EP1648823A2 - Method for preparing anisotropic silica aggregates - Google Patents

Method for preparing anisotropic silica aggregates

Info

Publication number
EP1648823A2
EP1648823A2 EP04767598A EP04767598A EP1648823A2 EP 1648823 A2 EP1648823 A2 EP 1648823A2 EP 04767598 A EP04767598 A EP 04767598A EP 04767598 A EP04767598 A EP 04767598A EP 1648823 A2 EP1648823 A2 EP 1648823A2
Authority
EP
European Patent Office
Prior art keywords
silica
particles
polymer
aggregates
acid
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP04767598A
Other languages
German (de)
French (fr)
Inventor
Lionel Ventelon
Julien Hernandez
Françoise LAFUMA
Christophe Chassenieux
Christelle Perreur
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Centre National de la Recherche Scientifique CNRS
Rhodia Chimie SAS
Original Assignee
Centre National de la Recherche Scientifique CNRS
Rhodia Chimie SAS
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Centre National de la Recherche Scientifique CNRS, Rhodia Chimie SAS filed Critical Centre National de la Recherche Scientifique CNRS
Publication of EP1648823A2 publication Critical patent/EP1648823A2/en
Withdrawn legal-status Critical Current

Links

Classifications

    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B33/00—Silicon; Compounds thereof
    • C01B33/113—Silicon oxides; Hydrates thereof
    • C01B33/12—Silica; Hydrates thereof, e.g. lepidoic silicic acid
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B33/00—Silicon; Compounds thereof
    • C01B33/113—Silicon oxides; Hydrates thereof
    • C01B33/12—Silica; Hydrates thereof, e.g. lepidoic silicic acid
    • C01B33/16—Preparation of silica xerogels
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
    • C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
    • C09C1/28—Compounds of silicon
    • C09C1/30—Silicic acid
    • C09C1/3009—Physical treatment, e.g. grinding; treatment with ultrasonic vibrations
    • C09C1/3036—Agglomeration, granulation, pelleting
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
    • C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
    • C09C1/28—Compounds of silicon
    • C09C1/30—Silicic acid
    • C09C1/3072—Treatment with macro-molecular organic compounds
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K3/00—Materials not provided for elsewhere
    • C09K3/14—Anti-slip materials; Abrasives
    • C09K3/1409—Abrasive particles per se
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/30—Particle morphology extending in three dimensions
    • C01P2004/32—Spheres
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/50—Agglomerated particles
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/64—Nanometer sized, i.e. from 1-100 nanometer
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/12—Surface area

