EP1044178A1

EP1044178A1 - Surface coated non-oxidic ceramics

Info

Publication number: EP1044178A1
Application number: EP98966404A
Authority: EP
Inventors: Juan Gonzalez-Blanco
Original assignee: HC Starck GmbH
Current assignee: HC Starck GmbH
Priority date: 1998-01-07
Filing date: 1998-12-24
Publication date: 2000-10-18
Also published as: JP2002500157A; TW562787B; DE19800310A1; KR20010033904A; WO1999035105A1

Abstract

Non-oxidic ceramics made of BN or the group of carbides, nitrides, borides and silicides of elements Ti, Zr, Hf, Cr, Mo, W, V, Nb, Ta, Si, Ge and Sn with an average particle size of 0.1- 50 nm whose surface is coated with at least one alpha amino acid.

Description

Surface-coated, non-oxide ceramics

The invention relates to non-oxide ceramics, the surface of which is coated with at least one α-amino acid, a process for their production and their use for the production of ceramic sintered bodies and layers.

According to EP-A 650 945, ceramic powders have already been described which are used for the production of ceramic sintered bodies and layers. However, these still have some disadvantages with regard to their processing properties, such as redispersibility and the product properties of products made therefrom.

If, for example, suspensions of these ceramic powders are used, they have a high degree of agglomeration of the primary particles, which makes high sintering temperatures necessary in order to sufficiently compress the moldings.

Non-oxide ceramics made from BN and from the group of carbides, nitrides, borides and silicides of the elements Ti, Zr, Hf, Cr, Mo, W, V, Nb, Ta, Si, Ge and Sn with an average primary particle size of 0 have now been found , 1 to 50 nm found, the

Surface is covered with at least one α-amino acid.

Surface coverage means that the α-amino acids are chemically or physically bound to the ceramic surface.

Preferred non-oxide ceramics are TiN, ZrN, TiC or SiC, in particular TiN or TiC.

The surface-coated, non-oxide ceramics are preferably powders. In the context of this application, an α-amino acid is understood to mean a compound which carries an amino group and a carboxylic acid group bonded to the same C atom - that is to say a structural element of the formula

contains.

In a preferred embodiment, the ceramics according to the invention are coated with aliphatic α-amino acids. Arginine, cysteine,

Ornithine, citrulline, lysine, aspartic acid and asparagine.

Aromatic α-amino acids such as tyrosine, in particular L-tyrosine and heterocyclic α-amino acids are also advantageous.

The L forms of these amino acids are generally used.

In a preferred embodiment, the ceramics according to the invention have a primary particle size of 0.5 to 30 nm.

The invention further relates to a process for producing the ceramics according to the invention, which is characterized in that a non-oxide ceramic made of BN and from the group of carbides, nitrides, borides and silicides of the elements Ti, Zr, Hf, Cr, Mo, W, V, Nb, Ta, Si, Ge and Sn treated with an average primary particle size of 0.1 to 50 nm, in water and / or an organic solvent at a temperature of 20 to 150 ° C. with at least one α-amino acid and optionally after filtration dries. Non-oxide ceramics used

The average primary particle size of the non-oxide ceramic used in the method according to the invention can be determined with the aid of electron microscopic images. It is preferably 0.1 to 50 nm, in particular 0.5 to 30 nm. The primary particles of the non-oxide ceramics preferably have a spherical structure. They can also be in the form of their agglomerates or aggregates, these having an average particle size of less than 500 nm, preferably less than 150 nm.

The non-oxide ceramics to be used can be crystalline or amorphous, preferably crystalline. They can be obtained, for example, by the process described in US Pat. No. 5,472,477 (= DE-A 4 214 719). The CVR (chemical vapor reaction) process is preferably used, with which particles with a very narrow size distribution can be produced without oversize particles and with high purity.

Characteristic of the non-oxide ceramics produced in this way, preferably in the form of their powders, is the complete absence of individual particles (primary particles) which are significantly larger than the average particle size. For example, the powders preferably have less than 1% individual particles which deviate more than 20% from the mean particle size; Particles that deviate more than 50% are practically absent.

