EP1831108A2 - Zirconium-hafnium mixed oxide powder - Google Patents

Zirconium-hafnium mixed oxide powder

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Publication number
EP1831108A2
EP1831108A2 EP05823955A EP05823955A EP1831108A2 EP 1831108 A2 EP1831108 A2 EP 1831108A2 EP 05823955 A EP05823955 A EP 05823955A EP 05823955 A EP05823955 A EP 05823955A EP 1831108 A2 EP1831108 A2 EP 1831108A2
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EP
European Patent Office
Prior art keywords
zirconium
hafnium
mixed oxide
oxide powder
dioxide
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP05823955A
Other languages
German (de)
French (fr)
Inventor
Stipan Katusic
Jürgen FLESCH
Volker Hamm
Witold Katerinak
Michael Krämer
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Evonik Operations GmbH
Original Assignee
Evonik Degussa GmbH
Degussa GmbH
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Publication date
Application filed by Evonik Degussa GmbH, Degussa GmbH filed Critical Evonik Degussa GmbH
Publication of EP1831108A2 publication Critical patent/EP1831108A2/en
Withdrawn legal-status Critical Current

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G25/00—Compounds of zirconium
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G27/00—Compounds of hafnium
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
    • C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
    • C01P2002/76—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by a space-group or by other symmetry indications
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/80—Crystal-structural characteristics defined by measured data other than those specified in group C01P2002/70
    • C01P2002/88—Crystal-structural characteristics defined by measured data other than those specified in group C01P2002/70 by thermal analysis data, e.g. TGA, DTA, DSC
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/64—Nanometer sized, i.e. from 1-100 nanometer
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/10—Solid density
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/12—Surface area
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/22—Rheological behaviour as dispersion, e.g. viscosity, sedimentation stability
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/80—Compositional purity

Definitions

  • the invention concerns a zirconium-hafnium mixed oxide powder, its preparation and use .
  • a pyrogenically prepared zirconium dioxide powder which can contain up to 4 wt . % of hafnium dioxide, is known from EP-A-717008. It is obtained by hydrolysing zirconium halides , preferably zirconium tetrachloride, in an oxygen/hydrogen flame . Removing the halide residues from the powder is problematic here . Although the halide content can be reduced to less than 0.6 wt . % with a neutralisation stage, there is generally still so much halide remaining on the powder that it is unsuitable for many applications .
  • a zirconium dioxide powder is known from EP-A-1142830 which has a BET surface area of between 1 and 600 m 2 /g and a chloride content of less than 0.05 wt . % .
  • Example 1 experiment 1 and 2 , zirconium dioxide powders having a hafnium dioxide content of approx . 2 wt . % are described. These are prepared by atomising an organic zirconium compound having a hafnium content of about 2 wt . %, dissolved in an organic solvent, with air or nitrogen using a nozzle and burning this mixture in a flame formed from hydrogen and air .
  • the BET surface area of the zirconium- hafnium mixed oxide powder obtained can be varied by altering the amount of atomising air .
  • the zirconium-hafnium mixed oxide powder has a compacted bulk density of over 150 g/1.
  • X-ray diffraction analysis shows monoclinic zirconium dioxide as the main constituent, along with tetragonal and cubic zirconium dioxide as secondary constituents .
  • the hafnium dioxide content is due to contamination of the zirconium dioxide precursor with hafnium compounds .
  • the formation of mixed oxides is emphasised as being particularly advantageous .
  • metal mixed oxide powders with the metal components Mi, M 2 , M 3 , ...M n can be easily obtained from a homogeneous solution containing the starting materials for the metal mixed oxides MiR, M 2 R, M 3 R, ...M n R, wherein R is any organic radical .
  • this powder is suitable for ceramic applications , it has been found that it is difficult to prepare highly- filled, stable, very fine-particle dispersions with this powder . Since many applications in the ceramic field start from a dispersion, it was necessary to improve the properties of the powder so that such dispersions can be obtained without difficulty .
  • the obj ect of the invention is therefore to provide a zirconium-hafnium mixed oxide powder which has a low halide content and can be easily incorporated into liquid media .
  • the obj ect of the invention is also to provide a process for preparing the zirconium-hafnium mixed oxide powder .