Definitions

  • the present invention relates to a process for the preparation of anisotropic silica aggregates.
  • Certain manufactured or industrial products incorporate in their manufacture silica particles in different forms, and in particular in the form of anisotropic aggregates. These silica particles are of interest as a reinforcing filler, as a viscosifying or texturing agent, or as a catalyst support in various fields.
  • the synthesis of anisotropic silica aggregates is delicate and difficult because of the amorphous nature of the silicon which implies that there is no preferential orientation during nucleation or growth of the solid.
  • anisotropic silica aggregates implies very strict control of the aggregation phenomena, that is to say of the interactions existing between the silica particles, which is very difficult and generally leads to a morphology of globally isotropic aggregate.
  • the aggregation phenomenon is essentially controlled either by the presence of salts, or by the concentration of particles, or by the presence of entities that can react with the surface of the silica and thus modify its surface, or by the acidity conditions. which modify the surface charge of silica and the reactivity of the silica surface (catalysis of oxidation).
  • it has become necessary to provide a process for the preparation of anisotropic silica aggregates which makes it possible to control the aggregation of silica particles.
  • the problem which the invention proposes to solve is to provide a process for the preparation of anisotropic aggregates, the implementation conditions of which allow the aggregation of the silica particles to be controlled.
  • the invention provides a process for the preparation of anisotropic silica aggregates which comprises the following steps: a) at least one polymer is brought into contact with non-aggregated silica particles and / or having a high degree of dispersion in aqueous medium, with an R ratio, mass of polymer related to the surface of the silica particles, of between 0.02 and 2 mg / m 2 and the value of the electrostatic charge of the surface of the silica particles being greater than or equal the value of the charge of the surface of the silica particles measured in an aqueous phase without added salts at a pH greater than or equal to 7; b) the aggregates obtained in step a) are consolidated either by heat treatment or by precipitation of an inorganic compound.
  • the subject of the invention is also a silica aggregate comprising a sequence of elementary silica particles the number of particles of which is between 5 and 15, of which at least 80% of the elementary particles are in contact with at most 2 particles and whose greatest measurable distance between 2 points of the aggregate is less than or equal to 5 times the average size of a particle elementary.
  • the advantage of the process according to the invention is that it allows the aggregation of the silica particles to be controlled under very simple conditions for implementing the process by simple addition of at least one polymer to the reaction medium.
  • step b) of consolidation can be carried out under saline conditions, that is to say by simple addition of salts of mineral cations which will precipitate at the grain boundaries.
  • this process makes it possible to obtain soils of anisotropic aggregates or powders by simple drying of the soil.
  • the method according to the invention also has the advantage of very fine control of the final size of the elementary particles, of the morphology of the aggregate and of the size of the aggregate. It thus makes it possible to produce anisotropic silica aggregates which are solid, irreversible, no longer breaking and easy to produce. These anisotropic aggregates, due to their original morphology, have reinforcing properties, viscosifying or texturing agents or catalyst support properties.
  • the invention firstly relates to a process for the preparation of anisotropic silica aggregates which comprises the following steps: a) at least one polymer is brought into contact with non-aggregated and / or high-grade silica particles dispersion in an aqueous medium, with a ratio R, mass of polymer related to the surface of the silica particles, of between 0.02 and 2 mg / m 2 and the value of the electrostatic charge of the surface of the silica particles being greater than or equal to the value of the charge of the surface of the silica particles measured in an aqueous phase without added salts at a pH greater than or equal to 7; b) the aggregates obtained in step a) are consolidated either by heat treatment or by precipitation of an inorganic compound.
  • Anisotropic aggregates are understood to mean, within the meaning of the invention, aggregates comprising at least 5 elementary particles and of which at least 50% (percentage by number) of elementary particles have 2 neighbors.
  • elementary particle means the basic element of the aggregate (also called the primary particle).
  • silica particles used in step a) of the process according to the invention are well dispersed and not aggregated.
  • the most favorable conditions for obtaining such particles are a desalinated medium and a high pH.
  • one will choose conditions of basic pH higher than 7, even more preferentially higher than 8.
  • the silica particles used are silica soils, which can be obtained by any process which makes it possible to obtain silica soils, in particular we can cite among others the processes with resins, ultrafiltration or even electrodialysis, but also the processes by polymerization of silicon aikoxide in organic solvent (Stôber type silica).
  • a silica sol will be used, the size of the silica particles of which is between 3 and 50 nm, even more preferably between 5 and 20 nm, the sizes being measured by transmission electron microscopy. Transmission electron microscopy observations were carried out on a Jeol 1200 device.
  • a drop of the sample to be observed is placed on a circular copper grid of
  • a silica sol will be used, the silica particles of which have a BET specific surface of between 50 and 880 m / g, preferably between 130 and
  • the BET specific surface is determined according to the BRUNAUER - EMMET - TELLER method described in "The journal of the American
  • step a) of the process according to the invention the silica particles are brought into contact with a polymer whose role is to aggregate the particles anisotropically.
  • the ratio R, mass of polymer related to the surface developed by the silica particles is preferably between 0.05 and 1.8 mg / m 2.
  • the polymer used in the process according to the invention advantageously has a particular affinity for the surface of the silica.
  • This polymer is generally an organic molecule, of hydrophilic type but can also have one or more hydrophobic parts
  • the polymer can be chosen from linear polymers, homopolymers, copolymers, grafted polymers or dendrimers. their composition may be based on a single monomeric unit or several reasons (statistical or block arrangement).
  • the polymer can have an electrostatic charge (anionic polymers containing less than 50% of anionic units or cationic polymers are preferred) or be uncharged.
  • the molecular mass of the polymer is not limiting since it is possible to produce * anisotropic aggregates with high masses as with low molecular masses.
  • the polymer used in the process according to the invention advantageously makes it possible to carry out aggregation under conditions where the silica has a high electrostatic surface charge (high pH, low ionic strength).
  • the presence of this surface charge causes the silica particles to aggregate anisotropically.
  • the polymer used in the process according to the invention is a polymer chosen from the following polymers, copolymers or graft polymers: polyoxyethylene (POE), polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), polyacrylamide (PAM), polymethacrylamides, poly (N-isopropylacrylamide) (PNIPAM) and other N-substituted derivatives, polysaccharides such as amylose, dextran, guar and modified derivatives or celluloses, polyvinylpyrrolidone-polyacideacrylic (PVP-PAA), polyoxyethylene-polyacideacrylic (POE-PAA) polyacrylamide-polyvinylpyrrolidone (PAM-PVP), polyvinyi * amino, polydiallyldimethylammonium (PDADMAC), polyacrylamide- polydiallyldimethylammonium (PAM-PDADMAC), polymers based on quaternized or non-amine
  • Step a) of the process according to the invention is preferably carried out in aqueous media at a basic pH greater than 7, even more preferably at a pH greater than 8. These pH values can vary depending on the nature of the reaction medium, and in particular in hydroalcoholic medium.
  • the anisotropic aggregate obtained in step a) is consolidated during step b) of the process. Aggregation by polymers (step a) generally leads to objects which may be breakable, as long as a mineral compound has not consolidated the silica aggregate.
  • Consolidation is therefore a necessary step which can consist in filing a mineral compound on anisotropic silica aggregates. This results in the formation of a seal which prevents subsequent breakage of the aggregate by a chemical or mechanical operation.
  • This consolidation is carried out either by heat treatment or by precipitation of an inorganic compound.
  • step b) consists of a heat treatment
  • the temperature of the heat treatment is at least 80 ° C., more particularly at least 100 ° C., preferably at least 120 ° C.
  • the duration of the heat treatment is determined as a function of the use which may be envisaged for the anisotropic silica aggregates. The duration of the heat treatment makes it possible to control the breakable nature of the aggregate.
  • This heat treatment can be carried out by autoclaving.
  • a colloidal dispersion of silica (silica sol) can be obtained, when a dispersion is heat treated.
  • Step b) of the process according to the invention can be carried out by precipitation of an inorganic compound.
  • the mineral compound is chosen from silicates, phosphates, silicophosphates, aluminates, silicoaluminates, cerium, zinc, iron, titanium, zirconium, carbonates, rare earths, cations divalent or their mixtures.
  • the mineral compound is a silicate or any common form of silicates such as metasilicates, disilicates and advantageously an alkali metal silicate, in particular sodium or potassium silicate.
  • the mineral compound is a sodium silicate having a weight ratio Rp SiO 2 / Na 2 O of between 0.5 and 4.
  • the silicate may have a concentration (expressed by mass of silica) of between 10 and 330 g / l, preferably between 15 and 300 g / l, in particular between 60 and 260 g / l.
  • the precipitation of the mineral compound is carried out according to the conventional conditions for precipitation of this compound. In the case of a silicate, the precipitation is carried out by simultaneously adding the silicate to be precipitated and an acidifying agent so as to maintain the pH at a value of at least 6.
  • a strong mineral acid such as sulfuric acid, nitric acid or hydrochloric acid, or an organic acid such as acetic acid, formic acid or carbonic acid.
  • the acidifying agent can be diluted or concentrated; its normality can be between 0.4 and 36 N, preferably between 0.6 and 3 N.
  • the acidifying agent would be sulfuric acid
  • its concentration can be between 20 and 180 g / l, preferably between 40 and 130 g / l.
  • sulfuric acid is used as the acidifying agent
  • sodium silicate as the silicate.
  • the precipitation of the mineral compound makes it possible to obtain a precipitate of a metal salt, a metal oxide or a metal hydroxide.
  • the salt is advantageously chosen from a silicate, a silicoaluminate, a silicophosphate, a phosphate, a carbonate.
  • the metal is advantageously a metal chosen from silicon, calcium, magnesium, cerium, zinc, iron, titanium, zirconium, aluminum.
  • a silica slurry is obtained which is then separated (liquid-solid separation).
  • This separation implemented in the preparation process according to the invention usually comprises filtration, followed by washing if necessary. Filtration is carried out by any suitable method, for example by means of a filter press, a band filter, a vacuum filter. The silica suspension or filter cake thus recovered is then dried.
  • the filter cake is not always in conditions allowing atomization, in particular because of its high viscosity.
  • the cake is then subjected to a disintegration operation.
  • This operation can be carried out mechanically, by passing the cake through a colloidal or ball mill.
  • the disintegration is generally carried out in the presence of an aluminum compound, in particular sodium aluminate and, optionally, in the presence of an acidifying agent as described above (in the latter case, the aluminum compound and the acidifying agent are generally added simultaneously).
  • the disintegration operation notably makes it possible to lower the viscosity of the suspension to be dried later.
  • the silica suspension thus recovered is then dried.
  • a colloidal dispersion can be obtained which can also then be dried.
  • the drying can be done by any means known per se.
  • the drying is carried out by atomization.
  • any suitable type of atomizer can be used, in particular a turbine, nozzle, liquid pressure or two-fluid atomizer.
  • a turbine atomizer is used, and, when filtration is carried out using a vacuum filter, a turbine atomizer is used .
  • the silica which can then be obtained is usually in the form of substantially spherical beads.
  • a grinding step can then be carried out on the recovered product.
  • the silica which can then be obtained is generally in the form of a powder.
  • the drying is carried out using a turbine atomizer, the silica which can then be obtained can be in the form of a powder.
  • the dried product in particular by a turbine atomizer or ground as indicated above can optionally be subjected to an agglomeration step, which consists for example of direct compression, wet granulation (i.e. - say with the use of a binder such as water, silica suspension, etc.), extrusion or, preferably, dry compaction.
  • the silica that can then be obtained by this agglomeration step is generally in the form of granules.
  • the powders, as well as the beads, of silica obtained by the process according to the invention thus offer the advantage, among other things, of having simple, effective and economical access to granules, in particular by conventional operations of placing shaped, such as for example granulation or compaction, without the latter causing degradation capable of masking, or even annihilating, the good intrinsic properties attached to these powders or these beads, as may be the case in prior art by using conventional powders.
  • the subject of the invention is also a silica aggregate comprising a series of elementary particles of silica the number of particles of which is between 5 and 15, of which at least 80% of the elementary particles are in contact with at most 2 particles and of which the greatest measurable distance between 2 points of the aggregate is less than or equal to 5 times the average size of an elementary particle.
  • the greatest measurable distance between 2 points of the aggregate is less than or equal to 4 times the average size of an elementary particle.
  • a subject of the invention is also the use of silicas produced from poly (N-isopropylacrylamide) as polymer or the aggregates mentioned above, as reinforcing filler of a composition of polymers, in particular plastics and rubber (for example shoe soles), texturing or anti-caking viscosity agent, anti-cracking agent in particular in the petroleum field, polishing agent in particular in toothpaste and paper, coating agent in particular in the textile field, absorbent of active material, catalyst support , element for battery separators.
  • silicas produced from poly (N-isopropylacrylamide) as polymer or the aggregates mentioned above, as reinforcing filler of a composition of polymers, in particular plastics and rubber (for example shoe soles), texturing or anti-caking viscosity agent, anti-cracking agent in particular in the petroleum field, polishing agent in particular in toothpaste and paper, coating agent in particular in the textile field, absorbent of active material, catalyst support , element for battery separators.
  • a polyoxyethylene (POE) solution with a molar mass of 10 6 g / mol is prepared at a concentration of 0.8 g / L by dilution with purified water and then brought to pH 9 (with sodium hydroxide).
  • 1 liter of silica sol (Ludox HS30 from Du Pont) is prepared at a concentration of 20 g / L by dilution with purified water then the soil is brought to pH 9. The particles have a diameter of around 12 nm (specific surface of 220 m 2 / g).
  • the POE solution is quickly introduced into the silica sol.
  • the mixing can also be carried out by introducing the sol into the POE solution or by simultaneous addition. The mixture is left to ripen for one hour. Under these conditions, the pH is close to 9 and the ratio R, POE / silica is 0.2 mg POE / m 2 of silica.
  • the final product has a surface area of 147 m2 / g, a dispersibility measured by particle size using a Sedigraph giving a rate of 96% of particles whose diameter is less than 0.3 microns.
  • the particle size analysis is based on a principle of sedimentation with a particle size measurement device such as the Sedigraph 5100 (249 ET 041), to analyze the sedimentation of the aggregates according to the invention.
  • the technique used can comprise a first step of dispersing a powder in an aqueous medium, and a step of deagglomeration by ultrasound, with a power probe of around 600 watts, more or less 20%, for 7 minutes. It is also possible to make the measurement directly on a dispersion or on a colloidal dispersion according to the invention, without prior steps.
  • Consolidation of the aggregates can also be carried out by autoclaving the POE / silica mixture.
  • the strengthening of the aggregates is due to redissolution-precipitation mechanisms at the grain boundaries: 700 mL of the silica sol / POE mixture with a silica concentration of 10 g / L and a POE concentration 10 ⁇ g / 0.4 g / L mol are introduced into a 1 L autoclave, the mixture is stirred and simultaneously heated to 130 ° C at a rise of 3 ° C / min. It is maintained at 130 ° C for 6 hours then cooled naturally to room temperature.
  • TEM Transmission electron microscopy
  • the table reads as follows for the first line: within an aggregate, 15% of the particles are in contact with only one particle, 72% of the particles are in contact with 2 particles, 12% of the particles are in contact with 3 particles and 1% of the particles are in contact with 4 particles.
  • a silica sol with a concentration of 22 g / L is prepared by diluting a Ludox HS30 sol with deionized water. The medium is brought to pH 9 by adding sodium hydroxide.
  • a solution of poly (N-isopropylacrylamide) with a molecular mass equal to 820,000 g / mol is prepared at a concentration of 7.3 g / l.
  • the anisotropic aggregate sol is prepared by introducing 10 mL of the silica sol into
  • the polymer / silica R ratio is 1.5 mg / m 2 .
  • the mixing is carried out with vigorous stirring in a few minutes and then stirring is maintained for 32 hours at a moderate speed.
  • the mixture is heated to 98 ° C for 48 hours.
  • EXAMPLE 3 A silica sol with a concentration of 22 g / L is prepared by diluting a LUDOX HS30 sol with deionized water. The medium is brought to pH 9 by adding sodium hydroxide. A poiy (N-isopropylacrylamide) solution of molecular mass equal to is prepared.
  • the anisotropic aggregate sol is prepared by introducing 10 ml of the silica sol into
  • the R / polymer / silica ratio is 1.36 mg / m 2 .
  • the mixing is carried out with vigorous stirring in a few minutes and then stirring is maintained for 32 hours at a moderate speed.
  • the mixture is heated to 98 ° C for 48 hours.
  • EXAMPLE 4 A silica sol with a concentration of 22 g / L is prepared by diluting a LUDOX HS30 sol with deionized water. The medium is brought to pH 9 by adding sodium hydroxide.
  • a solution of poly (N-isopropylacrylamide) of molecular mass equal to 820,000 g / mol is prepared at a concentration of 3.2 g / L
  • the anisotropic aggregate sol is prepared by introducing 10mL of the silica sol into 12mL of the polymer solution.
  • the polymer / silica R ratio is 0.8 mg / m 2 .
  • the mixing is carried out with vigorous stirring in a few minutes and then stirring is maintained for 32 hours at a moderate speed.
  • the mixture is heated to 98 ° C for 48 hours.

