WO2011157494A1

WO2011157494A1 - Zirconium dioxide-aluminium oxide composite powder and process for the production thereof

Info

Publication number: WO2011157494A1
Application number: PCT/EP2011/057673
Authority: WO
Inventors: Monika Oswald; Corinna Kissner
Original assignee: Evonik Degussa Gmbh
Priority date: 2010-06-17
Filing date: 2011-05-12
Publication date: 2011-12-22
Also published as: DE102010030216A1; TW201217302A

Abstract

Process for producing a zirconium dioxide-aluminium oxide composite powder which contains a) from 60 to 95% by weight of zirconium dioxide and from 5 to 40% by weight of aluminium oxide; and b) has a crystallite size after thermal treatment at 1500°C of from 50 to <100 nm, determined by X-ray structure analysis, in which c) a dispersion which contains c1) zirconium dioxide particles having an average particle diameter d₅₀ of from 50 to <100 nm as solid phase and c2) a solution composed of water and one or more aprotic polar solvents as liquid phase is d) reacted with a solution which is miscible with the liquid phase of the dispersion and d1) in each case one or more aluminium alkoxides and complexing agents in an aprotic polar solvent which is identical to or different from that of the dispersion or d2) in each case one or more aluminium salts in an aqueous solvent. Zirconium dioxide-aluminium oxide composite powder which can be obtained by means of this process.

Description

Zirconia-alumina composite powder and process for its preparation

The invention relates to a method for producing a zirconia-alumina composite powder and the zirconia-alumina composite powder itself obtainable by means of this method. A further subject matter relates to the use of the zirconia-alumina composite powder.

Ceramic materials based on mixtures of zirconia and alumina are referred to as "zirconia toughened alumina" (ZTA) and "alumina toughened zirconia" (ATZ), respectively, depending on whether alumina is dispersed in zirconia or vice versa. Through these mixtures, the properties of pure alumina or zirconia can be significantly improved. In the prior art, different manufacturing methods for such mixtures are known.

For example, these can be obtained by mechanical mixing, such as by means of a ball mill, or by co-precipitation of zirconium and aluminum salt solutions. In both cases, it is difficult to obtain reproducible results, since the mixture is often not finely divided and has inhomogeneities, so that no usable ceramics result.

DE-A-371491 1 discloses a hydrothermal process in which a common aqueous solution of zirconium and aluminum salts reacts at high pressures and temperatures in an autoclave. Such a method is not economical to carry out. The description relates to the preparation of a composite from a zirconium dioxide stabilized with 3 mol% yttrium and aluminum oxide with a particle size of about 10 nm.

From EP-A-435677 a method is known, are dispersed in the alpha-alumina particles having a particle size of 0.1 to 2 μηη in a zirconia with a particle size of not more than 0.1 μηη, and the mixture is then thermally treated ,

A disadvantage of the processes mentioned in the prior art is that they either are not economical to carry out and / or the resulting process products are not finely divided enough, have inhomogeneities and the sintered products have insufficient strength. Therefore, the technical object of the present application was to provide a method for producing a zirconia-alumina composite powder, which reduces or eliminates the disadvantages of the methods mentioned in the prior art. The zirconia-alumina composite powder itself is said to be at high temperatures

remain mechanically stable, that is, the structure should not significantly coarsen by grain growth.

The technical problem is solved by a method for producing a zirconia-alumina composite powder, which

a) 60 to 95 wt .-%, preferably 65 to 85 wt .-%, particularly preferably 70 to 80 wt%, zirconium dioxide and 5 to 40 wt .-%, preferably 15 to 35 wt .-%, particularly preferably Contains 20 to 30 wt .-% alumina and

b) whose crystallite size, after a thermal treatment at 1500 ° C., is 50 to <100 nm, determined by X-ray structure analysis,

in which one

c) a dispersion which

c1) zirconia particles with a mean particle diameter d ₅₀ from 50 to

<100 nm, preferably 60 to 90 nm, as a solid phase and

c2) a solution of water and one or more aprotic polar

Contains solvents as a liquid phase

d) with a solution which is miscible with the liquid phase of the dispersion and

d1) in each case one or more aluminum alkoxides and complexing agents in one

aprotic-polar solvent which is the same as or different from that of the dispersion, or

d2) each comprises one or more aluminum salts in an aqueous solvent,

brings to reaction.

