WO2000069976A1

WO2000069976A1 - Silica sol, composition containing the same, method for treating said silica sol and uses thereof

Info

Publication number: WO2000069976A1
Application number: PCT/FR2000/001286
Authority: WO
Inventors: Jacques Persello
Original assignee: Universite De Franche-Comte
Priority date: 1999-05-12
Filing date: 2000-05-12
Publication date: 2000-11-23
Also published as: AU4763000A; FR2794115A1

Abstract

The invention relates to a novel silica sol, to a composition containing said silica sol, to a method for treating the silica sol and to various uses thereof. The silica sol is surface-treated by grafting and/or by adsorption of at least one organic molecule and/or by doping with at least one doping agent, said sol comprising silica nanoparticles whose average size is between 3 and 50 nm. Said particles are monodispersed in a liquid phase and are present in a concentration greater than or equal to 5 % and preferably greater than or equal to 10 %.

Description

SILICA SOL, COMPOSITION COMPRISING SAME, TREATMENT METHOD AND USES THEREOF

The present invention relates to a silica sol, to a composition and to a pigment comprising it, to a surface treatment method as well as to various uses of this sol.

It is currently well known to use anticorrosion pigments for the metal, for example of the zinc phosphate, aluminum triphosphate, calcium silicate, zinc silicate type, in paint compositions.

The main drawback of such pigments is that they release the active substances which they contain, anywhere on the surface to which they are applied. Such a release therefore results in uneven protection of the support against corrosion. These pigments also have the drawback of not being able to be used on any type of metallic support. Their application also poses the problem of being specific to the nature of the support.

It is also known to incorporate pigments in the above-mentioned silica form or in the form of silica gel in paint compositions. However, these silicas have the drawback of dispersing at sizes greater than 0.2 μm. The process for manufacturing these concentrated aqueous silica soils consisting of nanoparticles is known in particular from document US 4,410,405. There also remains the need for a new silica sol having effective and general anticorrosive properties, applicable to all types of painted or unpainted metal support, possibly zmgue or chromate, which can be easily incorporated into emulsion compositions, for example of the paint type, and capable of gradually releasing the active substances only on the fragile areas to be protected or repaired. The subject of the invention is therefore a silica sol, comprising silica nanoparticles with an average size of between 3 and 50 nm, surface-treated by grafting and / or by adsorption of at least one organic molecule, and / or by doping with at least one doping agent, characterized in that the organic molecule is chosen from amines, polyamines, quaternary amines, a mo silanes, silanes, phosphonates, diamines, polyamines, polyacrylates, acids, diacids, triacids, polyacids, organic hydroxy acids, polyvinyl alcohols, polyoxyethylene, conductive polymers, silane derivatives of the following general formulas: (I) XR-Si (Y) ₃ , (II) XR-Si (Y) 2 R 'r or (III) XR-Si (R' R ") Y Where, - X is a group chosen from vinyl, methacrylate, methyl, phosphate, proton groups, when R is a chain carbon of type - (CH2 ^~ ) n ^{~ or n es} ^ ^an integer between 1 and 20,

- X is a group chosen by the amino, epoxy, polysulphide or mercapto groups when R is a carbon chain of the type - (CH2 ^~ ) _n " ^{or n is} equal to 19 or 20,

- R 'R "are independently of one another chosen from a proton, a hydroxide, an ester, an ether or a hydrocarbon chain of the type - (CH2 ^~ ) _n ^{~~ or n is an} integer between 1 and 20, and mixtures of all these constituents, said nanoparticles being present in a concentration greater than or equal to 5% and preferably greater than or equal to 10%. The floor according to the invention has the advantage of being able to be manufactured easily and quickly, of being able to increase the resistance of unpainted and untreated metal parts with respect to corrosion when these parts are covered with a composition comprising sol according to the invention, and to be able to replace all or part of the chromating layer of zinc parts.

Another advantage of the soil according to the invention is that it includes new sites due to the modification of its surface, which are nonexistent on an untreated silica sol.

Indeed, one can for example create positive sites by the addition of cation, such as aluminum ions, one can control the ratio negative sites / positive sites, one can create acid or basic sites. These new sites are likely to be able to form bonds of covalent, hydrogen or ionic nature.

Finally, the sol of the invention also presents other advantages of allowing better fixation of resins on the silica atoms, of allowing better compatibility of the silica atoms with other ingredients of a composition, of facilitating the dispersion of silica atoms when brought into contact with polymers or solvents, to show better fixing qualities on metals which have already undergone a pretreatment, and finally to allow better fixing on steel, of a paint composition comprising the floor of the invention. The mechanism of the anticorrosion process is based on an ion exchange mechanism between the ions present on the surface of the metal and the ions fixed on the support of amorphous and porous silica, so as to protect the surface of the metal. Preferably, this ion exchange takes place with calcium ions or with functionalized silanes, with amino derivatives, or with phosphates, all of which have good results in protecting metals against corrosion. . the organic molecule, which is grafted and / or adsorbed on the silica sol can be chosen from amines, polyamines, quaternary amines, amino silanes, silanes, phosphonates, diamines, polyamines, polyacrylates, acids, diacids, triacids, polyacids, organic hydroxy acids, polyvinyl alcohols, polyoxyethylenes, conductive polymers such as polyortho-toluidine, polyanilme, polythiophene, polypyrrole, as well as the salts of these conductive polymers (for example of the chloride or sulfate type), the silane derivatives of the following general formulas:

