EP1838614A2

EP1838614A2 - Method for producing mixed oxides by way of spray pyrolysis

Info

Publication number: EP1838614A2
Application number: EP05823940A
Authority: EP
Inventors: Günter Riedel; Matthias Koch; Stefan Ambrosius; Steffen Frank; Tarek Khalil; Lars Leidolph
Original assignee: Merck Patent GmbH
Current assignee: Ibu Tec Advanced Materials AG
Priority date: 2005-01-19
Filing date: 2005-12-24
Publication date: 2007-10-03
Also published as: KR20070094649A; US20080318761A1; JP2008529758A; DE102005002659A1; WO2006076964A3; CN101124180A; CN100575300C; AU2005325582A2; WO2006076964A2; AU2005325582A1

Abstract

The invention relates to a novel method for producing compact, spherical mixed oxide powders having an average particle size > 10 νm by way of spray pyrolysis. The invention also relates to the use of said powders as luminescent substances, as base material for luminescent substances or as a starting material for the manufacture of ceramics or for the production of high-density, high-strength and optionally transparent bulk material by way of hot-press molding techniques.

Description

Process for the preparation of mixed oxides by means of

spray pyrolysis

The present invention relates to a novel process for the production of compact, spherical mixed oxide powders having an average particle size <10 μm by spray pyrolysis, and to the use thereof.

Mixed oxide powders with particle sizes in the nanometer or submicrometer range are essentially produced by the following processes:

Mixing, drying and subsequent thermal decomposition of oxides, carbonates, nitrates, acetates, chlorides or the like. Salts (solid-state reaction); Coprecipitation and subsequent drying and calcination; SoI gel technique; Hydrolysis of alkoxides; Plasma spraying process; Spray pyrolysis of aqueous and organic salt solutions.

Spray pyrolysis (SP) is one of the aerosol processes characterized by the spraying of solutions, suspensions or dispersions in a reaction chamber (reactor) heated in different ways, as well as the formation and separation of solid particles. In contrast to the spray-drying with hot gas temperatures <300 ⁰ C in addition, the thermal decomposition of the starting materials used find in the spray pyrolysis as a high-temperature process in addition to the evaporation of the solvent (for. Example salts) and, for the formation of substances (., Oxides, mixed oxides ) instead of.

Differences in heat generation and transfer, the supply of energy and feed product, the type of aerosol production and the type of particle separation, there are a variety of process variants, which are also characterized by different reactor designs:

❖ Hot wall reactor - externally electrically heated pipe if necessary with separately controllable heating zones; low energy input at Einsprühpunkt;

^♦ > Flame pyrolysis reactor - energy and hot gas production by means of

Reaction of fuel gas (eg hydrogen) with oxygen or air; Spraying directly into the flame or into the hot combustion gases in the area near the flame; very high energy input at the injection point

^♦ : ^♦ hot gas reactor - hot gas generation by

# Electric gas heater (introducing the aerosol into the carrier gas, variable but mostly limited (low) energy input at the injection point)

# flameless, pulsating combustion of hydrogen or natural gas with air in a pulsation reactor; broadly controllable energy input at the point of injection; pulsating gas flow with a high degree of turbulence (see international patent application WO 02/072471 of Merck Patent GmbH)

Spray pyrolysis methods prove to be particularly effective if it is possible to achieve the desired powder properties such as grain size, particle size distribution, particle morphology and content of crystallographic phases without further aftertreatment.

The following process variants of the literature are described for this situation:

Kuntz et al. (DE 3916643 A1) claim a process for the production of oxidic ceramic powders by spray pyrolysis of metal nitrate solutions in the presence of organic substances acting as fuel, such as, for example, ethanol, isopropanol, tartaric acid or elemental carbon. It is the production of zinc oxide with additives of Bi, Mn, Cr, Co, Sb ₂ θ _3, and Bi ₂ Ti ₂ O ₇ - explained powder.

Hilarius (DE 4320836 A1) describes a process for producing a

Metal oxide powder containing the doping elements for a ceramic varistor based on doped zinc oxide, wherein the metal oxide powder crystalline phases having spinel and / or pyrochlore structure, characterized in that first compounds of the required doping elements in the proposed stoichiometric ratio to a mixed aqueous homogeneous-disperse solution and then subjected to the spray pyrolysis.

In DE 4307 333 A1 (Butzke) it is proposed to first disperse and emulsify the mixed nitrate solutions with the elements Zn, Sb, Bi, Co, Mn, Cr before the spray pyrolysis in an organic phase in order to produce finely divided, spherical metal oxide powders.

In the Journal of the Korean Ceramic Soc. 27 (1990), No. 8; Pp. 955-964 describes the preparation of Al ₂ O ₃ -ZrO ₂ composite powders with an emulsion

Spray pyrolysis method reported being used as starting materials Al ₂ (SO ₄₎ ₃ ^'14 H ₂ O and ZrOCl _^2' 8H ₂ O. It is a hot wall reactor with temperatures in the range of 900-950 ⁰ C applied. Due to the short residence times, the phase formation of alpha-Al ₂ O ₃ and tetragonal ZrO ₂ in the sense of a composite could be obtained only after an additional annealing at a temperature of 1200 ⁰ C and not directly reacted to a uniform phase uniform mixed oxide.

WO 0078672 A1 describes the use of a permeation u. Hot gas reactor, a spray pyrolysis method and the sputtering of metal salt solutions or suspensions by means of sputtering nozzle plate u. piezoceramic oscillator.

WO 02072471 A1 describes a process for the preparation of multinary metal oxide powders for their use as precursors for high-temperature superconductors, wherein the corresponding metal oxide powders are produced in a pulsation reactor and at least three elements selected from Cu. Bi, Pb, Y. Tl ₁ Hg, La, lanthanides, alkaline earth metals.