As a composite powder in the invention, a powder is referred to in the

Zirconium dioxide and alumina form a solid compound. It is assumed that a shell of alumina to zirconia particles, whether isolated or aggregated, forms and so prevents the growth of zirconia particles. Zirkondioxidpartikel are individual, mutually isolated particles, aggregates and / or agglomerates. The particles may preferably be present in the form of aggregated primary particles. The d ₅₀ value is the median value of the volume-weighted particle size distribution. The median value of the particle size distribution may be based on a tri-, bi- or monomodal distribution of the particles, wherein a monomodal distribution of the zirconia particles is preferred. The zirconia particles carry hydroxyl groups on their surface.

In a preferred embodiment, the zirconia particles of the dispersion are aggregated pyrogenic zirconia particles having a BET surface area of 20 to 100 m ² / g, more preferably 30 to 50 m ² / g. By pyrogen is to be understood that the particles were obtained by means of a flame hydrolysis or flame oxidation. By flame hydrolysis is meant, for example, the formation of zirconium dioxide by combustion of zirconium tetrachloride in a hydrogen / oxygen flame. Under

Flame oxidation is, for example, the formation of zirconia by the combustion of an organic zirconia precursor in a hydrogen / oxygen flame.

The zirconia particles may also be stabilized zirconia particles. Yttrium, cerium, calcium, magnesium or titanium are suitable as stabilizing elements, for example. Yttrium is the most frequently used stabilizing component, with a proportion of 1 to 8 mol%, calculated as yttrium oxide.

In the context of the invention, preference can be given to using an unstabilized zirconium dioxide powder in which the stabilizing elements mentioned are not present or are present only in such small amounts that they do not have a stabilizing effect. The powder has a zirconia content of at least 97% by weight, usually at least 99% by weight. In addition, it can be up to 2.5 wt .-%

Hafniumdioxid as a companion whose content should be included in the proportion of zirconium dioxide.

The content of zirconium dioxide in the dispersion is preferably 5 to 50 wt .-%, particularly preferably 10 to 40 wt .-% and most preferably 20 to 30 wt .-%. The proportion of water in the dispersion is preferably 10 to 50 wt .-% and particularly preferably 20 to 40 wt .-%. The proportion of aprotic-polar solvent is preferably 20 to 60 wt .-% and particularly preferably 30 to 50 wt .-%. The sum of the constituents zirconium dioxide, water and aprotic-polar solvent is preferably 90% by weight. or more, more preferably 95% by weight or more and most preferably 98% by weight or more, each based on the dispersion.

An aprotic-polar solvent in the context of the invention means a solvent whose structural formula does not contain a functional group from which

Hydrogen atoms can be split off as protons, but strongly polar

functional groups such as a carbonyl group, nitro group or

Contains nitrile group, which assign a dipole moment to the structure. The aprotic-polar solvent is preferably selected from the group consisting of acetone, diethyl ether, dimethylformamide, dioxane, ethyl acetate, methyl ethyl ketone, methyl isobutyl ketone,

Tetrahydrofuran and mixtures thereof selected.

The dispersion may further contain one or more surface-modifying additives. These additives may be present in a proportion of 0.1 to 10 wt .-%, preferably 0.5 to 5 wt .-%, each based on the dispersion. For the purposes of the invention, surface-modified means that at least part of the hydroxyl groups present on the surface of the zirconium dioxide particles have reacted with a means for modifying the surfaces to form a chemical bond. The chemical bond can be a covalent, ionic or coordinate bond between the surface modifier and the particle. Preference is given to using ammonium polyacrylates, polymethacrylates and polyethyleneimines. Particular preference may be given to using an ethanolamine salt of citric acid, for example Dolapix CE 64.

The dispersion according to the invention comprises a liquid phase containing water and an aprotic-polar solvent. It is made by taking one of

Predispersion starts, which contains no aprotic polar solvent. This predispersion may contain pH-regulating compounds, preferably basic-reacting compounds such as NaOH, KOH, NH ₃ or ammonium hydroxides. The predispersion has a pH of preferably 7.5 to 12 and more preferably 8 to 1 1.

According to the present invention, the dispersion is reacted with a solution comprising a) one or more aluminum alkoxides and complexing agents in an aprotic polar

Solvent or b) each comprises one or more aluminum salts in an aqueous solvent, reacted. The aluminum alkoxides mentioned under a) are preferably compounds of the type Al (OR) ₃ , with R = C 1 -C ₆ -alkyl, linear or branched or R = - (CH ₂ ) m -O- (CH ₂ ) n -CH ₃ , in which m is an integer from 1 to 6 and n is one integer from 0 to 6, where the radicals R may be the same or different. Examples are aluminum ethoxide, aluminum i-propoxide, aluminum n-butoxide,

Aluminum s-butoxide, aluminum t-butoxide, aluminum ethoxyethoxyethoxide, triethyl (tri-s-butoxy) dialuminium and mixtures thereof. Particularly preferred

Aluminum sec-butoxide.

