EP2054345A1

EP2054345A1 - Zirconium oxide and method for the production thereof

Info

Publication number: EP2054345A1
Application number: EP07787848A
Authority: EP
Inventors: Jörg LAUBE; Alfred GÜGEL; Ralph Otterstedt
Original assignee: HC Starck GmbH
Current assignee: HC Starck GmbH
Priority date: 2006-08-17
Filing date: 2007-07-24
Publication date: 2009-05-06
Also published as: CN101500943B; RU2009109346A; US8383266B2; KR20090053780A; US20100233579A1; CN101500943A; RU2442752C2; KR101323697B1; CN102745989A; JP2010500957A; UA98118C2; JP5745765B2; CN102745989B; WO2008019926A1

Abstract

The invention relates to a powdery zirconium oxide containing metal oxides from the group of scandium, yttrium, rare earths and/or the mixtures thereof. The invention also relates to a method for their production and to their use in fuel cells, in particular for producing electrolyte substrates for ceramic fuel cells.

Description

Zirconium oxide and process for its preparation

The invention relates to a powdery zirconium oxide containing metal oxides from the group of scandium, yttrium, rare earths and / or mixtures thereof, processes for its preparation, and its use in the fuel cells, in particular for the production of electrolyte substrates for ceramic fuel cells.

Pure zirconia (ZrO ₂ ) is available in three modifications. The cubic high-temperature phase changes below 230O ⁰ C into metastable tetragonal zirconium oxide, and between 1200 ⁰ C and 95O ⁰ C, the transition from tetragonal to monoclinic ZrO _{2 is} observed. Transformations between the monoclinic and the high-temperature phases during heating and cooling are associated with abrupt volume changes.

The sintering of zirconium dioxide takes place in a temperature range which takes place monoclinically and tetragonally significantly above the temperature of the reversible phase transformation. In order to avoid the re-conversion into the monoclinic phase, it is necessary to stabilize the high-temperature modifications with foreign oxides. The stabilized zirconium oxides are then present from room temperature to melting point in the same stabilized modification, ie the Voiumenänderungen on cooling for the production of ceramic components are avoided, Ullmann's Encyclopedia of Industrial Chemistry, VoL A28, 1996, p 556ff, Rompp Lexikon Chemie , 10th Edition 1999, p 3073. Therefore stabilized or partially stabilized zirconium oxide powders are used for the production of ceramic components, in which case the stabilizer oxides must be able to form a solid solution with the zirconium oxide. The amount of stabilizer required depends on the desired properties and the nature of the oxide, and inadequate homogeneities of the stabilizer in the ZrO ₂ gate lead to the presence of undesirable monoclinic, ie unstabilized, phase-to-phase phosphors. Shares In A Depending on the concentration, type and amount of the stabilizer oxides and the sintering conditions used, tailor-made zirconium oxide materials having improved properties can be produced which are used, for example, in construction and structural elements in modern mechanical engineering, in human medicine, in cutting tools and in thermal barrier coatings , In recent years, the yttria-doped zirconium oxides have been increasingly used in the production of ceramic fuel cells. An important property of the substrates for ceramic fuel cells produced from zirconium oxides is their electrical conductivity, which decisively affects the performance of the fuel cell.

According to WO 03/051790 stabilized zirconium oxides are usually prepared via two main processes in different variants.

According to the wet-chemical methods, solids which contain both metals are separated from aqueous or organic solutions or suspensions of zirconium and stabilizer precursors. As a rule, the separation of the solids takes place via co-precipitation and filtration of the hydroxides. However, other separation techniques such as SoI-GeI, evaporation, spray pyrolysis and hydrothermal method are used. After separation of the precipitated precursors they are then calcined at temperatures between 500 and 1500 ⁰ C. US 3957500 describes a co-precipitation process for producing a homogeneous mixture of zirconium and yttrium hydroxide. After calcination at 900 to 1500 ° C within 1 to 10 hours, the stabilized zirconia forms. A similar typical commercial process is described in US 4,810,680, in which basic zirconium carbonate and yttrium carbonate are dissolved in hydrochloric acid. Subsequently, the hydroxides are co-precipitated by the addition of ammonia or sodium hydroxide. The hydroxide mixture is washed, dried and calcined at 680 to 980 ⁰ C.

DE 10138573 discloses a nanoscale pyrogenically produced tetragonal yttrium stabilized zirconia (YSZ) powder and the process for its preparation. In this case, aqueous and / or alcoholic solutions of Zr and Y precursors such as nitrates and propionates by means of a nozzle in a reaction tube in which an oxyhydrogen flame of hydrogen and air burns, atomized and then burned at temperatures of 800 to 1000X. No. 5,750,459 describes the generation of gels or spherical or microsphere particles by dropping a Y / Zr nitrate solution into an ammonium hydroxide solution. Following separation and rinse the gels produced or agglomerates with water and subsequent calcination at temperatures above 550 ⁰ C and spherical microspherical stabilized Zirkoniumdäoxid powder are obtained. The high filtration rate of gel precursors is a major disadvantage compared to the traditional hydroxide precipitation process.

