HU192712B - Process for preparing ceramic bodies of fine crystalline structure - Google Patents

Abstract

In the process of the present invention ceramic bodies are produced by activating and shrinking oxygen-containing inorganic aluminum compounds, preferably aluminum hydroxide, boehmite, gamma-aluminum oxide, or alpha-aluminum oxide or mixtures thereof. The invention is characterized by the addition of 0.05 Ό, 5 wt% yttrium oxide or lanthanum oxide, or neodinyl oxide or an equivalent amount of alumina, as an additive, to the oxide of the invention by heating to oxide. the mixture is homogenized by grinding and heat-treated at a temperature of at least 1450 ° C. Thus, at least 80 wt.% of the additives are reacted with the aluminum oxide, and then the two or three kinds of alumina oxides activated in this way are mixed and the resulting mixture of pure oxides, expressed as total of 0.1-1 wt. the finished ceramic materials are transformed into mold bodies in a manner known per se, and are subsequently shrunk at temperatures above 1450 ° C. -1-

Description

FIELD OF THE INVENTION The present invention relates to a process for the production of ceramic bodies having a fine crystalline tissue structure of 99 to 99.9% by weight, having a fine crystalline tissue structure, having a long life and high reliability, an aluminum compound, preferably aluminum hydroxide, boehmite, gamma-alumina oxide or a mixture thereof by activation and shrinkage with additives. The ceramic bodies produced in accordance with the present invention are used primarily in fields related to oil mining.

It is known from alumina ceramic manufacturing technology that the higher the temperature required to compact the crude body, the clearer and coarser the crystalline granular material is, the easier it is to sinter, if it contains many useful additives and the specific surface area of the powder to be shaped. In addition, the calcination temperature of the raw material, the quality of the impurities and additives, the starting density, the gas atmosphere of the furnace, the sintering time, etc. must be taken into account. too.

Of course, the specific surface area of the base material cannot be increased at will. On the one hand, this is limited by the efficiency and aggregation of the milling equipment and, on the other hand, it is very difficult to form thick-walled bodies from too fine powder, since they can easily crack due to sintering of about 20% during sintering.

It is also known that shrinkage results in a grain size increase of about ten times as a function of temperature, which mainly reduces the mechanical strength and abrasion resistance of the ceramic body, although fine crystalline ceramics having an average particle size below 10 µm have the most excellent properties.

In all these, the ceramic manufacturers help by first calcining the raw materials to compact the granules, and then refining the coarser material by adding an additive that inhibits the growth of shrinkage during the shrinkage.

Such processes are described, for example, in U.S. Patent Nos. 3,377,176 and 4,174,973. U.S. Patent No. 1,264,914; British Patent Specification. It is known to inhibit particle size growth by the addition of a few tens of percent magnesium oxide and yttrium oxide.

The grinding of the above additives is also recommended by Búron [Amer. Ceram. Bull., 61 (2), 221 (1982)], however, these additives do not reduce the shrinkage temperature to below 1700 ° C, which would otherwise be desirable.

Various additives have been used by Abraham et al., Cercel Metall. Inst. Bucharest, 20, 505 (1979)]: magnesium oxide, titanium dioxide, chromium (III) oxide, manganese (II) oxide and nickel (II) oxide were ground to alumina, but at high temperatures, They had to undergo sintering at 1750 ° C for 6 hours.

A more homogeneous tissue ceramic may be obtained by adding magnesium other water-soluble compound to the alumina instead of the commonly used magnesium oxide, preferably prior to calcination, thus suggesting the use of magnesium nitrate solution in Shaw, Brit. Ceram. Trans. J., 83 (5), 138 (1984)] and Ikegami (J. Amer. Soc., 67 (3), 174 (1984)]. No. 172,193. According to the Hungarian patent, ultrafine alumina is produced by heat treatment of a solution containing a small amount of magnesium sulfate and a large amount of aluminum sulfate. Although the effect of the magnesium oxide thus obtained by heat treatment is more favorable, the shrinkage temperature remains too high.

