Ceramic or glass-ceramic article and methods for producing such article

Abstract

The present invention relates to a method of producing a (shaped) ceramic or glass-ceramic article, involving the steps of: (a) providing a powder or a powder mixture comprising ceramic or glass-ceramic material, (b) depositing a layer of said powder or powder mixture on a surface, (d) heating at least one region of said layer by means of an energy beam or a plurality of energy beams to a maximum temperature such that at least a part of said ceramic or glass-ceramic material in said at least one region is melted and (e) cooling said at least one region of said layer so that at least part of the material melted in step (d) is solidified, such that the layer is joined with said surface in said at least one region. The invention also relates to ceramic or glass-ceramic articles and their use.

Claims

1. Method of producing a ceramic or glass-ceramic article from a powder or powder mixture, comprising the steps of: (a) providing the powder or powder mixture comprising ceramic or glass-ceramic material, (b) depositing a layer of said powder or powder mixture on a surface, (d) heating at least one region of said layer by means of an energy beam or a plurality of energy beams to a maximum temperature such that at least a part of said ceramic or glass-ceramic material in said at least one region is melted, (e) cooling said at least one region of said layer so that at least part of the material melted in step (d) is solidified, such that the layer is joined with said surface in said at least one region, wherein the method includes a preheating step (c) wherein in the step (c) one or more of the at least one regions are, preheated, wherein the method comprises successive repetition of the steps (a), (b), (c), (d), and (e) to produce the ceramic or glass-ceramic article, wherein a successive surface of the layer produced by a preceding series of the steps (a), (b), (c), (d), and (e) is used in a respective subsequent step (b) as a surface for the following layer, wherein said powder or powder mixture comprises components that form an eutectic system with each other during solidification in the step (e), wherein, for each repetition, the step (a) starts before the step (b), the step (b) starts before the step (c), the step (c) starts before the step (d), and the step (d) starts before the step (e), and wherein at least 50 percent by weight of said powder or powder mixture is the eutectic system, wherein each of the components is selected from the group consisting of Al.sub.2O.sub.3, ZrO.sub.2, Y.sub.2O.sub.3, Na.sub.2O, Nb.sub.2O.sub.5, La.sub.2O.sub.3, CaO, SrO, CeO.sub.2, MgO, TiO.sub.2, Cr.sub.2O.sub.3, CuO, mixed oxides thereof, SiC, TiC, Si.sub.3N.sub.4 and AlN.

2. Method according to claim 1, wherein the step (c) further comprises preheating of the at least one region of said layer to a preheating temperature such that no part of said powder or powder mixture in said at least one region is melted.

3. Method according to claim 1, wherein the step (c) is conducted continuously, when the steps (a), (b), (c), (d), and (e) are repeated in sequence, the step (c) begins before the step (d) is conducted for the first time and ends after the step (d) is conducted for the last time.

4. Method according to claim 2, wherein in the step (c) the energy for preheating in the step (c) is directed to the surface of said layer.

5. Method according to claim 2, wherein in the step (c) said at least one region is preheated by laser irradiation, electron irradiation or microwave irradiation, preferably laser irradiation.

6. Method according to claim 2, wherein said ceramic or glass-ceramic material comprises a crystalline part, and wherein said preheating temperature of the step (c) is in the range of from 40% to 99% of the minimum temperature in Kelvin (K) at which the crystalline part of said ceramic or glass-ceramic material in said at least one region is melted, wherein the preheating temperature is in the range of from 900 C. to 2000 C.

7. Method according to claim 1, wherein for each component of said eutectic system, the fraction by weight of the each component of said eutectic system, is at least 25% by weight of said eutectic system.

8. Method according to claim 1, wherein at least 70 percent by weight of said powder or powder mixture is the eutectic system, wherein each of the components is selected from the group consisting of Al.sub.2O.sub.3, ZrO.sub.2, Y.sub.2O.sub.3, Na.sub.2O, Nb.sub.2O.sub.5, La.sub.2O.sub.3, CaO, SrO, CeO.sub.2, MgO, SiO.sub.2, TiO.sub.2, Cr.sub.2O.sub.3, CuO, Eu.sub.2O.sub.3, Er.sub.2O.sub.3, CoO, Gd.sub.2O.sub.3, the mixed oxides thereof, SiC, TiC, Si.sub.3N.sub.4 and AlN.

9. Method according to claim 1, wherein said powder or powder mixture comprises ZrO.sub.2 and Al.sub.2O.sub.3, and wherein the mixing ratio by weight of ZrO.sub.2 to Al.sub.2O.sub.3 is in the range of from 30:70 to 42.6:57.4.

10. Method according to claim 1, wherein said powder or powder mixture comprises ZrO.sub.2 and at least one component selected from the group consisting of MgO, Y.sub.2O.sub.3, CaO and CeO.sub.2.

11. Method of producing a composition comprising a ceramic or glass-ceramic article according to claim 1, wherein the maximum temperature is higher than the preheating temperature.

12. Method according to claim 1, wherein an intermediate product obtained following the final repetition of steps (a), (b), (c), (d), and (e) is subjected to a glass-infiltration at a temperature in the range of from 650 C. to 1200 C.

13. The method of claim 1, wherein during solidification in the step (e) from the molten ceramic or glass-ceramic material, two or more phases of distinct materials crystallize.

14. The method of claim 1, wherein for each component of the eutectic system, the fraction by weight of each of the components is at least 25% of the fraction by weight of said eutectic system.

15. The method of claim 1, wherein each of said layers has a thickness in the range of from 5 to 200 m.

16. The method of claim 1, wherein the components consist of Al.sub.2O.sub.3, ZrO.sub.2, and at least one of the components is selected from the group consisting of Y.sub.2O.sub.3, CeO.sub.2, MgO, wherein at least 50 percent by weight of said powder or powder mixture is Al.sub.2O.sub.3 and ZrO.sub.2, and wherein a weight ratio of ZrO.sub.2 to Al.sub.2O.sub.3 is in the range of from 3:7 to 7:3.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be described hereinafter in greater detail with reference to the following examples and the appended figures, in which:

(2) FIG. 1 is a schematic drawing of an apparatus according to the present invention for producing a ceramic or glass-ceramic article;

(3) FIG. 2 is a picture taken with a light-optical microscope of the surface the last layer of the ceramic article prepared in example 1 (see below);

DETAILED DESCRIPTION

(4) FIG. 1 shows an apparatus according to the present invention for producing a ceramic or glass-ceramic article. The apparatus is adapted for a method according to the present invention wherein steps (a), (b), (c), (d) and (e) are conducted. FIG. 1 shows a table top (15) with a circular opening (16). Underneath the opening (16) is a cylindrical support means (13) of the same size as opening (16) connected to a lever (18) to lower and raise support means (13). The surface of the support means (13) is lined with insulating material (14a). The ceramic or glass ceramic article (12) is mounted on a substrate (19) and the substrate is mounted on top of the insulating material (14a). The ceramic or glass ceramic article (12) is surrounded by a powder or a powder mixture (20). The powder or powder mixture (20), the ceramic or glass ceramic article (12), the substrate (19), the insulating material (14a) and the support means (13) are surrounded by a cylindrical arrangement of further insulating material (14b), such that the combined parts of insulating material (14a, 14b) form a chamber comprising the ceramic or glass ceramic article (12), the powder or powder mixture (20), the substrate (19) and the support means (13).