Disadvantage of all described wet chemical processes are the accumulating large amounts of wastewater. In addition, always extensive washes are required to to remove all by-products. However, if the washings are incomplete, exhaust gases such as HCI / CI ₂ or NO _x form during the precursor calcinations. The other method for producing the stabilized ZrO ₂ powder is the mixed-oxide or solid-state process. In this process, mixtures of zirconia and stabilizers are homogenized and then sintered to stabilized ZrO ₂ powder. The solid-state process is simple and inexpensive to perform. In contrast to wet-chemical processes, apart from recyclable water or steam, there are no by-products or contaminated wastewater and exhaust gases. The disadvantages of the process are the high sintering temperatures of> 1300 ° C. and the low homogeneity of the powders which, after sintering, contain from 25 to 30% by volume of monoclinic phase. To minimize the monoclinic phase contributions, the products are repeatedly ground and annealed in multiple stages, resulting in a significant increase in product cost. Stabilized ZrO ₂ powders are therefore hardly produced by the mixed-oxide process.

US 4542110 discloses a process for producing a sintered body by wet grinding a mixture of zirconia and yttria with addition of SiO ₂ and Al ₂ O ₃ as a sintering aid and subsequent drying and sintering of the mixture for 10 to 120 minutes at temperatures> 1300 ° C, preferably of between 1400 and 1500 ⁰ C ⁰ C. After repeated mixing and subsequent annealing of the cubic phase content increases to at least 95% by volume.

US 4360598 describes a process for producing a YSZ ceramic by mixing amorphous zirconia with yttria or a yttrium-containing salt followed by sintering. After sintering at temperatures of 1000 to 1550 ⁰ C ceramic bodies are obtained which contain mainly tetragonal and cubic zirconia.

EP 1076036 describes the preparation of zirconium oxides stabilized with yttrium or other metals by melting the precursors in high-frequency or medium-frequency furnaces at temperatures of 2200 to 3000 ^° C. DD 96467 discloses a fully stabilized cubic zirconia which is prepared by mixing basic zirconium carbonate and stabilizing additives such as calcium or yttria followed by sintering at 800 ° C / 3h. WO 03/051790 describes a process for producing tetragonal or mixtures of tetragonal and cubic zirconium dioxide. Disadvantage of the zirconia powder produced by the prior art via the mixed oxide process is their insufficient homogeneity of the stabilizers in the crystal lattice. Nevertheless, to ensure adequate stabilization, high - A -

Sintering temperatures required. However, these lead to higher production costs, also due to the additionally required process steps (breaking, classifying). Furthermore, the high sintering temperatures lead to undesirably lower BET values and to lower sintering activity of the powders. These powders are not suitable for use in ceramic fuel cells because of their low electrical balance and insufficient sintering activity.

The object of this invention is therefore to provide zirconium oxide powders for use in the ceramic fuel cells, which have high electrical conductivities and high mechanical strengths after sintering to gastight bodies.

It is also an object of the present invention to provide an economical process for producing the zirconia powders. The object is achieved by a powdery zirconium oxide containing up to 10 mol% of at least one of the metal oxides from the group of scandium, yttrium, rare earths and / or mixtures thereof, which has a filling density of at least 1.2 to 2.5 g / cm ³ , measured according to ASTM B 417.

The pulverulent zirconium oxides according to the invention preferably have a filling density of at least 1.2 to 2.3 g / cm ³ , more preferably of at least 1.6 to 2.0 g / cm ³ , particularly preferably of at least 1.3 to 1, 9 g / cm ³ and more preferably from 1, 5 to 1, 7 g / cm ³ . The zirconium oxides according to the invention are preferably characterized by a filling density of at least 1.5 to 2.5 g / cm ³ , more preferably of at least 1.6 to 2.3 g / cm ³ . The zirconium oxides according to the invention are particularly suitable as precursors for the production of substrates which are used in the ceramic fuel cells due to their high electrical conductivity. Good results are achieved when the zirconium oxides contain 3 to 10 mol% of yttrium oxide as a stabilizer. The zirconium oxides according to the invention preferably contain 3 to 6 mol%, particularly preferably 3 to 5 mol% and particularly preferably 3 to 4 mol% of yttrium oxide. The zirconium oxides according to the invention may also contain as stabilizer also preferably 3 to 10 mol%, preferably 3 to 7 mol%, particularly preferably 4 to 6 mol% ytterbium oxide (Yb ₂ O ₃ ).

The zirconium oxides according to the invention preferably have a D90 value of the powder particles of 0.5 to 1.2 μm, preferably 0.5 to 0.9 μm, particularly preferably 0.6 to 0.9 μm, measured according to ASTM C 1070.

The powders according to the invention are also distinguished by their specific surface area (BET). Preferably, the powders have BET values, measured according to ASTM D 3663, from 5 to 18 m ² / g, preferably from 5 to 15 m ² / g, preferably from 10 to 16 m ² / g, preferably from 7 to 13 m7g, particularly preferably from 9 to 12 m ² / g.

The zirconium dioxides according to the invention have very high monoclinic phase proportions. Surprisingly, and in contrast to the prior art, according to which due to the reversible phase transformation from monoclinic to tetragonal associated volume change fully or partially stabilized powder with only very low monoclinic phase fractions, up to 10 VoI% are suitable for the production of ceramic components The zirconium oxide powders according to the invention are suitable, despite monoclinic phase fractions, of up to 80% by volume for the production of ceramic substrates and, in particular, for applications in the electrolyte-supported ceramic fuel cells. The zirconium oxide powders according to the invention may have from 5 to 80% by volume of monoclinic phase fractions. The powders preferably have 20 to 80% by volume, preferably 20 to 60% by weight. %, particularly preferably 40 to 75% by volume, particularly preferably 45 to 70% by volume, of monoclinic phase fractions. The particular powders according to the invention have 40 to 55% by volume, preferably 45 to 55% by weight. % monoclinic phase shares.