(I) X-R-Si (Y) 3 '

(I I) X-R-Si (Y) 2 R '/ or

(I I I) X-R-S i (R 'R ") Y

OR

X is a group chosen from amine, hydroxide, epoxy, vinyl, polysulphide, methacrylate, metyl, fluoride, mercapto, phosphate, proton groups, Y is a group chosen from ethoxy, methoxy, chloro groups, R is a chain carbon of type - (- CH2-) _n - where n is an integer between 1 and 20, R and R "are independently of one another chosen from a proton, a hydroxide, an ester, an ether or a hydrocarbon chain of the type - (- CH2-) _n ^{~ or n es1: an} integer between 1 and 20. and mixtures of all these constituents The agent doping the silica sol can be in the form of an inclusion or a solid solution, and can be chosen from the salts of monovalent cations, divalent cations, tπvalent cations, quadruple cations in their chloride, nitrate, sulfate, phosphate, phosphonate, silicate, hydroxide, oxide, acetate or gluconate form, and mixtures thereof.

Preferably, the doping agent is present in an amount less than 10 ° by weight relative to the total weight of the silica.

Preferably, the silica sol does not comprise any doping agent.

The soil according to the invention makes it possible to prevent and / or inhibit any type of metallic corrosion. It is recalled that corrosion of a metal is a complex process which involves several electrochemical and chemical reactions.

Four distinct operations explain this process.

First there is the dissolution of the metal by its oxidation at an anionic site, followed by the reduction of an oxidizing species in solution in the vicinity of a cathodic site on the metal, then the migration of ions into solution in order to ensure the electrical neutrality of the system, and finally the transfer of electrons within the metal between the anodic and cathodic sites. To inhibit corrosion, just block one of these four steps, what the soil does of the invention by acting on at least one of them. By adsorbing on the active sites of the metal, seat of corrosion reactions, the soil inhibits or slows the start of the corrosion process. During one of the corrosion steps, the soil of the invention can stop corrosion by playing the role of soluble anode (in the case of treatment of the soil with zinc), or provide cations, such as ions calcium, magnesium, aluminum to form a passivating layer or even block the stages of corrosion due to the presence of corrosion inhibitors which have been adsorbed on the soil, such as phosphates, amines, silanes.

Ion exchange with calcium is the most commonly used process to inhibit corrosion. The sol of the invention also makes it possible to provide very good results when it is treated at the surface with a functionalized silane, with at least one amine derivative or with a phosphate. The quality of the result obtained depends both on the nature of the metallic support on which the soil is applied, as well as on the nature of the corrosion.

The liquid phase of the soil of the invention may comprise anions and free cations in a concentration less than or equal to 0.05 mol / l and preferably less than or equal to 0.005 mol / l. Preferably, the pH of the soil of the invention is between 3 and 11.

Soil can be defined by characteristics which are translucency, conductivity, and silica concentration.

The translucency of the soil is preferably greater than or equal to 95% and more preferably greater than or equal to 98%, with light transmission between 400 and 650nm.

The conductivity of the soil can be between 100 and 500μS / cm, when it includes a silica concentration of 10%.

The sol of the invention can have a silica concentration of between 1 and 300 g / l.

The sol of the invention has a nanometric silica dispersion of reduced polydispersity. Two other objects of the invention are an anticorrosion pigment and, a composition each comprising at least one silica sol according to the invention as defined above.

The composition may, in addition, comprise at least one additive chosen from latexes such as styrenes acrylates, styrenes butadienes, vinyl acetates, vinyl acetate modified maleic acetates or polyvinyl alcohol marketed under the brand RHODOPAS by the Company RHODIA, alkylsiliconates such as potassium methylpropylsiliconate marketed by the company Wacker, poly (oxyethylene) polyoxypropylene copolymers sold under the brand SYNPERONIC PE 135 by the company ICI, cationic surfactants (sold under the brand ARQUAD by the company AKZO NOBEL) , anionic surfactants

(laurylsulfate), nonionic surfactants (Triton

X100), amphoterics (Reweteric AMB 13 from itco), polyethylene emulsions, PTFE

(polytetrafluoroethylene), silicones, water-soluble polymers such as xanthan gums (Rhodopol from Rhodia), hydroxy- and carboxy-methylcelluloses (Natrosol from Hercules), silicone resins (Rhodorsil from Rhodia), epoxy ester resins (Residorl from V E37L from Hoechst), polyesters, alkyds, polyurethanes, polyols (polyvinyl alcohols, polyethylene glycol, polypyrolidone). This additive can be present in an amount ranging from 0.01 to 10% by weight relative to the total weight of the composition.

The sol may be present in the composition in an amount ranging from 0.1 to 5% by weight relative to the total weight of the composition.

The soil as defined above can be prepared according to the following known conventional operating method which comprises four stages.

