DD271511A5 - Ceramic composition and process for its preparation - Google Patents

Abstract

The invention relates to a method for producing a self-supporting ceramic composite body and subsequently produced refractory parts. The metal alloy and the permeable filler mass have at least one jointly defined surface finish and are oriented towards one another such that the formation of the oxidation reaction product takes place into the filler mass and in the direction of the surface finish. When the metal is heated, it reacts with the oxidizing agent to form the oxidation reaction product which penetrates the mass of the filler. This mass is heated to a second temperature so that a substantial portion of all non-oxidized metallic constituents oxidizes. The result is a ceramic composite body. Fig. 1

Description

271 S 11 - I -

A process for producing a self-supporting ceramic composite body and subsequently produced refractory parts

the invention

The invention relates to a process for producing a self-supporting ceramic composite body which consists of a ceramic matrix which is formed by oxidation of a parent metal containing an aluminum alloy, forming a polycrystalline material consisting essentially of an oxidation reaction product of the starting metal with one or more is formed of a plurality of oxidizing agents, and consists of embedded in the matrix one or more fillers ♦

The invention further relates to refractory parts which, when used, come into contact with molten metal, for example refractory products in steelworks. "

Characteristic of the known technical solutions

The subject matter of the present patent application is related to U.S. Patent Application No. 818,943, filed October 15, 1986, No. 776,964, filed September 17, 1985, No. 705,787, filed February 26, 1985, and U.S. Pat. No. 591,392, filed Mar. 16, 1984, entitled "New Ceramic Fabrics and Methods of Making the Same." These US patent applications describe the process for producing self-supporting ceramic bodies as the reaction product of the oxidation of an output metal source. Molten starting resin is reacted with a vapor phase oxidant to form an oxidation reaction product and the metal is migrated through the

Oxidation reaction product to the oxidizing agent and thereby constantly developing a polycrystalline ceramic body from the oxidation reaction product. The ceramic body produced may have metal constituents and / or be porous, which may or may not be related to one another. This process may be enhanced by means of an alloyed dopant, as is the case, for example, in the oxidation of an aluminum parent metal which oxidizes in air This process has been improved by the use of foreign dopants, which are applied to the surface of the parent metal, as described in U.S. Patent Application Nos. 822,999 filed 27 January 1986, No. 747,788, filed on May 25, 1990. Ouni 1985 and No. 632,636, filed on May 20, 1984, entitled "Process for Producing Self-supporting Ceramics".

The subject matter of the present application is also related to U.S. Patent Application Nos. 819,397, filed January 17, 1986, and No. 697,876, filed February 4, 1985, entitled "Ceramic Composite Products and Method of Making the Same" , These US patent applications describe a novel process for producing self-supporting ceramic composites by growing an oxidation product from a parent metal into a permeable filler, infiltrating the filler with a ceramic matrix.

Further developments of the above methods enable the fabrication of composite ceramic structures that 1. enclose one or more cavities that inversely mimic the geometry of a shaped parent base metal piece, and 2. have a negative pattern that is the positive pattern

2 71 S f 1

an inverse basic metal piece is simulated in reverse. This method is described in US patent application no. G23 542, filed 27 Oanuar, 1986, entitled "reverse reproduction process in the manufacture of composite ceramic products and products produced thereby" _t and in the US patent application no. 896,147 filed on 13. In August 1986 entitled "Process for Making Ceramic Composite Products with Reshaped Surfaces and Products Produced Therewith".

Methods have also been developed for making ceramic composite structures of particular shape or geometry. In these processes, a permeable filler preform is used into which the ceramic matrix grows by oxidation of a starting metal starting material, as described in U.S. Patent Application No. 861,025, filed May 8, 1986, entitled "Shaped ceramic composites and process for their preparation "is disclosed. Another method of making such ceramic composites involves the use of blocking agents to arrest or inhibit the growth of the oxidation reaction product at a particular time to determine the shape or geometry of the ceramic composite structure. This process is described in U.S. Patent Application No. 861,025, filed May 8, 1986, entitled "Process for Making Molded Ceramic Composites Using a Bulk".

The complete disclosure of all of the aforementioned US patent applications are expressly incorporated herein by reference

 Common to all of these US patent applications is the disclosure of

2 71 5 1

of the statements "θΙγ'ΘΘ ceramic body", which contains an oxidation reaction product "with which it is usually connected in three dimensions"'and optionally one or more non-oxidised constituents of the parent metal or cavities or both in white ¹ :. The metal phase and / or cavities may or may not be connected to each other. »This depends mainly on factors such as: B, the temperature at which the oxidation can occur, the composition of the starting metal, the presence of dopants, etc. If, for example, the growth process continues until the metal components are substantially removed (converted), the porosity then partially or nearly replaces completely the metal phase in the entire composite body, while at its surface a dense ceramic layer is formed · In this case, the porosity is most accessible from the surface of the ceramic body, from which the development of the matrix starts.