Abstract

The invention concerns a method for preparing anisotropic silica aggregates comprising the following steps: a) contacting at least one polymer with non-aggregated silica particles and/or highly dispersed in an aqueous medium, with a ratio R, polymer weight to silica particle surface, ranging between 0.03 and 2 mg/m2 and whereof the electrostatic value of the silica particle surface is not less than the value of the charge of the silica particle surface measured in an aqueous phase without added salts at a pH not less than 7; b) consolidating the aggregates obtained at step a) either by heat treatment, or by precipitation of a mineral compound. The invention also concerns a silica aggregate comprising a chaining of elementary particles whereof the number of particles ranges between 5 and 15, whereof 80 % of elementary particles are in contact with not more than 2 particles and whereof the greatest distance measurable between 2 points of the aggregate is not more than 5 times the average size of one elementary particle.

Description

PROCEDE DE PREPARATION D'AGREGATS ANISOTROPES DE SILICE La présente invention a pour objet un procédé de préparation d'agrégats anisotropes de silice. Certains produits manufacturés ou industriels incorporent dans leur fabrication des particules de silice sous différentes formes, et notamment sous forme d'agrégats anisotropes. Ces particules de silice présentent un intérêt comme charge renforçante, comme agent viscosant ou texturant, ou comme support de catalyseur dans différents domaines. Cependant la synthèse d'agrégats anisotropes de silice est délicate et difficile en raison du caractère amorphe de la siiice qui implique qu'il n'y a pas d'orientation préférentielle lors de la nucléation ou de la croissance du solide. De plus l'obtention d'agrégats anisotropes de silice implique un contrôle très strict des phénomènes d'agrégation, c'est-à-dire des interactions existant entre les particules de silice, qui est très difficile et conduit généralement à une morphologie d'agrégat globalement isotrope. Le phénomène d'agrégation est essentiellement contrôlé soit par la présence de sels, soit par la concentration en particules, soit par la présence d'entités pouvant réagir avec la surface de la silice et ainsi modifier sa surface, soit par les conditions d'acidité qui modifient la charge de surface de la silice et la réactivité de la surface de la silice (catalyse de l'oxolation). Afin de répondre aux exigences des industriels il est devenu nécessaire de fournir un procédé de préparation d'agrégats anisotropes de silice qui permette de contrôler l'agrégation des particules de silice. Aussi le problème que se propose de résoudre l'invention est de fournir un procédé de préparation d'agrégats anisotropes dont les conditions de mise en œuvre permettent de contrôler l'agrégation des particules de silice. Dans ce but l'invention propose un procédé de préparation d'agrégats anisotropes de silice qui comprend les étapes suivantes : a) on met en contact au moins un polymère avec des particules de silice non agrégées et / ou présentant un haut degré de dispersion en milieu aqueux, avec un rapport R, masse de polymère rapportée à la surface des particules de silice, compris entre 0,02 et 2 mg/m2 et dont la valeur de la charge électrostatique de la surface des particules de silice est supérieure ou égale à la valeur de la charge de la surface des particules de silice mesurée dans une phase aqueuse sans sels ajoutés à un pH supérieur ou égale à 7 ; b) on consolide les agrégats obtenus à l'étape a) soit par un traitement thermique, soit par précipitation d'un composé minéral. L'invention a également pour objet un agrégat de silice comprenant un enchaînement de particules élémentaires de silice dont le nombre de particules est compris entre 5 et 15, dont au moins 80% des particules élémentaires sont en contact avec au plus 2 particules et dont la plus grande distance mesurable entre 2 points de l'agrégat est inférieure ou égale à 5 fois la taille moyenne d'une particule élémentaire. L'avantage du procédé selon l'invention est de permettre le contrôle de l'agrégation des particules de silice dans des conditions très simples de mise en œuvre du procédé par simple ajout d'au moins un polymère dans le milieu réactionnel. D'autre part, l'étape b) de consolidation peut être réalisée dans des conditions salines c'est-à-dire par simple ajout de sels de cations minéraux qui vont précipiter aux joints de grain. Avantageusement, ce procédé permet d'obtenir des sols d'agrégats anisotropes ou des poudres par simple séchage du sol. Le procédé selon l'invention a encore pour avantage un contrôle très fin de la taille finale des particules élémentaires, de la morphologie de l'agrégat et de la taille de l'agrégat. Il permet ainsi de réaliser des agrégats de silice anisotropes qui sont solides, irréversibles, ne se brisant plus et facile à réaliser. Ces agrégats anisotropes de part leur morphologie originale possèdent des propriétés de renfort, d'agent viscosant ou texturant ou des propriétés de support de catalyseur. D'autres avantages et caractéristiques de l'invention apparaîtront clairement à la lecture de la description et des exemples donnés à titré purement illustratifs et non limitatifs qui vont suivre. L'invention a tout d'abord pour objet un procédé de préparation d'agrégats anisotropes de silice qui comprend les étapes suivantes : a) on met en contact au moins un polymère avec des particules de silice non agrégées et / ou présentant un haut degré de dispersion en milieu aqueux, avec un rapport R, masse de polymère rapportée à la surface des particules de silice, compris entre 0,02 et 2 mg/m2 et dont la valeur de la charge électrostatique de la surface des particules de silice est supérieure ou égale à la valeur de la charge de la surface des particules de silice mesurée dans une phase aqueuse sans sels ajoutés à un pH supérieur ou égale à 7 ; b) on consolide les agrégats obtenus à l'étape a) soit par un traitement thermique, soit par précipitation d'un composé minéral. On entend par agrégats anisotropes, au sens de l'invention, des agrégats comprenant au minimum 5 particules élémentaires et dont au moins 50% (pourcentage en nombre) des particules élémentaires ont 2 voisines. On entend par particule élémentaire, au sens de l'invention, l'élément de base de l'agrégat (encore appelé particule primaire). De préférence les particules de silice mises en œuvre dans l'étape a) du procédé selon l'invention sont bien dispersées et non agrégées. Pour obtenir de telles particules les conditions les plus favorables sont un milieu désalinisé et un pH élevé. De préférence, dans le cas où le procédé est mis en œuvre dans un milieu aqueux, on choisira des conditions de pH basique supérieur à 7, encore plus préférentiellement supérieur à 8. Avantageusement les particules de silice employées sont des sols de silice, qui peuvent être obtenus par n'importe quel procédé qui permet d'aboutir à des sols de silice, notamment on peut citer entre autres les procédés avec résines, l'ultrafiltration ou encore l'électrodialyse, mais aussi les procédés par polymérisation d'aikoxyde de silicium en solvant organique (silice de type Stôber). De préférence, on utilisera un sol de silice dont la taille des particules de silice est comprise entre 3 et 50 nm, encore plus préférentiellement entre 5 et 20 nm, les tailles étant mesurées par microscopie électroniques en transmission. Les observations en microscopie électronique en transmission ont été réalisées sur un appareil Jeol 1200.The present invention relates to a process for the preparation of anisotropic silica aggregates. Certain manufactured or industrial products incorporate in their manufacture silica particles in different forms, and in particular in the form of anisotropic aggregates. These silica particles are of interest as a reinforcing filler, as a viscosifying or texturing agent, or as a catalyst support in various fields. However, the synthesis of anisotropic silica aggregates is delicate and difficult because of the amorphous nature of the silicon which implies that there is no preferential orientation during nucleation or growth of the solid. Furthermore, obtaining anisotropic silica aggregates implies very strict control of the aggregation phenomena, that is to say of the interactions existing between the silica particles, which is very difficult and generally leads to a morphology of globally isotropic aggregate. The aggregation phenomenon is essentially controlled either by the presence of salts, or by the concentration of particles, or by the presence of entities that can react with the surface of the silica and thus modify its surface, or by the acidity conditions. which modify the surface charge of silica and the reactivity of the silica surface (catalysis of oxidation). In order to meet the requirements of manufacturers, it has become necessary to provide a process for the preparation of anisotropic silica aggregates which makes it possible to control the aggregation of silica particles. Also the problem which the invention proposes to solve is to provide a process for the preparation of anisotropic aggregates, the implementation conditions of which allow the aggregation of the silica particles to be controlled. For this purpose, the invention provides a process for the preparation of anisotropic silica aggregates which comprises the following steps: a) at least one polymer is brought into contact with non-aggregated silica particles and / or having a high degree of dispersion in aqueous medium, with an R ratio, mass of polymer related to the surface of the silica particles, of between 0.02 and 2 mg / m 2 and the value of the electrostatic charge of the surface of the silica particles being greater than or equal the value of the charge of the surface of the silica particles measured in an aqueous phase without added salts at a pH greater than or equal to 7; b) the aggregates obtained in step a) are consolidated either by heat treatment or by precipitation of an inorganic compound. The subject of the invention is also a silica aggregate comprising a sequence of elementary silica particles the number of particles of which is between 5 and 15, of which at least 80% of the elementary particles are in contact with at most 2 particles and whose greatest measurable distance between 2 points of the aggregate is less than or equal to 5 times the average size of a particle elementary. The