  • the invention provides a zirconium-hafnium mixed oxide powder in the form of aggregates of primary particles having a chloride content of at most 0.05 wt . % and having the following features : - BET surface area : 60 ⁇ 15 m 2 /g, average primary particle diameter : ⁇ 20 nm aggregate parameters : - average surface area : ⁇ 10000 nm 2 , average equivalent circle diameter : ⁇ 100 nm, average aggregate circumference : ⁇ 700 nm, content, based in each case on the total amount of powder, of - zirconium dioxide (ZrO 2 ) : 95 to 99.9 wt .
  • the zirconium-hafnium mixed oxide powder according to the invention is in the form of aggregates of primary particles .
  • the primary particles are non-porous .
  • the surfaces of these primary particles exhibit hydroxyl groups .
  • mixed oxide powder refers to a powder which has an intimate mixture of zirconium dioxide and hafnium dioxide at the primary particle level or aggregate level .
  • the primary particles in this case display Zr-O-Hf .
  • the BET surface area is determined in accordance with DIN 66131. Primary particle and aggregate dimensions are obtained by image analysis of TEM images .
  • the BET surface area can preferably be 60 + 5 m 2 /g .
  • the average primary particle diameter can preferably be 11 to 16 nm.
  • the aggregate parameters can preferably assume the following values : - average surface area : 5000-8000 nm 2 , average equivalent circle diameter : 50-90 nm, average aggregate circumference : 450-600 nm.
  • the content of zirconium dioxide can preferably be > 97 wt . %
  • the content of hafnium dioxide (HfO2) can preferably be 1 to 2.5 wt . %, based in each case on the total amount of powder .
  • the zirconium-hafnium mixed oxide powder according to the invention can also have an average, maximum aggregate diameter which is preferably less than 150 nm and particularly preferably 100-150 nm and an average, minimum aggregate diameter which is preferably less than 100 nm and particularly preferably 60-90 nm.
  • a zirconium-hafnium mixed oxide powder according to the invention which in X-ray diffraction analysis exhibits the reflexes of monoclinic and tetragonal zirconium dioxide only can also be preferred. Accordingly, cubic zirconium dioxide components cannot be detected in the preferred form.
  • the compacted bulk density can be 100 ⁇ 20 g/1.
  • the zirconium-hafnium mixed oxide powder according to the invention has a loss on drying of at most 2.0 wt . %, a loss on ignition of at most
  • the invention also provides a process for preparing the zirconium-hafnium mixed oxide powder according to the invention, wherein a solution containing the starting materials for the zirconium-hafnium mixed oxide powder, which is obtained by mixing a solution containing at least one zirconium carboxylate, a hafnium carboxylate and/or a carboxylate displaying proportions of zirconium and hafnium, in an organic solvent or organic solvent blend and a solution containing at least one zirconium alcoholate, a hafnium alcoholate and/or an alcoholate displaying proportions of zirconium and hafnium, in an organic solvent or organic solvent blend, and in which the starting compounds are present in accordance with the subsequently desired ratio of zirconium dioxide and hafnium dioxide and in which the ratio by weight of carboxylate/alcoholate is 30 : 70 to 90 : 10 , is atomised using an atomising gas to form an aerosol, the aerosol is allowed to burn into a reaction chamber in
  • Iambda2 defined as the ratio of oxygen present in the air used in total to oxygen necessary to burn the starting materials and the fuel gas , is greater than 1 or equal to 1 and lambdai > Iambda2, the residence time of the starting materials in the flame is 5 to 30 milliseconds , the hot gases and the solid products are cooled and the solid product is then separated from the gases .
  • a substantial feature of the process according to the invention is the ratio by weight of carboxylate to alcoholate . Outside the specified range a powder according to the invention cannot be obtained.
  • a further substantial feature of the process according to the invention is the introduction of secondary air into the reaction chamber . Introducing primary air alone does not lead to powders according to the invention .
  • the amounts of feed materials must also be adjusted within a narrow range such that lambdai and Iambda2 move within narrow limits .
  • Zirconium (IV) ethylate, zirconium (IV) n-propylate, zirconium (IV) isopropylate, zirconium (IV) n-butylate, zirconium (IV) tert-butylate, hafnium (IV) ethylate, hafnium (IV) n-propylate, hafnium (IV) isopropylate, hafnium (IV) n-butylate and/or hafnium (IV) tert-butylate can preferably be used as alcoholates .
