DE102012200652A1 - Slip for manufacturing ceramics and molded product for e.g. medical implants, comprises doped zirconia solid particles having tetragonal and monoclinic modification and specified mean agglomerate size, dispersed in liquid medium - Google Patents

Abstract

A slip comprises a liquid medium, and doped zirconia solid particles having tetragonal and monoclinic modification, dispersed in the liquid medium. Doped zirconia solid particles have mean agglomerate size of 20-300 nm. The ratio of peak intensities between tetragonal and monoclinic modifications is 1.3-20. Independent claims are included for the following: (1) granules, which contain doped zirconia solid particles; (2) ceramics, which are formed using slip and/or granules. The ceramics contain structure containing mean grain size of less than 500 nm, and sintering density of more than 90%; (3) manufacture of slip; and (4) manufacture of black ceramics.

Description

The invention relates to a ZrO ₂ -based ceramic material and its precursors in the form of powders, slips, granules or presintered shaped bodies and to a process for their preparation, wherein the ZrO ₂ precursors have a high sintering activity and form a finely divided ceramic structure. Moreover, the invention relates to the use of the ceramic material according to the invention on ZrO ₂ -Baisis in the medical and technical field, in particular for the production or coating of medical implants and technical machine parts.

Since the mid-1980s, zirconia has held a firm place among high-performance ceramics. Unstabilized zirconia (ZrO ₂ ) has a monoclinic crystal structure at room temperature and a tetragonal crystal structure at temperatures above 1170 ° C. Since there is a change in the lattice structure during the phase transition between tetragonal and monoclinic, which is associated with an increase in volume, pure ZrO _{2 is} mixed with stabilizers (also additives or doping elements) in order to avoid subsequent destruction in the sintering process. With the aid of these additives, for example from the group of oxides of rare earth metals (such as yttrium, cerium), a stabilization of the tetragonal phase is achieved. Such materials are commonly referred to as TZP (Tetragonal Zirconia Polycrytals) and, more particularly, depending on the stabilizing element, for example as Y-TZP or Ce-TZP. TZP is characterized by excellent properties, namely high flexural strength and high fracture toughness, with a modulus of elasticity comparable to that of steel.

The ceramic properties are directly related to a large number of influencing factors, starting with the type and quality of the raw materials and the doping elements, over the entire processing chain up to the final preparation of the ceramic shaped bodies.

For example, the dependence of the bending tensile strength on the grain size in the ceramic structure is known. Smaller grain sizes lead to higher strengths. If the ceramic structure has different grain sizes, the largest grain for strength is crucial.

Fine microstructures can be realized using two approaches. On the one hand, by adding suitable additives, it is possible to attempt to suppress grain growth during the sintering process. On the other hand, finer ZrO ₂ powders can be used. The sintering activity increases with decreasing particle size, which means that lower sintering temperatures are necessary. Lower sintering temperatures limit particle growth during the sintering process.

ZrO ₂ powders with nanoscale particle size are available which, due to their fine structure, have a particularly high sintering activity. On the other hand, however, there is often the difficulty of handling these finely divided powders and processing them in such a way that densely sintered microstructures actually result. In addition, finely divided powders, in particular nanoscale powders, are expensive because their production process is cost-intensive.

Alternatively, it is attempted to reduce the particle size of coarser granular powders by intensive grinding and thereby achieve this particle size effect. This can lead to a phase transformation from tetragonal to monoclinic. For example, in the case of ZrO ₂ partially stabilized with 3 mol% Y ₂ O ₃ it is known that the initially detectable tetragonal crystal phase is only reduced or no longer present after intensive grinding. Subsequent temperature treatment (eg during sintering) recrystallizes the tetragonal ZrO ₂ phase. This renewed phase transfer to tetragonal is usually associated with a change in volume, which can lead to cracks in the structure.

The invention is based on the object, an improved slurry containing at least ZrO ₂ particles, an improved granules containing at least ZrO ₂ particles, an improved prepared from the slurry and / or the granules presintered moldings, an improved from the To indicate slip and / or ceramic produced granules and improved methods for producing the slurry, the granules and the ceramic and their technical and medical applications.

With regard to the slip, the object is achieved according to the invention by a slip having the features of one of claims 1 to 4.

With regard to the granules, the object is achieved according to the invention by a granulate having the features of one of claims 5 to 7.

With respect to the ceramic, the object is achieved according to the invention by a ceramic having the features of one of claims 8 or 11.

With regard to the method for producing the slip, the object is achieved according to the invention by a method having the features of claim 9.

With regard to the method for producing the ceramic, the object is achieved according to the invention by a method having the features of claim 10.

With respect to the use of the object is achieved by a use with the features of claim 12th

With regard to the presintered shaped body, the object is achieved according to the invention by a presintered shaped body having the features of claim 13.

Advantageous embodiments of the invention are the subject of the dependent claims.

All percentages (%) are hereinafter by weight percent (wt%, i.e.,% w / w) unless otherwise specified.

A slurry according to the invention comprises a liquid medium having doped solid ZrO ₂ particles dispersed therein, comprising at least tetragonal and monoclinic modifications, wherein the ZrO ₂ particles have an average agglomerate size in the range of 20 nm to 300 nm and a ratio of peak intensities between the tetragonal and the monoclinic modification of 1.3 to 20.

A slip is a special form of suspension in which ceramic particles are dispersed as a solid phase in a liquid phase. As the dispersing medium (liquid medium), for example, water can be used.

The peak intensities are determined as follows: The phase composition is determined by means of X-ray powder diffractometry, for example with the diffractometer Bruker-AXS (Siemens) D5000. The basis for this is that each crystallographic phase has a unique pattern of the diffraction pattern (X-ray diffractograms); unique in terms of the position of the reflections, determined by the grating metric and with respect to the intensity distribution, which is essentially determined by the cell content of the crystal structure. The X-ray diffractogram shows typical maxima, so-called peaks. Their amplitudes, the peak intensities are given in counts per second (cps). The diffraction diagrams can be used with the ICDD / PDF2 ( International center for diffraction data, database set 1-45, 1995 version 2.16 ) Database are assigned to the crystallographic phases.

The ratio of the peak intensities is defined as the intensity value of a main peak of the tetragonal phase at a 2θ value of 30.2 ° (theta, Bragg angle) and the intensity value of the main peak of the monoclinic phase at a 2θ value of 28.2 ° (theta , Braggwinkel) formed as follows:
Peak tetragonal ZrO ₂ (2θ value = 28.2 °): peak monoclinic ZrO ₂ (2θ value = 28.2 °) = V

The main peak of the tetragonal ZrO ₂ phase (2θ value = 30.2 °) and the cubic (2θ value = 30.3 °) are close together. If both modifications are present, the intensities add up accordingly. By definition, the following applies: The intensity of the main peak at 2θ value = 30.2 ° is completely assigned to the terms peak and peak intensity for the tetragonal phase.

The main peak of the tetragonal phase at 2θ value = 30.2 ° applies hereinafter to the terms "peak intensity for the tetragonal phase" and the main peak of the monoclinic phase at 2θ value = 28.2 ° for the term "peak intensity for the monoclinic Phase". The peak levels as well as the theoretical peak intensities can be determined by the ICDD / PDF2 ( International Center for Diffraction Data, Database Set 1-45, 1995 Version 2.16 ). The reference was used here for the tetragonal phase "17-923" (ZrO ₂ zirconium oxide) and "37-1484" (Baddeleyite, syn)

The agglomerate size of the slurry indicates the size of the particle aggregates in the slurry. Agglomerates are composed of primary particles. The agglomerate sizes given below are to be understood as average agglomerate sizes d ₅₀ , unless explicitly stated otherwise. By the dispersing process, the agglomerates should be largely resolved. If this succeeds predominantly, the agglomerate size in the slurry approaches the primary particle size of the starting powder.