EP 0 371 211 describes a spray calcination for producing ceramic powder by spraying solutions or suspensions with a nozzle into a flame pyrolysis reactor. For spraying a combustible gas (hydrogen) is used. This means that the fuel gas and the salt solutions through a two-fluid nozzle in the same place in the - A -

Arrive reactor. The air required for combustion flows through a frit at the top of the reactor.

According to DE 195 05 133 A1, the hydrogen flame pyrolysis takes place by supplying the salt solutions with the oxygen gas as a component of the reaction gas to the reactor.

It is apparent from the specification of the patent EP 703 188 B1 that doped, amorphous and completely converted ZnO powders can be produced by reacting the combination of an oxidizing agent with a reducing agent in a temperature range between 220 and 260 ^° C. In an exothermic reaction, the desired oxide is formed in powder form.

EP 1 142 830 A1 discloses pyrolytically produced oxidic nanopowders, such as, for example, ZrO ₂ , TiO ₂ and Al ₂ O ₃ , which have a spec. Surface in the range of 1 - 600 m ² / g and a chloride content <0.05% claimed.

According to JP10338520, yttrium-aluminum oxide powders can be prepared by spray calcination of aqueous yttrium and aluminum salt solutions, preferably using poly (aluminum chloride) as a starting material.

WO2003 / 070640 A1 describes a process for producing nanopowders based on Al ₂ O ₃ , SiO ₂ ; TiO ₂ , ZrO ₂ and additions of

Transition metal oxides, lanthanides and actinides using a combination of metal alkoxides and carboxylates dissolved in oxidizing solvents. During pyrolysis, phase segregation occurs in at least two different phases.

In DE 102 57 001 A1 nanoscale (ie <0.1 .mu.m), pyrogenically prepared Mg-Al spinel having a stoichiometric ratio of Mg to Al of 1: 0.01 to 1: 20 and a process for its preparation claimed. This is characterized in that salt solutions or dispersions in a (oxyhydrogen) flame at temperatures above 200 ⁰ C are converted into MgAI ₂ O ₄ . A special feature of this invention is the Aerosol generation by ultrasonic or with the help of a one-fluid nozzle, which operates at high pressures (up to 10,000 bar, preferably up to 100 bar).

The disadvantage of this method is that generally only small product throughputs can be achieved with ultrasonic vibblers. Working at a pressure of up to 100 bar or even up to 10,000 bar is associated with very high technical complexity, so that this variant for spray pyrolysis on an industrial scale in itself is of no importance.

The above-mentioned methods or the products produced therewith furthermore have the following disadvantageous features:

To produce submicron or nanopowders, expensive metal-organic starting materials, mainly dissolved in organic solvents, are usually used.

Object of the present invention is therefore to overcome these disadvantages and to provide an inexpensive, easy to carry out process can be prepared by the mixed oxides as compact, spherical particles of a mean particle size <10 .mu.m. In particular, it is also an object of the present invention to provide mixed oxides which can be used for the production of high-density, high-strength, optionally transparent bulk material or as a base material for phosphors or as a phosphor or as a starting material for ceramic production.

By means of flame spray pyrolysis it is usually not possible to produce non-prone spastic full particles. This is especially true when using inexpensive chlorides and nitrates as starting materials (see Figure 1).

Surprisingly, the present object can be achieved by, on the one hand in a spray pyrolysis in their composition modified educt solutions are used, and on the other hand sprayed the educt solutions in pyrolysis with special temperature control and pyrolyzed, wherein during the pyrolysis an additional Fuel addition occurs at a point that is located in the reactor at a downstream location with respect to the Einsprühpunkt.

In particular, this object is achieved by using preferably aqueous salt solutions, suspensions or dispersions in conjunction with

Additives by which the droplet size of the sprayed solutions, suspensions or dispersions is significantly reduced. Furthermore, the solution of the object according to the invention by a special design of the spray pyrolysis method, which is based on the spraying of the feed material in a hot gas stream, preferably in the flameless, pulsating

Burn generated gas flow of a pulsation reactor in the form of an externally heated tubular reactor with a special temperature profile (hot wall reactor) is based.

The process according to the invention differs considerably from the processes known from the prior art by the reactor structure, the process design, the energy transfer, the course of the reaction of the actual mixed oxide formation.

It has been found that the above-mentioned disadvantages can be overcome by setting a certain ratio between the amount of injected air and the amount of injected educt solution when spraying by two-fluid nozzle, and by simultaneously lowering the energy input at Einsprühpunkt in conjunction with the introduction of additional fuel in the middle part of the pyrolysis reactor and introduction of inherent chemical energy by substances with an exothermic chemical decomposition reaction and at the same time oxidizing action. The additional addition of surfactant, e.g. B. in the form of a fatty alcohol ethoxylate, causes the formation of finer particles with even more even spherical shape.

The example of powders based on Mg and Y aluminates and Ba titanate it can be shown that by means of combination of the inventive measures finely dispersed, spherical powder having average particle sizes in the range of 0.01 - 2 microns can be prepared (see, for. B. pictures 2 to 6). Pores on the particles are up to 20,000 times longer in SEM imaging Magnification in contrast to the not inventive powders of Figure 1 can not be seen (see Figures 4 and 6).

In this case mixed nitrate solutions were used as starting materials, which contain the corresponding elements in the required stoichiometric ratio. As a chemical energy carrier ammonium nitrate was added to these solutions in a proportion of 10 - 50%, preferably 20 - 40%, based on the salt content of the starting solution. With a dilution of preferably 50%, the grain size can be further reduced.

According to the invention, it is necessary to reduce the energy input at the injection point in order to avoid rapid crust formation on the particles forming during the evaporation of the solvent. It first happens that in technically relevant Speisesurchsätzen due to the short residence times in the pyrolysis not always a complete conversion to the mixed oxides and the powders contain an ignition loss greater than 5%.

