DE10164727B4 - Process for the preparation of sintered inorganic granules or moldings based on carbon or molybdenum compounds in a ceramic matrix and their use - Google Patents

Abstract

Process for the production of ceramic granules or shaped articles, characterized by the following process steps:
(a) preparation and preparation of a raw material mixture comprising, in each case based on the total weight of the starting mixture, in addition to 10 to 95% by weight of a pulverulent, finely divided amorphous silica 2 to 50% by weight of carbon or up to 30% by weight at least one inorganic molybdenum compound, wherein the specific surface area (BET) of the silica is at least 15 m ² / g and silica fume as fume in the form of an ultrafine amorphous SiO ₂ dust with an amorphous SiO ₂ content of 85 to 98 wt .-% and a particle size up to 0.2 microns is used;
(b) compacting and shaping the mixture thus obtained;
(c) drying the compacted and formed mixture at temperatures of 50 ° C to 300 ° C and for a period of 0.5 to 10 hours; and finally
(d) ceramic firing of the dried mixture at temperatures of 700 ° C to 1700 ° C for a period of 0.5 to 6 hours under such conditions, ...

Description

The The present invention relates to a process for the preparation of ceramic granules or moldings and their use in friction or brake pads of vehicles or as refractory materials (refractory) Products). More specifically, the present invention relates a method of producing sintered, inorganic ceramic Granules and shaped articles based on powdered, finely divided amorphous silica, namely silica fume, as well as carbon, for example in the form of natural and synthetic graphites, carbon blacks, Carbon fibers, electrographites or petroleum coals and coal coke, or molybdenum disulfide as well as their use for Friction or brake pads and for refractory materials (refractory products).

At the Braking of vehicles are the brakes against the most off Metal existing brake drums or discs pressed when the hydraulic pressure in the filled with brake fluid, closed System increased becomes.

Because of the occurring during braking, relatively high temperatures must Brake pads off high temperature resistant and at the same time abrasion resistant materials.

Earlier For their production often asbestos fibers together with filling materials such as barium sulfate or stone meal and a lubricant such as graphite or lead, by binders such as phenol-formaldehyde resins or nitrile rubbers were held together to form a block. Because of the health hazard Effect of asbestos fibers, asbestos-free brake pads were finally developed, for example, based on mineral, glass, carbon, Metal, acrylic or aramid fibers.

A typical friction or brake lining is - apart from organic binders, organic and metallic fibers and metal powders - to a large extent from carbon carriers such. Natural and synthetic graphites, electrographites, carbon blacks, carbonized cokes from the coal and petroleum industries, from molybdenum disulfide and from natural and synthetic, inorganic oxidic raw materials. The interaction of these materials, which have abrasive and lubricating properties, ultimately results in a controlled friction or braking process. An outstanding role in friction linings is occupied by molybdenum disulphide (MoS ₂ ) and carbon carriers such as natural and synthetic graphites, electrographites, carbon blacks, carbon fibers, carbonized cokes from the hard coal and petroleum industries, since these materials can be used to determine frictional properties. However, a disadvantage of these conventional friction linings is, in particular, that these materials must be bound with organic binders in the friction material. However, since considerable temperatures can occur during friction linings during use, they may lead to premature wear of the brake lining due to destruction or yielding of the organic binders. In addition, the incorporation of larger molybdenum disulphide or carbon carrier amounts can lead to production and material difficulties.

The DE 40 24 547 A1 relates to a friction lining, which consists of an inorganic silicate-containing binder matrix, in which aggregates are integrated, wherein the binder matrix is made of a cured at elevated temperature mixture of finely divided SiO ₂ and at least partially water-soluble silicates and optionally alumina. The preparation of the silicate matrix is carried out at processing temperatures between 20 ° C and 100 ° C or curing between 80 ° C and 120 ° C under the mandatory presence of silicates, preferably at least partially water-soluble silicates are used. The binder matrix is formed on the basis of chemical processes, such as hydraulic or polycondensation processes.

Farther For example, US-A-4,732,878 relates to a process for making ceramic articles which from a continuous alumina / silica phase, a discontinuous carbon phase and optionally another discontinuous phase consist of silicon carbide, wherein the Preparation of incoming in a subsequent thermal treatment Starting matrix is done by a sol / gel process.

The object of the present invention is to provide a process for producing materials len, which are particularly suitable for the production of friction or brake linings and avoid the disadvantages of the prior art previously described. Furthermore, due to their properties, in particular because of their heat resistance, such materials should also be suitable for other applications, for example for refractory materials or refractory products.

The inventive task will be solved by the method according to the invention described below, which results in materials leads, which is particularly suitable for the production of brake or friction linings with improved properties and for the production of refractory materials or refractory products.