(5) The table top has a further opening (21) with a powder reservoir (11). Underneath powder reservoir (11) is a further support means (13) and a further lever (22).

(6) Above the table top is a deposition and leveling device (10) in form of a brush. The lower end of the brush consists of fibers that end close to or at the surface of the table top.

(7) Above the table top is further shown a laser beam (3) of a CO.sub.2-laser. The CO.sub.2-laser itself is not shown. Laser beam (3) has a Gauss distribution. Laser beam (3) enters into a beam homogenization optic (2), which homogenizes the Gauss distribution of laser beam (3). A defocused and homogenized laser beam (1) leaves beam homogenization optic (2) and is directed onto the opening in the table top containing the ceramic or glass ceramic article (12). It is incident on the surface of the ceramic or glass ceramic article (12) and on all areas of the opening and their surrounding areas where melting in step (d) will occur during the production of the ceramic or glass ceramic article (12).

(8) A further laser beam (8) of a Nd:YAG-laser is shown above the table top. The Nd:YAG-laser itself is not shown. Laser beam (8) is guided through an optical fiber (7) into a galvanometer scanner (6). The laser beam leaving the galvanometer scanner (6) is focused by focusing optic (5) yielding focused laser beam (4) which is incident on the surface of the ceramic or glass ceramic article (12).

(9) A pyrometer (9) is mounted above the table top and directed onto the surface of the ceramic or glass ceramic article (12) to measure its temperate.

(10) Laser beam (3), laser beam (8), galvanometer scanner (6), focusing optics (5) and pyrometer (9) are connected to a control device (not shown) which controls the procedure.

(11) At the beginning of each cycle, support means (13) is lowered by means of its lever (18) by the distance identical to the desired thickness of the layer to be deposited in step (b). In step (a) a powder or a powder mixture comprising ceramic or glass-ceramic material is provided by lifting the lever (22) of powder reservoir (11).

(12) In step (b) said powder or a powder mixture is deposited on the surface of the part of the article already produced (12) and the surrounding powder or powder mixture (20) that has not been melted in the previous cycles by means of deposition and leveling device (10). The deposition and leveling device (10) then brushes off the powder or powder mixture above the powder reservoir (11) that extends above the table top and deposits it on top of the ceramic or glass ceramic article (12) and the powder or a powder mixture (20) surrounding it. Parts of the powder or powder mixture extending above the table top are brushed off by deposition and leveling device (10). The powder of powder mixture is thereby deposited evenly.

(13) Preheating (step (c)) is applied continuously during the whole process of producing said ceramic or glass-ceramic article (12) by laser beam (1). Laser beam (1) provides the same amount of energy per time and area on the whole surface of said layer deposited in step (b).

(14) In step (d) laser beam (4) is guided onto said surface in a predetermined exposure pattern. Laser beam (4) is switched on when galvanometer scanner (6) directs its focus onto a region that is to be heated in step (d), and is switched off otherwise. The pyrometer (9) measures the surface temperature of the region of the surface heated by laser beam (4). The data is read out by said control device.

(15) After the focused laser beam (4) has finished heating a certain region, the region is cooled by heat transfer from the heated region to the atmosphere, neighboring regions of said layer deposited in step (b) and the previously produced layers and to other parts of chamber formed by insulating material (14a, 14b). This cooling constitutes step (e). Laser beam (1) which serves as preheating device, continuously heats the heated regions thereby reducing the cooling rate of the heated region. Insulating material (14a, 14b) reduces the cooling rate of the whole reaction chamber and thereby also reduces the cooling rate of the heated region(s). Crystallization of the melted regions is however still fast and no waiting period has to be observed before the next cycle begins. The next cycle begins therefore as soon as step (d) of the previous cycle has ended.

(16) FIG. 2 shows the surface of the last layer of the ceramic article prepared in example 1 (see below). Apart from an irregular general roughness of the surface, the surface bears traces of the tracks melted by the laser, as indicated by the white lines running from left to the right of the picture. It is thereby evident, that the layer shown in FIG. 1 consists of -a set of adjacent, joined tracks of ceramic material.

EXAMPLES

Example 1

(17) A powder Zaspher 260M (available from Innalox bv, 5932 NB Tegelen, The Netherlands) consisting of spherical powder particles of a diameter d.sub.50 of 35 m prepared by condensation from the gas phase is used. The powder consists of 39.5% by weight ZrO.sub.2, 1% by weight Y.sub.2O.sub.3 and 59.5% by weight Al.sub.2O.sub.3. In the selective laser melting apparatus according to FIG. 1 a layer of the powder with a thickness of approx. 100 m is deposited on a ceramic substrate of the dimensions 18 18 3 mm.sup.3 produced by conventional sintering of the same powder. The powder layer and the substrate are preheated to a temperature of 1700 C. at a rate of 2 K/s by a CO.sub.2-laser beam (1). The preheating to 1700 C. is done only once in the beginning of the build up process and then the preheating temperature is maintained approximately constant at 1700 C. during the whole build up process. The laser beam is incident on the substrate and an area surrounding the substrate and the intensity is homogeneous within the area irradiated. After a homogeneous temperature of 1700 C. is reached on the surface of the powder layer. The selected regions of the powder layer are selectively melted by means of a focused Nd:YAG-laser beam (4) with a circular focus with a diameter of 200 m on the surface of the powder layer. To melt the powder or powder mixture in the desired regions, the focus of the laser beam (4) is moved in straight adjacent lines over the area of the substrate at a speed of 100 mm/s whereby each two adjacent lines overlap by 140 m. The laser power is set to 60 W. The laser is switched on when it is moved over a region that is to be heated. It is switched off otherwise. After all the selected regions have been melted, the support means (13) is lowered by 50 m, a new layer of powder is deposited and the next cycle begins. The steps powder deposition, selective melting and lowering of the platform are repeated until the whole article has been built up. The CO.sub.2 laser beam (1) irradiates the ceramic article during the whole build up process, i.e. the temperature of the substrate and the emerging ceramic object is kept at approximately 1700 C. during the whole build up process. After completion of the build up process, the ceramic object and the substrate, still have a temperature of 1700 C. They are cooled to room temperature at a cooling rate of 0.2 K/s. The article prepared is separated from the substrate by sawing with a diamond wire saw. The ceramic article produced has the shape of a disc with a diameter of 14 mm and thickness of 2 mm. It is crack free and does not require any post processing. The bending strength was measured by the ball on three points method according to the norm DIN EN 843-1. This produced article has a bending strength of 536 MPa.