The invention further relates to an efficient and economical process for the preparation of the zirconium oxides according to the invention. The invention therefore also provides a process for the preparation of zirconium oxides doped with metal oxides from the group of scandium, yttrium and rare earths and / or mixtures thereof, comprising the following steps:

a) providing an aqueous suspension of zirconium oxide and the respective metal oxide in the desired stoichiometric ratio, including the stabilization of the suspension by dispersants; b) homogenizing the suspension by comminution using Mahlhiifsmitteln by entry of a specific net grinding energy of> 0.1 kWh per kg of solid used, c) drying of the suspension at a temperature> 80 ⁰ C to obtain a homogeneous oxide mixture, d) sintering the oxide mixture for phase formation at a temperature of at least 1200 ^° C., e) production of a suspension and comminution of the sintered product formed in step d) using grinding aids by introduction of a specific energy of> 0.1 kWh per kg of sintered product, f) drying of the Suspension, In Fig. 1, the inventive method is shown schematically. The process according to the invention produces from an zirconium oxide with a purity of at least 95%, preferably> 99% and at least one of the oxides from the group scandium, yttrium, rare earths and / or mixtures thereof in the desired stoichiometric ratio, an aqueous suspension which is at least 50% Wt% mixed oxide solids content. Naturally, the zirconium oxides used as raw materials may contain up to 3% by mass of HfO ₂ .

In order to prevent the agglomeration of the oxide particles and to produce a low-viscosity suspension which is easy to transport, these dispersants are added on a polyacrylate, polyelectrolyte or polyacryic acid base. Good results were achieved, for example, when using, based on the solids content of the suspensions, 1 to 12 percent by mass, preferably 3 to 8 percent by mass of the dispersants Doiapix CE 64 and / or Doiapix CA Zschimmer & Schwarz achieved. An important role in the process according to the invention is played by the morphological properties of the zirconium oxide precursor. It has been found that the zirconium oxide precursors with edge lengths (a, b, c) of the crystallites of a = 20 to 75 nm, b = 20-90 nm and c = 20 to 75 nm, preferably a = 30 to 75 nm, b = 30 to 75 and 0 = 30 to 75, particularly preferably from a = 35 to 50 nm, b = 45 to 60 nm and c = 35 to 45 nm lead to the inventive powders. It has furthermore been found that the zirconium oxide precursors have a specific surface area (BET) of 3 to 30 ^m.sup.2 / g, preferably 6 to 15 ^m.sup.2 / g, particularly preferably 6 to 11 ^m.sup.a / g, measured according to ASTM D 3663 lead to the zirconium oxides according to the invention. Decisive for the preparation of the zirconium oxides according to the invention is an intensive homogenization of the suspension by wet grinding. Various apparatuses can be used to carry out the grinding operations. Suitable for this are different types of ball mills. The comminution is preferably carried out in stirred ball mills. It has now been found that the wet grinding of the oxide mixture in a Rührwerkskugelmühie by entry of a specific effective net grinding energy, later also called energy input or Mahleineintrag (MEE), from 0.1 to 2.0 kWh per kg of solids used to the inventive powders with special properties.

The net grinding energy input (E _NE ττo) is determined as the difference between the gross grinding energy input (EBRUTT _O ) and the energy input when the mill is idling (E _EMPTY ). EBRUTTO ^we d recorded with a mounted on the mill power / energy meter (D 122 Gönnheimer). E _EMPTY is the product of the no-load power (PL _EER ) of the mill and the grinding time (t). Idle power is the power that is called the mill is required for operation at a given speed without filling with grinding media and suspension. The power consumption of the mill can be directly measured by

/ Energy meter are read.

ENETTO = EBRUTTO - EUEER (in kWh) where ELEER = P _LE ER ^* t.

The specific effective grinding energy input (MEE) results as a quotient of E _N eτo and the mass of the oxides (M) used.

MEE = E _NE ττo / MOXIDE (in kWh / kg)

The specific effective grinding energy input is preferably 0.2 to 1.5 kWh / kg, preferably 0.1 to 1.0 kW / h, preferably 0.2 to 1.0 kWh / kg, preferably 0.3 to 1.0 kWh / kg, more preferably 0.2 to 0.7 kWh / kg, more preferably 0.6 to 0.8 kW / kg of solid used, and particularly preferably 0.2 to 0.5 kWh / kg of solid used.

After homogenization and subsequent drying at temperatures of> 80 ° C, the oxide mixture is sintered at temperatures of at least 1200 ⁰ C.

Sintering at temperatures of 1200-1350 ⁰ C is preferred, most preferably carried out at 1250-1300 ⁰ C.

The sintered powders are then subjected to intensive wet grinding in order to obtain good, dispersible to the primary particle range powder for further processing. The solids concentration in the suspension can be up to 80

Percent by mass, preferably up to 70 percent by mass. Preferably, the

Solids concentration in the suspension 40 to 70 mass%, preferably 60 to 70, particularly preferably 50 to 60 mass%.