• (a) Vor- und Aufbereitung einer Rohstoffmischung, enthaltend, jeweils bezogen auf das Gesamtgewicht der Ausgangsmischung, neben 10 bis 95 Gew.-% eines pulverförmigen, feinteiligen amorphen Siliciumdioxids 2 bis 50 Gew.-% Kohlenstoff oder bis zu 30 Gew.-% mindestens einer anorganischen Molybdänverbindung, wobei die spezifische Oberfläche (BET) des Siliciumdioxids wenigstens 15 m²/g beträgt und als Siliciumdioxid Silica Fume in Form eines ultrafeinen amorphen SiO₂-Staubes mit einem amorphen SiO₂ Gehalt von 85 bis 98 Gew.-% und einer Partikelgröße bis 0,2 μm eingesetzt wird;
• (b) Verdichten und Formgebung der so erhaltenen Mischung;
• (c) Trocknung der verdichteten und geformten Mischung bei Temperaturen von 50°C bis 300°C und für eine Dauer von 0,5 bis 10 Stunden; und schließlich
• (d) keramischer Brand der getrockneten Mischung bei Temperaturen von 700°C bis 1.700°C für eine Dauer von 0,5 bis 6 Stunden unter solchen Bedingungen, daß im wesentlichen keine Oxidation des Kohlenstoffs erfolgt oder eine Reaktion der anorganischen Molybdänverbindung mit den anderen Bestandteilen der Mischung eintritt und gleichzeitig eine keramische und/oder chemische Verfestigung der Mischung durch Versinterung eintritt, so daß der Kohlenstoff oder die anorganische Molybdänverbindung in eine keramisch versinterte Matrix eingelagert werden.

The present invention thus relates to a process for the production of ceramic granules or moldings, in particular for the production of friction linings or brake linings and of refractory materials or refractory products, which is characterized by the following process steps:

• (a) preparation and preparation of a raw material mixture comprising, in each case based on the total weight of the starting mixture, in addition to 10 to 95% by weight of a pulverulent, finely divided amorphous silica 2 to 50% by weight of carbon or up to 30% by weight at least one inorganic molybdenum compound, wherein the specific surface area (BET) of the silica is at least 15 m ² / g and as silica fume in the form of an ultrafine amorphous SiO ₂ dust with an amorphous SiO ₂ content of 85 to 98 wt .-% and a particle size is used to 0.2 microns;
• (b) compacting and shaping the mixture thus obtained;
• (c) drying the compacted and formed mixture at temperatures of 50 ° C to 300 ° C and for a period of 0.5 to 10 hours; and finally
• (d) ceramic firing of the dried mixture at temperatures of 700 ° C to 1700 ° C for a period of 0.5 to 6 hours under such conditions that substantially no oxidation of the carbon occurs or reaction of the inorganic molybdenum compound with the other ingredients the mixture occurs and at the same time a ceramic and / or chemical solidification of the mixture occurs by sintering, so that the carbon or the inorganic molybdenum compound are incorporated into a ceramic sintered matrix.

In Process step (a) of the process according to the invention takes place first Preparation and preparation of the raw material mixture, in addition to powdered, finely divided amorphous silica in the form of silica fume as well Carbon or at least one inorganic molybdenum compound, especially molybdenum disulfide, contains.

The Preparation and preparation of the raw material mixture in step (a) takes place in general after per se Methods. During the preparation and preparation of the raw material mixture in particular, comminutes the individual mixture components to the desired particle size, if they are in different sizes, and homogeneous mixed together.

In particular, according to the invention either a semi-wet or preferably a wet processing under usual Conditions performed become. For semi-wet processing all mixture components are dried, if they are not already in the dry state, then optionally comminuted, unless the particles already have the appropriate particle sizes, subsequently mixed or homogenized and finally for the subsequent compaction and shaping moistened, z. B. with water or wet steam. In wet processing In contrast, the raw materials are wet-ground (eg in drum mills), if they do not yet have the appropriate particle sizes, or for example by stir with water z. B. converted into mixed whiskers in aqueous suspensions.

The Methods for the preparation and preparation of ceramic raw material mixtures are familiar to the expert. For further Details may be relevant Textbooks and reference books be referenced, for. B. on the from the series "Materials and components of electrical engineering" originating textbook by H. Schaumburg "Keramik", publisher B.G. Teubner Stuttgart, 1994.

As previously described the raw material mixture powdery, fine-particle amorphous silica in the form of silica fume as well Carbon or at least one inorganic molybdenum compound, in particular Molybdenum disulfide.

As the silica according to the invention, a powdery, finely divided amorphous silica is used. The content of amorphous silica is at least 85 wt .-%. According to the invention be Particularly suitable silica has an absolute density in the range of 2.0 to 2.5 g / cm ³ , a bulk density in the uncompressed state of 200 to 400 kg / m ³ or more and a bulk density in the compacted state of 450 to 800 kg / m ³ or more. The specific surface area (BET) is at least 15 m ² / g and should in particular be in the range of 15 to 30 m ² / g or greater.

As already described, so-called silica fume is used as the silica. Silica Fume is clearly characterized in the relevant literature as a technical term and refers to an ultrafine amorphous SiO ₂ dust, which is produced in particular during the production of silicon metal and ferrosilicon alloys as a by-product of the melting / reduction process. Characteristic of silica fume is the high amorphous SiO ₂ content of 85 to 98 wt.%. The particle sizes of silica fume are generally in the range of 0.1 to 0.2 microns with a nearly spherical shape. In addition, due to the small particle size, an extremely good reactivity and, associated therewith, very high strength values in the ceramic-fired end products. Thus, according to the invention, silica fume is used as a reactive inorganic material to produce a ceramic sintered matrix. According to the invention suitable Silica Fume, for example, sold by the company. Elkem Materials under the designation "Elkem Micro Silica ^®" and by the company. Fesil silica AS.

