EP1797006A2 - Method for production of nanoparticles with custom surface chemistry and corresponding colloids - Google Patents

Abstract

The invention relates to a method for production of a suspension of crystalline and/or consolidated, surface-modified, nanoscale particles in a dispersant, whereby said method comprises the following steps: a) a suspension of amorphous or partly-crystalline, non-surface-modified nanoscale particles is thermally-treated in a dispersant to crystallize and/or consolidate the particles and b) the suspension of the crystallised and/or consolidated non-surface-modified, nanoscale particles in the dispersant from (a) or in another dispersant is activated by mechanical stress in the presence of a modifier, such that the particles are surface-modified by the modifier to give a suspension of crystalline and/or consolidated surface-modified nanoscale particles. The dispersant can be removed from the obtained colloid to give the corresponding powder. Said method provides highly-dispersed particles with an average particle diameter of less than 20 nm which can be provided with a custom surface chemistry in a simple manner for the relevant application.

Description

Process for the preparation of nanoparticles with tailor-made surface chemistry and corresponding colloids

The present invention relates to a process for the preparation of colloids of crystalline and / or compacted, surface-modified, nanoscale particles in a dispersant and of powders of these crystalline and / or compacted, surface-modified, nanoscale particles.

The production of crystalline ZrO ₂ colloids with particle sizes in the lower nanometer range between 1 to 20 nm via hydrothermal synthesis has long been known. It is recognized that the use of stabilizing and / or surface-blocking substances can largely prevent the formation of agglomerates under hydrothermal conditions, thus making highly dispersed sols or modified ZrO ₂ particles accessible.

Thus, EP-A-0229657 and US-A-4784794 describe the preparation of highly dispersed, monoclinic ZrO ₂ sols by hydrothermal reaction of aqueous, zirconium-containing precursors obtained by the reaction of zirconyl chloride with water or by dissolution of zirconium salts in hydrochloric acid to be obtained. In this case, rod-shaped or ellipsoidal ZrO ₂ particles having a diameter of less than 10 nm are obtained. A disadvantage of this method is the very long duration of the hydrothermal reaction of more than 24 h, with a dilution to less than 1 mol / liter, a pH adjustment, which can be done by dialysis, ion exchange, ultrafiltration or addition of bases, and a subsequent Auf¬ concentration are required. This process is also limited to the production of ZrO 2 sols stabilized in aqueous HCl. Surface modification and doping are not described. Also, a mechanically activated surface modification under high shear is not provided.

US-A-5643497 discloses the preparation of stable aqueous zirconia sols having low surface activity for use as abrasives for the semiconductor industry. Production described. For this purpose, zirconium oxide powder is calcined, which was obtained from a sol having a particle size between 20 and 500 nm, and then dispersed again in water in the presence of water-soluble acids or bases. Stable ZrO ₂ colloids with a particle size of 20 to 1500 nm are obtained. The disadvantage is that the pulverization in a mill lasts between 20 and 100 h and is therefore uneconomical. For example, a grinding time of 96 h is required to obtain a particle size of 152 nm. Zirconia sols with particle sizes below 20 nm can not be prepared by this process.

US-A-5935275 and EP-A-0823885 describe the synthesis of weakly agglomerated nanoscale particles through the use of surfactants. The purpose of the surface-blocking substance is to control the particle size and to form a steric barrier against agglomeration. The surface-blocking substance may be removed from the surface of the particles and replaced with another surface-modifying substance. The removal of a surface-blocking substance is very expensive. According to this method, nanoscale particles in the range of 1 to 100 nm should be producible. A mechanically activated surface modification is not described.

US-A-5234870 describes processes for the preparation of transparent zirconia sols which are stable in the aqueous neutral and basic range as well as in organic solvents. However, the sols produced by hydrolysis at elevated temperature from zirconyl ammonium carbonate in the presence of a chelating agent are amorphous and thus can not be used in many areas. A mechanically activated surface modification under high shear is also not provided here.

HK Schmidt, R. Nass, D. Burgard, R. Nonninger describe in Mat. Res. Soc. Symp. Proc. Bd. 520; Pp. 21-31, entitled "Fabrication of agglomerate-free nanopowders by hydrothermal chemical processing", describes the preparation of nanoscale yttrium-stabilized ZrO ₂ by precipitation of Zr (O ¹¹ Pr) ₄ and Y (NO ₃ ) ₃ with aqueous Ammonia solution in the presence of an oleic acid ethylene oxide ester (OPE) as a surface-blocking substance with subsequent hydrothermal crystallization. Disadvantage of this method is the complicated removal of the surface-blocking substance. The powder is boiled in 8 N NaOH and toluene for 5 h, the residue obtained is subsequently washed several times with deionized water. Subsequent modification is by stirring with TODS. A mechanically activated surface modification under high shear is not provided.

In US-A-5037579 a hydrothermal process for the preparation of zirconia sols is described, wherein zirconium acetate / glacial acetic acid solutions are converted at 160 ⁰ C in zirconium oxide sols. The advantage of this method lies in the use of acetate solutions, which allows the use of steel autoclave. Sols with average particle sizes of 60 to 225 nm are obtained, these particles comprising agglomerates of subunits having an average size of 2 to 3 nm. Disadvantages of this process are the low concentrations of ZrO ₂ from 0.2 to 0.8 mol / liter, the complicated removal of unconverted zirconium acetate and excess glacial acetic acid and the subsequent concentration by ultrafiltration. This process is limited to the preparation of aqueous acetic acid stabilized ZrO ₂ sols. The use of other surface modifiers or doping of the particles are not described.

In US-A-6376590 a preparation of ZrO2 sols is described, which should have an average particle size of 7 to 20 nm. Starting from zirconium polyether carboxylates obtained from zirconium salts and polyether carboxylic acids, ZrO ₂ sols are obtained by hydrothermal hydrolysis. In general, the hydrothermal reaction is carried out above 175 ° C for 16 to 24 h. The ZrO ₂ particles are surface-modified with the corresponding polyether carboxylic acids, ie the acid liberated in the reaction serves as a surface-modifying component. Disadvantage of this method is that only a portion of the liberated polyether carboxylic acid is necessary for the surface modification of the particles. The excess part must be removed consuming. The polyethercarboxylic acids can also be replaced by other surface-modifying acids exchanged, but their use also requires a complex workup. A doping of the particles or a mechanically activated Oberflächen¬ modification under strong shear are not described.

The object of the present invention is to be able to produce surface-modified, crystalline and / or compacted, doped and undoped nanoparticles, in particular ZrO ₂ nanoparticles, or colloids thereof having an average particle size of not more than 20 nm, which are the various disadvantages of the prior art no longer exhibit the technology, but can be produced in a simple and cost-effective manner with high yield and with a surface chemistry that can be adapted specifically to the other requirements of the application, without requiring surface blocking and / or stabilizing substances during the thermal process , which must be subsequently removed and / or replaced by additional steps. Likewise, the method according to the invention should enable a broad spectrum of applications with regard to doping, dispersing medium and surface modification of the particles, in particular the ZrO ₂ particles, or the colloids thereof.

Surprisingly, this could be achieved by the process of the present invention, with which suspensions or colloids of crystalline and / or compacted, surface-modified, nanoscale particles or, after removal of the dispersant, a powder of these particles are obtained in a simple manner and with high yield can be, with it being particularly advantageous that the particles are not oberfiächenmodifiziert after thermal or hydrothermal treatment, so that the surface modification can be done in a simple manner and especially tailor made for later use. Surprisingly, in step b), good deagglomeration or deaggregation of the particles is achieved.

Accordingly, the present invention provides a process for producing a suspension of crystalline and / or compacted, surface-modified, nanoscale particles in a dispersant, the process comprising the following steps: a) a suspension of amorphous or partially crystalline, not surface-modified, nanoscale particles in a dispersant is heat treated to crystallize and / or compress the particles, and b) the suspension of the crystallized and / or compacted, not oberflächen¬ modified nanoscale particles in the dispersant of step a) or in another dispersant is activated in the presence of a modifier by mechanical stress, so that the particles are surface-modified by the modifier to form a suspension of crystalline and / or compacted, surface-modified, to obtain nanoscale particles.

The suspensions obtained are preferably colloidal solutions or colloids or sols. By removing the dispersant, a powder of the crystalline, surface-modified, nanoscale particles can be obtained from the resulting suspensions essentially without agglomeration or aggregation of the particles. By the method of the present invention, colloids or powders having an average particle diameter of not more than 20 nm can be obtained.

