EP2089163B1 - Amorphous submicron particles - Google Patents

Description

The invention relates to powdery amorphous solids having a very small average particle size and a narrow particle size distribution, a process for their preparation, and their use.

State of the art

Fine-particle, amorphous silicic acid and silicates have been industrially produced for decades. In general, the finest grinding in spiral or counter-jet mills with compressed air is carried out as a grinding gas, eg EP 0139279 ,

It is known that the achievable particle diameter is proportional to the root of the reciprocal of the collision velocity of the particles. The impact velocity in turn is determined by the jet velocity of the expanding gas jets of the respective grinding medium from the nozzles used. For this reason, preferably superheated steam can be used to generate very small particle sizes, since the acceleration capacity of steam is about 50% greater than that of air. However, the use of steam has the disadvantage that, in particular during the startup of the mill, condensation can occur in the entire grinding system, which generally results in the formation of agglomerates and crusts during the grinding process.

The average particle diameter d _{50 obtained} using conventional jet mills in the milling of amorphous silica, silicates or silica gels was therefore far above 1 μm. So z. B. in the US 3,367,742 describes a process for the milling of aerogels, in which aerogels are obtained with a mean particle diameter of 1.8 to 2.2 microns. Milling to a mean particle diameter of less than 1 μm is not possible with this technique. Furthermore, the particles of the US 3,367,742 a wide one Particle size distribution with particle diameters of 0.1 to 5.5 microns and a proportion of particles> 2 microns from 15 to 20%. A high proportion of large particles, ie> 2 microns, is disadvantageous for applications in coating systems, as it can not be produced thin films with a smooth surface. In the US 2,856,268 describes the mill-drying of silica gels in steam jet mills. However, the average particle diameters obtained were well above 2 μm.

An alternative Vermahlungsmöglichkeit provides the wet comminution, z. B. in ball mills, is. It leads to very finely divided suspensions of the products to be ground, see, for. B. WO 200002814 , It is not possible with the help of this technology to isolate a finely divided, agglomerate-free dry product, in particular without changing the porosimetric properties, from these suspensions.

It is an object of the present invention to provide novel finely divided, pulverulent, amorphous solids and a process for their preparation.

Further unspecified tasks arise from the overall context of the description as well as the claims and examples.

The inventors have surprisingly found that it is possible to grind amorphous solids by means of a very special, further specified in the claims 2 to 14 method to a mean particle size d ₅₀ of less than 1.5 microns and also a very narrow particle distribution to reach.

The object is thus achieved by the method specified in more detail in the claims and the description below and the amorphous solids specified there.

The invention relates to amorphous powdered solids having an average particle size d ₅₀ (TEM) <1.5 microns and a d ₉₀ value (TEM) <1.8 microns and a d ₉₉ value (TEM) <2 microns and it itself are silica gels, which also have a pore volume of 0.2 to 0.7 ml / g, or are silica gels which also have a pore volume of 0.8 to 1.5 ml / g or are silica gels , which also have a pore volume of 1.5 to 2.1 ml / g.

The invention also provides a process for producing the amorphous pulverulent solids according to the invention by grinding amorphous solids by means of a grinding system (milling apparatus), preferably comprising a jet mill, particularly preferably a milling system comprising a fluidized bed counter-jet mill or a dense bed jet mill or a spiral jet mill, characterized in that the mill in the milling phase with a resource selected from a group consisting of gas and steam, preferably water vapor, and a gas containing water vapor, is operated, and that the grinding chamber in a heating phase, ie before the actual operation with the operating means, so heated is that the temperature in the grinding chamber and at the mill outlet is higher than the dew point of the steam and / or equipment.

Furthermore, the present invention relates to the use of the amorphous solids according to the invention having an average particle size d ₅₀ <1.5 microns and a d ₉₀ value <1.8 microns and a d ₉₉ value <2 microns, z. In surface coating systems.

The inventive method is the first time succeeded, powdery amorphous solids having an average particle size d ₅₀ <1.5 microns and a narrow
Particle size distribution, expressed by the d ₉₀ value <1.8 microns and / or the d ₉₉ value <2 microns to produce.

The grinding of amorphous solids, in particular those containing a metal and / or metal oxide, for. As metals of the 3rd and 4th main group of the Periodic Table of the Elements, such as. As precipitated silicas, fumed silicas, silicates and silica gels, to achieve such small average particle sizes was previously possible only by wet milling. As a result, only dispersions could be obtained. The drying of these dispersions led to re-agglomeration of the amorphous particles, so that the effect of grinding was partially reversed and average particle sizes d ₅₀ <1.5 microns, and particle size distribution d ₉₀ value can not be reached <2 microns in the dried, powdered solids could. In the case of drying of gels, the porosity was also adversely affected.

Compared to the processes of the state of the art, in particular wet milling, the process according to the invention has the advantage that it is a dry milling process which leads directly to pulverulent products with a very small mean particle size, which can also have a high porosity in a particularly advantageous manner , The problem of reagglomeration during drying is eliminated because no grinding of the downstream drying step is necessary.

Another advantage of the method according to the invention in one of its preferred embodiments is the fact that the grinding can take place simultaneously with the drying, so that z. B. a filter cake can be further processed directly. This saves an additional drying step and at the same time increases the space-time yield.

In its preferred embodiments, the inventive method also has the advantage that when starting up the grinding system no or only very small amounts of condensate in the grinding system, especially in the mill arise. On cooling, dried gas can be used. As a result, no condensate is produced in the grinding system during cooling and the cooling phase is significantly shortened. The effective machine running times can thus be increased.

Finally, the fact that no or very little condensate is formed during startup in the milling system, prevents an already dried ground material is wet again, whereby the formation of agglomerates and crusts during the grinding process can be prevented.

The amorphous pulverulent solids produced by means of the process according to the invention have particularly good properties when used in surface coating systems, for example because of the very special and unique average particle sizes and particle size distributions. As a rheological aid, in paper coating and in paints or varnishes.

The products of the invention allow z. B. due to the very small average particle size and in particular the low d ₉₀ value and d ₉₉ value to produce very thin coatings.

The present invention will be described below in detail. Previously, some terms used in the description as well as in the claims are defined.

The terms powder and pulverulent solids are used interchangeably in the context of the present invention and each denote finely comminuted, solid substances from small dry particles, dry particles meaning that they are externally dry particles. Although these particles usually have a water content, this water is so firmly bound to the particles or in their capillaries that it is not released at room temperature and atmospheric pressure. In other words, it is perceptible by optical methods particulate matter and not suspensions or dispersions. Furthermore, these may be both surface-modified and non-surface-modified solids. The surface modification is preferably carried out with carbon-containing coating agents and can be carried out both before and after the grinding.

The solids according to the invention can be present as gel or as particles containing agglomerates and / or aggregates. Gel means that the solids are composed of a stable, three-dimensional, preferably homogeneous network of primary particles. Examples are silica gels.

Particles comprising aggregates and / or agglomerates in the sense of the present invention have no three-dimensional network or at least no network of primary particles extending over the entire particle. Instead, they have aggregates and agglomerates of primary particles. Examples of these are precipitated silicas and fumed silicas.

A description of the structural difference of silica gels as compared to precipitated SiO ₂ can be found in Iler RK, "The Chemistry of Silica", 1979, ISBN 0-471-02404-X, Chapter 5, page 462, and there in Figure 3.25. The content of this document is hereby expressly included in the description of this invention.

The process according to the invention is carried out in a milling system (milling apparatus), preferably in a milling system comprising a jet mill, particularly preferably comprising an opposed jet mill. For this purpose, a feed to be crushed is accelerated in expanding high-speed gas jets and comminuted by particle-particle collisions. As jet mills, very particular preference is given to using fluid bed counter-jet mills or dense-bed jet mills or spiral jet mills. In the case of the very special preferred fluidized bed counter-jet mill located in the lower third of the grinding chamber two or more Mahlstrahleinlässe, preferably in the form of grinding nozzles, which are preferably in a horizontal plane. The Mahlstrahleinlässe are particularly preferably arranged on the circumference of the preferably round mill container, that the grinding jets all meet at a point inside the grinding container. Particularly preferably, the grinding jet inlets are distributed uniformly over the circumference of the grinding container. In the case of three Mahlstrahleinlässe the distance would thus each be 120 °.

In a specific embodiment of the method according to the invention, the grinding system (grinding apparatus) comprises a separator, preferably a dynamic separator, particularly preferably a dynamic Schaufelradsichter, particularly preferably a separator according to Figure 2 and 3 ,

In a particularly preferred embodiment, a dynamic air classifier according to Figure 2a and 3a used. This dynamic air classifier includes a classifying wheel and a Sichtradwelle and a classifier housing, wherein between the classifying wheel and the classifier housing a classifier gap and between the Sichtradwelle and the classifier housing a shaft passage is formed, and is characterized in that a rinsing gap of the classifier gap and / or shaft passage with compressed Low energy gases take place.

By using a classifier in combination with the jet mill operated under the conditions according to the invention, the upper particle is confined, the product particles rising together with the expanded gas jets being passed through the classifier from the center of the grinding container and subsequently the product having a sufficient fineness , from the sifter and from the mill is executed. Too coarse particles return to the milling zone and are subjected to further comminution.

In the grinding system, a classifier can be connected downstream as a separate unit of the mill, but preferably an integrated classifier is used.