Surprisingly, it has been found that for further processing into densely sintered ceramic bodies with particularly high strengths, slip is particularly suitable if, on the one hand, they have an average agglomerate size in the range of 20 nm to 300 nm and, on the other hand, a ratio of peak intensities of 1.3 to 20 , The term "densely sintered" here is to be understood as meaning a relative sintering density of greater than 95%.

In a preferred embodiment, the average agglomerate size is 50 nm to 200 nm and the ratio of the peak intensities is from 1.4 to 15. As a result, sintered ceramic bodies with a relative density of more than 98% based on the theoretical density can be produced.

The theoretical density is the pure density (also called skeletal density, absolute or true density). This density can obtain a ceramic body with complete freedom from pores. For ZrO ₂ with 3 mol% Y ₂ O ₃ , a theoretical density of 6.08 g / cm ^{3 is} assumed here. Sintered density is the density that a ceramic molding achieves after sintering and indicates the ratio of mass to the total volume of the molding. Open and closed pores can be included. The relative sintered density indicates the ratio between sintered density and theoretical (maximum achievable) density and is expressed as a percentage. In the case that the sintering density corresponds to the theoretical density, a relative sintering density of 100% results.

In a further preferred embodiment, the average agglomerate size is 120 nm to 200 nm and the ratio of the peak intensities is from 1.5 to 10. As a result, densely sintered ceramic bodies having a relative density of more than 99% based on the theoretical density can be produced.

The ZrO ₂ particles in the slurry have a defined phase composition. Preferably, the ZrO ₂ particles in the slurry a phase mixture of greater than 0.5 wt .-% but less than 70 wt .-%, preferably less than 60 wt .-%, more preferably less than 50 wt .-% monoclinic ZrO ₂ modification and a tetragonal portion in the range of 5 wt .-% to 70 wt .-%, preferably in the range 10 wt .-% to 60 wt .-% and particularly preferably in the range 15 wt .-% to 40 wt .-% based on the solids content. In addition to the monoclinic and the tetragonal phase, the cubic ZrO ₂ modification and optionally other phases, such as an amorphous phase may be present. The ZrO ₂ particles in the slurry can be doped with 0.5 mol% to 5 mol% of Y ₂ O ₃ .

The slip may additionally contain Al ₂ O ₃ , in particular with a content in the range from 0.5% by weight to 50% by weight, preferably in the range from 5% by weight to 30% by weight, particularly preferably in the range 10 wt .-% to 25 wt .-%. The resulting ceramic bodies, known as ATZ ceramics (ATZ stands for "alumina toughened zirconia"), have particularly high strengths and are lighter than pure ZrO ₂ ceramics.

In a further embodiment, the slip additionally contains Al ₂ O ₃ , in particular with a proportion in the range from 50% by weight to 99% by weight, preferably in the range from 60% by weight to 90% by weight, particularly preferably in the range 65 wt .-% to 85 wt .-%. Ceramic bodies produced therefrom, known as ZTA ceramics (ZTA stands for "zirconia toughened alumina"), have a significantly higher toughness compared to pure aluminum oxide and are lighter than pure ZrO ₂ or ATZ ceramics.

The Al ₂ O ₃ particles may be added to the slurry before, during or after dispersion. Alternatively, a suitable aluminum-containing raw material component can also be added to the raw material mixture for the production of the powders or the powder production process. In this case, a powder mixture is formed with ZrO ₂ particles and Al ₂ O ₃ particles

The slips with Al ₂ O ₃ -containing particles also have, after dispersion, the agglomerate size according to the invention in the range from 20 nm to 300 nm, preferably in the range from 50 nm to 200 nm, particularly preferably in the range from 120 nm to 200 nm, wherein the same parameters, in particular those relating to the crystal structure and phase composition, apply to the sum of all ZrO ₂ particles in these slips as for pure ZrO ₂ slickeners.

In one embodiment, the peak intensity of the tetragonal phase of the ZrO ₂ particles in the slurry is set to 200 cps to 2000 cps, preferably to 250 cps to 1000 cps and more preferably to 300 cps to 800 cps, the agglomerate size ranging from 20 nm to 300 nm, preferably in the range of 50 nm to 200 nm, particularly preferably in the range of 120 nm to 200 nm. The slips thus adjusted are particularly suitable for further processing into ceramic moldings, in particular the phase transformations taking place during the sintering (for example conversion / recrystallization to the tetragonal phase) do not lead to significant cracking. Accordingly, ceramics with particularly high strengths are obtained.

In a preferred embodiment, the slip has a concentration of more than 40% by weight, preferably in the range between 50% by weight to 80% by weight, particularly preferably in the range between 60% by weight to 75% by weight. ZrO ₂ particles on. These slip are particularly suitable for further processing such as slip casting or similar processes.

At least one hydrogen-containing compound may be attached to the surface of the ZrO ₂ particles in the slurry or granules, the hydrogen content (H) of the hydrogen-containing compounds being from 0.06% by weight to 1.1% by weight, based on the ZrO ₂ . Particle is.

The ZrO ₂ particles may preferably be doped with from 0.5 mol% to 5 mol% of Y ₂ O ₃ , the proportion of the monoclinic modification of the ZrO _{2 being} less than 70% by weight and the proportion of the tetragonal phase being greater than May be 5 wt .-%.

A granule according to the invention comprises doped, solid ZrO ₂ particles comprising at least tetragonal and monoclinic modifications, the ZrO ₂ particles having a ratio of tetragonal and monoclinic peak intensities of 1.3 to 20.

The ZrO ₂ particles of the granules may be doped with 0.5 mol% to 5 mol% of Y ₂ O ₃ . The proportion of the monoclinic modification of the ZrO ₂ in the granules may be less than 70% by weight and the proportion of the tetragonal phase may be greater than 5% by weight.

The granules may have a moisture content of 0.1 wt .-% to 3 wt .-% and in addition compounds of hydrogen and oxygen without carbon with a content of 0.5 wt .-% to 10 wt .-% and a proportion of Carbon, bound in carbonaceous compounds, of less than 2%.

Granules that can be used for compression molding to form bodies are distinguished in the context of the present description of agglomerates, as compared to powder and non-dispersed Schlickeragglomeraten fundamental differences in the structure arise. In powder agglomerates or unbroken slip agglomerates, there is a bond between the ZrO ₂ particles. However, if the particles are dispersed in the slurry, the particles are largely coated with a dispersing additive. Subsequent reagglomeration (eg in the granules) does not result in any binding between ZrO ₂ particles, but between the particles is the dispersant component. It was found that this results in a significantly changed sintering behavior, whereby the sintering behavior is strongly influenced by the agglomerate size of the ZrO ₂ in the slurry. It is true that with a smaller agglomerate size, the sintering activity increases.

If the agglomerate size in the slurry decreases, a tendency for a higher sintering density is to be expected for ceramic shaped bodies produced therefrom. This results from the fact that in larger agglomerates usually more pores are included, which must be removed or closed in the sintering process. This type of pores within the agglomerates of the specific size and design can often be incompletely expelled or closed. If these agglomerates no longer exist or are significantly smaller, these pores need no longer be expelled or closed during the sintering process and higher sintering densities and thus higher strengths are achieved.

Surprisingly, it was found that the sintering densities obtained initially increase with decreasing agglomerate size (otherwise identical slips, identical procedure for the production of the ceramic). When falling below a defined agglomerate size in the slip, however, this dependence is reversed, that is, with then further decreasing agglomerate size lower sintering densities are achieved.