The non-oxide ceramics used in the process according to the invention can either be in the form of their primary particles, agglomerates or aggregates of primary particles or mixtures of the two. Agglomerates or aggregates are understood to be particles in which several primary particles interact with one another via van der Waals forces, or in which the primary part Chen are connected by surface reaction or "sintering" during the manufacturing process.

The non-oxide ceramics used can have extremely low oxygen contents of less than 10% by weight, based on the solid, preferably <1%, particularly preferably <0.1%.

Their high purity and surface purity are also characteristic. Due to the manufacturing process, the non-oxide ceramics to be used can be very sensitive to air or even pyrophoric. In order to eliminate this property, the non-oxidic ceramics can be surface-modified or oxidized or passivated in a defined manner by exposure to gas / steam mixtures before use in the method according to the invention.

Such non-oxide ceramics are used particularly preferably in the inventive process which have a content of NH ₄ -O ^Θ ® groups from 50 to 1000, preferably from 50 to 500, in particular 100 to 500 .mu.eq / g of non-oxide ceramics.

The invention therefore further relates to non-oxide ceramics made from BN and from the group of carbides, nitrides, borides and silicides of the elements Ti, Zr, Hf, Cr, Mo, W, V, Nb, Ta, Si, Ge and Sn with an average primary particle size from 0.1 to 50 nm, which have a content of -O ^Θ NH4 ^Φ groups of 50 to 1,000 μeq / g of non-oxide ceramic.

The NH4® groups are preferably located on the surface of the ceramics.

The ceramics according to the invention, ie both the -O ^Θ NH ^θ group-containing and the α-amino acid-containing, also preferably have a Cl content of less than 1 atom%, based on all atoms that are in a 5 nm thick surface layer of the ceramic particles. A correspondingly thick outer particle layer can be examined, for example, by means of ESCA (Electron Spectroscopy for Chemical Analysis), in particular according to the XPS method (X-ray photoelectron spectroscopy).

The -O ^Θ NH4® groups can be produced, for example, by reacting -OH groups on the ceramic surface with aqueous ammonia. The - OH groups in turn can be obtained, for example, by oxidation or passivation with oxygen-containing gases of the ceramic particles produced by the CVR process. This creates a monomolecular oxide layer on the

Ceramic surface, which shows hydroxyl groups. The number of -OH groups can be determined, for example, by conductometric titration. For example, the number of OH groups for a TiN particle obtained by the CVR process is about 300 μeq / g ceramic and the -O ^Θ NH4® amount after the ammonia treatment is correspondingly large.

The invention therefore further relates to a process for the production of -O ^Θ NH ®- group-containing ceramics, which is characterized in that at least one non-oxide ceramic from BN and from the group of carbides, nitrides, borides and silicides of the elements Ti, Zr, Hf , Cr, Mo, W, V, Nb, Ta, Si, Ge and Sn with an average primary particle size of 0.1 to 50 nm, with an aqueous NH ₃ solution at a temperature of 20 to 150 ° C, optionally under pressure , treated.

The ceramics used for this treatment are preferably after

CVR processes, for example analogous to the process described in US Pat. No. 5,472,477, have been obtained.

In the CVR process, gaseous starting materials, for example TiCl and NH3 for the production of TiN, are reacted in a reactor. The products are produced with the exclusion of wall reactions. The process is particularly advantageous Carried out in a tubular reactor with laminar flow of educts and products.

The starting materials are generally introduced into the reactor in coaxial partial streams. To mix them, a disturbing body is preferably built into the otherwise strictly laminar flow; this creates a Karman vortex street, defined in terms of intensity and expansion, in which the mixing takes place.

In order to prevent the energetically highly preferred deposition of the reaction participants on the reactor wall, the reaction medium is preferably shielded by an inert gas layer.

The NH ₃ treatment is preferably carried out in a 5-50% by weight aqueous NH ₃ solution. It is particularly preferably carried out at a temperature of 40-120 ° C.

In a further preferred embodiment of this NH ₃ treatment, the treated ceramic is filtered off, optionally washed with water and then dried.