The complexing agent mentioned under a) is preferably a chelating agent. Chelating agents are to be understood as meaning compounds with multidentate ligands which are linked by coordinative bonds to a zirconium atom. Examples are 1,3-diketones, beta-ketoesters, glycol ethers, diols, aminoalcohols, glycerol, aminothiols, dithiols, diamines, or mixtures thereof. Acetylacetone may preferably be used. The complexing agents are usually used in an amount of 0.5 to 20 mol, preferably 0.5 to 3 mol / mol of aluminum alkoxide. It is also possible precomplexed

Use aluminum alkoxides. These precomplexed are preferred

Aluminum alkoxides selected from the group consisting of aluminum s-butoxide-bis (ethylacetoacetate), aluminum di-s-butoxide-ethylacetoacetate, aluminum diisopropoxide-ethylacetoacetate, di-s-butoxyaluminoxytriethoxysilane, aluminum 9-octadecenyl-acetoacetate diisopropoxide, aluminum 2,4-bis pentanedione aluminum acetylacetonate, aluminum 2,2,6,6-tetramethyl-3,5-heptanedionate, aluminum hexafluoropentanedionate and mixtures thereof. The aluminum salts mentioned under b) are preferably selected from the group consisting of aluminum acrylate, aluminum chloride, aluminum methacrylate, aluminum nitrate,

Aluminum stearate and mixtures thereof.

In a particularly preferred embodiment of the invention, the method is carried out so that it is in the

a) zirconia of the zirconia dispersion around non-stabilized zirconia in the form of aggregated, pyrogenically prepared zirconia particles having a BET surface area of from 20 to 100 m ² / g, which is present in a proportion of from 40 to 60% by weight in the dispersion .

b) aluminum alkoxide to aluminum i-propoxide, aluminum n-butoxide and / or

Aluminum s-butoxide,

c) complexing agent to a 1, 3-diketone and / or a beta-ketoester

wherein the ratio of zirconia / aluminum alkoxide, calculated as Zr0 ₂ / Al ₂ 0 ₃ , 70:30 to 80:20. In a further particularly preferred embodiment of the invention, the method is carried out so that it is in the

b) Aluminum salt around aluminum nitrate

wherein the ratio of zirconia / aluminum nitrate, calculated as Zr0 ₂ / Al ₂ 0 ₃ , is 70:30 to 80:20. As a rule, in the process according to the invention, a further step follows, in which the solid reaction product is separated from the liquid phase of the reaction mixture. This can be achieved, for example, by evaporation, filtration, spray-drying,

Freeze-drying or vacuum drying.

The removal of the liquid phase may also be part of an optional tempering step, which is usually carried out in a temperature range of 400 to 1000 ° C. By this temperature treatment by-products, such as

Salt components, partially or completely removed. The removal of this

By-products can also be part of a sintering step, in which the

Composite powder to temperatures of 1200 to 1500 ° C are heated. A further subject of the invention is a zirconia-alumina composite powder obtainable by the process according to the invention,

a) which contains 60 to 95 wt .-% zirconium dioxide and 5 to 40 wt .-% alumina, and

The alumina content of the zirconia-alumina composite powder usually contains or consists of alpha alumina. Preferred is zirconia-alumina composite powder in which the zirconia is in unstabilized form.

The process according to the invention can also be carried out in such a way that granules, in particular spray granules, are obtained, which may optionally contain further substances, such as binders, dispersants or lubricants. Suitable binders may include polysaccharides, methylcellulose, polyvinyl alcohol, polyacrylic acid, polethylenic acid and / or waxes. Suitable dispersants may be polymers and copolymers of methacrylic and acrylic acids having low to medium molecular weights and their salts. Further dispersants may be citric and phosphonobutane tricarboxylic acid and salts thereof or salts of polybasic acids, in particular hydroxy acids, with polyvalent cations which optionally contain intact acid groups. Suitable lubricants are paraffin wax, polyethylene glycols (PEG), butyl stearate,

Stearic acid and stearates of ammonium, aluminum, lithium, magnesium, sodium and zinc, oleic acid, graphite and / or boron nitride. Stearic acid and stearates can be used with particular preference. Preferably, these granules are subjected to an annealing step at 400 to 1000 ° C.