In particular, when using a reactor with hot gas generation by pulsating, flameless combustion in the form of a ramjet tube (pulsation reactor) succeeds by introducing an additional amount of fuel gas (natural gas or hydrogen) to increase the energy input at the time at which no solvent inside the Particle is more present. This energy is used to thermally decompose any residual salt and to accelerate or complete the solid-state chemical processes of mixed oxide formation. The feeding of the reaction gas is carried out according to the invention after 20 - 40%, preferably 30% of the total residence time of the substances in the reactor.

Surprisingly, it was found that in a laboratory reactor of small size and short product residence times of about 200-500 milliseconds, starting from a Mg-Al mixed nitrate solution, the complete conversion to MgAl ₂ O ₄ can be achieved. The morphology of the particles produced in this way is spherical and the average particle size is 1, 8 microns. (see picture 7). The loss on ignition is here due to addition of OH Groups on the powder surface about 2%. This is not disadvantageous for further processing into a ceramic material, since the powder is very readily dispersible in water, since it has zeta potentials above 100 mV (4 <pH <6).

For this reason, it is also possible to produce submicron powder in the sense of a cost-effective top-down process by means of dispersion in water and subsequent comminution in annular gap or stirred ball mills (see particle size distribution of FIG. 8). On the other hand, this is also possible by separating off the coarse particles by means of sifting or comminution in fluidized bed counter-jet mills (see particle size distribution of FIG.

As was particularly surprising that not only by dissolving, but also by dispersing salts or hydroxides, such as. B. of Mg (OH) ₂ in aluminum nitrate solution spinel formation by spray pyrolysis in

Short-term reactors, such as. B. in laboratory reactors, without the X-ray detection of residual single oxides (see Figure 10). This significantly increases the metal content of the Ausgaηgsproduktes and the product discharge, but leads to higher average particle sizes of about 6 microns. This particle size can be surprisingly by adding ammonium nitrate and

Fettalkoholethoxylat and optionally by dilution of the starting solution can be reduced again. Depending on the water content of the Al nitrate solution, the Mg (OH) _{2 is} soluble or flocculates on further dilution finely dispersed. In both cases, homogeneous, finely dispersed spinel powder is produced. In a pilot plant reactor with a correspondingly increased product residence time in the order of 500-1000 milliseconds, larger throughputs can be achieved in this way, producing products with similar powder characteristics (see particle size distribution of Figure 11).

Another educt variant according to the invention is an aqueous

Magnesium acetate solution with dispersed therein AIO (OH) as an AI component (see Example 7). This makes it possible to produce ultrafine powder, which is completely converted in the pulsation reactor to spinel.

According to the invention, the production of submicron powder can also be achieved by the spray pyrolysis of a solution of Al tri isopropylate in petroleum ether subsequent dispersion of fine-grained Mg-ethylate. The high inherent chemical energy leads to the formation of particles in the range of 100-200 nm in the process of spray pyrolysis (see Figure 12). The temperature limitation takes place at the injection point by the arrangement of an upstream, pulsating hot gas generator, the educt injection and simultaneous cold air addition in the combustion chamber and the fuel supply in the resonance tube.

The starting material combination in the form of Ba acetate and tetra-isopropyl titanate also leads to spherical Ba titanate powders in the submicron range (see Example 9).

In the Y-Al-O system, phase formation is strongly influenced by the nature of the reactants and their thermal decomposition.

According to J. of Alloys and Compounds 255 (1997), pp. 102-105, it is difficult to produce phase-pure cubic Y ₃ Al ₅ O- ₁₂ (YAG), in particular by means of solid-state reaction processes. Even at annealing temperatures of 1600 ⁰ C in addition to the YAG cubic phase, the oxides of AI and Y, and the phases were YAlO ₃ (perovskite phase: YAP) and Y ₄ Al ₂ O ₉ (monoclinic phase: YAM) included.

In the process according to the invention, inter alia, the nitrates of yttrium and aluminum are used as starting materials for spray pyrolysis. In this case, the phase Y ₃ Al ₅ O ₁₂ corresponding to the starting chemical composition is initially not formed, but partially amorphous aluminum oxide and a phase mixture of yttrium aluminates in the form of about 90% YAIO ₃ and about 10% Y ₃ Al ₅ O ₁₂ . By a thermal aftertreatment in the temperature range of 900 ⁰ C to 1200 ⁰ C, preferably 1100 ⁰ C, the material can be completely converted into the cubic YAG phase (see Figure 13). This is necessary in particular for use as a phosphor.

However, it has been found that the partially reacted, unannealed powder has a higher reactivity in the production of densely sintered bulk material. Thus, when hot pressed this powder for 30 min at 1600 ⁰ C, a higher density (99.98% of the theoretical density compared to 98.7% at Use of the previously annealed powder) can be achieved. After an annealing process at 1200 ^° C. for heating the carbon, this material showed translucency, whereby with further optimization to minimize the crystallite size and residual porosity, a transparent material can be formed.

A particularly narrow particle size distribution can be achieved by mixing the starting material in the form of Y chloride solution mixed with an aluminum nitrate solution in a mixing ratio which is predetermined in accordance with the later stoichiometry (see Figure 14). This results in a hot wall reactor with a very short

Product residence time approx. 80% amorphous powder content. The crystalline phases are in addition to the target phase Y ₃ Al ₅ O _12, the phase YAIO ₃ in about the same proportion as well as highly reactive transition aluminas (kappa and theta phase) and yttria. This phase mixture can be converted by annealing at about 1000 ⁰ C in the YAG phase.

The characteristics described for the preparation of Mg-aluminate powder, that the particle morphology, the size and size distribution of which can be influenced in a targeted manner by the combination of additives in the form of water, ammonium nitrate and surfactant as well as control of the temperature conditions in the reactor, also apply to the yttrium aluminates too. In the powder produced according to the invention according to FIGS. 3 to 6, round solid particles up to approximately 2 μm in size can be seen.

An independent of the spray conditions influencing the particle size succeeds by the production and spray pyrolysis of emulsions.