This procedure makes it possible to carry out the synthesis of silica according to the following known chemical reaction:

xSι0 ₂ ; Na ₂ 0 + H S0 ₄ > XS1O2 + Na ₂ Sθ4 + H ₂ 0

In a first step, we first make a base stock by adding silicate, deionized water and acid to obtain silica particles. The amount of silicate in the base stock can either be equal to the total amount used in the reaction or represent only a part of it. The concentration of silica in the initial base stock can be less than 100 g / l, preferably less than 20 g / l when using a cationic resin alone as an acidifying agent, and preferably less than 2 g / l when using as an acidifying agent an ore acid.

During this step, various parameters are regularly checked, such as the temperature, the silica concentration, the pH, the neutralization rate. The temperature can vary from 20 ° to 95 ° C. Control of the number concentration of particles therefore allows control of the final size of the silica particles.

In a second step, an acidifying agent is added to the silica particles so as to increase the concentration of silica and the size of the silica particles. The addition of the acidifying agent causing a drop in pH, is done until a pH equal to at least 8, but generally between 9 and 11 is reached. Once this pH value is reached, and when the base stock comprises only part of the total amount of silica involved in the chemical reaction, a complementary and simultaneous addition of acidifying agent and the amount of remaining silicate are carried out.

The choice of silicate is made in a manner well known per se. One can use all the common formulas of silicates, such as metasilicates, disilicates, and more advantageously alkali metal silicates such as sodium silicate, potassium silicate. In the case where sodium silicate is used, the latter has a weight ratio Sιθ2 / a2θ of between 2 and 4, and more particularly between 3 and 3.8. The choice of acidifying agent is chosen so as to avoid an excessive increase in the salt concentration in the reaction medium, during acidification or at the end of acidification. The acidifying agent may optionally be a cationic cation exchange resin in its protonated form, or a more complex acidifying system consisting of a mineral or organic acid combined with a cationic resin and an anionic resin. As the mineral acid, sulfuric acid, acid can be used. hydrochloric acid, nitric acid, phosphoric acid and their mixture. As the organic acid, acetic acid, formic acid, carbonic acid and their mixture can be used. Resins such as weak acid type resins in protonated form such as polystyrene, polyacrylate or polymethacrylate resins containing carboxylic groups (sold under the brand IMAC HP 336 by Rohm and Haas or DOWEC CCR3 by Dow Chemical can also be used as the acid). ). Resins of the strong acid type can also be used, such as polystyrene resins containing sulfonate groups (sold under the name

^" DOWEC Marathon brand or under the AMBERLITE IR brand

120H) or containing phosphate groups (sold under the brand DUOLITE ES).

The concentration of silica in the final reaction mixture can be less than 50 g / l, preferably less than 20g / l and even more preferably less than 10g / l. The salt concentration formed in the final reaction mixture, at the end of this second step, is preferably less than 0.1 mol / l when using a mineral acid, and can be less than 0.01 mol / l when a cationic resin is used. The synthesis reaction, properly speaking, is complete, when all of the silicate and the acidifying agent have been added in an amount sufficient to reach a maximum pH value equal to 11.

In a third and penultimate step, the silica sol obtained at the end of the previous step is firstly filtered through a sieve having meshes of about 100 μm to remove for example the resin, then washed to remove all the soluble salts possibly formed during the synthesis which can be for example sodium sulphate when sulfuric acid is used as acidifier. When the acidifying agent is a resin, there is no salt formation. The washing of the soil can be carried out by bringing the silica sol into contact, on the one hand with a cationic resin in protonated form which then makes it possible to remove the cationic species soluble in the aqueous phase, and, on the other hand with a anionic resin in hydroxide form which makes it possible to remove the soluble anionic species.

During the whole washing process, the pH is from ^" pre een to htenu constant between 8 ^" and 10 ^"" so as to ^" avoid agglomeration of the particles. The pH can be kept constant by the simultaneous addition of two types of resins. The pH can also be adjusted by the additional addition of one of the two resins used for washing. Detection of the end of washing can be carried out by measuring the conductivity of the soil. reaches a value of about lmS / cm, the washing is stopped.

Washing can be carried out - when the silica concentration is at most 100g / l, and preferably less than 50 g / 1. The silica sol is washed until the molar concentration of free ionic species is at most 0.01 mol / l and preferably less than 0.005 mol / l.

According to a variant of this step, the washing is carried out by dialysis or by tangential filtration while keeping the volume of the silica sol constant by the addition of deionized water.

At the end of the washing, it is advantageous to adjust the pH of the silica sol to a value between 2 and 11. This adjustment can be carried out conventionally by adding cationic resin to lower the pH, or adding alkaline hydroxide (sodium hydroxide, potassium hydroxide) to increase the pH.

Finally in the last and fourth step, the silica sol is concentrated under vacuum, by ultrafiltration or by tangential filtration so as to release the water. This concentration can be carried out under reduced pressure, at a temperature below 80 °, and preferably below 60 ° C. This evaporation can be carried out at a speed of at least 100 g of water per liter of soil and per hour. According to an essential characteristic of the process of the invention, the silica sol, obtained at the end of the four known previous stages, is treated on the surface by grafting and / or by adsorption of at least one organic molecule or also by deposition of metal salt particles.

