Classifications

• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
  • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
  • C04B35/10—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on aluminium oxide
  • C04B35/111—Fine ceramics
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
  • C01F7/00—Compounds of aluminium
  • C01F7/02—Aluminium oxide; Aluminium hydroxide; Aluminates
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
  • C01F7/00—Compounds of aluminium
  • C01F7/02—Aluminium oxide; Aluminium hydroxide; Aluminates
  • C01F7/44—Dehydration of aluminium oxide or hydroxide, i.e. all conversions of one form into another involving a loss of water
  • C01F7/441—Dehydration of aluminium oxide or hydroxide, i.e. all conversions of one form into another involving a loss of water by calcination
  • C01F7/442—Dehydration of aluminium oxide or hydroxide, i.e. all conversions of one form into another involving a loss of water by calcination in presence of a calcination additive
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
  • C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
  • C04B35/64—Burning or sintering processes
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2006/00—Physical properties of inorganic compounds
  • C01P2006/80—Compositional purity

Definitions

• This invention relates to a process for the preparation of sintered aluminium oxide ceramics.
• the invention is concerned with a process for the preparation of highly reliable ceramical shaped articles of fine crystalline structure having a nominal aluminium oxide content of 99-99.9 % by weight, the said ceramics having a long lifetime, by activating, forming and sintering an aluminium compound - preferably aluminium hydroxide, bohmite, gamma-aluminium oxide or alpha-aluminium oxide or a mixture thereof - with additives.
• the ceramical shaped articles prepared according to the present invention are particularly suitable for use in mineral oil mining.
• the purer and coarser are the crystalline particles of the raw material used in the forming thereof, the higher temperature is required in sintering the shaped article to a compact structure. It is also known that if the powder comprises a high amount of useful additives and has a large specific surface, the sintering thereof is easier. In addition to the above factors the calcinating temperature of the raw material, the character of the contaminations
• the specific surface of the raw material can not be increased to any optional extent.
• the upper limit is determined on the one hand by the efficiency rate of the grinding apparatus and the phenomenon of aggregation, while on the other it is very difficult to prepare shaped articles having a large wall-thickness from finely ground powder because as a result of linear shrinkage occuring during sintering - which amounts to about 20 % - the shaped articles can easily crack.
• Ceramics having a more homogeneous crystal structure can be obtained by adding in the place of the generally used magnesium oxide rather an other water-soluble magnesium compound to aluminium oxide, preferably prior to calcination.
• a magnesium nitrate solution /Brit. Ceram. Trans. J. 83, /5/, 138 (1984); J. Amer. Ceram. Soc. 67, /3/, 174 (1984)/ can be used.
• aluminium oxide having an ultrafine particle size is prepared by subjecting a solution which contains a small amount of magnesium sulfate and a large amount of aluminium sulfate to thermal treatment. Although the effect of magnesium oxide thus prepared is more favourable, the required sintering temperature is stil too high.
• sintering-powder of the formula 13Be0.7Y 2 O 3 (Hungarian patent No. 163,714), titanium dioxide (J. Amer. Ceram. Soc. 55, /2/, 114 /1972/) or 1 % of tantalic/V/oxide, magnesium oxide and nickel/II/oxide (Amer. Ceram. Soc. Abstr. 225 /1983/) can be used.
• sintering temperature can be lowered even to 1400-1600 °C by adding simultaneously 2 % by weight of titanium dioxide and 2 % by weight of manganous/II/oxide or by introducing 3-6 % by weight of a silicate, particularly talc, cordierite or anortite (laid-open Hungarian patent application, publication No. T/32769).