(18) See also FIG. 2

Example 2

Powder Composition 80% ZrO2, 20% Al2O3

(19) 2.1 Preparation of Article (with Glass Infiltration, without Preheating)

(20) A powder consisting of 80% by weight of zirconia and 20% by weight of alumina powder with a powder particle size between 25 m and 45 m and a d.sub.50 value of 35 m is prepared by mixing two powders prepared separately by crushing, grinding and sieving a solidified alumina melt and a solidified zirconia melt, respectively. In a selective laser melting apparatus a layer of the powder with a thickness of approx. 100 m is deposited on an aluminium substrate. Subsequently a focussed CO.sub.2 laser beam is used to selectively melt regions of the powder layer. The beam diameter is 300 m on the surface of the powder layer. To melt the powder or powder mixture in the desired regions, the focus of the laser beam (4) is moved in straight adjacent lines over area of the substrate whereby each two adjacent lines overlap by 190 m at a speed of 100 mm/s. The laser power is set to 120 W. The laser is switched on when it moves over a region that is to be heated. It is switched off otherwise. After all the selected regions have been melted, a new layer of powder of a thickness of 50 m is deposited and the next cycle begins. These steps are repeated until the whole article has been built up. The article prepared is separated from the substrate by sawing with a diamond wire saw. The ceramic article produced contains a large number of microcracks. In order to improve the bending strength and other physical properties, a glass infiltration procedure is performed subsequently. For this purpose a glass is formed out of the following oxides:

(21) TABLE-US-00001 Component wt % SiO.sub.2 21 B.sub.2O.sub.3 24 Al.sub.2O.sub.3 35 Li.sub.2O 15 CaO 5 Total 100

(22) For glass infiltration powder of the glass produced is placed in a crucible and the object is placed on top of the glass powder. The crucible is then heated in a furnace to a temperature of 950 C. for 1 hour. The article is subsequently cooled to ambient temperature. The article produced has the dimensions 5 mm6 mm45 mm. The bending strength was measured by the ball on three points method according to the norm DIN EN 843-1. The produced article has a bending strength of 48 MPa.

(23) 2.2 Preparation of Article (without Glass Infiltration, with Preheating)

(24) The experimental conditions are as described in Example 2.1.

(25) However, an additional preheating step according to step (c) of the present invention is conducted and no glass infiltration step is carried out.

(26) The initial powder layer and the substrate are preheated to a temperature of 1700 C. at a rate of 2 K/s by a CO.sub.2-laser beam. The preheating to 1700 C. is done only once in the beginning of the build up process and then the preheating temperature is maintained approximately constant at 1700 C. during the whole build up process.

(27) The bending strength of the produced article was above 200 MPa.

Example 3

Powder Composition 80% ZrO2, 20% Al2O3

(28) 3.1 Preparation of Article (with Glass Infiltration, without Preheating), Examination of Precipitation Behaviour

(29) The experimental conditions are as described in Example 2.1 The precipitation behaviour in a region is examined in more detail, after the laser has been switched off:

(30) It is observed that ZrO.sub.2 crystals precipitate first from the melt, as soon as the temperature falls below 2200 C. This way the ZrO.sub.2 content in the melt is continuously reduced during further cooling down to a temperature of 1860 C. At that temperature, the remaining melt has exactly the eutectic composition (41.5 wt. % ZrO.sub.2/58.5 wt. % Al.sub.2O.sub.3). This melt represents 30.4 wt. % of the total mass of the deposited powder. When this eutectic melt finally solidifies, a fine grained two phase microstructure with grain sizes smaller than 1 m is formed. The larger ZrO.sub.2 crystals solidified earlier are embedded in this fine grained matrix.

(31) 3.2 Preparation of Article (without Glass Infiltration, with Preheating), Examination of Precipitation Behaviour

(32) The experimental conditions are as described in Example 2.2.

(33) The observations are similar to those of Example 3.1. However, the ZrO.sub.2 crystals solidifying initially are larger than those of Example 3.1.

Example 4

Powder Composition 41.5% ZrO2, 58.5% Al2O3

(34) 4.1 Preparation of Article (with Glass Infiltration, without Preheating), Examination of Precipitation Behaviour

(35) The experimental conditions are similar to those described in Example 2.1. However, an initial powder consisting of 41.5% by weight of zirconia and 58.5% by weight of alumina powder with a powder particle size between 25 m and 45 m and a d.sub.50 value of 35 m is used.

(36) The precipitation behaviour in a region is examined in more detail, after the laser has been switched off, analogous to the examination according to example 3.1.

(37) It is observed that essentially the complete solidified material consists at least essentially of eutectic fine grained material.

(38) 4.2 Preparation of Article (without Glass Infiltration, with Preheating), Examination of Precipitation Behaviour

(39) The experimental conditions are similar to those described in Example 2.2. However, an initial powder consisting of 41.5% by weight of zirconia and 58.5% by weight of alumina powder with a powder particle size between 25 m and 45 m and a d.sub.50 value of 35 m is used.

(40) The precipitation behaviour in a region is examined in more detail, after the laser has been switched off, analogous to the examination according to example 3.2.

(41) It is observed that essentially the complete solidified material consists at least essentially of eutectic fine grained material.

(42) 4.3 Comparison of Bending Strengths

(43) The respective bending strength of the articles produced according to Examples 4.1 and 4.2, respectively, were compared.

(44) It was observed that the bending strength of the article produced according to Example 4.2 was higher than the bending strength of the article produced according to Example 4.1.

(45) 5. Comparison Example:

(46) The experimental conditions are similar to those described in Example 2. However, an initial powder consisting of 100% by weight of alumina powder with a powder particle size between 25 m and 45 m and a d.sub.50 value of 35 m is used.

(47) The precipitation behaviour in a region is examined in more detail, after the laser has been switched off, analogous to the examination according to example 3.

(48) It is observed that a rather coarse microstructure is formed (grain size >10 m), probably because grain growth is not limited by other phases.

(49) In the following embodiments are described which illustrate the present invention. The invention is not restricted to these embodiments. Throughout the present text, the features of preferred embodiments of the present invention (in particular preferred methods of the present invention) can be combined with features of other preferred embodiments, as long as said features do not contradict each other.