Various additives have been used to reduce the shrinkage temperature, such as the sintering of formula 13ΒεΟ.7Υ2θβ [163,704; Hungarian Patent Specification]; titanium dioxide (Bruch, J. Amer. Ceram. Soc., 55 (2), 114 (1972)] or 1% tantalum (V) oxide, magnesium oxide and nickel (II) oxide (Coble, Amer. Ceram. Soc. Abstr., 225, 1983].

The shrinkage temperature can be reduced to 1400-1600 ° C by the simultaneous addition of 2% by weight of titanium dioxide and 2% by weight of manganese (II) oxide or by addition of 3-6% by weight of silicate, in particular talc, cordierite or amortite. However, the properties of the ceramic so produced depend on many other materials already present. This may be advantageous in some cases, such as the easier metallization or economical production of alumina-based ceramics, but does not allow the production of high purity alumina ceramics.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a process that allows the production of ceramics consisting of at least 99% by weight of alumina by relatively low temperature sintering using a minimum amount of grain size inhibiting and shrinkage enhancing additive.

It has been found that the above object is achieved by providing 0.05-0.5% by weight of yttrium oxide or an equivalent amount of the yttrium salt to be converted to the oxide to be heated to the alumina compound (s) which is the base material of the ceramic bodies. the mixture is preferably homogenized by milling and then calcining with at least 80% by weight of yttrium oxide with alumina and / or 0.05Ό of the same or different aluminum compound (s), expressed as alumina, 5% by weight of lanthanum oxide or an equivalent amount of lanthanum salt which can be converted to heating oxide, is conveniently homogenized by milling and then calcined with at least 80% by weight of lanthanum oxide and / or the same or different alumina compounds. can be exceeded for compounds in alumina 0.05-0.5% by weight of neodymium oxide or equivalent neodymium salt which can be converted to neodymium oxide by heating, preferably by homogenization of the mixture by milling, followed by calcination of at least 80% by weight of neodymium oxide. then mixing the two or three kinds of alumina activated in this way and milling the resulting blend containing 0.1 to 1% by weight of the additive, expressed as pure oxides, to form the finished ceramic base into molds known per se. and finally shrink at temperatures above 1450 ° C.

The invention is based on the discovery that a much more advantageous material for ceramic purposes is obtained by grinding the anti-shrinking additive and recrystallization additives not into the already "over-burned alumina", but before the final heat treatment and perform heat treatment that modifies the granules, causing the change of the granules.

The present invention is based on the further discovery. that the beneficial effect of the invention can be achieved only if the anti-particle growth and shrinkage additives are added separately to the aluminum compound and the mixture of aluminum compound and a given additive is subjected to separate calcination. That is, as many types of additives are processed, so many activated alumina are produced and subsequently milled in the desired proportions to form a finely divided ceramic base ready for molding.

The present invention is also based on the discovery that trivalent rare earth metal compounds having an ion beam compatible with aluminum ion beam can be advantageously used to inhibit particle growth and to promote recrystallization so that oxides of these rare earth metals are stably incorporated into the oxide of the alumina. Under the conditions of the process of the present invention, these rare earth oxides have a significant effect on the shrinkage behavior as well as the final properties of the finished polycrystalline woven ceramic, even in the tens of percent by weight.

Preferred aluminum compounds in the process of the present invention are aluminum hydroxide [Al / OH / g], boehmite [A10 / OH /], gamma-modified alumina [Al2O3] formed at temperatures below 1000 [deg.] C. or 1300-1500 [deg.] C. temperature-reactive, alpha-alumina reactive. Use a mixture of several aluminum compounds.

It is particularly preferred to use a pre-calcined alpha-alumina at 1300-1500 ° C.

