DE19800310A1 - Surface-coated, non-oxide ceramics - Google Patents

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

The invention relates to non-oxide ceramics whose surface with at least an α-amino acid is occupied, a process for their preparation and their Use for the production of ceramic sintered bodies and layers.

According to EP-A 650 945 ceramic powders have already been described for the production of ceramic sintered bodies and layers. However, these have in With regard to their processing properties such as Redispersibility and the product properties of products made from it some disadvantages.

If, for example, suspensions of these ceramic powders are used, so indicate these have a high degree of agglomeration of the primary particles, resulting in high sintering temperatures required to compress the moldings sufficiently.

Non-oxidic ceramics 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 were found, the Surface is covered with at least one α-amino acid.

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

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

The surface-coated, non-oxide ceramics are preferably for powder.  

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 included aliphatic α-amino acids. Arginine, cysteine, Ornithine, citrulline, lysine, aspartic acid and asparagine.

But also aromatic α-amino acids such as tyrosine, in particular L-tyrosine and heterocyclic α-amino acids are 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 method for producing the invention Ceramics, which is characterized in that a non-oxide ceramic 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, in water and / or an organic solvent at a Treated 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 those used in the process according to the invention Non-oxide ceramics can be taken with the help of electron micrographs be determined. 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 one spherical structure. They can also be in the form of their agglomerates or aggregates are present, these having an average particle size of less than 500 nm, preferred have less than 150 nm.

The non-oxide ceramics to be used can be crystalline or amorphous, preferably crystalline. For example, you can use the method described in US-A-5,472,477 (≘ DE-A 4 214 719) can be obtained. It is preferred the CVR (chemical vapor reaction) process is used, with which particles with a very narrow size distribution without oversize and with high purity to let.

Characteristic of the non-oxide ceramics thus produced, preferably in Form of their powder, is the complete absence of individual particles (primary particles), which are much larger than the average particle size. So point the powder preferably less than 1% individual particles that are more than 20% of the middle Particle size differ; Particles that deviate more than 50% are practically not available.

The non-oxide ceramics used in the process according to the invention can either in the form of their primary particles, agglomerates or aggregates of Primary particles or mixtures of the two are present. As agglomerates or Aggregates are understood to be particles in which several primary particles are van-der- Waals forces interact with each other, or in which the primary particles by surface reaction or "sintering" during the manufacturing process are interconnected.  

The non-oxide ceramics used can have extremely low oxygen levels of less than 10 wt .-%, based on the solid, preferably <1%, esp which preferably have <0.1%.

Their high purity and surface purity are also characteristic. Conditionally Due to the manufacturing process, the non-oxide kerami to be used be very sensitive to air or even pyrophoric. To eliminate this property gene, the non-oxide ceramics before use in the fiction procedures in a defined manner by exposure to gas / steam mix surface modified or oxidized or passivated.

Particularly preferred non-oxidic ceramics are used in the method according to the invention, which have a content of -O ^⊖ NH ₄ ^⊕ groups of 50 to 1000, preferably from 50 to 500, in particular 100 to 500 µeq / g of non-oxide ceramic.

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 ^⊖ NH ₄ ^⊕ groups of 50 to 1000 µeq / g of non-oxide ceramic.

The NH ₄ ^⊕ groups are preferably on the surface of the ceramics.

The ceramics ^{according to the} invention, ie both the -O ^⊖ NH ₄ ^⊕ group-containing and the α-amino acid-containing, also preferably have a Cl content of less than 1 atom%, based on all atoms which are in a 5th nm thick surface layer of the ceramic particles.

A correspondingly thick outer particle layer can, for example, by means of ESCA (Electron Spectroscopy for Chemical Analysis) are examined, especially after the XPS process (X-ray photoelectron spectroscopy).  

The -O ^⊖ NH ₄ ^⊕ groups can be prepared, 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 ^⊖ NH ₄ ^⊕ amount after the ammonia treatment is correspondingly large.

The invention therefore further relates to a process for the preparation of ceramics containing -O ^⊖ NH ₄ ^⊕ groups, which is characterized in that at least one 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 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, if appropriate under pressure, treated.

The ceramics used for this treatment are preferably according to the CVR Process, for example analogous to the process described in US Pat. No. 5,472,477, been obtained.

In the CVR process, gaseous starting materials, for example TiCl ₄ and NH ₃ for the production of TiN, are reacted in a reactor. The products are created with the exclusion of wall reactions. The process in a tubular reactor with laminar flow of starting materials and products is particularly advantageous.

The starting materials are generally in coaxial partial flows into the reactor brought in. To mix them, an interference body is preferred in the otherwise strict laminar flow built in; this defines one in intensity and broadening Karman vortex street in which the mixing takes place.  

In order to achieve the energetically highly preferred separation of the reactants on the To prevent the reactor wall, the reaction medium is preferred by an inert shielded 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 with the following equipment possible: fluid bed dryer, paddle dryer, spray dryer, drying cabinet and Vacuum dryer.

