EP1731631B1 - Production of a composite material - Google Patents

Abstract

In a process to form a composite material to reinforce a metal structure, an anode containing carbon and a metal oxide are brought into electrolytic contact with a cathode in the vicinity of the material to be strengthened. The metal is deposited under cathode conditions, the membrane sub-dividing the electrolytic cell into anode and cathode chambers. The anode is an inorganic substance containing CaCl 2. The metal oxide is a lightweight metal e.g. Al, Mg, Ti, Ni, Nb, W and/or Zr. The strengthening material is an electrically-conducting fiber, particle, open-pored foam, metal, carbon, or ceramic e.g. SiC. Also claimed is an electrolytic cell for the production of the composite material.

Description

The invention relates to a method for producing a composite material and to an apparatus for carrying out this method.

From deposits, metals are often mined in the form of metal oxides. Depending on the ore, more or less expensive processes for reducing the oxides and cleaning foreign substances are used to recover the metal. This will be explained in more detail below with reference to the production of titanium.

To reduce titanium oxides, the Kroll process is usually used ( W. Kroll, Production of Ductile Titanium, Transact. Electrochem. Soc. 78 (1940), pp. 35-37 ). Starting product for this is rutile (TiO ₂ ) or ilmenite (FeTiO ₃ ), which is prepared after the mining extraction. Essential for the process is the chlorination intermediate, which generates titanium tetrachloride (TiCl ₄ ) from titanium oxides and removes impurities. The final reduction of TiCl ₄ to titanium occurs with magnesium. The resulting magnesium chloride is decomposed electrolytically and recycled to the circuit as chlorine and magnesium. The end product of this process is a porous but pure titanium sponge. The process consists of a chain of several sub-processes. This results in equipment and energy a considerable effort.

The titanium sponge obtained by the Kroll process or any other process can be processed by remelting, alloying other elements, forging or rolling to semi-finished products, from which corresponding components can be produced. For extreme applications in terms of strength and rigidity, further processing into titanium matrix composites (TMC) is also possible. For this purpose, a number of methods exist, one of which is briefly described below. Starting material of existing processes is always a semi-finished titanium alloy.

The difficulty in the production of TMCs is the high melting point and the reactivity of the titanium alloys. Therefore, methods have been developed that allow for composite fabrication below the matrix melt temperature. The lowest possible process temperature in conjunction with short cycle times is the prerequisite for minimizing harmful reaction products.

The use of relatively thick monofilaments (thickness between 100 and 140 μm) of silicon carbide allows processes that would not be rational with finer fibers. These are, for example, methods in which the individual fibers are coated with the matrix material. The fiber volume content is adjusted via the coating thickness. The coated fibers are bundled and encapsulated in a sleeve of the matrix material. In a subsequent pressing operation in a hot-isostatic press, the composite is consolidated at about 1900 bar and in a temperature range of 920 to 980 ° C ( Leyens, C., Hausmann, J., Kumpfert, J., Long Fiber Reinforced Titanium Matrix Composites: Fabrication, Properties, Applications, in Titanium and Titanium Alloys, Peters, M., Leyens, C., eds. 2002, Wiley-VCH: Weinheim. Pp. 321-350 ). This process gives a composite material of the highest quality. In contrast to other methods, a nearly ideal hexagonal fiber arrangement can be achieved. A mutual contact of the fibers is almost excluded by the fiber coating. This is the basic requirement for excellent mechanical properties. In addition to the titanium fabrication process described above, a number of other process steps are required to produce the titanium matrix composites. Therefore, the cost of producing titanium matrix composites is again significantly higher than that for the production of titanium and titanium alloys. However, not only titanium matrix composites but also composites with other metallic matrices, such as aluminum, magnesium, nickel and their alloys, are concerned with this issue.