• a silicate particularly talc, cordierite or anortite
• the above objects can be achieved by adding to the aluminium compound (s) which form(s) the basic material of the ceramical shaped articles in an amount of at least 0.05 % by weight (related to the aluminium oxide content thereof) yttrium oxide or an equivalent amount of an yttrium salt which can be converted into oxide by heating; homogenizing the mixture, preferably by grinding; reacting at least 80 % by weight of the yttrium oxide with aluminium oxide by means of calcination; adding to an identical or different aluminium compound(s) in an amount of at least 0.05 % by weight (related to the aluminium oxide content thereof) lanthanum oxide or an equivalent amount of a lanthanum salt which can be converted into oxide by heating; homogenizing the mixture, preferably by grinding; reacting at least 80 % by weight of the lanthanum oxide with aluminium oxide by means of calcination; adding to identical or different aluminium compound(s) in an amount of at least 0.05 % by weight (related to the aluminium oxide content thereof) y
• the present invention is based on the recognition that a product being more suitable for ceramical purposes can be obtained by adding the additives which, inhibit particle-size growth and promote recrystallization prior to the last firing treatment rather than to the already “over-calcinated” aluminium oxide and thus carrying out calcination which induces the change of modification and compacts the particle-aggregation in the presence of the said additives.
• the present invention is based on the further recognition that the desired useful effect of the present invention can only be achieved if the additives which inhibit particle-size growth and promote sintering are added not together simultaneously but separately to the aluminium-compound and if the mixture(s) of the aluminium oxide and each individual additive are separately subjected to calcination.
• the number of activated aluminium oxides prepared is identical with the number of additives used and the separately activated aluminium oxides are subsequently admixed and ground in the desired ratio to yield a ceramical basic material having a fine particle structure which can be then formed.
• the present invention is based on the further recognition that compounds of trivalent rare earth metal having an ionic radius which is compatible with that of aluminium inhibit particle-size growth and promote recrystallization in a favourable manner.
• the oxides of the said rare earth metals are incorporated in a stable manner into the crystal lattice of aluminium oxide under thermal effect.
• oxides of rare metal oxides exert a favourable effect on sintering properties and the final characteristics of the ready-for-use polycrystalline ceramics already when used in an amount of some tenth % by weight.
• aluminium compound preferably aluminium hydroxide (Al/OH/ 3 ), bohmite (A10/OH/), gamma-modification of aluminium oxide fired at a temperature below 1000 °C
• Al 2 O 3 Al 2 O 3
• alpha-aluminium oxide calcinated at 1300--1500 oC can be used.
• a mixture of several aluminium compounds can be used as well.
• additives such as yttrium oxide (Y 2 O 3 , mp. :2415oC) and/or lanthanum oxide(La 2 ( mp. : 2307 °C) and/or neodymian oxide (Nd 2 O 3 , mp. : 2272 °C) additives react on heating with aluminium compounds e.g. with gamma- and/or alpha-aluminium oxide (Al 2 O 3 , mp. : 2040 oC).
• the above oxides can be, however, replaced by yttrium, lanthanum or neodymian salts which are converted into the corresponding oxide on heating.
• the said metal salts can also be added in the form of an aqueous solution to the aluminium compound.
• the aluminium compound or a mixture of aluminium compounds at least 0.05 % by weight and preferably not more than 10 % by weight - related to the pure aluminium oxide content - of yttrium oxide or an equivalent amount of an yttrium salt which can be converted into oxide by heating is added; the mixture thus obtained is homogenized - preferably by grinding - and thereafte calcinated at a temperature of 1500-1600 °C so long until at least 80 % of the yttrium oxide reacts with aluminium oxide. It has been found that in case of a pre-compacted (e.g. by pressing) powder at least 5-8 hours of thermal treatment is required.
• Two or three (at least two) of the aluminium oxides of "Type A", “Type B” and “Type C”, respectively, thus obtained are admixed in such a ratio that the total amount of the additives - expressed in pure oxides - should be 0.1-1.0 % by weight.
• a mixture of type A+B or A+C or B+C or A+B+C is prepared.
• the powder mixture thus obtained is formed in a manner per se, preferably by die-casting, dry-pressing, slip-casting, extrusion, etc.
• the shaped articles are sintered at a temperature between 1460 and 1700 °C, preferably at 1600 °C for 2-10 hours, advantageously for 6 hours.