The nanoscale starting particles are subjected to a heat treatment in step a) for crystallization and / or densification, without the particles being or being surface-modified. Although agglomerated or aggregated particles can thereby be obtained, in step b), surprisingly, deagglomeration or deaggregation of the particles takes place so that particles having an average particle diameter of not more than 20 nm and even down to 1 nm can be obtained.

In this case, it is of particular advantage that in step b) it is possible to start from not surface-modified particles, so that the surface modification can be tailored to the intended application. Elaborate removal of a surface modification present on the particles and subsequent functionalization with suitable groups are not required. On the one hand, this novel process avoids complex process steps, such as the removal of the surface modifiers required in the production / crystallization, and on the other hand, application-optimized powders or colloids can be produced by the mechano-chemical deagglomeration or deaggregation step.

1 shows an X-ray diffraction diagram of ZrO ₂ particles which are used as starting material for the method according to the invention. FIG. 2 shows an X-ray diffraction diagram of the ZrO ₂ particles of FIG. 1 after the heat treatment of the invention.

In step a), a suspension of amorphous or partially crystalline, non-surface-modified, nanoscale particles in a dispersant is subjected to a heat treatment, wherein no modifying agents are present which lead to a surface modification of the particles under the conditions used. Without a modifier, a heat treatment always leads to a more or less strong agglomeration / aggregation of the particles (van der Waals forces / particle growth).

The particles used are solid particles or solid particles of any suitable material. It may preferably be inorganic particles. Examples of inorganic particles are particles of an element, an alloy or an element compound. The inorganic particles preferably consist of metals, alloys and in particular of metal compounds and compounds of semiconductor elements, such as Si or Ge, or boron.

Examples of particles of one element are particles of carbon, such as carbon black or activated carbon, of a semiconductor, such as silicon (including technical grade Si, ferrosilicon and pure silicon) or germanium, or a metal, such as iron (including steel), chromium, Tin, copper, aluminum, titanium, gold and zinc. Examples of particles of an alloy may be particles of bronze or brass. Examples of the preferred metal compounds and compounds of Halbleiter¬ elements or boron are oxides which are optionally hydrated, such as ZnO, CdO, SiO ₂ , GeO ₂ , TiO ₂ , Al-coated rutile, ZrO ₂ , CeO ₂ , SnO ₂ , Al ₂ O ₃ (in all modifi cations, especially as corundum, boehmite, AIO (OH), also as aluminum hydroxide), manganese oxides, In ₂ O ₃ , Y ₂ O ₃ , La ₂ O ₃ , iron oxides such as Fe ₂ O ₃ , Cu ₂ O, Ta ₂ O ₅ , Nb ₂ O ₅ , V ₂ O ₅ , MoO ₃ or WO ₃ , BaO and CaO, corresponding mixed oxides, eg indium tin oxide (ITO), antimony tin oxide (ATO) fluoro-doped tin oxide (FTO), calcium tungstate and perovskite structure such as BaTiO ₃ , BaSnO ₃ and PbTiO ₃ , chalcogenides such as sulfides (eg CdS, ZnS, PbS and Ag ₂ S), selenides (eg GaSe, CdSe and ZnSe) and tellurides (eg ZnTe or CdTe), halides such as AgCl, AgBr, AgI, CuCl, CuBr, CdI ₂ and PbI ₂ , carbides such as CdC ₂ or SiC, silicides such as MoSi ₂ , arsenides such as AIAs, GaAs and GeAs, antimonides, such as InSb, N Itride, such as BN, AIN, Si ₃ N ₄ and Ti ₃ N ₄ , phosphides, such as GaP, InP, Zn ₃ P ₂ and Cd ₃ P ₂ , as well as carbonates, sulfates, phosphates, silicates, zirconates, aluminates and stannates of elements , in particular of metals or Si, for example carbonates of calcium and / or magnesium, silicates, such as alkali silicates, talc, clays (kaolin) or mica, and sulfates of barium or calcium. Further examples of suitable particles are also magnetite, maghemite, spinels (eg MgO-Al ₂ O ₃ ), MuMt, eskolait, tialite, SiO ₂ TiO ₂ , or bioceramics, eg calcium phosphate and hydroxyapatite. It can be particles of glass or ceramic.

These may be, for example, particles which are usually used for the production of glass (eg borosilicate glass, soda lime glass or silica glass), glass ceramic or ceramic (eg based on the oxides SiO ₂ , BeO, Al ₂ O ₃ , ZrO ₂ or MgO or the corresponding mixed oxides, electric and magnetic ceramics, such as titanates and ferrites, or non-oxide ceramics, such as silicon nitride, silicon carbide, boron nitride or boron carbide) can be used. It can also be particles that serve as fillers or pigments. Technically important fillers are, for example, fillers based on SiO ₂ , such as quartz, cristobalite, tripolite, novaculite, kieselguhr, silica, pyrogenic silicic acids, precipitated silicas and silica gels, silicates, such as talc, pyrophyllite, kaolin, mica, muscovite, phlogopite, vermiculite, wollastonite and perlites, carbonates, such as calcites, dolomites, chalks and synthetic calcium carbonates, carbon black, sulphates, such as Barite and Leichtspat, iron mica, glasses, aluminum hydroxides, Alumi¬ niumoxide and titanium dioxide.

It is also possible to use mixtures of these particles. Particularly preferred materials for the particles are oxide particles or hydrated oxide particles, in particular metal or semimetal oxides, hydrated metal or semimetal oxides or mixtures thereof. Preferred are oxides or hydrated oxides, at least one element selected from Mg, Ca, Sr, Ba, Al, Si, Sn, Pb, Bi, Ti, Zr, V, Mn, Nb, Ta, Cr, Mo, W, Fe, Co, Ru, Zn, Ce, Y, Sc, Eu, In and La or mixtures thereof. Particularly preferred examples are ZrO ₂ , TiO ₂ , SnO ₂ , ITO (indium tin oxide), ATO (antimony-doped tin oxide), In ₂ O ₃ , Y ₂ O ₃ , CeO ₂ , BaTiO ₃ , SnTiO ₃ , ZnO , BaO and CaO, which are optionally hydrated.

The preparation of the starting particles can be carried out in the usual way, e.g. by flame pyrolysis, plasma processes, gas-phase condensation processes, colloid techniques, precipitation processes, sol-gel processes, controlled nucleation and growth processes, MOCVD processes and (micro) emulsion processes. These methods are described in detail in the literature. Preferably, the particles are obtained by the sol-gel method or precipitation method. Suitable particles may also be commercially available. Thus, e.g. commercially available sols such as e.g. Zirconia sols from Nyacol be used.

The particles may also be doped, preferably with at least one other metal. For doping, any suitable metal compound may be added in the preparation of the particles, eg an oxide, salt or complex compound, eg halides, nitrates, sulfates, carboxylates (eg acetates) or acetylacetonates used as molecular precursors in the preparation of the particles , The other metal may be present in the compound in any suitable oxidation precursor. Examples of suitable metals for the metal compound are W, Mo, Zn, Cu, Ag, Au, Sn, In, Fe, Co, Ni, Mn, Ru, V, Nb, Ir, Rh, Os, Pd and Pt. Particularly preferred metals for doping are Mg, Ca, Y, Sc and Ce, in particular for ZrO ₂ . Specific examples of metal compounds for doping are Y (NO ₃ ) ₃ -4H ₂ O, Sc (NO ₃ ) ₃ -6H ₂ O, WO ₃ , MoO ₃ , FeCl ₃ , silver acetate, zinc chloride, copper (II) chloride, indium (III) oxide and tin (IV) acetate. The atomic ratio of doping element / element of the basic compound, eg Zr, can be selected as required and is for example from 0.0005: 1 to 0.2: 1.

As the starting material, non-surface-modified particles in the form of a powder or a suspension may be used in a dispersing agent. The powder is suspended in a dispersant. The suspension can be used as it is or the dispersant can be exchanged by known methods for another dispersant more suitable for the particular purpose. The particles can also be obtained in the dispersant by precipitating a dissolved precursor in situ. The resulting particles are amorphous or semi-crystalline, nanoscale particles that are not surface modified.