This surprising finding is based on the fact that in order to achieve lower agglomerate sizes, a higher energy input must be made in the slurry. With increasing energy input, however, the crystal structure is increasingly damaged or undergoes a transformation (phase transformation). The investigation of the phase composition by means of X-ray phase analysis shows that with progressive Dispersing or grinding time decreases the peak intensity of the tetragonal ZrO ₂ modification. The monoclinic phase increases.

The moldable granules can be made from the slips. It has surprisingly been found that the hydrogen-containing compounds bound to the particle surface during the dispersion have a particularly favorable effect on the pressing behavior of granules produced therefrom. Thus, for example, the amount of otherwise necessary pressing and lubricants can be reduced.

A pre-sintered shaped article according to the invention can be formed from the slip according to one of claims 1 to 4 and / or from the granulate according to one of claims 5 to 7, wherein the ZrO ₂ particles have a ratio of the peak intensities of the tetragonal and monoclinic phases of 1, 3 to 20 have.

A ceramic according to the invention is formed from the slurry according to any one of claims 1 to 4 and / or from the granules according to any one of claims 5 to 7, wherein the ceramic structure has a mean grain size in the range of less than 500 nm and a sintering density of greater than 90%. having.

In a method according to the invention for producing the slip, at least ZrO ₂ powder comprising at least tetragonal modifications is ground and / or dispersed in at least one liquid dispersing medium, wherein an energy input during the dispersion and / or grinding is controlled and / or regulated such that the resulting solid ZrO ₂ particles in the slurry after dispersion and / or milling have an average agglomerate size in the range between 20 nm and 300 nm and an intensity ratio between the tetragonal and the monoclinic ZrO ₂ modification of 1.3 to 20.

Milling is understood to mean comminution of particles or separation of hard agglomerates by mechanical energy. In both cases, chemical binding forces are broken up. Aggregates are corresponding structures made of chemically combined (intergrown) particles. Agglomerates, on the other hand, are formed by particles, whereby the bonding force here is purely physical, for example due to surface energy. Typically, mixtures of agglomerates and aggregates occur, so that the term agglomerates also includes a small proportion of aggregated structures. Dispersion is understood to mean the fine distribution of solid particles in a liquid phase, but no particle comminution must take place, and only particle agglomerations can be dissolved.

A significant advantage when using finely divided particles or agglomerates resulting from the grinding or dispersion for the production of ceramics is that their sintering activity is significantly increased and thereby the necessary maximum sintering temperature can be selected lower. Due to a lower sintering temperature, the grain growth during sintering is lower, the sintered structure accordingly has a finer grain structure, which causes a higher strength.

The controlled and / or controlled input of energy during grinding or dispersing causes only limited damage to or transformation of the tetragonal phase crystal lattice, unlike conventional methods in which the tetragonal phase crystal lattice is damaged to such an extent in the X-ray phase analysis Lattice disruption (amorphization) or almost complete phase transformation is no longer detectable. In the method according to the invention only a limited conversion and / or damage of the tetragonal phase by the energy input, for example, a limited conversion into the monoclinic phase, so that it prevents that in subsequent sintering to undesirable cracking in the ceramic structure. This slip is suitable for the further processing and production of ceramics with particularly high strengths.

The energy input can be influenced for example by the rotational speed of a grinder and / or the grinding or dispersion time.

In addition, a dispersant, preferably in the range of 0.1 to 3.0 wt .-% (active substance of the dispersant based on the ZrO ₂ content) may be added to the slurry. In this concentration range, a particularly good dispersion and a sufficiently good stabilization of the slurry are achieved.

These slips can be prepared in such a way that the liquid medium is initially introduced, optionally the dispersant supplied, the components are well mixed and then the ZrO ₂ powder is fed, with a good mixing by, for example, stirrers, Disolver, Ultratorax or Ultrasound is advantageous. Alternatively, the slurry preparation may also be carried out directly in the apparatus in which the dispersion and / or grinding takes place, for example in a bead mill. For this purpose, for example, water and the dispersant are initially introduced and gradually fed to the ZrO ₂ powder. Other sequences are also possible.

The slips produced in this way initially have an agglomerate size above 300 nm, usually well above 500 nm. In order to reduce the agglomerate size below 300 nm, it is usually necessary to introduce a high energy, for example mechanical shear, into the slurry. This can be done for example by mills, for example by bead mills. The energy input, in particular when using bead mills, the lattice structure and / or the modification can be influenced. Amorphization, lattice mismatches and / or modification changes (for example tetragonal ZrO ₂ in monoclinic ZrO ₂ ) can arise. According to the invention, the energy input is controlled such that a defined order of the crystal structure results or a defined proportion of tetragonal ZrO ₂ is retained.

The energy input in the dispersion is controlled in particular so that the conversion of the crystalline tetragonal ZrO ₂ phase and the proportion of the monoclinic ZrO ₂ phase does not exceed a defined level. The measure used here is the ratio between the peak intensity of the reflections of the monoclinic and crystalline ZrO ₂ phases in the diffraction diagram of X-ray diffractometric powder diffractometry.

In one embodiment of the process, the ZrO ₂ powders are predispersed or pre-ground in dry processes. Under predispersion or premilling is to be understood that the agglomerates are at least partially broken or destroyed. Dry process means that no dispersion or grinding takes place in a liquid dispersion medium, but liquid components can be added separately to the ZrO ₂ or separately in the process, but which at least partially serve to coat the particles and thus promote the dispersion process or stabilize the dissolved / broken agglomerates. Such dry processes can be carried out, for example, in jet mills, fluid bed jet mills, spiral mills, centrifugal mills, impact mills or the like. For example, the dry methods may be based on the principle of particle fracture by collision in a pressurized medium and at high speeds. An example of this is the RINA-JET turbo air jet mill by Riera Nadeu.

From the thus predispersed or premilled ZrO ₂ powder, slips are produced according to the invention. Surprisingly, it was found that by the combination of dry predispersion or pre-grinding followed by dispersion into a liquid medium slip result, in which the lattice structure of the ZrO ₂ particles with the same agglomerate size changed or damaged less compared to wet grinding, that is These slips have a higher proportion of the tetragonal modification of ZrO ₂ .

When dispersing the ZrO ₂ particles, hydrogen-containing groups and / or compounds (hydrogen-containing compounds consisting of hydrogen and oxygen without carbon), such as, for example, hydroxyl groups or hydroxide compounds, can accumulate on their surfaces. The concentration of the hydrogen-containing groups and / or compounds increases with the length and intensity of the dispersion. Therefore, the proportion of hydrogen-containing groups and / or compounds is a measure of the intensity of the dispersion. The proportion of these phases can be determined by drying the slips or the granules prepared therefrom at 50 ° C. to constant weight (thus separating the physically bound adhesive water (moisture)) and then determining the weight loss at 200 ° C. Alternatively, the proportion of these phases can be determined by determining the H ^- fraction (for example by means of a carbon-hydrogen analyzer), which is liberated in the range between 50 ° C. and 200 ° C., on the slurry dried at 50 ° C. Typically, this value is converted to H ₂ O ⁺ (water of crystallization) and reported. Thus, a uniform spelling is taken into account, even if no deduction can be made to the present bond. The ZrO ₂ particles may have a hydrogen content bound in the hydrogen-containing phases and attached to the ZrO ₂ particles of from 0.06 wt.% To 1.1 wt.% (Corresponding to about 0.5 wt 10 wt .-% H ₂ O ^- ), preferably from 0.11 wt .-% to 0.89 wt .-% (corresponds to about 1 wt .-% to 8 wt .-% H ₂ O ^- ), especially preferably from 0.33 wt .-% to 0.67 wt .-% (corresponding to about 3 wt .-% to 6 wt .-% H ₂ O ⁺ ) have.