  • Alcoholates containing a zirconium and a hafnium component are particularly preferred.
  • Zirconium acetate, zirconium propionate, zirconium oxalate, zirconium octoate, zirconium-2-ethyl hexanoate, zirconium neodecanoate and/or zirconium stearate, hafnium acetate, hafnium propionate, hafnium oxalate, hafnium octoate, hafnium-2-ethyl hexanoate and/or hafnium neodecanoate can preferably be used as carboxylates .
  • Carboxylates containing a zirconium and a hafnium component are particularly preferred.
  • Hafnium compounds are generally contained in zirconium compounds in a proportion of 1 to 5 wt . % . However, zirconium compounds and hafnium compounds can also be obtained in degrees of purity of 99 wt . % and higher .
  • the desired hafnium dioxide content of 0.01 to 4 wt . % can be established by any combination of hafnium contents in the starting compounds .
  • the solutions containing zirconium and/or hafnium carboxylate also contain the carboxylic acid on which the carboxylate is based and the solutions containing zirconium and/or hafnium alcoholate also contain the alcohol on which the alcoholate is based.
  • the invention also provides the use of the zirconium- hafnium mixed oxide powder to prepare dispersions , as a filler, as a support, as a catalytically active substance, in fuel cells , as a dental material, to produce membranes , as an additive in the silicone and rubber industry, to adjust the rheology of liquid systems , to stabilise heat shields , in the paint industry, as a coloured pigment, to produce piezoelectric materials .
  • Image analysis The primary particle and aggregate sizes are determined by image analysis .
  • the image analyses are performed using an H 7500 TEM device supplied by Hitachi and a MegaView II CCD camera supplied by SIS .
  • the image magnification for analysis is 30000 : 1 with a pixel density of 3.2 nm.
  • the number of particles analysed is greater than 1000. Preparation takes place in accordance with ASTM 3849- 89.
  • the lower threshold limit in terms of detection is 50 pixels .
  • the content of zirconium dioxide and hafnium dioxide is determined by X-ray fluorescence analysis and/or chemical analysis .
  • Zirconium octoate (as TiTO 2 ) 24 .40 - 24 .37 24 .40
  • Hafnium octoate (as Hf ⁇ 2) 0 30 - 0 03 3 50
  • Hafnium n-propanolate (as HfC>2) - 0 .50 - -
  • Solution 1 and solution 2 are mixed in a ratio of 90 : 10 at a temperature of 5O 0 C .
  • 1500 g/h of the resulting homogeneous solution are atomised with 5 Nm 3 /h of air using a nozzle having a diameter of 0.8 mm.
  • the resulting aerosol is transferred to a flame formed from hydrogen (5.0 Nm 3 /h) and primary air (10 Nm 3 /h) and burned into a reaction chamber .
  • Example 2 (according to the invention) is performed in an analogous way to Example 1 , but the ratio of solution 1 to solution 2 is now 50 : 50 and the mass flux of the mixed solution is 1600 g/h .
  • Example 3 (according to the invention) is performed in an analogous way to Example 1 , but the ratio of solution 1 to solution 2 is now 70 : 30 and the mass flux of the mixed solution is 1800 g/h .
  • Example 4 (according to the invention) is performed in an analogous way to Example 1 , but the nozzle diameter is now 0.5 mm.
  • Example 5 (according to the invention) is performed in an analogous way to Example 1 , but with 90 wt . % of solution 3 instead of solution 1.
  • Example 6 (according to the invention) is performed in an analogous way to Example 1 , but using solution 2 and solution 4 in a ratio of 70 : 30.
  • the mass flux of the mixed solution is 1600 g/h .
  • Example 7 comparative example
  • Example 8 comparative example only solution 2 is supplied to the flame .
  • Example 9 (comparative example) is performed in an analogous way to Example 1 , but the ratio of solution 1 to solution 2 is now 10 : 90.
  • Example 10 (comparative example) is performed in an analogous way to Example 1 , but without secondary air .
  • Example 11 (comparative example) is performed in an analogous way to Example 1 , but with a reduction in the amounts of air .
  • the average residence time is 40 ms .