For the preparation of the starting particles, molecular precursors of the particles dissolved in a solvent, e.g. be subjected to a condensation and / or precipitation reaction. The molecular precursors may be e.g. hydrolyzable compounds, salts or soluble hydroxides. The conversion into solid particles can be carried out e.g. by a precipitation reaction in which poorly soluble compounds are formed. Preferably, the particles are obtained by adding water to the solution of the molecular precursors and / or by changing the pH. The adjustment of the pH required for the precipitation can be achieved in principle by using any basic or acidic compound which is soluble in the respective solvent.

In the following, various possibilities for producing particles using the example of the production of ZrO _{2 will be} explained. Particles of other optionally hydrated elemental oxides can be prepared analogously using the corresponding element compounds, where Zr is in each case to be replaced by the desired element or a mixture of two or more elements.

Examples of precursors for zirconium oxide are discussed below. Examples of other molecular precursors are Y (NO ₃ ) ₃ (optionally hydrated, for Y ₂ O ₃ ); Zn-acetate, Mn-acetate; FeCl ₂ , FeCl ₃ (for iron oxides); Al (NO ₃ ) ₃ (for Al ₂ O ₃ ); SnCl ₄ , SbCl ₃ (for tin oxide or ATO, respectively); Aluminum alcoholates such as Al (O ⁵ Bu) ₃ , titanium alkoxides such as Ti (O ¹ Pr) ₄ (for Al-coated rutile); Ba (OH) ₂ , titanium alkoxides such as titanium tetra- propoxide (for barium titanate); Na ₂ WO ₄ , calcium carboxylates such as Ca (O ₂ Pr) ₂ (for calcium tungstate); or InCI ₃ , SnCI ₄ (for ITO).

Examples of suitable molecular precursors for Zr are ZrO (NO ₃ ) ₂ , ZrCl ₄ or zirconium alcoholates (Zr (OR ₄ ), where R is alkyl, preferably C 1 -C ₄ -alkyl). Examples of dopants are listed above.

Preferably, from a solution or a sol containing zirconium in a suitable form, for example as a molecular compound or salt, amorphous or semi-crystalline nanoscale particles of ZrO ₂ or hydrated ZrO _{2 are} precipitated by changing the pH and / or by addition of water , If doped particles are to be produced, the sol or solution additionally contains one or more doping elements likewise in the form of molecular precursors which can be precipitated, for example, as oxide or hydrated oxide. The doping elements are, for example, those which are suitable for the production of glass or ceramic, for example Mg, Ca, Y, Sc and Ce.

The zirconium-containing solution or zirconium-containing sol may be both aqueous and non-aqueous (organic). An aqueous starting solution contains Zr-containing molecular precursors in a dissolved form and molecular precursors optionally containing doping elements, which can be precipitated by changing the pH as oxide or hydrated oxide of Zr, which is optionally doped. Corresponding nonaqueous solutions may contain corresponding molecular precursors which can be precipitated without changing the pH, e.g. by mere addition of water.

The zirconium-containing molecular precursor comprising oxide or hydrated oxide and, if appropriate, the molecular precursors containing further precipitable elements for doping are preferably hydrolyzable salts in aqueous starting solutions; hydrolyzable compounds and, in particular, hydrolyzable organometallic compounds are preferred in nonaqueous solutions. Next It is also possible to use simple salt solutions which can be prepared, for example, by hydrolyzing a metal alkoxide which is dissolved in, for example, a short-chain alcohol (for example a C ₁ -C ₃ -alcohol) by addition of water.

A general method for the preparation of nanoscale particles of hydrolyzable compounds is the sol-gel method. In the sol-gel process, usually hydrolyzable compounds are hydrolyzed with water, optionally with acidic or basic catalysis, and optionally at least partially condensed. The hydrolysis and / or condensation reactions lead to the formation of compounds or condensates with hydroxyl, oxo groups and / or oxo bridges which serve as precursors. It is possible to use stoichiometric amounts of water, but also smaller or larger quantities. The forming SoI can be determined by suitable parameters, e.g. Condensation degree, solvent or pH to which the viscosity desired for the coating composition is adjusted. Further details of the sol-gel process are e.g. at CJ. Brinker, G.W. Scherer: "SoI-GeI Science - The Physics and Chemistry of Sol-Ge-Processing", Academic Press, Boston, San Diego, New York, Sydney (1990).

The mean particle diameter of the nanoscale particles used in step a) can be greater than that of the particles obtained by the process according to the invention. At least, larger particles are usually present after the execution of step a), since the particles are then usually present in agglomerated or aggregated form. Nanoscale particles have an average particle diameter of less than 1 μm. The nanoscale particles used in step a) preferably have an average particle diameter of less than 0.2 μm.

The nanoscale particles used in step a) are amorphous or partially crystalline. Furthermore, the nanoscale particles used in step a) are not surface-modified particles, ie no modifying agents are present on the surface. As the dispersant, any solvent can be used so long as it does not dissolve or substantially dissolve the particles to be treated. The suitable dispersant is preferably selected from water or organic solvents, depending on the particles to be treated, but also inorganic solvents such as carbon disulfide are conceivable.

A particularly preferred dispersant is water, especially deionized water. Suitable organic dispersants are both polar and nonpolar and aprotic solvents. Examples of these are alcohols, e.g. aliphatic and alicyclic alcohols having 1 to 8 carbon atoms (especially methanol, ethanol, n- and i-propanol, butanol, octanol, cyclohexanol), ketones, e.g. aliphatic and alicyclic ketones of 1 to 8 carbon atoms (especially acetone, butanone and cyclohexanone), esters such as e.g. Ethyl acetate and glycol esters, ethers, e.g. Diethyl ether, dibutyl ether, anisole, dioxane, tetrahydrofuran and tetrahydropyran, glycol ethers such as mono-, di-, tri- and polyglycol ethers, glycols such as ethylene glycol, diethylene glycol and propylene glycol, amides and other nitrogen compounds, e.g. Dimethylacetamide, dimethylformamide, pyridine, N-methylpyrrolidine and acetonitrile, sulfoxides and sulfones, e.g. Sulfolane and dimethyl sulfoxide, nitro compounds, such as nitrobenzene, halogenated hydrocarbons, such as dichloromethane, chloroform, carbon tetrachloride, trichlorethylene, tetrachloroethene, ethylene chloride, chlorofluorocarbons, aliphatic, alicyclic or aromatic hydrocarbons, e.g. with 5 to 15 carbon atoms, such as e.g. Pentane, hexane, heptane and octane, cyclohexane, benzines, petroleum ethers, methylcyclohexane, decalin, terpene solvents, benzene, toluene and xylene. Of course, mixtures of such dispersants can be used.

Preferred organic dispersants are aliphatic and alicyclic alcohols such as ethanol, n- and i-propanol, glycols such as ethylene glycol, and aliphatic, alicyclic and aromatic hydrocarbons such as hexane, heptane, toluene and o-, m- and p-xylene. Particularly preferred dispersants are ethanol and toluene. After the suspension of nanoscale particles has been formed or provided by any of the above methods, it undergoes conditions which result in densification and / or crystallization of the nanoscale particles. The specific conditions, such as temperature, pressure and duration, of course, for example, depend on the nature and nature of the particles used and the solvent, the mode of operation and also on each other. The person skilled in the art can choose the appropriate conditions for the compaction and / or crystallization of the particles on the basis of his expertise. Appropriate areas are given below. The heat treatment is expediently carried out under conditions in which the suspension or more precisely the dispersant remains essentially in the liquid phase, ie the crystallization / densification in the liquid phase takes place.

The suspension is exposed to crystallization and / or compression of an elevated temperature and optionally to an elevated pressure. This treatment is preferably carried out below the critical data of the solvent present. Of course, the elevated temperatures must also ensure that the solvent does not decompose or only slightly decomposes. This treatment can be carried out both in a batch process and in a continuous manner. Through the use of continuous systems, the reaction time can be significantly reduced. In general, the duration of treatment may be e.g. 1 minute to 3 days or 1 minute to 24 hours. The treatment time, in particular in the case of continuous processes, is preferably in the range from 1 minute to 2 hours, preferably from 5 minutes to 60 minutes, particularly preferably from 10 minutes to 30 minutes.

By elevated temperature is meant for the heat treatment in general a temperature of at least 60 ° C and particularly preferably at least 80 ° C, for example 120 to 400 ° C. The heat treatment is particularly preferably carried out in a temperature range from 150 to 350 ^° C. The pressure can be ambient pressure or excess pressure, for example in the range from 1 to 300 bar. The heat treatment preferably takes place at elevated pressure of more than 1 bar. The pressure may be at least about 5 bar, for example. Preferably, an elevated pressure of about 10 to 300 bar is used. For example, the suspension containing the nanoscale particles is preferably added to a pressure vessel without further pretreatment and, if appropriate, treated at the appropriate pressure and temperature. Conveniently, an autogenous pressure is built up, ie by the heating, in particular on the boiling point of the solvent, a pressure is built up in the closed pressure vessel or autoclave.

