EP2935151A1

EP2935151A1 - Ceramic material

Info

Publication number: EP2935151A1
Application number: EP13811508.4A
Authority: EP
Inventors: Lars Schnetter; Frank Wittig
Original assignee: Ceramtec ETEC GmbH
Current assignee: Ceramtec ETEC GmbH
Priority date: 2012-12-19
Filing date: 2013-12-19
Publication date: 2015-10-28
Also published as: KR20150097714A; RU2015129336A; IL239343A0; AU2013360718A1; JP2016500362A; US20150299044A1; CN105263885A; WO2014096142A1; DE102013226579A1; US20180093923A1

Abstract

The invention relates to the production of transparent ceramics. The invention relates in particular to the use of raw materials containing impurities for producing transparent ceramics.

Description

Ceramic material

The invention relates to ceramic materials; In particular, the invention relates to ceramic materials for the production of transparent ceramics.

Transparent ceramics and their preparation are known from the prior art. DE 10 2004 004 259 B3, for example, discloses a polycrystalline ceramic with a high mechanical load capacity, which has a true in-line transmission (RIT) of more than 75% of the theoretical maximum value for a 0.8 mm thick polished disk and at wavelengths between 600 and 650 nm, wherein the mean grain size D is in the range between 60 nm and 10 μιτι.

The transparency of polycrystalline ceramic disks is influenced by various factors. So of course, a material must be used that has only a very low light absorption. In addition, the transparency of polycrystalline ceramic discs depends essentially on the light scattering, which results from the crystal structure on the one hand and from the microstructure of the ceramic body on the other hand. Materials with cubic crystal systems are preferably used because birefringence does not occur. Furthermore, the processes for the production of transparent ceramics are optimized in such a way that the lowest possible porosity occurs, or the pore size is below the wavelength of the light, in order to minimize the light scattering at phase boundaries.

Another important factor in the production of transparent ceramics is the use of high-purity raw materials, since even the smallest impurities of more than 100 ppm lead to white or black spots in the ceramic. Therefore, in principle, only raw materials are used which have a purity of> 99.99%, preferably even> 99.9999%. These raw materials are very expensive.

The object of the invention is thus to provide alternative ceramic materials which are suitable for the production of transparent ceramics and which are less expensive than the high purity raw materials known in the art.

The object is achieved by means of a ceramic material according to claim 1. This ceramic material is characterized in that it consists of metal oxides, which are obtained by calcination of hydrotalcites. The material can preferably be used to produce transparent ceramics.

Hydrotalcites according to the invention are metal hydroxides prepared by a hydrotalcite process. A transparent ceramic according to the invention is understood to mean a ceramic which has an RIT of at least 40% at 300 nm, 600 nm and / or 1500 nm wavelength of the light. Theoretically, the transparency is independent of thickness, if a perfect material is present and from it a perfect ceramic was produced. As soon as the ceramic, however, pores o.ä. contains a scattering effect at the phase boundaries of the pores, which becomes stronger with increasing thickness of the ceramic. This effect leads to a decreasing transparency. Therefore, referred to in this document transparencies refer to ceramics with wall thicknesses between 50 μιτι and 100 mm.

Particularly preferably, the hydrotalcites, from which the ceramic material according to the invention is obtained by calcining, are produced by means of a hydrotalcite process.

Hydrotalcite processes are known in the art. Such a method is described for example in EP 0 807 086 B1. A hydrotalcite process in the context of this invention is understood as meaning a process which comprises at least the following steps:

• Providing the metal, such as aluminum, and an alcohol, such as ethanol

• Implementation of metal and alcohol to the metal Al koholat, for example aluminum alkoxide, with liberation of hydrogen Implementation of the metal alcohol with addition of water to the metal hydroxide, for example boehmite, with release of the alcohol.

According to a particularly preferred embodiment of the invention, the metal oxides which are obtained by calcination from the metal hydroxides, between 100 and 500 ppm, preferably between 100 and 200 ppm impurities, in particular of Fe, Mn, Cr, V, Zn, Sn, Ti, Si, Zr, Ca, Na, K, Li, Y, Ni, Co, Cu. This is particularly advantageous because lower requirements are placed on the purity of the raw materials than in the case of materials according to the prior art. Usually only raw materials with a purity of> 99.99% or raw materials containing <100 ppm impurities are used here. The required lower degree of purity, which does not sacrifice transparency, thus allows the use of significantly less expensive raw materials.