An essential feature of the method according to the invention is that the actual grinding step is preceded by a heating phase, in which it is ensured that the grinding chamber, particularly preferably all essential components of the mill and / or the grinding system, at which water and / or water vapor could condense, is heated so / that its temperature is above the dew point of the vapor. The heating can be done in principle by any heating method. Preferably, however, the heating takes place in that hot gas is passed through the mill and / or the entire grinding system, so that the temperature of the gas at the mill outlet is higher than the dew point of the vapor. Particular care is taken here that the hot gas preferably heats all essential components of the mill and / or the entire grinding system, which come into contact with the steam, sufficiently.

In principle, any gas and / or gas mixtures can be used as the heating gas, but hot air and / or combustion gases and / or inert gases are preferably used. The temperature of the hot gas is above the dew point of the water vapor.

The hot gas can in principle be introduced into the milling space as desired. Preferably, there are in the grinding room inlets or nozzles. These inlets or nozzles can be the same inlets or nozzles through which the grinding jets are also passed during the grinding phase (grinding nozzles). But it is also possible that in the grinding chamber separate inlets or nozzles (heating nozzles) are present, through which the hot gas and / or gas mixture can be introduced. In a preferred embodiment, the heating gas or heating gas mixture is introduced through at least two, preferably three or more, in-plane inlets or nozzles, which are so arranged on the circumference of the preferably round mill container that the rays all meet at a point inside the grinding container. Particularly preferably, the inlets or nozzles are distributed uniformly over the circumference of the grinding container.

During grinding, a gas and / or a vapor, preferably water vapor and / or a gas / steam mixture is depressurized by the grinding jet inlets, preferably in the form of grinding nozzles. This equipment usually has a much higher speed of sound than air (343 m / s), preferably at least 450 m / s on. Advantageously, the equipment comprises water vapor and / or hydrogen gas and / or argon and / or helium. Particularly preferred is superheated steam. In order to achieve a very fine grinding, it has proved to be particularly advantageous that the operating means at a pressure of 15 to 250 bar, more preferably from 20 to 150 bar, most preferably 30 to 70 bar and particularly preferably 40 to 65 bar relaxed in the mill. Also particularly preferably, the operating means has a temperature of 200 to 800 ° C, particularly preferably 250 to 600 ° C and in particular 300 to 400 ° C.

In the case of steam as a resource, so in particular when the steam supply line is connected to a source of steam, it proves to be particularly advantageous if the grinding or inlet nozzles are connected to a steam supply line, which is equipped with expansion bends.

Furthermore, it has proven to be advantageous if the surface of the jet mill has the smallest possible value and / or the flow paths are at least largely free of projections and / or if the components of the jet mill are designed to prevent mass accumulation. By these measures, a deposit of the ground material in the mill can be additionally prevented.

With reference to the preferred and specific embodiments of the method according to the invention described below as well as the preferred and particularly suitable designs of jet mills and the drawings and descriptions of the drawings, the invention will be described only by way of example, d. H. it is not limited to these embodiments and examples of application or to the respective feature combinations within individual embodiments.

Individual features that are indicated and / or illustrated in connection with specific embodiments are not limited to these embodiments or the combination with the other features of these embodiments, but may in the technical possibilities, with any other variants, even if they are in the documents are not treated separately.

The same reference numerals in the individual figures and illustrations of the drawings designate the same or similar or identical or similar components. On the basis of the representations in the drawing, those features are also clear, which are not provided with reference numerals, regardless of whether such features are described below or not. On the other hand, features that are included in the present description but are not visible or illustrated in the drawing will be readily understood by those skilled in the art.

As already indicated above, in the process according to the invention, a jet mill, preferably an opposed jet mill, with integrated sifter, preferably an integrated dynamic air sifter, can be used to produce very fine particles. Particularly preferably, the air classifier includes a classifying wheel and a classifying wheel shaft and a classifier housing, wherein between the classifying wheel and the classifier housing a classifier gap and between the classifying wheel shaft and the classifier housing a shaft passage is formed and is operated in such a way that a gap cooling of the separator gap and / or shaft passage with compressed low-energy gases takes place.

Preferably, the purge gas is used at a pressure of not more than at least approximately 0.4 bar, particularly preferably not more than at least approximately 0.3 bar and in particular not more than approximately 0.2 bar above the internal mill pressure. In this case, the internal mill pressure can be at least approximately in the range of 0.1 to 0.5 bar.

Furthermore, it is preferred if the purge gas is used at a temperature of about 80 to about 120 ° C., in particular approximately 100 ° C., and / or if low-pressure compressed air, in particular from about 0.3 bar to about 0, is used as the purge gas. 4 bar is used.

The rotational speed of a classifier rotor of the air classifier and the internal amplification ratio V (= Di / DF) can be selected or adjusted or regulated such that the peripheral speed of the operating medium (B) at a dip tube or outlet port assigned to the classifying wheel is up to 0.8. achieved times the speed of sound of the working medium. In the formula V (= Di / DF), Di = inner diameter of the classifier wheel (8), i. the distance between the inner edges of the blades (34) and DF = inner diameter of the dip tube (20). In a particularly preferred embodiment, the inner diameter of the classifying wheel Di = 280 mm and the inner diameter of the dip tube DF = 100 m. For definition of the amplification ratio see also Dr. med. R. Nied, "Fluid Mechanics and Thermodynamics in Mechanical Process Engineering", available at Unternehmensberatung Dr. med. Roland Nied, 86486 Bonstetten, Germany. Also available from NETZSCH-CONDUX Mahltechnik GmbH, Rodenbacher Chaussee 1, 63457 Hanau, Germany.

This can be further developed in that the speed of a classifying rotor of the air classifier and the inner Reinforcement ratio V (= Di / DF) are chosen or set or controlled so that the peripheral speed of the operating means (B) on the dip tube or outlet nozzle up to 0.7 times, and more preferably up to 0.6 times the speed of sound of the working medium reached.

In particular, it may also be advantageously provided that the sifting rotor has a clear height which increases with decreasing radius, wherein preferably the throughflow area of the sifting rotor is at least approximately constant. Alternatively or additionally, it may be advantageous for the classifier rotor to have an exchangeable, co-rotating dip tube. In yet another variant, it is preferred if a fine-material outlet chamber is provided, which has a cross-sectional widening in the flow direction.

Furthermore, the jet mill according to the invention can advantageously contain, in particular, an air classifier which can combine individual characteristics or combinations of features of the air classifier according to the EP 0 472 930 B1 contains. Through this reference, to avoid mere identical assumption of the entire disclosure content of EP 0 472 930 B1 fully incorporated herein. In particular, the air classifier may comprise means for reducing the peripheral components of the flow according to the EP 0 472 930 B1 contain. In this case, it can be provided, in particular, that a discharge nozzle assigned to the classifying wheel of the air classifier, which is constructed as a dip tube, has a cross-sectional widening designed to be rounded in the direction of flow, preferably in order to avoid vortex formations.

Fig. 1

zeigt diagrammartig ein Ausführungsbeispiel einer Strahlmüle in einer teilweise geschnittenen Schemazeichnung,

Fig. 2

zeigt ein Ausführungsbeispiel eines Windsichters einer Strahlmühle in vertikaler Anordnung und als schematischer Mittellängsschnitt, wobei dem Sichtrad das Auslassrohr für das Gemisch aus Sichtluft und Feststoffpartikeln zugeordnet ist,

Fig. 2a

zeigt ein Ausführungsbeispiel eines Windsichters analog Figur 2 jedoch mit Spaltspülung von Sichterspalt 8a und Wellendurchführung 35b,

Fig. 3

zeigt in schematischer Darstellung und als Vertikalschnitt ein Sichtrad eines Windsichters

Fig. 3a

zeigt in schematischer Darstellung und als Vertikalschnitt ein Sichtrad eines Windsichters analog Figur 3 jedoch mit Spaltspülung von Sichterspalt 8a und Wellendurchführung 35b.

Figur 4:

zeigt die Partikelverteilung von Silica 1 (unvermahlen)

Figur 5:

zeigt eine TEM-Aufnahme von Beispiel 1

Figur 6:

zeigt ein Histogramm des Äquivalenzdurchmesser von Beispiel 1

Figur 7:

zeigt eine TEM-Aufnahme von Beispiel 2

Figur 8:

zeigt ein Histogramm des Äquivalenzdurchmesser von Beispiel 2

Figur 9:

zeigt eine TEM-Aufnahme von Beispiel 3a

Figur 10:

zeigt ein Histogramm des Äquivalenzdurchmesser von Beispiel 3a

Figur 11:

zeigt eine TEM-Aufnahme von Beispiel 3b

Figur 12:

zeigt ein Histogramm des Äquivalenzdurchmesser von Beispiel 3b

Preferred and / or advantageous embodiments of the grinding system or the mill which can be used in the process according to the invention result from the Figures 1 to 3a as well as the associated description, wherein it should again be emphasized that these embodiments merely illustrate the invention by way of example, ie it is not related to these embodiments and examples of application or to the respective ones Feature combinations within individual embodiments limited.

Fig. 1

shows diagrammatically an embodiment of a jet in a partially cut schematic drawing,

Fig. 2

shows an embodiment of an air classifier of a jet mill in a vertical arrangement and as a schematic central longitudinal section, wherein the classifying wheel is associated with the outlet pipe for the mixture of classifying air and solid particles,

Fig. 2a

shows an embodiment of an air classifier analog FIG. 2 but with rinsing of the separator gap 8a and shaft passage 35b,

Fig. 3

shows a schematic representation and a vertical section of a classifying wheel of an air classifier

Fig. 3a

shows in a schematic representation and as a vertical section a classifying wheel of an air classifier analog FIG. 3 however, with gap rinsing of the classifier gap 8a and shaft passage 35b.