In the process described in DE 4307 333, the material to be sprayed is introduced into an externally, electrically heated tubular reactor or preferably directly into the region of the flame produced by combustion of a combustible gas such as propane, butane or natural gas and (air) oxygen. As particularly useful there is called a combined arrangement of gas burner and injector, wherein the injection nozzle is preferably arranged centrally in the burner head. It is stated that this ensures maximum contact of the sprayed emulsion droplets with the burner flame. In the literature [Journal of Korean Ceramic Soc. 27 (1990), No. 8; S. 955-964] is also an electrically heated tubular reactor.

In contrast, the emulsion with the inventive

Spraying process in the produced by means of pulsating flameless combustion of natural gas or hydrogen with hot air stream, the temperature in the central part of the reactor is limited to about 1030 ⁰ C.

The preparation of the emulsion is carried out, for example, by intensive mixing of the salt solution and the dispersion medium and the emulsifier in a high-pressure homogenizer of the type of Niro Soavi.

Here, as emulsifiers, sorbitan fatty acid derivatives or particularly advantageously a mixture of these with a random copolymer containing hydrophobic and hydrophilic side chains in a ratio of 4: 1 to 2: 3; Preferably, a random copolymer consisting of dodecyl methacrylate and hydroxyethyl methacrylate in a ratio of 1: 1 to 3: 1 are used as described in European Patent Application No. 04023002.1 of Merck Patent GmbH, filed on 28.09.2004.

Corresponding copolymers can be defined by the general formula I

in which the radicals X and Y are conventional nonionic or ionic

Correspond to monomers and

R ^{1 is} hydrogen or a hydrophobic side group, preferably selected from the branched or unbranched alkyl radicals having at least 4 carbon atoms in which one or more, preferably all H atoms may be replaced by fluorine atoms, and independently of R ¹ R ^{2 is} a hydrophilic side group which preferably has a phosphonate, sulfonate, polyol or polyether radical. Particularly preferred according to the invention are those polymers in which -YR ^{2 is} a betaine structure.

In this context, those copolymers according to formula I are again particularly preferred in which X and Y independently of one another are -O-, - C (= O) -O-, -C (= O) -NH-, - (CH ₂ V Furthermore, in the use according to the invention copolymers in which at least one structural unit contains at least one quaternary nitrogen atom, where R ^{2 is} preferably a side group - (CH ₂ ) m - (N ⁺ (CH ₃ ) ₂ ) - ( CH ₂ ) _n -SO ₃ ^" or a side group - (CH ₂ ) _m - (N ⁺ (CH ₃ ) 2) - (CH ₂ ) _n -PO ₃ ^2" , where m is an integer from the range of 1 to 30 is preferably from the range 1 to 6, particularly preferably 2, and n is an integer from the range of 1 to 30, preferably from the range 1 to 8, particularly preferably 3, particularly advantageous properties.

The emulsion has improved stability when using such an emulsifier mixture (no segregation within 12 hours). This leads to the simplification of the technological process, to the improvement of the powder morphology (see Figure 15) as well as to the increase of the reproducibility of the powder properties.

The introduction of combustible substances with the emulsion such as petroleum ether in the reactor must be compensated by reducing the fuel gas supply to the reactor accordingly, so that it does not lead to the formation of hard agglomerates. By setting a reference temperature of 1000 to 1050 ⁰ C in the resonance tube of the pulsation reactor, this is guaranteed and still the complete spinel formation is achieved.

The powders having the different particle sizes and particle size distributions prepared by the above-described means can be further processed in various ways. For the production of high-density, fine-crystalline, possibly transparent ceramics at relatively low sintering temperatures, finely dispersed powders offer considerable advantages, with powders of about 100 nm particle size being able to be used for the hot-pressing technology. With other ceramic methods, these powders are usually not or only with increased technical effort in the

Shaping processable. For these methods, the use of powders in the submicrometer range is recommended.

If special properties such as high mechanical strengths and / or optical transparency are to be achieved, then powders with mean particle sizes of 0.3-0.6 μm and narrow particle size distributions, eg. B. characterized by dgg values of the particle size volume distribution in the range of 1 to 3 microns advantageously applicable (see Figure 8 and 9).

With rare earth elements (SE), such as As Ce, Pr, Nd, Sm ₁ Eu, Gd, Tb, Dy, Er, Tm, Yb and mixtures thereof, doped magnesium or yttrium aluminates are used according to the prior art as a phosphor material, the above SE -Metals are effective as activator Eiemente [Angew. Chem. 110 (1998); Pp. 3250-3272]. Examples include:

Y ₃ Al ₅ O ₂ : Ce; (Yi _-x Gd _x ) ₃ (Al _1-y Ga _y ) ₅ Oi ₂ : Ce; Y ₃ (Al ₁ Ga) ₅ O ₁₂ Tb; BaMgAI ₁₀ Oi ₇ : Eu; BaMgAI ₁₀ Oi ₇ : Eu, Mn; (Ce, Tb) MgAlnO ₁₉ : Eu; Sr ₄ Ah ₄ O ₂₅ : Eu; SrAl ₁₂ Oi ₉ : Ce.

From specialist literature accessible to the person skilled in the art (Römpp's Chemie Lexikon - Version 1.0, Stuttgart / New York: Georg Thieme Verlag 1995;

Ullmann's Encyclopedia of Industrial Chemistry, 2002; Wiley-VCH Verlag GmbH & Co. KGaA; Article Online Posting Date: June 15, 2000) is known that the production of phosphors on an industrial scale in electric or gas-fired furnaces depending on the nature of the raw materials at temperatures between about 700 ° u , 1600 ° takes place. Especially in solid-state reaction

Flux-free processes and subsequent calcinations at relatively high temperatures of up to 1600 ° C typically do not result in compact, spherical particles which would be advantageous for such applications. Examples include: cerium magnesium aluminates such as. B. Ce _o.65 Tb 0. ₃₅ MgAI n O1 ₉ , prepared by coprecipitation of the metal hydroxides from nitrate solutions with NH ₄ OH and subsequent annealing at 700 C for 2 h and then 1 h at 1500 ⁰ C.