advantage of the process according to the invention is that it allows the aggregation of the silica particles to be controlled under very simple conditions for implementing the process by simple addition of at least one polymer to the reaction medium. On the other hand, step b) of consolidation can be carried out under saline conditions, that is to say by simple addition of salts of mineral cations which will precipitate at the grain boundaries. Advantageously, this process makes it possible to obtain soils of anisotropic aggregates or powders by simple drying of the soil. The method according to the invention also has the advantage of very fine control of the final size of the elementary particles, of the morphology of the aggregate and of the size of the aggregate. It thus makes it possible to produce anisotropic silica aggregates which are solid, irreversible, no longer breaking and easy to produce. These anisotropic aggregates, due to their original morphology, have reinforcing properties, viscosifying or texturing agents or catalyst support properties. Other advantages and characteristics of the invention will appear clearly on reading the description and examples given for purely illustrative and nonlimiting reasons which will follow. The invention firstly relates to a process for the preparation of anisotropic silica aggregates which comprises the following steps: a) at least one polymer is brought into contact with non-aggregated and / or high-grade silica particles dispersion in an aqueous medium, with a ratio R, mass of polymer related to the surface of the silica particles, of between 0.02 and 2 mg / m 2 and the value of the electrostatic charge of the surface of the silica particles being greater than or equal to the value of the charge of the surface of the silica particles measured in an aqueous phase without added salts at a pH greater than or equal to 7; b) the aggregates obtained in step a) are consolidated either by heat treatment or by precipitation of an inorganic compound. Anisotropic aggregates are understood to mean, within the meaning of the invention, aggregates comprising at least 5 elementary particles and of which at least 50% (percentage by number) of elementary particles have 2 neighbors. For the purposes of the invention, the term elementary particle means the basic element of the aggregate (also called the primary particle). Preferably the silica particles used in step a) of the process according to the invention are well dispersed and not aggregated. The most favorable conditions for obtaining such particles are a desalinated medium and a high pH. Preferably, in the case where the process is carried out in an aqueous medium, one will choose conditions of basic pH higher than 7, even more preferentially higher than 8. Advantageously the silica particles used are silica soils, which can be obtained by any process which makes it possible to obtain silica soils, in particular we can cite among others the processes with resins, ultrafiltration or even electrodialysis, but also the processes by polymerization of silicon aikoxide in organic solvent (Stôber type silica). Preferably, a silica sol will be used, the size of the silica particles of which is between 3 and 50 nm, even more preferably between 5 and 20 nm, the sizes being measured by transmission electron microscopy. Transmission electron microscopy observations were carried out on a Jeol 1200 device.
Une goutte de l'échantillon à observer est déposée sur une grille circulaire de cuivre deA drop of the sample to be observed is placed on a circular copper grid of
3 mm de diamètre recouverte d'une membrane de collodion et de carbone hydrophylisé.3 mm in diameter covered with a collodion membrane and hydrophylized carbon.
Avec du papier filtre, le surplus est absorbé de façon à ne laisser sur la grille qu'un mince film de liquide. La grille est ensuite laissée à sécher à température ambiante. De préférence, on utilisera un sol de silice dont les particules de silices présentent une surface spécifique BET comprise entre 50 et 880 m /g, de préférence entre 130 etWith filter paper, the excess is absorbed so that only a thin film of liquid is left on the grid. The grid is then left to dry at room temperature. Preferably, a silica sol will be used, the silica particles of which have a BET specific surface of between 50 and 880 m / g, preferably between 130 and
530 m2/g, mesuré sur un sol séché. La surface spécifique BET est déterminée selon la méthode de BRUNAUER - EMMET - TELLER décrite dans "The journal of the American530 m 2 / g, measured on dried soil. The BET specific surface is determined according to the BRUNAUER - EMMET - TELLER method described in "The journal of the American
Chemical Society", Vol. 60, page 309, février 1938 et correspondant à la norme internationale ISO 5794/1 (annexe D). On peut par exemple utiliser les sols de silice de type Ludox 12 nm et 220 m2/g (HS30 en particulier). A l'étape a) du procédé selon l'invention, les particules de silice sont mises en contact avec un polymère dont le rôle est d'agréger les particules de manière anisotrope. Le rapport R, masse de polymère rapportée à la surface développée par les particules de silice, est de préférence compris entre 0,05 et 1 ,8 mg/m2 . Le polymère mis en œuvre dans le procédé selon l'invention présente avantageusement une affinité particulière pour la surface de la silice. Ce polymère est généralement une molécule organique, de fype hydrophile mais peut également posséder une ou plusieurs parties hydrophobes. Le polymère peut être choisi parmi les polymères linéaires, les homopolymères, les copolymères, les polymères greffés ou les dendrimères. Leur composition peut être basée sur un seul motif monomère ou plusieurs motifs (arrangement statistique ou en bloc). Le polymère peut posséder une charge électrostatique (on préférera des polymères anioniques contenant moins de 50% de motifs anioniques ou des polymères cationiques) ou être non chargé. La masse moléculaire du polymère n'est pas limitative puisqu'il est possible de réaliser des * agrégats anisotropes avec des hautes masses comme avec de faibles masses moléculaires. Le polymère mis en œuvre dans le procédé selon l'invention permet avantageusement de réaliser l'agrégation dans des conditions où la silice possède une forte charge électrostatique de surface (pH élevé, faible force ionique). Avantageusement la présence de cette charge de surface conduit les particules de silice à s'agréger de manière anisotrope. De préférence, le polymère mis en œuvre dans le procédé selon l'invention est un polymère choisi parmi les polymères, copolymères ou polymères greffés suivants : polyoxyéthylène (POE), alcool polyvinylique (APV), polyvinylpyrrolidone (PVP), polyacrylamide (PAM), polymethacrylamides, poly(N-isopropylacrylamide) (PNIPAM) et autres dérivés N-substitués, polysaccharides tels que amylose, dextrane, guar et dérivés ou celluloses modifiées, polyvinylpyrrolidone-polyacideacrylique (PVP-PAA), polyoxyéthylène-polyacideacrylique (POE-PAA), polyacrylamide-polyvinylpyrrolidone (PAM-PVP), polyvinyi * aminé, polydiallyldimethylammonium (PDADMAC), polyacrylamide- polydiallyldimethylammonium (PAM-PDADMAC), les polymères à base d'aminés quatemisés ou non et leurs copolymères avec les monomères non ioniques ou anioniques comme le polyéthylène imine, le polyvinylimidazole, les divers polyamino alkyl acrylates et méthacrylates, les copolymères statistiques ou greffés de monomères anioniques (acide acrylique ou méthacrylique entre autres) avec des monomères cationiques ou non ioniques, polysaccharides carboxyméthylés. Ces polymères présentent des interactions privilégiées avec la surface de la silice et peuvent entrer en interaction avec la surface de la silice, par exemple par liaison hydrogène, par interaction électrostatique ou en se fixant de manière iono-covalente ou covalente. L'étape a) du procédé selon l'invention est de préférence réalisée en milieux aqueux à pH basique supérieur à 7, encore plus préférentiellement à un pH supérieur à 8. Ces valeurs de pH peuvent varier en fonction de la nature du milieu réactionnel, et notamment en milieu hydroalcoolique. Dans un deuxième temps, l'agrégat anisotrope obtenu à l'étape a) est consolidé au cours de l'étape b) du procédé. L'agrégation par des polymères (étape a) conduit généralement à des objets qui peuvent être sécables, tant qu'un composé minéral n'a pas consolidé l'agrégat de silice. La consolidation est donc une étape nécessaire qui peut consister à déposer un composé minéral sur les agrégats de silice anisotropes. Ceci aboutit à la formation d'un joint qui évite la cassure ultérieure de l'agrégat par une opération chimique ou mécanique. Cette consolidation est réalisée soit par un traitement thermique, soit par précipitation d'un composé minéral. Lorsque l'étape b) consiste en un traitement thermique, la température du traitement thermique est d'au moins 80°C, plus particulièrement d'au moins 100°C, de préférence d'au moins 120°C. La durée du traitement thermique est déterminée en fonction de l'utilisation susceptible d'être envisagée pour les agrégats de silice anisotrope. La durée du traitement thermique permet de contrôler le caractère sécable de l'agrégat. Ce traitement thermique peut être réalisé par autoclavage. A l'issu du traitement thermique, on peut obtenir une dispersion colloïdale de silice (sol de silice), lorsqu'on traite thermiquement une dispersion. L'étape b) du procédé selon l'invention peut être réalisée par précipitation d'un composé minéral. Dans ce dernier cas, le composé minéral est choisi parmi les silicates, les phosphates, les silicophosphates, les aluminates, les silicoaluminates, le cérium, le zinc, le fer, le titane, le zirconium, les carbonates, les terres rares, les cations divalents ou leurs mélanges. De préférence, le composé minéral est un silicate ou toute forme courante de silicates tels que métasilicates, disilicates et avantageusement un silicate de métal alcalin, notamment le silicate de sodium ou de potassium. De préférence, le composé minéral est un silicate de sodium présentant un rapport pondéral Rp SiO2 /Na2O compris entre 0,5 et 4. Le silicate peut présenter une concentration (exprimée en masse de silice) comprise entre 10 et 330 g/l, de préférence comprise entre 15 et 300 g/l, en particulier comprise entre 60 et 260 g/l. Avantageusement la précipitation du composé minéral est réalisée selon les conditions classiques de