The grafting treatment is therefore carried out when the resins and the salts have all been removed. An attachment is then carried out, by grafting and / or by adsorption, of organic molecules by means of a chemical reaction with the silanol sites present on the surface of the silica sol. The bonds formed are covalent in nature and are therefore identifiable by conventional spectroscopic techniques such as infrared, nuclear magnetic resonance.

The organic molecule is preferably chosen from amines, amino silanes, silanes, phosphonates, diam es, polyamines, polyacrylates, organic hydroxy acids, polyvinyl alcohols, polyoxyéhylènes, conductive polymers. The organic molecule can also be chosen from silane derivatives of the following general formulas:

(I) XR-Si (Y) ₃ , (II) XR-Si (Y) ₂ R ', or (III) XR-Si (R'R ") Y WHERE X is a group chosen from amine and hydroxide groups , epoxy, vinyl, polysulfide, methacrylate, methyl, fluoride, mercapto, phosphate, proton, Y is a group chosen from the groups ethoxy, methoxy, chloro,

R is a carbon chain of the type - (- CH2 ~) n- where n is an integer between 1 and 20, R 'and R "are independently of each other chosen from a proton, a hydroxide, an ester , an ether or a hydrocarbon chain of the type - (- CH2) n- where n is an integer between 1 and 20. The organic molecule can also be chosen from mixtures of all these constituents. at the end of the last step, but before the resins are removed. Optionally, additional cationic resin is added so as to reduce the pH to a value between 8 and 2. The metal oxide particles become fixed then on the surface of the silica particles by a phenomenon of co-aggregation.

According to the present invention, the silica sol can optionally be doped using at least one doping agent in the form of an inclusion or a solid solution. This treatment with a doping agent consists in carrying out a co-addition of silicates, of an acid with the doping agent. The doping agent is incorporated into the last layers of silica in the form of an inclusion or a solid solution. The doping agent can be added before the end of the second step, and can be chosen from the salts of monovalent cations, divalent cations, tπvalent cations, quadrivalent cations, the salts possibly being in their chloride, nitrate, sulfate form , phosphate, phosphonate, silicate, hydroxide, oxide, acetate or gluconate or mixtures thereof.

The doping agent can be chosen from calcium hydroxide, magnesium hydroxide, aluminum sulphate, zinc sulphate, calcium sulphate, cerium nitrate, cerium oxide, alum sodium ate, sodium zmcate, sodium phosphate, sodium phosphonate, and mixtures thereof.

Preferably, the doping agent is introduced in the last phase of addition of the acid. The concentration by weight of doping agent is preferably less than 10% relative to the weight of silica. The doping agent is preferably introduced at a pH greater than 8 and even more preferably greater than 10.

Preferably, the silica sol does not comprise any doping agent.

The doping agent may be present in an amount less than 10% by weight relative to the total weight of the silica.

The treated soil obtained according to the process as defined above, may have a chemical treatment rate of between 0.1 and 50%, and more particularly between 0.1 and 5%. The last objects of the invention are different uses of this soil.

One is the use of soil as an anticorrosive agent for metal. Another is the use of the soil as an adhesion initiator intended to facilitate the adhesion of a layer of polymer or mineral to a support. Yet another is the use of soil as a raw material to obtain mineral membranes with pore sizes less than 20nm. In this case, the use of such a treated soil according to the invention makes it possible to obtain better selectivity of the molecules to be separated, such as pollutants, gases. The membranes thus obtained have the advantage of being biocompatible and thus allowing the separation of biological species.

The invention also relates to a use of the soil as a rheological additive in the composition of emulsions, such as suspensions, paints, varnishes, coatings or ceramics. Soil is also used as a reinforcing filler in plastics, such as elastomers, rubbers or silicones.

Another use of the soil of the invention is a use as an additive in redispersible agrochemical compositions.

Finally, a final use of the soil of the invention is as an ingredient in ceramic materials intended for the field of optics and / or electronics. The invention will now be described with the aid of the examples which follow and which are given solely by way of illustration.

In Examples 1 to 7, the acidifying agent is a cationic resin. EXAMPLE 1: Silica sol treated with 1-hydroxyethylene acid 1, 1-phosphide (OH) cjPpCpH ^ O _?

In a first step, a base is formed by introducing into a stainless steel reactor fitted with a turbine stirring system, heating by electrical elements, and a temperature and pH regulation system, 10400g of purified water with conductivity less than 5μS / cm and having a temperature equal to 25 ° C, and 5600g of sodium silicate with a weight ratio Sιθ2 / Na2θ equal to 3.25 and a mass concentration of silica of 260g / kg.

In a second step, after a waiting time of 10 minutes, 6000 g of cationic resin suspension in protonated form containing 28% dry extract (of IMAC HP 336 type from ROHM AND HAAS) are introduced into the reaction medium. bring the pH of the reaction medium to a final pH of 10.8 +/- 0.2. The duration of this simultaneous introduction is fixed at 30 minutes. A silica sol is thus obtained with a silica concentration of approximately 60 g / kg and having a pH of 10.8.