The slip can be further components, in particular pressing, sliding and sintering aids are added. The addition of these additives can take place before, during or after the dispersion.

For the production of the ZrO ₂ powder materials used for the production of the slurry, fundamentally different thermal processes may be suitable, such as, for example, flame or spray pyrolysis, production in plasma or pulsation reactors, but also wet-chemical processes such as precipitation reactions or sol-gel processes are suitable. Such powders are produced, for example, by a production process in the pulsating hot gas stream, as disclosed in the published patent applications DE 10 2006 046 803 A1 . DE 10 2007 003 744 A1 or DE 10 2008 006 607 A1 is known received.

Alternatively, such ZrO ₂ powders can also be obtained by optionally drying a suitable raw material mixture and thermally treating this raw material mixture in the range of 500 ° C to 1300 ° C.

Likewise, zirconium-containing raw material components such as salts can be converted into a solution, to this zirconium-containing raw material solution, the doping elements are added, so that the doping elements are present dissolved. Preference is given to raw material solutions, since the elements in the solution form an almost ideal solution, that is, they are almost ideally homogeneously mixed. This raw material solution can be introduced in a hot gas stream at a hot gas temperature at the feed location of 50 ° C. to 500 ° C., preferably in the range from 80 ° C. to 150 ° C., the solid particles forming from the raw material solution. This can be done for example by spray drying. The powder and / or granules thus produced are then thermally treated at 500 ° C to 1300 ° C, preferably at 700 ° C to 1200 ° C, more preferably at 900 ° C to 1100 ° C, since in this temperature range experience shows a particularly good Relationship between low aggregation and sufficient crystallinity prevails. As a result, these powders can be dispersed in the slurry with a comparatively low energy input up to the agglomerate size according to the invention.

Alternatively, to prepare the ZrO ₂ powder, the prepared raw material solution containing doping elements may be directly exposed to a pulsating or non-pulsating hot gas stream having a hot gas temperature at the feed location of 800 ° C to 1300 ° C, preferably in the range of 900 ° C to 1200 ° C preferably be supplied in the range 1000 ° C to 1200 ° C.

Particularly suitable are those ZrO ₂ powder from which slips with a low agglomerate size can be produced even at low energy input. Such powders have a structure with a low primary particle size and the lowest possible aggregation. Aggregation is understood here to mean the aggregation of primary particles, with strong binding forces, in particular chemical bonds, being present due to sintering phenomena between the particles.

The powders used have a carbon content of less than 0.2% by weight, preferably less than 0.1% by weight, more preferably less than 0.05% by weight. According to experience, low carbon contents lead to better compaction properties during sintering and thus to higher densities. In addition, elemental carbon often can not be completely removed during sintering, which is accompanied by an undesirable discoloration of the ceramic.

In a preferred embodiment, the specific surface area (according to BET) of the powders is in the range from 3 m ² / g to 15 m ² / g, preferably in the range from 4 m ² / g to 10m ² / g, particularly preferably 5 m ² / g up to 8 m ² / g. Powders with higher specific surface areas are more difficult to handle and often cause difficulties in dispersing. Lower specific surface areas are an indicator of larger primary particle diameters and / or hard aggregation. In these powders, the agglomerate sizes according to the invention can be achieved in the slurry only with high energy input.

The ZrO ₂ powders used are doped. By doping the ZrO ₂ certain modifications such as the tetragonal or cubic phase of ZrO _{2 are to be} fully or partially stabilized. This is predominantly necessary in the field of ceramic production, since a phase change, in particular between monoclinic and tetragonal or cubic, is associated with volume changes, which can lead to cracks. Stabilizer additives in the form of other metal oxides, such as, for example, calcium oxide, magnesium oxide, yttrium oxide or cerium oxide, are added to the ZrO ₂ , individually or in combinations. Depending on the proportion of stabilizer additives, for example, the tetragonal high-temperature phase of the zirconium dioxide can be fully or partially stabilized up to room temperature. The type of stabilizer determines which modification is stabilized or partially stabilized by the ZrO ₂ . In a preferred variant, the powders used are yttrium-stabilized ZrO ₂ , the doping concentration being in the range from 0.5 mol% to 5 mol%, preferably in the range from 2 mol% to 3.5 mol% lies. By doping with yttrium in this concentration range, particularly high flexural tensile strengths and densities are achieved. Particularly high critical fracture toughness K _IC is achieved at a concentration of 2 mol% to 3 mol%, especially at 2.5 mol% to 2 mol% yttrium.

The ZrO ₂ powders used may contain further constituents which typically result from the clays of the raw materials, for example hafnium, for example, is often associated in an oxidic form with ZrO ₂ . By definition, hafnium is not considered to be a doping agent in the following since it is present as a paragenesis in the raw material and is not deliberately added. The proportion of these components, which is registered by the Zr raw material, depends on the type of Zr raw material. In addition, traces of contamination may occur, on the one hand due to the raw materials, on the other hand due to the thermal production process of the powder materials. The sum of the acceptable impurities depends on the use and the desired properties of the ceramic. Typically, impurities less than 1%, preferably less than 0.5%, more preferably less than 0.1% and most preferably less than 0.05%, based on the powder material, are acceptable.

Frequently, ZrO ₂ raw materials are used for the production process, which are highly chlorine- and / or sulfur-containing, for example in the form of salts. Through the manufacturing process, these raw materials are largely converted, but usually not completely. Correspondingly, fractions of Cl and / or S or their compounds remain in ZrO ₂ . For the production of ceramics, S and Cl are considered to be particularly disturbing, since in particular the strength properties are strongly negatively influenced. In addition, Cl can be incorporated into the lattice structure of the ZrO ₂ , which in addition to undesirable changes in the properties of the ZrO2 also be associated in addition a change in color, which is also undesirable.

The ZrO ₂ powders used have a particularly low proportion of Cl (chlorine) and S (sulfur) or on their compounds. The proportion of chlorine (Cl) is less than 1000 ppm, preferably less than 500 ppm, more preferably less than 200 ppm and the sulfur concentration (expressed as S) is less than 800 ppm, preferably less than 200 ppm, more preferably less than 100 ppm.

In a preferred embodiment, the ZrO ₂ powder is present, for example by doping with yttrium, at least proportionally in the tetragonal modification, preferably with a proportion of greater than 50% by weight, particularly preferably with a proportion greater than 75% by weight. In addition, the monoclinic modification of ZrO ₂ may also be present, preferably in the range of less than 30% by weight, more preferably in the range of less than 15% by weight. In addition, other phases are possible, in particular cubic ZrO ₂ or X-ray amorphous phases, which can therefore be identified in the X-ray phase analysis only as amorphous.

By dispersing or grinding, the tetragonal phase is at least partially damaged and / or converted. If the ZrO ₂ powder has such a high proportion, ultimately a higher proportion of tetragonal phase results after dispersion or milling, which leads to better ceramic properties. With such a high proportion of tetragonal ZrO ₂ modification, it can be ensured that the ratio according to the invention between tetragonal and monoclinic phase is present after dispersion or milling.

Forming processes serve the purpose of reshaping a ceramic heap by external forces such that both the desired geometric shape and a permanent cohesion with optimum homogeneous compression is achieved. In principle, three ceramic molding processes can be distinguished: casting, plastic molding and pressing, wherein in principle all of the ZrO ₂ particles can be used to produce moldings which form a ceramic structure during a sintering process.