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

If the process according to the invention for producing the α-amino acid-coated ceramics takes place in an organic solvent or solvent mixture, suitable organic solvents are: aliphatic C ₁ -C ₄ alcohols, such as methanol, ethanol, isopropanol, n-propanol, n- Butanol, isobutanol 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, trimethylolpropane, polyethylene glycol with an average molecular weight of from 400 to 1500, preferably from 400 to 1500 to 4000 g / mol or glycerol, monohydroxy ether, preferably monohydroxyalkyl ether, particularly preferably mono-C ₁ -C ₄ alkyl glycol ether such as ethylene glycol monoalkyl, monoethyl, diethylene glycol monomethyl ether or diethylene glycol monoethyl ether. Diethylene glycol monobutyl ether, dipropylene glycol monoethyl ether, thiodiglycol, triethylene glycol monomethyl ether or monoethyl ether, furthermore 2-pyrrolidone, N-methyl-2-pyrrolidone, N-ethyl-pyrrolidone, N-vinyl-pyrrolidone, 1,3-dimethyl-imidazolidone and dimethylformamide. Mixtures of the solvents mentioned are also suitable.

The process according to the invention is preferably carried out at a temperature of 60 ° C. up to the boiling point of the solvent system used at normal pressure. It is particularly preferred to work under reflux. At higher temperatures the process can also be carried out under 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.

Wet grinding can also be carried out before or during the process according to the invention the ceramic to be used 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 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, for example by means of a homogeneous grinding suspension Agitator bucket, dissolver and similar units if necessary after a Pre-shredding chipped (i.e. introduced and homogenized).

The grinding suspension can also contain proportions of low-boiling solvents (boiling point <150 ° C), which may occur in the course of a subsequent Fine grinding can be carried out by evaporation. But it can also Proportions of higher boiling solvents or other additives, e.g. B. grinding aid, Ent foaming or wetting agents.

The wet crushing of the ceramics to be used includes both the pre-crushers reduction as well as fine grinding. The suspension concentration is preferably tration above the desired concentration of the finished preparation. The  Desired final solids concentration is preferably after the Wet shredding set. After the pre-shredding there is a Grinding to the desired fine particle distribution. Come for this grind Aggregates such as B. kneaders, roller mills, kneading screws, ball mills, rotor Stator mills, dissolvers, corundum disk mills, vibratory 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. B. be steel. The Milling temperature is preferably in the range of 20 to 150 ° C, but usually at room temperature, possibly below the cloud point of the given if additionally used surface-active compounds as dispersants (Grinding aid).

The α-amino acid is preferably in an amount of 0.1 to 20 wt .-%, based on the amount of ceramic used. Is particularly preferred an amount of 1 to 10% by weight.

Any excess α-amino acid can, for example, according to the inventions process according to the invention by filtration from the surface-coated ceramic be separated.

Excess α-amino acid can also be centrifuged, for example Suspension and then decanting off the supernatant are separated. Membrane or microfiltration processes can also be considered.

The still moist obtained by the process according to the invention, i. H. water or Solvent-dampened surface-covered ceramics are then ge dries. Drying temperatures of 20 to are preferably used 150 ° C, especially 50-120 ° C, with the application of vacuum also an advantage can be.  

Drying is generally done using conventional drying apparatus such as paddle dryers, drying cabinets, spray dryers, swirls bed dryer 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 Powder before.

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

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

The suspensions according to the invention preferably contain 5 to 50% by weight, ins particularly 10 to 35% by weight, based on the suspension, of the invention 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.

Other additives include, for example, cationic, anionic, amphoteric and / or nonionic dispersants in question, for example those that in Surfactants Europe, A Directory of Surface Active Agents avanlable in Europe (Edited by Gordon Hollis, Royal Society of Chemistry, Cambridge (1995) are listed as well as 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. This  aqueous suspensions are particularly suitable for the production of green bodies, preferably using the slip casting method and layers. This green Bodies can then be made into composite materials with improved mechanical Properties are sintered.

With the aqueous suspensions according to the invention, layers, for example, be produced by dipping or doctoring. The so produced Layers can protect metals, ceramics, Improve cutting, drilling and milling materials. This also improves them Corrosion layers reachable.

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

The invention further relates to a method for producing the invention Suspensions, which is characterized in that the inventive, with α-amino acid-coated ceramic, preferably in the form of its powder, in Suspended 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 usual apparatuses such as, for example, rotor-stator mixers, ultrasound devices, jet dispersers or high-pressure homogenizers.

The suspensions containing organic solvents are preferably so prepared that the organic solvent added to the aqueous suspensions and the water by suitable methods, for example by distillation Will get removed.

The invention further relates to a method for producing ceramic sinter body, which is characterized in that the Suspen invention  sions together with other ceramic powders or suspensions or after removing the dispersing medium from water and / or solvent into basic bodies or layers, processed and then sintered.