The treatment is usually a lyothermal and preferably a hydrothermal treatment. A hydrothermal treatment generally means a heat treatment of an aqueous solution or suspension under overpressure, e.g. at a temperature above the boiling point of the Lösungs¬ means and a pressure above 1 bar. In the aqueous solution, the dispersing agent comprises water or it preferably consists essentially of water.

By the treatment according to step a), crystalline and / or compressed particles are obtained from amorphous or partially crystalline particles. Semicrystalline particles include not only crystalline phases but also amorphous phases, i. it can be detected amorphous areas. Crystalline particles consist essentially entirely of crystalline phase, i. there is essentially no amorphous portion or measurable amorphous portion. Compacted particles are here particles which are for the most part or preferably substantially maximally compressed, that is, can not be densified further based on their chemical structure. Nanoparticles can e.g. have less ordered areas in the outer area of the particle, resulting in X-ray propagation. These areas may be densified by the method of the invention.

Crystallization and compression are often mutually dependent. Thus, a seal can often be associated with a crystallization. In a crystallization is usually also a compaction. According to the present invention, crystalline, surface-modified, nanoscale particles are preferably obtained, ie, the particles essentially contain no amorphous particles. In this case, heat treatment is carried out in step a) in order to crystallize the particles. The obtained crystalline particles are then surface-modified in step b). As explained above, such crystallization is often associated with compaction of the particles.

The proportion of crystalline and amorphous phases in particles can be examined by X-ray diffraction diagrams. Crystalline particles usually show a baseline from which individual peaks emerge. For example, are in Ulimanns, Encyclopedia of Industrial Chemistry, Verlag Chemie, 4th Edition, Vol. 5, pages 256 and 257, X-ray diffraction patterns of particles with different content of crystalline phase listed. The person skilled in the art can determine whether an amorphous fraction can still be measured in the particles.

1 shows an X-ray diffraction diagram of ZKV particles which were used as starting particles for the process. The diagram shows that amorphous phases are present in the particles. For example, the hump at about 30 ° indicates that the particles also contain crystalline phases. The particles are thus partially crystalline. Fig. 2 shows an X-ray diffraction pattern of the particles of Fig. 1, from which after crystallization according to step a) crystalline particles have been obtained. The crystalline particles show in the diagram e.g. Peaks at about 30 °, 50 ° and 60 °.

In this way, crystallized and / or compacted, not surface-modified, nanoscale particles are obtained as a suspension in a dispersant, which are usually more or less agglomerated or aggregated. The suspension may be used as it is directly or, if another dispersant is more convenient, after replacement of the dispersant in step b). It is also possible to interpose a purification step in order to at least partially or completely remove process by-products in the suspension obtained after step a). In the cleaning step, the dispersant is preferably at least partially replaced with fresh dispersant, which may be the same as before or otherwise.

In the optional purification step, the suspensions of densified or crystallized particles of process by-products, such as alcohols, are passed through the hydrolysis of alkoxides are formed, or ionic impurities which arise when using salt solutions, separated and, if necessary, concentrated or dried. The removal of the process by-products can be done by simple removal (even partial) or replacement of the solvent. All methods known to those skilled in the art are suitable for this purpose.

The preferred starting point is that nanoparticles agglomerate or flocculate at their isoelectric point. For this purpose, the suspensions obtained from the heat treatment are adjusted to the corresponding isoelectronic pH and flocculated. The adjustment takes place by means of acids and bases. The supernatant containing the process by-products is removed after sedimentation of the nanoscale particles. The resulting high-solids sedimentation product contains the nanoscale particles, by addition of e.g. distilled water is again obtained diluted suspensions. If appropriate, the process of flocculation and the removal of the supernatant can be repeated until the process by-products have been removed or largely removed.

In this way, high-purity and high-solids nanoscale particles containing suspensions can be prepared in an organic solvent or preferably aqueous suspensions. From these, by complete removal of the organic solvent or water by methods such as e.g. Distillation or freeze-drying powder can be produced. It is also possible to prepare non-aqueous suspensions from the high-purity aqueous suspensions containing the particles. This can e.g. by processes such as solvent exchange.

In step b), suspensions or colloids of crystalline and / or compacted, surface-surface-modified, nanoscale particles are obtained from the crystallized and / or compacted, non-surface-modified, nanoscale particles obtained in step a), which have optionally been subjected to a purification step or a dispersant exchange , produced by passing the suspension directly to a mechanically activated process under high shear in the presence of a Surface modifier is subjected. In this case, a specific surface modification takes place and at the same time a stabilization of the particles against agglomeration. As a rule, deagglomeration or deaggregation of the particles also takes place. From the obtained colloids, powders can be obtained from the particles by removing the dispersant.

The particles are mechanically activated in the dispersant in the presence of a modifying agent, that is to say, in the mechanical activation, in the presence of the modifying agent, an interaction of the modifying agent with the particle or the comminuted particle takes place, preferably a chemical bond. As a rule, this mechanical activation also leads to deagglomeration or deaggregation, i. a crushing. The mechanical input of energy is in particular so high that the particles are surface-modified. Such a reaction under mechanical stress is also called chemo-mechanical reaction.

It is known to those skilled in the art that there are usually groups on the surface of particles which are not found in this form inside the particles. Usually, these surface groups are functional groups that are generally relatively reactive. For example, as such surface groups, residual valences such as hydroxy groups and oxy groups, e.g. for metal oxide particles, or thiol groups and thio groups, e.g. for metal sulfides, or amino, amide and imide groups, e.g. with nitrides.

As a modifier, all compounds which can strongly interact with the surface of the particles or surfactants can be used. It is also possible to use more than one surface-modifying substance, e.g. a mixture of at least two. In one variant of the method, the modifier used can also act as a dispersant at the same time, so that the same compound is used for both.

The modifying agent preferably has at least one functional group which at least under the conditions of mechanical activation chemical bond with the surface groups of the particles can enter. The chemical bond is preferably a covalent, ionic or coordinate bond between the modifier and the particle, but also hydrogen bonds. By a coordinative bond is meant a complex formation. Thus, for example, an acid / base reaction according to Bronsted or Lewis, a complex formation or an esterification can take place between the functional groups of the modifier and the particle.

The functional group comprising the modifying agent is preferably carboxylic acid groups, acid chloride groups, ester groups, nitrile and isonitrile groups, OH groups, SH groups, epoxide groups, anhydride groups, acid amide groups, primary, secondary and tertiary amino groups, Si-OH Groups, hydrolyzable groups of silanes (groups Si-OR explained below) or CH-acid groups, as in β-dicarbonyl compounds.

The modifying agent may also comprise more than one such functional group, e.g. in betaines, amino acids or EDTA.

In addition to the at least one functional group which can form a chemical bond with the surface group of the particle, the modifying agent generally has a molecular radical which, after linking the modifying agent via the functional group, modifies the properties of the particle. The remainder of the molecule or a part thereof may be, for example, hydrophobic or hydrophilic or carry a second functional group in order to functionalize the colloid particles with respect to the environment, ie to stabilize, compatibilize, inertise or reactivate, for example. In this way, the colloid particles obtained according to the invention are provided with a function or surface functionalization by this molecular residue. The invention makes it possible to obtain nanoscale particles with tailor-made surface chemistry adapted to the desired intended use. Depending on the system, covalent bonds, ionic bonds and complex bonds may be present as principles for the coupling to the particles, but hydrogen bonds are also suitable. Hydrophobic molecule radicals can be, for example, alkyl, aryl, alkaryl, aralkyl or fluorine-containing alkyl groups which, if the environment is suitable, can lead to inerting or repulsion. Examples of hydrophilic groups would be hydroxy, alkoxy or polyether groups. The optionally present second functional group of the modifying agent may be, for example, an acidic, basic or ionic group. It may also be a functional group suitable for a chemical reaction with a selected reactant. The second functional group can be the same, which is also suitable as a functional group for binding to the particle, so that reference is made to the examples mentioned there. Other examples of a second functional group would be epoxy, acryloxy, methacryloxy, acrylate or methacrylate groups. There may be two or more of the same or different such functional groups.