As a drying process, all those with which

Water can be removed. For example, this is possible with the following equipment: fluidized bed dryer, paddle dryer, spray dryer, drying cabinet and vacuum dryer.

The invention therefore also relates to the non-oxide ceramics obtainable by this NH ₃ treatment process, preferably in the form of their powders.

If the method according to the invention for the production of the α-amino acid is documented

Ceramics made in an organic solvent or solvent mixture should be mentioned as suitable organic solvents: aliphatic

C _] -C4 alcohols, such as methanol, ethanol, isopropanol, n-propanol, n-butanol, iso- butanol or tert-butanol, aliphatic ketones, such as acetone, methyl ethyl ketone, methyl isobutyl ketone or diacetone alcohol, polyols, such as ethylene glycol, propylene glycol, butylene glycol, diethylene glycol, triethylene glycol, trimethylol propane, polyethylene glycol with an average molecular weight of 1500 to 1500 to preferably 400 to 1500 g / mol or glycerol, monohydroxy ether, preferably monohydroxy alkyl ether, particularly preferred such as ethylene glycol monoalkyl, monoethyl, diethylene glycol monomethyl ether or diethylene glycol monoethyl ether. Diethylene glycol monobutyl ether, dipropylene glycol monoethyl ether, thiodiglycol, methylene glycol monomethyl ether or monoethyl ether, furthermore 2-pyrrolidone, N-methyl-2-pyrrolidone, N-ethyl-pyrrolidone, N-vinyl-pyrrolidone, 1,3-

Dimethyl-imidazolidone, dimethylacetamide and dimethylformamide. Mixtures of the solvents mentioned are also suitable.

The process according to the invention is preferably carried out at from 60 ° C. to the boiling point of the solvent system used in each case

Normal pressure. It is particularly preferred to work under reflux. At higher temperatures, the process can also be carried out with the application of an external pressure, in particular 2 to 10 bar.

The process according to the invention is particularly preferred in water or aqueous

Solvent mixtures carried out.

Before or during the process according to the invention, the ceramic to be used can also be wet-ground together with at least part of the α-amino acid, for example on a 2-roller grinding device. In general, the ceramic to be used is in powder form or in the form of the water-moist press cake together with a portion of the α-amino acid and water, preferably deionized water, to form a homogeneous grinding suspension, for example by means of an agitator bucket, dissolver and similar units, if appropriate after a pre-comminution and homogenized). The grinding suspension can also contain fractions of low-boiling solvents (boiling point <150 ° C.), which can be removed by evaporation in the course of a subsequent fine grinding. However, it can also contain proportions of higher-boiling solvents or other additives, for example grinding aids, defoamers or wetting agents.

The wet comminution of the ceramics to be used includes both the pre-comminution and the fine grinding. The suspension concentration is preferably above the desired concentration of the finished preparation. The desired final solids concentration is preferably set after the wet comminution. Following the pre-comminution, grinding is carried out to the desired particle size distribution. Units such as e.g. Kneaders, roller mills, kneading screws, ball mills, rotor-stator mills, dissolvers, corundum disc mills, vibrating mills and in particular high-speed, continuously or discontinuously charged agitator ball mills with grinding media with a diameter of 0.1 to 2 mm in question. The grinding media can be made of glass, ceramic or metal, e.g. Be steel. The grinding temperature is preferably in the range from 20 to 150 ° C., but generally at room temperature, if appropriate below the cloud point of the optionally additionally used surface-active compounds as dispersing agents (grinding aids).

The α-amino acid is preferably used in an amount of 0.1 to 20% by weight, based on the amount of ceramic used. One is particularly preferred

Amount from 1 to 10% by weight.

Any excess α-amino acid can, for example, be separated from the surface-coated ceramic by filtration using the process according to the invention. Excess α-amino acid can also be separated off, for example, by centrifuging the suspension and then decanting off the supernatant. Membrane or micro filtration processes are also suitable.

The still moist, i.e. water- or solvent-moist surface-covered ceramics are then dried. Drying temperatures of 20 to 150 ° C., in particular 50-120 ° C., are preferably used, although the application of a vacuum can also be advantageous.