It is believed that the higher level of contamination is possible because the impurities are very finely divided and very homogeneous, possibly at the atomic level, present in the material. In any case, they do not form a separate phase, for example a grain boundary phase, which would lead to a reduction in transparency in the sintered ceramic. It is believed that the impurities are incorporated in the lattice of metal oxides. This means the incorporation of the metal cations in the lattice of the spinel, for example, cation lattice, interstitial sites, or the like.

It is surprising that not only no deterioration of the transparency is observed, but that it also does not come to a significant coloring of the ceramic. In particular transparent ceramics can be produced with the raw material according to the invention which have a deviation in the RIT value of <10% between 300 nm and 700 nm, in particular at 300 nm and 700 nm, and thus obtain a high white value.

By means of the hydrotalcite process, preference is given to producing metal hydroxides whose metal oxides have a cubic crystal system. Besides oxides like the Al 2 O 3 or MgO particularly preferably spinels, in particular Mg-Al spinels are produced. However, transparent ceramics of ZrO 2, oxides of mixtures of Y and Al and materials of the mixtures of Al, N, O or even non-cubic aluminum oxide can preferably be produced by this process.

In contrast to the prior art, for example DE 10 2004 004 259 B3, the use of the material according to the invention completely dispenses with the use of sintering aids. Sintering aids allow the use of lower sintering temperatures with less grain growth. However, the sintering aids must be at least partially expelled again by means of volatile compounds such as LiF, since they would otherwise be present as a separate phase in the ceramic, which in turn would have negative effects on the transparency. These additives are not necessary in the use of the ceramic material according to this invention for the production of transparent ceramics.

In the following the invention will be explained in more detail by means of exemplary embodiments. example 1

A MgOAl ₂ O ₃ raw material with a total of 406 ppm impurities, produced by the hydrotalcite process, with the following composition (ICP analysis) is used:

MgO: 28.9%,

Na: 18 ppm,

Si: 196 ppm,

Fe: 98 ppm,

Cr: 7 ppm,

Ti: 10 ppm,

Mn: 40 ppm,

Zn: 37 ppm,

Rest: AI2O3. Specific surface area (BET): 18 m ² / g,

Starting particle size distribution d90: 5.5 μητι, d50 2.4 μητι, d10: 0.8 μηη

1500 g of the raw material are added to 1500 g of deionized water with 7%

Diammonium hydrogen citrate stirred. The thus prehomogenized slip is ground with a stirred ball mill (500 m Al ₂ O 3 grinding beads) until an energy input of 1.60 kWh / kg is reached. The following particle size distribution is then available: d90: 375 nm, d50: 224 nm, d10: 138 nm (measured with a Nanoflex measuring instrument from Microtrac). The specific surface area (BET) is 25.5 m ² / g.

The thus prepared slurry is mixed with 6% of a short-chain polyethylene glycol and granulated by means of a freeze-spray process. After this

Freeze-drying is a moldable granulate from which test pieces are formed having a net basis of 2.17 g / cm ³ . These are pre-sintered at 1455 ° C for 2 h at 3.519 g / cm ³ and then post-densified at 1650 ° C for 6 h at 200 MPa hot isostatic (HIP = hot isostatic pressing).

The samples are ground and polished to a thickness of 2 mm for a transmission measurement:

The following RIT values were determined as a function of the wavelength:

300 nm: 74%, 600 nm: 78%, 700 nm: 80%, 1500 nm: 81%.