DE 42 04 120 C1 describes a process for producing a carbon fiber-aluminum composite in organic solvents, in which the fibers are merely coated in a first step and in a second step the coated fibers are placed in a molten metal to obtain the composite. The anode compartment is not separated from the cathode compartment by a membrane. In this document, the metal is already used in its target state (metallic) as the anode material. In addition, the coating of the fibers serves as an auxiliary layer for further composite material production.

Also in WO 2005/019501 A2 described method does not use a membrane for separating the anodes from the cathode chamber.

US 4,341,823 A also describes a two-step process for producing a fiber-metal composite, in which the fibers are first electroless plating coated with metal and then dipped into a lead melt after several further coating operations to obtain the finished composite material.

In EP 0 339 464 A1 Metal particles are first electrolessly provided with a thin copper layer and further processed in a second step by means of electroplating to form a composite material.

EP 1 489 192 A1 describes a process for the production of titanium-fiber composites, wherein the fibers to be coated must be provided with a slurry in a first step, and then coated with titanium in a second step.

FR 2 297 261 describes a device for electrochemical aqueous processes, which does not take into account the high temperatures of molten salt.

It is common to most of the electrolytic production processes that the oxygen produced on the anode side can not be removed sufficiently quickly. This would be a conductive material necessary, which additionally has a high oxygen affinity. Furthermore, at least two steps are usually necessary for the production of the composite material.

For the production of titanium is in the JP 2004-143557 A described that the anode may consist of a carbon plate, wherein titanium dioxide is reduced in a metal salt melt to titanium.

CN 1376813 describes the production of Al-Ti alloys using a carbonaceous anode containing titanium dioxide.

The invention is therefore based on the object to find a method and an apparatus for producing a metal-fiber composite material, after which the composite material is available in one step and the resulting oxygen can be easily removed without restricting the process otherwise. Another object of the invention is the electrolysis of a Me _x O _y -C anode with the aim of environmentally friendly one-stage and chlorine-free production of cost-effective composites with Me metal matrix.

The object of the present invention is further to provide composites with a metal matrix, in particular of metals, which have a melting point above the decomposition temperatures of the reinforcing material or tend to undesirable reactions between the metal and the reinforcing material.

The object underlying the invention is achieved in a first embodiment by a method for producing a metal-reinforcing material composite material according to claim 1.

The membrane or the diaphragm is therefore essential for the invention, so that the carbon located in the anode compartment can not get to the cathode and react there with the very reactive metals such as Ti. Furthermore, the membrane causes the preferably existing loose bed of carbon and metal oxides remains limited to the anode compartment. The membrane is advantageously designed so that it is permeable to ions at most, so that larger particles remain in the anode compartment. Therefore, the membrane is preferably made of fireclay or porous Al ₂ O ₃ -FF materials (refractory) and preferably has a thickness in a range of 8 to 15 mm.

By electrolysis of metal oxide-carbon anodes in molten salts, the metal can be dissolved in the electrolyte and deposited on the cathode. Compared to the previously known methods, the proposed process is characterized by a significantly reduced number of process steps, in particular if the process of metal production is taken into consideration. This results in significant economic and environmental benefits.

The essential idea of the invention is therefore a new method of metal production with the Combine composite production directly. As a result, the number of process steps for producing a composite material with metal matrix compared to the prior art can be significantly reduced. Advantage is a much more resource-friendly and environmentally friendly production of the composite material. This can be achieved by an electrolytic process in which an anode of metal oxides and carbon is used, by means of which the metal is dissolved in a molten salt and deposited on preferably formed as a cathode reinforcing material.

If, as a cathode, it is advantageous to use a material which at the same time serves as a reinforcing material in a composite material, for example ceramic or carbon fibers, then a metal matrix composite material is obtained as the end product, without the need for an auxiliary cathode.

The composite material obtainable by the process according to the invention may initially have pores and / or be very brittle. In this case, the material can advantageously be compacted by a subsequent pressing operation. The pressing can be unidirectional or isostatic with or without the influence of heat. Furthermore, it corresponds to a preferred embodiment of the method according to the invention, when a reinforcing material is coated with the metallic matrix and this is pressed in a subsequent pressing operation to form a compact composite material.