  • Example 12 (comparative example) is performed in an analogous way to Example 1 , but the amounts used are chosen such that lambdai is outside the claimed range .
  • Example 13 (comparative example) is performed in an analogous way to Example 10 , but with an increased mass flux of solution .
  • Example 14 42.14 kg of demineralised water and 1.75 kg of Dolapix CE64 (Zschimmer & Schwartz ) are placed in a batch container and then the 43.9 kg of powder Pl are added using the suction pipe of the Ystral Conti-TDS 3 (stator slot : 4 mm collar and 1 mm collar, rotor/stator gap approx . 1 mm) under shear conditions .
  • the intake nozzle is closed and shearing is continued for a further 10 min at 3000 rpm.
  • (pre-) dispersion obtained in this way has a content of zirconium mixed oxide powder of 50 wt . % .
  • This pre- dispersion is passed in five cycles through a high-energy Sugino Ultimaizer HJP-25050 mill at a pressure of 2500 bar and with diamond nozzles of 0.3 mm diameter .
  • the dispersion thus obtained has a median value of 112 nm and a viscosity at 1000 s '1 of 27 mPas . It is stable for at least 6 months against sedimentation, baking and thickening .

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Abstract

Zirconium-hafnium mixed oxide powder in the form of aggregates of primary particles having a carbon content of at most 0.05 wt . % and having the following features: - BET surface area: 60 ± 15 m2/g, average primary particle diameter: < 20 nm, aggregate parameters : average surface area: < 10000 nm2, - average equivalent circle diameter: < 100 nm, average aggregate circumference: < 700 nm, content, based in each case on the total amount of powder, of zirconium dioxide (ZrO2) : 95 to 99.9 wt.%, - hafnium dioxide (HfO2) : 0.1 to 5 wt.%, carbon: 0 to 0.15 wt.%, - chloride: 0 to 0.05 wt.% the sum of the proportions of zirconium dioxide and hafnium dioxide being at least 99.8 wt.%.

Description

Zirconium-hafnium mixed oxide powder
The invention concerns a zirconium-hafnium mixed oxide powder, its preparation and use .
A pyrogenically prepared zirconium dioxide powder, which can contain up to 4 wt . % of hafnium dioxide, is known from EP-A-717008. It is obtained by hydrolysing zirconium halides , preferably zirconium tetrachloride, in an oxygen/hydrogen flame . Removing the halide residues from the powder is problematic here . Although the halide content can be reduced to less than 0.6 wt . % with a neutralisation stage, there is generally still so much halide remaining on the powder that it is unsuitable for many applications .
A zirconium dioxide powder is known from EP-A-1142830 which has a BET surface area of between 1 and 600 m2/g and a chloride content of less than 0.05 wt . % . In Example 1 , experiment 1 and 2 , zirconium dioxide powders having a hafnium dioxide content of approx . 2 wt . % are described. These are prepared by atomising an organic zirconium compound having a hafnium content of about 2 wt . %, dissolved in an organic solvent, with air or nitrogen using a nozzle and burning this mixture in a flame formed from hydrogen and air . The BET surface area of the zirconium- hafnium mixed oxide powder obtained can be varied by altering the amount of atomising air . The zirconium-hafnium mixed oxide powder has a compacted bulk density of over 150 g/1. X-ray diffraction analysis shows monoclinic zirconium dioxide as the main constituent, along with tetragonal and cubic zirconium dioxide as secondary constituents .
The hafnium dioxide content is due to contamination of the zirconium dioxide precursor with hafnium compounds . In EP-A-1142830 the formation of mixed oxides is emphasised as being particularly advantageous . According to this publication, metal mixed oxide powders with the metal components Mi, M2, M3, ...Mn can be easily obtained from a homogeneous solution containing the starting materials for the metal mixed oxides MiR, M2R, M3R, ...MnR, wherein R is any organic radical .
Although this powder is suitable for ceramic applications , it has been found that it is difficult to prepare highly- filled, stable, very fine-particle dispersions with this powder . Since many applications in the ceramic field start from a dispersion, it was necessary to improve the properties of the powder so that such dispersions can be obtained without difficulty .
The obj ect of the invention is therefore to provide a zirconium-hafnium mixed oxide powder which has a low halide content and can be easily incorporated into liquid media .
The obj ect of the invention is also to provide a process for preparing the zirconium-hafnium mixed oxide powder .