Of the Content of powdery, finely divided amorphous silica in the starting or raw mixture can vary within wide limits. Inven tion according to the content of silica in the starting mixture 10 to 95 wt .-%, in particular 15 to 90 Wt .-%, preferably 20 to 85 wt .-%, based on the total weight the starting mixture.

Next powdered, finely divided amorphous silica, the starting mixture still contains carbon or at least one inorganic molybdenum compound, in particular molybdenum disulfide.

According to the invention suitable Carbon is especially selected from the group of graphites such as natural and synthetic graphites, in particular in the form of graphite flakes and / or graphite dust (eg electrographite), carbon blacks of all kinds, carbon fibers, Cokes such. B. carbonized cokes from the coal or oil industry (eg, petroleum or hard coal coke) and mixtures of the aforementioned compounds.

Of the Content of carbon in the raw mixture can be in wide limits vary. According to the invention, the content of carbon in the starting mixture 2 to 50% by weight, in particular 5 to 40% by weight, preferably 5 to 30 wt .-%, based on the total weight of Starting mixture.

If the starting mixture contains an inorganic molybdenum compound, in particular a molybdenum mineral or molybdenum ore, preferably molybdenum disulfide (MoS ₂ , molybdenite, molybdenum luster) is used. Molybdenum disulfide is the most common molybdenum mineral and also the most technically significant molybdenum ore. It is characterized in particular by its due to the layer grid, the graphite-like sliding properties.

Of the Content of inorganic molybdenum compound, especially molybdenum disulfide, in the starting or raw mixture can vary within wide limits. According to the invention, the content inorganic molybdenum compound, especially molybdenum disulfide, in the starting mixture up to 30 wt .-%, in particular up to 15 Wt .-%, preferably up to 10 wt .-%, particularly preferably up to 8 wt .-%, based on the total weight of the starting mixture.

According to one particular embodiment The present invention may further provide at least an inorganic oxidic raw material and / or mineral component be added.

These other, other oxidic raw materials and / or mineral components should in particular serve, during the ceramic fire with the powdered, finely divided amorphous silica, preferably silica fume, react or sinter or as a friction lining component be supplied in a form of the starting mixture or the offset, so that you only as sintered, coarse constituents in the reactive matrix available. In other words, preferred are those oxidic Raw materials or mineral constituents used with the powdery, can react fine-particle amorphous silica or the ceramic matrix can educate, d. H. sinter with the matrix.

Finely ground, synthetic and natural raw materials are preferably used for inorganic materials and / or oxide mineral mixtures for producing the granules and shaped bodies according to the invention used, which are available as processed raw materials. In particular, raw materials are used, which already come into play in friction linings. Essentially, these are the following substances: sintered clay, Tabulartonerden, fused corundum (normal corundum), normal corundum, calcined Bauxite, enamel and sintered mullite, andalusite, kyanite, sillimanite, disthen, staurolite, chamottes, clays, metakaolin, bentonites, diatoms, natural and synthetic amorphous silicas, quartz, cristobalite, quartz glass, natural baddeleyite and synthetic stabilized and unstabilized zirconia, zirconium silicate, fused and sintered zircon mullite, zircon corundum, rutile, ilmenite, alkali and alkaline earth titanates, sintered and melted spinel, chrome ore, fused and sintered magnesia, olivine , synthetic cordierite (indialite), talc, serpentine, sepiolite, wollastonite, xonotlite, spodumene, petalite, lepidolite, garnets, feldspars, nepheline, minerals of the pyroxene and amphibole group, minerals of the mica group such as muscovite, biotite and vermiculite, zeolites, carbonates such as Magnesite, calcite, dolomite, siderite and rhodochrosite, sulf such as barite, anhydrite and gypsum, apatite, borates such as borax colemanite, uxlex, hydroboracite.

Of the Content of inorganic oxidic raw material and / or mineral constituent in the starting mixture can vary widely. In general is the content of inorganic oxidic raw material and / or mineral constituent in the starting mixture 5 to 70% by weight, in particular 10 to 65% by weight, preferably 15 to 60 wt .-%, based on the total weight of Starting mixture.

Of others can the starting mix as well Minerals, inorganic fibers such as quartz glass fibers, alumina fibers, Glass fibers, aluminum silicate fibers or basalt fibers, rock wool, Slags, fly ash, glazes, frits, cements such as alumina cements and Portland cements are added.

As well can the granules of the invention and shaped bodies also contain carbides and nitrides, such as silicon carbide, silicon nitride, Boron carbide, boron nitride, titanium carbide and the like. a. These can either be directly from the starting mixture be added or starting from the ceramic fire in situ be generated from suitable starting compounds.