FIG. 4:

shows the particle distribution of silica 1 (unmilled)

FIG. 5:

shows a TEM image of Example 1

FIG. 6:

shows a histogram of the equivalent diameter of Example 1

FIG. 7:

shows a TEM image of Example 2

FIG. 8:

shows a histogram of the equivalent diameter of Example 2

FIG. 9:

shows a TEM image of Example 3a

FIG. 10:

shows a histogram of the equivalent diameter of Example 3a

FIG. 11:

shows a TEM image of Example 3b

FIG. 12:

shows a histogram of the equivalent diameter of Example 3b

Individual features that are indicated and / or illustrated in connection with specific embodiments are not limited to these embodiments or the combination with the other features of these embodiments, but may in the context of the technical feasible, with any other variants, even if they in the documents are not treated separately.

The same reference numerals in the individual figures and illustrations of the drawings designate the same or similar or the same and similar components. On the basis of the representations in the drawing, those features are also clear, which are not provided with reference numerals, regardless of whether such features are described below or not. On the other hand, features that are included in the present description but are not visible or illustrated in the drawing will be readily understood by those skilled in the art.

In the Fig. 1 is an embodiment of a jet mill 1 with a cylindrical housing 2, which encloses a grinding chamber 3, a Mahlgutaufgabe 4 approximately half the height of the grinding chamber 3, at least one Mahlstrahleneinlass 5 in the lower region of the grinding chamber 3 and a product outlet 6 in the upper region of the grinding chamber. 3 shown. There, an air classifier 7 is arranged with a rotatable classifying wheel 8, with which the ground material (Not shown) is classified to dissipate only regrind below a certain grain size through the product outlet 6 from the grinding chamber 3 and feed millbase with a grain size above the selected value to another grinding process.

The classifying wheel 8 can be a classifying wheel which is common in air classifiers and whose blades (see later, for example, in connection with FIG Fig. 3 ) define radially extending blade channels, at the outer ends of which the classifying air enters and entrains particles of smaller grain size or mass to the central outlet and to the product outlet 6, while larger particles or particles of larger mass are rejected under the influence of centrifugal force. Particularly preferred are the air classifier 7 and / or at least its classifying wheel 8 with at least one design feature according to the EP 0 472 930 B1 fitted.

It can only be a Mahlstrahleinlass 5 z. B. consisting of a single, radially directed inlet opening or inlet nozzle 9 may be provided to impinge a single grinding jet 10 on the Mahlgutpartikel that get from the Mahlgutaufgabe 4 in the area of the grinding jet 10, with high energy and disassemble the Mahlgutpartikel into smaller particles to let in, sucked by the classifying wheel 8 and, as far as they have a correspondingly small size or mass, are conveyed through the product outlet 6 to the outside. However, a better effect is achieved with pairwise diametrically opposed Mahlstrahleinlässen 5, which form two colliding grinding jets 10, which cause the particle separation more intense than is possible with only one grinding jet 10, especially when multiple Mahlstrahlpaare are generated.

Preferably, two or more Mahlstrahleinlässe, preferably grinding nozzles, in particular 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12 Mahlstrahleinlässe used, which are mounted in the lower third of, preferably cylindrical housing of the grinding chamber. These Mahlstrahleinlässe are ideally in a plane and evenly distributed over the circumference of the grinding container arranged so that the grinding jets all meet at a point inside the grinding container. Particularly preferably, the inlets or nozzles are distributed uniformly over the circumference of the grinding container. With three grinding jets this would be an angle of 120 ° between the respective inlets or nozzles. In general one can say that the larger the grinding chamber, the more inlets or grinding nozzles are used.

In a preferred embodiment of the method according to the invention, the grinding chamber may contain, in addition to the grinding jet inlets, heating openings 5a, preferably in the form of heating nozzles, through which hot gas can be passed into the mill in the heating phase. These nozzles or openings can - as already described above - be arranged in the same plane as the grinding openings or nozzles 5. It can one, but preferably several, more preferably 2, 3, 4, 5, 6, 7 or 8 heating openings or nozzles 5a may be included.

In a very particularly preferred embodiment, the mill contains two heating nozzles or openings and three grinding nozzles or openings.

Furthermore, for example, the processing temperature can be influenced by using an internal heat source 11 between Mahlgutaufgabe 4 and the range of grinding jets 10 or a corresponding heat source 12 in the area outside the Mahlgutaufgabe 4 or by processing particles of already warm ground material, while avoiding heat loss in the Mahlgutaufgabe 4 passes, to which a feed tube 13 is surrounded by a temperature-insulating jacket 14. The heating source 11 or 12, when used, may be arbitrary in nature and therefore purposely operational and selected according to market availability, so that further explanation is not required.

For the temperature, in particular the temperature of the grinding jet or the grinding jets 10 is relevant and the Temperature of the ground material should at least approximately correspond to this grinding jet temperature.

To form the grinding jets 10 introduced into the grinding chamber 3 by grinding jet inlets 5, superheated steam is used for this purpose in the present exemplary embodiment. It is assumed that the heat content of the steam after the inlet nozzle 9 of the respective Mahlstrahleinlasses 5 is not significantly lower than in front of this inlet nozzle 9. Because the necessary energy for the impact crushing is primarily to be available as flow energy, in contrast, the pressure drop between the inlet 15 of the inlet nozzle 9 and the outlet 16 be considerable (the pressure energy will be largely implemented in flow energy) and also the temperature drop will not be negligible. In particular, this temperature drop is to be compensated so far by the heating of the ground material that regrind and grinding jet 10 in the region of the center 17 of the grinding chamber 3 at least two colliding grinding jets 10 or a multiple of two grinding jets 10 have the same temperature.

For the design and implementation of the preparation of the grinding jet 10 from superheated steam, in particular in the form of a closed system is on the DE 198 24 062 A1 Reference is made in its entirety to the entire contents of this disclosure for the purpose of avoiding merely identical assumption. By a closed system, for example, a grinding of hot slag as regrind with optimum efficiency is possible.

Representing the present embodiment of the jet mill 1 is representative of any supply of a resource or medium B, a reservoir or generating means 18, for example, a tank 18a, from which the operating medium or operating medium B via line 19 to the Mahlstrahleinlass 5 or the Mahlstrahleinlässen to the formation of the grinding jet 10 and the grinding jets 10 is passed.

In particular, starting from a jet mill 1 equipped with an air classifier 7, the relevant embodiments being intended and to be understood as exemplary only and not as limiting, a method for producing very fine particles is carried out with this jet mill 1 with an integrated dynamic air classifier 7. The innovation over conventional jet mills, in addition to the fact that the grinding phase is preceded by a heating phase in which all the parts in contact with the steam are heated to a temperature above the dew point of the steam, and the fact that a preferably integrated classifier is used is that the rotational speed of the classifying rotor or classifying wheel 8 of the air classifier 7 and the internal amplification ratio V (= Di / DF) are preferably selected, adjusted or regulated so that the peripheral speed of a resource B on a dip tube or outlet port 20 associated with the classifying wheel 8 reaches up to 0.8 times, preferably up to 0.7 times and more preferably up to 0.6 times the speed of sound of the working medium or medium B.

With reference to the previously described variant with superheated steam as operating medium or operating medium B or as an alternative to this, it is particularly advantageous to use as operating means gases or vapors B which have a higher and in particular significantly higher speed of sound than air (343 m / s). Specifically, gases or vapors B having an acoustic velocity of at least 450 m / s are used as the operating means. Thus, the production and the yield of very fine particles compared to processes with other equipment, as they are conventionally used according to knowledge of practice, significantly improved and thus optimizes the process as a whole.

As the resource B, a fluid is used, preferably the water vapor already mentioned, but also hydrogen gas or helium gas.

In a preferred embodiment, the jet mill 1, which is in particular a fluidized bed jet mill or a dense bed jet mill or a spiral jet mill, designed or designed with the integrated dynamic air classifier 7 to produce very fine particles or provided with suitable means that the speed of the Sichtrotors or Sichtrades 8 of the air classifier 7 and the internal gain ratio V (= Di / DF) are selected or set or controllable or that the peripheral speed of the resource B on the dip tube or outlet nozzle 20 to 0.8 times, preferably until 0.7 times and more preferably reaches up to 0.6 times the speed of sound of the working medium or medium B.

Furthermore, the jet mill 1 is preferably equipped with a source, for example the reservoir or generating device 18 for steam or superheated steam or other suitable reservoir or generating device, for a resource B or is associated with such a resource source, resulting in a resource B for operation with a higher and in particular much higher speed of sound than air (343 m / s), such as preferably a speed of sound of at least 450 m / s, is fed. This resource, such as the steam or hot steam reservoir or generator 18, contains gases or vapors B for use in operation of the jet mill 1, particularly the water vapor already mentioned above, but hydrogen gas or helium gas are also preferred alternatives.

In particular, when using hot steam as the operating medium B, it is advantageous to provide with expansion arcs (not shown) equipped line devices 19, which are then also referred to as a steam supply line to the inlet or grinding nozzles 9, so preferably when the steam supply line to a source of steam is connected as a reservoir or generating means 18.

Another advantageous aspect when using steam as operating medium B is to provide the jet mill 1 with as small a surface as possible, or in other words, to optimize the jet mill 1 with regard to the smallest possible surface area. Especially in connection with the water vapor as a resource B, it is particularly advantageous to avoid heat exchange or heat loss and thus energy loss in the system. This purpose is also served by the further alternative or additional design measure, namely to design or optimize the components of the jet mill 1 in order to avoid mass accumulations. This can be realized, for example, by using as thin as possible flanges in and for connecting the line devices 19.