Ceramic refractory products have proved their worth in applications requiring good thermal shock resistance, corrosion and erosion resistance on contact with molten metals. Such parts can be used, for example, in control devices for controlling molten metal flows in molten metal transport devices, for example, in the manufacture and processing of steel. Such uses include, for example, gate valves, sub-entry nozzles, and ladle hoods. Gate valves ¹ are used to regulate the flow of molten metal from a ladle. In general, the gate valve systems, including some rotary valve designs, consist of a stationary nozzle attached to and within a movable plate

715

attached let. The flow of molten metals from the ladle is regulated by movement of the plate «by dl ·; Openings thereby be completely or partially aligned. When spouting the ladle and Abeperrzuetand the openings are not on top of each other. The important advantage of a slide closure system over a conventional stopper rod system is the better reliability of spalling, the ability to control melt flow, and the prevention of molten metal flow Ansauyens · Nevertheless, even the best Schieberverchlußsysteme, such as high-alumina Schieberverschlußsysteme, for some molten metals unsuitable » For example, for special steel grades, such. B. low-carbon manganese-rich steels. These corrosive steel blends strongly attack the binders used in most high alumina slide gate closures.

Most known refractory products for Schleber compounds include either tar-coated high alumina or calcined magnesia. However, such refractory products for gate valves do not have the criteria of thermal shock, corrosion and erosion resistance, a long shroud of the ladle, a long casting time, and to endure long preheating, and therefore have a short life.

Object of the invention

The object of the invention is to increase the thermal shock, corrosion and erosion resistance of refractory products and their lifetime extension, so that

271

For example, a long preheating and holding of ladles as well as a long casting time in steel mills is achieved «

Explanation of the essence of the invention

The invention has for its object to develop a process for producing a self-supporting ceramic composite body and subsequently produced refractory components, which makes it possible to oxidize a base metal at elevated temperatures in a permeable filler mass.

Erfindungugemäß this object is achieved in that a metal Ausgangsetück "is comprised aligned of an aluminum alloy with at least 1 Masee-% zinc _t, and a permeable Füllstoffmasee against each other, so that a polycrystalline material as a result of oxidation of a metal starting piece (hereinafter referred to as "base metal" and defined below) grows into a permeable filler mass. The filler mass has at least one specified surface finish and is filled with a polycrystalline material to such specified termination to form a ceramic composite body. Under the process conditions of the present invention, the molten parent metal oxidizes from its original surface (i.e., the surface exposed to the oxidizer) from the outside toward the oxidant and into the filler mass by migrating through its own oxidation reaction product into it. This leads to new ceramic Grundmaseegemischen with a matrix of a ceramic polycrystalline material in which the fillers are embedded.

271 5 1

The parent metal used in the growth process of the ceramic base lake is an aluminum alloy having at least about 1% by weight of zinc, and this base metal is first heated to a temperature above its melting point but below the melting point of the oxidation reaction product, leaving a body or molten pool of molten parent metal which is reacted with an oxidizing agent, preferably a vapor phase oxidizing agent such as air, to form the oxidation reaction product. At this first temperature or within this first temperature range the body of molten metal is at least a portion of the oxidation product in contact, which extends between de ¹ * body of molten metal and the oxidant. The molten metal is drawn through the oxidation reaction product to the oxidizer and into the bulk of the filler to cause the continuous formation of the oxidation reaction product 8 at the interface between the oxidant and the previously formed oxidation reaction product. The reaction is continued until the filler is up to the specified surface finish with each oxidation reaction product, by growth of the latter, which includes inclusions of unoxidized metal particles of the parent metal.

The resulting ceramic composite body consists of filler and a ceramic matrix which is a polycrystalline oxydafion reaction product and contains residual non-oxidized constituents of the parent metal, mostly aluminum and zinc, or other metals. The ceramic composite is at a second temperature (or within this second temperature range) above

271S 1

heated at the first temperature but below the melting point of the oxidation reaction 8 products 8 so that at least a substantial portion of the remaining non-oxidized metal constituents are removed or oxidized, for example by evaporation or oxidation of the metal constituents of the polycrystalline material without substantial formation of the oxidation reaction product over the specified surface finish In addition, "Heating to this second temperature may be carried out either in a vacuum, in a protective gas atmosphere or, better, in an atmosphere containing oxygen, but best in air." Part of the removed metal phase is mainly replaced by pores or voids. Other metal phases are oxidized in situ, transforming the metal into an oxidized species. The final structure consists of a ceramic matrix and filler, and the ceramic matrix consists essentially of an oxidation reaction product and intervening pores, at least a portion of which is accessible from one or more surfaces of the composite ceramic body Diameter less than about 6 microns, which prevents the penetration of some substances, such as molten steel.