The additive is yttrium oxide [Υ 2θ 3 ′ 24 24 2415 ° C] and / or lanthanum oxide [La ₂ O ₃ , op. 2307 ° C and / or neodymium oxide [Nd ₂ O ₃ , m.p. 2272 ° C], which upon heating react with aluminum compounds such as gamma and / or alpha alumina [Α ^ Οβ, m.p. 2040 ° C]. However, instead of the above oxides, yttrium, lanthanum and neodymium salts, such as sulfates, which are converted to oxides upon heating, may be used. The metal salt may also be added to the aluminum compound in aqueous solution.

0.05 to 0.5% by weight, preferably 0.2% by weight, of yttrium oxide, or an equivalent amount of the yttrium salt, which can be converted to oxide by heating, for the above-mentioned aluminum compound or mixture of aluminum compounds, based on the pure aluminum oxide content. the mixture is homogenized, preferably by grinding, and then generally calcined at 1500-1600 ° C until at least 80% of the yttrium oxide has reacted with the alumina. In our experience, this requires a heat treatment of at least 4-6 hours for the pre-compacted powder. As a result of the solid phase reaction, compounds YAIO3 and Y3AI5O12, m.p. 1860-1930 ° C, are formed, which are incorporated finely in alumina. In this way, the present specification provides calcined alumina, designated "Type A", which is fine-grained, since the introduced yttrium oxide exhibits an anti-particle growth inhibitory effect on both this calcination and subsequent color shift. In our experience, this effect may be enhanced by the presence of a small amount of magnesium oxide.

0.05 to 0.5% by weight, preferably 0, based on the pure alumina content, of the same or different aluminum compound or aluminum compound mixture as the starting aluminum compound or aluminum compound mixture used to produce the type A alumina. 3% by weight of lanthanum oxide or an equivalent amount of lanthanum salt which can be converted to an oxide by heating at a temperature of at least 1450 ° C is then followed in a similar manner to the preparation of type A alumina. In this case, the active compound, AlgLaOg, with a melting point of 1830 ° C, which is homogeneously distributed in the alumina, is formed, which greatly facilitates the shrinkage. The resulting calcined alumina is referred to herein as "B-type alumina".

For the same or different alumina compound (s) as used in the preparation of the alumina type A or type B, 0.05-0.5% by weight based on the pure alumina content, preferably 0.3% by weight of neodymium oxide, or an equivalent amount of neodymium salt that can be converted to heat oxidation, is added followed by a procedure similar to that used for the preparation of type A alumina. During calcination, the active compounds described by the formulas AlNdO2 and AlgNd20jj, m.p. 1750-2050 ° C, are formed which both promote shrinkage and inhibit grain growth. The resulting calcined alumina is referred to herein as "C-type alumina".

According to the present invention, at least two of the resulting Α, B and C alumina oxides are mixed in such a proportion that the total amount of additives, expressed as pure oxides, is 0.1 to 1% by weight. Thus, a mixture of type A + B, A * C, B + C or típusú * B + C is prepared, preferably by grinding, and then the powder-35 mixture is ground to dry granulation by wet or dry milling. Grinding preferably produces a powder mixture in which 90-95% by weight of the particles are smaller than 4-6mm, and within that 50% of the particles are less than 1-3mm, preferably less than 1mm.

The powder blend thus obtained is shaped in a manner known per se, for example by injection molding, extrusion, molding, extrusion, etc., and then compacted at a temperature of 1460-1700 ° C, preferably 1550 ° C, for 2-10 hours, usually 4 hours. Typically, heating is carried out at 100-300 ° C / hour.

The parameters used for sintering are chosen depending on the chemical composition of the powder mixture, the starting raw density, the size of the shaped bodies and the wall thickness, preferably using an oxidizing atmosphere, i.e., shrinking in the presence of air.