Energy loss and other flow-related impairments can also be contained or avoided if the components of the jet mill 1 are designed or optimized to avoid condensation. It may even be included for this purpose special equipment (not shown) for condensation prevention. Furthermore, it is advantageous if the flow paths are optimized at least largely free of projections or to that extent. In other words, with these design variants, individually or in any combination, the principle is implemented to avoid as much as possible or anything that can become cold and thus where condensation can occur.

Furthermore, it is advantageous and therefore preferred if the classifying rotor has a clear height which increases with decreasing radius, that is to say towards its axis, wherein in particular the throughflow area of the classifying rotor is at least approximately constant. First or alternatively, a fine-material outlet chamber can be provided, which has a cross-sectional widening in the flow direction.

A particularly preferred embodiment of the jet mill 1 is that the sifting rotor 8 has a replaceable, with rotating dip tube 20.

The following are with reference to the Fig. 2 and 3 further details and variants of preferred embodiments of the jet mill 1 and its components explained.

The jet mill 1 preferably contains, as the schematic representation in the Fig. 2 it can be seen, an integrated air classifier 7, which is, for example, in types of jet mill 1 as fluidized bed jet mill or as a dense bed jet mill or as a spiral jet mill to a dynamic air classifier 7, which is advantageously arranged in the center of the grinding chamber 3 of the jet mill 1. Depending on the grinding gas volume flow and classifier speed, the desired fineness of the material to be ground can be influenced.

In the air classifier 7 of the jet mill 1 according to the Fig. 2 the entire vertical air classifier 7 is enclosed by a classifier housing 21, which consists essentially of the upper housing part 22 and the lower housing part 23. The upper housing part 22 and the lower housing part 23 are provided at the upper or lower edge, each with an outwardly directed peripheral flange 24 and 25 respectively. The two peripheral flanges 24, 25 are in the installation or functional state of the air classifier 8 on each other and are fixed by suitable means against each other. Suitable means for fixing are, for example, screw connections (not shown). As releasable fastening means may also serve brackets (not shown) or the like.

At a virtually arbitrary point of the flange circumference, both circumferential flanges 24 and 25 are connected to one another by a hinge 26 so that the upper housing part 22 can be pivoted upward in the direction of the arrow 27 after loosening the flange connecting means relative to the lower housing part 23 and the upper housing part 22 from below and the lower housing part 23 are accessible from above. The housing base 23 in turn is formed in two parts and it consists essentially of the cylindrical Sichtraumgehäuse 28 with the peripheral flange 25 at its upper open end and a discharge cone 29, which tapers conically downwards. The discharge cone 29 and the Sichtraumgehäuse 28 are at the upper and lower ends with flanges 30, 31 to each other and the two flanges 30, 31 of discharge cone 29 and Sichtraumgehäuse 28 are like the peripheral flanges 24, 25 connected by releasable fastening means (not shown). The thus assembled classifier housing 21 is suspended in or on support arms 28a, of which several as evenly spaced around the circumference of the classifier or compressor housing 21 of the air classifier 7 of the jet mill 1 are distributed and attack the cylindrical Sichtraumgehäuse 28.

An essential part of the housing installations of the air classifier 7 is in turn the classifying wheel 8 with an upper cover plate 32, with an axially spaced lower downstream cover plate 33 and arranged between the outer edges of the two cover plates 32 and 33, fixedly connected to these and evenly around the circumference of Classifying wheel 8 distributed blades 34 with appropriate contour. In this air classifier 7, the drive of the classifying wheel 8 is effected via the upper cover disk 32, while the lower cover disk 33 is the downstream cover disk. The storage of the classifying wheel 8 comprises a positively driven forcibly Sichtradwelle 35, which is led out with the upper end of the classifier housing 21 and rotatably supports the classifying wheel 8 with its lower end within the classifier housing 21 in flying storage. The removal of the Sichtradwelle 35 from the classifier housing 21 takes place in a pair of machined plates 36, 37 which close the classifier housing 21 at the upper end of an upwardly frustoconical housing end portion 38, the Sichtradwelle 35 lead and seal this shaft passage without obstructing the rotational movement of the Sichtradwelle 35 , Appropriately, the upper plate 36 as a rotatably associated with the Sichtradwelle 35 and rotatable about pivot bearing 35a the lower plate 37 may be supported, which in turn is associated with a housing end portion 38. The underside of the downstream cover disk 33 lies in the common plane between the peripheral flanges 24 and 25, so that the classifying wheel 8 is arranged in its entirety within the hinged housing upper part 22. In the region of the conical housing end portion 38, the upper housing part 22 also has a tubular product feed nozzle 39 of the Mahlgutaufgabe 4, the longitudinal axis parallel to the axis of rotation 40 of the classifying wheel 8 and its drive or Sichtradwelle 35 and as far as possible from this axis of rotation 40 of the classifying wheel 8 and its Drive or Sichtradwelle removed 35, the housing upper part 22 is disposed radially outboard.

In a particularly preferred embodiment according to FIG. 2a and 3a The integrated dynamic air classifier 1 includes a classifying wheel 8 and a classifying wheel shaft 35 as well as a classifier housing, as already explained. In this case, a classifier gap 8a is defined between the classifying wheel 8 and the classifier housing 21, and a shaft bushing 35b is formed between the classifying wheel shaft and the classifier housing 21 (see Fig. 2a and 3a ). In particular, starting from a jet mill 1 equipped with such an air classifier 7, wherein the relevant embodiments are to be understood as exemplary only and not as limiting, a method for producing very fine particles is carried out with this jet mill 1 with an integrated dynamic air classifier 7. The innovation compared to conventional jet mills is in addition to the fact that the grinding chamber is heated to a temperature above the dew point of the steam before the grinding phase, in that there is a gap mulling of classifier gap 8a and / or shaft passage 35b with compressed low-energy gases. The special feature of this embodiment is precisely the combination of the use of these compressed low-energy gases with the high-energy superheated steam, with which the mill through the Mahlstrahleinlässe, in particular grinding nozzles or therein grinding nozzles, is charged. It At the same time, high-energy media and low-energy media are used.

Both in the embodiment according to FIG. 2 and 3 2a and 3a, the classifier housing 21 receives the coaxial with the classifying wheel 8 arranged tubular outlet nozzle 20 which lies with its upper end just below the downstream cover plate 33 of the classifying wheel 8, but without being connected to this. At the lower end of the tube formed as a discharge nozzle 20, an outlet chamber 41 is attached coaxially, which is also tubular, but whose diameter is substantially greater than the diameter of the outlet nozzle 20 and in the present embodiment, at least twice as large as the diameter of the outlet nozzle 20. At the transition between the outlet nozzle 20 and the outlet chamber 41 so there is a significant diameter jump. The outlet nozzle 20 is inserted into an upper cover plate 42 of the outlet chamber 41. Below the outlet chamber 41 is closed by a removable cover 43. The assembly of outlet nozzle 20 and outlet chamber 41 is held in a plurality of support arms 44 which are evenly distributed star-shaped around the circumference of the unit, connected with their inner ends in the region of the outlet nozzle 20 fixed to the unit and secured with their outer ends on the classifier housing 21.

The outlet nozzle 20 is surrounded by a conical annular housing 45 whose lower, larger outer diameter corresponds at least approximately to the diameter of the outlet chamber 41 and its upper, smaller outer diameter at least approximately the diameter of the classifying wheel 8. At the conical wall of the ring housing 45, the support arms 44 terminate and are firmly connected to this wall, which in turn is part of the assembly of outlet nozzle 20 and outlet chamber 41.

The support arms 44 and the annular housing 45 are parts of the scavenging air device (not shown), wherein the scavenging air the Penetration of matter from the interior of the classifier housing 21 in the gap between the classifying wheel 8 or more precisely its lower cover plate 3 and the outlet nozzle 20 prevents. In order to get this scavenging air into the ring housing 45 and from there into the gap to be kept clear, the support arms 44 are formed as tubes, with their outer end portions passed through the wall of the classifier housing 21 and connected via a suction filter 46 to a purge air source (not shown) , The annular housing 45 is closed at the top by a perforated plate 47 and the gap itself can be adjusted by an axially adjustable annular disc in the area between perforated plate 47 and lower cover plate 33 of the classifying wheel 8.

The outlet from the outlet chamber 41 is formed by a fines discharge pipe 48, which is led into the separator housing 21 from the outside and is connected in a tangential arrangement to the outlet chamber 41. The fine material discharge pipe 48 is part of the product outlet 6. The lining of the junction of the fine material discharge pipe 48 with the outlet chamber 41 serves as a deflecting cone 49.

At the lower end of the conical housing end section 38, a sighting air inlet spiral 50 and a coarse material discharge 51 are assigned to the housing end section 38 in a horizontal arrangement. The direction of rotation of the sighting air inlet spiral 50 is opposite to the direction of rotation of the classifying wheel 8. Grobgutaustrag 51 is the housing end portion 38 detachably associated with the lower end of the Gehäusendabschnittes 38 a flange 52 and the upper end of Grobgutaustrages 51 assigned a flange 53 and both flanges 52 and 53 are in turn releasably connected together by known means when the air classifier ready to be sold.

The dispersing zone to be designed is designated 54. Flanges machined on the inner edge (chamfered) for a clean flow guidance and a simple lining are designated with 55.

Finally, a replaceable protective tube 56 is still applied to the inner wall of the outlet nozzle 20 as a wearing part and a corresponding replaceable protective tube 57 may be applied to the inner wall of the outlet chamber 41.