The products of the present invention are substantially ceramic, that is, mainly inorganic and free of metal, although they may also have some metal inclusions or islands. These products are useful or manufactured especially for refractory products. According to the present invention, the latter include, but are not limited to, industrial refractory sliding firebricks made by moving with the bottom of a container, a

271S ti

Ladle ο. which contain molten metal, such as steel, "to facilitate and regulate the flow of molten metal through an opening in the ladle."

According to the present specification and claims, "oxidation reaction product" means the product of the reaction of metals with an oxidant to form an oxide. In accordance with the present specification and claims, "oxidant" means one or more suitable electron acceptors or electron splitters and may be a solid Liquid or a gas (vapor), or any combination of these conditions under process conditions.

The term "outer metal ¹ * as used in the present specification and in the claims refers to the aluminum alloy metal which usually contains at least about 1 to 10% by mass of zinc and which is the precursor of the polycrystalline oxidation product and contains aluminum alloy metal and commercially available aluminum alloy metal, which generally contains at least 1 to 10% by mass of zinc as well as foreign bodies and / or alloy constituents. «

Execution! The invention will be described below in an Ausführungsbeispiol

be explained in more detail.

In the accompanying drawings show:

FIG. 1 is a schematic cross-sectional view in elevation showing a complex of an aluminum alloy base metal with a filler deposited thereon and a carrier layer in a Feuerfeettiegel; and FIG

2715 1t

- 10 -

Figure 2 is a partial schematic vertical cross-section through a spool valve displaced between a top plate and the bottom of a ladle and a tube holder holding the tube through which the molten metal flows after leaving the ladle.

According to the drawings for the practice of the present invention, an output metal body 10 of an aluminum alloy having at least about 1 to 10 mass% zinc is formed into a block, strand, rod, plate or the like Filler mass 12 having at least one predetermined surface finish 14 are provided side by side and aligned with each other so that the oxidation reaction product grows into the filler 12 toward the specified surface finish 14 so that the filler mass 12 or a portion thereof is infiltrated by the growing oxidation reaction product. The parent metal 10 and filler mass 12 are embedded in a suitable substrate 16 which is substantially reactive under the conditions of the process and is such that the oxidation is not continued therein, and the "upper or exposed surface of the filler mass with the surface of the Embedding is flush (see FIG. 1). Suitable embedding materials are, for example, certain types of particulate clay. "The whole or construction is in a suitable refractory container or crucible 18".

The filler mass 12 is preferably made of a ceramic or refractory material and may be a grid or arrangement of a bed of particles, granules, powder, adhesive.

271 p

- 11 -

flocculants, refractory fiber, fibers, tubes, tubes, beads, whiskers or the like, or a combination thereof. The filler mass 12 may be either loose or bonded and has interstitial spaces, openings, spaces and the like so as to be permeable to the oxidant and the growing oxidation reaction product. Further, suitable fillers may be, for example, metal oxides, borides, Nitrides or carbides of a metal of the group of aluminum, cerium, hafnium, lanthanum, silicon, neodymium, praseodymium; Samarium, scandium, thorium, uranium, titanium, yttrium and zirconium. Some of these fillers may require protective coatings to prevent them from reacting and / or oxidizing under the conditions of the process. In one embodiment of the invention, the filler contains about 3 to 10% by mass silica, for example, combined with alumina. "An old particularly favorable alumina filler has a mesh size of about 5 to 500 mesh (U.S. Standard Sieve). Silicone carbide filler may have a mesh size of about 500 to 1000 (USA standard sieve).

In either case, the design is designed so that the oxidation reaction product grows into the filler mass 12 so that the gap between the filler particles is substantially filled by the grown oxidation reaction product. A matrix of the polycrystalline material, desalted by the growth of the oxidation reaction product, simply grows in and / or around the filler mass 12 so that the latter is preferably embedded and infiltrated to its predetermined surface finish 14 without substantially disturbing or displacing the filler mass 12

- 12 -

becomes. Thus, no external forces occur which could interfere with or disturb the location of the filler mass 12 "and no complicated and expensive high tempera ture high-pressure processes and devices are required, as in the known conventional methods to achieve a dense ceramic composite structure , In addition, the stringent chemical and physical compatibility requirements required in pressureless sintering to produce ceramic composites are largely reduced or eliminated by the present invention.

A solid, liquid or vapor phase oxidant, or a combination of such oxidants may be used. Vapor phase oxidants include without limitation oxygen, oxygen-argon, or other inert gas mixtures and air.

Solid oxidizers consist of reducible oxides, such as silica, tin oxide or zinc oxide. When a solid oxidizing agent is used, it is usually dispersed throughout the filler bed or through a portion of the bed of the starting metal, in the form of particles admixed with the filler or as coatings on the filler particles. When a liquid oxidizing agent is used, the entire filler bed or a portion thereof adjacent to the molten metal is coated or soaked, for example, by immersion in the oxidizing agent to impregnate the filler. A suitable liquid oxidizer contains glass types which melt at low temperatures.