Carbon in the anode compartment can easily bind the resulting oxygen and, being conductive, reintroduce it to the molten salt, or optionally transport it and release it to the environment. Preferably, carbon is used in the anode space in the form of a loose bed. The carbon may be present for example as a solid petroleum pitch or as coke. If the carbon is in the form of a loose bed of solid petroleum pitch, it may optionally melt at the necessary process temperature and encase the metal oxide particles. The use of carbon in the anode space significantly improves the conductivity of the anode compared to the metal oxide alone and thus makes the process considerably more efficient. Furthermore, carbon has the advantage of easy availability which can not be underestimated compared with comparable materials.

It has proven to be particularly advantageous to use an inorganic, in particular completely inorganic, anode. Thereby, the process can be carried out at high temperatures, such as prevail in a molten salt.

Salt melts according to the invention include melts in which inorganic salts (electrolytes) are more or less dissociated in their ions. One distinguishes salt melts, which consist of one, and those, which consist of several components. In the art, molten salts are used as heat transfer agents, for example in heating baths (salt baths) and in heat exchangers, recently also as heat storage (for example with KF · 4 H ₂ O, melting point 18.5 ° C), for covering and cleaning molten Metals (descaling, prevention of air entry and dissolution of oxidic impurities) or in the heat treatment of metallic workpieces (in particular during tempering and hardening of steel and in nitriding), for electroplating of refractory materials and in batteries.

Preferably, the process is carried out in a molten salt, wherein the salts are in turn preferably selected from conventional fluxes, for example from the group of chlorides and fluorides and mixtures thereof. The salts are preferably metal salts of the first and second main groups, more preferably metals selected from the group K, Li, Ca and Mg, and mixtures thereof. For example, the metal oxide in the anode compartment can be chlorinated, become itself an electrolyte, and then deposit on the cathode. The halide ion becomes part of the molten salt again.

Preference is given to using a metal oxide of the refractory and / or light metals, in particular the metals Al, Mg, Ti, Ni, Nb, W and / or Zr, and very particularly preferably TiO ₂ or Al ₂ O ₃ , since these metals with reinforcing materials particularly lightweight yet mechanically strong and torsion-free composites result. The metal oxide is preferably used as a loose bed, as granules or as a powder. Another advantage of this embodiment is that no expensive Ti metal is needed for the production of a composite material, for example with Ti, but the much cheaper TiO ₂ can be used.

Light metal in the context of the invention are metallic materials having a specific density of at most 4.5, in particular 5 g / cm ³ . These include, for example, Mg, Al, Be and Ti and their alloys. Light metals are preferably used where the weight of components plays a role in terms of optimal energy use, for example in aviation and automotive technology, but also in building services.

Advantageously, the anode current density is adjusted so that the forming Ti-chlorides dissolve in the salt (electrolyte) and do not volatilize. This will cause the chemical equilibrium within the electrolytic cell to be longer stable and prolong the maintenance intervals accordingly. Furthermore, many of these volatile salts are toxic and / or corrosive and should therefore be avoided to save costly removal devices.

According to the invention, a reinforcing material in the form of fibers, particles and / or an open-pore foam is used. Especially when using fibers or foam, a particularly high rigidity of the composite material can be achieved. If an open-pore foam is used, the result is a composite material similar to the so-called melt infiltration with a high mechanical isotropy. In the case that the reinforcing material comprises fibers, the fiber material is preferably a metal, a ceramic or carbon, wherein among the fibers cylindrical bodies having a diameter in a range of 4 to 500 microns and a length, the at least 10 times the diameter, preferably. When using electrically non-conductive ceramics as a fiber material, these can preferably be doped to produce the conductivity, deliberately contaminated or coated conductive. However, a corresponding precoating, doping or targeted contamination is not absolutely necessary.