Drying is generally carried out using the usual drying apparatus such as paddle dryers, drying cupboards, spray dryers, fluidized bed dryers etc. The residual water content after drying is preferably less than 2% by weight, based on the ceramic.

The surface-coated ceramic according to the invention thus obtained is preferably in the form of a powder.

The ceramic according to the invention is preferably used in the form of its aqueous or solvent-containing suspension, for example for the production of ceramic composite materials from non-oxidic and / or oxidic components. The suspensions can also be used to manufacture metallic composite materials.

The invention therefore furthermore relates to suspensions containing the surface-coated ceramic and water and / or an organic solvent according to the invention.

The suspensions according to the invention preferably contain 5 to 50% by weight, in particular 10 to 35% by weight, based on the suspension, of the α-

Amino acid-coated ceramics, 50 to 95, in particular 65 to 90 wt .-%, based on the suspension, water and / or organic solvent and optionally other additives.

Further additives include, for example, cationic, anionic, amphoteric and / or nonionic dispersants, for example those which are listed in the “Surfactants Europe, A Directory of Surface Active Agents avanable in Europe (Edited by Gordon Hollis, Royal Society of Chemistry, Cambridge ( 1995) and pH regulators such as NaOH, ammonia, aminomethylpropanol and N, N-dimethylaminoethanol.

Aqueous suspensions of the ceramics according to the invention are particularly preferred, preferably those with a pH of 7-10, in particular 8-9. These aqueous suspensions are particularly suitable for the production of green bodies, preferably by the slip casting process and layers. These green bodies can then be sintered into composite materials with improved mechanical properties.

The aqueous suspensions according to the invention can also be used to produce layers, for example by dipping or knife coating. The layers produced in this way can, for example, protect the wear of metals, ceramics,

Improve cutting, drilling and milling materials. Furthermore, improved corrosion layers can be achieved as a result.

The solvent-containing suspensions are preferably used for pigmenting plastics.

The invention further relates to a process for the preparation of the suspensions according to the invention, which is characterized in that the ceramic according to the invention, coated with α-amino acid, preferably in the form of its powder, is suspended in water and / or one or more organic solvents. In a preferred embodiment of this process, the dispersion is carried out in water, preferably at a pH of 7-10, in particular in the presence of NH ₃ . The dispersion is preferably carried out using the customary apparatuses, such as, for example, rotor-stator mixers, ultrasound devices, jet dispersers or high-pressure homogenizers.

The suspensions containing organic solvents are preferably prepared by adding the organic solvent to the aqueous suspensions and removing the water by suitable methods, for example by distillation.

The invention further relates to a process for the production of ceramic sintered bodies, which is characterized in that the suspensions according to the invention, if appropriate together with other ceramic powders or suspensions, are processed before or after removal of the dispersing medium from water and / or solvent to give green bodies or layers and then sinters.

In this context, further ceramics include, for example, those with particle sizes of up to several μm. Al ₂ O, TiC, SiC and Si ₃ N4 are to be mentioned as ceramics. These ceramic blends are ideal for the production of ceramic sintered bodies or layers.

The ceramic suspensions obtained by the process according to the invention or the dry surface-coated ceramic powders can be used for the production of

Green bodies or sintered bodies or layers can be processed in various ways. For example, extrusion masses can be produced, which can be sintered into finished moldings after extrusion. 20 to 80, in particular 30 to 70 and particularly preferably 40 to 60 parts by weight of the ceramic powder according to the invention (either as such or in the form of a suspension as described above, for example) are usually used per 100 parts by weight of extrusion compositions. sion, 10 to 70, in particular 20 to 60 and particularly preferably 30 to 50 parts by weight of dispersing medium and 0.5 to 20, in particular 2 to 15, particularly preferably 5 to 10 parts by weight of additives which consist of binders, plasticizers and Mixtures of these are used.