Other ceramics in this context include, for example, those with particle sizes of up to several μm. In particular, Al ₂ O ₃ , TiC, SiC and Si ₃ N _{4 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 in various ways be working. For example, extrusion masses can be produced according to the Extrusion can be sintered into finished moldings. Here are usually 20 to 80, in particular 30 to 70, per 100 parts by weight of extrusion compositions and particularly preferably 40 to 60 parts by weight of the ceramic according to the invention powder (either as such or in the form of a Sus pension, 10 to 70, in particular 20 to 60 and particularly preferably 30 to 50% by weight Parts of dispersing medium and 0.5 to 20, in particular 2 to 15, particularly preferably 5 up to 10 parts by weight of additives consisting of binders, plasticizers and mixtures of which are used.

The binders and plasticizers mentioned are preferably made from modified graced celluloses (e.g. methyl cellulose, ethyl cellulose, propyl cellulose and carboxy modified cellulose), polyalkylene glycols (especially polyethylene glycol and Polypropylene glycol, preferably with an average molecular weight from 400 to 50,000), dialkyl phthalates (e.g. dimethyl phthalate, diethyl phthalate, Dipropyl phthalate and dibutyl phthalate) and mixtures of these substances elects. Of course, other binders and plasticizers can also be used be such. B. polyvinyl alcohol etc.  

The above binders and plasticizers are needed to make an extrusion capable mass and sufficient dimensional stability after shaping guarantee.

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

Other preferred shaping processes are electrophoresis, slip casting, the slip casting and filter pressing as well as combinations of electrical phoresis and slip casting, slip die casting or filter presses; also the spray casting, fiber spinning, gel casting and centrifuging. With this shaping compact molded bodies with high green densities are obtained. Likewise it is possible to use the suspensions for coating purposes. Suitable Coating processes are e.g. B. diving, spin coating, knife coating, brushing and the Electrophoresis. As substrates come e.g. B. metals, ceramics, hard metals, glass and cermets in question.

The green bodies or layers produced can then be dried and one Undergo sintering treatment. It has surprisingly been shown that the desired compression takes place at relatively low temperatures. Furthermore, surprisingly, no sintering additives are required. The sintered temperature is usually in the range of 0.4 to 0.6 of melting or decomposition temperature. This is significantly lower than in the prior art, where usually temperatures close to the melting or decomposition temperature, sinter additive and possibly still pressure are 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 the Theory and a high hardness.  

The ceramic sintered molded body according to the invention find z. B. Application as

• - Bulk ceramic z. B. for abrasive 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;
• - hard material type metal / ceramic composites;
• - cermets;
• - Microporous layers for filtration purposes, e.g. B. Micro Ultra Nano Filtration and reverse osmosis.

The following examples serve to further explain the present invention, but without restricting it.

Examples example 1

2 g of L-arginine were dissolved in 250 mL of a solvent mixture of ethanol / water (1: 1) dissolved. 10 g of solid TiN (prepared according to CVR Ver drive according to the method of US-A-5 472 477 with a primary particle distribution from 0.5 to 30 nm) in portions with intensive mixing (magnetic stirrer) added. The suspension was refluxed at about 90 to 100 ° C for 5 hours heated (patio heater). The suspension was then removed using a round filter Cellulose acetate / cellulose nitrate with a pore size of 0.45 µm with a glass frit suctioned off and washed with deionized water. Then the filter Cake dried in a drying cabinet at 70 ° C for 10 hours.

5 g of the modified TiN powder were taken up in 50 mL water and the pH is adjusted to pH = 9 with dilute ammonia solution. Subsequently the suspension was 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:

Example 2

150 ml of a 10% ammonia solution were mixed thoroughly (Magnetic stirrer) 15 g solid TiN (manufactured according to the CVR process, see example 1, with a primary particle distribution of 0.5 to 30 nm) added in portions and Heated at 80 ° C for a period of 2 hours. Then the Suspension over a round filter made of cellulose acetate / cellulose nitrate with a Aspirated pore size of 1.2 microns with a glass frit. The filter kitchen turned 10 Dried in a drying cabinet at 70 ° C for hours.

The Cl content on the particle surface of the pretreated TiN rose from 2.9 0.8 atomic% can be reduced. The analysis was carried out by ESCA (Electron Spectros copy for Chemical Analysis), according to the XPS (x-ray photoelectron spectroscopy).

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 by NH ₃ above, 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 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 is adjusted to pH = 9 with dilute ammonia solution. Subsequently the suspension was 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:

Claims (11)

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 upper surface is occupied by 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 of which is covered with arginine. 5. A method 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 a medium Primary particle size from 0.1 to 50 nm in water and / or an organic Solvent at a temperature of 20 to 150 ° C with at least one Treated 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 have a content of -O ^⊖ NH ₄ ^⊕ groups of 50 to 1000 µeq / g of non-oxide ceramic. 7. A process for the production of 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 method for producing suspensions according to claim 8, characterized characterized in that the non-oxide ceramic according to claim 1, in Suspended water and / or an organic solvent. 10. A process for the production of ceramic sintered bodies and layers, thereby characterized in that the suspensions according to claim 8, if appropriate together with other ceramic powders or suspensions, before or after Remove the dispersing medium (water and / or solvent) to green bodies or layers processed and then sintered. 11. Ceramic sintered body or layers obtainable according to the procedure below Claim 10.