(50) 1. Method of producing a ceramic or glass-ceramic article comprising the steps of:

(51) (a) providing a powder or a powder mixture comprising ceramic or glass-ceramic material,

(52) (b) depositing a layer of said powder or powder mixture on a surface,

(53) (d) heating at least one region of said layer by means of an energy beam or a plurality of energy beams to a maximum temperature such that at least a part of said ceramic or glass-ceramic material in said at least one region is melted,

(54) (e) cooling said at least one region of said layer so that at least part of the material melted in step (d) is solidified, such that the layer is joined with said surface in said at least one region,

(55) wherein preferably during solidification in step (e) from the molten ceramic or glass-ceramic material two or more phases of distinct materials crystallize.

(56) 2. Method according to embodiment 1, wherein the method comprises the successive repetition of steps (a), (b), (d), and (e), wherein the surface of the layer produced by a preceding series of steps (a) to (e) is used in a respective subsequent step (b) as surface for the following layer.

(57) 3. Method according to any of embodiments 1 or 2, wherein the method comprises between step (b) and step (d) the following separate step:

(58) (c) preheating of at least one region of said layer to a preheating temperature such that no part of said ceramic or glass-ceramic material in said at least one region is melted.

(59) 4. Method according to any of embodiment 2 or 3, wherein step (c) is conducted continuously and wherein if steps (a) to (e) are not repeated, step (c) is beginning before step (d) and is ending after step (d) or alternatively, if steps (a) to (e) are repeated, step (c) is beginning before step (d) is conducted for the first time and is ending after step (d) is conducted for the last time.

(60) 5. Method according to embodiment 3 or 4, wherein in step (c) the energy for preheating in step (c) is directed to the surface of said layer.

(61) 6. Method according to any of embodiments 3 to 5, wherein in step (c) the layer is preheated by means of an energy beam or a plurality of energy beams.

(62) 7. Method according to embodiment 6, wherein in step (c) said energy beam or at least one of said plurality of energy beams is directed to said layer in a predetermined exposure pattern.

(63) 8. Method according to any of embodiments 6 or 7, wherein in step (c) said energy beam or at least one of said plurality of energy beams is repeatedly directed to said at least one region of said layer in step (c).

(64) 9. Method according to any of embodiments 3 to 7, wherein one, two, a plurality or all regions of said layer are preheated in step (c) and are also heated in step (d).

(65) 10. Method according to any of embodiments 3 to 9, wherein all regions of said layer heated in step (d) are preheated in step (c).

(66) 11. Method according to any of embodiments 3 to 10, wherein said at least one region is preheated in step (c) by at least one defocused energy beam.

(67) 12. Method according to any of embodiments 3 to 11, wherein in step (c) said at least one region is preheated by laser irradiation, electron irradiation or microwave irradiation, preferably laser irradiation.

(68) 13. Method according to any of embodiments 3 to 12, wherein said preheating temperature is in the range of from 900 C. to 2000 C., preferably in the range of from 1200 C. to 1800 C.

(69) 14. Method according to any of embodiments 3 to 13, wherein said preheating temperature is in the range of from 40% to 99%, preferably in the range of from 60% to 95% of the minimum temperature in Kelvin (K) at which a crystalline part of said ceramic or glass-ceramic material in said at least one region is melted, wherein the preheating temperature preferably is in the range of from 900 C. to 2000 C., more preferably in the range of from 1200 C. to 1800 C.

(70) 15. Method according to any of embodiments 3 to 14, preferably according to embodiment 13, wherein in step (c) said at least one region is preheated by one or more laser beams, preferably laser beams of a laser selected from the group consisting of CO.sub.2-laser, Nd: YAG-laser, fiber laser and diode laser.

(71) 16. Method according to any of embodiments 3 to 15, wherein in step (c) one, two, a plurality or all regions are preheated.

(72) 17. Method according to any of embodiments 6 to 16, wherein in step (c) said energy beam or said plurality of energy beams is directed to one, two, a plurality or all regions of said layer in a predetermined exposure pattern.

(73) 18. Method according to any of embodiments 3 to 15, wherein the preheating is applied continuously during the whole process of producing said ceramic or glass-ceramic article.

(74) 19. Method according to embodiment 18, wherein the whole procedure is performed in an apparatus comprising a chamber which comprises the powder or powder mixture to be used in step (b), the originally provided surface, and the ceramic or glass-ceramic article so far produced, and wherein the whole chamber and its content are preheated to the same temperature.

(75) 20. Method according to any of the preceding embodiments, wherein heating and, if appropriate preheating is conducted such that that the powder or powder mixture in some or all regions that are not heated in step (d) is not changed in chemical composition, particle size and/or flow characteristics.

(76) 21. Method according to any of the preceding embodiments, wherein said powder or powder mixture comprises components that form an eutectic system with each other,

(77) wherein preferably said powder or powder mixture comprises two, three or more ceramic components that form an eutectic system with each other,

(78) wherein preferably said powder or powder mixture comprises two, three or more ceramic components that form an eutectic system with each other, such that during solidification in step (e) from the molten ceramic or glass-ceramic material at the eutectic point of said eutectic system two or more phases of distinct materials crystallize,

(79) wherein preferably said powder or powder mixture comprises two, three or more ceramic components that form an eutectic system with each other, such that during solidification in step (e) from the molten ceramic or glass-ceramic material at the eutectic point of said eutectic system two or more phases of distinct materials crystallize, wherein the total fraction by weight of said two, three or more ceramic components that form said eutectic system with each other is at least 50%, preferably at least 70%, more preferably at least 80%, of the powder or powder mixture,

(80) wherein more preferably at least one, preferably all, of the ceramic components forming said eutectic system with another ceramic component are selected from the group consisting of Al.sub.2O.sub.3, ZrO.sub.2, Y.sub.2O.sub.3, Na.sub.2O, Nb.sub.2O.sub.5, La.sub.2O.sub.3, CaO, SrO, CeO.sub.2, MgO, SiO.sub.2, TiO.sub.2, Cr.sub.2O.sub.3, CuO, Eu.sub.2O.sub.3, Er.sub.2O.sub.3, CoO, Gd.sub.2O.sub.3, the mixed oxides thereof, especially MgAl.sub.2O.sub.4 Y.sub.3Al.sub.5O.sub.12, Er.sub.3Al.sub.5O.sub.12, NiAl.sub.2O.sub.4, LaAlO.sub.3 and La.sub.2ZrO.sub.7, SiC, TiC, Si.sub.3N.sub.4 and AlN.