The speed of these second solid phase reactions during compression heat treatment (color deflection) is ultimately determined by the temperature, time, etc. employed. in addition, the metal oxides of different melting points and affinities and their lower melting point compounds formed during calcination are determined by the rate at which they undergo a complex mechanism. Meanwhile, the compounds with lower melting point are gradually "enriched" in the crystal lattice, with a large excess of alumina, while the volume of the shaped body is reduced. Since the reactions in this system proceed over time as the temperature rises, the linear shrinkage of the molded body by about 15-17% is gradual, which prevents cracking of the ceramic, which is very advantageous. This is further facilitated by the lower shrinkage of the additives! also lower thermal expansion due to temperature.

In addition, simple or complex shaped bodies can be produced economically using known ceramic manufacturing equipment.

Generally, ceramics made using different grades of aluminum compounds and additives are more suited to a specific application. Thus, products made from A + B blends exhibit high reliability in electronic, electrical, A + C blends with primarily high mechanical and wear resistance, while B + C blends have outstanding thermal and chemical properties. For A + B + C blends, the lowest temperature shrinkage is obtained, which is mainly large in complex shape. it is advantageous for the production of deeply shaped or threaded, smooth-surface shaped bodies.

In the practice of the present invention, U.S. Pat. The treatment disclosed in Hungarian Patent No. 5,198,123, according to which after calcination in the presence of a small amount of an aqueous solution of aluminum sulphate, the alumina powder remains loose in structure and very easily milled to a fine grain. 165 357 pages are also useful. It is also a process for polyisobutylene stamping aids according to Hungarian Patent Application No. 4,600,12, which enables to produce a bulk density of about 2.4 g / cm ^{3 at} low specific pressures.

Other known additives for the production of ceramic products with special properties may also be used in the process of the invention. Thus, silicate for promoting the metallization and solderability of alumina ceramics [177,450]. zirconium oxide, chromium oxide to enhance heat shock resistance, or metal chromium, cobalt, etc. to enhance impact resistance and high temperature variations. with the so-called cermets can also be made.

The invention is illustrated in detail by the following examples:

Example 7 (Mixture A + B)

A corundum ball mill is weighed with 998 g of alumina equivalent to 1557 g of technical grade aluminum hydroxide [Al / OH / g] dried to constant weight. 4.2 g of technical grade yttrium sulfate [Yg / SO2 / g], equivalent to 2 g of yttrium oxide, are separately weighed, and then a saturated aqueous solution is prepared at room temperature, and the aluminum hydroxide solution is poured together for 2 hours. The semi-dry powder is then calcined at 1500 ° C for 3 hours by heat treatment. The activated alumina (type A) thus activated is subjected to fine grinding as described below.

997 g of aluminum hydroxide of the same quality as the above grade are also weighed into a mill with corundum balls. 3 g of technical grade lanthanum oxide (LagOg) having an average particle size of less than 1 µm (95%) are weighed and preferably calcined in a dry medium at 1500 ° C for 4 hours after homogenization.

500 g of the thus obtained activated alumina (type B) is ground with 500 g of the above type A alumina, preferably in a corundum ball mill, in a dry medium such that 95% of the particle size is / im, within which 50% should be less than 2mm.

After sieving, the mill is molded in a known manner by paraffin injection molding, and the corpuscles are then fractured in an air (oxidizing) atmosphere at 1550 [deg.] C. for 8 to 10 hours after demineralization.

The ceramics thus prepared, having a nominal content of 99.5 wt% ^Al 2 ° 3 '0.2 wt% YgOg and 0.3 wt% LagOg, had a density of 3.92 g / cm ³ and a water uptake of 0% (fuchsin test negative). . Bending strength 400 MPa. The dielectric loss coefficient at 10 MHz, measured at 20 ° C, is 2-4 x 10 4, while the dielectric constant is 9.2. Electrical insulation resistance: 20 kV / mm. The average particle size of the ceramic (measured by microscopic images) is 4.6mm, the surface roughness (based on talysufr measurements) R _a = 3 µm. Rockwell hardness: 82.

-4Ί

Uses: mainly for electrical insulation applications, eg as high frequency coil body, heating element holder, terminal block, earth conductor.