The design for high-performance ceramics can generally be divided into wet and dry processes. Here, the conventional slip casting, the pressure slip casting and the injection molding have established as wet molding. Axial and isostatic pressing as a molding process are used predominantly for the manufacture of simple geometry ceramic components. These pressing methods are often used commercially because of their automation.

In one embodiment, the slips are first converted into moldable granules, for example by means of spray granulation, which are particularly suitable for axial and isostatic pressing as a molding process. Spray granulation is the drying of liquids (solutions, suspensions, melts) with the simultaneous construction of granules. Germs for the granules can be submitted (foreign nuclei) or formed by abrasion and breakage (intrinsic germs). The sprayed liquid coats the seeds and is dried. By varying the type and concentration of additives added, As dispersants, binders, pressing aids and lubricants, as well as by targeted adjustment of the process parameters in the granulation process, such as process temperature, residence time or drop size, can be specifically influenced on the strength, shape and granule size distribution. Preference is given to granules consisting of full granules with an ideal spherical shape (eg, for better flowability) and an average granule size of the granules in the range of 5 .mu.m to 500 .mu.m, preferably 10 .mu.m to 200 .mu.m, more preferably 20 .mu.m to 150 .mu.m.

The shaping is then carried out by pressing, whereby the axial and the isostatic pressing (CIP = cold isostatic pressing) differs. The latter, in turn, can be subdivided into wet and dry die technology. In addition, the pressing process can also be combined with a temperature cycle. In this case we speak of hot or hot isostatic pressing (HP or HIP).

Like the slips, these granules are also particularly suitable for further processing into densely sintered ceramic bodies having particularly high strengths if they have a ratio of the tetragonal and monoclinic phase peak intensities of from 1.3 to 20, preferably from 1.4 to 15, particularly preferably from 1.5 to 10.

The granules represent a phase mixture of at least monoclinic and tetragonal ZrO ₂ , wherein according to the invention at least 0.5 wt .-% but less than 70 wt .-%, preferably less than 60 wt .-%, more preferably less than 50 wt. % monoclinic ZrO ₂ modification is present and the tetragonal portion in the range of 5 wt .-% to 70 wt .-%, preferably in the range 10 wt .-% to 60 wt%, and particularly preferably in the range 15 wt. % to 40 wt .-% based on the solids content. In addition to the monoclinic and the tetragonal phase, the cubic ZrO ₂ modification and optionally other phases, such as an amorphous phase may be present.

The granules may contain pressing agents, lubricants or other auxiliaries (eg binders). Such additives are used, for example, to adjust the strength of the granules so that they promote the formation of a compact, particularly homogeneous microstructure during pressing. The organic part of these additives (carbon-containing compounds, the additives may be purely organic compounds), is removed again in the binder removal and / or the sintering process. These components initially leave behind pores, which must then be closed by sintering. The same applies to physically bound water, for example, adhesive water or also referred to as moisture, and the hydrogen-containing compounds on the ZrO ₂ particle surface, which are deposited by the dispersing and grinding process. These components are thus also part of the green compact and are separated in the debinding and sintering process, removed and leave first pores. If the proportion of organic components, water (moisture) or hydrogen-containing compounds is very large, in particular the sum value, the many pores can not be completely closed. In addition, cracks can increasingly form due to the then greater shrinkage. Both are associated with the loss of strength. The granules therefore preferably have a moisture content (= weight loss on drying at 50 ° C. to constant weight) of from 0.1% by weight to 3% by weight, preferably from 0.3% by weight to 1% by weight. and a proportion of hydrogen-containing components (determined on samples dried at 50 ° C, the weight loss is determined at 200 ° C), ie compounds of hydrogen and oxygen without carbon in the range of 0.5 wt .-% to 10 wt. -% H ₂ O ⁺ , preferably from 1 wt .-% to 8 wt .-% H ₂ O ⁺ , more preferably 3 wt .-% to 6 wt .-% H ₂ O ⁺ on. The loss on ignition (= weight loss on annealing at 1000 ° C. for 2 hours of samples dried at 50 ° C.) is in the range from 0.2% by weight to 20% by weight, preferably in the range from 1% by weight to 10 Wt .-%, particularly preferably in the range 5 wt .-% to 10 wt .-% and forms the sum of organic components and hydrogen-containing compounds (H ₂ O ⁺ ). The granules may have a carbon content bound in the carbonaceous compounds in the range of less than 2% by weight, preferably less than 1.5% by weight, more preferably less than 1% by weight.

The granules produced in this way can be used to produce pressed moldings which are suitable for a subsequent sintering process.

Alternatively, the slurry may be further processed through other molding processes such as slip casting, die casting, ceramic injection molding, hot casting, gel casting, or freeze casting + Quickset ^™ . Both hot-casting and injection molding processes are suitable for the production of small, complicated-shaped components, with injection molding being more suitable for series production. Very high surface qualities can be achieved with sintered hot-cast or injection-molded parts, so that reworking by means of grinding or polishing is often unnecessary. A particularly advantageous method is the so-called DCC method (direct coagulation casting). This method is based on the Destabilization of high-solids suspensions by in situ enzyme-catalyzed reactions. This allows the pH of the suspension to be shifted from its stable, low-viscosity region to its isoelectric point, whereupon the suspension coagulates and solidifies. Thus, highly flowable suspensions can be poured into molds and demolded as wet, solid green bodies. Alternatively, the shaping can also take place via plastic shaping, for example by means of extrusion.

The moldings may already correspond to the desired shape of the ceramic, taking into account the shrinkage occurring during sintering. Alternatively, the shaped bodies can also be reworked. In a preferred variant, the moldings are pre-sintered at temperatures between 600 ° C. to 1300 ° C., preferably between 800 ° C. and 1200 ° C., so that the moldings achieve a higher strength and / or debind the moldings, ie the organic constituents are at least partially burned out become. These moldings thus obtained are referred to as "presintered moldings". Subsequently, the shape of the presintered molded body can be processed and / or sintered. These presintered moldings are particularly suitable for further processing into densely sintered ceramic bodies having particularly high strengths if they have a ratio of the tetragonal and monoclinic phase peak intensities of 1.3 to 20, preferably 1.4 to 15, particularly preferably 1, 5 to 10 have.

The ZrO ₂ particles after dispersion, in the present case in the form of a slip, bound in the granules or bonded as presintered shaped bodies, have a particularly high sintering activity. The sintering activity is measured in a dilatometer on defined test specimens, the linear thermal expansion of a test specimen being determined as a function of the temperature. The thermal expansion is a measure of how the entropy of a body reacts to changes in volume. For this purpose, first test specimens are produced. The preparation of the test specimens with dimensions of 25 mm by 9 mm by 5 mm takes place here by definition by uniaxial compression of the granules at 100 MPa and subsequent isostatic recompression at 330 MPa. The debindering (= dissolving out of the organic additives that were required for dispersion or shaping of the workpiece) takes place at a heating rate of 1 K / min to 1000 ° C. The dilatometric examination of the moldings is then carried out to 1500 ° C at a heating rate of 5 K / min. The ZrO ₂ particles or the molded articles produced therefrom had a sintering beginning (thermodynamic fixed point at which the shrinkage of the test specimen starts due to incipient sintering, the detection is carried out by dilatometric examination) of less than 1100 ° C., preferably less than 1000 ° C to, more preferably less than 900 ° C on. The temperature for the sintering end (shrinkage of the test specimen is completed, the ceramic bodies are largely densely sintered) is less than 1500 ° C, preferably less than 1450 ° C, more preferably less than 1400 ° C.