précipitation de ce composé. Dans le cas d'un silicate, la précipitation est réalisée en ajoutant simultanément le silicate à précipiter et un agent acidifiant de manière à maintenir le pH à une valeur d'au moins 6. On utilise généralement comme agent acidifiant un acide minéral fort tel que l'acide sulfurique, l'acide nitrique ou l'acide chlorhydrique, ou un acide organique tel que l'acide acétique, l'acide formique ou l'acide carbonique. L'agent acidifiant peut être dilué ou concentré; sa normalité peut être comprise entre 0,4 et 36 N, de préférence entre 0,6 et 3 N. En particulier, dans le cas où l'agent acidifiant serait l'acide sulfurique, sa concentration peut être comprise entre 20 et 180 g/l, de préférence entre 40 et 130 g/l. De manière générale, on emploie, comme agent acidifiant, l'acide sulfurique, et, comme silicate, le silicate de sodium. La précipitation du composé minéral permet d'obtenir un précipité d'un sel métallique, d'un oxyde métallique ou d'un hydroxyde métallique. Le sel est avantageusement choisi parmi un silicate, un silicoaluminate, un silicophosphate, un phosphate, un carbonate. Le métal est avantageusement un métal choisi parmi le silicium, le calcium, le magnésium, le cérium, le zinc, le fer, le titane, le zirconium, l'aluminium. Avantageusement on obtient à l'issue de l'étape b) qui vient d'être décrite et qui est réalisée par précipitation d'un composé minéral, une bouillie de silice qui est ensuite séparée (séparation liquide-solide). Cette séparation mise en œuvre dans le procédé de préparation selon l'invention comprend habituellement une filtration, suivie d'un lavage si nécessaire. La filtration s'effectue selon toute méthode convenable, par exemple au moyen d'un filtre presse, d'un filtre à bande, d'un filtre sous vide. La suspension de silice ou gâteau de filtration ainsi récupérée est ensuite séchée.Chemical Society ", Vol. 60, page 309, February 1938 and corresponding to the international standard ISO 5794/1 (appendix D). It is possible, for example, to use silica soils of the Ludox type 12 nm and 220 m 2 / g (HS30 In particular). In step a) of the process according to the invention, the silica particles are brought into contact with a polymer whose role is to aggregate the particles anisotropically. The ratio R, mass of polymer related to the surface developed by the silica particles is preferably between 0.05 and 1.8 mg / m 2. The polymer used in the process according to the invention advantageously has a particular affinity for the surface of the silica. This polymer is generally an organic molecule, of hydrophilic type but can also have one or more hydrophobic parts The polymer can be chosen from linear polymers, homopolymers, copolymers, grafted polymers or dendrimers. their composition may be based on a single monomeric unit or several reasons (statistical or block arrangement). The polymer can have an electrostatic charge (anionic polymers containing less than 50% of anionic units or cationic polymers are preferred) or be uncharged. The molecular mass of the polymer is not limiting since it is possible to produce * anisotropic aggregates with high masses as with low molecular masses. The polymer used in the process according to the invention advantageously makes it possible to carry out aggregation under conditions where the silica has a high electrostatic surface charge (high pH, low ionic strength). Advantageously, the presence of this surface charge causes the silica particles to aggregate anisotropically. Preferably, the polymer used in the process according to the invention is a polymer chosen from the following polymers, copolymers or graft polymers: polyoxyethylene (POE), polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), polyacrylamide (PAM), polymethacrylamides, poly (N-isopropylacrylamide) (PNIPAM) and other N-substituted derivatives, polysaccharides such as amylose, dextran, guar and modified derivatives or celluloses, polyvinylpyrrolidone-polyacideacrylic (PVP-PAA), polyoxyethylene-polyacideacrylic (POE-PAA) polyacrylamide-polyvinylpyrrolidone (PAM-PVP), polyvinyi * amino, polydiallyldimethylammonium (PDADMAC), polyacrylamide- polydiallyldimethylammonium (PAM-PDADMAC), polymers based on quaternized or non-amines and their copolymers with nonionic or anionic monomers such as poly imine, polyvinylimidazole, various polyamino alkyl acrylates and methacrylates, random or graft copolymers of my anionic omers (acrylic or methacrylic acid among others) with cationic or nonionic monomers, carboxymethylated polysaccharides. These polymers exhibit privileged interactions with the surface of the silica and can interact with the surface of the silica, for example by hydrogen bonding, by electrostatic interaction or by fixing in an iono-covalent or covalent manner. Step a) of the process according to the invention is preferably carried out in aqueous media at a basic pH greater than 7, even more preferably at a pH greater than 8. These pH values can vary depending on the nature of the reaction medium, and in particular in hydroalcoholic medium. In a second step, the anisotropic aggregate obtained in step a) is consolidated during step b) of the process. Aggregation by polymers (step a) generally leads to objects which may be breakable, as long as a mineral compound has not consolidated the silica aggregate. Consolidation is therefore a necessary step which can consist in filing a mineral compound on anisotropic silica aggregates. This results in the formation of a seal which prevents subsequent breakage of the aggregate by a chemical or mechanical operation. This consolidation is carried out either by heat treatment or by precipitation of an inorganic compound. When step b) consists of a heat treatment, the temperature of the heat treatment is at least 80 ° C., more particularly at least 100 ° C., preferably at least 120 ° C. The duration of the heat treatment is determined as a function of the use which may be envisaged for the anisotropic silica aggregates. The duration of the heat treatment makes it possible to control the breakable nature of the aggregate. This heat treatment can be carried out by autoclaving. At the end of the heat treatment, a colloidal dispersion of silica (silica sol) can be obtained, when a dispersion is heat treated. Step b) of the process according to the invention can be carried out by precipitation of an inorganic compound. In the latter case, the mineral compound is chosen from silicates, phosphates, silicophosphates, aluminates, silicoaluminates, cerium, zinc, iron, titanium, zirconium, carbonates, rare earths, cations divalent or their mixtures. Preferably, the mineral compound is a silicate or any common form of silicates such as metasilicates, disilicates and advantageously an alkali metal silicate, in particular sodium or potassium silicate. Preferably, the mineral compound is a sodium silicate having a weight ratio Rp SiO 2 / Na 2 O of between 0.5 and 4. The silicate may have a concentration (expressed by mass of silica) of between 10 and 330 g / l, preferably between 15 and 300 g / l, in particular between 60 and 260 g / l. Advantageously, the precipitation of the mineral compound is carried out according to the conventional conditions for precipitation of this compound. In the case of a silicate, the precipitation is carried out by simultaneously adding the silicate to be precipitated and an acidifying agent so as to maintain the pH at a value of at least 6. A strong mineral acid such as sulfuric acid, nitric acid or hydrochloric acid, or an organic acid such as acetic acid, formic acid or carbonic acid. The acidifying agent can be diluted or concentrated; its normality can be between 0.4 and 36 N, preferably between 0.6 and 3 N. In particular, in the case where the acidifying agent would be sulfuric acid, its concentration can be between 20 and 180 g / l, preferably between 40 and 130 g / l. In general, sulfuric acid is used as the acidifying agent, and sodium silicate as the silicate. The precipitation of the mineral compound makes it possible to obtain a precipitate of a metal salt, a metal oxide or a metal hydroxide. The salt is advantageously chosen from a silicate, a silicoaluminate, a silicophosphate, a phosphate, a carbonate. The metal is advantageously a metal chosen from silicon, calcium, magnesium, cerium, zinc, iron, titanium, zirconium, aluminum. Advantageously, at the end of step b) which has just been described and which is produced by precipitation of an inorganic compound, a silica slurry is obtained which is then separated (liquid-solid separation). This separation implemented in the preparation process according to the invention usually comprises filtration, followed by washing if necessary. Filtration is carried out by any suitable method, for example by means of a filter press, a band filter, a vacuum filter. The silica suspension or filter cake thus recovered is then dried.