At the beginning of the operation of the air classifier 7 in the illustrated operating state, view air is introduced into the air classifier 7 at a pressure gradient and at a suitably chosen entry speed via the sighting air inlet spiral 50. As a result of the introduction of the classifying air by means of a spiral, in particular in conjunction with the conicity of the housing end portion 38, the classifying air rises spirally upward into the region of the classifying wheel 8. At the same time, the "product" of solid particles of different mass is introduced into the classifier housing 21 via the product feed port 39. From this product, the coarse material, d. H. the proportion of particles with greater mass against the classifying air in the region of the coarse material output 51 and is provided for further processing. The fines, d. H. the proportion of particles of lesser mass is mixed with the classifying air, passes from the outside to the inside radially through the classifying wheel 8 into the outlet nozzle 20, into the outlet chamber 41 and finally via a fine material outlet pipe 48 into a fine material outlet or outlet 58, and from there into a filter in that the resources are separated from each other in the form of a fluid, such as air, and fines. Coarser fines constituents are thrown radially out of the classifying wheel 8 and mixed with the coarse material in order to leave the classifier housing 21 with the coarse material or to circle in the classifier housing 21 until it has become fines of such a grain size that it is discharged with the classifying air.

As a result of the abrupt cross-sectional widening from the outlet nozzle 20 to the outlet chamber 41, there is a significant reduction in the flow velocity of the fine-material-air mixture. This mixture is thus at very low flow rate through the outlet chamber 41st get over the fines exit pipe 48 into the fines outlet 58 and produce only a small amount of abrasion on the wall of the outlet chamber 41. Therefore, the protective tube 57 is only a highly precautionary measure. However, the reasons for a good separation technology high flow velocity in the classifying wheel 8 still prevails in the discharge or outlet pipe 20, therefore, the protective tube 56 is more important than the protective tube 57. Particularly significant is the diameter jump with a diameter extension in the transition from the outlet nozzle 20 into the outlet chamber 41st

Incidentally, the air classifier 7 can again be well maintained by the division of the classifier housing 21 in the manner described and the assignment of the classifier components to the individual sub-housings and defective components can be replaced with relatively little effort and within short maintenance times.

While in the schematic representation of Fig. 2 2a, the classifying wheel 8 with the two cover disks 32 and 33 and the blade ring 59 arranged therebetween with the blades 34 is shown in already known, conventional form with parallel and parallel-sided cover disks 32 and 33 Fig. 3 or 3a, the classifying wheel 8 is shown for a further embodiment of the air classifier 7 of an advantageous development.

This classifying wheel 8 according to the Fig. 3 or 3a contains in addition to the blade ring 59 with the blades 34, the upper cover plate 32 and the axially downstream lower downstream cover plate 33 and is rotatable about the axis of rotation 40 and thus the longitudinal axis of the air classifier 7. The diametrical extent of the classifying wheel 8 is perpendicular to the axis of rotation 40, ie to the longitudinal axis of the air classifier 7, regardless of whether the axis of rotation 40 and thus said longitudinal axis is vertical or horizontal. The lower downstream cover disk 33 concentrically encloses the outlet nozzle 20. The blades 34 are connected to both cover disks 33 and 32. Deviating from the prior art, the two cover plates 32 and 33 are conical and preferably such that the distance between the upper cover plate 32 from the outflow side cover 33 from the rim 59 of the blades 34 inwards, ie toward the axis of rotation 40, and Although preferably continuous, such as linear or non-linear, and with further preference so that the surface of the flow-through cylinder jacket for each radius between the blade outlet edges and outlet nozzle 20 remains at least approximately constant. The decreasing due to the decreasing radius in known solutions outflow rate remains at least approximately constant in this solution.

Except for the above and in the Fig. 3 and 3a explained variant of the design of the upper cover plate 32 and the lower cover plate 33, it is also possible that only one of these two cover plates 32 or 33 is conical in the manner explained and the other cover plate 33 and 32 is flat, as in connection with the embodiment according to the Fig. 2 for both covers 32 and 33 is the case. In particular, the shape of the non-parallel-sided cover disk may be such that at least approximately so that the surface of the cylinder jacket through which flows through remains constant for each radius between blade outlet edges and outlet nozzle 20.

The invention, in particular the method according to the invention is illustrated by way of example in the description and in the drawing only and not limited thereto, but includes all variations, modifications, substitutions and combinations that the skilled person the present documents in particular in the context of the claims and the General representations in the introduction of this description and the description of the embodiments and their representations in the drawing and combine with his expert knowledge and the prior art. In particular, all individual features and Design options of the invention and its variants can be combined.

With the method described in detail above, any particles, in particular amorphous particles can be ground so that powdered solids having an average particle size d ₅₀ (TEM) <1.5 microns and a d ₉₀ value (TEM) <1.8 microns and a d ₉₉ value (TEM) <2 μm. In particular, it is possible to achieve these particle sizes or particle size distributions via dry milling.

The amorphous solids according to the invention are characterized in that they have an average particle size (TEM) d ₅₀ <1.5 μm, preferably d ₅₀ <1 μm, particularly preferably d ₅₀ from 0.01 to 1 μm, very particularly preferably d ₅₀ from 0.05 to 0.9 microns, more preferably d ₅₀ from 0.05 to 0.8 microns, more preferably from 0.05 to 0.5 microns and most preferably from 0.08 to 0.25 microns and a d ₉₀ value (TEM) <1.8 μm, preferably d ₉₀ from 0.1 to 1.5 μm, more preferably d ₉₀ from 0.1 to 1.0 μm, and very particularly preferably d ₉₀ from 0.1 to 0 , 5 microns and a d ₉₉ value (TEM) <2 microns, preferably d ₉₉ <1.8 microns, more preferably d ₉₉ <1.5 microns, most preferably d ₉₉ from 0.1 to 1.0 microns and particularly preferably have d ₉₉ of 0.25 to 1.0 microns. All previously mentioned particle sizes refer to the particle size determination by means of TEM analysis and image evaluation.

The amorphous solids of the invention are silica gels,
where silica gels include both hydro, aerosol and xerogels.

In a specific embodiment, the amorphous solids according to the invention are silica gels, in particular xerogels or aerogels, having an average particle size d ₅₀ (TEM) <1.5 μm, preferably d ₅₀ <1 μm, particularly preferably d ₅₀ of 0 , 01 to 1 .mu.m, most preferably d ₅₀ from 0.05 to 0.9 microns, more preferably d ₅₀ from 0.05 to 0.8 microns, more preferably from 0.05 to 0.5 microns and most preferably of 0.1 to 0.25 microns and a d ₉₀ value (TEM) of <1.8 microns, preferably d ₉₀ 0.05 to 1.8 .mu.m, particularly preferably d ₉₀ of 0.1 to 1.5 microns, most preferably d _{90 is} from 0.1 to 1.0 μm, particularly preferably d ₉₀ from 0.1 to 0.5 μm and especially preferably d ₉₀ from 0.2 to 0.4 μm and a d ₉₉ value (TEM ) <2 μm, preferably d ₉₉ <1.8 μm, particularly preferably d ₉₉ from 0.05 to 1.5 μm, very particularly preferably d ₉₉ from 0.1 to 1.0 μm, particularly preferably d ₉₉ of 0.25 to 1.0 μm, and more preferably d ₉₉ from 0.25 to 0.8 μm. All previously mentioned particle sizes refer to the particle size determination by means of TEM analysis and image evaluation.

The reaction conditions and the physical / chemical data of the precipitated silicas according to the invention are determined by the following methods:

Particle size determinations

In the following examples, particle sizes are named at various points, which were measured by one of the three following methods. The reason for this is that the particle sizes mentioned there extend over a very wide particle size range (~100 nm to 1000 μm). Depending on the expected particle size of the sample to be examined therefore each of a different one of the three particle size measurement methods come into question.

Particles with an expected average particle size of approx.> 50 μm were determined by sieving. Particles with an expected average particle size of approx. 1 - 50 μm were examined by means of the laser diffraction method and for particles with an expected average particle size <1.5 μm the TEM analysis + image processing was used.

Which method was used to determine the particle sizes mentioned in the examples is indicated in the tables by footnote. The particle sizes mentioned in the claims relate exclusively to the determination of the particle size by means of transmission electron microscopy (TEM) in combination with image analysis.

1. Determination of particle distribution by sieving

To determine the particle distribution, the sieve fractions are determined by means of a shaker (Retsch AS 200 Basic).

• Staubwanne, 45 µm, 63 µm, 125µm, 250 µm, 355 µm, 500 µm.

For the sieve analysis, the test sieves with a defined mesh size are stacked in the following order:

• Dust pan, 45 μm, 63 μm, 125 μm, 250 μm, 355 μm, 500 μm.

The resulting sieve tower is mounted on the screening machine. For sieving, 100 g of solid are weighed to the nearest 0.1 g and added to the top sieve of the sieve tower. It is shaken for 5 minutes at an amplitude of 85.

After the screening has been switched off automatically, the individual fractions are weighed back to 0.1 g. The fractions must be weighed immediately after shaking, otherwise it can lead to distorted results due to moisture losses.

The combined weights of the individual fractions should be at least 95 g to evaluate the result.

2. Determination of the particle size distribution by means of laser diffraction (Horiba LA 920)

The determination of the particle distribution is based on the principle of laser diffraction on a laser diffractometer (Horiba, LA-920).