Example 2

A MgOAl ₂ O ₃ raw material with 232 ppm impurities, produced by the hydrotalcite method, with the following composition (ICP analysis) is used:

MgO: 33.9%

Na: 18 ppm

Si: 83 ppm Fe: 71 ppm

Ca: 5 ppm

Cr: 4 ppm

Ni: 2 ppm

Ti: 18 ppm

Mn: 27 ppm

Cu: 1 ppm

Zr: 3 ppm

Remainder: Al ₂ O ₃

Specific surface area (BET): 58 m ² / g

Starting particle size distribution d90: 7.85 μιτι, d50 3.2 μιτι, d10: 0.9 μιτι

The treatment is carried out analogously to Example 1 until an energy input of 1.05 kWh / kg is reached. The following particle size distribution is then present: d90: 345 nm, d50: 195 nm, d10: 124 nm (measured with a Nanoflex measuring instrument from Microtrac), BET 23.5 m ² / g.

Freeze-drying is a moldable granulate from which test pieces are formed having a net basis of 2.07 g / cm ³ . These are pre-sintered at 1400 ° C for 2 h at 3.512 g / cm ³ and then post-densified at 1650 ° C for 6 h at 200 MPa hot isostatic.

The following RIT values were determined as a function of the wavelength:

300 nm: 60%, 600 nm: 71%, 700 nm: 75%, 1500 nm: 77%.

Example 3 A MgOAl ₂ O ₃ raw material with 156 ppm impurities, which was produced by the hydrotalcite process and has the following composition (ICP analysis), is used:

28.9%,

Na: 22 ppm

Si 83 ppm

Fe: 31 ppm

Cr: 1 ppm,

Ca: 3 ppm,

Ti: 1 ppm,

Mn: 8 ppm,

Zn: 7 ppm,

AI ₂ O ₃ : remainder

Specific surface area (BET): 7.3 m ² / g

Starting particle size distribution d90: 4.7 μιτι, d50 2.1 μιτι, d10: 0.3 μιτι

600 g of the raw material are added to 600 g of deionized water at 4.7%

Diammonium hydrogen citrate stirred. The thus pre-homogenised slip is ground with a stirred ball mill (500 m Al ₂ O 3 grinding beads) until an energy input of 1.5 kWh / kg is reached. The specific surface area (BET) is then 51.3 m ² / g.

The thus prepared slip is admixed with 5% of an aqueous polymer dispersion and 4% of a fatty acid preparation and granulated by means of a freeze spray method. After freeze-drying, there is a moldable granule from which test pieces having a net basis of 2.18 g / cm ^{3 are} formed. These are pre-sintered at 1550 ° C for 2 h to 3.413 g / cm ³ and then post-densified at 1650 ° C for 6 h at 200 MPa hot isostatic.

The samples are ground and polished to a transmission measurement of 2 mm thickness: The following RIT values were determined as a function of the wavelength: 300 nm: 70%, 600 nm: 75%, 700 nm: 77%, 1500 nm: 79%.

Example 4 (Comparative Example)

A MgOAl ₂ O ₃ raw material with 461 ppm impurities, which was not produced by the hydrotalcite process, is used. The following composition was determined by ICP analysis:

Mg: 17.1%,

AI: 37.9%,

Na: 69 ppm,

K: 32 ppm,

Ca: 130 ppm

Ti: 19 ppm,

V: 41 ppm,

Cr: 14 ppm,

Mn: 7 ppm,

Fe: 95 ppm,

Ni: 5 ppm,

Zn: 14 ppm,

Ga: 35 ppm,

Rest: O.

Specific surface 22.2 m ² / g.

540 g raw material is stirred into 800 g deionized water with 1, 5% diammonium hydrogen citrate. This slurry is milled with a stirred ball mill (500 μιτι AI ₂ O 3 grinding beads) until an energy input of 1, 50 kWh / kg is reached. The following particle size distribution is then present: d90: 234 nm, d50: 156 nm, d10: 84 nm (measured with a Nanoflex measuring device from Microtrac), BET 68.1 m ² / g. The slip is granulated as described in Examples 1 and 2. The compacts produced with a net comparable green density of 1 89 g / cm ³ are at 1430 ° C for 2 h to 3.524 g / cm ³ pre-sintered and then hot isostatic pressed at 1650 ° C, for 6 hours at 200 MPa.

The samples are ground and polished to a thickness of 2 mm for a transmission measurement: no RIT values can be measured. The samples are

opaque.