• the heating rate is approximately 100-300 °C/hour.
• the velocity of the solid-phase reactions which take place during the second sintering thermal treatment is determined - in addition to the temperature, time, etc. used - after all by the velocity of the reactions which are regulated by complicated mechanisms and take place amoung the metal oxides of various melting points and affinity and also the compounds having a lower melting points and formed from the said oxides during calcination. During these procedures the compounds of lower melting point become gradually enriched and are incorporated into the crystal lattice of the aluminium oxide being present in large excess, whereby the volume of the shaped article is decreased.
• a further advantage of the process of the present invention is that it enables the preparation of shaped articles of both simple and complicated form by using known and conventional equipments generally applied in the manufacture of ceramics.
• alumina ceramics prepared by using aluminium compounds and additives of various qualities meet the requirements of use at a given field of application to an increased extent.
• Products prepared from mixtures of "Type A+B” can be used for highly reliable electronical and electrotechnical purposes. Mixtures of "Type A+C” are particularly suitable for the preparation of products for use where his mechanical abrasion resistance and long lifetime are required.
• Products prepared from mixtures of "Type B+C” possess outstanding thermal technical properties and chemical resistance.
• Products obtained from mixtures of "Type A+B+C” can be sintered at the lowest temperature which is particularly advantageous in the manufacture of large-sized shaped articles which, have a smooth surface and are either deeply jointed or equipped with a turn.
• the treatment disclosed in Hungarian patent No. 179,981 is accomplished, whereby calcination is carried out in the presence of a small amount of an aluminium sulfate solution, the aluminium oxide powder thus obtained has a loose structure and can be readily ground to a fine particle-size.
• the process disclosed in Hungarian patent No. 165,357 relating to a poly-isobutylene dry-pressing compaction aid is also useful: the aid process provides a green density of about 2.4 g/cm already when applying a small specific pressure.
• additives can also be used in order to ob tain ceramical products of special characteristics.
• silicates can be added which promote metallization and brazing or soldering of aluminium oxide ceramics (Hungarian patent No. 177,450) or zirconium oxide or chrome oxide increasing the thermal shock resistance can be introduced.
• the present invention enables furtheron the preparation of so-called “cermetes” by adding metallic chrome or cobalt which increase shatter- and shockproofness and resistance against large thermal shock.
• a “semi-dry” powder is prepared by pressing under a pressure of 0.1 MPa, the powder is compacted and calcinated in a heating sheath at 1500 °C for 5 hours.
• the activated aluminium oxide (“Type A”) thus obtained is subsequently subjected to fine grinding.
• 500 g of aluminium oxide ("Type B” ) thus obtained and 500 g of aluminium oxide ("Type A”) are ground together in a mill equipped with alumina balls in dry medium to a degree that 95 % of the ground product has a median particle-size below 5 ⁇ m and 50 % below 2 ⁇ m.
• the milled product is formed by paraffine die-casting in a known manner, the shaped articles are made free of paraffine and sintered in az oxidizing (air) atmosphers at a temperature of 1550 °C for 8-10 hours.
• the sintered ceramics thus obtained have a nominal aluminium oxide content of 99.5 % by weight and Y 2 O 3 content of 0.2 % by weight, and La 2 O 3 content of 0.3 % by weight.
• Apparent density 3.92 g/cm 3 ; water absorption: 0 % (Fuchsine probe negative).
• Bending strength 400 MP Dielectric loss factor (measured at 10 MHz and 20 °C): 2-4 x 10 -4 ; the dielectric constant: 9.2; electrical breakdown strength: 20 kV/mm.
• the average particle-size: 4.6 ⁇ m ; surface roughness (based on talysurf measurements) R a 3 ⁇ m /C.L.A./. Rockwell hardness 82.
• Field of application particularly for insulator purposes in electric industry, e.g. high frequency coil body, heating element supporter, clinch relée, core transmitter, construction ports for electronic values and electrical instruments, etc.