First, the sample of the amorphous solid in 100 ml of water without the addition of dispersing additives in a 150 ml beaker (diameter: 6 cm) is dispersed so that a dispersion with a weight fraction of 1 wt .-% SiO ₂ is formed. This dispersion is then dispersed intensively (300 W, not pulsed) with an ultrasonic finger (Dr. Hielscher UP400s, Sonotrode H7) over a period of 5 min. For this, the ultrasound finger is to be mounted in such a way that its lower end dips to about 1 cm above the bottom of the beaker. Immediately following the dispersion, the particle size distribution is determined from a partial sample of the dispersion subjected to ultrasound with the laser diffractometer (Horiba LA-920). For evaluation with the supplied standard software of the Horiba LA-920, a refractive index of 1.09 must be selected.

All measurements are carried out at room temperature. The particle size distribution and the relevant variables such. For example, particle size d ₉₀ and d ₉₉ are automatically calculated and graphed by the instrument. The instructions in the operating instructions must be observed.

3. Determination of Particle Size by Transmission Electron Microscopy (TEM) and Image Analysis

The transmission electron micrographs (TEM) are generated on the basis of ASTM D 3849-02.

For the image-analytical measurements, a transmission electron microscope (Hitachi H-7500, with a maximum acceleration voltage of 120 KV) is used. The digital image processing is done by a software of the company Soft Imaging Systems (SIS, Münster / Westphalia). The program version iTEM 5.0 is used.

For the determinations, about 10-15 mg of the amorphous solid are dispersed in an isopropanol / water mixture (20 ml isopropanol / 10 ml distilled water) and ultrasonicated for 15 min (ultrasound processor UP 100, Dr. Hielscher GmbH, HF - power 100 W, HF frequency 35 kHz). Thereafter, a small amount (about 1 ml) is removed from the finished dispersion and then applied to the carrier mesh. The excess dispersion is absorbed with filter paper. Then the netting is dried.

The choice of magnification is described in ITEM WK 5338 (ASTM) and depends on the primary particle size of the amorphous solid to be investigated. Typically, in the case of silicas, the electron optical magnification 50,000: 1 and the final magnification 200,000: 1 are selected. For digital imaging systems, ASTM D 3849 specifies the appropriate resolution in nm / pixel depending on the primary particle size of the amorphous solid to be measured.

The recording conditions must be arranged in such a way that the reproducibility of the measurements can be guaranteed.

The individual particles to be characterized on the basis of the TEM images must be imaged with sufficiently sharp contours be. The distribution of the particles should not be too dense. The particles should be as separate as possible. There should be as few overlaps as possible.

After screening various image sections of a TEM preparation, suitable areas are selected accordingly. It should be noted that the ratio of small, medium and large particles for each sample is representative and characteristic and no selective preference of small or large particles by the operator.

The total number of aggregates to be measured depends on the range of aggregate sizes: the larger this is, the more particles have to be detected in order to arrive at an adequate statistical statement. For silicas, about 2500 individual particles are measured.

The primary particle sizes and size distributions are determined on the basis of TEM images specially prepared for this purpose; these are analyzed by means of a particle size analyzer TGZ3 according to Endter and Gebauer (Sales: Carl Zeiss). The entire measurement process is supported by the analysis software DASYLab 6.0 - 32.

First, the measuring ranges are calibrated according to the size range of the particles to be examined (determination of the smallest and largest particles), after which the measurements are made. An enlarged transparency of a TEM image is positioned on the evaluation desk so that the center of gravity of a particle lies approximately in the middle of the measurement mark. Then, by turning the handwheel on the TGZ3, the diameter of the circular measuring mark is changed until the best possible surface alignment with the image object to be analyzed is achieved.

Often, the structures to be analyzed are not circular. Then it is true that they project beyond the measuring mark Surface portions of the particles must be adapted to those surface portions of the measurement mark, which are outside the particle boundary. If this adjustment has taken place, the actual counting process is triggered by actuation of a foot switch. The particle in the area of the measuring mark is perforated by a knock-down marking pen.

Thereafter, the TEM film is again shifted on the evaluation lectern until a new particle is adjusted below the measurement mark. A new adjustment and counting procedure takes place. This is repeated until all of the evaluation statistics are characterized according to required particles.

The number of particles to be counted depends on the range of the particle size: the larger it is, the more particles must be detected in order to arrive at an adequate statistical statement. For silicas, about 2500 individual particles are measured.

After completion of the evaluation, the values of the individual counters are logged.

The average particle size d ₅₀ is the mean value of the equivalence diameter of all particles evaluated. In order to determine the particle sizes d ₉₀ and d ₉₉ , the equivalent diameters of all the particles evaluated are in classes of 25 nm each (0-25 nm, 25-50 nm, 50-100 nm, ... 925-950 nm, 950-975 nm, 975-1000 nm) and the frequencies in the respective classes are determined. From the cumulative representation of this frequency distribution, the particle sizes d ₉₀ (ie 90% of the particles evaluated have a smaller equivalent diameter) and d ₉₉ can be determined.

Determination of specific surface area (BET)

The specific nitrogen surface area (hereinafter referred to as the BET surface area) of the pulverulent solids is determined on the basis of ISO 5794-1 / Annex D with the TRISTAR 3000 device (Micromeritics) after the multipoint determination in accordance with DIN ISO 9277.

Determination of the N ₂ Pore volume and pore radius distribution of mesoporous solids by nitrogen sorption

The measuring principle is based on nitrogen sorption at 77 K (volumetric method) and can be used for mesoporous solids (2 nm to 50 nm pore diameter).

The determination of the pore size distribution is carried out according to DIN 66134 (determination of the pore size distribution and the specific surface of mesoporous solids by nitrogen sorption, according to Barrett, Joyner and Halenda (BJH)).

Drying of the amorphous solids takes place in a drying cabinet. Sample preparation and measurement are carried out with the ASAP 2400 device (Micromeritics). As measuring gases nitrogen 5.0 and helium 5.0 are used. The cooling bath is liquid nitrogen. Weighing weights are precisely determined with an analytical balance in [mg] to one decimal place.

The sample to be tested is pre-dried at 105 ° C for 15-20 h. Of these, 0.3 to 1 g are weighed into a sample vessel. The sample vessel is connected to the ASAP 2400 device and baked at 200 ° C. for 60 minutes under vacuum (final vacuum <10 μm Hg). The sample cools to room temperature under vacuum, is blanketed with nitrogen and weighed. The difference to the weight of the filled with nitrogen sample vessel without solid results in the exact weight.

The measurement is carried out according to the operating instructions of the ASAP 2400.

For evaluation of the N ₂ pore volume (pore diameter <50 nm), the adsorbed volume is determined on the basis of the desorption branch (pore volume for pores with a pore diameter <50 nm).

The pore radius distribution is calculated from the measured nitrogen isotherms according to the BJH method ( EP Barett, LG Joyner, PH Halenda, J. Amer. Chem. Soc., Vol. 73, 373 (1951 )) and displayed as a distribution curve.

The average pore size (pore diameter, APD) is calculated according to the Wheeler equation $$\begin{array}{l}\mathrm{APD}\left[\mathrm{nm}\right]=4000*\mathrm{mesopore}\left[{\mathrm{cm}}^3/\mathrm{G}\right]/\mathrm{BET\; surface\; area}\\ \left[{\mathrm{m}}^2/\mathrm{G}\right],\end{array}$$

Determination of the moisture or the loss of drying

The moisture of amorphous solids is determined according to DIN EN ISO 787-2 after drying for 2 hours in a convection oven at 105 ° C. This drying loss consists predominantly of water moisture.

Determination of pH

The determination of the pH of the amorphous solids is carried out as a 5% aqueous suspension at room temperature based on DIN EN ISO 787-9. Compared to the specifications of this standard, the initial weights were changed (5.00 g SiO ₂ to 100 ml deionized water).

Determination of DBP uptake

• 12.50 g pulverförmiger, amorpher Feststoff (Feuchtegehalt 4 ± 2 %) werden in die Kneterkammer (Artikel Nummer 279061) des Brabender-Absorptometer "E" gegeben (ohne Dämpfung des Ausgangsfilters des Drehmomentaufnehmers). Unter ständigem Mischen (Umlaufgeschwindigkeit der Kneterschaufeln 125 U/min) tropft man bei Raumtemperatur durch den "Dosimaten Brabender T 90/50" Dibutylphthalat mit einer Geschwindigkeit von 4 ml/min in die Mischung. Das Einmischen erfolgt mit nur geringem Kraftbedarf und wird anhand der Digitalanzeige verfolgt. Gegen Ende der Bestimmung wird das Gemisch pastös, was mittels eines steilen Anstieges des Kraftbedarfs angezeigt wird. Bei einer Anzeige von 600 digits (Drehmoment von 0.6 Nm) wird durch einen elektrischen Kontakt sowohl der Kneter als auch die DBP-Dosierung abgeschaltet. Der Synchronmotor für die DBP-Zufuhr ist mit einem digitalen Zählwerk gekoppelt, so dass der Verbrauch an DBP in ml abgelesen werden kann.

The DBP absorption (DBP number), which is a measure of the absorbency of amorphous solids, is determined on the basis of the DIN 53601 standard as follows:

• 12.50 g of powdery, amorphous solid (moisture content 4 ± 2%) are added to the kneader chamber (item number 279061) of the Brabender Absorptometer "E" (without damping the output filter of the torque transducer). With constant mixing (rotary speed of the kneader blades 125 rpm) is added dropwise at room temperature through the "Dosimaten Brabender T 90/50" dibutyl phthalate at a rate of 4 ml / min in the mixture. The mixing takes place with only a small force requirement and is tracked on the basis of the digital display. Towards the end of the determination, the mixture becomes pasty, which is indicated by a steep increase in the power requirement. With a display of 600 digits (torque of 0.6 Nm), both the kneader and the DBP metering are switched off by an electrical contact. The synchronous motor for the DBP supply is coupled to a digital counter so that the consumption of DBP in ml can be read.