Around especially wear-resistant To obtain final products, it is recommended that the starting mixture Particles of the respective mixture components, whose mean particle diameter - in Trap of the rest matrix-forming materials, in particular the oxidic raw materials and / or mineral constituents, if present - not more than 0,2 mm and in particular ≦ 100 μm, preferably ≦ 50 μm or less, are. The remaining Blend components, in particular the carbon carrier and optionally further additives and fillers (eg minerals etc.), if available, can but also much larger, medium Particle diameter or particle sizes of up to 10 mm, in particular up to 5 mm, preferably up to 1 mm, more preferably up to 0.5 mm and smaller, without this wear resistance of the products substantially.

The individual blend ingredients should be under the process conditions especially not resolvable be.

to Preparation of the starting mixture of these are generally water and in general also so-called process chemicals, which the processability or ease of handling of the raw mixture, added, in particular thinning agent (Condenser), Plasticizers, dispersants and / or binders (eg. Permanent or temporary Binder).

With In other words, the dry offset or the dry starting mixture moistened with water for processing and if necessary with known process aids (such as plasticizers, dispersants, liquefiers and temporary Binders). The use of process aids (process chemicals) but is by no means mandatory.

When examples for according to the invention suitable Binders can for example, the following compounds are mentioned: sodium, Potassium and / or Lithium water glasses, Silica brine, natural and synthetic amorphous silicas, Portland cements, alumina cements, phosphates, in particular and alkaline earth phosphates and monoaluminum phosphate, borates, boric acid, clays, Kaolin, metakaolin, aluminum hydroxide, calcium hydroxide, magnesium sulfate, Magnesium chloride, magnesium hydroxide, aluminum hydroxychloride, sodium aluminate and zirconium oxychlorides, zirconium acetates and phosphates.

As examples of temporary binders suitable according to the invention, it is possible to cite all compounds which are familiar to the person skilled in the art for that purpose, in particular temporary binders Basis of organic compounds such. As lignosulfonates, methylcelluloses, gelatin etc.

the Step (a) closes then in process step (b) of the method according to the invention the densification and the shaping of those obtained in step (a) Mix on.

The Compression and shaping in step (b) are carried out according to common, known granulation and Kompaktierungsverfahren and conventional molding processes. It can be referred to the general literature, for example to the already cited book by H. Schaumburg.

Preferably Compacting and shaping take place in one step, in particular by extrusion. However, it is also possible to compact (compact) and to perform the shaping separately.

Purely the following compaction and / or shaping methods are examples called extruding, pelletizing (eg by means of Pelletizing plate), spray-drying, Pressing (eg dry pressing or isostatic pressing with granules), Granulation, pouring (eg injection molding) Etc.

the Process step (b) closes then in process step (c) of the method according to the invention the drying of the mixture compacted and shaped in step (b) at.

The Drying of the compacted and formed mixture takes place at temperatures from 50 ° C up to 300 ° C. The drying time is between 0.5 and 10 hours, in particular between 1 and 5 hours, preferably between 1 and 3 hours. In general, the drying is carried out under atmospheric pressure; however If necessary, the drying can be carried out under reduced pressure or performed in a vacuum become.

the Step (c) closes finally in process step (d) of the process according to the invention, the ceramic Fire the mixture dried in step (c).

The Steps (c) and (d) can continuously or continuously merge into each other, z. B. by stepless Temperature increase.

Of the ceramic firing of the mixture dried in step (c) under such conditions that no or substantially no oxidation of the carbon takes place, or a reaction of the inorganic molybdenum compound, in particular of the molybdenum disulfide, enters with the other ingredients of the mixture and at the same time a ceramic or chemical solidification of the mixture by sintering is achieved, so that the Carbon carrier or the inorganic molybdenum compound into a ceramic sintered matrix based on pulverulent, finely divided amorphous silica are stored.

The ceramic sintered matrix is thus based on the powdered, finely divided amorphous silica in the form of silica fume and optionally the inorganic oxidic raw material or mineral constituent, as defined above, formed by ceramic sintering, wherein the carbon or the inorganic molybdenum compound, in particular molybdenum disulfide, preferably in homogeneous distribution, embedded in this matrix are.

in the In general, the ceramic fire in step (d) of the method according to the invention in a largely oxygen, especially atmospheric oxygen shielded, closed system performed.

According to one preferred embodiment the method according to the invention the ceramic fire in step (d) becomes inert or reducing or non-oxidizing conditions, in particular with exclusion of atmospheric oxygen, preferably in a vacuum or under a protective gas atmosphere. As protective gases can in particular hydrogen, nitrogen, ammonia gas and / or noble gases be used.

The granules and shaped bodies according to the invention are therefore preferably fired under protective gas or under reduced pressure or under reduced pressure, ie under conditions in which no substantial oxidation of the carbon takes place and a reaction of the inorganic molybdenum compound, in particular of the molybdenum disulfide, with the other constituents of the mixture , but at the same time a ceramic or chemical solidification of the mixture by sintering or by chemical bonding of the inorganic materials or the mineral oxide mixtures is achieved. In the method according to the invention, the granules or moldings are thus under inert gas, such as. As hydrogen, nitrogen, on moni akgas and noble gases, or in a vacuum, ie burned in a largely shielded from oxygen, closed system. This system may also consist of granular electrographite, natural graphite flake, or refractory container filled with granular, carbonized cokes of the coal or petroleum industry - hereinafter referred to as the "embedding method" - in which the carbonaceous granules or moldings are embedded are so that neither a vacuum applied nor a separate protective gas must be supplied. Combinations of inert gas and embedding methods are also possible.