The modifier preferably has a molecular weight of not more than 500, more preferably not more than 400, and especially not more than 200. The compounds are preferably liquid under normal conditions. The functional groups carrying these compounds depend primarily on the surface groups of the particulates and the desired interaction with the environment. Molecular weight also plays an important role in diffusion to the freshly formed particle surfaces. Small molecules lead to a rapid occupancy of the surface and thus reduce recombination.

Accordingly, examples of suitable modifying agents are saturated or unsaturated mono- and polycarboxylic acids, the corresponding acid anhydrides, acid chlorides, esters and acid amides, amino acids, imines, nitriles, isonitriles, epoxy compounds, mono- and polyamines, β-dicarbonyls such as β-diketones, silanes and metal compounds having a functional group capable of reacting with the surface groups of the particles. Particularly preferably used modifying agents are silanes, carboxylic acids, β-dicarbonyls, amino acids and amines. The carbon chain of these compounds may be interrupted by O, S, or NH groups. One or more modifiers may be used. Preferred saturated or unsaturated monocarboxylic and polycarboxylic acids (preferably monocarboxylic acids) are those having 1 to 24 carbon atoms, such as, for example, formic acid, acetic acid, propionic acid, butyric acid, pentanoic acid, hexanoic acid, acrylic acid, methacrylic acid, crotonic acid, citric acid, adipic acid, succinic acid, Glutaric acid, oxalic acid, maleic acid, fumaric acid, itaconic acid and stearic acid and the corresponding acid anhydrides, chlorides, esters and amides, for example caprolactam. Of these carboxylic acids mentioned above, those are also included whose carbon chain is interrupted by O, S or NH groups. Particularly preferred are ether carboxylic acids such as mono- and polyether carboxylic acids and the corresponding acid anhydrides, chlorides, esters and amides, for example methoxyacetic acid, 3,6-dioxaheptanoic acid and 3,6,9-trioxadecanoic acid.

Examples of preferred mono- and polyamines are those of the general formula Ch-nNHn, where n = 0, 1 or 2 and the radicals Q independently of one another are alkyl having 1 to 12, in particular 1 to 6 and particularly preferably 1 to 4, carbon atoms, for example methyl , Ethyl, n- and i-propyl and butyl, and aryl, alkaryl or aralkyl having 6 to 24 carbon atoms, such as phenyl, naphthyl, ToIyI and benzyl, and polyalkyleneamines of the general formula Y 2 N (-Z-NY) _y - Y, wherein Y is independently Q or H, wherein Q is as defined above, y is an integer from 1 to 6, preferably 1 to 3, and Z is an alkylene group having 1 to 4, preferably 2 or 3 Kohlenstoff¬ atoms , Concrete examples are methylamine, dimethylamine, trimethylamine, ethylamine, aniline, N-methylaniline, diphenylamine, triphenylamine, toluidine, ethylenediamine, diethylenetriamine.

Preferred β-dicarbonyl compounds are those having 4 to 12, in particular 5 to 8, carbon atoms, for example diketones, such as acetylacetone, 2,4-hexanedione, 3,5-heptanedione, acetoacetic acid, C 1 -C ₄ -alkyl acetoacetate, such as acetoacetic acid ethyl ester, diacetyl and acetonylacetone.

Examples of amino acids are β-alanine, glycine, valine, aminocaproic acid, leucine and isoleucine. Preferably used silanes have at least one nonhydrolyzable group or a hydroxy group, more preferably hydrolyzable organosilanes are used, which additionally have at least one nonhydrolyzable radical. Preferred silanes have the general formula (I)

RaSiX ( _4- a) (I) wherein the radicals R are the same or different and are not hydrolyzable groups, the radicals X are the same or different and represent hydrolyzable groups or hydroxy groups and a is 1, 2 or 3. The value a is preferably 1.

In the general formula (I), the hydrolysable groups X, which may be the same or different, for example, hydrogen or halogen (F, Cl, Br or I), alkoxy (preferably Ci _-6 alkoxy, such as methoxy, ethoxy, n-propoxy, i-propoxy and butoxy), aryloxy (preferably C ₆ i ₀ aryloxy, such as phenoxy), acyloxy (preferably _{Ci-6-acyloxy,} such as acetoxy or propionyloxy), alkylcarboxylic carbonyl (preferably C ₂ - ₇ alkyl-carbonyl such as acetyl), amino, monoalkylamino or dialkylamino having preferably 1 to 12, especially 1 to 6 carbon atoms. Preferred hydrolyzable radicals are halogen, alkoxy groups and acyl oxy groups. Particularly preferred hydrolysable radicals are C _1-4 alkoxy groups, in particular methoxy and ethoxy.

The nonhydrolyzable radicals R, which may be the same or different, may be nonhydrolyzable radicals R with or without a functional group.

The non-hydrolyzable radical R without a functional group is, for example, alkyl (preferably C _1-8 -alkyl, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl and tert-butyl, pentyl, hexyl, octyl or cyclohexyl), alkenyl (preferably C _2-6 alkenyl such as vinyl, 1-propenyl, 2-propenyl and butenyl), alkynyl (preferably C _2-6 alkynyl such as acetylenyl and propargyl), aryl (preferably C _6-10 -aryl, such as phenyl and naphthyl) and corresponding alkaryls and aralkyls (eg ToIyI, Beπzyl and phenethyl). The radicals R and X may optionally have one or more customary substituents, such as halogen or alkoxy. Preference is given to alkyltrialkoxysilanes. Examples are:

CH ₃ SiCl ₃ , CH ₃ Si (OC ₂ Hs) ₃ , CH ₃ Si (OCHs) ₃ , C ₂ H ₅ SiCl ₃ , C ₂ H ₅ Si (OC ₂ Hs) ₃ , C ₂ H ₅ Si (OCHs) ₃ , C ₃ H ₇ Si (OC ₂ Hs) ₃ , (C ₂ H ₅ O) ₃ SiC ₃ H ₆ Cl, (CH ₂ ) ₂ SiCl ₂ , (CH ₃ ) ₂ Si (OC ₂ H ₅ ) ₂ , CH _{3) 2} Si (OH) _2, C ₆ H ₅ Si (OCH _{3) S,} C ₆ H ₅ Si (OC ₂ Hs) _3, C ₆ H ₅ CH ₂ CH ₂ Si (OCH ₃₎ S, (C ₆ Hs) ₂ SiCl ₂ , (C ₆ H ₅ ) ₂ Si (OC ₂ H ₅ ) ₂ , (iC ₃ H ₇ ) ₃ SiOH, CH ₂ = CHSi (OOCCH ₃ ) ₃ , CH ₂ = CHSiCl ₃ , CH ₂ = CH-Si (OC ₂ Hs) ₃ , CH ₂ = CHSi (OC ₂ Hs) ₃ , CH ₂ = CH-Si (OC ₂ H ₄ OCH ₃ ) ₃ , CH ₂ = CH-CH ₂ -Si (OC ₂ Hs) ₃ , CH ₂ = CH-CH ₂ -Si (OC ₂ Hs) ₃ , CH ₂ = CH-CH ₂ -Si (OOCCH ₃ ) ₃ , n-C ₆ Hi ₃ -CH ₂ -CH ₂ -Si ( OC ₂ Hs) ₃ , and nC ₈ H ₁₇ -CH ₂ -CH ₂ -Si (OC ₂ H ₅ ) ₃ .

The nonhydrolyzable radical R having a functional group may e.g. as a functional group an epoxide (eg glycidyl or glycidyloxy), hydroxy, ether, amino, monoalkylamino, dialkylamino, optionally substituted anilino, amide, carboxy, acrylic, acryloxy, methacrylic, Methacryloxy, mercapto, cyano, alkoxy, isocyanato, aldehyde, alkylcarbonyl, acid anhydride and Phosphorsäure¬ group. These functional groups are bonded to the silicon atom via alkylene, alkenylene or arylene bridging groups which may be interrupted by oxygen or -NH groups. The bridging groups preferably contain 1 to 18, preferably 1 to 8 and in particular 1 to 6 carbon atoms.

The divalent bridging groups mentioned and optionally present substituents, as in the case of the alkylamino groups, are derived, for example, from from the above-mentioned monovalent alkyl, alkenyl, aryl, alkaryl or aralkyl radicals. Of course, the radical R may also have more than one functional group.