• mit DBP = DBP-Aufnahme in g/100g
• V = Verbrauch an DBP in ml
• D = Dichte von DBP in g/ml (1,047 g/ml bei 20 °C)
• E = Einwaage an Kieselsäure in g
• K = Korrekturwert gemäß Feuchtekorrekturtabelle in g/100g

The DBP recording is given in units of [g / 100g] without decimal places and is calculated using the following formula: $$\mathit{DBP}=\frac{V*D*100}{e}*\frac{G}{100G}+K$$

• with DBP = DBP uptake in g / 100g
• V = consumption of DBP in ml
• D = density of DBP in g / ml (1.047 g / ml at 20 ° C)
• E = weight of silica in g
• K = correction value according to the humidity correction table in g / 100g

The DBP image is defined for anhydrous, amorphous solids. When using wet precipitated silicas or silica gels, the correction value K for the calculation of the To consider DBP inclusion. This value can be determined from the following correction table, eg. For example, a water content of the silica of 5.8% would mean a 33 g / (100 g) addition for DBP uptake. The moisture content of the silica or of the silica gel is determined according to the method "Determination of the moisture or the drying loss" described below.

Moisture correction table for dibutyl phthalate uptake - anhydrous % Moisture % Humidity .0 .2 .4 .6 .8th 0 0 2 4 5 7 1 9 10 12 13 15 2 16 18 19 20 22 3 23 24 26 27 28 4 28 29 29 30 31 5 31 32 32 33 33 6 34 34 35 35 36 7 36 37 38 38 39 8th 39 40 40 41 41 9 42 43 43 44 44 10 45 45 46 46 47

Determination of tamped density

The determination of the tamped density is based on DIN EN ISO 787-11.

A defined amount of a previously unsorted sample is filled into a graduated glass cylinder and subjected to a fixed number of stacks by means of a tamping volumeter. During the stamping, the sample condenses. As a result of the examination, the tamped density is obtained.

The measurements are carried out on a tamping volumeter with counter from Engelsmann, Ludwigshafen, type STAV 2003.

First, a 250 ml glass cylinder is tared on a precision balance. Subsequently, 200 ml of the amorphous solid are filled with the aid of a powder funnel in the tared measuring cylinder so that no cavities form. The sample quantity is then weighed to the nearest 0.01 g. Thereafter, lightly tapping the cylinder so that the surface of the silica in the cylinder is horizontal. The measuring cylinder is in The measuring cylinder holder of the tamping volumeter used and tamped 1250 times. The volume of the mashed sample is read to 1 ml after a single ramming pass.

D(t):

Stampfdichte [g/l]

V:

Volumen der Kieselsäure nach dem Stampfen [ml]

m:

Masse der Kieselsäure [g]

The tamped density D (t) is calculated as follows: $$\mathrm{D}\left(\mathrm{t}\right)=\mathrm{m}*1000/\mathrm{V}$$

D (t):

Tamped density [g / l]

V:

Volume of silica after pounding [ml]

m:

Mass of silica [g]

Determination of the alkali number

The alkali number determination (AZ) is understood to mean the consumption of hydrochloric acid in ml (at 50 ml test volume, 50 ml distilled water and a hydrochloric acid used of concentration 0.5 mol / l) in a direct potentiometric titration of alkaline solutions or suspensions up to a pH of 8.30. The free alkali content of the solution or suspension is hereby recorded.

The pH device (Knick, type: 766 pH meter Calimatic with temperature sensor) and the pH electrode (combination electrode from Schott, type N7680) are heated at room temperature with the aid of two buffer solutions (pH = 7.00 and pH = 10.00) calibrated. The combination electrode is immersed in the 40 ° C tempered solution or suspension consisting of 50.0 ml of sample and 50.0 ml of deionized water. Then add hydrochloric acid solution of concentration 0.5 mol / l dropwise until a constant pH of 8.30 is reached. Due to the slowly adjusting equilibrium between the silica and the free alkali content it takes a waiting time of 15 minutes until a final reading of the Acid consumption. For the selected molar amounts and concentrations, the read-out hydrochloric acid consumption in ml corresponds directly to the alkali number, which is given dimensionlessly.

The examples below serve, as already stated, to illustrate and explain the invention in more detail, but in no way limit it.

Starting materials : Silica 1:

The precipitated silica used as the starting material to be ground was prepared according to the following procedure:
The water glass and the sulfuric acid used at various points in the following recipe for the preparation of the silica 1 are characterized as follows: Water glass: Density 1.348 kg / l, 27.0 wt% SiO ₂ , 8.05 wt% Na ₂ O Sulfuric acid: Density 1.83 kg / l, 94% by weight

117 m ^{3 of} water are placed in a 150 m ³ precipitation tank with inclined base, MIG inclined blade agitation system and Ekato fluid shear turbine and 2.7 m ^{3 of} water glass are added. The ratio of water glass to water is adjusted so that there is an alkali number of 7. Subsequently, the Heated template to 90 ° C. After reaching the temperature, water glass at a metering rate of 10.2 m ³ / h and sulfuric acid at a metering rate of 1.55 m ³ / h are metered in simultaneously with stirring over a period of 75 min. Thereafter, water glass at a metering rate of 18.8 m ³ / h and sulfuric acid at a metering rate of 1.55 m ³ / h are added simultaneously for a further 75 min with stirring at 90 ° C. If necessary, the dosing rate of the sulfuric acid is corrected during the entire time of addition so that an alkali number of 7 is maintained during this period.

Thereafter, the Wasserglasdosierung is switched off. Sulfuric acid is then added over 15 minutes so that a pH value of 8.5 is reached. At this pH, the suspension is stirred for a period of 30 minutes (= aged). Thereafter, the pH of the suspension is adjusted to 3.8 by addition of sulfuric acid within about 12 min. During precipitation, aging and acidification, the temperature of the precipitation suspension is maintained at 90 ° C.

The resulting suspension is filtered with a membrane filter press and the filter cake washed with deionized water until a conductivity of <10 mS / cm is observed in the wash water. The filter cake is then present with a solids content of <25%.

The drying of the filter cake takes place in a spin-flash dryer.

The data of silica 1 are given in Table 1.

Hydrogel production

From water glass (density 1.348 kg / l, 27.0 wt .-% SiO ₂ , 8.05 wt .-% Na ₂ O) and 45% sulfuric acid, a silica gel (= hydrogel) is prepared.

For this purpose, 45% strength by weight sulfuric acid and soda water glass are intensively mixed in such a way that a reactant ratio corresponding to an excess of acid (0.25 N) and an SiO ₂ concentration of 18.5% by weight is established. The resulting hydrogel is stored overnight (about 12 h) and then broken to a particle size of about 1 cm. It is washed with deionized water at 30-50 ° C until the conductivity of the wash water is below 5 mS / cm.

Silica 2 (hydrogel)

The hydrogel prepared as described above is aged with ammonia addition at pH 9 and 80 ° C for 10-12 hours, and then adjusted to pH 3 with 45 wt .-% sulfuric acid. The hydrogel then has a solids content of 34-35%. It is then coarsely ground on a pin mill (Alpine Type 160Z) to a particle size of approx. 150 μm. The hydrogel has a residual moisture of 67%.

The data of silica 2 are given in Table 1.

Silica 3a:

Silica 2 is by means of spin flash dryer (Anhydro A / S, APV, type SFD47, T _a = 350 ° C, T _out = 130 ° C) dried so that, after drying, it has a final moisture content of about 2%.

The data of silica 3a are given in Table 1.

Silica 3b:

The hydrogel prepared as described above is further washed at about 80 ° C until the conductivity of the wash water is below 2 mS / cm and dried in a convection oven (Fresenberger POH 1600.200) at 160 ° C to a residual moisture content of <5%. In order to achieve a more uniform dosing behavior and grinding result, the xerogel is pre-shredded to a particle size <100 μm (Alpine AFG 200).

The data of silica 3b are given in Table 1.

Silica 3c:

The hydrogel prepared as described above is aged with addition of ammonia at pH 9 and 80 ° C for 4 hours, then adjusted with 45 wt .-% sulfuric acid to about pH 3 and in a convection oven (Fresenberger POH 1600.200) at 160 ° C to a Residual moisture of <5% dried. In order to achieve a more uniform dosing behavior and grinding result, the xerogel is pre-shredded to a particle size <100 μm (Alpine AFG 200).

The data of silica 3c are given in Table 1. Table 1 - Physico-chemical data of the unmilled starting materials Silica 1 Silica 2 Silica 3a Silica 3b Silica 3c Particle size distribution by laser diffraction (Horiba LA 920) d ₅₀ [.Mu.m] 22.3 nb nb nb nb d ₉₉ [.Mu.m] 85.1 nb nb nb nb d ₁₀ [.Mu.m] 8.8 nb nb nb nb Particle size distribution using sieve analysis > 250 μm % nb nb nb 0, 0 0.2 > 125 μm % nb nb nb 1.06 2.8 > 63 μm % nb nb nb 43.6 57.8 > 45 μm % nb nb nb 44.0 36.0 <45 μm % nb nb nb 10.8 2, 9 humidity % 4.8 67% <3% <5% <5% PH value - 6.7 nb nb nb nb nb = not determined

Examples 1 - 3: Milling according to the invention

To prepare the actual grinding with superheated steam, a fluidized bed counter-jet mill according to FIG. 1 . 2a and 3a first via the two heating nozzles 5a (of which in FIG. 1 only one shown), which are charged with 10 bar and 160 ° C hot compressed air, heated to a mill outlet temperature of about 105 ° C.