Then proceed to a filtration of the silica sol on a nylon fabric having pores of about 100 μm to remove the resin. In a third step, the reaction temperature is raised from 25 ° to 70 ° C in about 15 minutes. Then introduced 5.1 g of acιde-1-hydroxy ethylene 1.1 diphosphonic acid 60O acid (DEQUEST 2010 MONSATO). The reaction medium is left at this temperature for 20 minutes.

In a fourth step, the medium is cooled to 25 ° C., and then approximately 800 g of resin of the type described above is introduced. This addition is done until a pH value of the medium is obtained reactional equal to 10.00 +/- 0.1. The duration of this introduction is fixed at approximately 10 minutes. At the end of this step, the reaction mixture is allowed to mature at 25 ° C and at a pH equal to 10 for 30 minutes. We then proceed to a second filtration of the silica sol on a nylon fabric having pores of about 100 μm to remove the resin. This gives a transparent silica sol having a pH of 10 and a silica concentration of 15 g / kg. At the end of this step, the sol is concentrated to a silica concentration of 95 g / kg by evaporation under vacuum at 60 ° C. The duration of the operation is 6 hours.

EXAMPLE 2 Silica Sol Treated with Amino-Tris-methylene-Phosphonic Acid C ^ H- | 2NQ9P3

The procedure of Example 1 is repeated, in which 11.2 g of a 50% aqueous solution of ammo-tris-methylenephosphonic acid (DEQUEST 2000 from MONSATO) are added in the third step to obtain a rate grafting of 3840ppm.

EXAMPLE 3 Silica Sol Treated with Sodium Dihydrogen Phosphate Dihydrate

The procedure of example 1 is repeated, in which, in the third step, 50.5 g of 15% aqueous solution of sodium dihydrogen phosphate dihydrate are added to obtain a grafting rate of 5200 ppm.

EXAMPLE 4 Silica Sol Treated with Polyphosphate Acid (H _{n +?} P _n θ _{3n +]} __) _ The procedure of Example 1 is repeated, in which 46.6 g of a 10% aqueous polyphosphoric acid solution to obtain a grafting rate of 3200ppm. EXAMPLE 5 Silica Sol Treated with the Potassium Sol of the Phosphoric Ester

The procedure of example 1 is repeated, in which 3.2 g of potassium salt of a phosphoric ester (Atlas G2203 from ICI Surfactants) is added at the end of step 4 to obtain a grafting rate of 3840ppm. The sol is then concentrated to a silica concentration of 95 g / kg by evaporation under vacuum at 60 ° C. EXAMPLE 6 Silica Sol Treated with Tetramethylammonium Hydroxide

The procedure of example 1 is repeated, in which 8.7 g of 25% aqueous tetramethylammonium hydroxide solution is added at the end of step 4 to obtain a grafting rate of 1500 ppm. The sol is then concentrated to a silica concentration of 95 g / kg by evaporation under vacuum at 60 ° C.

EXAMPLE 7 Silica Sol Treated with 3-aminopropyl-trlethoxysliane The procedure of Example 1 is repeated, in which the silica sol, obtained at the end of step 4, having a pH equal to 10 and a silica concentration of 15g / kg is transferred to a reactor fitted with an eccentric high speed dispersion system (10000t / mm) (deflocculating toothed blades), having four blades and a centered propeller rotating at 300t / mm. 223 g of an aqueous solution containing 11.65 g of 3-ammopropyl-triethoxysilane (A1100 from WITCO) and 9.71 g of pure acetic acid are added at 20 ° C. and over 10 minutes. The mixture is left to age for 30 minutes. After a maturing time of 15 minutes, the sol is then concentrated to a silica concentration of 95 g / kg by evaporation under vacuum at 60 ° C. In Examples 8 to 11, the acidifying agent is sulfuric acid.

EXAMPLE 8 Synthesis of the silica sol In a first step, 8137 g of purified water with a conductivity of less than 5 μS / cm are introduced into a stainless steel reactor equipped with a turbine stirring system, with element heating. electrical, and a temperature and pH control system. The whole is heated to a temperature equal to 60 ° C. Then introduced in 15 minutes, at a constant temperature of 60 ° C and with constant stirring 220t / mm, 902g of sodium silicate having a weight ratio Sιθ2 / Na2θ equal to 3.25 and having a mass concentration of silica of 50g / kg.

In a second step, the reaction temperature is raised from 60 ° C to 90 ° C in about 15 minutes, then maintained at 90 ° C until the end of the reaction. 7648 g of silicate of the type described above and approximately 6170 g of dilute sulfuric acid with an acid concentration equal to 29 g / kg are then introduced jointly into the reaction medium. This simultaneous introduction of acid and silicate is carried out in such a way that the pH of the reaction medium is constantly equal to 9 +/- 0.1, and the temperature equal to 90 ° C. The duration of this simultaneous introduction is fixed at 90 minutes. After introduction of all of the silicate, the reaction mixture is left to mature at 90 ° C., at a pH of 9, for 30 minutes. The reaction medium is cooled to 25 ° C. This gives a silica sol with a silica concentration of 18.71 g / kg and a pH of 10.5.