Preferably, the wet grinding at a specific effective grinding energy input from 0.4 to 2.5 kWh / kg, more preferably from 0.7 to 1, 9 kWh / kg, particularly preferably from 0.4 to 1, 0 kWh / kg, in particular preferably from 0.4 to 0.8 kWh / kg and more preferably from 0.4 to 0.6 kWh / kg of solid carried out.

After grinding, the suspension is dried at temperatures of ≥ 8O ⁰ C.

The drying in a spray dryer at temperatures of ≥ 80 ⁰ C is preferred, preferably from ≥ 100 ⁰ C, particularly preferably of> 11O ⁰ C.

The novel zirconium oxide powders produced by the process according to the invention are particularly suitable for the production of substrates and in particular for the production of electrolyte substrates for ceramic fuel cells.

The zirconium oxide powders according to the invention can be pressed into particularly dense compacts.

The invention also relates to compacts consisting of zirconium oxides according to the invention. The compacts according to the invention have a Green density, which is 54 to 65%, preferably 56 to 62%, particularly preferably 56 to 58% of the theoretical density.

The green density of the compacts can be determined by the geometric method. In this case, specimens of 1 cm ² surface and a height of 5-10 mm are pressed uniaxially with a pressure of 100 MPa. Thereafter, the specimens are post-densified isostatically with 2000 MPa and then their volume (V) according to the formula

V = a x b x c calculated, where a, b, c - mean edge lengths of the specimens. The green density is determined by dividing the mass of the specimens by the volume of the sample. The pul verförmigen zirconium oxides according to the invention are also distinguished by their high sintering activity. The compacts produced from the zirconium oxide powders of the invention are characterized in that they form gas-tight sintered bodies of high strength after sintering.

The density of a sintered compact can be determined by the buoyancy method. For this purpose, the mass of the specimen in air and in water at 21 ⁰ C is measured and the density according to the formula

Density of the sample = mass of the sample in air x density (water at 21 ° C)

Mass of the sample in air - mass of the sample in water

certainly.

The invention also sintered substrates for electrolyte-supported ceramic fuel cells consisting of zirconium oxides according to the invention.

The sintered substrates according to the invention are distinguished by their high specific electrical conductivity, later also called SEL. The level of specific electrical conductivity depends on the type and concentration of the added metal oxide component and the temperature. Thus, substrates of the zirconium oxides according to the invention with 3.5 mol% Y ₂ O _{3 show} a SEL of at least 2.5 S / m, preferably of at least 2.7 S / m, particularly preferably of at least 2.9 S / m, measured at 850 ^° C. The substrates of zirconium oxides according to the invention with 4 mol% Yb ₂ O ₃ have an SEL of at least 3.8 S / m, preferably at least 4.2 S / m. The substrates with 6 mol% Yb ₂ O ₃ are distinguished by a SEL of at least 6.6 S / m, preferably 6.8 S / m.

The specific electrical conductivity can be determined by means of a 4-point direct current measurement. From the powders, ceramic test pieces of about 50 mm in length, 10 mm in width and a thickness of about 100 μm are produced by film casting. The film casting slip is prepared by adding 250g of powder to 202g of a commercial target! available binder (eg Ferro, Binder B73208) with the addition of grinding aids 418 g 3YSZ-Mahtzyltndem (12mm diameter) and 418 g 3YSZ grinding cylinder (10mm diameter) from Tosoh be mixed in a 1 liter plastic bottle. The Foliengießschlicker is homogenized for 48 hours on a roller bench. Then the grinding cylinders are separated and the slurry degassed for 24 hours by slowly rotating in a 0.5 liter PE bottle. The slurry is poured through a filter on a flat surface and brought by means of a doctor blade to a height of about 250 microns. After 7-24h drying strips are cut from the film, which after 1 hour sintering at 1500 ° C, the above-mentioned test specimens.

After the height (H) and width (B) of the test specimen were measured with a micrometer accurate to +/- 1 micron, four contact strips of fritless platinum paste (Matek, Jülich) over the entire width of the specimen by means of a template on the test specimen applied and baked at 1200 ⁰ C 1h. The distance between the inner contact strips (L) is 25.5 mm. The outer contact strips are located at a distance of 7 mm to inner contact strips. The baked platinum contacts of the sample are pressed onto fixed platinum contacts of the measuring holder by means of a body of aluminum oxide with a mass of 20 g. At the outer contacts a direct current (I) of 150 μA is applied while the voltage (U) between the inner contacts is measured by means of a digital voltmeter. To eliminate the influence of polarization or contact effects on the internal electrodes, the polarity and magnitude of the current are varied. The independence of the conductivity of polarization or contact effects on the inner electrodes is ensured by the fact that the change in the polarity and magnitude of the current lead to no change in the conductivity.

The specific electrical conductivity (SEL) of the sample is calculated according to the formula

SEL, [S / m] = ^U ^ ^V]

H [m] xB [m]

calculated.

The substrates according to the invention are also distinguished by their high mechanical properties

Strength out. Thus, the substrates according to the invention with 3.5 mol% Y ₂ O ₃ a Strength from 2000 to 2500 MPa. The substrates with 8.9 mol% Y ₂ O ₃ show a strength of 900 to 1000 MPa. The 4 mol% Yb ₂ O ₃ substrates have a strength of 2000 to 2100 MPa, with 6 mol% Yb ₂ O ₃ of 1050 to 1150 MPa. The mechanical strength can be determined by the ball-ring method, based on DIN 52292.