According to the invention ceramic fire in step (d) of the process according to the invention at temperatures of 700 ° C up to 1,700 ° C, especially 900 ° C up to 1,500 ° C, preferably 1,000 ° C up to 1,350 ° C, carried out. The Duration is according to the invention 0.5 to 6 hours, especially 1 to 5 hours, preferably 1.5 to 4.5 Hours.

With the method according to the invention manages to turn into a ceramic matrix that is not insignificant Part of sintered or ceramic fired silica in Form of silica fume, molybdenum disulfide or carbon, especially in the form of natural or synthetic graphites, carbon black, and carbon fibers carbonated cokes from the coal and petroleum industries, too In larger quantities incorporate. For this it is necessary, under "inert or reducing Sintering conditions "ceramic Produce granules or molded parts. This is to be achieved by the molded mixture of molybdenum disulfide or carbon carrier (s) and optionally oxidic inorganic materials under protective gases and / or in a largely closed so-called "coal bed" (embedding method) be burned.

Essential supports this process is improved by the use of powdered, finely divided amorphous silica in the form of silica fume. by virtue of has the small particle size Silica Fume an extraordinary good reactivity, resulting in very high strength values in the ceramic fired End products leads.

To Knowledge of the applicant so far no attempts have been made been, powdery, finely divided amorphous silica in the form of silica fume in Friction or brake pads to recycle, especially not in combination with molybdenum disulfide or carbon based on natural and synthetic graphites, Soot, electrographite, Petrol and coal coke.

With the method according to the invention can Thus, ceramic granules or moldings are obtained. in this connection these are, in particular, ceramic granules or shaped bodies which Carbon or at least one inorganic molybdenum compound, especially molybdenum disulfide, embedded - preferably in homogeneous distribution - in a ceramic matrix based on sintered or ceramic having fumed silica in the form of silica fume, wherein the granules or shaped bodies optionally may also contain other ingredients. Of the Content of carbon or molybdenum disulfide in the products according to the invention is in the range of 2 to 50 wt .-%.

Another The present invention also relates to the use of according to the inventive method available ceramic granules or shaped bodies for the production of friction or brake linings.

The Friction or brake pads can for example, completely from the method according to the invention available moldings consist. To do this the moldings before and / or after the ceramic fire in the form of the friction or Brake pads to be brought. equally can those according to the inventive method available moldings or granules are incorporated into the friction or brake pads, z. B. together with known fillers or binders (For example, organic binders such as phenol-formaldehyde resins or nitrile rubbers containing the moldings or granules according to the invention can stick together to a block).

For the production of friction linings, there are a number of advantages based on the granules or shaped bodies obtainable by the process according to the invention: On the one hand, the use of pulverulent, finely divided amorphous silica in the form of silica leads to distinct increases in strength in the resulting granules and shaped bodies. Furthermore, the production of friction linings is much more effective due to better compressibility of the wet carbonaceous or molybdenum disulfide-containing ceramic mass. Since, according to the invention, many granules or shaped bodies differing in their composition can be produced, the properties of the resulting granules can also be obtained Control friction linings in a targeted manner. Due to the fact that grinding and lubricating components are located close to each other in a very dense and ceramic manner in the micro range, more effective braking processes are finally achieved. The high surface temperatures that occur during a braking process are quickly dissipated by the finely divided graphite to cooler areas. The carbon in the granule or tablet acts as a stopper due to its platelet, needle, stick or fiber shape in the sintered material. Another advantage results from the fact that targeted new inorganic compounds can be synthesized in combination with carbon carriers.

Another The present invention also relates to the use of according to the inventive method available ceramic granules and shaped bodies for the production of refractory materials or refractory products.

Of the The term "refractory materials" or "refractory products" is used herein especially as a collective term for non-metallic materials - however including those containing a proportion of metal (eg cermets) - used, which have a sailing cone drop point of at least 1,500 ° C and which can be used industrially at continuous temperatures of over 800 ° C. When refractory materials or refractory products act in particular, molded, fired or unfired (chemically bound), rarely cast-molten stones or unformed Products which are either directly on delivery or after Adding a liquid can be used z. B. as high temperature materials. Major customers for refractory materials or refractory products are, for example, iron and steel industry, Furthermore, the glass, cement, lime and porcelain industry and the Furnace and stove industry (eg for refractory lining).

The The present invention will become apparent from the following embodiments However, which illustrates the present invention in no way restrict should.

EMBODIMENTS

Example 1:

A mix of 15.0% by weight Graphite dust / electro-graphite, 25.5% by weight Silica Fume and 59.5% by weight aluminum oxide is pasted with the addition of conventional process chemicals with water to a plastic mass and then pulled by means of an extruder to a diameter of about 1.0 cm thick strand, which is then mechanically cut into about 2.0 to 3.0 cm long sections. The thus prepared elongated, extruded graphite-containing parts are dried and fired in a sealed refractory vessel filled with petroleum coke at 1350 ° C for three to four hours. After cooling, elongated ceramic granules of high mechanical strength, in which due to the reducing conditions graphite dust / electrode graphite is incorporated. Analytically almost no loss of carbon is detectable. Likewise, visually no visible combustion phenomena in the granules are identified.