Barium magnesium aluminates such. B BaMg ₂ Al ₁₆ O ₂₇ IEu ²⁺ prepared by mixing Al ₂ O ₃ , BaCO ₃ , MgCO ₃ , and Eu ₂ O ₃ in the presence of a

Flux and a low reducing atmosphere at 1100 to 1200 ⁰ C.

The inventive method is not only applicable for the production of spherical particles of different particle sizes. It also offers the

Possibility to produce such material systems in a corresponding manner, because starting from the mixing and spraying of salt solutions, a multiplicity of different dopants, even in small quantities, can be introduced and homogeneously distributed. Even if a post-annealing process is necessary to set a particular phase composition, the temperature to be set can be set lower and the powder morphology and homogeneity retained until the final product.

On comparison of an undoped and doped with Ce, Y ₃ Al ₅ O ₂ material can be found that even with the dopant (s. Example 12) vorliegendes after the spray pyrolysis powder by a thermal post-treatment at 1200 ⁰ C completely into the cubic crystal Phase is converted.

These powders, because of their spherical morphology and the higher packing density that can be achieved with respect to other geometric shapes, can be advantageously used as the phosphor base material. These are then particularly advantageous for the production of white light emitting lighting systems by combining a blue emitter with the o.g. Phosphors z. B. for inorganic and organic light emitting diodes used.

The variability of the powder which can be produced according to the invention also makes possible the simple and inexpensive production of abrasion- and scratch-resistant layers, which can also be transparent and with the methods of plasma spraying, flame spraying, spin coatings, dip coatings customary in the art optionally subsequent thermal treatment can be generated.

Examples

For a better understanding and clarification of the invention, examples which, with the exception of example 1, are within the scope of the present invention are given below. These examples also serve to illustrate possible variants. Due to the general validity of the described principle of the invention, however, the examples are not suitable for reducing the scope of protection of the present application only to these.

The temperatures given in the examples always apply to ⁰ C. It goes without saying that in both the description and in the examples the added amounts of the components in the compositions always add up to a total of 100%. Given percentages are always to be seen in the given context. However, they usually refer to the mass of the specified partial or total quantity.

Example 1 (comparative example, not according to the invention)

Magnesium nitrate hexahydrate (quality for analysis by Merck KGaA) and aluminum nitrate nonahydrate (quality for analysis by Merck KGaA) are each dissolved separately in ultrapure water so that the solutions have a metal content of 6.365% Mg or 4, 70% AI. The metal contents are determined by means of complexometric titration. Then, by means of intensive stirring, a Mg-Al mixed nitrate solution is prepared which contains the elements Mg and Al in a molar ratio of 1: 2.

This is sprayed with a feed rate of 2kg / h into a flame generated by combustion of hydrogen and air (hydrogen flame pyrolysis reactor). The flame temperature is> 1000 ° C, the reactor temperature at the reference point (reactor end at which the Reaction gases escape from the reaction space) is 700 ° C. The powder discharge is 0.2 kg / h.

Powder associations: - loss on ignition: 0.86%

- Grain size distribution: Cl ₅₀ = 4.7 microns, dg ₅ = 15.2 microns, d _99i9 = 38 microns

- Particle morphology: irregularly shaped, many pores (see picture 1)

- specific surface area (BET): 38 m ² / g

- Phases (X-ray diffractometry): Spinel (MgAl ₂ O ₄ ) well crystallized.

Example 2 (according to the invention)

Magnesium nitrate hexahydrate (quality for analysis by Merck KGaA) and aluminum nitrate nonahydrate (quality for analysis by Merck KGaA) are each dissolved separately in ultrapure water, so that the solutions have a

Metal content of 6.365% Mg or 4.70% AI have. The metal contents are determined by means of complexometric titration. Thereafter, an Mg-Al mixed nitrate solution is prepared by intensive stirring, which contains the elements Mg and Al in a molar ratio 1: 2. The solution is diluted with ultrapure water in the ratio 1: 1.

There is a further addition of ammonium nitrate (quality for analysis of the company. Merck KGaA) in an amount of 35% based on the Nitratsalzgehalt and of a fatty alcohol ethoxylate (Lutensol AO3 BASF AG) in an amount of 10% based on the mass of the total Solution.

After stirring for 2 hours, this mixture is introduced at a feed rate of 10 kg / h by means of a two-fluid nozzle (ratio feed: air = 0.5) in the hot gas flow generated by flameless combustion of natural gas and air, the combustion chamber of a pulsation reactor (pilot plant scale). The combustion chamber temperature is 726 ⁰ C. After the hot gas flow has flowed through the combustion chamber with the newly formed solid particles and the reaction gases, it is reheated in the resonance tube by supplying more fuel in the form of hydrogen to 1027 ⁰ C. Before entering the filter, the gas particle stream is cooled by supplying ambient air to about 160 ⁰ C. As a result, cost-effective cassette filters instead of hot gas filters can be used to separate the powder particles from the gas stream.

The basic design of the pulsation reactor including the temperature profile is shown in Figure 16.

Further reactor parameters: - Ratio of combustion air quantity to fuel quantity (natural gas): 26: 1

- ratio of additional fuel quantity (H2) to fuel quantity (natural gas): 4.25: 1

- Air to feed ratio (solution) at the two-fluid nozzle: 2.35: 1.

Powder Properties:

- loss on ignition: 1, 6%

- particle size distribution: d ₅₀ = 1, 8 μm, d ₉₅ = 3.4 μm, d ₉₉ , ₉ = 6 // m (see Figure 7)

Particle morphology: spherical particles (see Figure 2) - specific surface area (BET): 25 m ² / g

- Phases (X-ray diffractometry): Spinel (MgAl ₂ O ₄ ) well crystallized.