The invention provides a zirconium-hafnium mixed oxide powder in the form of aggregates of primary particles having a chloride content of at most 0.05 wt . % and having the following features : - BET surface area : 60 ± 15 m2/g, average primary particle diameter : < 20 nm aggregate parameters : - average surface area : < 10000 nm2, average equivalent circle diameter : < 100 nm, average aggregate circumference : < 700 nm, content, based in each case on the total amount of powder, of - zirconium dioxide (ZrO2) : 95 to 99.9 wt . %, hafnium oxide (HfO2) : 0.1 to 5 wt . %, carbon : 0 to 0.15 wt . %, chloride : 0 to 0.05 wt . % the sum of the proportions of zirconium dioxide and hafnium dioxide being at least 99.8 wt . % . The zirconium-hafnium mixed oxide powder according to the invention is in the form of aggregates of primary particles . The primary particles are non-porous . The surfaces of these primary particles exhibit hydroxyl groups .
The term mixed oxide powder refers to a powder which has an intimate mixture of zirconium dioxide and hafnium dioxide at the primary particle level or aggregate level . The primary particles in this case display Zr-O-Hf . There can additionally also be areas of hafnium dioxide alongside zirconium dioxide in the primary particles .
The BET surface area is determined in accordance with DIN 66131. Primary particle and aggregate dimensions are obtained by image analysis of TEM images . The BET surface area can preferably be 60 + 5 m2/g .
The average primary particle diameter can preferably be 11 to 16 nm.
The aggregate parameters can preferably assume the following values : - average surface area : 5000-8000 nm2, average equivalent circle diameter : 50-90 nm, average aggregate circumference : 450-600 nm.
The content of zirconium dioxide (ZrC>2) can preferably be > 97 wt . %, the content of hafnium dioxide (HfO2) can preferably be 1 to 2.5 wt . %, based in each case on the total amount of powder .
The zirconium-hafnium mixed oxide powder according to the invention can also have an average, maximum aggregate diameter which is preferably less than 150 nm and particularly preferably 100-150 nm and an average, minimum aggregate diameter which is preferably less than 100 nm and particularly preferably 60-90 nm.
A zirconium-hafnium mixed oxide powder according to the invention which in X-ray diffraction analysis exhibits the reflexes of monoclinic and tetragonal zirconium dioxide only can also be preferred. Accordingly, cubic zirconium dioxide components cannot be detected in the preferred form. In a preferred form of the zirconium-hafnium mixed oxide powder according to the invention the compacted bulk density can be 100 ± 20 g/1.
It can also be preferable if the zirconium-hafnium mixed oxide powder according to the invention has a loss on drying of at most 2.0 wt . %, a loss on ignition of at most
3.0 wt . %, and a pH of 4.0 to 6.0 , determined in a 4-percent aqueous dispersion .
The invention also provides a process for preparing the zirconium-hafnium mixed oxide powder according to the invention, wherein a solution containing the starting materials for the zirconium-hafnium mixed oxide powder, which is obtained by mixing a solution containing at least one zirconium carboxylate, a hafnium carboxylate and/or a carboxylate displaying proportions of zirconium and hafnium, in an organic solvent or organic solvent blend and a solution containing at least one zirconium alcoholate, a hafnium alcoholate and/or an alcoholate displaying proportions of zirconium and hafnium, in an organic solvent or organic solvent blend, and in which the starting compounds are present in accordance with the subsequently desired ratio of zirconium dioxide and hafnium dioxide and in which the ratio by weight of carboxylate/alcoholate is 30 : 70 to 90 : 10 , is atomised using an atomising gas to form an aerosol, the aerosol is allowed to burn into a reaction chamber in a flame produced from a fuel gas , preferably hydrogen, and air (primary air) , and air (secondary air) is additionally introduced into the reaction chamber, such that lambdai, defined as the ratio of oxygen present in the air used in total to oxygen necessary to burn the fuel gas , is 1.5 to 4 and
Iambda2, defined as the ratio of oxygen present in the air used in total to oxygen necessary to burn the starting materials and the fuel gas , is greater than 1 or equal to 1 and lambdai > Iambda2, the residence time of the starting materials in the flame is 5 to 30 milliseconds , the hot gases and the solid products are cooled and the solid product is then separated from the gases .