• Type C the activated aluminium. oxide
• Type A aluminium oxide
• the ground material is formed by slip-casting method, dried and sintered at 1650 oC in air for 6-10 hours, depending on the size and wall-thickness of the shaped article.
• the nominal aluminium oxide content of the product amounts to 99.7 % by weight, the Nd 2 O 3 amounts to 0.2 % by weight, the Y 2 O 3 content is 0.06 % by weight.
• Field of application for purposes where large hardness, and high abrasion resistance is required; e.g. press inset, pressing plate, sliding bearing, elements of slurry and slime pumps in mineral oil industry, sand blaster nozzles, etc.
• each activated aluminium oxide i. e . 100-100 g of " Types B and C" each
• 3000 g of alumina ot type "G" 3000 g of alumina ot type "G" to a degree that 95 % of the particle have an average particle-size below 5/um and 50 % thereof below 1-2 ⁇ m.
• the ground product is formed by paraffine die-casting, the paraffine is removed and the forms are sintered in the air at 1550 °C for 10 hours or at 1600 °C for 6 ho
• the nominal aluminium oxide content of the sintered articles thus obtained amounts to 99.4 % by weight, the La 2 O 3 content is 0.3 % by weight, the Nd 2 O 3 content amounts to 0.3 % by weight.
• Field of application mainly for use in thermal technics e.g. laboratory and pilot plant annealing pot, crucible cover, furnace underplate, supporter for electric heating wire, plasma mouth, etc.
• thermal technics e.g. laboratory and pilot plant annealing pot, crucible cover, furnace underplate, supporter for electric heating wire, plasma mouth, etc.
• Example 4 (Mixture of "Type A+B") Into a grinding mill equipped with alumina balls of high purity 999.5 g of aluminium oxide (comprising 99.99 % by weight of aluminium oxide and having a total alkali content not more than 0.002 % by weight; calcinated at a temperature not exceeding 1100 oC; manufacturer SZIKKTI Budapest) are weighed in. Separate ly 1. 1g of yttrium sulfate of analytical purity (equivalent of 0.5 g of yttrium oxide) are weighed in and dissolved in distilled water to yield a saturated solution at room temperature. The solution thus obtained is poured to the aluminium oxide, and homogenized by grinding for 2 hours. The “semi-dry” powder thus obtained is sieved, compacted and calcinated at 1500 oC in air atmosphere for 6 hours. Thus aluminium oxide of "Type A” is obtained.
• the two aluminium oxide types activated by different additives are ground in a weight ratio of 1:1 to a degree that 95 % of the particles have an average particle-size below 4-5 /urn and 40-50 % below 1 ⁇ m.
• the powder mixture thus obtained is formed by the known poly-isobutylene dry-pressing method (Hungarian patent No. 165,357) and sintered at 1680-1700 oC for 2-4 hours in the air.
• the nominal aluminium oxide content of the so-called high purity sintered articles thus obtained amounts to 99.9 % by weight, the Y 2 O 3 content is 0.05 % by weight and the La 2 O 3 content amounts to 0.05 % by weight.
• Field of application particularly in microelectronics for low-and highfrequency purposes, for highly reliable active and passive insulation purposes, e.g. substrate for thinlayer integrating circuit in polished form, tunable URH coil body, output head of computers and other purposes where high abrasion resistance is required, e.g. wire drawing gauge, cutting tool or melt crusible for metals of high purity, catode ceramics for electron ray welder, etc.
• Example 5 (Mixture of "Type A+C") Into a mill equipped with alumina balls 995 g of alumina of Type “G” calcinated at a temperature not exceeding 1300 oC are weighed in whereupon 4 g of technical grade yttrium oxide and 1 g of technical grade magnesium oxide (MgO) are weighed in. The powder mixture is ground - preferably in the dry - to a degree that 90 % of the particles have an average particle-size below 5 ⁇ m and 50 % thereof being below 2 ⁇ m. The powder is sieved and calcinated at 1500 oC for 8 hours.