Example 3 (according to the invention)

Yttrium nitrate hexahydrate (Merck KGaA) and aluminum nitrate nonahydrate (quality for analysis by Merck KGaA) are each dissolved separately in ultrapure water so that the solutions have a metal content of 15.4% Y or 4.7% AI have. The metal contents are determined by means of complexometric titration. Thereafter, a Y-Al mixed nitrate solution is prepared by intensive stirring, wherein the elements Y and AI in a molar ratio of 3: 5 are included. The solution is diluted with ultrapure water in the ratio 1: 1.

There is a further addition of ammonium nitrate (quality for analysis of the company. Merck KGaA) in an amount of 35% based on the nitrate salt content and from a fatty alcohol ethoxylate (Lutensol AO3 from BASF) in an amount of 10% based on the mass of the total solution.

After stirring for 2 hours, this mixture with a feed throughput of 10 kg / h by means of two-fluid nozzle (ratio feed: air = 0.5) in the

Hot gas stream, produced by flameless combustion of natural gas and air, the combustion chamber of a pulsation reactor (pilot plant scale) introduced. The combustion chamber temperature is 695 ⁰ C. After the hot gas stream has flowed through the combustion chamber with the newly formed solid particles and the reaction gases, it is again heated to 1025 ^° C. in the resonance tube by supplying further fuel in the form of hydrogen.

- Air to feed ratio (solution) at the two-fluid nozzle: 2.35: 1.

Powder Properties:

Ignition loss: 0.5%

- particle size distribution: d ₅₀ = 1, 4 μm, dgs = 3 μm, d ₉₉ , ₉ = 5 μm - Particle morphology: spherical particles (see Figures 5 and 6)

- specific surface area (BET): 7 m ² / g

Phases (X-ray diffractometry): crystalline fractions in the form of 11% Y ₃ Al ₅ O ₁₂ (YAG) and 89% YAIO ₃ (YAP)

After annealing for ⁴ h at 1200 ^° C. in air: - specific surface area (BET): 5 m ² / g

- Phases (X-ray diffractometry): 100% Y ₃ Al ₅ O ₂ (YAG)

Example 4 (according to the invention)

Preparation of the solutions and spray pyrolysis in the pulsation reactor according to Example 2. The discharged from the reactor powder is dispersed in deionized water, so that the solids content is 30% by weight. In a ring-gap ball mill of the "Coball MiII" type from Fryma, the dispersion is ground for 200 minutes using 1 mm Al ₂ O ₃ spheres with the following parameters:

Rotor speed - 1900 rpm; corresponds to a peripheral speed of 13 m / s

- Throughput - 40 kg / h - pH - 8

- total energy input - 4.7 kWh.

The suspension is then dried in a Niro Minor laboratory spray dryer.

Powder Properties:

- loss on ignition: 1, 6%

Grain size distribution: d ₅ o = 0.4 μm, d ₉₅ = 2.8 μm, 4μm (see Fig. 8).

Particle morphology: spherical particles - specific surface area (BET): 35 m ² / g

- Phases (X-ray diffractometry): Spinel (MgAl ₂ O ₄ ).

Example 5 (according to the invention)

Production of the Y nitrate and Al nitrate solutions and spray pyrolysis in the pulsation reactor are carried out according to Example 3.

The powder produced is annealed for 4 h at 113O ⁰ C in a chamber furnace for the fullest possible formation of YAG phase and then contains 98.5% cubic Y3AI5O12 (YAG) and 1, 5% hexagonal YAI ₁₂ Oi ₉ ■ Then, the coarse particle separation is carried out with the channel wheel classifier 100MZR with a Sichterrad-speed of 19 000 U / min, an air flow of 15 m ³ / h and a product throughput of 0.4 kg / h.

Powder associations: - Ignition loss: 0.5%

- Grain size distribution: d ₅₀ = 0.48 μm, dg ₅ = 1.7 μm, d _{99? 9} = 3 μm (see Fig. 9). Particle morphology: spherical particles

- specific surface area (BET): 21 m ² / g

Example 6 (according to the invention)

In 1.2 kg of aluminum nitrate solution having a metal content of 4.5%, 0.06 kg of Mg (OH) _{2 of} the type Magnifin-H10 from the company Magnesia-Produkte GmbH are dispersed and, after addition of 0.254 kg of ammonium nitrate, sprayed into the laboratory reactor and pyrolyzed , wherein the adjustment of the temperature profile in analogy to Example 2 takes place.

Reactor parameters:

- Temperature combustion chamber: 800 ⁰ C - Temperature resonance tube: 1080 ⁰ C

- Ratio of combustion air quantity to fuel quantity (natural gas): 40: 1

- Feed factor: air at the two-fluid nozzle: 0.4.

Powder Industry: - Loss on ignition: 2.0%

- Grain size distribution: d ₅₀ = 3.2 microns, d ₉₅ = 8.6 microns, d ₉₉ , ₉ = 15 microns

Particle morphology: spherical particles

- specific surface area (BET): 18 m ² / g

- Phases (X-ray diffractometry): Spinel (MgAl ₂ O ₄ ) without detection of residual single oxides (see Figure 10).

The spraying of this suspension, which is again diluted in a ratio of 1: 1 with ultrapure water, in a pilot plant reactor according to Example 2 leads to the following powder properties:

- loss on ignition: 1, 2%

- Grain size distribution: d ₅ o = 2.1 μm, d ₉₅ = 4.4 μm, d _{99 | 9} = 6 μm (see Figure 11).

Particle morphology: spherical particles

- specific surface area (BET): 26 m ² / g - phases (X-ray diffractometry): spinel (MgAl ₂ O ₄ ) Example 7 (according to the invention)

In a magnesium acetate solution (aqueous), AIO (OH) is dispersed as an AI component with the following weight: - 2.145 kg of Mg acetate '4 H ₂ O dissolved in 2.95 kg of water

1.20 kg AIO (OH) of the type Martoxal BN-2A from Abemarle Corp.