A substantial feature of the process according to the invention is the ratio by weight of carboxylate to alcoholate . Outside the specified range a powder according to the invention cannot be obtained.
A further substantial feature of the process according to the invention is the introduction of secondary air into the reaction chamber . Introducing primary air alone does not lead to powders according to the invention .
The amounts of feed materials must also be adjusted within a narrow range such that lambdai and Iambda2 move within narrow limits .
Finally the amounts of feed materials and the reactor design must be chosen such that the average residence time of the starting materials moves within narrow limits .
Zirconium (IV) ethylate, zirconium (IV) n-propylate, zirconium (IV) isopropylate, zirconium (IV) n-butylate, zirconium (IV) tert-butylate, hafnium (IV) ethylate, hafnium (IV) n-propylate, hafnium (IV) isopropylate, hafnium (IV) n-butylate and/or hafnium (IV) tert-butylate can preferably be used as alcoholates .
Alcoholates containing a zirconium and a hafnium component are particularly preferred.
Zirconium acetate, zirconium propionate, zirconium oxalate, zirconium octoate, zirconium-2-ethyl hexanoate, zirconium neodecanoate and/or zirconium stearate, hafnium acetate, hafnium propionate, hafnium oxalate, hafnium octoate, hafnium-2-ethyl hexanoate and/or hafnium neodecanoate can preferably be used as carboxylates .
Carboxylates containing a zirconium and a hafnium component are particularly preferred.
Hafnium compounds are generally contained in zirconium compounds in a proportion of 1 to 5 wt . % . However, zirconium compounds and hafnium compounds can also be obtained in degrees of purity of 99 wt . % and higher . The desired hafnium dioxide content of 0.01 to 4 wt . % can be established by any combination of hafnium contents in the starting compounds .
Methanol, ethanol, n-propanol, isopropanol, n-butanol, tert-butanol, 2-propanone, 2-butanone, diethyl ether, tert- butyl-methyl ether, tetrahydrofuran, Ci-Cs carboxylic acids , ethyl acetate, toluene and/or benzine can be used as organic solvents or as a constituent of organic solvent blends .
In a particularly preferred embodiment, the solutions containing zirconium and/or hafnium carboxylate also contain the carboxylic acid on which the carboxylate is based and the solutions containing zirconium and/or hafnium alcoholate also contain the alcohol on which the alcoholate is based.
The invention also provides the use of the zirconium- hafnium mixed oxide powder to prepare dispersions , as a filler, as a support, as a catalytically active substance, in fuel cells , as a dental material, to produce membranes , as an additive in the silicone and rubber industry, to adjust the rheology of liquid systems , to stabilise heat shields , in the paint industry, as a coloured pigment, to produce piezoelectric materials .
Examples :
Analysis :
BET : determined in accordance with DIN 66131 TEM/EDX : Energy dispersive X-ray analysis (EDX) TEM: Jeol 2070-F; EDX : Noran Voyager 4.2.3
Image analysis : The primary particle and aggregate sizes are determined by image analysis . The image analyses are performed using an H 7500 TEM device supplied by Hitachi and a MegaView II CCD camera supplied by SIS . The image magnification for analysis is 30000 : 1 with a pixel density of 3.2 nm. The number of particles analysed is greater than 1000. Preparation takes place in accordance with ASTM 3849- 89. The lower threshold limit in terms of detection is 50 pixels .
The content of zirconium dioxide and hafnium dioxide is determined by X-ray fluorescence analysis and/or chemical analysis .
Solutions used:
The solutions listed in Table 1 were used.
Table 1 : Solutions used
Solution 1 2 3 4
Zirconium octoate (as TiTO2) 24 .40 - 24 .37 24 .40
Hafnium octoate (as Hfθ2) 0 30 - 0 03 3 50
Zirconium n-propanolate (as ZrC>2) - 27 .80 - -
Hafnium n-propanolate (as HfC>2) - 0 .50 - -
Octanoic acid 39 .60 - 39 .60 39 .60 n-Propanol - 30 .50 - -
Tetra-n-propanolate - 41 .20 - -
2- (2-Butoxyethoxy) ethanol 3 50 - 3 50 3 50
White spirit 32 .20 - 32 .50 29 .00 Example 1 (according to the invention) :
Solution 1 and solution 2 are mixed in a ratio of 90 : 10 at a temperature of 5O 0C . 1500 g/h of the resulting homogeneous solution are atomised with 5 Nm3/h of air using a nozzle having a diameter of 0.8 mm.