Example 2 (Type A + C mixture)

Weigh into a mill containing corundum cores 997 g of alumina equivalent to 1525 g of dried technical grade aluminum hydroxide and 3 g of neodymium oxide with a particle size of less than 95%, on average, and after 2 hours of homogenization Stir at ca. 1500 ° C for 4 hours.

100 g of activated alumina (type C) thus prepared are weighed into a mill, 500 g of alumina type A prepared according to Example 1 are weighed and the powder mixture is finely ground as described in Example 1.

Subsequently, the stock is poured into gypsum by casting with an aqueous medium, and after drying at 1650 ° C in an air atmosphere, depending on the size and thickness of the moldings, is heat-shrunk for 6-10 hours.

The resulting nominally 99.7% by weight of ^ Oj, 0.2 wt% for ^ O ^ and 0.06 wt% Υ2θ3 ^{reserve lN} IU ceramics density of 3.94 g / cm ^third Water uptake: 0% (fuchsin test negative). Bending strength: 420 MPa. Hardness: Mohs 9. Average particle size 5.4 µm.

Application: for applications with high strength and high abrasion resistance, for example as press pad, pressure plate, slide bearing, petroleum sludge and slurry pump element, sandblasting nozzle, etc.

Example 3 (B + C mixture)

997 g of calcareous alkaline-poor alumina "G" (Almásfüzitő Alumina Factory), calcined at a temperature of up to 1300 ° C, are charged into a mill with corundum balls. 3 g of lanthanum oxide with a particle size of less than 1 µm (95% average) were added and calcined by heat treatment (type B) for 4 hours.

In parallel, 997 g of alumina G were weighed and 3 g of neodymium oxide having a particle size of less than 1 µm (95%) were added and then ground and calcined (type C).

After cooling, the alumina, activated in both ways, is milled in a 1: 1 weight ratio so that 95% of the particles are on average below 5 µm, and within that 50% are below 1-2 µm.

The mill is molded with paraffin injection molding, decaffeinated and finally compacted in an atmosphere of air at 1500 ° C for 10 hours or at 1600 ° C for 4 hours.

The ceramics thus prepared having a nominal density of 99.4% by weight of Α ^ Οβ, 0.3% by weight and 0.3% by weight of Ι ^^ ^β have a density of 3.9 g / cm ³ . Water uptake: 0%. Bending strength: 400 MPa. Softening point: 1740 ° C. Average particle size: 5.7 µm.

Their use is mainly related to thermotechnical applications such as laboratory and semi-industrial incandescent crucibles, jar covers, furnace washers, electric filament holders, plasmators, etc.

Example 4 (Type A + B mixture)

999.5 g of alumina, calcined at a temperature of up to 1100 ° C, containing 99.99% by weight of Al 2 O and up to 0.002% by weight of alkali (SZIKKTI, Budapest) is charged to a mill with high purity corundum. Separately weighed 1.1 g of yttrium sulphate equivalent to 0.5 g of yttrium oxide, prepare a solution saturated with distilled water at room temperature and add to the weighed alumina. Subsequently, the mixture was homogenized for 1 hour. The semi-dry powder is sieved and then calcined in an incinerator under air atmosphere at 1500 ° C for 3 hours (Type A).

At the same time, 999.5 g of high purity alumina is weighed into a grinding mill and a solution of 0.9 g of lanthanum sulphate [La2 / 10SO / 3] equilibrated in water equivalent to 0.5 g of lanthanum oxide is prepared. . It is homogenized by casting on alumina or calcined as above (type B).

The alumina activated by the two types of additives is ground in a weight ratio of 1: 1, so that 95% of the particles are below 4-5 µm and within that 40-50% are below 1 µm.

The powder mixture thus obtained is known by dry polyisobutylene dry compression. U.S. Patent No. 4,194,198, and then compacted to a solid temperature in an atmosphere of air at 1680-1700 ° C for 2-3 hours.