The suspension is sprayed by means of two-fluid nozzle in the laboratory reactor and pyrolyzed, the adjustment of the temperature profile in analogy to Example 2 takes place.

Reactor parameters:

- Temperature combustion chamber: 780 ⁰ C

- Temperature of the resonance tube: 1054 ⁰ C - Ratio of the quantity of combustion air to the quantity of fuel (natural gas): 40: 1

- Feed factor: air at the two-substance nozzle: 0.4.

Powder properties: - Ignition loss: 3.1% - Grain size distribution: d ₅₀ = 2.1 μm, d ₉₅ = 4.3 μm, _{d 9i9} = 8 μm

Particle morphology: spherical particles

- specific surface area (BET): 30 m ² / g

- Phases (X-ray diffractometry): crystalline fractions of spinel (MgAl ₂ O ₄ ) u. Oxides of Mg u. AI

When processing in the pilot plant reactor with the reactor parameters according to Example 2, the complete conversion to spinel takes place.

Example 8 (according to the invention)

Al-tri-isopropoxide is in petroleum ether (boiling range petroleum benzine of 100- 140 ⁰ C from Merck KGaA.) Dissolved with subsequent dispersion of fine-grained Mg ethylate, so that Mg and Al in a molar ratio of 1: 2 are present. The spray pyrolysis then takes place in a laboratory pulsation reactor under the following conditions: Reactor parameters:

- Temperature combustion chamber: 795 ⁰ C

- Temperature resonance tube: 954 ⁰ C

- Ratio of the quantity of combustion air to the quantity of fuel (natural gas): 41: 1 - factor of feed: air at the two-substance nozzle: 0,4.

To set the temperature profile, i. lowered temperature at Einsprühpunkt and subsequent temperature increase in the resonance tube, a combustion chamber upstream hot gas generator is used. By adding cooling air into the combustion chamber and supplying energy in the resonance tube, the setting of the o.g. Temperatures.

In this case, only a small additional fuel gas supply takes place because of the additional energy input by petroleum ether.

Pulvereiαenschaften:

- Ignition loss: 3.5%

Particle size in the range of 100-200nm (according to REM, see Figure 12)

Particle morphology: spherical particles

- specific surface area (BET): 55 m ² / g - phases (X-ray diffractometry): spinel (MgAl ₂ O ₄ )

Example 9 (according to the invention)

194.59 g of barium acetate are stirred into 500 ml of isopropanol. It forms a white suspension (mixture 1).

Separately, a mixture of 217.61 g of tetra-isopropyl orthotitanate and 500 ml

Isopropanol prepared (mixture 2).

Mixture 1 and mixture 2 are combined with stirring.

This suspension is sprayed in the laboratory reactor at 800 ^° C. in the combustion chamber and, as described in Example 8, pyrolyzed.

Powder Properties:

Particle morphology: d50 = 150 nm, d95 = 220 nm, d99.9 = 1 μm Particle morphology: spherical particles - Specific surface area (BET: 15 m ² / g) Phases (X-ray diffractometry): BaTiO ₃ (tetragonal), residues of TiO ₂ (rutile)

Example 10 (according to the invention)

An Mg-Al mixed nitrate solution according to Example 2 is prepared. Emulsifier is then dissolved in the form of a random copolymer consisting of dodecyl methacrylate and hydroxyethyl methacrylate in a ratio of 2: 1 with a molecular weight of 5000 g / mol in petroleum ether (petroleum spirit with boiling range 100 to 140 ⁰ C from. Merck KGaA), so that a 35 % solution is created. This solution is mixed in a ratio of 2: 1 with the Mg-Al mixed nitrate solution by means of a stirrer. The resulting mixture is transferred by pumping medium high pressure homogenizer type Niro / Soavi in about 0.5 h in an emulsion in which the salt solution are dispersed as preformed droplets in petroleum ether. The spray pyrolysis is then carried out in a pulsation reactor (pilot plant scale) with the following conditions:

Reactor parameters:

- Temperature combustion chamber: 1023 ⁰ C - Temperature of the resonance tube: 1026 ⁰ C

- Ratio of combustion air quantity to fuel quantity (natural gas): 36: 1

- Ratio of air to feed material at the two-substance nozzle: 5.7: 1. In this case, no additional fuel gas supply takes place because of the additional energy input by the petroleum ether. Powder Properties:

Ignition loss: 4.5%

- Particle size distribution: d ₅₀ = 0.8 μm, dg ₅ = 1, 5 μm, d _{9 9} , ₉ = 2.5 μm - Particle morphology: spherical particles

- specific surface area (BET): 28 m ² / g

- Phases (X-ray diffractometry): spinel (MgAl ₂ O ₄ ) Example 11 (according to the invention)

Yttrium nitrate hexahydrate (Merck KGaA), aluminum nitrate nonahydrate (quality for analysis by Merck KGaA) and cerium nitrate hexahydrate (quality "pure" from Merck KGaA) are each dissolved separately in ultrapure water, so that the Solutions have a metal content of 15.4% by mass of Y, 4.7% by mass of Al and 25.2% by mass of Ce, followed by the preparation of a Y-Al-Ce mixed nitrate solution which comprises the elements Y, Al and Ce in molar form This solution is diluted with ultrapure water in a ratio of 1: 1 and then there is a further addition of ammonium nitrate (quality for analysis by Merck KGaA) in an amount of 35% based on the nitrate salt content

This mixture is sprayed by means of two-fluid nozzle in a laboratory reactor, wherein the adjustment of the temperature profile in analogy to Example 2 takes place. The particles are separated from the hot gas stream by means of hot gas filters.

Reactor parameters: - Combustion chamber temperature: 760 ⁰ C

- Temperature resonance tube: 1075 ⁰ C

- Ratio of combustion air quantity to fuel quantity (natural gas): 42: 1

- Feed factor: air at the two-fluid nozzle: 0.4.