The thus obtained granules can further processed and broken, for example, in grains, such as they z. For example the processing of brake pads required are. It is also possible to use the electrode graphite to replace with graphite dust and the plastic mass by a narrow nozzle of about 0.1 cm in diameter, whereby ceramic parts arise, according to the above-described conditions of fire and treatment as solid, stem to fibrous Pins are obtained. Such ceramic moldings can, for example a reinforcing Effect in friction linings cause. Furthermore, you can these products for Refractory materials or refractory products are used.

Example 2 (comparison):

A mix of 5.0% by weight molybdenum disulfide, 20.0% by weight Graphite dust or graphite dust / electrographite, 33.5% by weight Silica Fume, 15.0% by weight Calcium carbonate and 26.5% by weight aluminum oxide is pressed after addition of conventional process chemicals and water to a small plate in the dimensions of a brake pad. Subsequently, the shaped body in a bed - consisting of granular electrographite - fired, which is poured to protect against the influence of oxygen in a refractory wall and sealed by a hermetically sealed cover. After a fire at 1300 ° C for four hours to obtain a shaped body containing molybdenum disulfide and graphite dust or graphite dust / electrographite in the sintered ceramic matrix. The molded body can be used as a friction or brake pad.

Example 3:

A mix of 20% by weight Graphite flakes, 31% by weight Silica Fume and 49% by weight Calcium carbonate (particle size <10 μm) is thickened with the addition of conventional process chemicals and water to a plastic mass and pulled through an extruder to a 3.0 cm thick strand. The strands cut into about 2 to 3 cm long pieces are dried and then fired at 1250 ° C for four hours in a refractory crucible filled with nitrogen and filled with electrographite. The solid granules after firing consist predominantly of pseudo-wollastonite with graphite flakes embedded in the ceramic matrix.

Farther Is it possible, these granules with natural and synthetic raw materials. So in addition approx. 20% by weight of a natural, fibrous formed wollastonite raw material (aspect ratio 17: 1) of the mixture added and fired in the manner described above. In the same Way became coarser Raw materials of fine corundum (grain size 0.1 to 0.5 mm), enamel magnesia (grain size 0.1 to 0.3 mm), sintered magnesia (grit 0.1 to 0.5 mm), burnt bauxite (grain size 0.1 to 0.5 mm), zircon sand (grain size 0.1 to 0.3 mm), garnet (grain size 0.1 to 0.3 mm), andalusite (grain size 0.1 to 0.5 mm) or potassium feldspar (grain size 0.1 to 0.3 mm) of the above cited Mixture added and corresponding granules at partially modified Burning temperatures and firing times produced. Because of the rough Grain structure of the added raw materials occurs marginal sintering with the basic matrix to form new connections. There the reaction times and reaction temperatures are not so long and are not that high that one full Implementation of the coarser grains occurs, "compounds" are achieved in which the properties of individual minerals for a friction lining continue come to fruition. The amount of coarser grains added is in a wide range variable. Also mixtures of different coarser raw materials are possible. at all granules do not burn graphite.

Of the For example, flake graphite in the basic offset listed above may also by carbon fibers, graphite dust, by coarse electrographite (0.2 to 1.5 mm), petroleum or hard coal cokes are replaced or be blended with it. Furthermore, it is possible molybdenum disulfide to inflict the misalignment and in a similar way - as previously described - too burn. Likewise, the amount of carbon carriers and molybdenum sulfide variable. Technically interesting quantities are especially in the field from 5 to 20 wt .-% in the fired or fired Granulates.

The previously described and produced granules can be subsequently processed and in one for the Reibbelagherstellung corresponding grain size can be brought.

Example 4:

A mix of 8.00% by weight Graphite dust or electrographite or petroleum or hard coal coke, 13.00% by weight Silica Fume, 53.00% by weight Kyanitmehl (particle size <44 microns) and 26.00% by weight Portland cement is processed with the addition of conventional process chemicals and water to a pourable mass and poured into a friction lining corresponding shape. The hydraulically set cement paste is dried and fired at 1250 ° C for five hours. The resulting, very solid shaped body contains - as was determined by X-ray analysis - predominantly anorthite and graphite.

The Mass, for example, by other temperature-stable compounds and minerals are modified. So coarser grits z. B. Zirkonmullitschmelzprodukten, Sintered and smelted clay, sintered and enamel mullite, fired Bauxite grains, Fireclay grains, Andalusite crystals or zircon, rutile and ilmenite sands of the mass in mixture or the offset as a single raw material in parts by weight from, for example, 5.00 to 30.00 wt.% are added.

Also let yourself Modify the mixture such that instead of Portland cement Use is made of alumina cement, with wollastonite flour, in combination with silica fume, also leading to anorthite.