From a dried green film, round samples of about 34 mm in diameter are punched and then sintered at 1500 ⁰ C for one hour. After sintering, the round samples have a radius (r ₃ ) of about 27 mm and a thickness (t) of about 100 μm. From 20 pieces of the sintered samples, the force F necessary for the fracture is successively determined in a ball-and-ring arrangement by means of a testing machine from Instron. The ring has a diameter (r ₂ ) of 5.6 mm. The transverse contraction number v is assumed to be 0.30. The test speed is 0.5 mm / min. The breakage of the sample is detected by means of ultrasonic measuring head. The radius of the loaded surface (rO is approximately assumed to be t / 3. The radial tensile stress occurring at fracture is calculated according to the following formula:

From the 20 readings a Weibull statistic is used. The strengths mentioned in the examples emerge from this standard statistical evaluation. Due to the usual approximation of the diameter of the loaded surface (s), a systematic overestimation of the calculated fracture stresses can occur. Therefore, the sample thickness is listed in the following examples. For the same sample thickness, a comparison of different sample materials is possible.

The zirconium oxides according to the invention are preferably used for the production of electrolyte substrates and / or functional layers in fuel cells. The invention therefore relates to a fuel cell containing a substrate of zirconium oxide according to the invention. The invention also provides a fuel cell which has at least one functional layer which contains at least one of the zirconium oxide powders according to the invention. In a preferred embodiment, the fuel cell according to the invention is an anode-supported or an electrolyte-supported cell.

The invention will be explained in more detail by way of examples. Examples

In the following examples, the following measurement methods were used for the analysis:

- specific surface BET-ASTM D 3663,

Particle size distribution - Microtrac X100, ASTM C 1070 with 10 min ultrasonic pretreatment,

- Crystallite size - XRD line profile analysis

- Monoclinic phase content - Determination according to Dirats / PWA-N 62 - Filling density ASTM B 417

example 1

In a cooled with water double-walled storage tank 10.74 liters of demineralized water were submitted and with stirring with a schnei! running agitator 23.5 kg ZrO2 with a specific surface area of 7.54 m ² / g and Kristailit edge lengths of a = 47 nm, b = 58 nm, c = 43 nm and 1.56 kg Y ₂ O ₃ with a specific Surface suspended 5.36 m ² / g, ie, the solids content was 70 percent by mass. To stabilize the suspension, initially 0.37 kg of a 1: 1 mixture of the two dispersing agent qualities Dolapix CE 64 and Dolapix CA from Zschimmer & Schwarz were added, whereby an increase in the zeta potential was achieved. During milling, further dispersing aid quantities of the Dolapix CA / CE64 mixture were continuously metered in to further stabilize the surfaces and charges newly created with progressive comminution, so that the suspension remained low-viscosity despite the high solids concentration during the comminution and could be stirred and conveyed well , The suspension was pumped via a membrane pump from the feed tank through a polypropylene-lined ball mill LMK 4 of Netzsch Feinmahltechnik and then returned to the feed tank, ie the crushing was carried out in the circulation process. The mill space was filled with 10 kg of mahic balls, 0.6 mm diameter yttria-stabilized zirconia (YSZ). The speed of the stirrer shaft was 1950 min ^'1 . The net grinding energy input (ENETT _O ) was determined as the difference between the gross grinding energy input (E _BR uττo) and the energy input at idling of the mill (ELEER). E _BR U _TΓO is measured using a letst / energy meter mounted on the mill (D. 122 from Gönnheimer). E _EMPTY is the product of the no-load power (PLEER) of the mowing and grinding time (t).

ENETTO = EBRUTTO - E _EMPTY (in kWh), where EtEER ⁼ P EMPTY t.

The specific effective grinding energy input (MEE) results as a quotient of ENETTO and the mass of the oxides (M) used.

MEE = EN _E TTO / MOXIDE (in kWh / kg)

In the example, up to a gross grinding energy input of 30.6 kWh was milled. The recorded idle power at the predetermined rotational speed of the agitator shaft 1950 min ^"1 was 1.30 kW, and the grinding time 9 hours. It resulted in a net milling energy 0.754 kWh / kg.

After completion of the milling, the suspension was spray-dried. The inlet temperature of the spray dryer was 300 ⁰ C, the outlet temperature of 105 ⁰ C. spray drying, cyclone discharge and material were combined and protection sieved through a 250 micron sieve. The spray dried product had a specific surface area of 15.9 rrvVg.

Subsequently, the homogenized material Vorstoff mixture was sintered in a hood furnace type "NT 440" from Nabertherm with blowing air at 1300 "C with a holding time of 2 hours, the heating and cooling rate was 5 K / min. The sintered product was in turn comminuted in the stirred ball mill with a specific net grinding energy input of 0.75 kWh / kg and then spray-dried. In order to destroy coarse sintered agglomerates, this time the milling was carried out in two stages with YSZ grinding balls, using milling beads with a diameter of 2 mm in the first stage and grinding beads of 0.6 mm in the second stage. The Mahlkugel change took place after a specific net Mahlenergäeeintrag of 0.3 Wh / kg, in contrast to the Vorstoffmahlungen proved in the crushing of the sintered products a one-time addition of 1% dispersing aid, based on the solid used, as sufficient.

The zirconia powder obtained had a specific surface area of 10.63 m ² / g, a dgo value of 0.71 μm and a bulk density of 1.81 g / cm ³ . The Y ₂ O ₃ content was 3.5% by volume. The monoclinic phase fraction was 41% by volume.

