.5, aging the reaction mixture to obtain precipitated silica and recovering the precipitated silica from the reaction mixture.

A process for preparing precipitated silica, is disclosed. The process includes preparing an aqueous solution of sodium silicate having a pH in a range of 10.6 to 10.8, simultaneously adding to said aqueous solution of sodium silicate, a sodium silicate solution, water and an acid in at least two phases to obtain a reaction mixture, wherein in an initial phase the sodium silicate solution, the water and the acid is added till the sodium ion concentration of the reaction mixture is in range of 0.13 normal to 0.57 normal and in a final phase the sodium silicate solution, the water and the acid is added till the sodium ion concentration of the reaction mixture is in a range of 0.3 to 0.9 normal; acidifying the reaction mixture with the acid to a pH in a range of 3 to 4.5, aging the reaction mixture to obtain precipitated silica and recovering the precipitated silica from the reaction mixture.

To provide hollow silica particles having a dense silica shell layer.

A method for producing hollow silica particles, which comprises: adjusting the pH of an oil-in-water emulsion containing an aqueous phase, an oil phase and a surfactant to at most 3.0 and adding a first silica material to the oil-in-water emulsion, adding a second silica material to the emulsion having the first silica material added, at its pH of at least 8, in the presence of alkali metal ions, to obtain a hollow silica precursor dispersion, and obtaining a hollow silica precursor from the hollow silica precursor dispersion and obtaining hollow silica particles from the hollow silica precursor.

To provide hollow silica particles having a dense silica shell layer.

A method for producing hollow silica particles, which comprises: adjusting the pH of an oil-in-water emulsion containing an aqueous phase, an oil phase and a surfactant to at most 3.0 and adding a first silica material to the oil-in-water emulsion, adding a second silica material to the emulsion having the first silica material added, at its pH of at least 8, in the presence of alkali metal ions, to obtain a hollow silica precursor dispersion, and obtaining a hollow silica precursor from the hollow silica precursor dispersion and obtaining hollow silica particles from the hollow silica precursor.

This invention describes the encapsulation of and self-assembly of meso (nano) porous silica particles from inorganic an inexpensive silica precursor, sodium silicate. The particles have a well defined shape, high surface area, and high uniformity of the pore size, the properties that are typically found for high quality mesoporous material synthesized from organic silica precursors. The disclosure illustrates a synthesis of hard spheres, discoids, and a mixture comprising discoids, gyroids and fibers, termed as origami.

A porous silica particle optimized as the scrubbing agent is used for a cleansing cosmetic. The porous silica particle has an average circularity of 0.1 to 0.5, a pore volume of 1.0 to 2.0 ml/g, a mode diameter of 50 to 600 μm, and a ratio of the maximum particle diameter to the mode diameter of 3.0 or less. The porous silica particle moreover has a median size of 0.5 to 25 μm and the maximum particle diameter of 1 to 100 μm, after rubbing with a load of 1.0 to 1.4 KPa for 30 seconds. With the cleansing cosmetic containing this particle, the skin is rubbed by the frictional force generated by the friction with the skin at the rubbing. Therefore, the mild peeling effect for the stratum corneum is obtained and the damage of the skin and the micro damage on the stratum corneum can be prevented.

A porous silica particle optimized as the scrubbing agent is used for a cleansing cosmetic. The porous silica particle has an average circularity of 0.1 to 0.5, a pore volume of 1.0 to 2.0 ml/g, a mode diameter of 50 to 600 μm, and a ratio of the maximum particle diameter to the mode diameter of 3.0 or less. The porous silica particle moreover has a median size of 0.5 to 25 μm and the maximum particle diameter of 1 to 100 μm, after rubbing with a load of 1.0 to 1.4 KPa for 30 seconds. With the cleansing cosmetic containing this particle, the skin is rubbed by the frictional force generated by the friction with the skin at the rubbing. Therefore, the mild peeling effect for the stratum corneum is obtained and the damage of the skin and the micro damage on the stratum corneum can be prevented.

A silica-based particle dispersion including a silica-based particle group and a high polishing rate and high surface precision is achieved to a silica-based substrate or a NiP-plated substrate to be polished or the like. A silica-based particle dispersion containing a group including irregularly-shaped and non-irregularly-shaped silica-based particles, wherein the irregularly-shaped silica-based particles each have a plurality of small holes thereinside and a covering silica layer which covers the core, and the silica-based particle group satisfies [1]-[3]. [1] Having an average particle size (D.sub.1) of 100-600 nm, and a particle size (D.sub.2) of 30-300 nm in terms of specific surface area. [2] An irregular-shape degree D (D=D.sub.1/D.sub.3) represented by the average particle size (D.sub.1) and a projected area-equivalent particle size (D.sub.3) being in the range of 1.1-5.0. [3] When waveform separation is performed on a volume-reference particle size distribution, a multi-peak distribution in which three or more peaks are detected.