The resulting aerosol is transferred to a flame formed from hydrogen (5.0 Nm3/h) and primary air (10 Nm3/h) and burned into a reaction chamber .
20 Nm3/h of (secondary) air are also introduced into the reaction chamber . The hot gases and the solid products are then cooled in a cooling section . The zirconium-hafnium mixed oxide powder obtained is separated off in filters .
Example 2 (according to the invention) is performed in an analogous way to Example 1 , but the ratio of solution 1 to solution 2 is now 50 : 50 and the mass flux of the mixed solution is 1600 g/h .
Example 3 (according to the invention) is performed in an analogous way to Example 1 , but the ratio of solution 1 to solution 2 is now 70 : 30 and the mass flux of the mixed solution is 1800 g/h .
Example 4 (according to the invention) is performed in an analogous way to Example 1 , but the nozzle diameter is now 0.5 mm.
Example 5 (according to the invention) is performed in an analogous way to Example 1 , but with 90 wt . % of solution 3 instead of solution 1.
Example 6 (according to the invention) is performed in an analogous way to Example 1 , but using solution 2 and solution 4 in a ratio of 70 : 30. The mass flux of the mixed solution is 1600 g/h .
In Example 7 (comparative example) only solution 1 is supplied to the flame . In Example 8 (comparative example) only solution 2 is supplied to the flame .
Example 9 (comparative example) is performed in an analogous way to Example 1 , but the ratio of solution 1 to solution 2 is now 10 : 90.
Example 10 (comparative example) is performed in an analogous way to Example 1 , but without secondary air .
Example 11 (comparative example) is performed in an analogous way to Example 1 , but with a reduction in the amounts of air . The average residence time is 40 ms .
Example 12 (comparative example) is performed in an analogous way to Example 1 , but the amounts used are chosen such that lambdai is outside the claimed range .
Example 13 (comparative example) is performed in an analogous way to Example 10 , but with an increased mass flux of solution .
The amounts of feed materials used in each example are shown in Table 2.
The physico-chemical parameters of the powders from Examples 1 to 13 are shown in Table 3.
Dispersion
Example 14 : 42.14 kg of demineralised water and 1.75 kg of Dolapix CE64 (Zschimmer & Schwartz ) are placed in a batch container and then the 43.9 kg of powder Pl are added using the suction pipe of the Ystral Conti-TDS 3 (stator slot : 4 mm collar and 1 mm collar, rotor/stator gap approx . 1 mm) under shear conditions . On completion of the drawing-in process the intake nozzle is closed and shearing is continued for a further 10 min at 3000 rpm. The
(pre-) dispersion obtained in this way has a content of zirconium mixed oxide powder of 50 wt . % . This pre- dispersion is passed in five cycles through a high-energy Sugino Ultimaizer HJP-25050 mill at a pressure of 2500 bar and with diamond nozzles of 0.3 mm diameter . The dispersion thus obtained has a median value of 112 nm and a viscosity at 1000 s'1 of 27 mPas . It is stable for at least 6 months against sedimentation, baking and thickening .
Table 2 : Feed materials and amounts used
Table 3 : Analytical values for zirconium-hafnium mixed oxide powder
m: monoclinic, t : tetragonal, c : cubic; at room temperature (23 C) ; ** - : not determined

Claims

Claims :
1. Zirconium-hafnium mixed oxide powder in the form of aggregates of primary particles and having the following features : - BET surface area : 60 ± 15 m2/g, average primary particle diameter : < 20 nm, aggregate parameters : average surface area : < 10000 nm2, average equivalent circle diameter : < 100 nm, - average aggregate circumference : < 700 nm, content, based in each case on the total amount of powder, of zirconium dioxide (ZrC>2) : 95 to 99.9 wt . %, hafnium dioxide (HfO2) : 0.1 to 5 wt . %, - carbon : 0 to 0.15 wt . %, - chloride : 0 to 0.05 wt . % the sum of the proportions of zirconium dioxide and hafnium dioxide being at least 99.8 wt . % .