Example 5 (Comparative Example)

A MgOAl ₂ O ₃ raw material with 60 ppm impurities, which was not produced by the hydrotalcite process, is used. Reaction rate in spinel (crystalline phase determination by X-ray diffractometry) 99.5%, free alpha-Al ₂ O ₃ 0.4%, free MgO 0.1%. The following impurities were determined by ICP analysis: Na: 15 ppm,

K: 32 ppm,

Fe: 2 ppm,

Si: 1 1 ppm

Remainder O. average particle size d50 (Sedigraph): 0.18 μιτι.

specific surface area (BET): 28.2 m ² / g.

4000 g of raw material are stirred into 3605 g of deionized water with 2.3% diammonium hydrogen citrate. This slurry is ground with a stirred ball mill (500 μηη grinding beads) until an energy input of 0.85 kWh / kg is reached. The following particle size distribution is then present: d90: 252 nm, d50: 152 nm, d10: 101 nm (measured with a Zetasizer measuring instrument from Malvern), BET 31, 7 m ² / g. The thus prepared slurry is mixed with 6% of a short-chain polyethylene glycol and granulated by means of a freeze-spray process. After this

Freeze-drying is a moldable granulate, are formed from the sample with a net green density of 1, 91 g / cm ³ . These are pre-sintered at 1530 ° C for 2 h at 3.057 g / cm ³ and then post-densified at 1650 ° C for 4 h at 200 MPa hot isostatic.

The following RIT values were determined as a function of the wavelength:

300 nm: 86%, 600 nm: 85%, 700 nm: 84%, 1500 nm: 87%.

Example 6 (comparative example)

A MgOAl ₂ O ₃ raw material with 398 ppm impurities, which was not produced by the hydrotalcite process, is used. The following composition was determined by ICP analysis:

17.1%,

37.9%,

Na: 46 ppm,

K: 25 ppm,

Ca: 145 ppm

Ti: 15 ppm,

V: 27 ppm,

Cr: 5 ppm,

Mn: _ 5 ppm,

Fe: 80 ppm,

Ni: 5 ppm,

Zn: 1 1 ppm,

Ga: 34 ppm,

O: rest Specific surface area 20.1 m ² / g.

540 g of raw material is used in 800 g of deionized water with 1, 5%

Diammonium hydrogen citrate stirred. This slip will come with a

Agitator ball mill (500 μιτι AI ₂ O3 grinding beads) ground until an energy input of 1, 0 kWh / kg is reached. The following particle size distribution is then present: d90: 274 nm, d50: 156 nm, d10: 101 nm (measured with a Nanoflex measuring instrument from Microtrac), BET 58.0 m ² / g.

The slip is granulated as described in Example 5. The comparatively produced compacts having a net green density of 1.87 g / cm ³ are pre-sintered at 1410 ° C. for 2 h to 3.452 g / cm ³ and then hot isostatically compressed at 1650 ° C. for 6 h at 200 MPa.

opaque.

Claims

claims

1 . Ceramic material comprising metal oxides obtained by calcination of hydrotalcites, characterized in that the material is used to produce transparent ceramics having a RIT value> 40% at 300 nm, 600 nm or 1500 nm wavelength of the light.

2. Ceramic material according to claim 1, characterized in that the material for the production of transparent ceramics having a deviation in the RIT value of <10% between 300 nm and 700 nm wavelength of the light.

3. Ceramic material according to claim 1 or 2, characterized in that the metal oxides between 100 and 500 ppm, preferably between 100 and 200 ppm of impurities, in particular of Fe, Mn, Cr, V, Zn, Sn, Ti, Si, Zr, Ca , Na, K, Li, Y, Ni, Co and / or Cu.

4. Material according to claim 3, characterized in that the impurities at the atomic level are finely distributed in the metal oxides.

5. Ceramic material according to one of the preceding claims, characterized in that the metal oxides have a cubic crystal system.

6. Ceramic material according to one of the preceding claims, characterized in that the metal oxides with cubic crystal system spinels, in particular Mg-Al spinels, ZrO2, oxides of the mixtures of Y and AI, mixing materials of Al, N, O and alumina in the cubic and not cubic crystal structure.

7. Use of a ceramic material according to any one of the preceding claims for the production of transparent ceramics.