' Il y a lieu de noter que le gâteau de filtration n'est pas toujours dans des conditions permettant une atomisation notamment à cause de sa viscosité élevée. D'une manière connue en soi, on soumet alors le gâteau à une opération de délitage. Cette opération peut être réalisée mécaniquement, par passage du gâteau dans un broyeur de type colloïdal ou à bille. Le délitage est généralement effectué en présence d'un composé de l'aluminium, en particulier d'aluminate de sodium et, éventuellement, en présence d'un agent acidifiant tel que décrit précédemment (dans ce dernier cas, le composé de l'aluminium et l'agent acidifiant sont généralement ajoutés de manière simultanée). L'opération de délitage permet notamment d'abaisser la viscosité de la suspension à sécher ultérieurement. La suspension de silice ainsi récupérée est ensuite séchée. A l'issue de l'étape b), qui est réalisée par traitement thermique, on peut obtenir une dispersion colloïdale qui peut aussi ensuite être séchée. Dans ces 2 cas, le séchage peut se faire selon tout moyen connu en soi. De préférence, le séchage se fait par atomisation. A cet effet, on peut utiliser tout type d'atomiseur convenable, notamment un atomiseur à turbines, à buses, à pression liquide ou à deux fluides. En général, lorsque la filtration est effectuée à l'aide d'un filtre presse, on utilise un atomiseur à buses, et, lorsque la filtration est effectuée à l'aide d'un filtre sous-vide, on utilise un atomiseur à turbines. Lorsque le séchage est effectué à l'aide d'un atomiseur à buses, la silice susceptible d'être alors obtenue se présente habituellement sous forme de billes sensiblement sphériques. A l'issue du séchage, on peut alors procéder à une étape de broyage sur le produit récupéré. La silice qui est alors susceptible d'être obtenue se présente généralement sous forme d'une poudre. Lorsque le séchage est effectué à l'aide d'un atomiseur à turbines, la silice susceptible d'être alors obtenue peut se présenter sous la forme d'une poudre. Enfin, le produit séché (notamment par un atomiseur à turbines) ou broyé tel qu'indiqué précédemment peut éventuellement être soumis à une étape d'agglomération, qui consiste par exemple en une compression directe, une granulation voie humide (c'est-à-dire avec utilisation d'un liant tel que l'eau, suspension de silice ...), une extrusion ou, de préférence, un compactage à sec. Lorsque l'on met en œuvre cette dernière technique, il peut s'avérer opportun, avant de procéder au compactage, de désaérer (opération appelée également pré-densification ou dégazage) les produits pulvérulents de manière à éliminer l'air inclus dans ceux-ci et assurer un compactage plus régulier. La silice susceptible d'être alors obtenue par cette étape d'agglomération se présente généralement sous la forme de granulés. Les poudres, de même que les billes, de silice obtenues par le procédé selon l'invention offrent ainsi l'avantage, entre autre, d'accéder de manière simple, efficace et économique, à des granulés, notamment par des opérations classiques de mise en forme, telles que par exemple une granulation ou un compactage, sans que ces dernières n'entraînent de dégradations susceptibles de masquer, voire annihiler, les bonnes propriétés intrinsèques attachées à ces poudres ou ces billes, comme cela peut être le cas dans l'art antérieur en mettant en œuvre des poudres classiques. Dans un cas particulier du procédé selon l'invention, il est possible d'utiliser à titre de polymère dans l'étape a), le poly(N-isopropylacrylamide). Les silices susceptibles d'être obtenues par le procédé de l'invention utilisant à titre de polymère dans l'étape a), le poly(N-isopropylacrylamide), constituent également un des objets de la présente invention. L'invention a également pour objet un agrégat de silice comprenant un enchaînement de particules élémentaires de silice dont le nombre de particules est compris entre 5 et 15, dont au moins 80% des particules élémentaires sont en contact avec au plus 2 particules et dont la plus grande distance mesurable entre 2 points de l'agrégat est inférieure ou égale à 5 fois la taille moyenne d'une particule élémentaire. De préférence, la plus grande distance mesurable entre 2 points de l'agrégat est inférieure ou égale à 4 fois la taille moyenne d'une particule élémentaire. L'invention a également pour objet l'utilisation des silices réalisées à partir du poly(N-isopropylacrylamide) à titre de polymère ou des agrégats cités précédemment, comme charge renforçante d'une composition de polymères notamment de plastiques et de caoutchouc (par exemple de semelles de chaussures), agent viscosant texturant ou anti-mottant, agent anti-craquage notamment dans le domaine pétrolier, agent de polissage notamment des dentifrices et papiers, agent de revêtement notamment dans le domaine textile, absorbant de matière active, support de catalyseur, élément pour séparateurs de batteries.'It should be noted that the filter cake is not always in conditions allowing atomization, in particular because of its high viscosity. In a manner known per se, the cake is then subjected to a disintegration operation. This operation can be carried out mechanically, by passing the cake through a colloidal or ball mill. The disintegration is generally carried out in the presence of an aluminum compound, in particular sodium aluminate and, optionally, in the presence of an acidifying agent as described above (in the latter case, the aluminum compound and the acidifying agent are generally added simultaneously). The disintegration operation notably makes it possible to lower the viscosity of the suspension to be dried later. The silica suspension thus recovered is then dried. At the end of step b), which is carried out by heat treatment, a colloidal dispersion can be obtained which can also then be dried. In these 2 cases, the drying can be done by any means known per se. Preferably, the drying is carried out by atomization. For this purpose, any suitable type of atomizer can be used, in particular a turbine, nozzle, liquid pressure or two-fluid atomizer. In general, when filtration is carried out using a filter press, a nozzle atomizer is used, and, when filtration is carried out using a vacuum filter, a turbine atomizer is used . When the drying is carried out using a nozzle atomizer, the silica which can then be obtained is usually in the form of substantially spherical beads. After drying, a grinding step can then be carried out on the recovered product. The silica which can then be obtained is generally in the form of a powder. When the drying is carried out using a turbine atomizer, the silica which can then be obtained can be in the form of a powder. Finally, the dried product (in particular by a turbine atomizer) or ground as indicated above can optionally be subjected to an agglomeration step, which consists for example of direct compression, wet granulation (i.e. - say with the use of a binder such as water, silica suspension, etc.), extrusion or, preferably, dry compaction. When the latter technique is used, it may prove advisable, before proceeding to compaction, to deaerate (operation also called pre-densification or degassing) the powdery products so as to eliminate the air included in them. and ensure more regular compaction. The silica that can then be obtained by this agglomeration step is generally in the form of granules. The powders, as well as the beads, of silica obtained by the process according to the invention thus offer the advantage, among other things, of having simple, effective and economical access to granules, in particular by conventional operations of placing shaped, such as for example granulation or compaction, without the latter causing degradation capable of masking, or even annihilating, the good intrinsic properties attached to these powders or these beads, as may be the case in prior art by using conventional powders. In a particular case of the process according to the invention, it is possible to use, as polymer in step a), poly (N-isopropylacrylamide). The silicas capable of being obtained by the process of the invention using, as the polymer in step a), poly (N-isopropylacrylamide), also constitute one of the objects of the present invention. The subject of the invention is also a silica aggregate comprising a series of elementary particles of silica the number of particles of which is between 5 and 15, of which at least 80% of the elementary particles are in contact with at most 2 particles and of which the greatest measurable distance between 2 points of the aggregate is less than or equal to 5 times the average size of an elementary particle. Preferably, the greatest measurable distance between 2 points of the aggregate is less than or equal to 4 times the average size of an elementary particle. A subject of the invention is also the use of silicas produced from poly (N-isopropylacrylamide) as polymer or the aggregates mentioned above, as reinforcing filler of a composition of polymers, in particular plastics and rubber (for example shoe soles), texturing or anti-caking viscosity agent, anti-cracking agent in particular in the petroleum field, polishing agent in particular in toothpaste and paper, coating agent in particular in the textile field, absorbent of active material, catalyst support , element for battery separators.
Les exemples suivants illustrent l'invention sans toutefois en limiter la portée.The following examples illustrate the invention without, however, limiting its scope.
EXEMPLESEXAMPLES
Exemple 1 :Example 1:
1 litre d'une solution de polyoxyéthylène (POE) de masse molaire 106 g/mol est préparé à une concentration de 0,8 g/L par dilution à l'eau épurée puis amené à pH 9 (par de la soude). 1 litre de sol de silice (Ludox HS30 de Du Pont) est préparé à une concentration de 20 g/L par dilution à l'eau épurée puis le sol est amené à pH 9. Les particules ont un diamètre de l'ordre de 12 nm (surface spécifique de 220 m2/g). La solution de POE est rapidement introduite dans le sol de silice. Le mélange peut également être réalisé en introduisant le sol dans la solution de POE ou en addition simultanée. Le mélange est laissé à mûrir pendant une heure. Dans ces conditions, le pH est voisin de 9 et le ratio R, POE/silice vaut 0,2 mg de POE/m2 de silice.1 liter of a polyoxyethylene (POE) solution with a molar mass of 10 6 g / mol is prepared at a concentration of 0.8 g / L by dilution with purified water and then brought to pH 9 (with sodium hydroxide). 1 liter of silica sol (Ludox HS30 from Du Pont) is prepared at a concentration of 20 g / L by dilution with purified water then the soil is brought to pH 9. The particles have a diameter of around 12 nm (specific surface of 220 m 2 / g). The POE solution is quickly introduced into the silica sol. The mixing can also be carried out by introducing the sol into the POE solution or by simultaneous addition. The mixture is left to ripen for one hour. Under these conditions, the pH is close to 9 and the ratio R, POE / silica is 0.2 mg POE / m 2 of silica.