In the context of the present invention, a zirconia-alumina composite powder is understood to mean a powder which may optionally be a thermal one

Treatment was subjected to up to 1000 ° C, but not sintered, that is, was exposed to temperatures of 1200 ° C or more. The sintered zirconia-alumina composite powder is a further object of the invention. It is obtainable by thermal treatment of the zirconia-alumina composite powder at 1500 ° C and

a) contains 60 to 95 wt .-%, preferably 65 to 85 wt .-%, particularly preferably 70 to 80 wt .-%, zirconium dioxide and 5 to 40 wt .-%, preferably 15 to 35 wt .-%, especially preferably 20 to 30 wt .-% alumina and

b) the crystallite size, determined by X-ray structure analysis, is 50 to <100 nm.

Another object of the invention is the use of the zirconia-alumina composite powder or the sintered zirconia-alumina composite powder as a component of ceramic components and ceramic coatings, for example, for composites and turbines.

The present invention provides a process for producing a zirconia-alumina composite powder and the powder itself. The structure of the powder does not significantly coarsen at high temperatures due to grain growth. It is therefore possible to produce components made therefrom or coated therewith under extreme conditions

To use conditions without causing damage. Examples

crystallite size:

For this purpose, in each case the total amount of the composite powder produced in the examples is heated in an open Al ₂ O ₃ crucible (AlSint) at a heating rate of 5 K / min to 1000 ° C., 1200 ° C. or 1500 ° C. and over a period of 1 Held at this temperature for an hour and then allowed to cool to room temperature unregulated.

Of the composite powders thus obtained, the crystallite size is determined by means of X-ray diffraction by broadening the Baddeleyite (1 1 1) diffraction reflection with the following formula, known as Scherrer's formula: d = k / bcos0, where d = crystallite size, k =

Scherrer factor (set approximately 1), λ = wavelength of the used

X-radiation, Θ = diffraction angle of the (1 1 1) reflection (radiation: Cu K-alpha 1) and b = integral width of the (1 1 1) -reflexes. The integral width of the reflex is determined by a single-line Fourier analysis method using the "Line Profile" ^® program from Philips, to calculate the integral width of the (1 1 1) reflection due to the influence of crystallite size device-related broadening of the reflection and the influence of the lattice distortion, determined by the Cauchy-part of the reflex, subtracted, using NBS silicon as reference.

Determination of the particle diameter in the dispersion by means of dynamic light scattering. Apparatus used: Horiba LA 910. Dispersion D1: 42.14 kg demineralized water and 1.75 kg Dolapix CE64 (from Zschimmer and Schwartz) are placed in a mixing tank and then, using the suction pipe of the Ystral Conti-TDS 3 (stator slots 4 mm wreath and 1 mm wreath, rotor / stator distance about 1 mm) under shear conditions, the 43.9 kg of zirconia powder prepared according to EP-A-1 142830, Example 1 was added. After completion of the retraction of the intake manifold is closed and still sheared at 3000 U / min for 10 min. The predispersion thus obtained is passed in five passes through a high-energy mill Sugino Ultimaizer HJP-25050 at a pressure of 2500 bar and diamond nozzles of 0.3 mm diameter. The resulting dispersion has an average particle size d ₅₀ of 80 nm and a zirconium dioxide content of 50% by weight. Example 1: 50 g of aluminum sec-butoxide (ASB) are added rapidly with stirring to 90 g of acetone and 40.6 g of acetylacetone and then stirred for 5 minutes. To this mixture, a dispersion D2 consisting of 85 g of dispersion D1 and 85 g of acetone is added rapidly and then stirred for 5 minutes. The batch is dried at room temperature. The resulting solid has an 80:20 ratio of ZrO ₂ / Al ₂ O ₃ . The crystallite size determined as described above is 37 nm for the sample treated at 1200 ° C. and 80 nm for the sample treated at 1500 ° C.

Example 2: 72.5 g of aluminum sec-butoxide (ASB) are added rapidly with stirring to 130.5 g of acetone and 58.9 g of acetylacetone and then stirred for 5 minutes. To this mixture is rapidly a dispersion D2 consisting of 70 g of dispersion D1 and 70 g

Acetone added and then stirred for 5 minutes. The batch is dried at room temperature. The resulting solid has a 70:30 ratio of ZrO ₂ / Al ₂ O ₃ . The average crystallite size of the sample treated at 1200 ° C. is 26 nm, and the sample treated at 1500 ° C. is 80 nm. EXAMPLE 3 23.75 g of the dispersion are added to a solution of 14 g of aluminum nitrate nonahydrate in 14 g of water with stirring D1 and stirred for 30 minutes. The batch is dried at room temperature. The resulting solid has a 70:30 ratio of ZrO ₂ / Al ₂ O ₃ . The average crystallite size of the sample treated at 1200 ° C. is 35 nm, and in the sample treated at 1500 ° C. 70 nm.