2. Zirconium-hafnium mixed oxide powder according to claim 1 , characterised in that the average, maximum aggregate diameter is less than 150 nm and the average, minimum aggregate diameter is less than 100 nm.
3. Zirconium-hafnium mixed oxide powder according to claims 1 or 2 , characterised in that in X-ray diffraction analysis the powder exhibits the reflexes of monoclinic and tetragonal zirconium dioxide only .
4. Zirconium-hafnium mixed oxide powder according to claims 1 to 3, characterised in that it has a compacted bulk density of 100 ± 20 g/1.
5. Zirconium-hafnium mixed oxide powder according to claims 1 to 4 , characterised in that it has a loss on drying of at most 2.0 wt . %, a loss on ignition of at most 3.0 wt . %, and a pH of 4.0 to 6.0 , determined in a 4-percent aqueous dispersion .
6. Process for preparing the zirconium-hafnium mixed oxide powder according to claims 1 to 5, characterised in that - a solution containing as starting materials for the zirconium-hafnium mixed oxide powder, which is obtained by mixing a solution containing at least one zirconium carboxylate, a hafnium carboxylate and/or a carboxylate displaying proportions of zirconium and hafnium, in an organic solvent or organic solvent blend and a solution containing at least one zirconium alcoholate, a hafnium alcoholate and/or an alcoholate displaying proportions of zirconium and hafnium, in an organic solvent or organic solvent blend, and in which the starting compounds are present in accordance with the subsequently desired ratio of zirconium dioxide and hafnium dioxide and in which the ratio by weight of carboxylate/alcoholate is 30 : 70 to 90 : 10 , is atomised using an atomising gas to form an aerosol, the aerosol is allowed to burn into a reaction chamber in a flame produced from a fuel gas , preferably hydrogen, and air (primary air) , and air (secondary air) is additionally introduced into the reaction chamber, such that lambdai, defined as the ratio of oxygen present in the air used in total to oxygen necessary to burn the fuel gas , is 1.5 to 4 and
Iambda2, defined as the ratio of oxygen present in the air used in total to oxygen necessary to burn the starting materials and the fuel gas , is greater than 1 or equal to 1 and lambdai > Iambda2, and the residence time of the starting materials in the flame is 5 to 30 milliseconds , - the hot gases and the solid products are cooled and the solid product is then separated from the gases .
7. Process according to claim 6, characterised in that zirconium (IV) ethylate, zirconium (IV) n-propylate, zirconium (IV) isopropylate, zirconium (IV) n-butylate, zirconium (IV) tert-butylate, hafnium (IV) ethylate, hafnium (IV) n-propylate, hafnium (IV) isopropylate, and/or hafnium (IV) tert-butylate are used as alcoholate .
8. Process according to claim 6, characterised in that zirconium acetate, zirconium propionate, zirconium oxalate, zirconium octoate, zirconium-2-ethyl hexanoate, zirconium neodecanoate and/or zirconium stearate, hafnium acetate, zirconium propionate, hafnium oxalate, hafnium octoate, hafnium-2-ethyl hexanoate and/or hafnium neodecanoate are used as carboxylate .
9. Process according to claims 6 to 8 , characterised in that the organic solvent is methanol, ethanol, n-propanol, isopropanol, n-butanol, tert-butanol, 2-propanone, 2- butanone, diethyl ether, tert-butyl-methyl ether, tetrahydrofuran, Ci-Cs carboxylic acids , ethyl acetate, toluene and/or benzine,
10. Process according to claims 6 to 9, characterised in that the solutions containing zirconium and/or hafnium carboxylate also contain the carboxylic acid on which the carboxylate is based and the solutions containing zirconium and/or hafnium alcoholate also contain the alcohol on which the alcoholate is based.
11. Use of the zirconium-hafnium mixed oxide powder according to claims 1 to 5 to prepare dispersions , as a filler, as a support, as a catalytically active substance, in fuel cells , as a dental material, to produce membranes , as an additive in the silicone and rubber industry, to adjust the rheology of liquid systems , to stabilise heat shields , in the paint industry, as a coloured pigment, to produce piezoelectric materials .
EP05823955A 2004-12-22 2005-12-20 Zirconium-hafnium mixed oxide powder Withdrawn EP1831108A2 (en)

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