The so-called. high purity shaped bodies with a nominal Α ^ Οβ content of 99.9% by weight, 0.05% by weight of Y2O1 and 0.05% by weight of Ε3β0β. Density: 3.96 g / cm ³ , Water uptake: 0%.

Bending strength: 420 MPa. Dielectric loss factor at 10 MHz at 20 ° C: 1x10 ⁴ , 9.6 GHz: 7x10 4. Dielectric constant: 9.8. Specific (volumetric) resistance at 100 V at 20 ° C: 10 ^ Ohm.cin, surface resistance: 10 ^ Ohm, cm ² . The average particle size of the ceramic is 7.2 / y. Surface roughness, R _a = 4.8 which. Rockwell hardness: 90.

Applications: primarily for microelectronic applications, for low and high frequency applications, for high reliability, active and passive insulation applications, such as thin-layer integrated circuit board in polished finish, tunable URH coil body, computer remover, and for applications where increased ceramic wear is desired such as wire drawing caliber, cutting stone, or due to its softening at temperatures above 1800 ° C, melting crucible for high purity metals, cathode ceramic for electron beam welding, etc.

Example 5 (A + C mixture)

995 g of alumina "G" calcined at 1300 ° C are weighed into a corundum ball mill, 4 g of technical grade yttrium oxide and 1 g of technical magnesium oxide (MgO) are added. The powder mixture is milled, preferably in a dry medium, so that 90% of the particles are below 5 µm and within that 50% are below 2 µm. After sieving, it is calcined at 1500 ° C for 4 hours and the resulting alumina (type A) is processed as follows.

In parallel, 995 g of gamma-alumina and 5 g of technical grade neodymium oxide are annealed at a temperature of up to 1000 ° C. The powder mixture is ground and calcined as above.

The resulting alumina (type C) is ground in a 1: 1 weight ratio, preferably in aqueous medium, to the type A alumina so that 95% of the particles are

5 to 6 µm, and within that 50% should be below 3 µm.

The suspension is poured into a suitable gypsum mold in a known manner in the presence of a surfactant, dried after removal and finally compacted at 1480-1500 ° C in an atmosphere of air for 8-10 hours.

The ceramics thus prepared have a nominal A ^Oj content of 99% by weight, 0.4% by weight Υ2θ3> θΊ% by weight MgO and 0.5% by weight Ν02θβ. Density: 3.90 g / cm ³ , Water uptake: 0%, Bending strength: 400 MPa. Average particle size · 4.5 µm. Surface roughness, R _a = 3.3 µm.

Applications: textile fiber guide, brick puller, glass cutting body, chemical pump element and valve seat, etc.

Example 6 (B + C mixture)

A corundum ball mill is charged with 996 g of alumina equivalent to 1172 g of technical grade dried boehmite [A10 / OH]. Separately, 13.6 g of technical grade lanthanum nitrate [La / NO2] equivalent to 4 g of lanthanum oxide are weighed to form a saturated aqueous solution at room temperature. This is added to the weighed buhmith and homogenized for 2 hours.

The semi-dry powder is then placed in an incandescent bag and calcined in an atmosphere of air at 1600 ° C for 3 hours. and the resulting alumina (type B) is used as follows.

mill separately was charged with 996 g of not more than 1500 ° C fired ,, G, ceramic aluminum oxide, and was poured into 4 g of neodymium oxide equivalent, 16.7 g technical grade neodymium nitrate [Nd / NO _3/3] at room temperature with saturated aqueous solution of and subjected to homogenization for 2 hours. At the end of this, the wet powder is calcined at 1600 ° C for 3 hours in an incubator.

The thus prepared (type C) active alumina is ground in a ratio of 1: 1 by weight with the above (type B) activated alumina, such that the average particle size is 95% for 5 min and 50% for 2%. below mm.