Consolidation des agrégats : Dans un réacteur agité de 4 litres, le mélange POE/silice est chauffé à 85°C et le pH ajusté à 9. Une solution de silicate de sodium de rapport pondéral Rp de 3,55 (Rp=SiO2/Na2O) à une concentration de 57 g/L en SiO2 et une solution d'acide sulfurique à 20 g/L sont simultanément ajoutés dans le réacteur Le débit d'ajout de la solution de silicate est fixé à 12 g/min, le débit d'ajout de la solution d'acide sulfurique est régulé de manière à maintenir le pH constant à 9. La durée de l'addition simultanée varie suivant le taux de consolidation (= masse de silice ajoutée/masse de siiice initialement présente dans le pied de cuve) que l'on désire obtenir. Classiquement, pour des particules de 12 nm, un taux de consolidation de 50% permet de renforcer efficacement les agrégats. En fin d'addition, l'ajout de silicate est stoppé et le pH est abaissé à 4. La suspension est filtrée, lavée puis séchée (étuve, atomisation). Il est possible d'ajouter des coagulants en fin d'addition simultanée pour faciliter la filtration : par exemple, l'ajout d'une solution de MgSO4 0,4 mol/L à raison de 50 mL de solution pour 600 mL de suspension facilite la filtration et les lavages successifs.Consolidation of the aggregates: In a stirred 4-liter reactor, the POE / silica mixture is heated to 85 ° C. and the pH adjusted to 9. A sodium silicate solution with a weight ratio Rp of 3.55 (Rp = SiO 2 / Na 2 O) at a concentration of 57 g / L of SiO 2 and a sulfuric acid solution of 20 g / L are simultaneously added to the reactor The rate of addition of the silicate solution is fixed at 12 g / min , the rate of addition of the sulfuric acid solution is regulated so as to keep the pH constant at 9. The duration of the simultaneous addition varies according to the consolidation rate (= mass of silica added / mass of silicon initially present in the base) that we want to obtain. Conventionally, for 12 nm particles, a consolidation rate of 50% makes it possible to effectively reinforce the aggregates. At the end of the addition, the addition of silicate is stopped and the pH is lowered to 4. The suspension is filtered, washed and then dried (oven, atomization). It is possible to add coagulants at the end of simultaneous addition to facilitate filtration: for example, the addition of a 0.4 mol / L MgSO 4 solution at the rate of 50 ml of solution for 600 ml of suspension facilitates filtration and successive washings.
Le produit final a une surface de 147 m2/g, une dispersibilité mesurée par granulométrie à l'aide d'un Sedigraph donnant un taux de 96% de particules dont le diamètre est inférieur à 0,3 microns. L'analyse granulométrique est basée sur un principe de sédimentation avec un appareil de mesure granulométrique tel que le Sedigraph 5100 (249 ET 041), pour analyser la sédimentation des agrégats selon l'invention. La technique mise en œuvre peut comprendre une première étape de dispersion d'une poudre en milieu aqueux, et d'une étape de désagglomération par ultrasons, avec une sonde de puissance environ 600 watts, plus ou moins 20%, pendant 7 minutes. Il est également possible de faire directement la mesure sur une dispersion ou sur une dispersion colloïdale selon l'invention, sans étapes préalables.The final product has a surface area of 147 m2 / g, a dispersibility measured by particle size using a Sedigraph giving a rate of 96% of particles whose diameter is less than 0.3 microns. The particle size analysis is based on a principle of sedimentation with a particle size measurement device such as the Sedigraph 5100 (249 ET 041), to analyze the sedimentation of the aggregates according to the invention. The technique used can comprise a first step of dispersing a powder in an aqueous medium, and a step of deagglomeration by ultrasound, with a power probe of around 600 watts, more or less 20%, for 7 minutes. It is also possible to make the measurement directly on a dispersion or on a colloidal dispersion according to the invention, without prior steps.
La consolidation des agrégats peut également être réalisée par autoclavage du mélange POE/silice. Dans ce cas, le renforcement des agrégats est du à des mécanismes de redissolution-précipitation aux joints de grain : 700 mL du mélange sol de silice / POE avec une concentration en silice de 10 g/L et une concentration en POE 10δ g/mol de 0,4 g/L sont introduits dans un autoclave de 1 L. le mélange est agité et simultanément chauffé jusqu'à 130°C à raison d'une montée de 3°C/min. Il est maintenu à 130°C pendant 6 heures puis refroidi naturellement jusqu'à température ambiante.Consolidation of the aggregates can also be carried out by autoclaving the POE / silica mixture. In this case, the strengthening of the aggregates is due to redissolution-precipitation mechanisms at the grain boundaries: 700 mL of the silica sol / POE mixture with a silica concentration of 10 g / L and a POE concentration 10 δ g / 0.4 g / L mol are introduced into a 1 L autoclave, the mixture is stirred and simultaneously heated to 130 ° C at a rise of 3 ° C / min. It is maintained at 130 ° C for 6 hours then cooled naturally to room temperature.
La microscopie électronique en transmission (MET) montre des agrégats anisotropes dont la majorité comprend au moins une dizaine de particules. Les clichés sont réalisés par cryogénation des échantillons afin d'éviter une éventuelle agrégation lors du séchage. Dans le cas où l'échantillon à observer est une poudre, celle-ci est dispersée dans de l'eau à une teneur de l'ordre de 1 mg/l. Un passage dans un bain à ultrasons permet de désaglomérer le produit. Sur ces clichés, il est possible de déterminer le Nombre de particules voisines au sein de l'agrégat (Tableau 1).Transmission electron microscopy (TEM) shows anisotropic aggregates, the majority of which include at least ten particles. The photos are taken by cryogenics of the samples in order to avoid possible aggregation during drying. In the case where the sample to be observed is a powder, it is dispersed in water at a content of the order of 1 mg / l. Passing through an ultrasonic bath allows the product to agglomerate. On these pictures, it is possible to determine the Number of neighboring particles within the aggregate (Table 1).
Tableau 1 :Table 1:
Le tableau se lit comme suit pour la première ligne : au sein d'un agrégat, 15% des particules ne sont en contact qu'avec une seule particule, 72% des particules sont en contact avec 2 particules, 12% des particules sont en contact avec 3 particules et 1% des particules sont en contact avec 4 particules. The table reads as follows for the first line: within an aggregate, 15% of the particles are in contact with only one particle, 72% of the particles are in contact with 2 particles, 12% of the particles are in contact with 3 particles and 1% of the particles are in contact with 4 particles.
Ces chiffres indiquent que les agrégats sont plutôt linéaires et peu branchés.These figures indicate that the aggregates are rather linear and not very connected.
Exemple 2 :Example 2:
On prépare un sol de silice de concentration de 22 g/L par dilution d'un sol Ludox HS30 à l'eau permutée. Le milieu est amené à pH 9 par ajout de soude.A silica sol with a concentration of 22 g / L is prepared by diluting a Ludox HS30 sol with deionized water. The medium is brought to pH 9 by adding sodium hydroxide.
On prépare une solution de poly(N-isopropylacrylamide) de masse moléculaire égale à 820000 g/mol à une concentratrion de 7,3 g/l.A solution of poly (N-isopropylacrylamide) with a molecular mass equal to 820,000 g / mol is prepared at a concentration of 7.3 g / l.
Le sol d'agrégat anisotrope est préparé par introduction de 10 mL du sol de silice dansThe anisotropic aggregate sol is prepared by introducing 10 mL of the silica sol into
10 mL de la solution de polymère. Le ratio R polymère/silice est de 1 ,5 mg/m2.10 mL of the polymer solution. The polymer / silica R ratio is 1.5 mg / m 2 .
Le mélange est réalisé sous forte agitation en quelques minutes puis l'agitation est maintenue pendant 32 heures à une vitesse modérée. Le mélange est mis à chauffer à 98°C pendant 48 heures.The mixing is carried out with vigorous stirring in a few minutes and then stirring is maintained for 32 hours at a moderate speed. The mixture is heated to 98 ° C for 48 hours.
Exemple 3 on prépare un sol de silice de concentration 22g/L par dilution d'un sol LUDOX HS30 à l'eau permutée. Le milieu est amené à pH 9 par ajout de soude. On prépare une solution de poiy(N-isopropylacrylamide) de masse moléculaire égale àEXAMPLE 3 A silica sol with a concentration of 22 g / L is prepared by diluting a LUDOX HS30 sol with deionized water. The medium is brought to pH 9 by adding sodium hydroxide. A poiy (N-isopropylacrylamide) solution of molecular mass equal to is prepared.
820.000 g/mol à une concentration de 5.5g/L820,000 g / mol at a concentration of 5.5g / L
Le sol d'agrégat anisotrope est préparé par introduction de 10mL du sol de silice dansThe anisotropic aggregate sol is prepared by introducing 10 ml of the silica sol into
12mL de la solution de polymère. Le ratio R polymère/silice est de 1.36mg/m2.12mL of the polymer solution. The R / polymer / silica ratio is 1.36 mg / m 2 .
Le mélange est réalisé sous forte agitation en quelques minutes puis l'agitation est maintenue pendant 32 heures à une vitesse modérée.The mixing is carried out with vigorous stirring in a few minutes and then stirring is maintained for 32 hours at a moderate speed.
Le mélange est mis à chauffer à 98°C pendant 48 heures.The mixture is heated to 98 ° C for 48 hours.
Exemple 4 on prépare un sol de silice de concentration 22g/L par dilution d'un sol LUDOX HS30 à l'eau permutée. Le milieu est amené à pH 9 par ajout de soude.EXAMPLE 4 A silica sol with a concentration of 22 g / L is prepared by diluting a LUDOX HS30 sol with deionized water. The medium is brought to pH 9 by adding sodium hydroxide.
On prépare une solution de poly(N-isopropylacrylamide) de masse moléculaire égale à 820.000 g/mol à une concentration de 3.2g/L Le sol d'agrégat anisotrope est préparé par introduction de 10mL du sol de silice dans 12mL de la solution de polymère. Le ratio R polymère/silice est de 0.8 mg/m2. Le mélange est réalisé sous forte agitation en quelques minutes puis l'agitation est maintenue pendant 32 heures à une vitesse modérée. Le mélange est mis à chauffer à 98°C pendant 48 heures.A solution of poly (N-isopropylacrylamide) of molecular mass equal to 820,000 g / mol is prepared at a concentration of 3.2 g / L The anisotropic aggregate sol is prepared by introducing 10mL of the silica sol into 12mL of the polymer solution. The polymer / silica R ratio is 0.8 mg / m 2 . The mixing is carried out with vigorous stirring in a few minutes and then stirring is maintained for 32 hours at a moderate speed. The mixture is heated to 98 ° C for 48 hours.
Résultats des exemples 2 à 4 : par microscopie, on observe des agrégats constitués d'enchaînements de 6 à 10 particules pour lesquels la plus grande distance mesurable entre deux points de l'enchaînement est inférieur à 50 nm. Au moins 85% des particules élémentaires sont en contact avec au plus 2 particules. Results of Examples 2 to 4: by microscopy, aggregates consisting of chains of 6 to 10 particles are observed for which the greatest measurable distance between two points of the chain is less than 50 nm. At least 85% of the elementary particles are in contact with at most 2 particles.