The powder was pressed uniaxially with a pressure of 100 MPa into compacts. Thereafter, the specimens were post-densified isostatically with 2000 MPa. The compacts showed a green density of 3.44 g / cm ³ . The density of the compacts after sintering at 1500 ° C / 1 h was 6.01 g / cm ³ (98.2% of the theoretical density). The powder was very easy to process via foil casting, drying and sintering for one hour at 1500 ⁰ C to electrolyte substrates. The sintered at 850 ⁰ C substrates showed a specific electrical conductivity of 2.70 S / m. The mechanical strength of 90 μm thick substrates, determined by the ball-ring method, was 2413 MPa. The zirconia in the sintered substrates was nearly completely stabilized, the monoclinic phase content was <1 Vo! %.

Example 2

23.5 kg ZrO ₂ with a specific surface area of 9.71 m ² / g and crystallite edge lengths of a = 36 nm, b = 46 nm, c = 36 nm and 1.56 kg Y ₂ O ₃ with a specific surface area of 5.36 m ² / g were suspended in 10.7 liters of water. The solids content of the suspension was 70 percent by mass. The homogenized precursor mixture showed a specific surface area of 19.28 m ² / g after spray-drying. The implementation of the example was carried out analogously to Example 1.

The zirconia powder obtained had a specific surface area of 9.43 m ² / g, a d ₉₀ value of 0.57 μm and a filling density of 1.84 g / cm ³ . The Y ₂ O ₃ content was 3.5 mol%. The monoclinic phase fraction of the powder was 39% by volume. The powder was pressed uniaxially with a pressure of 100 MPa into compacts. Thereafter, the specimens were post-densified isostatically with 2000 MPa. The compacts showed a green density of 3.49 g / cm ³ . The density of the compacts after sintering at 1500 ° C / 1h was 6.01 g / cm ³ . The powder can be processed very well by film casting, drying and sintering at 1500 ^° C. for one hour to form electrolyte substrates. The sintered substrates showed an electrical conductivity (SEL) of 2.72 S / m at 850 ^° C. The mechanical strength of 90 μm thick substrates was 1954 MPa. The zirconia in the sintered substrates was completely stabilized, ie monoclinic ZrO ₂ phase was no longer detectable by X-ray analysis.

Example 3

66 kg ZrO ₂ with a specific surface area of 6.63 rrrVg and crystallite edge lengths of a = 50 nm, b = 59 nm, c = 44 nm and 4.4 kg of Y ₂ O ₃ with a specific surface area of 3.74 m ² / g were suspended in 47 liters of water. The solids content was thereby

60 percent by mass. The precursor grinding was carried out at a specific net Mahienergieeintrag of 0.50 kWh / kg solid. The homogenized precursor mixture showed a specific surface area of 14 ^m.sup.2 / g after spray-drying. The further implementation of the example was carried out analogously to Example 1. The product obtained had a specific surface area of 10.60 m ² / g, a d _Θ0 value of 0.64 μm and a filling density of 1.72 g / cm ³ . The Y ₂ O ₃ content was 3.5 mol%. The monoclinic phase fraction of the powder was 50% by volume. The powder was pressed uniaxially with a pressure of 100 MPa into compacts. Thereafter, the specimens were post-densified isostatically with 2000 MPa. The compacts showed a green density of 3.46 g / cm ^3. The density after sintering at 1500 ° C / 1 h was 6.01 g / cm ³ . The powder was very easy to process via Foiiengießen, drying and sintering for 1 hour at 1500 ⁰ C to electrolyte substrates. The sintered substrates showed a specific electrical conductivity (SEL) of 2.73 S / m at 850 ° C. The mechanical strength of 90 μm thick substrates was 2390 MPa. The zirconia in the sintered substrates was completely stabilized, ie monoclinic ZrO ₂ ~ phase was undetectable by X-ray analysis.

Example 4

93.7 kg ZrO ₂ with a specific surface area of 6.63 m ² / g and crystallite edge lengths of a = 50 nm, b = 59 nm, c = 44 nm and 6.2 kg Y ₂ O ₃ with a specific surface area of 3.74 m ² / g were suspended in 66.6 liters of water. The solids content of the suspension was 60 percent by mass. The procedure was analogous to Example 1. The resulting powder had a specific surface area of 11 m ² / g, a d ^ value of 1, 16 microns and a filling density of 1.67 g / cm ³ . The Y ₂ O ₃ content was 3.5 mol%. The monoclinic phase content of the powders was 60% by volume. The powder was pressed uniaxially with a pressure of 100 MPa into compacts. Thereafter, the specimens were post-densified isostatically with 2000 MPa.

The compacts showed a green density of 3.35 g / cm ³ . The density after sintering at 1500 ° C / 1h was 6.09 g / cm ³ . The powder was very easy to process via foil casting, drying and sintering for one hour at 1500 ⁰ C to electrolyte substrates. The sintered substrates had a (SEL), measured at 850 ^° C., of 2.83 S / m. The mechanical strength of 90 μm thick substrates was 2191 MPa. The zirconia in the sintered substrates was completely stabilized, ie monocrystalline ZrO ₂ phase was undetectable by X-ray analysis. Example 5

46.5 kg ZrO ₂ with a specific surface area of 7.67 m ² / g and crystallite edge lengths of a - 47 nm, b = 56 nm, c = 43 nm and 3.2 kg of Y ₂ O ₃ with a specific surface area of 7 m ² / g were suspended in 33.2 liters of water. The solids content of the suspension was 60 percent by mass. The procedure was carried out analogously Beispie! 1. The resulting powder had a specific surface area of 11.48 m ² / g, a d ₉₀ value of 0.7 μm and a filling density of 1.71 g / cm ³ . The Y ₂ O ₃ content was 3.5 mol%. The monoclinic phase aspect! the powder was 45 Vo! %. The powder was pressed uniaxially with a pressure of 100 MPa into compacts. Thereafter, the specimens were post-densified isostatically with 2000 MPa.

