A material or biomaterial comprising silicic acid condensates having a low degree of cross-linking, and methods for its production are subject-matter of the invention. A method for the production of silicic acid structures having a low degree of cross-linking is disclosed, wherein a sol is produced, wherein further condensation is prevented when specific cross-linking of the silicic acid is reached, wherein, preferably, structures having a size of 0.5-1000 nm are produced, e.g. polyhedral structures or aggregates of the same. Further condensation can be prevented by means of mixing with a polymer. In one embodiment, this comprises nano-structured, silicon dioxide (SiO.sub.2) having a low degree of cross-linking that is embedded in a polymer matrix. The material can be used in medicine for therapeutic purposes, and can enter into direct contact with biological tissue of the body in this connection. This material herein enters into chemical, physical, and biological interactions with the corresponding biological systems. It can herein be decomposed, and can act as a supplier for the silicic acid required for metabolism. Furthermore, it can have a supportive or shielding effect. It can be present as a granulate, microparticles, fiber, and as a woven or nonwoven fabric produced therefrom, or as a layer on implants or wound dressings. The material can be used as a medical device or as a nutritional supplement.

A method for producing an active silicic acid solution in which the existing amount of foreign matters as plate-like fine particles is reduced and a method for producing a silica sol in which such foreign matters are reduced. The method fulfills the following condition; the existing amount of plate-like fine particles having a length of one side of 0.2 to 4.0 m and a thickness of 1 to 100 nm is measured to be 0% to 30% in accordance with measuring method A, the method including the steps of: preparing an active silicic acid solution by subjecting an alkali silicate aqueous solution having a silica concentration of 0.5% by mass to 10.0% by mass to cation-exchange to remove alkaline components; and filtering the active silicic acid solution through a filter whose removal rate of particles having a primary particle size of 1.0 m is 50% or more.

A method for producing an active silicic acid solution in which the existing amount of foreign matters as plate-like fine particles is reduced and a method for producing a silica sol in which such foreign matters are reduced. The method fulfills the following condition: the existing amount of plate-like fine particles having a length of one side of 0.2 to 4.0 m and a thickness of 1 to 100 nm is measured to be 0% to 30% in accordance with measuring method A, the method including the steps of: preparing an active silicic acid solution by subjecting an alkali silicate aqueous solution having a silica concentration of 0.5% by mass to 10.0% by mass to cation-exchange to remove alkaline components; and filtering the active silicic acid solution through a filter whose removal rate of particles having a primary particle size of 1.0 m is 50% or more.

Intended is to provide a cation-modified silica dispersion wherein viscosity change with lapse of time is suppressed, and also intended is to suppress the variation in performance of a product using the dispersion as a raw material (for example, a polishing agent).

A cation-modified silica raw material dispersion which is being stored after being adjusted to less than pH 7.0.

A material or biomaterial comprising silicic acid condensates having a low degree of cross-linking, and methods for its production are subject-matter of the invention. A method for the production of silicic acid structures having a low degree of cross-linking is disclosed, wherein a sol is produced, wherein further condensation is prevented when specific cross-linking of the silicic acid is reached, wherein, preferably, structures having a size of 0.5-1000 nm are produced, e.g. polyhedral structures or aggregates of the same. Further condensation can be prevented by means of mixing with a polymer. In one embodiment, this comprises nano-structured, silicon dioxide (SiO.sub.2) having a low degree of cross-linking that is embedded in a polymer matrix. The material can be used in medicine for therapeutic purposes, and can enter into direct contact with biological tissue of the body in this connection. This material herein enters into chemical, physical, and biological interactions with the corresponding biological systems. It can herein be decomposed, and can act as a supplier for the silicic acid required for metabolism. Furthermore, it can have a supportive or shielding effect. It can be present as a granulate, microparticles, fiber, and as a woven or nonwoven fabric produced therefrom, or as a layer on implants or wound dressings. The material can be used as a medical device or as a nutritional supplement.