In a third step, the silica sol is then washed at a constant pH of 10.5 by simultaneous addition suspension of cationic resins in protonated form and anionic resins in hydroxide form having a respective concentration of 50% in the reaction medium and, with stirring of 200 t / min. This simultaneous introduction of dispersion of action resins and anion resins is carried out in such a way that the pH of the reaction medium is constantly equal to 10.00 +/- 0.1. This simultaneous addition is done until a ground conductivity value less than 1 μS / c is obtained. The duration of the washing operation is 30 minutes. Thereafter, a complementary introduction of cationic resins is carried out to bring the pH of the silica sol to a value of 8.5, and the mixture thus obtained is left to stand for 60 minutes. The mixture consisting of the resin and the silica sol thus formed is then filtered a first time on a filter having a porosity equal to 100 μm. A second filtration of the soil is then carried out on a filter with a porosity of less than 10 μm. This gives a transparent silica sol having a pH of 8.5 and a silica concentration of 15 g / kg.

In a fourth step, the soil is finally concentrated in silica at 150 g / kg by evaporation under vacuum at 60 ° C. The duration of the operation lasts approximately 6 hours. EXAMPLE 9 Silica Sol Treated by Calcium Doping

The procedure of Example 8 is repeated, modifying the second step according to the following terms. The reaction temperature is then brought from 60 ° to 90 ° C in about 15 minutes, then maintained at 90 ° C until the end of the reaction. 6900 g of sodium silicate and approximately 5629 g of sulfuric acid are then introduced jointly into the reaction medium. diluted acid concentration equal to 29g / kg. This simultaneous introduction of acid and silicate is carried out in such a way that the pH of the reaction medium is constantly equal to 9.00 ± 0.1 and the temperature equal to 90 ° C. The duration of this simultaneous introduction is fixed at 75 minutes.

750 g of sodium silicate, 276 g of lime milk with a Ca (OH) 2 concentration of 20, 12 g / kg and, approximately 685 g of sulfuric acid are then introduced jointly into the reaction medium.

This operation is carried out in such a way that the pH of the reaction medium is constantly equal to 9.00 +/- 0.1. The duration of this simultaneous introduction is fixed at 10 minutes. After carrying out the doping, the reaction mixture is left to mature at 90 ° C. and at a pH equal to 9 for 30 minutes. After cooling to 25 ° C., a silica sol with a silica concentration of 18.21 g / kg and having a pH of 10.5 is thus obtained. We then repeat steps 3 and 4 of Example 8 to obtain a calcium-treated silica sol.

EXAMPLE 10 Silica self treated with zinc doping

In a stainless steel reactor equipped with a turbine stirring system, heating by electrical elements, and a temperature and pH regulation system, 8200 g of purified water having a conductivity lower than 5μS / cm and having a temperature equal to 60 ° C. Then introduced in 15 minutes at a constant temperature of 60 ° C and with constant stirring of 220 rpm, 900 g of sodium silicate having a Siθ2 / a2θ weight ratio equal to 3.25 and a mass concentration of silica of 50 g / kg . The reaction temperature is then brought from 60 ° C. to 90 ° C in about 15 minutes, then maintained at 90 ° C until the end of the reaction.

6500 g of sodium silicate and approximately 5358 g of dilute sulfuric acid with an acid concentration equal to 29 g / kg are then introduced jointly into the reaction medium. This simultaneous introduction of acid and silicate is carried out in such a way that the pH of the simultaneous reaction medium is fixed at

70 minutes. 3253 g of sodium silicate, 1164 g of a zinc sulphate solution with a concentration of

ZnSO4, equal to 20g / kg and approximately 2462g of sulfuric acid. The sulfuric acid flow is adjusted so that the pH of the reaction medium is constantly equal to 9 +/- 0.1. The duration of this simultaneous introduction of the 3 reagents is fixed at 35 minutes. After the end of the dosing operation, the reaction mixture is allowed to mature at 90 ° C and at a pH of 9 for 30 minutes. After cooling to 25 ° C., a silica sol with a silica concentration of 19.14 g / kg and having a pH of 10.5 is thus obtained.

We then repeat steps 3 and 4 of Example 8 to obtain a zinc-treated silica sol.

EXAMPLE 11 Silica Sol Treated by Céπum Doping

In a stainless steel reactor equipped with a turbine stirring system, heating by electrical elements, and a temperature and pH regulation system, 10000 g of purified water with conductivity less than 5 μS are introduced. / cm and having a temperature equal to 90 ° C.

Then introduced in 15 minutes at a constant temperature of 90 ° C and with constant stirring at 220 rpm, 600 g of sodium silicate having a weight ratio Sιθ2 / a2θ equal to 3.34 and having a mass concentration of silica of 35 g / kg.

The reaction temperature is maintained at 90 ° C until the end of the reaction. 6500 g of sodium silicate and approximately 6523 g of dilute sulfuric acid having an acid concentration equal to 16 g / kg are then introduced jointly into the reaction medium. This simultaneous introduction of the acid and of the sodium silicate is carried out in such a way that the pH of the reaction medium is constantly equal to 9.1 +/- 0.1. The duration of this simultaneous introduction is fixed at 70 minutes.

Then 163g of sodium silicate and 228g of cerium sol with a concentration expressed in Ceθ2 of 80g / kg and having a N rapport3 / Ceθ2 mass ratio are then introduced jointly into the reaction medium. The duration of this simultaneous introduction is fixed at 10 minutes.