(81) 22. Method according to any of the preceding embodiments, wherein at least 50 percent by weight, preferably at least 70 percent by weight of said powder or powder mixture consist of components that form an eutectic system with each other.

(82) 23. Method according to any of embodiments 21 or 22, wherein for each component of said eutectic system the fraction by weight of the component, based on the weight of the eutectic system in the powder or powder mixture, is at least 25%, preferably at least 50%, especially preferred at least 70% and most preferred at least 90% of the fraction by weight of the same component in the eutectic mixture of said eutectic system.

(83) 24. Method according to any of the preceding embodiments, wherein said powder or powder mixture comprises one or more compounds selected from the group consisting of Al.sub.2O.sub.3, ZrO.sub.2, Y.sub.2O.sub.3, Na.sub.2O, Nb.sub.2O.sub.5, La.sub.2O.sub.3, CaO, SrO, CeO.sub.2, MgO, SiO.sub.2, TiO.sub.2, Cr.sub.2O.sub.3, CuO, Eu.sub.2O.sub.3, Er.sub.2O.sub.3, CoO, Gd.sub.2O.sub.3, the mixed oxides thereof, SiC, TiC, Si.sub.3N.sub.4 and AlN.

(84) 25. Method according to any of the preceding embodiments, preferably according to any of embodiments to 21 to 24, wherein at least 50 percent by weight, preferably at least 70 percent, more preferably at least 80% by weight, by weight of said powder or powder mixture consist of one or more compounds selected from the group consisting of Al.sub.2O.sub.3, ZrO.sub.2, Y.sub.2O.sub.3, Na.sub.2O, Nb.sub.2O.sub.5, La.sub.2O.sub.3, CaO, SrO, CeO.sub.2, MgO, SiO.sub.2, TiO.sub.2, Cr.sub.2O.sub.3, CuO, Eu.sub.2O.sub.3, Er.sub.2O.sub.3, CoO, Gd.sub.2O.sub.3, the mixed oxides thereof (especially MgAl.sub.2O.sub.4, Y.sub.3Al.sub.5O.sub.12, Er.sub.3Al.sub.5O.sub.12, NiAl.sub.2O.sub.4 LaAlO.sub.3 and La.sub.2ZrO.sub.7) SiC, TiC, Si.sub.3N.sub.4 and AlN.

(85) 26. Method according to any of the preceding embodiments, wherein at least 50 percent by weight, preferably at least 70 percent by weight of said powder or powder mixture consist of one or more oxides selected from the group consisting of ZrO.sub.2, Al.sub.2O.sub.3, SiO.sub.2, MgO, Y.sub.2O.sub.3, Cr.sub.2O.sub.3, Na.sub.2O, TiO.sub.2, La.sub.2O.sub.3, and the mixed oxides thereof, especially MgAl.sub.2O.sub.4.

(86) 27. Method according to any of the preceding embodiments, preferably according to any of embodiments 21 to 23, wherein said powder or powder mixture comprises ZrO.sub.2 and Al.sub.2O.sub.3.

(87) 28. Method according to any of the preceding embodiments, preferably according to any of embodiments 21 to 23, wherein said powder or powder mixture comprises ZrO.sub.2 and Al.sub.2O.sub.3, and wherein the mixing ratio by weight of ZrO.sub.2 to Al.sub.2O.sub.3 is in the range of from 1:4 to 4:1, preferably in the range of from 3:7 to 7:3.

(88) 29. Method according to any of the preceding embodiments, preferably according to any of embodiments 21 to 23, wherein said powder or powder mixture comprises ZrO.sub.2 and Al.sub.2O.sub.3, and wherein the mixing ratio by weight of ZrO.sub.2 to Al.sub.2O.sub.3 is in the range of from 30:70 to 42.6:57.4, preferably of from 35:65 to 42.6:57.4 and especially preferred in the range of from 39:61 to 42.6:57.4

(89) 30. Method according to any of the preceding embodiments, preferably according to any of embodiments 21 to 23, wherein said powder or powder mixture comprises ZrO.sub.2 and Al.sub.2O.sub.3, and wherein the mixing ratio by weight of ZrO.sub.2 to Al.sub.2O.sub.3 is 42.6 to 57.4.

(90) 31. Method according to any of the preceding embodiments, wherein said powder or powder mixture consists of 42.6 percent by weight of ZrO.sub.2 and 57.4 percent by weight of Al.sub.2O.sub.3.

(91) 32. Method according to any of the preceding embodiments, wherein said powder or powder mixture comprises ZrO.sub.2 and Al.sub.2O.sub.3 and one or more compounds selected from the group consisting of MgO, SiO.sub.2, Spinell and Mullite.

(92) 33. Method according to any of the preceding embodiments, comprising the following separate step: Preheating of said powder or powder mixture before step (b) to a powder preheating temperature, such that no part of said ceramic or glass-ceramic material is melted.

(93) 34. Method according to embodiment 33, wherein said powder preheating temperature is in the range of from 800 to 2000 C., preferably in the range of from 900 to 1500.

(94) 35. Method according to embodiment 33, wherein said powder preheating temperature is in the range of from 30% to 90%, preferably of from 40% to 70% of the temperature in Kelvin where at least a part of said ceramic or glass-ceramic material in said at least one region is melted.

(95) 36. Method according to any of embodiments 33 to 35, wherein in step (b) said powder preheating temperature is lower than the temperature of any region of said surface in step (b).

(96) 37. Method according to any of embodiments 33 to 36, wherein said powder or powder mixture is preheated before step (b) by means of an energy radiation, preferably by means of microwave radiation or infrared radiation or a radiant heater.

(97) 38. Method according to any of the preceding embodiments, comprising the following step: Preheating of said surface before step (b) to a surface preheating temperature such that no part of the material of said surface is melted and no part of said ceramic or glass-ceramic material in said powder or powder mixture is melted.

(98) 39. Method according to any of embodiments 1 to 35 or 37 or 38, wherein in step (b) the surface and said powder or powder mixture being deposited on the surface have the same temperature.

(99) 40. Method according to any of the preceding embodiments, wherein said energy beam or at least one energy beam of said plurality of energy beams used in step (d) is a focused energy beam, preferably a focused laser beam of a CO.sub.2-laser or a Nd: YAG-laser or a focused electron beam.

(100) 41. Method according to any of the preceding embodiments, wherein in step (d) the powder or powder mixture in said region is completely melted throughout the entire thickness of said layer.

(101) 42. Method according to any of the preceding embodiments, wherein in step (d) the powder or powder mixture in said region is (completely) molten and the resulting melt is heated to a temperature that is in the range of from 1.025 to 1.5 times, preferably of from 1.05 to 1.25 times, the temperature in Kelvin of the highest melting component of said powder or powder mixture.