An unbridled crystal growth in the sintering process can be prevented or reduced by additives such as MgO, CaO, TiO ₂ in the concentration range of 0.05% to 1%, which result in a uniform, densely sintered ceramic body with small grain size. Furthermore, 0.05% by weight to 1.5% by weight of Al ₂ O ₃ may be provided in order, for example, to reduce the hydrothermal aging. This can significantly slow down the aging process. It is also possible to add sintering aids. These additives may be added to the slurry before, during or after dispersion / milling. Alternatively, such additives may already be present in the ZrO ₂ powders and / or added.

The slip and / or granules according to the invention are suitable for the production of high-performance ceramics, ie ceramics with, for example, particularly high strengths. For this example, the granules are pressed into shaped bodies (so-called green body or green compacts), for example by uniaxial and / or isostatic pressing method, then optionally debinded and then sintered.

If the sintering takes place in the presence of sufficient oxygen in the sintering atmosphere, for example by air-sintering atmosphere, the ceramics have white or slightly creamy color (white ZrO ₂ ceramic).

In a process for the production of black ceramics, slip and / or granules are transferred into shaped bodies, subjected to binder removal, and these shaped bodies are sintered under a reducing atmosphere to produce a ceramic structure with an average particle size of less than 500 nm. The ceramic produced in this way comprises stabilized and / or partially stabilized ZrO ₂ , prepared from slip and / or granules, wherein a black coloring of the ceramic is effected by the sintering atmosphere used in the process and no additional black-coloring components are contained, wherein the ceramic has a mean grain size of less than 500 nm.

In a preferred embodiment, the green bodies are debinded under an oxidizing atmosphere and then the sintering takes place under a non-oxidizing atmosphere, preferably under a reducing atmosphere, more preferably under an H ₂ atmosphere. The black ZrO ₂ ceramics are obtained. By properly polishing this black ceramic, a surface can be created that is highly lustrous and very similar to a dark steel surface. Compared to conventionally black-colored ZrO ₂ ceramics there is the advantage here that no coloring components (eg pigments) must be incorporated into the ceramic, but can be decided solely on the composition of the sintering atmosphere, whether a white or black ZrO ₂ ceramic should be formed. Black ceramics produced in this way contain, in addition to the stabilized or partially stabilized ZrO _2, no further components, in particular no colorants. Exceptions here are only the above-listed possible impurities and / or components that are registered by the mineral paragenes through the raw materials and / or Al ₂ O ₃ . However, these components also do not produce blackening. Black ceramics are particularly interesting for aesthetic applications, for example for designer applications such as parts of watches or watch cases.

After sintering (white or black ZrO ₂ ceramic), a ceramic structure is obtained which has a sintering density of greater than 90%, preferably greater than 95%, more preferably greater than 98% and most preferably greater than 99% in relation to the theoretical density. The ceramic structure has an average particle size of less than 500 nm, preferably less than 300 nm, particularly preferably less than 250 nm. The particle size distribution is narrow so that the d ₉₉ value is less than three times the d ₅₀ value (mean particle size). This ZrO ₂ structure has a high strength. The bending tensile strength after DIN EN 843-1 is more than 700 MPa, preferably more than 900 MPa, and more preferably more than 1020 MPa.

The ceramic thus obtained can be further densified by subsequent process steps, for example by hot isostatic pressing (HIP), preferably sintering densities of 99%, particularly preferably more than 99.5% and particularly preferably more than 99.8% of the theoretical density of Materials are achieved. Higher densities and thus a lower percentage of pores are known to result in higher strengths.

The slip, granules, presintered moldings and / or the ceramics can be used to produce or coat a) medical implants, in particular in dental or joint prosthetics or b) technical machine components, in particular bearing parts, engine or turbine parts, sealing parts, nozzle parts or Probe parts are used.

Particularly suitable is the use of the ceramics according to the invention in medicine, in particular as bioceramics, for example for the production or coating of implants for bone or joint prosthetics or in the dental field (dental prosthetics). Other typical applications of these ceramics are in the technical field for the production or coating of various components that are exposed to particularly high mechanical and / or thermal loads, such as extrusion dies, wear-resistant machine parts (dies, seals, gaskets bearing parts), sliding and counter rings for Mechanical seals, engine parts, such as rocker arms, cylinder liners, piston crowns. The ceramic can also be used for coatings of other materials, for example for turbine coating or lining. Also suitable is the ceramic in the range of functional components, such as oxygen probes (lambda probe).

Embodiments of the invention are explained in more detail below with reference to drawings.

Show:

1 superimposed diffractograms of a ZrO ₂ material before a grinding process and at various stages of the milling process, and

2 superimposed diffractograms of a ZrO ₂ material before a grinding operation, during the grinding process and after sintering.

Corresponding parts are provided in all figures with the same reference numerals.

The following measurement conditions and preparation conditions for determining the peak intensity apply to all the following information: Recorder: Bruker-AXS diffractometer (Siemens) D5000 with Cu tube (CuKα λ = 1.5418 Å), the X-ray tube is operated with a voltage of 40 kV and a current of 20 mA (generator parameter), Aperture and divergence diaphragm V20, recording conditions Increment = 0.04 ° 2θ and count time = 2 sec. Sample preparation: The sample to be examined is carefully ground by hand in an agate mortar. Evaluation: - Evaluation software Diffrac-AT (V3.2). - First, the ground is subtracted (Standrade setting and then the curve is smoothed (factor 0.300) - This is the height of the peak (= [cps] = peak intensity) determined.

1 shows superimposed diffractograms of a ZrO ₂ material prior to a dispersing or milling operation and at various stages of the milling process.

A phase composition of the ZrO ₂ material is determined by means of X-ray powder diffractometry, for example with the diffractometer Bruker-AXS (Siemens) D5000. The basis for this is that each crystallographic phase has a unique pattern of the diffraction pattern (X-ray diffractograms); unique in terms of the position of the reflections, determined by the grating metric and with respect to the intensity distribution, which is essentially determined by the cell content of the crystal structure. The X-ray diffractogram shows typical maxima, so-called peaks. Their amplitudes, the peak intensities I are given in counts per second (cps) and mapped in the diffractogram over a Bragg angle 2θ.

A peak intensity I _{tetra_A} , I _{tetra_B} , I _{tetra_C} , I _{tetra_D} at a Bragg angle 2θ _tetra of 30.2 ° is assigned to a tetragonal modification of ZrO ₂ . A peak intensity I _{mono_A} , I _{mono_B} , I _{mono_C} , I _{mono_D} , at a Bragg angle 2θ _mono of 28.2 ° is assigned to a monoclinic modification of ZrO ₂ .

The peak intensities I _{tetra_A} and I _{mono_A} for intensities of ZrO ₂ particles are in front of a dispersion.

The peak intensities I _{tetra_B} and I _{mono_B} represent the intensities of the ZrO ₂ particles after two hours of milling in a bead mill.

The peak intensities I _{tetra_C} and I _{mono_C} represent the intensities of the ZrO ₂ particles after six hours of milling in the bead mill.

The peak intensities I _{tetra_D} and I _{mono_D} represent the intensities of the ZrO ₂ particles after ten hours of milling in the bead mill.

With increasing energy input through the grinding, the crystal structure is increasingly damaged or undergoes a transformation (phase transformation). The ZrO ₂ particles were intensively dispersed or ground in a bead mill (Netzsch Labstar, 0.2 mm grinding ball size, 2000 rpm, 0.7 kW power input). The investigation of the phase composition by means of X-ray phase analysis shows that as the dispersing or grinding time progresses, the peak intensity of the tetragonal ZrO ₂ modification decreases. The monoclinic phase increases.