Preferred examples of non-hydrolysable radicals R having functional groups are a glycidyl or glycidyloxy- (C _-20) alkylene radical, such as beta-glycidyloxyethyl, γ-glycidyloxypropyl, δ-Glycidyloxybutyl, ε-Glycidyloxypentyl, ω-Glycidyloxyhexyl, and 2- (3,4-epoxycyclohexyl) ethyl, a (meth) acryloxy (Ci _-6) -alkylene radical, for example (meth) acrylic oxymethyl, (meth) acryloxyethyl, (meth) acryloxypropyl or (meth) acryloxybutyl, and a 3-lsocyanatopropylrest. Particularly preferred radicals are γ-glycidyloxypropyl and (meth) acryloxypropyl. ((Meth) acryl is methacrylic or acrylic).

Concrete examples of such silanes are γ-glycidyloxypropyltrimethoxysilane (GPTS), γ-glycidyloxypropyltriethoxysilane (GPTES), 3-isocyanatopropyltriethoxysilane, 3-isocyanato-propyldichlorosilane, 3-aminopropyltrimethoxysilane (APTS), 3-aminopropyltriethoxysilane (APTES), N- (2 -Aminoethyl) -3-aminoproyltrimethoxysilane, N- [N '- (2'-aminoethyl) -2-aminoethyl] -3-aminopropyltrimethoxysilane, hydroxymethyltriethoxysilane, 2- [methoxy (polyethyleneoxy) propyl] trimethoxysilane, bis (hydroxyethyl) 3-aminopropyltriethoxysilane, N-hydroxyethyl-N-methylaminopropyltriethoxysilane, 3- (meth) acryloxypropyltriethoxysilane and 3- (meth) acryloxypropyltrimethoxysilane.

Furthermore, the use of silanes is possible which at least partially have organic radicals which are substituted by fluorine. Such silanes are described in detail in WO 92/21729. For this purpose, hydrolyzable silanes having at least one nonhydrolyzable radical which have the general formula

Rf (R) _b SiX ₍₃ -b) (II)

wherein X and R are as defined in formula (I), Rf is a nonhydrolyzable group having 1 to 30 fluorine atoms bonded to carbon atoms, preferably separated from Si by at least two atoms, preferably an ethylene group, and b 0, 1 or 2 is. R is in particular a radical without a functional group, preferably an alkyl group such as methyl or ethyl. Preferably, the groups contain Rf 3 to 25 and especially 3 to 18 fluorine atoms which are bonded to aliphatic carbon atoms. R f is preferably a fluorinated alkyl group of 3 to 20 carbon atoms and examples are CF ₃ CH ₂ CH ₂ -, C ₂ F ₅ CH ₂ CH ₂ -, nC ₆ Fi ₃ CH ₂ CH ₂ -, JC ₃ F ₇ OCH ₂ CH ₂ CH ₂ -, nC ₈ F ₁₇ CH ₂ CH ₂ - and nC ₁₀ F ₂ i-CH ₂ CH ₂ -.

Examples of fluorosilanes which can be used are CF ₃ CH ₂ CH ₂ SiCl ₂ (CH ₃ ), CF ₃ CH ₂ CH ₂ SiC [(CH ₃ ) ₂ , CF ₃ CH ₂ CH ₂ Si (CH ₃ ) (OCH ₃ ) ₂ , C ₂ F ₅ -CH ₂ CH ₂ -SiZ ₃ , nC ₆ F ₁₃ - CH ₂ CH ₂ SiZ ₃ , nC ₈ F ₁₇ -CH ₂ CH ₂ -SiZ ₃ , nC ₁₀ F ₂₁ -CH ₂ CH ₂ -SiZ ₃ with (Z = OCH ₃ , OC ₂ H ₅ or Cl), 1-C ₃ F ₇ O-CH ₂ CH ₂ CH ₂ -SiCl ₂ (CH ₃ ), nC ₆ F ₁₃ -CH ₂ CH ₂ -Si (OCH ₂ CH ₃ ) 2, nC ₆ F ₁₃ -CH ₂ CH ₂ -SiCl ₂ (CH ₃ ) and π-C ₆ Fi ₃ -CH ₂ CH ₂ -SiCl (CH ₃ ) ₂ .

The silanes can be prepared by known methods; see. W. NoII, "Chemistry and Technology of Silicones", Verlag Chemie GmbH, Weinheim / Bergstrasse (1968).

Examples of metal compounds which have a functional group are metal compounds of a metal M from the main groups III to V and / or the subgroups II to IV of the Periodic Table of the Elements. Preference is given to compounds of Al, Ti or Zr. Examples of these are R ₀ MX _4-C (M = Ti or Zr and c = 1, 2, 3), wherein X and R are as defined above in formula (I), wherein one R or more R together also represents a complexing agent , such as a ß-dicarbonyl compound or a (mono) carboxylic acid, can stand. Preference is given to zirconium and titanium tetraalcoholates in which part of the alkoxy groups has been replaced by a complexing agent such as, for example, a β-dicarbonyl compound or a carboxylic acid, preferably a monocarboxylic acid.

Surfactants may also be used as modifiers. Surfactants can form micelles. Most of the modifiers discussed above are not surfactants, i. they do not form micelles even at high concentrations. This behavior relates to the pure dispersant. In the presence of the particles, the modifiers naturally also enter into the chemical interactions with the particles described according to the invention. All conventional surfactants known to those skilled in the art can be used. Usually, modifiers which are not surfactants, e.g. the ones discussed above.

As the dispersant, any solvent can be used as long as it does not or substantially not dissolve the particles to be treated and is also inert or substantially inert to the modifier used. As examples, the solvents mentioned for step a) can be listed. Often it is useful to carry out step a) and b) in the same solvents. The substances used according to the invention can be mixed with one another in any desired sequence. The mixture can be carried out directly in the device for the mechanical activation or previously in a separate container, eg a mixer. Preferably, no further additives are added otherwise, ie the mixture consists of at least one dispersing agent, at least one modifying agent, which in special case may correspond to the dispersing agent, and the particles. Examples of additives which are optionally mixed are defoamers, pressing aids, organic binders, photocatalysts, colorants, sintering aids, preservatives and rheological additives. The addition of additives is only necessary if they are needed for further processing. Therefore, these additives may also be added after the processing according to the invention. An advantage for a previous addition may be in the homogenous mixture obtained by the milling.

For the mechanical activation is usually a strong shear, whereby surface-modified particles are obtained. The mechanically activated high shear process may be carried out by conventional and known means, such as crushing, kneading or grinding equipment. Examples of suitable devices are dispersers, turbine agitators, jet jet dispersers, roller mills, mills and kneaders. Preferably kneaders and mills are used. Examples of mills and kneaders are mills with loose Mahl¬ tools, such as ball, rod, drum, cone, tube, autogenous, planetary, vibrating and stirrer mills, Scherwalzenkneter, mortar mills and Kolloid¬ mills.

The appropriate temperature for the particular system may optionally be adjusted by those skilled in the art. The mechanically activated process preferably takes place at room temperature or ambient temperature (eg 15 to 30 ^° C.), ie it is not heated. The mechanical activation may cause heating of the suspension. This may be desirable. If necessary, but can also be cooled. Cooling units usually prevent the temperature from rising to the boiling point of the solvent. Normally, work is carried out in such a way that during the mechanical activation a tempe- Temperature of ambient temperature to 7O ⁰ C or 60 ⁰ C ₁ preferably ambient temperature to below 5O ⁰ C, is achieved. The temperature is preferably below the boiling point of the solvent used.

The duration of the mechanical activation depends in particular on the solids content of the suspensions used, the dispersant and the surface modifier, it can be from several minutes to days.

The mechanical stress for activation can also be done in a two- or multi-stage design. It can e.g. consist of upstream steps and a subsequent step, wherein the modifying agent in each step or only in at least one step, e.g. the last, may be present. For example, when grinding with grinding media, a grinding step with coarser grinding media can be used upstream in order to achieve the optimum, efficient starting particle size for the final step.

The particle content of the suspensions, which are subjected to the mechanically activated process under high shear depends, inter alia. from the device used. The particle content in kneaders is generally between 98 and 50% by volume of the suspension. When using mills, the particle content is generally up to 60% by volume of the suspension. The weight ratio of particles / modifier is generally 100: 1 to 100: 35, in particular 100: 2 to 100: 25 and particularly preferably 100: 4 to 100: 20.