(102) 43. Method according to any of the preceding embodiments, wherein said powder or powder mixture comprises or consists of particles selected from the group consisting of primary particles, agglomerates, or mixtures thereof.

(103) 44. Method according to any of the preceding embodiments, wherein said powder or powder mixture comprises or consists of agglomerates obtained or obtainable by spray drying or powder jetting.

(104) 45. Method according to any of the preceding embodiments, wherein said powder or powder mixture comprises or consists of primary particles prepared by grinding, solidification from gas phase or dense sintered agglomerates obtained or obtainable by spray drying or powder jetting.

(105) 46. Method according to any of the preceding embodiments, wherein said powder or powder mixture consists of particles with a d.sub.50 particle size in the range of from 1 to 100 m, preferably in the range of from 15 to 70 m

(106) 47. Method according to any of the preceding embodiments, wherein said powder or powder mixture is a bimodal or a multimodal powder mixture.

(107) 48. Method according to embodiment 47, wherein said powder or powder mixture is a bimodal powder mixture and the particles of a first fraction have a d.sub.50 particle size in the range of from 1 to less than 15 m, and the particles of a second fraction have a particle size in the range of from 15 to 100 m.

(108) 49. Method according to any of the preceding embodiments, wherein after step (b), but before step (d), or if step (c) is conducted before step (c), said layer deposited in step (b) has a thickness in the range of from 5 to 200 m, preferably in the range of from 20 to 70 m.

(109) 50. Method according to any of the preceding embodiments, wherein during or after step (b) but before step (d) or (c), respectively, said layer is mechanically compressed.

(110) 51. Method according to any of the preceding embodiments, wherein said powder or powder mixture comprises ZrO.sub.2 and at least one component selected from the group consisting of MgO, Y.sub.2O.sub.3, CaO and CeO.sub.2.

(111) 52. Method according to embodiment 51, wherein said powder or powder mixture comprises ZrO.sub.2 and at least one component selected from the group consisting of Y.sub.2O.sub.3, CeO.sub.2 and MgO and wherein the amount of the component or components selected from said group is preferably sufficient to stabilize at least 50% by volume, preferably at least 75% by volume of the ZrO.sub.2 in the final article in the tetragonal form and wherein, if selected, in particular if selected as sole component from the group, the amount of Y.sub.2O.sub.3 is preferably in the range of 1 to 7 percent by weight, the amount of CeO.sub.2 is preferably in the range of 5 to 15 percent by weight and the amount of MgO is preferably in the range of 3 to 10 percent by weight based on the amount of ZrO.sub.2.

(112) 53. Method according to any of embodiments 51 or 52, wherein in said ceramic or glass-ceramic article at least 50 percent by volume and preferably at least 75 percent by volume of the total volume of ZrO.sub.2 in the article is tetragonal stabilized, doped ZrO.sub.2.

(113) 54. Method of producing a ceramic or glass-ceramic article according to embodiment 1, comprising the steps of:

(114) (a) providing a powder or a powder mixture comprising ceramic or glass-ceramic material, wherein said powder or powder mixture preferably comprises components that form an eutectic system with each other,

(115) (b) depositing a layer of said powder or powder mixture on a surface,

(116) (c) preheating of at least one region of said layer to a preheating temperature such that no part of said ceramic or glass-ceramic material in said at least one region is melted,

(117) (d) heating of at least one region of said layer by means of an energy beam or a plurality of energy beams to a maximum temperature such that at least a part of said ceramic or glass-ceramic material in said at least one region is melted, wherein the maximum temperature is higher than the preheating temperature,

(118) (e) cooling of said at least one region of said layer so that at least part of the material melted in step (d) is solidified, such that the layer is joined with said surface,

(119) (f) repeating of steps (a) to (e), whereby the surface of the layer produced by each foregoing series of steps (a) to (e) is used in step (b) of the repetition as surface for the following layer.

(120) 55. Method according to any of the preceding embodiments, wherein, if steps (a) to (e) are not repeated, after step (e), or if steps (a) to (e) are repeated, after the final repetition of steps (a) to (e) a glass-infiltration of the intermediate product obtained is performed at a temperature in the range of from 650 C. to 1200 C., preferably in the range of from 850 C. to 1000 C.

(121) 56. Method according to any of the preceding embodiments, wherein, if steps (a) to (e) are not repeated, after step (e), or if steps (a) to (e) are repeated, after the final repetition of steps (a) to (e) a glass-infiltration of the intermediate product obtained is performed under process conditions which are selected such that less than 5% by weight of the intermediate product is dissolved in the glass used for glass infiltration.

(122) 57. Method according to any of the preceding embodiments, wherein, if steps (a) to (e) are not repeated, after step (e), or if steps (a) to (e) are repeated, after the final repetition of steps (a) to (e), a treatment for improving bending strength is performed.

(123) 58. Method according to any of the preceding embodiments, wherein, if steps (a) to (e) are not repeated, after step (e), or if steps (a) to (e) are repeated, after the final repetition of steps (a) to (e) a glass-infiltration of the intermediate product obtained is performed and wherein the glass infiltration is performed in a vacuum.

(124) 59. Method according to any of the preceding embodiments, wherein, if steps (a) to (e) are not repeated, after step (e), or if steps (a) to (e) are repeated, after the final repetition of steps (a) to (e) a glass-infiltration of the intermediate product obtained is performed with a glass which comprises or consists of at least one compound selected from but favorably all compounds of the group consisting of ZrO.sub.2, SiO.sub.2, B.sub.2O.sub.3, Al.sub.2O.sub.3, Li.sub.2O and CaO.

(125) 60. Method according to any of the preceding embodiments, wherein, if steps (a) to (e) are not repeated, after step (e), or if steps (a) to (e) are repeated, after the final repetition of steps (a) to (e) a glass-infiltration of the intermediate product obtained is performed, such that said ceramic or glass-ceramic article after glass infiltration has a bending strength of at least 25 MPa, preferably of at least 250 MPa and more preferably of at least 500 MPa.

(126) 61. Method according to any of the preceding embodiments, wherein said ceramic or glass-ceramic article is produced on a substrate.

(127) 62. Method according to embodiment 61, wherein said ceramic or glass-ceramic article is produced on a substrate comprising a support means and/or a connector.

(128) 63. Method according to embodiment 62, wherein the support means or the connector has a predetermined breaking point to facilitate the separation of said ceramic or glass-ceramic article.

(129) 64. Method according to any of the preceding embodiments, wherein the process is controlled by a computer and/or a control unit.

(130) 65. Method according to embodiment 63, wherein the energy beam, in particular its intensity (power), focus, pathway, speed and/or the like is controlled and guided by a computer system.