Example 5:

A mix of 10.0% by weight Graphite dust (particle size <20 μm), 24.0% by weight Silica Fume and 66.0% by weight Magnesium carbonate (particle size <100 μm) is prepared with the addition of conventional process chemicals and water to a slurry and processed via a spray dryer to spray granules. The granules are fired for two hours at 1450 ° C with exclusion of air in a bed of electrographite. The solidified spray granules contain predominantly forsterite and graphite on mineral phases. Excess magnesium carbonate or with the addition of melt or sintered magnesia granules are obtained with forsterite, periclase and graphite. The sintered granules can be processed in particular directly in friction linings.

Example 6:

A mix of 20.0% by weight Graphite flakes (particle size <0.20 to 0.30 mm), 24.0% by weight Silica Fume and 66.0% by weight Bone ash (apatite, particle size <44 μm) is dry mixed and then treated with the addition of conventional process chemicals, liquid binder and water on a pelletizing plate to spherical granules. The 2 to 3 mm pellets are fired under nitrogen gas at 1200 ° C for four hours. Very solid, spherical granules are obtained which, for example, can be further processed into additives in brake linings.

Example 7:

A mix of 16.0% by weight MoS ₂ , 31.0% by weight Silica Fume, 41.0% by weight Alumina cement (Alcoa 270) and 12.0% by weight Wollastonite (<200 mesh) is prepared under usual conditions as a slip and poured into a mold. The whole is then dried and fired at 1250 ° C for three hours in embedding. The hard resulting ceramic contains MoS ₂ and anorthite.

Example 8:

A mix of 12.0% by weight MoS ₂ , 24.0% by weight Silica Fume, 40.0% by weight Corundum and 24.0% by weight Alumina (99.5% Al ₂ O ₃ ) is pasted under standard conditions and pressed through an extruder die. The strands are fired at 1300 ° C under nitrogen gas in the embedding process. Very hard ceramic parts are obtained, which can be used, for example, as granules for friction linings.

Example 9:

A mix of 23.0% by weight MoS ₂ , 29.0% by weight Silica Fume and 48.0% by weight Nepheline (syenite flour, particle size <44 μm) is prepared under usual conditions, and the moistened mixture is pressed into small plates and then fired at 1200 ° C for three hours. Both the molybdenum disulfide-containing hard ceramic material per se and mixtures which are enriched with fused alumina or with mullite or with bauxite or zirconium zirconium grain sizes in the grain range of 0.1 to 0.3 mm, after the ceramic fire (z. B. in embedding) and appropriate treatment can be used as an additive for friction linings.

Claims (30)