The binders and plasticizers mentioned are preferably made from modified celluloses (e.g. methyl cellulose, ethyl cellulose, propyl cellulose and carboxy-modified cellulose), polyalkylene glycols (in particular polyethylene glycol and polypropylene glycol, preferably with an average molecular weight of 400 to 50,000), dialkyl phthalates (e.g. dimethyl phthalate,

Diethyl phthalate, dipropyl phthalate and dibutyl phthalate) and mixtures of these substances are selected. Of course, other binders and plasticizers can also be used, e.g. Polyvinyl alcohol etc.

The above binders and plasticizers are required in order to ensure an extrudable mass and sufficient dimensional stability after shaping.

After thorough mixing of the above components (e.g. in a conventional mixing device), part of the dispersion medium can be removed (preferably under reduced pressure) until the extrusion masses have the desired solids content. Preferred solids contents of the extrusion mass are at least 30 and in particular at least 40% by volume.

Other preferred shaping processes are electrophoresis, slip casting, slip die casting and filter pressing as well as combinations of electrophoresis and slip casting, slip die casting or filter presses; furthermore injection molding, fiber spinning, gel casting and centrifuging. With these shaping processes, compact shaped bodies with high green densities are obtained. It is also possible to use the suspensions for coating purposes. Suitable

Coating processes are, for example, dipping, spin-coating, knife coating, brushing and the Electrophoresis. Metals, ceramics, hard metals, glass and cermets are suitable as substrates.

The green bodies or layers produced can then be dried and subjected to a sintering treatment. It has surprisingly been found that the desired compression takes place at relatively low temperatures. Furthermore, surprisingly, no sintering additives are required. The sintering temperature is usually in the range of 0.4 to 0.6 of the melting or decomposition temperature. This is significantly lower than according to the prior art, where temperatures close to the melting or decomposition temperature, sintering additives and, if appropriate, pressure are usually required.

The ceramic sintered bodies or layers obtained are characterized by a nanoscale structure with a grain size below 100 nm, a density> 95% of theory and high hardness.

The ceramic sintered moldings according to the invention find e.g. Application as

Bulk ceramics e.g. for grinding powder;

Coating material for metals, ceramics and glass for decorative purposes, wear protection, tribological applications, corrosion protection, in particular as a layer on cutting tools and abrasives or grinding powders;

- Component in ceramic / ceramic composites. Al 2 O ₃ , TiC, SiC and Si ₃ N ₄ are particularly suitable as the matrix phase.

Component of nanocomposites;

- Sintering aids for coarser ceramics; Metal / ceramic composites of the hard materials type;

Cermets;

Microporous layers for filtration purposes, e.g. Micro ultra nano filtration and reverse osmosis.

The following examples serve to further illustrate the present invention without, however, restricting it.

Examples

example 1

2 g of L-arginine were dissolved in 250 mL of a solvent mixture of ethanol / water

(1: 1) resolved. 10 g of solid TiN (prepared by the CVR process according to the process according to US Pat. No. 5,472,477 with a primary particle distribution of 0.5 to 30 nm) were added to this solution in portions with thorough mixing (magnetic stirrer). The suspension was heated under reflux at about 90 to 100 ° C for 5 hours (patio heater). The suspension was then over a

Round filter made of cellulose acetate / cellulose nitrate with a pore size of 0.45 μm is suctioned off with a glass frit and washed with deionized water. The filter cake was then dried in a drying cabinet at 70 ° C. for 10 hours.

5 g of the modified TiN powder were taken up with 50 mL water and the pH was adjusted to pH = 9 with dilute ammonia solution. The suspension was then treated with an ultrasound finger for 5 minutes (power: 200 watts).

For particle characterization of the suspension, an aliquot was diluted with the above-mentioned solution and the average particle diameter of TiN was determined by the dynamic light scattering method (scattered light distribution). 145 nm were found. The following values for the mass distribution were determined using the ultracentrifuge (mass distribution) method:

(Note: The primary particles and agglomerates (or aggregates) are to be understood here as particles). Example 2

15 g of solid TiN (prepared by the CVR method, see Example 1, with a primary particle distribution of 0.5 to 30 nm) were added in portions and over a period of time to 150 ml of a 10% strength ammonia solution with intensive mixing (magnetic stirrer) heated at 80 ° C for 2 hours. The suspension was then sucked off through a round filter made of cellulose acetate / cellulose nitrate with a pore size of 1.2 μm using a glass frit. The filter cake was dried in a drying cabinet at 70 ° C. for 10 hours.