By a subsequent thermal treatment, for example in the sintering, a recrystallization or reconversion takes place in the tetragonal modification. 2 shows by way of example that the ZrO ₂ particles before dispersing / grinding have a high intensity of the tetragonal phase, by the dispersing / grinding the tetragonal phase is reduced, wherein after sintering the tetragonal modification with comparable intensity as before the dispersion / grinding is present.

A peak intensity I _{tetra_A} , I _{tetra_C} , I _{tetra_E} at a Bragg angle 2θ _tetra of 30.2 ° is assigned to a tetragonal modification of ZrO ₂ . A peak intensity I _{mono_A} , I _{mono_C} , I _{mono_E} , at a Bragg angle 2θ _mono of 28.2 ° is assigned to a monoclinic modification of ZrO ₂ .

The peak intensities I _{tetra_A} and I _{mono_A represent} intensities of the ZrO ₂ particles before the dispersion.

The peak intensities I _{tetra_C} and I _{mono_C} represent the intensities of the ZrO ₂ particles after six hours of milling in the bead mill.

The peak intensities I _{tetra_E} and I _{mono_E} represent the intensities of the ZrO ₂ particles in the sintered ceramic.

Example 1)

First, a solution of 48.2 kg of sixty percent acetic acid and 48.2 kg of Zr carbonate is prepared with heating. For this purpose, 3.4 kg of Y acetate (YC ₆ H ₉ O ₆ × 4H ₂ O) are dissolved and 0.11 kg of Al ₂ O _{3 are} added. This raw material mixture thus formed is at a throughput of 40 kg / h using a peristaltic pump in a pulsating hot gas flow of a pulsation reactor (known from DE 10 2006 046 803 A1 ) At the beginning of a resonance tube with respect to the hot gas stream directly behind the combustion chamber via a 1.8 mm titanium nozzle finely dusted and thermally abandoned. The temperature at the job site is 850 ° C.

Before entering the separation device, the hot gas stream containing the particles formed is cooled to approximately 160 ° C. by supplying cooling air. As a separator for separating the finely divided particles from the hot gas stream, a bag filter is used. The resulting ZrO ₂ powder is then thermally treated in a rotary kiln at 900 ° C thermally. The powder material produced in this way has yttrium-doped ZrO ₂ particles. The doping of the ZrO ₂ particles is 3 mol% based on the ZrO ₂ - share. With the X-ray phase analysis, in addition to traces (at the detection limit, <2% by weight) of monoclinic ZrO ₂ as a crystalline phase, the tetragonal ZrO ₂ modification and smaller amounts of cubic ZrO _{2 could} be determined. The peak intensity for the tetragonal phase (diffraction reflection at 2θ value = 30.2 °) was 2321 cps. The specific surface area is 6 m ² / g. The carbon content (C _ges ) is 0.06 wt .-%. The determined chlorine content is 187 ppm, the S content is 85 ppm. In the quantitative phase analysis by means of Rietveld refinement (Software AutoQuant from GE-Seifert), 84.5% by weight of tetragonal ZrO ₂ , 0.1% by weight of monoclinic ZrO ₂ and 13.5% by weight of cubic ZrO were used ₂ and 1.9% further phases.

From the produced ZrO ₂ powder material is an aqueous slurry having the composition 40 wt .-% ZrO ₂ powder material, 58.5 wt .-% water, 1.5 wt .-% dispersing and liquefying agent (Dolapix CE 64, Zschimmer & Schwarz GmbH & Co.KG). The dispersion / grinding of this slip takes place in a bead mill (LMZ ZETA RS System, NETZSCH-Feinmahltechnik GmbH). As grinding balls ZrO ₂ grinding balls were used with the size 0.2-0.3 mm and a degree of filling of 85% and set a rotor speed of 1000 U / min and a flow rate through the grinding chamber of 380 kg / h.

After dispersion / milling, the slurry has a mean agglomerate size of 169 nm. The X-ray phase analysis is used to determine monoclinic, tetragonal and cubic ZrO ₂ on the dried slurry (dried at 100 ° C.). The main peak of the tetragonal phase (2θ value = 30.2 °) is 525 cps, the main peak of the monoclinic phase (2θ value = 28.2 °) is 186 cps. Accordingly, there is an intensity ratio between tetragonal and monoclinic phase of 2.82. In the quantitative phase analysis by means of Rietveld refinement, 21.7% by weight of tetragonal ZrO ₂ , 49.3% by weight of monoclinic ZrO ₂ and 25.6% by weight of cubic ZrO ₂ and also 3.4% further phases were determined. The ZrO ₂ particles have a hydrogen content, bound in the hydrogen-containing phases and attached to the ZrO ₂ particles of 0.1 wt .-% (corresponding to about 0.91 wt .-% H ₂ O ⁺ ) on.

1.5% by weight of polyethylene glycol (PEG 4000) as lubricant and 0.5% by weight of Optapix PAF II (Zschimmer & Schwarz GmbH & Co. KG) are added to this slurry, the concentration being based in each case on the ZrO ₂ - Particle is. This slip is converted to granules in a spray granulation at 105 ° C. The resulting granules have a nearly spherical shape, hollow sphere structure and shell formation is not significantly detectable, the average granule size is 50 microns. The phase composition of the inorganic components corresponds to that of the dried-up slurry above. The ZrO ₂ granules produced in this way are suitable for the production of ceramic bodies.

By dilatometric investigation on separately produced from this granules compacts (25 mm × 7 mm × 5 mm), a sintering end of 1425 ° C was determined.

The granules produced in this way have a particularly good pressing behavior. From the granules are square green compacts (size about 2.7 cm × 1.2 cm × 0.6 cm) by uniaxial compression at 100 MPa and subsequent isostatic recompression at 330 MPa. The green compacts have a density of 52.34%. No significant cracks were visually detected on the green compacts.

Debinding of these green compacts takes place at a heating rate of 1 K / min to 1000 ° C. For the subsequent sintering, a heating rate of 5 K / min and a maximum sintering temperature of 1450 ° C. were selected. A crack-free ceramic having a sintered density of 99.25% and an open porosity of less than 0.1% was obtained. On the ceramic structure, an average particle size of 240 nm was determined by means of a line-cutting method. The bending tensile strength after DIN EN 843-1 amounted to this ceramic 1125 MPa. With the X-ray phase analysis, an intensity of the main peak of the tetragonal phase (2θ value = 30.2 °) of 525 cps, the main peak of the monoclinic phase (2θ value = 28.2 °) 205 cps is determined on the ceramic.

Example 2)

Ceramics are produced as in Example 1. Here, however, the resulting ceramics are densified by hot isostatic pressing (HIP) at a heating rate of 2 K / min to 1450 ° C and a holding time of one hour there. On the cooled ceramics, a sealant value of 99.81% of the theoretical density and a bending tensile strength become after DIN EN 843-1 of 1278 MPa.