(131) 66. Method according to any of the preceding embodiments, wherein the temperature of the surface of said layer is at least once measured by a pyrometer.

(132) 67. Method according to any of the preceding embodiments, preferably according to embodiment 65, wherein the temperature of the surface of said layer is at least once measured during step (c).

(133) 68. Method according to embodiments 66 or 67, wherein the data corresponding to the measured temperature are used for process monitoring and/or process control, preferably using a computer.

(134) 69. Method according to any of the preceding embodiments, wherein the average grain size in said produced ceramic or glass-ceramic article produced is 10 m or smaller, preferably 2.5 m or smaller.

(135) 70. Method according to any of the preceding embodiments, wherein said ceramic or glass-ceramic article has a bending strength of at least 25 MPa, preferably of at least 250 MPa and more preferably of at least 500 MPa.

(136) 71. Method according to any of the preceding embodiments, wherein the fracture toughness of said ceramic or glass-ceramic article is at least 4 MPa*m.sup.1/2, preferably at least 6 MPa*m.sup.1/2.

(137) 72. Method according to any of the preceding embodiments, wherein the material or at least part of the material solidified in step (e) has an m value maximum in the temperature range of from 1350 C. to 1500 C. of at least 0.5, preferably of at least 0.75.

(138) 73. Method according to any of the preceding embodiments, wherein the fraction of the glass phase in said ceramic or glass-ceramic article is 40 percent by volume or less, preferably 10 percent by volume or less.

(139) 74. Method according to any of the preceding embodiments, wherein the porosity of said ceramic or glass-ceramic article produced is no more than 30 percent by volume, preferably no more than 5 percent by volume.

(140) 75. Method according to any of the preceding embodiments, wherein said ceramic or glass-ceramic article is a dental article, in particular a dental restoration or frame.

(141) 76. Method according to embodiment 75, wherein said ceramic or glass-ceramic dental article is a crown, a bridge, an inlay, an onlay or an abutment.

(142) 77. Method according to any of embodiments 1 to 76, wherein said ceramic or glass-ceramic (preferably dental) article is tooth-colored.

(143) 78. Ceramic or glass-ceramic article prepared by a method according to any of the preceding embodiments.

(144) 79. Ceramic or glass-ceramic article according to embodiment 76, wherein the article is a dental article.

(145) 80. Ceramic or glass-ceramic article according to embodiment 78 to 79, wherein the article is a dental restoration or frame.

(146) 81. Ceramic or glass-ceramic article according to any of embodiments 78 to 80, wherein the article is a crown, a bridge, an inlay, an onlay or an abutment.

(147) 82. Ceramic or glass-ceramic article according to any of embodiments 78 to 81, wherein the article is tooth-colored.

(148) 83. Ceramic or glass-ceramic article according to any of embodiments 78 to 82, wherein the average particle grain size in the article is 10 m or smaller, preferably 2.5 m or smaller.

(149) 84. Ceramic or glass-ceramic according to any of embodiments 78 to 83, wherein said article has a bending strength of at least 25 MPa, preferably of at least 250 MPa and more preferably of at least 500 MPa.

(150) 85. Ceramic or glass-ceramic article according to any of embodiments 78 to 84, wherein the fracture toughness of the article is at least 4 MPa*m.sup.1/2, preferably at least 6 MPa*m.sup.1/2.

(151) 86. Ceramic or glass-ceramic article according to any of embodiments 78 to 85, comprising or consisting of material that has an m value maximum in the temperature range of from 1350 C. to 1500 C. of at least 0.5, preferably of at least 0.75.

(152) 87. Ceramic or glass-ceramic article according to any of embodiments 78 to 86, consisting of material that has a chemical solubility is 100 g/cm.sup.2 or less, preferably 20 g/cm.sup.2 or less.

(153) 88. Ceramic or glass-ceramic article according to any of embodiments 78 to 87, wherein the fraction of the glass phase in the article is 40 percent by volume or less, preferably 10 percent by volume or less.

(154) 89. Ceramic or glass-ceramic article according to any of embodiments 78 to 88, wherein the porosity of the article is no more than 30 percent by volume, preferably no more than 5 percent by volume.

(155) 90. Use of a ceramic or glass-ceramic article according to any of embodiments 78 to 89 as a dental article, in particular as a dental restoration or frame, or in the electronic industry.

(156) 91. Apparatus for producing a ceramic or glass-ceramic article, wherein the apparatus comprises at least one energy beam source for providing at least two energy beams operable independently of each other, at least one storage container for a powder or a powder mixture, a substrate for depositing a layer of said powder or a powder mixture, a powder deposition device for depositing a layer or layers of said powder or powder mixture on the substrate, means to direct the energy beams onto the surface or surfaces of the layer or layers of the powder or powder mixture.

(157) 92. Apparatus according to embodiment 91, wherein the apparatus comprises a pyrometer for measuring the temperature on the surface of the layer.

(158) 93. Apparatus according to any of embodiments 91 or 92, wherein the container comprises a powder or a powder mixture, which comprises components that form an eutectic system with each other.

(159) 94. Apparatus according to any of embodiments 91 or 93, comprising insulation material with a heat transfer coefficient of 20 W/(m.sup.2K) or less, preferably 10 W/(m.sup.2K) or less.

(160) 95. Ceramic or glass-ceramic article comprising a set of adjacent, joined layers of ceramic or glass-ceramic material, wherein said layers have a thickness in the range of from 5 to 200 m,

(161) and/or a set of adjacent, joined tracks of ceramic or glass-ceramic material,

(162) wherein said article has a bending strength of at least 25 MPa, preferably of at least 250 MPa and more preferably of at least 500 MPa.

(163) 96. Ceramic or glass-ceramic article according to embodiment 95, wherein said layers have a thickness in the range of from 20 to 70 m.

(164) 97. Ceramic or glass-ceramic article according to any of embodiments 95 or 96, with a bending strength of at least 25 MPa, preferably of at least 250 MPa and more preferably of at least 500 MPa.

(165) 98. Ceramic or glass-ceramic article according to any of embodiments 95 to 97, wherein the average grain size in the article is 10 m or smaller, preferably 2.5 m or smaller.

(166) 99. Ceramic or glass-ceramic article according to any of embodiments 95 to 98, wherein the fracture toughness of the article is at least 4 MPa*m.sup.1/2, preferably at least 6 MPa*m.sup.1/2.

(167) 100. Ceramic or glass-ceramic article according to any of embodiments 95 to 99, wherein the article comprises a glass phase, the fraction of the glass phase in the article being no more than 40 percent by volume, preferably no more than 10 percent by volume.