At the end of the doping operation, the reaction mixture is left to mature at 90 ° C. after adjusting the pH to 9 for 30 minutes. After cooling to 25 ° C., a silica sol is thus obtained having a silica concentration of 105 g / kg.

We then repeat steps 3 and 4 of Example 8 to obtain a concentrated silica sol treated with cerium.

EXAMPLE 12 Silica Sol Treated by Doping with Aluminum

Example 8 is repeated by modifying the fourth step. The transparent silica sol having a pH of 8.5 and a silica concentration of 15 g / kg obtained at the end of step 3, is heated to 60 ° C. 50 g of an aqueous solution of sodium alummate with an Al 2 O 3 concentration equal to 7% and of Al / Na molar ratio equal to 0.304. The mixture is heated at 60 ° C for 12 minutes. The sol is then concentrated to a silica concentration of 160 g / kg by evaporation under vacuum at 60 ° C. The duration of the operation is 6 hours.

EXAMPLE 13 Silica Sol Treated by Doping with a Conductive Polymer: Polyanil

Example 8 is repeated by modifying the third step, bringing the final pH to 3 by adding cationic resin instead of 8.5. The final sol having a pH equal to 3 and a silica concentration of 15 g / kg, is cooled to 5 ° C. 3 g of polyanilme are added thereto under vigorous stirring. 10 g of ammonium persulfate are then added and the mixture is left to mature for 5 hours. The soil is then concentrated to 150 g / kg by evaporation under vacuum at 50 ° C.

COMPARATIVE EXAMPLE

Table (I) below shows the differences between a soil of the state of the art and the soil according to the invention. These differences are characterized by the measurement of conductivity, light transmission, viscosity and particle diameter for each of the soils.

Board

The state of the art floors are sold under the Ludox and Klebosol brands respectively by the companies DU PONT and CLARIAN.

As can easily be seen, the soil according to the invention has a very low conductivity, maximum light transmission, and a viscosity significantly lower than the soils of the prior art.

Furthermore, the average diameter of the soil particles of the invention is much smaller than that of the particles of known soils.

Accelerated anticorrosion test: This test consists in immersing, at a temperature of around 25 ° C, an ordinary steel plate with a surface of 20cπ.2 and a thickness of 2mm in 100ml of rainwater with a constant composition. Water transmission is measured using a Metrom photocolorimeter at 550nm wavelength and for an optical path of 10cm as a function of time.

The steel plates are degreased beforehand by washing with acetone followed by washing with ethanol and washing with water. The plates are then immersed in a 1M sodium hydroxide solution, then rinsed with deionized water and finally immersed for 30 minutes in the sol according to the invention dilutes 1% silica by adding water and heated to 80 ° C.

The results are collated in the table (II below.

Table (II) It can be seen that a steel plate treated with the soil according to the invention gives an average light transmission value of approximately 96.67%. The transmission values clearly show that the treated steel plate shows no signs of rust.

Indeed, the presence of rust disturbs the water and therefore does not make it possible to obtain a transmission of light of such good quality. On the other hand, the very low light transmission values of the steel plate treated with the soil of the state of the art clearly show that the plate comprises rust which can appear simply in the form of traces. Of course, the invention is in no way limited to the embodiments described, which have been given only by way of example. In particular, it includes all the means constituting technical equivalents of the means described as well as their combinations, if these are carried out according to the spirit of the invention.

Claims

1. Silica sol, comprising silica nanoparticles with an average size of between 3 and 50 nm, surface treatment by grafting and / or by adsorption of at least one organic molecule, and / or by doping with at least one doping agent, characterized in that the organic molecule is chosen from ammes, polyamines, quaternary ammes, ammo silanes, silanes, phosphonates, diamonds, polyamines, polyacrylates, acids, diacids, triacids , polyacids, organic hydroxy acids, polyvinyl alcohols, polyoxyethylene, conductive polymers, silane derivatives of the following general formulas:

(I) XR-Si (Y) ₃ , (II) XR-Si (Y) 2 R 'or (III) XR-Si (R' R ") Y Where,

- X is a group chosen from the groups vmyl, methacrylate, methyl, phosphate, proton, when R is a carbon chain of the type - (CH2 ^~ ) _n - or n is an integer between 1 and 20,

- X is a group chosen by the ammes, epoxy, polysulphide, mercapto groups when R is a carbon chain of the type - (CH2 ~) _n - or n is equal to 19 or 20,

- R 'R "are independently of each other chosen from a proton, a hydroxide, an ester, an ether or a hydrocarbon chain of the type - (CH2 ^~ ) _n - or n is an integer between 1 and 20 , and mixtures of all these constituents, said nanoparticles being present in a concentration greater than or equal to 5 and preferably greater than or equal to 10%.

2. Sol according to claim 1, characterized in that the doping agent is in the form of an inclusion or a solid solution, and is chosen from the salts of monovalent cations, divalent cations, tπvalent cations, quadπvalent cations under their chloride, nitrate, sulfate, phosphate, phosphonate, silicate, hydroxide, oxide, acetate or gluconate form, and mixtures thereof.