Examples 3)

Analogously to Example 1, a raw material mixture is produced. This raw material mixture in the form of a raw material suspension thus formed is introduced at a throughput of 20 kg / h by means of a peristaltic pump in a non - pulsating hot gas stream of a Sprühgranulierers over a 1.8 mm titanium die and thermally treated, the temperature at the job site is 105 ° C. , The powder thus obtained is then thermally treated in a rotary kiln at 900 ° C. This forms ZrO ₂ particles. The powder material produced in this way has yttrium-doped ZrO ₂ particles. The doping of the ZrO ₂ particles is 3 mol% based on the ZrO ₂ - share. With the X-ray phase analysis, in addition to traces (at the detection limit, <2% by weight) of monoclinic ZrO ₂ as the crystalline phase, only the tetragonal ZrO ₂ modification could be determined. The peak intensity for the tetragonal phase (diffraction reflection at 2θ value = 30.1 °) was 3089 cps. The specific surface area is 5 m ² / g. The carbon content (C _ges ) is 0.09 wt.%. The determined chlorine content is 175 ppm, the S content is 97 ppm. In quantitative phase analysis by Rietveld refinement (Software AutoQuant from GE-Seifert), 86.7% by weight of tetragonal ZrO ₂ , 0.5% by weight of monoclinic ZrO ₂ and 12.1% by weight of cubic ZrO were used ₂ and 0.7% further phases determined.

The slip production and dispersion / grinding of this slurry is carried out analogously to Example 1. After dispersing / grinding, the slurry has an average agglomerate size of 165 nm. The X-ray phase analysis is used to determine monoclinic, tetragonal and cubic ZrO ₂ on the dried slurry (dried at 100 ° C.). The main peak of the tetragonal phase (2θ value = 30.2 °) is 367 cps, the main peak of the monoclinic phase (2θ value = 28.2 °) is 189 cps. Accordingly, there is an intensity ratio between tetragonal and monoclinic phase of 1.94. In the quantitative phase analysis by means of Rietveld refinement, 11.1% by weight of tetragonal ZrO ₂ , 55.2% by weight of monoclinic ZrO ₂ and 32.5% by weight of cubic ZrO ₂ and 1.2% further phases were determined.

The granulation of this slurry is carried out analogously to Example 1. The resulting granules have a nearly spherical shape, hollow sphere structure and shell formation is not significantly detectable, the average granule size is 57 microns. The ZrO ₂ granules produced in this way are suitable for the production of ceramic bodies.

This granulate has a particularly good pressing behavior. From the granules were squared green compacts (size about 2.7 cm × 1.2 cm × 0.6 cm) by uniaxial compression at 100 MPa and subsequent isostatic recompression at 330 MPa. The green compacts have a density of 51.87%. No cracks were detected on the green compacts.

2θ

Braggwinkel

2θ mono

Braggwinkel der monoklinen Modifikation

2θ tetra

Braggwinkel der tetragonalen Modifikation

I

Peakintensität

Imono_A, Imono_B, Imono_C, Imono_D

Peakintensität der monoklinen Modifikation

Itetra_A, Itetra_B, Itetra_C, Itetra_D

Peakintensität der tetragonalen Modifikation

Debinding and sintering were carried out as in Example 1. A crack-free ceramic having a sintered density of 99.09% and an open porosity of less than 0.1% was obtained. On the ceramic structure was determined by means of an intersection method an average particle size of 245 nm. The bending tensile strength was after DIN EN 843-1 amounted to this ceramic 1029 MPa.

2θ

Bragg angle

2θ mono

Bragg angle of the monoclinic modification

2θ tetra

Bragg angle of the tetragonal modification

I

peak intensity

Imono_A, Imono_B, Imono_C, Imono_D

Peak intensity of the monoclinic modification

Itetra_A, Itetra_B, Itetra_C, Itetra_D

Peak intensity of the tetragonal modification

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102006046803 A1 [0061, 0113]
• DE 102007003744 A1 [0061]
• DE 102008006607 A1 [0061]

Cited non-patent literature

• International center for diffraction data, database set 1-45, 1995 version 2.16 [0020]
• International Center for Diffraction Data, Database Set 1-45, 1995 Version 2.16 [0023]
• DIN-EN-843-1 [0090]
• DIN-EN-843-1 [0120]
• DIN-EN-843-1 [0121]
• DIN-EN-843-1 [0126]

Claims (13)

A slurry comprising a liquid medium having doped solid ZrO ₂ particles dispersed therein comprising at least tetragonal and monoclinic modifications, said ZrO ₂ particles having an average agglomerate size in the range of 20 nm to 300 nm and a ratio of peak intensities (I) between have the tetragonal and the monoclinic modification of 1.3 to 20. A slurry according to claim 1, further comprising Al ₂ O ₃ particles. A slip according to any one of claims 1 or 2, characterized in that at least one hydrogen-containing compound is attached to the surface of the ZrO ₂ particles, wherein the hydrogen content of the hydrogen-containing compounds from 0.06 wt .-% to 1.1 wt .-% based to the ZrO ₂ particles. A slip according to one of the preceding claims, wherein the ZrO ₂ particles are doped with from 0.5 mol% to 5 mol% Y ₂ O ₃ and / or the proportion of the monoclinic modification of the ZrO _{2 is} less than 70 wt% and the proportion of the tetragonal phase is greater than 5% by weight. Granules comprising doped solid ZrO ₂ particles comprising at least tetragonal and monoclinic modifications, wherein the ZrO ₂ particles have a ratio of the peak intensities (I) of the tetragonal and the monoclinic phase of from 1.3 to 20. Granules according to claim 5, characterized in that the ZrO ₂ particles are doped with 0.5 mol% to 5 mol% Y ₂ O ₃ and / or the proportion of the monoclinic modification of the ZrO _{2 is} less than 70 wt% and the proportion of the tetragonal phase is greater than 5% by weight. Granules according to one of claims 5 or 6, having a moisture content of 0.1 wt .-% to 3 wt .-%, in addition compounds of hydrogen and oxygen without carbon with a content of 0.5 wt .-% to 10 wt. % and a carbon content bound in carbonaceous compounds of less than 2%. Ceramic, formed from the slurry according to any one of claims 1 to 4 and / or from the granules according to one of claims 5 to 7, characterized in that the ceramic structure has a mean grain size in the range of less than 500 nm and a sintering density of greater than 90% , A process for preparing a slurry according to any one of claims 1 to 4, wherein at least ZrO ₂ powder comprising at least tetragonal modifications, ground and / or dispersed in at least one liquid dispersing medium, wherein an energy input during the dispersion and / or grinding so controlled and or that the resulting solid ZrO ₂ particles in the slurry after dispersion and / or milling have an average agglomerate size in the range between 20 nm and 300 nm and an intensity ratio between the tetragonal and the monoclinic ZrO ₂ modification of 1.3 to 20 have. Process for the preparation of black ceramics, characterized in that slip according to one of claims 1 to 4 and / or granules according to one of claims 5 to 7 are transferred into shaped bodies and debinded and these shaped bodies are sintered under reducing atmosphere, wherein a ceramic structure with a average grain size of less than 500 nm is generated. A ceramic comprising stabilized and / or partially stabilized ZrO ₂ prepared from a slip according to any one of claims 1 to 4 and / or granules according to any one of claims 5 to 7 by the method of claim 10, wherein a black coloring of the ceramic by the in the used sintering atmosphere is effected and no additional black coloring components are contained, wherein the ceramic has an average grain size of less than 500 nm. Use of the slip according to any one of claims 1 to 4 and / or the granules according to any one of claims 5 to 7 and / or the ceramic according to any one of claims 8 or 11 for the production or coating of a) medical implants, in particular in dental or joint prosthetics or of b) technical machine components, in particular of bearing parts, engine or turbine parts, sealing parts, nozzle parts or probe parts. A pre-sintered shaped body formed from the slurry according to any one of claims 1 to 4 and / or from the granulate according to any one of claims 5 to 7, wherein the ZrO _{2 is} at least in the monoclinic and tetragonal phase with a ratio of the tetragonal and monoclinic phase peak intensities from 1.3 to 20.

Images