Zinc or dopant (described in more detail below) accelerates or facilitates growth of the oxidation reaction product and subsequent removal

271 5 1

- 13 -

the non-oxidized metal parts from the formed Oxydationsprodukt. The zinc dopant is added to the aluminum parent metal and contains about 1 to 10 mass%, preferably about 4 to 7 mass%. Additional dopants (as described in the aforementioned copending patent applications) can be used in conjunction with the parent metal. For example, by mixing the oozing liquor with the parent metal, by externally coating the surface of the parent metal, or by combining or mixing the dopant with the filler 12, magnesium may be used, for example, to increase the doping effect of zinc.

An aluminum parent metal body 10, together with the permeable filler mass 12, is placed in a crucible or other refractory crucible such that at least one metal surface of the base mesh is exposed to the adjacent or surrounding mass of filler 12. When a vapor-phase oxidant is used, the filler mass is permeable to the gaseous oxidant present in the oxidative environment (mostly air at ambient atmospheric pressure). The resulting composition is then heated to a first temperature range in the presence of the oxidant in a suitable oven (not shown in the figures), the temperature of which is in the range generally between about 850 and 1450 C, or better, between about 950 and 1100C to increase, so that a molten bath or a body of molten parent metal is formed. The temperature range depends on the filler mass 12, the dopant or doping concentration, the oxidizing agent, or any combination of these factors. In this temperature range, the base metal begins to penetrate through the oxide layer that normally protects the aluminum source metal.

27t ft

- 14 -

If the parent metal is still exposed to the oxidizing agent at high temperatures, the continuous oxidation of the starting metal body IO may produce a polycrystalline oxidation reaction product of increasing thickness. This growing oxidation reaction product gradually penetrates into the permeable filler masses 12 and thus into the bulk of the oxidation product which also may contain non-oxidized starting metal components. This produces a cohesive composite. The growing polycrystalline matrix penetrates the filler mass 12 at a substantially constant rate (i.e., with a substantially constant increase in thickness as a function of time) provided that the source of oxidant is relatively kjonetant. for example, by allowing sufficient air exchange (or replacement of the oxidizing atmosphere) in the oven. The exchange of the Oxydationsatmosphäre can, if it is air, done favorably by means of air channels in the oven. The matrix continues to grow until the polycrystalline oxidation product has penetrated the filler mass 12 up to the specified surface finish 14. This is best done when almost all of the parent metal body 10 is consumed, that is, when almost all of the parent metal body 10 has been converted to the matrix.

The ceramic composites initially prepared by oxidation of the aluminum alloy parent metal with the oxidizer consist of filler most conveniently infiltrated and embedded to the final seal with the polycrystalline oxidation product from the reaction of the parent metal with the oxidizer and one or more non-oxidized metal constituents of the starting point

271 p. 11

- 15 -

metals are aluminum and zinc and other metals, according to the composition of the parent metal. The volume fraction of the residual metal (the nltoxydierten metal components) can be very different. Depending on whether the oxidation process takes place so far that the starting aluminum alloy is consumed. For example, a ceramic composite body made of aluminum alloy metal and 50% by volume filler in air at about 1000 ^° C. may contain about 0.5 to 10% by volume residual metal.

For producing a composite ceramic body which is almost free of metallic constituents, such as composite used for refractory sliding gate valves, the metallic elements (residual metal) present after the first heat treatment are substantially removed and / or by means of a second heating in situ oxidized. The ceramic composite body initially produced is heated to a temperature higher than the first temperature heated in the formation of the ceramic composite body. In addition to the second heating, the temperature may be raised so that the residual metal substantially vaporizes and / or oxidizes. This second heating may take place in an oxygen-containing or neutral atmosphere or in a vacuum. An oxygen-containing atmosphere is more favorable because there the removal of the residual metal by oxidation can take place at lower temperatures than is the case with removal by evaporation in a neutral atmosphere or in vacuum. For reasons of economy, air is most favorable at atmospheric pressure.

271S 1 ι

- 16 -

The microstructure is heated in the oven in the desired atmosphere, usually at a temperature in the range between about 1250 and 2000 ⁰ C, but most preferably at least about 1400 ⁰ C or at between 1400 and 1600 ⁰ C. This temperature is higher as the temperature used in the manufacture of the initially formed ceramic composite body. At these high temperatures, nearly all remaining non-oxidized metal elements of the aluminum alloy base metal are removed or converted to an oxide which does not grow beyond the specified surface finish. It is believed that the removal of most of the remaining non-oxidized metal elements is essentially due to volatilization of the metal Zinkdotlerstoffs is supported. Part of the remaining aluminum metal oxydi. * t in situ, without affecting the specified completion of the piece. The zinc dopant not only accelerates or facilitates the growth of the oxidation product but also volatilizes at high temperatures, resulting in porosity and high surface area. This in turn accelerates the oxidation of the residual non-oxidized Mdtall components of the starting aluminum alloy in the composite body. As mentioned earlier, the amount of zinc to be added to the starting aluminum metal is best between about 4 and 10% by mass (based on the mass of the aluminum parent metal). The zinc may also be used directly unalloyed commercial pure aluminum of, for example, 99 %, 99.5 % or 99.7 % . If desired, high purity or extra pure aluminum having a purity of, for example, 99.9 % or more may be used as the basis for the addition of the addition. This may be necessary if the refractory end product is in communication