The mill is downstream of the filtration of the ground material a filter unit (not in FIG. 1 shown), the filter housing is heated in the lower third indirectly via attached heating coils by means of 6 bar saturated steam also to prevent condensation. All equipment surfaces in the area of the mill, the separation filter, as well as the supply lines for steam and hot compressed air are particularly insulated.

After reaching the desired heating temperature, the supply of the heating nozzles with hot compressed air is switched off and the admission of the three grinding nozzles with superheated steam (38 bar (abs), 330 ° C) started.

To protect the filter medium used in the separating filter and for setting a certain residual water content of the ground material preferably from 2 to 6%, water is injected in the starting phase and during grinding in the grinding chamber of the mill via a two-fluid nozzle operated with compressed air in dependence on the mill outlet temperature.

The product task is started when the relevant process parameters (see Table 2) are constant. The regulation of the feed quantity is dependent on the self-adjusting stream. The classifier flow regulates the feed quantity such that approx. 70% of the nominal flow can not be exceeded.

As an entry member (4) acts while a speed-controlled feeder, which doses the feed material from a storage container via serving as a barometric conclusion cycle lock in the standing under pressure Mahlkammer.

The crushing of the coarse material takes place in the expanding steam jets (grinding gas). Together with the expanded grinding gas, the product particles in the center of the mill container rise to the classifying wheel. Depending on the set speed of the sifter and the amount of grinding steam (see Table 1), the particles which have a sufficient fineness pass with the grinding steam into the fine-material outlet and from there into the downstream one Separation system, while too coarse particles go back into the grinding zone and subjected to a further crushing. The discharge of the separated fine material from the separation filter in the subsequent ensiling and packaging is done by means of rotary valve.

The grinding pressure of the grinding gas prevailing at the grinding nozzles, or the resulting amount of grinding gas in conjunction with the speed of the dynamic Schaufelradsichters determine the fineness of the grain distribution function and the upper grain limit.

The relevant process parameters can be found in Table 2, the product parameters in Table 3: Table 2 example example 1 Example 2 Example 3a Example 3b Example 3c starting material Silica 1 Silica 2 Silica 3a Silica 3b Silica 3c Nozzle diameter [Mm] 2.5 2.5 2.5 2.5 2.5 nozzle type Laval Laval Laval Laval Laval number [Piece] 3 3 3 3 3 Mill internal pressure [bar abs.] 1.306 1,305 1,305 1,304 1,305 inlet pressure [bar abs.] 37.9 37.5 36.9 37.0 37.0 inlet temperature [° C] 325 284 327 324 326 Mill outlet temperature [° C] 149.8 117 140.3 140.1 139.7 classifier [min ^-1 ] 5619 5500 5491 5497 5516 classifier flow [A%] 54.5 53.9 60.2 56.0 56.5 Stanchion diameter [Mm] 100 100 100 100 100 example 1 Example 2 Example 3a Example 3b Example 3c d ₅₀ ¹⁾ nm 125 106 136 140 89 nm 275 175 275 250 200 d ₉₉ ¹⁾ nm 525 300 575 850 625 BET surface area m ² / g 122 354 345 539 421 N ₂ pore volume ml / g nb 1.51 1.77 0.36 0, 93 Average pore size nm nb 17.1 20.5 2.7 8.8 DBP (anhydrous) g / 100g 235 293 306 124 202 tapped density g / l 42 39 36 224 96 Drying loss % 4.4 6.1 5.5 6.3 6.4 ¹⁾ Determination of Particle Size Distribution by Transmission Electron Microscopy (TEM) and Image Analysis

LIST OF REFERENCE NUMBERS

1

jet mill

2

cylindrical housing

3

grinding chamber

4

Mahlgutaufgabe

5

milling jet

5a

heating nozzles

6

product outlet

7

air classifier

8th

classifying wheel

8a

classifier

9

Inlet opening or inlet nozzle

10

milling jet

11

heating source

12

heating source

13

feed pipe

14

temperature-insulating jacket

15

inlet

16

outlet

17

Center of the grinding chamber

18

Reservoir or generating device

19

line devices

20

outlet connection

21

classifier

22

Housing top

23

Housing bottom

24

circumferential flange

25

circumferential flange

26

joint

27

arrow

28

Classifying chamber housing

28a

carrying arms

29

discharge cone

30

flange

31

flange

32

cover disc

33

cover disc

34

shovel

35

classifying wheel shaft

35a

pivot bearing

35b

Shaft bushing

36

upper machined plates

37

lower machined plate

38

housing end

39

Product feeding connection

40

axis of rotation

41

exit chamber

42

upper cover plate

43

removable lid

44

carrying arms

45

conical ring housing

46

Suction

47

perforated plate

48

Feingutaustragrohr

49

deflection cone

50

Air inlet spiral

51

coarse material

52

flange

53

flange

54

dispersing zone

55

flanges and lining machined on the inside edge (beveled)

56

replaceable thermowell

57

replaceable thermowell

58

Fines outlet / outlet

59

blade ring

Claims (16)

1. Amorphous pulverulent solids having a median particle size d₅₀ (TEM) of < 1.5 µm and a d₉₀ value (TEM) of < 1.8 µm and a d₉₉ value (TEM) of < 2 µm and they are silica gels which additionally have a pore volume of 0.2 to 0.7 ml/g or in that they are silica gels which additionally have a pore volume of 0.8 to 1.5 ml/g or they are silica gels which additionally have a pore volume of 1.5 to 2.1 ml/g.
2. Process for preparing amorphous solids according to Claim 1 by milling amorphous solids by means of a milling system (milling apparatus), preferably a milling system comprising a jet mill, particularly preferably a milling system comprising a fluidized-bed opposed jet mill or a dense-bed jet mill or a spiral jet mill, characterized in that the mill is operated in the milling phase with an operating medium selected from the group consisting of gas and/or vapour, preferably steam, and/or a gas containing steam, and in that the milling chamber is heated in a heat-up phase, i.e. before the actual operation with the operating medium, in such a way that the temperature in the milling chamber and/or at the mill exit is higher than the dew point of the vapour and/or operating medium.
3. Process according to Claim 2, characterized in that the milling system or the mill is operated in the heat-up phase with hot gas and/or a gas mixture, preferably with hot air and/or combustion gases and/or inert gases and/or mixtures thereof.
4. Process according to Claim 3, characterized in that the hot gas and/or gas mixture is passed into the milling chamber during the heat-up phase through inlets, preferably nozzles, which differ from those through which the operating medium is let down during the milling phase, and/or the hot gas and/or gas mixture is passed into the milling chamber during the heat-up phase through the inlets, preferably nozzles, through which the operating medium is also let down during the milling phase.
5. Process according to one of Claims 2 to 4, characterized in that dry gas and/or a dry gas mixture, preferably dry air and/or combustion gas and/or inert gas and/or a mixture thereof is passed through the mill for cooling.
6. Process according to one of Claims 2 to 5, characterized in that condensation of the steam on assemblies and/or components of the milling system or of the mill is prevented.
7. Process according to one of Claims 2 to 6, characterized in that the temperature of the operating medium in the milling phase is in the range of 200 to 800°C and/or in that the pressure of the operating medium in the milling phase is in the range of 15 to 250 bar.
8. Process according to one of Claims 2 to 7, characterized in that classification of the milled material is effected, preferably by means of an integrated and/or dynamic classifier, particularly preferably means by of an integrated dynamic paddle wheel classifier and/or air classifier.
9. Process according to Claim 8, characterized in that a jet mill (1) comprising an integrated dynamic air classifier (7) is used, the speed of a classifying rotor or wheel (8) of the air classifier (7) and the internal amplification ratio V (= Di/DF) being chosen or set so that the circumferential speed of the operating medium (B) at a dip tube or outlet nozzle (20) coordinated with the classifying wheel reaches up to 0.8 times the sound velocity of the operating medium (B).
10. Process according to either of Claims 8 and 9, characterized in that a milling system is used in which flushing of the gap between the classifying wheel and the classifier housing (classifier gap) and/or the shaft lead-through between the classifying wheel shaft and the classifier housing is possible and/or is carried out.
11. Process according to any of Claims 8 to 10, characterized in that a jet mill (1) comprising an integrated dynamic air classifier (7) which contains a classifying wheel (8) and a classifying wheel shaft (35) and a classifying wheel housing (21), a classifier gap (8a) being formed between the classifying wheel (8) and the classifying wheel housing (21) and a shaft lead-through (35b) being formed between the classifying wheel shaft (35) and the classifier housing (21), is used, and in that flushing of classifier gap (8a) and/or shaft lead-through (35b) with compressed gases of low energy content is effected.
12. Process according to any of Claims 8 to 11, characterized in that the amount of milling gas which enters the classifier is regulated so that the median particle size (TEM) d₅₀ of the milled material obtained is less than 1.5 µm and/or the d₉₀ value is < 2 µm and/or the d₉₉ value is < 2 µm.
13. Process according to any of Claims 2 to 12, characterized in that the amorphous solids are gels or particles containing aggregates and/or agglomerates, preferably amorphous solids containing or consisting of at least one metal and/or at least one metal oxide, particularly preferably amorphous oxides of metals of the 3rd and 4th main group of the Periodic Table of the Elements.
14. Process according to any of Claims 2 to 13, characterized in that amorphous particles which have already been subjected to a drying step are milled or in that a filter cake of amorphous particles or a hydrogel is milled or simultaneously milled and dried.
15. Use of the amorphous solids according to Claim 1 in coating systems.
16. Coating material containing at least one amorphous solid according to Claim 1.

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