Claims

claims:

1 . A process for producing a zirconia-alumina composite powder which contains a) 60 to 95% by weight of zirconium dioxide and 5 to 40% by weight of aluminum oxide and b) its crystallite size, after thermal treatment at 1500 ° C, 50 to <100 nm, determined by X-ray diffraction analysis,

in which one

c) a dispersion which

c1) zirconia particles with an average particle diameter d ₅₀ of 50 to <

100 nm as a solid phase and

c2) a solution of water and one or more aprotic polar

Contains solvents as a liquid phase

d) with a solution which is miscible with the liquid phase of the dispersion and d1) in each case one or more aluminum alkoxides and complexing agents in one

aprotic-polar solvent which is the same as or different from that of the dispersion or

d2) in each case one or more aluminum salts in a water-containing

solvent

includes, reacts.

2. The method according to claim 1,

characterized in that

the zirconia particles of the dispersion comprise aggregated pyrogenic zirconia particles having a BET surface area of from 20 to 100 m ² / g.

3. Process according to claims 1 or 2,

characterized in that

the zirconia of the dispersion is an unstabilized zirconia.

4. Process according to claims 1 to 3,

characterized in that

the aprotic polar solvent selected from the group consisting of acetone, diethyl ether, dimethylformamide, dioxane, ethyl acetate, methyl ethyl ketone, methyl isobutyl ketone,

Tetra h yd rofu ran and mixtures thereof is selected. Process according to claims 1 to 4,

characterized in that

be used as aluminum alkoxides compounds of the type AI (OR) ₃ , with R = CrC ₆ alkyl, linear or branched or

R = - (CH ₂ ) m -O- (CH ₂ ) n -CH ₃ , where m is an integer from 1 to 6 and n is an integer

Number from 0 to 6 means stand, where

the radicals R may be the same or different.

Process according to claims 1 to 5,

characterized in that

the aluminum salt is selected from the group consisting of aluminum acrylate, aluminum chloride, aluminum methacrylate, aluminum nitrate, aluminum stearate and mixtures thereof.

Process according to claims 1 to 6,

characterized in that

after reacting the dispersion with the solution, removing the solid reaction product from the liquid phase of the reaction mixture.

Method according to claim 7,

characterized in that

to convert the solid reaction product into granules.

Method according to claim 1,

characterized in that the a) zirconium dioxide of the zirconium dioxide dispersion is unstabilized zirconium dioxide in the form of aggregated, pyrogenic zirconium dioxide particles having a BET surface area of from 20 to 100 m ² / g, which contains from 40 to 60 Wt .-% is present in the dispersion,

b) aluminum alkoxide to aluminum i-propoxide, aluminum n-butoxide and / or

Aluminum s-butoxide,

c) complexing agent to a 1, 3-diketone and / or a beta-ketoester, wherein the ratio of zirconia / aluminum alkoxide, calculated as Zr0 ₂ Al ₂ 0 ₃ , 70:30 to 80:20.

10. The method according to claim 1,

characterized in that it is in the

a) zirconia zirconia dispersion to non-stabilized zirconia in the form of aggregated pyrogenic zirconia particles having a BET surface area of 20 to 100 m ² / g, which in a proportion of 40 to 60 wt .-% in the

Dispersion is present,

b) aluminum salt is aluminum nitrate, wherein the ratio of zirconia / aluminum nitrate, calculated as Zr0 ₂ Al ₂ 0 ₃ , 70:30 to 80:20.

1 1. Zirconia-alumina composite powder, which

a) 60 to 95 wt .-% zirconium dioxide and 5 to 40 wt .-% alumina and b) after a thermal treatment at 1500 ° C in the by

X - ray structure analysis determined crystallite size determination for the

Zirconium dioxide content has values of 50 to 100 nm,

obtainable by the process according to claims 1 to 10. 12. Zirconia-alumina composite powder according to claim 1 1,

characterized in that

the zirconium dioxide is in unstabilized form.

13. Sintered zirconia-alumina composite powder obtainable by thermal treatment of the zirconia-alumina composite powder according to claims 11 or 12 at 1500 ° C, wherein the sintered zirconia-alumina composite powder a) 60 to 95 wt .-% zirconia and 5 contains up to 40% by weight of aluminum oxide and b) b) the crystallite size of the zirconium dioxide fraction, determined by

X-ray diffraction analysis, from 50 to 100 nm.

14. The use of the zirconia-alumina composite powder according to claim 11 or 12 or the sintered zirconia-alumina composite powder according to

Claim 13 as a component of ceramic components and ceramic

Coatings.