3. Soil according to claim 1, characterized in that the liquid phase comprises anions and free cations in a concentration less than or equal to 0.05 mol / 1, and preferably less than or equal to 0.005 mol / 1.

4. Soil according to one of the preceding claims, characterized in that the pH is between 3 and 11.

5. Floor according to one of the preceding claims, characterized in that it has a translucency defined by a light transmission between 400 to 650 nm, greater than or equal to 95%, and preferably greater than or equal to 98%.

6. Soil according to one of the preceding claims, characterized in that it has a conductivity, measured at a concentration of 10% of silica, ranging from 100 to 500 μS / cm.

7. Soil according to one of the preceding claims, characterized in that the silica concentration is between 1 and 300 g / 1.

8. Anti-corrosion pigment comprising at least one silica sol as defined according to one of claims 1 to 7.

9. Composition comprising at least one silica sol as defined according to one of claims 1 to 7 and at least one additive chosen from latexes, alkylsiliconates, water-soluble polymers, surfactants, polymer emulsions, polymeric resins , polyols and copolymers.

10. Composition according to claim 9, characterized in that the sol is present in an amount ranging from 0.01 to 5% by weight relative to the total weight of the composition.

11. Composition according to claim 9, characterized in that the additive is present in an amount ranging from 0.01 to 10% by weight relative to the total weight of the composition.

12. A method of treating the surface of the soil as defined according to one of claims 1 to 7, consisting in: manufacturing a base stock by adding silicates, water and acid at a temperature ranging from 20 ° at 95 ° C to obtain silica particles,

- adding, on said silica particles, silica in the form of silicate, and at least one acidifying agent to increase the concentration of silica and the size of the silica particles, - filtering and then washing the silica particles obtained in keeping the pH constant between 8 and 10, by the simultaneous addition of a cationic resin and an anionic resin;

- Concentrating the soil obtained by evaporation under vacuum or by ultrafiltration, then performing the surface treatment of the soil by grafting and / or by adsorption of at least one organic molecule, or by depositing particles of metal salts.

13. Method according to claim 12, characterized in that one adds, before the end of the second step, at least one doping agent, in the form of inclusion or solid solution, chosen from the salts of monovalent cations, cations divalent, tπvalent cations, quadπvalent cations in their chloride, nitrate, sulfate, phosphate, phosphonate, silicate, hydroxide, oxide, acetate or gluconate form, and mixtures thereof.

14. Method according to claim 13, characterized in that the doping agent is chosen from calcium hydroxides, magnesium hydroxide, aluminum sulfate, zinc sulfate, calcium sulfate, cerium nitrate , cerium oxide, sodium alummate, sodium zmcate, sodium phosphate, phosphonate, and mixtures thereof.

15. Method according to one of claims 13 or

14, characterized in that the doping agent is introduced in the last phase of addition of the acid.

16. Method according to one of claims 13 to

15, characterized in that the doping agent is introduced at a pH greater than 8 and preferably at a pH greater than 10.

17. Method according to one of claims 13 to 16, characterized in that the doping agent is present in an amount less than 10% by weight relative to the total weight of the silica.

18. The method of claim 12, characterized in that the organic molecule is chosen from ammes, polyamines, quaternary ammes, amino silanes, silanes, phosphonates, diam es, polyamines, polyacrylates, acids , diacids, triacids, polyacids, organic hydroxy acids, polyvinyl alcohols, polyoxyethylenes, conductive polymers and mixtures of these constituents.

19. Method according to claim 12, characterized in that the surface treatment of the silica sol, by grafting or by adsorption, is between 0.1 and 50%, and preferably between 0.1 and 5%.

20. The method of claim 12, characterized in that the organic molecule is chosen from silane derivatives of general formulas.

(I) XR-Si (Y) ₃ , (II) XR-Si (Y) ₂ R ', or (III) XR-Si (R' R ") Y Where, X is a group chosen from amino groups, hydroxide, epoxy, vmyl, polysulfide, methacrylate, methyl, fluoride, mercapto, phosphate, proton,

Y is a group chosen from ethoxy, methoxy, chloro groups;

R is a carbon chain of the type - (CH2 ~) _n - where n is an integer between 1 and 20,

R 'and R "are independently of each other chosen from a proton, a hydroxide, an ester, an ether or a hydrocarbon chain of the type - (CH2 -) _n - where n is an integer between 1 and 20 ,

21. Use of the soil as defined according to one of claims 1 to 7 as an anticorrosion agent.

22. Use according to claim 21, characterized in that the soil is an anticorrosion agent for the metal.

23. Use of the soil as defined according to one of claims 1 to 7 as an adhesion initiator intended to facilitate the adhesion of a layer of polymer or mineral to a support.

24. Use of the soil as defined according to one of claims 1 to 7 as a raw material for obtaining mineral membranes.

25. Use of the soil as defined according to one of claims 1 to 7 as a rheological additive in emulsions.

26. Use of the soil as defined according to one of claims 1 to 7 as a reinforcing filler in plastics.

27. Use of the soil as defined according to one of claims 1 to 7 as an additive present in redispersible agrochemical compositions.

28. Use of the soil as defined according to one of claims 1 to 7 as an ingredient in ceramic materials intended for the field of optics and / or electronics.