Powder Properties:

Ignition loss: 0.5%

- Grain size distribution: d ₅ o = 1, 9 microns, d ₉₅ = 4.1 microns, d ₉₉ , ₉ = 7 microns

Particle morphology: spherical particles - specific surface area (BET): 6.9 m ² / g

Phases (X-ray diffractometry): crystalline fractions in the form of Y ₃ Al ₅ O ₂ , YAIO ₃ , Y ₂ O ₃ and amorphous fractions, presumably in the form of oxides

After annealing for 4 h at 1200 ° C in air: - specific surface area (BET): 4.5 m ² / g

- Phases (X-ray diffractometry): 100% cubic mixed crystal phase.

Claims

PATENT APPLICATIONS

1. A process for the preparation of mixed oxide powders with compact, spherical particles of average particle size <10 .mu.m by spray pyrolysis, by reacting the starting materials in the form of salts, oxides, hydroxides, organometallic compounds individually or in a mixture in solution, suspension or dispersion and these in a hot gas stream generated by pulsating, flameless combustion of natural gas-air mixtures or hydrogen-air mixtures in a reactor

'0 sprayed, pyrolyzed and converted to mixed oxides or their precursors, characterized in that either the temperature at the injection is limited to 600 - 1000 ⁰ C, preferably 700 - 800 ⁰ C, and to accelerate the Mischoxidbildung ^ additional fuel in the pyrolysis reactor is supplied at a location which is based on the hot gas stream at a downstream location behind the Einsprühpunkt, or sprayed to control the particle size, a solution, suspension or dispersion in the form of a water / oil emulsion and pyrolyzed. 0

2. The method according to claim 1, characterized in that the addition of additional fuel in the form of natural gas or hydrogen after a residence time of the substances in the reactor of 20 - 40%, preferably 30% of the total residence time takes place. 5

3. The method according to claim 1, characterized in that are used as starting materials nitrates, chlorides, hydroxides, acetates, ethylates, butylates or isopropylates, or mixtures thereof. 0

4. The method according to claims 1 to 3, characterized in that as

Starting materials Salts, hydroxides or organometallic compounds of elements of groups IIA (IUPAC: 2), INA (13), HIB (3) and IVB (4) VIB and VIIB can be used. 5

5. The method according to claims 1 to 4, characterized in that are used as starting materials salts, oxides, hydroxides or organometallic compounds of Al and / or Ti of elements of the groups IIA and HIB.

6. The method according to claim 1 to 5, characterized in that to be sprayed solution, dispersion or suspension, an inorganic material is added, which generates additional thermal energy through its exothermic decomposition and at the same time acts oxidizing.

7. The method according to claim 6, characterized in that the additionally added substance is a nitrate, preferably an ammonium nitrate and that the addition amount of 10 to 80%, preferably 25-50% based on the amount Edukt- is.

5

8. The method according to claim 1-6, characterized in that the solution to be sprayed, dispersion or suspension, a surfactant is added.

A process according to claim 8, characterized in that a fatty alcohol ethoxylate in an amount of 1-10% by weight, preferably 3-6%, based on the total amount of the solution, is used as the surfactant.

10. The method according to claim 1, characterized in that for the preparation of a water / oil emulsion, a mixture of dissolved in water nitrates and / or chlorides introduced into a hydrocarbon, dispersed by means of mechanical shear forces to droplets and stabilized by the addition of an adjuvant.

0 11. The method according to claim 10, characterized in that a

Petroleum benzine is used with a boiling range of 80-180 ⁰ C, preferably 100- 140 ⁰ C in combination with emulsifiers which are soluble therein and have an HLB (Hydrophylic-Lipophylic balance) value in the range 2-8. 5

12. The method according to claims 10 and 1 1, characterized in that are used as emulsifiers sorbitan fatty acid derivatives and mixtures thereof with different HLB value.

13. The method according to claims 10 to 12, characterized in that as emulsifiers a mixture of fatty acid sorbitan esters and a random copolymer containing at least one monomer with a hydrophilic and at least one monomer having a hydrophobic side chain and a molecular weight between 1000 and 50,000, ° preferably between 2000 and 20,000 is used.

14. The method according to claim 13, wherein as a random copolymer copolymers of the general of formula I.

5

0

be used, wherein the radicals X and Y correspond to conventional nonionic or ionic monomers and R ^{1 is} hydrogen or a hydrophobic side group selected from the branched or unbranched alkyl radicals having at least 4 carbon atoms in which one or more, H atoms are replaced by fluorine atoms can, means and independently of R ¹

R ^{2 is} a hydrophilic side group having a phosphonate, sulfonate, polyol or polyether radical.

15. mixed oxide powder based on aluminates and titanates, prepared according to one or more of claims 1-14, characterized in that the average particle size is in the range of 1-5 microns, a specific surface area (according to BET) in the range of 3 - 30 m ² / g, preferably 5 - has 15 m ² / g and a compact, spherical

Having morphology.

16. mixed oxide powder based on aluminates and titanates, prepared according to one or more of claims 1-14, characterized in that the average grain size is in the range of 0.1-1 // m, a specific surface area (according to BET) in the range of 10-60 m ² / g, preferably 20 - 40 m ² / g and has a compact, spherical morphology.

17. Use of a mixed oxide powder according to claims 15 or 16, for the production of high density, high strength, optionally transparent bulk material.

18. Mixed oxide powder based on aluminates and titanates, prepared according to one of claims 1 to 14, characterized in that its mean grain size is in the range of 0.01-0.2 μm, a specific surface area (according to BET) in the range of 20 - 100 m ² / g, preferably 40- 80 m ² / g and has a spherical morphology.

19. Use of a mixed oxide powder according to claim 18 for the production of high-density, high-strength and optionally transparent BuIk material by means of hot-pressing technology.

20. Use of a mixed oxide powder according to any one of claims 15, 16, 18 as a base material for phosphors or as a phosphor or as a starting material for the ceramic production.