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.

Landscapes

• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Engineering & Computer Science (AREA)
• Inorganic Chemistry (AREA)
• Nanotechnology (AREA)
• Materials Engineering (AREA)
• Condensed Matter Physics & Semiconductors (AREA)
• General Physics & Mathematics (AREA)
• Composite Materials (AREA)
• Crystallography & Structural Chemistry (AREA)
• Physics & Mathematics (AREA)
• Dispersion Chemistry (AREA)
• Silicon Compounds (AREA)
• Compositions Of Macromolecular Compounds (AREA)
• Pigments, Carbon Blacks, Or Wood Stains (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=33522940

Family Applications (1)

Country Status (5)

Families Citing this family (5)

Family Cites Families (4)

• 2003
  • 2003-07-10 FR FR0308467A patent/FR2857351B1/fr not_active Expired - Fee Related
• 2004
  • 2004-07-07 JP JP2006518288A patent/JP4574614B2/ja not_active Expired - Fee Related
  • 2004-07-07 US US10/563,792 patent/US7884153B2/en not_active Expired - Fee Related
  • 2004-07-07 WO PCT/FR2004/001763 patent/WO2005007574A2/fr active Application Filing
  • 2004-07-07 EP EP04767598A patent/EP1648823A2/de not_active Withdrawn

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events