27t S

- 17 -

with very high purity molten metals where even traces of foreign matter are undesirable. On the other hand, some zinc containing commercial wrought alloys or cast alloys can be used where the zinc content is higher than 1.0%, but better than higher than 4.0 % . and where the presence of other alloying elements does not affect the ultimate purpose. For example, an alloy containing 5.0-6.0 % zinc, 1.2-1.8 % magnesium, 0.08-0.18 % zirconium and the maximum allowable levels of the following elements: silicon (0.25%) , Iron (0.40%), copper (0.25%), manganese (0.10%), chromium (0.05 %), titanium (0.10 %) and other elements (0.05% each to to a total of 0.15 %) (all mass%, but with aluminum being the major fraction, one of the alloys that would be a suitable starting metal for the invention). In this case, the magnesium present in the alloy would be the doping effect of zinc If desired, the composite body may be cooled and removed from the oven, and then one or more surfaces of the cooled body may be machined to the appropriate dimensions (eg, milled, polished, ground, etc.) be favorable in the production of ceramic products with exact dimensions According to the present invention, the ceramic composite bodies of the invention can be made for use as refractories for spool valves. The spool valve, which is generally designated 20 in FIG. 2, contacts an upper plate 22 or the bottom of a ladle 24 containing molten metal 26 (ie, molten steel). The upper plate 22 is fixedly connected to the ladle 24 and has an opening 28 which is in direct communication with the pan opening 30 at the bottom of

2715 I ι

- 18 -

Ladle 24 is. The spool valve 20 has a spool closure assembly 32 having at least one spool port 34. A drive, such as a throttle cylinder or the like, is connected to the spool closure 20 so as to push or rotate the spool closure on the lower surface of the top plate 22 the slide opening 34 with the opening 28 in the upper plate and the socket opening 30 is either overlying or not. A tube holder, shown as 36 in the figure, holds a tube 38 and supports the spool valve! 20, the upper plate 22 and the ladle 24, which is connected to the upper mat 22. The tube 38 passes the molten metal 26, after it leaves the ladle 24, through the slide closure 20. The refractory slide valve 20 by means of the drive 36 is arranged so that the slide opening 34 de9 refractory slide valve in relation to the opening of the upper plate 28 with the Ladle opening 30 of the ladle 24 is completely displaced, so the molten metal 26 does not flow from the ladle 24. Thus, the molten metal (as will be explained in more detail below) does not penetrate into the pores of the ceramic matrix in the Schleuberverachlußkonstruktion 32 of the slide valve 20. If the slide valve 20 is displaced along the upper plate 22 and the lower part of the ladle 24, so that the slide opening 34 is above the opening 28 in the upper plate and over the ladle opening 34 *, the molten metal 26 flows by gravity from the ladle 24 through the corresponding Ladle openings 34 * into the R The gate closure structure 32 must be extremely smooth, that is with maximum deviations of 0.0127 mm, and must be pressed firmly against the base of the top plate 22 so that no molten metal escapes between the interfaces. The slider closure structure 32 and the upper

271

- 19 -

Plate 22 is made of refractory materials or elements that can be machined smoothly (e.g., by milling, grinding, polishing, etc.) ₍ such that the top plate 2? And slide gate structure 32 of gate valve 20 are open and closed The spool closure structure 32 of the spool valve 20 should not have too large pores, otherwise the molten metal would penetrate into the pores and weaken the spool closure structure 32. In addition, the spool closure structure 32 must be extremely durable have good thermal shock resistance and consist of refractory materials or elements that are strong enough to withstand the chemical corrosion and erosion effects of the molten metal compounds To produce a Schioberverschlußkonstruktion 32 of a ceramic composite fabric with the aforementioned properties and / or criteria, the ceramic composite should contain a ceramic matrix consisting essentially of non-metallic and inorganic materials. Any greater amount of unoxidized metallic constituents within a ceramic composite, such as aluminum, could compromise the performance of the material, for example, by reducing its hot strength and possibly increasing the growth of the oxidation beyond the dimensions of the gate valve and causing the gates to stick together. Likewise, the resistance to heat shocks could be compromised. As a result, the gate valve 20 would fail or need to be replaced after a short use, most likely because it crumbles, ruptures or its surface grows.