A material or biomaterial comprising silicic acid condensates having a low degree of cross-linking, and methods for its production are subject-matter of the invention. A method for the production of silicic acid structures having a low degree of cross-linking is disclosed, wherein a sol is produced, wherein further condensation is prevented when specific cross-linking of the silicic acid is reached, wherein, preferably, structures having a size of 0.5-1000 nm are produced, e.g. polyhedral structures or aggregates of the same. Further condensation can be prevented by means of mixing with a polymer. In one embodiment, this comprises nano-structured, silicon dioxide (SiO.sub.2) having a low degree of cross-linking that is embedded in a polymer matrix. The material can be used in medicine for therapeutic purposes, and can enter into direct contact with biological tissue of the body in this connection. This material herein enters into chemical, physical, and biological interactions with the corresponding biological systems. It can herein be decomposed, and can act as a supplier for the silicic acid required for metabolism. Furthermore, it can have a supportive or shielding effect. It can be present as a granulate, microparticles, fiber, and as a woven or nonwoven fabric produced therefrom, or as a layer on implants or wound dressings. The material can be used as a medical device or as a nutritional supplement.

The present invention relates to a process for preparing aqueous colloidal silica sols of high purity from silicate solutions, to aqueous colloidal silica sols with a specific profile of impurities, and to the use thereof. The invention further encompasses high-purity aqueous silica obtained as an intermediate in the course of the purification process, high-purity silicon dioxide obtainable by dewatering, and the use thereof.

To provide a method for producing an alkali silicate aqueous solution containing a reduced amount of foreign substance of plate-like fine particles and a method for producing a silica sol containing a reduced amount of foreign substance of plate-like fine particles. A method for producing an alkali silicate aqueous solution fulfilling the following condition: the existing amount of plate-like fine particles having a length of one side of 0.2 to 4.0 m and a thickness of 1 to 100 nm is determined to be 0 to 30%. The method for producing an alkali silicate aqueous solution includes the steps of adjusting a silica concentration of an alkali silicate aqueous solution to 0.5 to 10.0% by mass and filtering the alkali silicate aqueous solution through a filter having a removal rate of particles with a primary particle size of 1.0 m of 50% or more.

A stabilized aqueous active silica solution including at least one stabilizing agent selected from an acid, potassium hydroxide, ammonia and an organic base, whose content is 0.167 to 10% by mass/SiO2 relative to solution. The acid is an inorganic or organic acid. The inorganic acid is sulfuric or nitric acid. The organic acid is citric acid. The base is an amine or quaternary ammonium hydroxide. The viscosity of the solution that has a SiO2 concentration of 2.8 to 3.3% by mass, measured by the Ostwald method at 23 C. within 3 hours after production, is 0.5 to 20 mPa.Math.s. The viscosity of the solution measured after storage at 23 C. for 3 days is higher by 5.0 times or less than that of the solution measured within 3 hours. Also, a silica sol including silica particles having an average primary particle diameter of 5 to 300 nm.

An additive-containing silica sol in which a scattering intensity (I) of the additive-containing silica sol as a function of scattering vector (q) determined by a small-angle scattering method using X-rays satisfies Formulae (2) and (3):

[00001]$\begin{array}{cc}0.1\left(I_{m\mathrm{ax}}^B\right)/\left(I_0^B\right)-\left(I_{m\mathrm{ax}}^A\right)/\left(I_0^A\right)4.8& \mathrm{Formula}\left(2\right)\end{array}$$\begin{array}{cc}1\left(I_{m\mathrm{ax}}^A\right)/\left(I_0^A\right)& \mathrm{For}\mathrm{mula}\left(3\right)\end{array}$

where I.sup.B.sub.0 and I.sup.A.sub.0 are respectively scattering intensities when scattering vector (q) nm.sup.1 of the silica sol is 0.05 if a silica particle concentration in the silica sol before (I.sup.B.sub.0) and after (I.sup.A.sub.0) an additive is added is 3.5% by mass, and I.sup.B.sub.max and I.sup.A.sub.max are respectively scattering intensities when the scattering vector (q) nm.sup.1 of the silica sol is a maximum value if the silica particle concentration in the silica sol before (I.sup.B.sub.max) and after (I.sup.A.sub.max) the additive is added is 3.5% by mass. A HAZE value of the silica sol after storage at 20 C. for 24 hours is lower than before the additive is added.