(168) 101. Ceramic or glass-ceramic article according to any of embodiments 95 to 102, wherein the article comprises a glass phase, which comprises or consists of compounds selected from the group consisting of ZrO.sub.2, SiO.sub.2, B.sub.2O.sub.3, Al.sub.2O.sub.3, Li.sub.2O, ZrO.sub.2 and CaO.

(169) 102. Ceramic or glass-ceramic article according to any of embodiments 95 to 101, wherein the porosity of the article is no more than 30 percent by volume, preferably no more than 5 percent by volume.

(170) 103. Ceramic or glass-ceramic article, preferably according to any of embodiments 95 to 102, comprising a set of adjacent, joined layers of ceramic or glass-ceramic material, wherein said layers have a thickness in the range of from 5 to 200 m,

(171) and/or a set of adjacent, joined tracks of ceramic or glass-ceramic material,

(172) wherein said ceramic or glass-ceramic material comprises components that form an eutectic system with each other.

(173) 104. Ceramic or glass-ceramic article according to any of embodiments 95 to 103, wherein at least 50 percent by weight, preferably at least 70 percent by weight, more preferably at least 80%, of said ceramic or glass-ceramic material consist of components that form an eutectic system with each other.

(174) 105. Ceramic or glass-ceramic article according to any of embodiments 103 or 104, wherein for each component of said eutectic system the fraction by weight of the component in said ceramic or glass-ceramic material, based on the weight of the eutectic system in the powder or powder mixture, is at least 25%, preferably at least 50%, especially preferred at least 70% and most preferred at least 90% of the fraction by weight of the same component in the eutectic mixture of said eutectic system.

(175) 106. Ceramic or glass-ceramic article according to any of embodiments 95 to 105, comprising one or more compounds selected from the group consisting of Al.sub.2O.sub.3, ZrO.sub.2,

(176) Y.sub.2O.sub.3, Na.sub.2O, Nb.sub.2O.sub.5, La.sub.2O.sub.3, CaO, SrO, CeO.sub.2, MgO, SiO.sub.2, TiO.sub.2, Cr.sub.2O.sub.3, CuO, Eu.sub.2O.sub.3, Er.sub.2O.sub.3, CoO, Gd.sub.2O.sub.3, the mixed oxides thereof especially MgAl.sub.2O.sub.4, Y.sub.3Al.sub.5O.sub.12, Er.sub.3Al.sub.5O.sub.12, NiAl.sub.2O.sub.4, LaAlO.sub.3 and La.sub.2ZrO.sub.7, SiC, TiC, Si.sub.3N.sub.4 and AlN.

(177) 107. Ceramic or glass-ceramic article according to any of embodiments 95 to 105, wherein at least 50 percent by weight, preferably at least 70 percent by weight of said article consist of one or more compounds selected from the group consisting of Al.sub.2O.sub.3, ZrO.sub.2, Y.sub.2O.sub.3, Na.sub.2O, Nb.sub.2O.sub.5, La.sub.2O.sub.3, CaO, SrO, CeO.sub.2, MgO, SiO.sub.2, TiO.sub.2, Cr.sub.2O.sub.3, CuO, Eu.sub.2O.sub.3, Er.sub.2O.sub.3, CoO, Gd.sub.2O.sub.3, the mixed oxides thereof, especially MgAl.sub.2O.sub.4, Y.sub.3Al.sub.5O.sub.12, Er.sub.3Al.sub.5O.sub.12, NiAl.sub.2O.sub.4, LaAlO.sub.3 and La.sub.2ZrO.sub.7, SiC, TiC, Si.sub.3N.sub.4 and AlN.

(178) 108. Ceramic or glass-ceramic article according to any of embodiments 95 to 107, wherein at least 50 percent by weight, preferably at least 70 percent by weight of said article consist of one or more oxides selected from the group consisting of ZrO.sub.2, Al.sub.2O.sub.3, SiO.sub.2, MgO, Y.sub.2O.sub.3, Cr.sub.2O.sub.3, Na.sub.2O, TiO.sub.2, La.sub.2O.sub.3, and the mixed oxides thereof.

(179) 109. Ceramic or glass-ceramic article according to any of embodiments 95 to 108, preferably according to any of embodiments 103 to 105, wherein said article comprises ZrO.sub.2 and Al.sub.2O.sub.3.

(180) 110. Ceramic or glass-ceramic article according to any of embodiments 95 to 109, preferably according to any of embodiments 103 to 105, wherein the mixing ratio by weight of ZrO.sub.2 to Al.sub.2O.sub.3 is in the range of from 1:4 to 4:1, preferably in the range of from 3:7 to 7:3.

(181) 111. Ceramic or glass-ceramic article according to any of embodiments 95 to 110, preferably according to any of embodiments 103 to 105, wherein the mixing ratio by weight of ZrO.sub.2 to Al.sub.2O.sub.3 is 42.6 to 57.4.

(182) 112. Ceramic or glass-ceramic article according to any of embodiments 95 to 111, wherein said article consists of 42.6 percent by weight of ZrO.sub.2 and 57.4 percent by weight of Al.sub.2O.sub.3.

(183) 113. Ceramic or glass-ceramic article according to any of embodiments 103 to 112, comprising tetragonal stabilized, doped ZrO.sub.2.

(184) 114. Ceramic or glass-ceramic article according to embodiment 113, wherein the tetragonal stabilized doped ZrO.sub.2 is ZrO.sub.2 doped with at least one component selected from the group comprising Y.sub.2O.sub.3, CeO.sub.2 and MgO and wherein, if selected, in particular if selected as sole component from the group, the amount of Y.sub.2O.sub.3 is preferably in the range of 1 to 7 percent by weight, the amount of CeO.sub.2 is preferably in the range of 5 to 15 percent by weight and the amount of MgO is preferably in the range of 3 to 10 percent by weight based on the amount of ZrO.sub.2.

(185) 115. Ceramic or glass-ceramic article according to any of embodiments 113 or 114, wherein the amount of the component or components selected from said group is preferably sufficient to stabilize at least 50% by volume, preferably at least 75% by volume of the ZrO.sub.2 in the final article in the tetragonal form.

(186) 116. Ceramic or glass-ceramic article according to any of embodiments 78 to 115, wherein said article is a dental restoration or frame.

(187) 117. Ceramic or glass-ceramic article according to any of embodiments 95 to 116, wherein said article is a crown, a bridge, an inlay, an onlay or an abutment.

(188) 118. Ceramic or glass-ceramic article according to any of embodiments 95 to 117, wherein said article is tooth-colored.

(189) 119. Ceramic or glass-ceramic article, preferably according to any of embodiments 95 to 118, characterized in that the article can be produced by a method according to any of embodiments 1 to 75.