- 20 -

The ceramic composite obtained after removal and / or oxidation of almost all remaining metal elements from the aluminum parent metal is a ceramic composite that is mostly between about 5 and 98 percent by volume of the total volume of the composite containing one or more fillers contained in embedded in a polycrystalline ceramic matrix. The polycrystalline ceramic matrix is comprised of about 94.5 or more mass% (of the bulk of the polycrystalline oxidation product (linked alpha alumina), about 5 % or more zinc aluminate, and about 0.5 or less mole percent of non-oxidized metal elements of the aluminum parent metal ·

The polycrystalline ceramic matrix has a certain porosity, ranging from about 2 to 25 vol .-% of the polycrystalline ceramic matrix, but usually not more than 10 % . It is believed that some porosity is necessary for the desired thermal shock resistance of the refractory product. At least part of the porous surface is accessible from the surface, but most often 5 % of these porous surfaces have pore diameters of about 1 to 8 microns. It is best if the pore openings accessible from the surface have an average diameter of 6 or less microns, and 6 is the average of a normal Gaussian distribution function. An alumina-based ceramic composite having surface apertures whose diameter is 6 microns or smaller is particularly suitable for making sliding-gate fireclay stakes because the molten steel does not penetrate the structure.

The ceramic composite structure of the present invention

2 7 ί 5 f

- 21 -

1st indicated as follows; Three-point bending test for a heat breaking strength of about 241.15 to about 447.85 Mpa at 1400 ⁰ C in N _2, depending on the size of the Tonerdefüllstoffs; by a heat shock resistance parameter (resistance to crack propagation, Rst) of about 15.6 ⁰ C /

6.5 cm; a volume stability (thermal expansion in accordance with ASTM E228.71 from room temperature to 1500 ⁰ C mi's subsequent cooling) of 0.15% or less of linear changes and without any changes in the thermodynamic flux, the rupture or Verbiegenfführen; and by one

Corrosion resistance (air / metal wear in inches with a

2 larger diagonal bar of 6.5 cm, 20 min rotation test, made of Al tempered steel as described in the example below) of 1.02 mm or less.

The ceramic composite of the present invention has substantially clean grain boundaries in which the grain sizes between the crystallites have no other phase. Most notably, the grain boundaries have no sill-containing phases. This feature is particularly important for refractories for steel mills. Low melting fumed silicates are present in almost any conventional alumina refractory, and this material reacts with the molten alloy, causing it to dissolve into the liquid steel, eventually resulting in cracking, crumbling and fracturing of the structure.

In addition, the composite bodies of the present invention do not require provisions for inhibiting oxidation of the binder phase, since it is a fully oxidized matrix, as opposed to the carbon-bonded clay refractory products currently found in the Japanese market for gate valves.

2715 If

- 22 -

In a particularly effective method of carrying out the present invention, the filler is poured into a preform which has the same shape as the desired end product. The preform can be made by any of the many conventional ceramic body production methods (such as straightforward pressing, isostatic pressing "Slip casting, sedimentation casting, strip casting, injection molding, fiber wrapping for U8W fiber"), depending mainly on the properties of the filler, which method is used. The fact that the particles are bound prior to infiltration can be achieved by light sintering or by using various organic or inorganic binders which do not interfere with the process or add unwanted by-products to the final fabric. The preform is made to have sufficient shape integrity and green strength and should be permeable to the oxidation product and preferably characterized by a porosity of between about 5 and 90% by volume, but most preferably between about and 50% by volume. It is also possible to use admixtures of fillers with the corresponding mesh sizes. Then, the preform is contacted with the molten metal at one or more surfaces until the growth and impregnation of the preform is completed to its surface boundaries.

In conjunction with the filler or preform, an inhibitor may be used to prevent the growth or development of the oxidation product beyond the hinaue limit. After the first and before the second heat treatment, the end limit is removed by any suitable means. Suitable barrier means may be made of any material,

- 23 -

Mixture, element, a composition o. Ä. Which maintains a certain integrity under the process conditions of the present invention, is non-volatile, and as possible to the vapor phase oxidant permeable and thereby inhibit the further growth of the oxidation product locally, prevent, stop , obstructing "can. Suitable barrier agents for aluminum parent metal are calcium sulfate (calcined gypsum), calcium silicate, and Portland cement, as well as mixtures of these materials, which are usually applied to the surface of the filler in the form of a slurry or paste. A preferred barrier agent is a mixture consisting half of calcined gypsum and half of calcium silicate. This barrier agent may also contain a suitable combustible or volatile substance which is removed on heating, or a substance which dissolves on heating to increase the porosity and permeability of the barrier material. The barrier means can be easily removed from the composite body, for example, by sandblasting, grinding, etc. With a preform, especially together with a limiting means, clean shapes are achieved, thus minimizing or eliminating the costly machining or grinding.

As a further practical embodiment of the invention, the addition of dopants in conjunction with the starting metal can favorably influence the oxidation reaction process. The function or functions of the dopant may depend on a number of factors unrelated to the dopant itself. These factors include, for example, the particular source metal, the desired end product, the particular combination of dopants, when two or more dopants are used, the use of an external one

- 24 -

applied dopant in conjunction with an alloyed dopant, the concentration of the dopant, the Oxydationsmilieu and the process conditions. The dopant (s) used in the methods should be substantially removed or oxidized on the second heating so that they do not affect the properties of the final product.