The Cl content on the particle surface of the pretreated TiN could be reduced from 2.9 to 0.8 atom%. The analysis was carried out by ESCA (Electron Spectroscopy for Chemical Analysis), using the XPS (x-ray photoelectron spectroscopy) method.

2 g of L-arginine were dissolved in 250 mL of a solvent mixture of ethanol / water (1: 1). 10 g of solid TiN, pretreated by NH ₃ and pretreated according to the above method, were added to this solution in portions with thorough mixing (magnetic stirrer). The suspension was under at 90 to 100 ° C for 5 hours

Reflux heated (patio heater). The suspension was then sucked off through a round filter made of cellulose acetate / cellulose nitrate with a pore size of 0.45 μm using a glass frit and washed with deionized water. The filter cake was then dried in a drying cabinet at 70 ° C. for 10 hours.

5 g of the modified TiN powder were taken up in 50 ml of water and the pH was adjusted to pH = 9 with dilute ammonia solution. The suspension was then treated with an ultrasound finger for 5 minutes (power: 200 watts). For particle characterization of the suspension, an aliquot was diluted with the above-mentioned solution and the average particle diameter of TiN was determined by the dynamic light scattering method (scattered light distribution). 138 nm were found. The following values for the mass distribution were determined using the ultracentrifuge (mass distribution) method:

(Note: The primary particles and agglomerates (or aggregates) are to be understood here as particles).

Claims

claims

1. Non-oxide ceramics from BN or from the group of carbides, nitrides, borides and silicides of the elements, Ti, Zr, Hf, Cr, Mo, W, V, Nb, Ta, Si, Ge and Sn with an average primary particle size of 0 , 1 to 50 nm, the

Surface is covered with at least one α-amino acid.

2. Non-oxide ceramics according to claim 1, selected from the group TiN, ZrN, TiC and SiC.

3. Non-oxide ceramics according to claim 1, selected from the group TiN and TiC.

4. Non-oxide ceramics according to claim 1, characterized in that the surface is coated with arginine.

5. A process for producing non-oxide ceramics according to claim 1, characterized in that a non-oxide ceramic made of BN or from the group of carbides, nitrides, borides and silicides of the elements Ti, Zr, Hf, Cr, Mo, W, V, Nb , Ta, Si, Ge and Sn with an average primary particle size of 0.1 to 50 nm in water and / or an organic solvent at a temperature of 20 to 150 ° C treated with at least one α-amino acid and optionally dried after filtration.

6. Non-oxide ceramics from BN or from the group of carbides, nitrides,

Borides and silicides of the elements Ti, Zr, Hf, Cr, Mo, W, V, Nb, Ta, Si, Ge and Sn with an average primary particle size of 0.1 to 50 nm, which contain -O ^Θ NH4®- Have groups of 50 to 1,000 μeq / g of non-oxide ceramic.

7. A method for producing ceramics according to claim 6, characterized in that at least one non-oxide ceramic made of BN or from the group of carbides, nitrides, borides and silicides of the elements Ti, Zr, Hf, Cr, Mo, W, V, Nb, Ta, Si, Ge and Sn with an average primary particle size of 0.1 to 50 nm treated with an aqueous NH ₃ solution at a temperature of 20 to 150 ° C.

8. suspensions containing at least one non-oxide ceramic according to claim 1 and water and / or organic solvent.

9. A process for the preparation of suspensions according to claim 8, characterized in that the non-oxide ceramic according to claim 1, suspended in water and / or an organic solvent.

10. A process for the production of ceramic sintered bodies and layers, characterized in that the suspensions according to claim 8, optionally together with other ceramic powders or suspensions, are processed before or after removal of the dispersing medium (water and / or solvent) to form green bodies or layers and then sinters.

11. Ceramic sintered body or layers obtainable according to the method of claim 10.