The compacts showed a green density of 3.5 g / cm ³ - The density after sintering at 1500 ° C / 1 h was 6.02 g / cm ³ . The powder was very easy to process via foil casting, drying and sintering for one hour at 1500 ⁰ C to electrolyte substrates. The sintered substrates had a (SEL), measured at 850 ^° C., of 2.87 S / m. The mechanical strength of 90 μm thick substrates was 2285 MPa. The zirconia in the sintered substrates was completely stabilized, ie monoclinic ZrO ₂ phase was undetectable by X-ray analysis,

Example 6

Using the process described in Example 1, doped ZrO ₂ powders having different Y ₂ O ₃ contents were prepared. Zirconia was used with a specific surface area of 7.67 m ² / g and crystallite edge lengths of a - 47 nm, b = 56 and c = 43 nm and also used in Example 5 Y ₂ O ₃ with a specific surface area of 7 m ² / g. The properties of the resulting powders, compacts and substrates are shown in Table 1. The table shows that with increasing amounts of yttrium oxide, the specific electrical conductivity increases. FIG. 2 shows the mechanical strength and specific electrical conductivity of substrates produced in Examples 1 to 6 from zirconium oxides according to the invention, as a function of the Y ₂ O ₃ content. Table 1

Example 7

According to the procedure described in Example 1, a with 4 mol%

Yb ₂ O ₃ doped ZrO ₂ powder produced. It was used 22.1 kg of the also in

Example 5 used ZrO ₂ and 2.9 kg of Yb ₂ O ₃ having a specific surface area of

3.77 m ² / g in 10.7 liters of water. The solids content of the suspension was 70

Mass percent.

The product obtained had a specific surface area of 10.89 m ² / g, a d _go value of 0.79 μm and a filling density of 1.73 g / cm ³ . The monokinine phase fraction of the

Powder was 30% by volume. The powder was added uniaxially with a pressure of 100 MPa

Pressed pressed bodies. Thereafter, the specimens were post-densified isostatically with 2000 MPa.

The compacts showed a green density of 3.66 g / cm ³ The density after sintering at 1500 ° C / 1 h was 6.32 g / cm ³ The powder was very good at film casting,

Dry and one-hour sintering at 1500 ⁰ C to process electrolyte substrates. As shown in Fig. 3, the sintered substrates of ytterbium oxide doped ZrO ₂ (YbSZ) at 850 ⁰ C exhibited a specific electric conductivity of 4.21 S / m, which was thus significantly higher than comparable substrates having 4 mol% Y ₂ O ₃ doped ZrO ₂ (YSZ), example! 6. The mechanical strength of 95 microns thick substrates was 2066 MPa. The zirconia in the sintered substrates was completely stabilized, ie monoclinic ZrO ₂ phase was undetectable by X-ray analysis.

Example 8

According to Example 7, a ZrO ₂ powder doped with δ rnol% Yb ₂ O _{3 was} prepared, starting from 20.8 kg ZrO ₂ and 4.2 kg Yb ₂ O _3.

The product obtained had a specific surface area of 9.07 m ² / g, a d ₉₀ value of 0.77 μm and a filling density of 1.84 g / cm ³ . The monoclinic phase content of the powders was 13% by volume. The powder was pressed uniaxially with a pressure of 100 MPa into compacts. Thereafter, the specimens were post-densified isostatically with 2000 MPa.

The compacts showed a green density of 3.74 g / cm ³ . The density after sintering at 1500 ° C / 1h was 6.49 g / cm ³ . The powder was very easy to process via foil casting, drying and sintering at 1500 ⁰ C for ¹ hour to form electrolyte substrates. As shown in Fig. 3, the sintered substrates (6YbSZ) show at 850 ⁰ C, a conductivity of 6.85 S / m, which is thus significantly higher than comparable substrates containing 6 mol% of Y ₂ O ₃ doped ZrO ₂ from example 6. The mechanical strength of 95 μm thick substrates was 1108 MPa. The zirconia in the sintered substrates was completely stabilized, ie monoclinic ZrO ₂ phase was undetectable by X-ray analysis.

Claims

claims

1. A powdery zirconium oxide containing up to 10 mol% of at least one of the metal oxides from the group consisting of scandium, yttrium, rare earths and / or mixtures thereof, which has a bulk density of 1.2 to 2.5 g / cm ³ , measured according to ASTM

B 417, has.

2. A powdery zirconium oxide according to claim 1, characterized in that it has a filling density of 1.3 to 1.9 g / cm ³ .

3. A powdery zirconium oxide according to claim 1 or 2, characterized in that it contains 3 to 10 mol% of Y ₂ O ₃ .

4. A powdery zirconium oxide according to at least one of claims 1 to 3, characterized in that it contains 3 to 6 mol% of Y ₂ O ₃ .