The dopant (θ) used in conjunction with the starting metal may be 1. provided in the form of alloying elements of the parent metal, 2. may be applied to at least part of the surface of the parent metal. O 3 may be added to the filler bed or preform or a part thereof become. However, two or more of the 1st, 2nd, and 3rd techniques can be used in combination. An alloyed dopant may for example be used in conjunction with an externally added dopant. In the third technique, one or more dopants are added to the filler bed or preform. In this case, the addition may take place in any suitable manner, for example by distributing the dopants in one part or the entire preform in the form of a coating or particles, but most preferably at least in a part of the preform adjacent to the parent metal. For example, silica added to an alumina undercoat is particularly useful with air-oxidized alumina starting metal. The addition of any dopant to the preform may also be accomplished by applying a layer of one or more dopants to and into the preform, including their interior openings, gaps, passages, spaces, or the like, which render them permeable.

The invention will be further illustrated by the following example.

2715ft

- 25 -

example

A cast aluminum alloy block measuring 25.4 mm χ 63.5 mm χ 215.9 mm was placed horizontally on top of a layer of a mixture of commercially available coarse grained pure clay 8-14 and 5 mass% SiCl with a mesh size of 500 and then with The alloy contained about 5 to 6.5 Maese% zinc, about 0.25 mass% or less copper, about 0.4 to 0, .6 mass% chromium, about 0.15 mass% or less of silicon, about 0.40 mass % or less of iron, about 0.25 mass% or less up to 0.50 mass% of magnesium, about 0.10 mass% or less manganese, about 0.15 to 0.25 mass% titanium, about 0.20 mass% or less of other metals, with a maximum amount of about 0.05 mass% or less, and the whole is compensated with aluminum ,

The ingot embedded in the clay was placed in a suitable refractory crucible and placed in a simple flame oven. Natural convection and diffusion allowed air to enter the oven through random openings in the walls of the oven. The unit was processed at a setting temperature of 1000 ⁰ C for 144 hours, namely n3ch an eight-hour warm-up time of the oven to reach this set temperature. After 144stündigen Efwärmung the sample was cooled in a further eight hours to less than 600 ⁰ C. Thereafter, the resulting ceramic composite body was removed from the oven. The body contained residual amounts of zinc, aluminum and silicon.

In order to remove at least a large part of the residual amounts of zinc, aluminum and silicon, the ceramic composite body was again in a fouorfesten crucible in the

271 5 m

- 26 -

Flame furnace set and worked for eight hours at a setting temperature of 1400 ⁰ C, after the first warming of the furnace for a full hour to this temperature. After the eight hour heat treatment, the composite ceramic body was cooled at 600 ^° C. for a further eight hours and then removed from the oven. After the second heat treatment at 1400 ^° C., the original gray metallic earth base became white, indicating that very little residual metal remained was. The microstructure of the ceramic composite indicated a very homogeneous, porous, fine-grained (diameter dp grains about 6 microns) bulk clay basis. The residual amounts of zinc volatilized, effectively expelling the aluminum and silicon residuals and making room for in situ oxidation of some of the aluminum during the second heating to 1400 ^° C. Finally, this resulted in a ceramic composite with greater porosity and low metal content , The second heating to 1400 ^° C did not cause any further substantial growth of the oxidation reaction product beyond the originally established terminus of the composite body, although aluminum, zinc and silicon were present prior to a second heating to 1400 ^° C. The flexural test gave (at room temperature) a breaking strength (MOR) of about 275.6 MPa for the final product and a retained strength (MOR) of about 165.36 MPa after five rapid heats and cools between room temperature and 1200 C, 10 minutes each Holding time at any temperature. X-ray studies of the ceramic product showed clay and some smaller amounts of zinc alurinate.

To investigate the effect of molten steel on this ceramic product, it was quartered and placed in four holders for samples threaded by means of a grinder

27ί 5 1

- 27 -

This device consisted of a steel frame with an electric motor with variable speed, which is connected to the bearing shaft. The four ceramic parts were rotated with the brackets around the center axis of the stored shaft. "The outer corners of each part traversed a distance of 15 240.0 mm per minute at 48 min., A steel sheet (carbon fiber, sulfur, phosphorus, and oxygen) heated to 1593 ⁰ C and its surface before Ver-.such purifies "the four ceramic parts were heated to 1093 ⁰ C and then immersed into the molten steel and rotated at a speed of 48 min" for 20 minutes in the Rotationsteetvorrlchtung. Then the parts were removed from the holders, cooled and examined for the effect of the molten steel on the ceramic body. It was found that the ceramic body strongly resisted the penetration of steel, did not react with the volatile steel and did not crack during the experiment due to the temperature difference. As a result, ceramic composite bodies are suitable for refractory products in steel works, such as slide valves which come into contact with molten steel.