The amount of particles / grinding media present in the grinding chamber necessarily results from the solids content of the suspension and the degree of filling of grinding balls used and the bulk density of the grinding balls.

The mechanically activated process can be supported by additional energy input (in addition to the applied mechanical energy), for example by means of micro wave and / or ultrasound, whereby these two methods can also be used simultaneously. The energy input into the dispersion takes place directly in the Device for mechanical activation, but can also be done outside the Vor¬ direction in the product cycle.

The process can be carried out both continuously in one-pass operation, multiple-pass operation (pendulum process) or cyclic process and batchwise in batch operation.

As a result of the mechanical activation in the presence of the activating agent, modifier is at least partially chemically bound to the particles, which as a rule are simultaneously deagglomerated and / or deaggregated.

After step b) highly dispersed surface-modified nanoscale particles below 100 nm can be obtained. The average particle diameter of the particles obtained is generally not more than 50 nm, preferably not more than 30 nm and particularly preferably not more than 20 nm. The process according to the invention makes it even possible to use surface-modified, crystalline and / or compacted, doped and undoped Produce nanoparticles or colloids having an average particle diameter or a mean smallest dimension down to about 1 nm.

Unless stated otherwise, the average particle diameter here means the particle diameter based on the volume average (d.sub.50 value), an UPA (Ultrafine Particle Analyzer, Leeds Northrup (laser-optical, dynamic laser light scattering)) being used for the measurement. For the determination of very small particles (eg less than 3.5 nm) quantitative image analyzes with electron microscopic methods (eg via HR-TEM) can also be used. Since the particle diameters in the image plane are determined in these methods, the values can differ from the values determined by UPA since UPA measurements give particle diameters which can be regarded as average three-dimensional diameters. Particle diameters are sometimes referred to as particle sizes. The average particle diameter is also sometimes given as the mean smallest dimension, which may be the mean diameter or the mean height or width, whichever is smaller. The mean smallest dimension is for example the average particle diameter for spherical particles and the mean height for platelet-shaped particles. The mean smallest dimension also refers here to the volume average.

Those skilled in the art are aware of methods for determining this smallest dimension as well as the details of these methods. Another methodology used is e.g. the x-ray disc centrifuge.

From the resulting surface-modified, doped and undoped colloids, the nanoparticles can be obtained by removing the dispersant as a powder. For removal, any known method may be used, e.g. Evaporation, centrifugation or filtration.

On the resulting particles are on the surface of the bound Modifizierungsmittelmoleküle whose functionality can control the properties of the particles. The particles may then be resupplied in the same or another suitable dispersant, with no or relatively little aggregation, so that the average particle diameter can be substantially maintained.

The surface-modified, crystalline and / or compacted, doped and undoped nanoparticles or colloids can be worked up further by known methods. They can be reacted, for example, with other surface modifiers, they can be dispersed in organic or aqueous solvents, and soluble polymers, oligomers or organic monomers or sols or additives, such as those listed above, can be admixed. Such mixtures, work-ups or the surface-modified, crystalline and / or densified, doped and undoped nanoparticles or colloids as such can be used, for example, for the production of coatings or moldings or for other applications. Examples of possible fields of use of the surface-modified, crystalline and / or compacted, doped or undoped nanoparticles or colloids or of mixtures comprising these, in particular for corresponding ZrO ₂ particles, include the production of moldings, films, membranes and coatings or of compounds or hybrid materials. The products, in particular the coatings or layers, can serve for very different purposes, for example as coatings with low-energy surfaces or as abrasion-resistant, oxygen-ion conductive, microbicidal, photocatalytic, microstructurable or microstructured, holographic, conductive, UV-absorbing, photochromic and / or electrochromic products or layers.

The following examples serve to further illustrate the present invention.

Examples

example 1

A mixture of 1.720 g of Y (NO _{3) 3} ^* 4H ₂ O and 25.5 kg Zirconiumpropylat was dissolved in 12.8 kg of ethanol. The resulting solution was added dropwise with stirring at room temperature to 32 kg of an aqueous ammoniacal solution (pH 10 - 1 1). After completion of the addition, the suspension was thermally treated in a continuous tubular reactor at a temperature of 24O ⁰ C and a pressure of 50 bar. The mean residence time of the suspension in the reactor is at least 30 minutes. The suspension thus obtained was adjusted to pH = 7.8-8.3 by addition of ammoniacal solution with stirring, sedimentation taking place after the end of the stirring. The supernatant was removed. While stirring, distilled water was again added and the pH was again adjusted to pH = 7.8-8.3. This washing process was repeated until the conductivity of the supernatant reached <10 μS. The supernatant was removed and a solids-containing suspension was obtained, which was freeze-dried. Approximately 900 g of this freeze-dried powder were placed in a 2-shaft kneader (maximum filling volume 2 liters). After addition of 50 g of water and 135 g of TODS (3,6,9-trioxadecanoic acid), a highly viscous paste was kneaded. The highly viscous mass was kneaded at a temperature <55 ⁰ C for about 6 hours. Thus, an 83% by weight paste of nanoscale ZrO ₂ (cubic, stabilized with 4 moles of Y ₂ O ₃ ) surface-modified with TODS and having an average particle size of 4 - 8 nm (TEM) and a mean particle size Particle diameter dso = 13 nm (UPA).

Example 2

1,085 g of the paste prepared from Example 1 (83 wt .-% ZrO ₂ ) were dispersed by mechanical stirring in 715 g of water. In this way, a 50% strength by weight suspension of nanoscale ZrO ₂ (cubic, stabilized with 4 mol of Y ₂ O _{3) was} surface-modified with TODS and had an average particle size of 4 to 8 nm (TEM) and a medium particle size Particle diameter d ₅₀ = 14 nm (UPA). Example 3

1,085 g of the paste prepared from Example 1 (83 wt .-% Z1O ₂ ) were converted by freeze drying in a powder. This gave a nanoscale ZrO ₂ powder (cubic, stabilized with 4 mol of Y ₂ O ₃ ) surface-modified with TODS and having an average particle size of 4 to 8 nm (TEM) and an average particle diameter d ₅ o = 16 nm (UPA).

Example 4

In a reaction vessel, 970 g of ethanol, 400 g of the freeze-dried powder of Example 1 and 30 g of acetylacetone were added and mixed for 30 minutes with mechanical stirring. The mixture obtained was milled in a stirred ball mill for 6 hours (Drais Pearl MiII PML-H / V, zirconium oxide grinding chamber clothing, gross grinding chamber volume 1, 2 l, 4,100 rpm, 1,700 g of grinding balls (zirconium silicate), ball diameter 0 , 3 - 0.4 mm, continuous operation in Kreis¬ method). In this way, a 40% strength by weight suspension of nanoscale ZrO ₂ (cubic, stabilized with 4 mol of Y ₂ O ₃ ) with surface modification of acetylacetone and an average particle size of 4 to 8 nm (TEM) and a mean particle diameter dso = 12 nm (UPA).

Example 5

6.4 kg of ethanol were added to 25.5 kg of zirconium propylate and added dropwise with stirring at room temperature to 32 kg of an aqueous, slightly ammoniacal solution (pH = 8). After completion of the addition the suspension was bar thermally treated in a konti¬ ously working tubular reactor at a temperature of 240 ⁰ C and a pressure of 50th The mean residence time of the suspension in the reactor is at least 30 minutes. The suspension thus obtained is adjusted by addition of ammoniacal solution with stirring to pH = 7.8 to 8.3, wherein sedimentation takes place after the end of the stirring. The supernatant was removed. While stirring, distilled water was again added and the pH was again adjusted to pH = 7.8-8.3. This washing process was repeated until the conductivity of the supernatant reached <10 μS. The supernatant was removed and subsequent centrifugation gave a high-strength fabric-containing paste with a solids content of 40 wt .-%. 1 kg of this paste was mixed with 60 g of TODS and mechanically stirred for 30 min. The suspension obtained is milled in a stirred ball mill for 4 h (Drais Pearl MiII PML-H / V, zirconium oxide grinding chamber lining, gross grinding volume 1, 2 l, 4,100 rpm, 1,700 g of grinding balls, zirconium silicate, ball diameter 0.3-0.4 mm , continuous operation in the circular process). In this way, a 37.7 wt .-% suspension of nanoscale ZrO ₂ , which was surface-modified with TODS and an average particle size of 8 - 10 nm (TEM) and an average particle diameter dso = 13 nm (UPA) had.