• the activated aluminium oxide (“Type A”) is processed as follows:
• the activated aluminium oxides of "Types A and C" are ground together, preferably in aqueous medium, at a ratio of 1:1 to a degree that 95 % of the particles have an average particle-size below 5-6 ⁇ m and 50 % thereof below 3 ⁇ m.
• the suspension is cast into a suitable plaster of Paris die in a known manner in the presence of a surfactant, whereupon the shaped article is removed, dried and sintered at 1480-1500 °C in the air for 8-12 hours.
• the nominal aluminium oxide content of the ceramics thus obtained amounts to 99 % by weight, the Y 2 O 3 content is 0.4 % by weight, the MgO content amounts to 0.1 % by weight and the Nd 2 O 3 content is 0.5 % by weight.
• the "semi-dry" powder thus obtained is pre-compacted, put into a heating sheath and calcinated on the air at 1600 o C for 5 hours.
• the aluminium oxide of "Type B” thus obtained may be used as follows: Into a grinding mill 996 g of ceramic aluminium oxide of type "G"(the firing at a temperature not exceeding 1500 °C) are weighed in, whereupon a saturated aqueous solution (at room temperature) of 16.7 g of technical grade neodymian nitrate (Nd/NO 3 / 3 ) (equivalent to 4 g of neodymian oxide) is added and the mixture subjected to homogenizing by grinding for 2 hours. The powder (“semi-dry”) thus obtained is compacted by pressing, then put into a heating sheath and calcinated at 1600 oC for 6 hours.
• the active aluminium oxide "Type C”, thus obtained, is ground together with the above activated aluminium oxide of "Type B" in a ratio of 1:1 to a degree that 95 % of the average particle-size is below 5 ⁇ m and 50 % below 2 ⁇ m.
• the finely ground powder mixture is processed in a known manner and extruded to shaped articles which are sintered at 1480-1550 oC - preferably in sus-pended form - for 8-10 hours in an oxidizing atmosphere (air).
• the nominal aluminium oxide content of the shaped articles thus obtained amount to 99.2 % by weight, the La 2 O 3 content is 0.4 % by weight, the Nd 2 O 3 content amounts to 0.4 % by weight.
• the three portions of activated aluminium oxide powders - weighing 500 g each - are combined and ground fine in a mill equipped with alumina balls to a degree that 90 % of the average particle size is below 5 ⁇ m, and 50 % being below 1-2 ⁇ m.
• One part of the milled product is formed by isostatic pressing and the remaining part by die-casting to yields more complicated shaped articles.
• the former articles are pre-fired and sintered in the air atmosphere at 1560-1600 °C for 6-10 hours.
• the nominal aluminium oxide content of the ceramical sintered articles thus obtained amounts to 99.2 % by weight, the Y 2 O content is 0.2 % by weight, the Nd 2 O 3 content amounts to 0.3 % by weight.
• Fields of application for general electrotechnical purposes, e.g. as insulating pearl, coil supporter, cable gripi for mechanical purposes e.g. as sand blaster, thread leader in textile industry, abradant in metal industry and polishing body, in thermal technics e.g. welding nozzle under protecting gas atmosphere heat resistant underplate; in chemical industry as acid and alkali resistant valve balls, pin elements, snout, etc.

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• 1987
  • 1987-03-05 JP JP87501482A patent/JPH01502425A/ja active Pending
  • 1987-03-05 CH CH4216/88A patent/CH676593A5/de not_active IP Right Cessation
  • 1987-03-05 WO PCT/HU1987/000008 patent/WO1988006574A1/en active Application Filing
  • 1987-03-05 DE DE873790917T patent/DE3790917T1/de not_active Withdrawn
  • 1987-03-30 FR FR8704391A patent/FR2613355B3/fr not_active Expired
• 1988
  • 1988-11-07 GB GB8826046A patent/GB2208858B/en not_active Expired - Fee Related

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