Subsequently, the finely ground powder mixture is prepared by extrusion to form forine bodies and after drying at a temperature of 1480-1500 ° C.

preferably suspended in heat for 6 to 10 hours to provide air (oxidizing) atmosphere in the furnace.

The shaped bodies produced in this way have a nominal A 2 O content of 99.2%, 0.4% and

0.4% by weight with Ν02θ3. Density: 3.90 g / rn ³ , water uptake: 0%. Bending strength: 400 MPa. Softening point: 1720 ° C. Average particle size: 4.2 nm. The applications are mainly related to thermotechnical applications such as capillary pyrometer and tube, glow tube, furnace rails, and also in chemical industry as acid-proof piping, stir bar and stem, sealing rod, etc.

Example 7 (A + B + C mixture)

497 g of technical grade gamma alumina and 3 g of technical grade yttrium oxide with a grain size of 1 µm were weighed into a corundum ball mill and calcined at 1500 ° C for 3 hours (type A) after homogenization.

495.5 g of technical grade gamma alumina are weighed twice and then 4.5 to 4.5 g of lanthanum oxide and neodymium oxide having an average particle size of 4.5 µm are added. The powders are calcined separately (type B and type C, respectively).

The cooled 3x500 g powder is finely ground in a corundum ball mill to give an average particle size of 90% below 5 µm and within 50% below 11-2λιπι.

One part of the mill is known to be molded by isostatic molding and the other part is formed by injection molding to form more complex shaped bodies and then, after pre-firing, is densely compacted in an air atmosphere oven at 1460-1500 ° C for 6-10 hours.

The ceramic bodies produced in this way have a nominal A ^ Oytartalina of 99.2 wt%, 0.2 wt% ^ 2θ3 'θ'3 wt% Nd, Ο ^ and 0.3 wt% lanthanum oxide. Density: 3.94 and for injection molding: 3.90 g / m ³ , water uptake: 0%. Average particle size: 4 µm surface roughness, R _a = 2.2> un. Bending strength: 410 and 380 MPa, respectively. Softening point: 1710 ° C.

Uses for general electrotechnical applications as insulating bead, coil holder, cable clamp, mechanical use as sandblasting nozzle, textile fiber deflector, metal abrasive and polishing body, for thermotechnical applications as shielding gas nozzle, heat-resistant washer, .

The above examples illustrate that the process of the invention provides ceramic products with very favorable properties.

Claims (5)

Claims CLAIMS 1. A process for the production of ceramic bead bodies having fine-crystalline woven fabrics comprising 99 to 99.9% by weight of aluminine oxide. -611 aluminum compound, preferably aluminum hydroxide, boehmite, gamma-aluminium oxide, or alpha-alumina, or a mixture thereof, with additives, characterized in that the oxygen-containing inorganic aluminum compound (s) 0.05 to 0.5% by weight of yttrium oxide or lanthanum oxide or neodymium oxide or equivalent salts thereof, expressed as alumina (expressed as oxide), or by grinding thereof, and homogenizing and heat treating at a temperature of at least 1450 ° C. reacting at least 80% by weight of the additives with the alumina, then mixing the two or three kinds of alumina activated in this way, and milling the resulting mixture, containing 0.1-1% by weight of the additive, expressed as pure oxides, the finished ceramic raw materials are formed into molded bodies in a manner known per se, and finally sintered at temperatures above 1450 ° C. Process according to claim 1, characterized in that the starting aluminum compound is calcined alpha-alumina at 1300-1500 ° C. 3. A process according to claim 1, wherein for activating the parent aluminum compound, it is present in an amount expressed as alumina. 0.2-0.3% by weight of yttrium oxide, lanthanum oxide and neodymium oxide. 4. A process according to claim 1, wherein the total amount of additives in the sintered ceramic material is from 0.5 to 0.6% by weight. Method according to claim 1, characterized in that the sintering of the molds is carried out at a temperature between 1460 and 1700 ° C, preferably at 1550 ° C. 20.