Example 6

1 kg of the 40 wt .-% ZrO ₂ paste prepared in Example 5 was freeze dried. The resulting powder was mixed in 600 g of water with 60 g of N- (2-hydroxyethyl) iminodiacetic acid and mechanically stirred for 30 min. The resulting mixture was milled in a stirred ball mill for 6 h (Drais Pearl MiII PML-HA /, zirconium oxide grinding chamber lining, gross grinding volume 1.2 l, 4,100 rpm, 1,700 g of grinding balls, zirconium silicate, ball diameter 0.3-0.4 mm , continuous operation in the circular process). This gave a 37.7 wt .-% suspension of nanoscale ZrO ₂ with N- (2-hydroxyethyl) iminodiacetic surface-modified and an average particle size of 8 - 10 nm (TEM) and a mean particle diameter d ₅ o = 11 nm (UPA).

Example 7

2.5 kg of the 40 wt .-% suspension obtained in Example 5 were freeze-dried. The resulting powder was placed in a 2-shaft kneader (maximum filling volume 2 liters). After adding 50 g of water and 150 g of TODS, a high-viscosity paste was kneaded. The highly viscous mass was kneaded at a temperature <55 ° C for about 6 hours. Was obtained in this way a 83 wt .-% paste surface-modified nanoscale ZrO ₂ with TOD and an average particle size of 8-10 nm (TEM) and an average diameter d Partikel¬ ₅ o = 18 nm (UPA). Example δ

1,200 g of the paste prepared from Example 7 (83 wt .-% ZrO ₂ ) were dispersed by mechanical stirring in 1300 g of water. In this way, a 40% strength by weight suspension of nanoscale ZrO _{2 was} surface-modified with TODS and having an average particle size of 8-10 nm (TEM) and an average particle diameter d ₅₀ = 18 nm (UPA).

Example 9

1,200 g of the paste prepared from Example 7 (83 wt .-% ZrO ₂ ) were converted by freeze drying in a powder. This gave a nanoscale, ZrO ₂ powder, surface-modified with TODS and having an average particle size of 8-10 nm (TEM) and an average particle diameter d ₅₀ = 20 nm (UPA).

Example 10

3,200 g of distilled water were placed in a stirred tank. 2,550 g of zirconium propylate are mixed with 640 g of ethanol and added dropwise at room temperature with stirring to the water. 7,200 ml of the precipitated suspension were placed in a 10 liter batch autoclave. The autoclave is purged three times with nitrogen at a pressure of 10 bar. The suspension is autoclaved with 10 bar pre-pressure (N ₂ ) at a temperature of 230 ⁰ C for 3 hours. The pressure is approx. 50 bar. The suspension thus obtained was adjusted to pH = 7.8-8.3 by addition of ammoniacal solution with stirring, sedimentation taking place after the end of the stirring. The supernatant was removed. While stirring, distilled water was again added and the pH was again adjusted to pH = 7.8-8.3. This washing process is repeated until the conductivity of the supernatant has reached a value <10 μS. The supernatant was removed and a solids-containing suspension was obtained, which was freeze-dried. 900 g of this freeze-dried powder were placed in a 2-shaft kneader (maximum filling volume 2 liters). After adding 50 g of water and 112.5 g of TODS, a high-viscosity paste was kneaded. The highly viscous mass was kneaded at a temperature <55 ° C for about 8 hours. The plasticine was in 735.5 g Water dispersed by mechanical stirring. In this way, a 50% strength by weight suspension of nanoscale ZrO _{2 was} surface-modified with TODS and had an average particle size of 8-12 nm (TEM) and an average particle diameter d 50 = 18 nm (UPA).

Claims

claims

1. A process for producing a suspension of crystalline and / or compacted, surface-modified, nanoscale particles in a dispersant, the process comprising the following steps: a) a suspension of amorphous or partially crystalline, not surface-modified, nanoscale particles in a dispersant is heat-treated to crystallize and / or densify the particles, and b) the suspension of the crystallized and / or compacted non surface-modified, nanoscale particles in the dispersant of step a) or in another dispersant activated in the presence of a modifier by mechanical stress, so that the particles are oberflächen¬ modified by the modifier to obtain a suspension of crystalline and / or ver¬ density, surface-modified, nanoscale particles.

2. The method according to claim 1, characterized in that the heat treatment in step a) is carried out at elevated pressure.

3. The method according to claim 1 or 2, characterized in that the heat treatment is carried out at a temperature of at least 60 ⁰ C.

4. The method according to claim 2 or 3, characterized in that the heat treatment is carried out at a pressure of at least 5 bar.

5. The method according to any one of claims 1 to 4, characterized in that the modifying agent for surface modification is chemically bonded to the surface of the particles.

6. The method of any of claims 1 to 5, characterized in that the mechanical activation is effected by a device for strong shear of the suspension, for example, a crushing, kneading or grinding device.

7. The method according to any one of claims 1 to 6, characterized in that for mechanical activation dispersants, turbine agitators, Düsenstrahldis- pergators, roller mills, mills or kneaders are used.

8. The method according to any one of claims 1 to 7, characterized in that the mechanical activation is carried out without external heating.

9. The method according to any one of claims 1 to 8, characterized in that the mechanical activation is carried out in one, two or more stages, wherein at least one of the stages is carried out in the presence of Modifizierungs¬ means.

10. The method according to any one of claims 1 to 9, characterized in that the mechanical activation is supported by an additional energy input into the suspension, wherein the additional energy input can take place inside or outside the device for high shear.

11. The method according to claim 10, characterized in that the additional energy input via ultrasound and / or microwave, wherein the additional energy input can also be done simultaneously via ultrasound and microwaves.

12. The method according to any one of claims 1 to 11, characterized in that the dispersant is also used as a modifier.

13. The method according to any one of claims 1 to 12, characterized in that the weight ratio of particles to modifier in step b) is 100: 1 to 100: 35.

14. The method according to any one of claims 1 to 13, characterized in that the average diameter of the particles obtained after step b) is not more than 20 nm.

15. The method according to any one of claims 1 to 14, characterized in that the suspension obtained by step a) is purified to at least partially remove Prozeßneben¬ products before step b) is performed.

16. The method according to claim 15, characterized in that the particles are flocculated in the suspension for cleaning, the resulting supernatant removed and the sedimentation product is diluted with a fresh dispersant to at least partially replace the spent by the process by-products spent dispersant , wherein the cleaning process can be repeated several times.

17. The method according to any one of claims 1 to 16, characterized in that the starting suspension of amorphous or partially crystalline, not surface-modified, nanoscale particles of step a) is obtained by

I) molecular precursors of the particles in the dispersant are subjected to a condensation and / or precipitation reaction,

II) a powder of amorphous or partially crystalline, not surface-modified, nanoscale particles is suspended in the dispersant or

III) the dispersant of a suspension of amorphous or partially crystalline, not surface-modified, nanoscale particles is exchanged for the desired dispersant.

18. The method according to any one of claims 1 to 17, characterized in that it is the particles are doped or undoped particles.

19. The method according to any one of claims 1 to 18, characterized in that the particles are oxide particles or hydrated oxide particles.

20. The method according to any one of claims 1 to 19, characterized in that it is the particles to a compound, preferably an oxide or a hydrated oxide, at least one element selected from Mg, Ca, Sr, Ba, Al, Si, Sn, Pb, Sb, Bi, Ti, Zr, V, Mn, Nb, Ta, Cr, Mo, W, Fe, Co, Ru, Zn, Ce, Y, Sc, Eu, in and La or mixtures thereof.

21. The method according to any one of claims 19 and 20, characterized in that the particles are ZrO ₂ , TiO ₂ , Al-coated rutile, SnO ₂ , Al ₂ O ₃ , ITO (indium tin oxide), ATO (Antimony-doped tin oxide), In ₂ O ₃ , Y ₂ O ₃ , CeO ₂ , ZnO, manganese oxides, iron oxides, BaO or CaO or doped oxides thereof, such as BaTiO ₃ , SnTiO ₃ and calcium tungstate, and / or hydrated oxides thereof or Mixtures of these are.

22. The method according to claim 21, characterized in that it is doped or undoped ZrO ₂ in the particles.

23. The method according to any one of the preceding claims, characterized in that crystalline particles are obtained by the heat treatment in step a) by crystallization.

24. A process for the preparation of crystalline and / or compacted, surface-modified, nanoscale particles, which comprises preparing a suspension of the particles in a dispersant by the process of one of claims 1 to 22 and removing the dispersant.