Process for the production of ceramic granules or shaped bodies, characterized by the following process steps: (a) preparation and preparation of a raw material mixture containing, in each case based on the total weight of the starting mixture, besides 10 to 95% by weight of a pulverulent, finely divided amorphous silica 2 to 50% by weight of carbon or up to 30% by weight of at least one inorganic molybdenum compound, wherein the specific surface area (BET) of the silica is at least 15 m ² / g and as silica silica fume in the form of an ultrafine amorphous SiO ₂ dust is used with an amorphous SiO ₂ content of 85 to 98 wt .-% and a particle size of up to 0.2 microns; (b) compacting and shaping the mixture thus obtained; (c) drying the compacted and formed mixture at temperatures of 50 ° C to 300 ° C and for a period of 0.5 to 10 hours; and finally (d) ceramic firing of the dried mixture at temperatures of 700 ° C to 1700 ° C for a period of 0.5 to 6 hours under such conditions that substantially no oxidation of the carbon occurs or a reaction of the inorganic molybdenum compound with the other components of the mixture occurs and at the same time a ceramic and / or chemical solidification of the mixture occurs by sintering, so that the carbon or the inorganic molybdenum compound are incorporated into a ceramic sintered matrix. Method according to claim 1, characterized in that that as molybdenum compound Molybdenum disulfide used becomes. Method according to claim 1 or 2, characterized that the Carbon selected is selected from the group of graphites such as natural and synthetic graphites, in particular in the form of graphite flakes and / or graphite dust, carbon blacks, carbon fibers and cokes such as carbonized cokes from the coal or petroleum industry. Method according to one of the preceding claims, characterized characterized in that Home mix as well at least one inorganic oxidic raw material and / or mineral constituent is added. Process according to Claim 4, characterized in that the inorganic oxidic raw material and / or mineral constituent is selected from the group of sintered earths, tabular earth, fused corundum, in particular corundum, normal corundum, bauxites, in particular calcined bauxites, enamel and sintered mullite, andalusite, kyanite, sillimanite, disthene, staurolite, chamotte, clays, metakaolin, bentonites, Diatoms, natural and synthetic amorphous silicas, quartz, cristobalite, quartz glass, natural baddeleyite and synthetic stabilized and / or unstabilized zirconium oxide, zirconium silicate, fused and sintered zircon mullite, zircon corundum, rutile, ilmenite, alkali and alkaline earth titanates, sintered and melted spinels, chrome ore, Fusion and sintered magnesia, olivine, synthetic cordierite (indialite), talc, serpentine, sepiolite, wollastonites, xonotlite, spodumene, petalite, lepidolite, garnets, feldspars, nepheline, minerals of the pyroxene and amphibole group, minerals of the mica group such as muscovite, biotite and Vermiculite, zeolites, carbonates such as magnesite, calcite, dolomite, siderite and rhodochrosite, sulphates such as barytes, anhydrite and gypsum, apatite and borates such as borax, colemanite, uxlex and hydroboracite. Method according to one of the preceding claims, characterized characterized in that Content of powdery, finely divided amorphous silica in the starting mixture 15th to 90 wt .-%, preferably 20 to 85 wt .-%, based on the total weight of the starting mixture. Method according to one of the preceding claims, characterized characterized in that Content of carbon in the starting mixture 5 to 40 wt .-%, preferably before 5 to 30% by weight, based on the total weight of the starting mixture. Method according to one of the preceding claims, characterized characterized in that Content of inorganic molybdenum compound, especially molybdenum disulfide, in the starting mixture up to 15 wt .-%, preferably up to 10 Wt .-%, particularly preferably up to 8 wt .-%, is based on the total weight of the starting mixture. Method according to one of the preceding claims, characterized characterized in that Content of inorganic oxidic raw material and / or mineral constituent in the starting mixture 5 to 70 wt .-%, in particular 10 to 65 Wt .-%, preferably 15 to 60 wt .-%, based on the total weight of Starting mixture. Method according to one of the preceding claims, characterized characterized in that Home mix as well Minerals, inorganic fibers such as quartz glass fibers, alumina fibers, Glass fibers, aluminum silicate fibers or basalt fibers, rock wool, Slags, flyashes, glasses, Frits, cements such as alumina cements and Portland cements added become. Method according to one of the preceding claims, characterized characterized in that Home mix as well Carbides and nitrides such as silicon carbides, silicon nitrides, boron carbides, Boron nitrides and / or titanium carbides are added. Method according to one of the preceding claims, characterized characterized in that Starting mixture comprises particles of the respective mixture constituents whose average particle diameter in the case of the other matrix-forming materials, in particular oxidic raw materials and / or mineral components, if available, at most 0.2 mm and in particular ≤ 100 microns, preferably ≤ 50 microns, are. Method according to one of the preceding claims, characterized characterized in that individual mixture components under the process conditions not resolvable are. Method according to one of the preceding claims, characterized characterized in that Home mix as well Water and optionally also process chemicals, in particular Thinning agent, Plasticizer, dispersant and / or binder added become. Method according to claim 14, characterized in that that as Bindemitel sodium, potassium and / or lithium water glasses, silica sols, natural and synthetic amorphous silicas, Portland cements, alumina cements, phosphates, in particular and alkaline earth phosphates and monoaluminum phosphates, borates, boric acids, clays, Kaolin, metakaolin, aluminum hydroxide, calcium hydroxide, magnesium sulfate, Magnesium chloride, magnesium hydroxide, aluminum hydroxychloride, sodium aluminate, Zirconium oxychlorides and / or zirconium acetates and phosphates become. A method according to claim 14, characterized in that a temporary binder is added as a binder, in particular a temporary binder based on organic compounds such as lignin nate, methylcelluloses or gelatin. Method according to one of the preceding claims, characterized characterized in that Preparation and preparation of the raw material mixture in step (a) a semi-wet or preferably a wet preparation under usual Conditions. Method according to one of the preceding claims, characterized characterized in that Compacting and shaping in step (b) according to standard granulation and compaction processes and conventional molding processes he follows. Method according to one of the preceding claims, characterized characterized in that Drying of the compacted and optionally shaped mixture in step (c) for a duration of 1 to 5 hours, preferably 1 to 3 hours, is performed, optionally under vacuum. Method according to one of the preceding claims, characterized characterized in that ceramic fire in step (d) in a largely of oxygen, in particular atmospheric oxygen, shielded, closed system he follows. Method according to one of the preceding claims, characterized characterized in that ceramic fire in step (d) under inert or reducing Conditions, in particular with exclusion of atmospheric oxygen, preferably in a vacuum or under a protective gas atmosphere. Method according to claim 21, characterized that as Protective gas hydrogen, nitrogen, ammonia gas and / or noble gases be used. Method according to one of the preceding claims, characterized characterized in that ceramic fire in step (d) at temperatures of 900 ° C to 1500 ° C, preferably 1000 ° C up to 1,350 ° C, for one Duration of 1 to 5 hours, preferably 1.5 to 4.5 hours. Method according to one of the preceding claims, characterized characterized in that ceramic fire in step (d) in a refractory container, in embedded in the carbonaceous granules or moldings to be fired are done becomes. Method according to Claim 24, characterized that the ceramic fire in step (d) in a grained electrographite, with natural Graphite flakes and / or with grained, carbonized cokes from the coal or petroleum industry filled refractory container carried out becomes. Method according to one of the preceding claims, characterized characterized in that ceramic firing in step (d) takes place in the embedding process. Method according to one of the preceding claims Production of Ceramic Granules or Moldings for Friction or brake pads. Method according to one of the preceding claims Production of ceramic granules or shaped bodies for refractory materials or refractory products. Use of according to the method according to claims 1 to 28 available ceramic granules or shaped bodies for producing friction or brake pads. Use of according to the method according to claims 1 to 28 available ceramic granules or shaped articles for the production of refractory materials or refractory products.