Claims (16)

27f 5 f claims A process for the preparation of a self-supporting ceramic composite "of a koramiechen base, which is formed by oxidation of an aluminum alloy contained base metals» to form a polycrystalline material which is formed essentially from an oxidation reaction product of the starting metal with one or more oxidants, and consists of one or more fillers embedded in the matrix, characterized in that it comprises the following steps χ a) positioning of a starting metal, consisting of an aluminum alloy with at least 1% by mass of zinc next to a permeable Füllmesmaese with at least one specified surface finish, and the alignment of the starting metal and filler against each other so that in the oxidation reaction of the starting metal with an oxidizing an Oxydationsreaktionsprodukt in forming the filler mass into and in the direction of the predetermined surface finish; b) heating the discharge metal to a first temperature above cfine melting point, but lower than the melting point of said oxidation reaction product to form a body of molten parent metal, reacting the molten base metal with said oxidizing agent at said first temperature and forming the oxidation product wherein, at the first temperature, at least a portion of the oxidation reaction product is in contact with the body; The melted metal and oxidizing agent expands and expands between them, so that the molten metal is drawn through the oxidation reaction product to the oxidizing agent and adjoining filler mass, and further oxidation reaction product in the filler mass and at the interface between the oxidizing agent and the previously formed oxidation reaction product Forms the reaction until the filler mass is infiltrated with a ceramic base, which also contains residual metallic elements of the parent metal, to the specified common surface finish; and c) heating the mass infiltrated according to step b) either in an oxygen-containing atmosphere of an inert atmosphere or in vacuum to a second temperature above the first but below the melting point of the oxidation reaction product, so that at least a substantial portion of the remaining non-oxidized Metal elements are removed or oxidized from or in the mass, essentially without formation of the oxidation product beyond the specified surface finish, resulting in a self-supporting ceramic composite. 2. The method according to claim 1, dedurch characterized in that in addition to zinc at least one dopant is used in conjunction with the Auagangsmetall, 3. The method according to claim 1 or 2, characterized in that the filler contains approximately between 3 and 10% by mass of silica. 2715 4. The method according to claim 1 or 2, characterized in that «the oxidizing agent is an oxygen-containing gas and the oxidation reaction product is an oxide of aluminum. 5. The method according to claim 4, characterized in that said oxidant is air at atmospheric pressure « A method according to claim 1 or 2, characterized in that said first temperature is approximately between 850 and ⁰ C. 7. The method according to claim 1, characterized in that said first temperature is between 950 and 1100 ^° C. 8. The method according to claim 1, characterized in that said second temperature is higher than about Ϊ250 ⁰ G. 9. The method according to claim 1, characterized in that the tesa;
is · said second temperature at least about 1400 ⁰ C. 10. The method according to claim 1, characterized in that the heating (c) takes place at said second temperature in air at atmospheric pressure. 11. The method according to claim 1 or 2, characterized in that the filler of one or more metal oxides, borides, nitrides of a metal from the group of aluminum, cerium, HafniumijLanthan, silicone, neodymium, praseodymium, samarium, scandium, thorium, uranium, Titanium, yttrium and zirconium exists. 2715 II 12. Tempting according to claim 1 or 2, characterized in that the filler consists of a material in the form of granules, particles, powders, fibers, hair-tufts, aggregates, pellets, tubes, refractory pulp, tubes or a combination thereof. 13 »Process according to claim 1 or 2, characterized in that the filler contains alumina or silicon carbide. A method according to claim 1 or 2, characterized in that the ceramic matrix which forms upon heating (c) is porous and at least partially accessible from one or more surfaces of the ceramic composite body. 15. The method according to claim 14, characterized in that the pore openings of the porosity have an average diameter of less than about 6 microns · IG. Refractory part used where molten metal is used, characterized in that the structure of the part contains a ceramic matrix escaping by oxidation of a parent metal containing an aluminum alloy having at least about 1% by mass of zinc, so that Polycrystalline material is formed, which consists essentially of an oxidation product of the reaction of the starting metal »with an oxidizing agent, and one or more fillers, which are embedded in the matrix. 17. Refractory member according to claim 16, characterized in that it comprises a slide valve refractory, whose At least one pusher opening has feet which generally have a flat surface so that it contacts a ladle having a ladle opening and containing molten metal, thereby permitting the molten metal to come into contact pour the ladle through the ladle opening and the gate opening and regulate the flow. 18. Refractory member according to claim 16 or 17, characterized in that the filler contains approximately between 3 and 10% by mass of silica. 19. Feuerfostteil according to claim 16 or 17, characterized in that the filler contains toner cube with a mesh size between about 5 and 1300. 20. Feuerfeotteil according to claim 16 or 17, characterized in that the ceramic matrix is porous and at least a portion thereof is accessible from one or more surfaces of the ceramic matrix, wherein the porosity pore openings having a mean diameter of less than about 6 microns comprises , H ^le C? ¹¹ ύ 5? 1 ¹ ? drawings