5. A powdery zirconium oxide according to at least one of claims 1 to 4, characterized in that it contains 3 to 4 mol% of Y ₂ O ₃ .

6. A powdery zirconium oxide according to at least one of claims 1 to 5, characterized in that it contains 3 to 10 mol% of Yb ₂ O ₃ .

7. A powdery zirconium oxide according to at least one of claims 1 to 5, characterized in that it contains 3 to 7 mol% of Yb ₂ O ₃ .

8. The powdery zirconium oxide according to at least one of claims 1 to 7, characterized in that it has a BET specific surface area of from 5 to 18 m ² / g, measured according to ASTM D 3663.

9. The powdery zirconium oxide according to at least one of claims 1 to 7, characterized in that it has a BET specific surface area of 10 to 16 m ² / g, measured according to ASTM D 3663.

10. A powdery zirconium oxide according to at least one of claims 1 to 9, characterized in that it comprises 5 to 80% by volume of monoclinic phase fractions.

Powdered zirconium oxide according to at least one of claims 1 to 10, characterized in that it has 20 to 80% by mass of monoclinic phases.

Powdered zirconium oxide according to at least one of Claims 1 to 11, characterized in that it has 45 to 70% by volume of monoclinic phase fractions.

13. A process for producing zirconium oxides doped with metal oxides from the group consisting of scandium, yttrium and rare earths and / or mixtures thereof comprising the following steps: a) providing an aqueous suspension of zirconium oxide and the respective metal oxide in the stoichiometric ratio, including the stabilization of the suspension by dispersants , b) homogenizing the suspension by comminution using grinding aids by introducing a specific net grinding energy of> 0.1 kWh per kg of solid used, c) drying the suspension at temperatures ≥ 8O ⁰ C to obtain a homogeneous oxide mixture, d) sintering the oxide mixture at temperatures of at least 1200 ⁰ C, e) generating a suspension and comminution of the formed in step d)

Sinterproduktes by entry of a specific energy of> 0.1 kWh per kg of sintered product, g) drying of the suspension.

14. The method according to claim 13, characterized in that the edge lengths (a, b, c) of the crystallites of the zirconium oxide raw material used have values of a = 20 to 75 nm, b = 20 to 90 nm and c = 20 to 75 nm ,

15. The method according to claim 13, characterized in that the edge lengths (a, b, c) of the crystallites of the zirconium oxide raw material used have values of a = 30 to 50 nm, b = 45 to 60 nm and c = 35 to 45 nm ,

16. The method according to claim 13, characterized in that the zirconium oxide raw materials used have a BET specific surface BET of 3 to 30 m ² / g, measured according to ASTW! D 3663.

17. The method according to claim 13, characterized in that the zirconium oxide raw materials used have a BET specific surface BET of 6 to 11 m ^z / g, measured according to ASTM D 3663.

18. The method according to claim 13, characterized in that the homogenization of the raw materials by wet grinding at a specific net Mahlenergieeintrag of 0.2 to 1, 5 kWh / kg solids is performed.

19. The method according to claim 13, characterized in that the homogenization of the raw materials by NassmahJung at a specific net

Mahienergieeintrag of 0.3 to 1, 0 kWh / kg solids is performed.

20. The method according to claim 13, characterized in that the homogenization of the raw materials by wet grinding at a specific net grinding energy input of 0.6 to 0.8 kWh / kg solids is performed.

21. The method according to claim 13, characterized in that the suspension is spray-dried.

22. The method according to claim 13, characterized in that the sintering is carried out at temperatures of 1200 to 135O ⁰ C.

23. The method according to claim 13, characterized in that the sintering is carried out at temperatures of 1250 to 1300 ⁰ C.

24. The method according to claim 13, characterized in that the wet grinding of the sintered oxide mixture is carried out at a specific net grinding energy input of 0.5-2.5 kWh / kg of oxide mixture.

25. The method according to claim 13, characterized in that the wet grinding of the sintered oxide mixture at a specific net grinding energy input of 0.7-1, 9 kWh / kg oxide mixture is performed.

26. compact consisting of pulverulent zirconium oxide according to one or more of claims 1 to 12.

27. A compact according to claim 26, which has a green density of 54 to 65% of the theoretical sintered density.

28. A compact according to claim 26, which has a green density of 56 to 62% of the theoretical sintered density.

29. A compact according to claim 26, which has a green density of 56 to 58% of the theoretical sintered density.

30. A substrate for electrolyte-supported ceramic fuel cells, consisting of powdery zirconium oxide according to one or more of claims 1 to 12.

31. A substrate according to claim 30, which has a specific electrical conductivity (SEL) of at least 2.5 S / m, measured at 850 ⁰ C.

32. A substrate according to claim 30, which has a specific electrical conductivity (SEL) of at least 3.8 S / m, measured at 850 ^° C.

33. A substrate according to claim 30, which has a specific electrical conductivity (SEL) of at least 6.6 S / m, measured at 850 ⁰ C.

34. Use of the zirconium oxide according to one or more of claims 1 to 12 for the production of electrolyte substrates and / or functional layers in fuel cells.

35. A fuel cell containing a substrate according to claim 30.

36. Fuel cell, which has at least one functional layer containing a zirconium oxide according to one or more of the preceding claims.

37. A fuel cell according to claim 40 or 41, which is an anode-supported or an electrolyte-supported cell.