The present invention provides a means capable of suppressing the formation of fine particles in a method for producing a silica sol. The present invention relates to a method for producing a silica sol, including synthesizing a silica sol by, in a reaction liquid containing an alkoxysilane or a condensate thereof, water, and an alkali catalyst, allowing the alkoxysilane or condensate thereof to react with the water in the presence of the alkali catalyst, wherein the alkali catalyst is not additionally supplied after the start of the synthesis until the finish time of the synthesis, and during 90% or more of the time between when 5 minutes have elapsed from the time point when the electrical conductivity of the reaction liquid reaches a local maximum for the first time and the finish time of the synthesis, the proportion of the value of the electrical conductivity of the reaction liquid is more than 90% relative to the value of the electrical conductivity at the time when 5 minutes have elapsed from the time point when the local maximum is reached.

Provided is a silica that exhibits a high matting property when utilized as a matting agent for a paint, and can also suppress the occurrence of cloudiness. The silica has an aggregated structure in which primary particles are aggregated, has a particle diameter ratio R represented by the following equation (1) of from 4.3 to 5.2, has an absorbance of 0.6 or less for light having a wavelength of 700 nm as an aqueous dispersion having a concentration of 1.48 mass %, and has a particle density measured with a He pycnometer of 2.18 g/cm.sup.3 or more: Equation (1) R=.sup.LD50/.sup.CD50 (in the equation (1), .sup.LD50 represents a volume-based 50% cumulative particle diameter (μm) of the silica measured based on a laser diffraction/scattering method, and .sup.CD50 represents a volume-based 50% cumulative particle diameter (μm) of the silica measured based on a Coulter counter method).

There are provided a coating composition being possible to form a cured film which has excellent transparency and weather resistance, and especially hardness. A coating composition obtained by which a silicon-containing substance as a component (M) and a silica colloidal particle having a primary particle diameter of 2 to 80 nm as a component (S) are mixed, and then the component (M) is hydrolyzed, and the resulting aqueous solution is subsequently mixed with a colloidal particle (C) wherein a component (F) is a modified metal oxide colloidal particle (C) having a primary particle diameter of 2 to 100 nm, which includes a metal oxide colloidal particle (A) having a primary particle diameter of 2 to 60 nm as a core, whose surface is coated with a coating (B) formed of an acidic oxide colloidal particle.

There are provided a coating composition being possible to form a cured film which has excellent transparency and weather resistance, and especially hardness. A coating composition obtained by which a silicon-containing substance as a component (M) and a silica colloidal particle having a primary particle diameter of 2 to 80 nm as a component (S) are mixed, and then the component (M) is hydrolyzed, and the resulting aqueous solution is subsequently mixed with a colloidal particle (C) wherein a component (F) is a modified metal oxide colloidal particle (C) having a primary particle diameter of 2 to 100 nm, which includes a metal oxide colloidal particle (A) having a primary particle diameter of 2 to 60 nm as a core, whose surface is coated with a coating (B) formed of an acidic oxide colloidal particle.

Provided is a loss circulation material that may consist essentially of an acidic nanosilica dispersion and an activator. The acidic nanosilica dispersion may consist of acidic silica nanoparticles, stabilizer, and water, and may have a pH in a range of 3 to 6. The activator may be one or more from the group consisting of sodium bicarbonate, sodium chloride, or an amine salt. A method is provided for controlling lost circulation in a lost circulation zone in a wellbore comprising introducing the loss circulation material and forming a gelled solid from the loss circulation material in the lost circulation zone.

Provided is a loss circulation material that may consist essentially of an acidic nanosilica dispersion and an activator. The acidic nanosilica dispersion may consist of acidic silica nanoparticles, stabilizer, and water, and may have a pH in a range of 3 to 6. The activator may be one or more from the group consisting of sodium bicarbonate, sodium chloride, or an amine salt. A method is provided for controlling lost circulation in a lost circulation zone in a wellbore comprising introducing the loss circulation material and forming a gelled solid from the loss circulation material in the lost circulation zone.

A colloidal dispersion of particles of silica having a particle size of from 3 nm to 100 nm, to which ions of one or more metals are adsorbed, selected from metals having atomic numbers 21-31, 39-46, 48-50, 57-82, and 89-93, and a method for preparing the dispersion. The dispersion may be used in various fields of use of metals.

The present invention refers to a stable sodium and iron silicate solution that has a weight ratio of SiO.sub.2 to Na.sub.2O from 1.5 to 2.5 and a total percentage of solids, expressed by the sum of SiO.sub.2 and Na.sub.2O, from 20% to 55%. Said solution also has a soluble iron content, expressed by Fe, from 0.1% to 7%, and a water content from 38% to 79.9%. The present invention also refers to the process for preparing said stable solution of sodium and iron silicate, which comprises the steps of: (a) providing a siliceous material containing iron; (b) submitting said siliceous material containing iron to a hydrothermal treatment with caustic soda under high temperature and controlled pressure; and (c) filtering said reacted solution to separate the reacted portion of the hydrothermal treatment from the unreacted portion. Additionally, the present invention refers to the uses of said stable sodium and iron silicate solution.

The present invention refers to a stable sodium and iron silicate solution that has a weight ratio of SiO.sub.2 to Na.sub.2O from 1.5 to 2.5 and a total percentage of solids, expressed by the sum of SiO.sub.2 and Na.sub.2O, from 20% to 55%. Said solution also has a soluble iron content, expressed by Fe, from 0.1% to 7%, and a water content from 38% to 79.9%. The present invention also refers to the process for preparing said stable solution of sodium and iron silicate, which comprises the steps of: (a) providing a siliceous material containing iron; (b) submitting said siliceous material containing iron to a hydrothermal treatment with caustic soda under high temperature and controlled pressure; and (c) filtering said reacted solution to separate the reacted portion of the hydrothermal treatment from the unreacted portion. Additionally, the present invention refers to the uses of said stable sodium and iron silicate solution.

Silica aerogels with improved properties are disclosed together with methods for synthesizing such aerogels. The improved properties include lower thermal conductivity (better insulating capacity), lower acoustic velocity, lower dielectric constant and improved ductility. Greater tunability of the refractive index can also be achieved. The silica aerogels are prepared by a sol-gel processing method that provides better control of the formation or aerogel structures. Generally speaking, the improvements arise from control of the synthesis to create a morphology of primary clusters and diverse-sized secondary clusters of dense silica aerogels separated by less densely packed regions. By providing a broader range of secondary clusters and/or pore sizes and loose connectivity between clusters, reductions can be achieved in thermal conductivity and flexural modulus.