Claims

REVENDICATIONS
1. Procédé de préparation d'agrégats anisotropes de silice qui comprend les étapes suivantes : a) on met en contact au moins un polymère avec des particules de silice non agrégées et / ou présentant un haut degré de dispersion en milieu aqueux, avec un rapport R, masse de polymère rapportée à la surface des particules de silice, compris entre 0,02 et 2 mg/m2 et dont la valeur de la charge électrostatique de la surface des particules de silice est supérieure ou égale à la valeur de la charge de la surface des particules de silice mesurée dans une phase aqueuse sans sels ajoutés à un pH supérieur ou égale à 7 ; b) on consolide les agrégats obtenus à l'étape a) soit par un traitement thermique, soit par précipitation d'un composé minéral.1. Process for the preparation of anisotropic silica aggregates which comprises the following stages: a) at least one polymer is brought into contact with non-aggregated silica particles and / or having a high degree of dispersion in an aqueous medium, with a ratio R, mass of polymer related to the surface of the silica particles, between 0.02 and 2 mg / m 2 and whose value of the electrostatic charge of the surface of the silica particles is greater than or equal to the value of the charge the surface area of the silica particles measured in an aqueous phase without added salts at a pH greater than or equal to 7; b) the aggregates obtained in step a) are consolidated either by heat treatment or by precipitation of an inorganic compound.
2. Procédé selon la revendication 1 caractérisé en ce que l'on réalise l'étape a) avec un rapport R, masse de polymère sur surface des particules de silice compris entre 0,05 et 1 ,8 mg/m2 .2. Method according to claim 1 characterized in that step a) is carried out with a ratio R, mass of polymer on the surface of the silica particles between 0.05 and 1.8 mg / m 2 .
3. Procédé selon l'une des revendications précédentes caractérisé en ce que l'on utilise un sol de silice dont la taille des particules de silice est comprise entre 3 et 50 nm, de préférence entre 5 et 20 nm.3. Method according to one of the preceding claims, characterized in that a silica sol is used, the size of the silica particles of which is between 3 and 50 nm, preferably between 5 and 20 nm.
4. Procédé selon l'une des revendications précédentes caractérisé en ce que l'on utilise un polymère choisi parmi les polymères linéaires, les homopolymères, les copolymères, les dendrimères ou les polymères greffés.4. Method according to one of the preceding claims, characterized in that a polymer chosen from linear polymers, homopolymers, copolymers, dendrimers or graft polymers is used.
5. Procédé selon la revendication 4 caractérisé en ce que l'on utilise un polymère choisi parmi la liste constituée par le groupe de polymères suivants : polyoxyéthylène (POE), alcool polyvinylique (APV), polyvinylpyrrolidone (PVP), polyacrylamide (PAM), polymethacrylamides, poly(N-isopropylacrylamide) (PNIPAM) et autres dérivés N-substitués, polysaccharides, en particulier l'amylose ou le dextrane, guar et dérivés, celluloses modifiées, polyvinylpyrrolidone- polyacideacrylique (PVP-PAA), polyoxyéthylène-polyacideacrylique (POE-PAA), polyacrylamide-polyvinylpyrrolidone (PAM-PVP), polyvinyl aminé, polydiallyldimethylammonium (PDADMAC), polyacrylamide- polydiallyldimethylammonium (PAM-PDADMAC), les polymères à base d'aminés quaternisés ou non, en particulier le polyéthylène imine, et ses copolymères avec des monomères non ioniques ou anioniques, polyvinylimidazole, polyamino alkyl acrylates et méthacrylates, les copolymères statistiques ou greffés de monomères anioniques tels que l'acide acrylique ou méthacrylique avec des monomères cationiques ou non ioniques et les polysaccharides carboxyméthylés.5. Method according to claim 4 characterized in that one uses a polymer chosen from the list consisting of the following group of polymers: polyoxyethylene (POE), polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), polyacrylamide (PAM), polymethacrylamides, poly (N-isopropylacrylamide) (PNIPAM) and other N-substituted derivatives, polysaccharides, in particular amylose or dextran, guar and derivatives, modified celluloses, polyvinylpyrrolidone- polyacideacrylic (PVP-PAA), polyoxyethylene-polyacideacrylic (POE -PAA), polyacrylamide-polyvinylpyrrolidone (PAM-PVP), polyvinyl amino, polydiallyldimethylammonium (PDADMAC), polyacrylamide- polydiallyldimethylammonium (PAM-PDADMAC), polymers based on quaternized or non-quaternized amines, in particular polyethylene imine, and its copolymers with nonionic or anionic monomers, polyvinylimidazole, polyamino alkyl acrylates and methacrylates, random or grafted copolymers of monomer es anionics such as acrylic or methacrylic acid with cationic or nonionic monomers and carboxymethylated polysaccharides.
6. Procédé selon l'une des revendications précédentes caractérisé en ce que l'on réalise à l'étape b) un traitement thermique à une température d'au moins 80°C, plus particulièrement d'au moins 100°C, de préférence d'au moins 120°C.6. Method according to one of the preceding claims, characterized in that a heat treatment is carried out in step b) at a temperature of at least 80 ° C, more particularly of at least 100 ° C, preferably at least 120 ° C.
7. Procédé selon l'une des revendications précédentes caractérisé en ce que l'on réalise à l'étape b) la précipitation d'un composé minéral choisi parmi les silicates, les phosphates, les silicophosphates, les aluminates, les silicoaluminates, le cérium, le zinc, le fer, le titane, le zirconium, les carbonates, les terres rares, les cations divalents ou leurs mélanges.7. Method according to one of the preceding claims, characterized in that, in step b), the precipitation of a mineral compound chosen from silicates, phosphates, silicophosphates, aluminates, silicoaluminates, cerium is carried out. , zinc, iron, titanium, zirconium, carbonates, rare earths, divalent cations or their mixtures.
8. Procédé selon la revendication 7 caractérisé en ce que le composé minéral est un silicate de sodium présentant un rapport pondéral Rp SiO2 /Na2O compris entre 0,5 et 4.8. Method according to claim 7 characterized in that the mineral compound is a sodium silicate having a weight ratio Rp SiO 2 / Na 2 O of between 0.5 and 4.
9. Procédé selon la revendication 7 ou 8 caractérisé en ce que l'on réalise la précipitation du silicate en ajoutant simultanément le silicate à précipiter et un agent acidifiant de manière à maintenir le pH à une valeur d'au moins 6.9. Method according to claim 7 or 8 characterized in that the precipitation of the silicate is carried out by simultaneously adding the silicate to be precipitated and an acidifying agent so as to maintain the pH at a value of at least 6.
10. Procédé selon la revendication 9 caractérisé en ce que l'on ajoute un agent acidifiant choisi parmi l'acide sulfurique, l'acide nitrique ou l'acide chlorhydrique, ou un acide organique tel que l'acide acétique, l'acide formique ou l'acide carbonique.10. Method according to claim 9 characterized in that one adds an acidifying agent chosen from sulfuric acid, nitric acid or hydrochloric acid, or an organic acid such as acetic acid, formic acid or carbonic acid.
11. Procédé selon l'une des revendications précédentes caractérisé en ce que l'on utilise à titre de polymère le poly(N-isopropylacrylamide).11. Method according to one of the preceding claims, characterized in that poly (N-isopropylacrylamide) is used as the polymer.
12. Produit susceptible d'être obtenu selon le procédé de la revendication 11.12. Product capable of being obtained according to the method of claim 11.
13. Agrégat de silice comprenant un enchaînement de particules élémentaires de silice dont le nombre de particules est compris entre 5 et 15, dont au moins 80% des particules élémentaires sont en contact avec au plus 2 particules et dont la plus grande distance mesurable entre 2 points de l'agrégat est inférieure ou égale à 5 fois la taille moyenne d'une particule élémentaire. 13. Silica aggregate comprising a sequence of elementary particles of silica the number of particles of which is between 5 and 15, of which at least 80% of the elementary particles are in contact with at most 2 particles and of which the greatest measurable distance between 2 points of the aggregate is less than or equal to 5 times the average size of an elementary particle.
4. Utilisation du produit selon la revendication 12 ou 13 comme charge renforçante d'une composition de polymères notamment de plastiques et de caoutchouc, agent viscosant texturant ou anti-mottant, agent anti-craquage notamment dans le domaine pétrolier, agent de polissage notamment des dentifrices et papiers, agent de revêtement notamment dans le domaine textile, absorbant de matière active, support de catalyseur, élément pour séparateurs de batteries. 4. Use of the product according to claim 12 or 13 as a reinforcing filler for a composition of polymers, in particular plastics and rubber, texturing or anti-caking viscosity agent, anti-cracking agent in particular in the petroleum field, polishing agent in particular of toothpaste and paper, coating agent in particular in the textile field, absorbent of active material, catalyst support, element for battery separators.
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US7884153B2 (en) 2011-02-08
WO2005007574A2 (en) 2005-01-27
FR2857351B1 (en) 2005-08-26
US20070219305A1 (en) 2007-09-20
JP4574614B2 (en) 2010-11-04
FR2857351A1 (en) 2005-01-14
JP2007527351A (en) 2007-09-27
WO2005007574A3 (en) 2005-06-30

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