Advantageously, a reinforcing material of metal, carbon and / or ceramic, in particular of SiC, is used. It has been found that mechanically particularly stable composites are available compared to other materials.

Preferably, the reinforcing material is conductive or conductive coated, since this can then be used as a cathode itself and makes an auxiliary cathode superfluous.

The reinforcing material is preferably used without pretreatment with the metal oxide. As a result, an additional process step can be saved and the process can be significantly streamlined. It has been found that the omission of the pretreatment does not lead to any substantial loss of the properties of the resulting composite material.

The reinforcing material, the metal oxide and the process conditions are advantageously selected so that the metal resulting from the metal oxide during the electrolysis does not react chemically or in a limited way with the reinforcing material and thereby is produced to a corresponding composite material. This achieves bonding of the reinforcing material to the metal, which has excellent mechanical properties such as high strength and rigidity.

The process is preferably carried out at temperatures in a range of 400 to 900 ° C, more preferably in a range of 800 to 900 ° C. By this compared to the prior art low temperatures can be saved significantly costs. These low temperatures are obtainable, for example, by molten salts containing a mixture of LiCl, KCl and CaCl ₂ .

The electrolytically produced composite material is advantageously subjected to a subsequent pressing operation, optionally with heat treatment, whereby this compacted and so a compact composite material is produced. Intermediate product is preferably a SiC fiber, which is preferably coated with titanium. For example, such a coated fiber can serve as a raw material for making a composite by compressing bundles thereof and thereby densifying the metallic coating to form the matrix in a compact composite.

The cathode material and / or the anode material is preferably continuously supplied and removed. This can also do that entire process can be carried out continuously, thus simplifying the manufacturing process.

The avoidance of a costly reworking of the raw materials leads to an environmentally friendly, for example, titanium production with lower energy consumption, since the separate production of TiCl _{4 is} eliminated. Concurrent with this titanium production, substantial steps are being taken to manufacture the titanium matrix composite. Furthermore, the raw materials are used extremely efficiently, since waste quantities are largely eliminated by numerous intermediate steps and reworking.

In a further embodiment, the object according to the invention is achieved by an electrolytic cell for producing a composite material comprising at least one anode space and at least one cathode space which is separated from the anode space by a membrane (ie a diaphragm), characterized in that the anode is a conductive one Anode, containing carbon and at least one metal oxide, wherein the cathode space, a reinforcing material in the form of fibers, particles and / or an open-cell foam in a molten salt electrolyte is provided.

Considerations of the known metal extraction processes, in particular the production of Mg show that it is possible to directly recover light metals by electrolysis with an anode of a metal oxide-carbon mixture (electrochemical reduction with integrated chlorination). In this electrolysis process, the cell space is divided by a diaphragm in the cathode and anode chamber. A mixture of Me _x O _y and carbon is used in the anode chamber, wherein Me advantageously an element from the group of refractory or light metals, in particular Al, Mg, Ti, Ni, Nb, W or Zr. The electrolyte used is a molten, preferably chlorine-containing, salt, for example CaCl ₂ or a mixture of different salts.

An auxiliary cathode may be provided in the cathode compartment. This is necessary even if the reinforcing material is not conductive or the reinforcing material can not act as a cathode for another reason. In this case, the cathode space is partially or completely filled with the reinforcing material. The metal is now deposited on the auxiliary cathode and thus grows around the reinforcing material to obtain the composite material according to the invention.

Advantageously, a plurality of anode compartments may be provided. This is particularly advantageous because it also allows the deposition of alloys, in particular with concentration gradients.

Advantageously, the cathode itself consists of the reinforcing material, which is coated conductive or conductive for this purpose. As a result, an additional auxiliary cathode is no longer imperative, even if it can still be used.

• Fig. 1: Querschnitt einer erfindungsgemäßen Vorrichtung, wobei das Verstärkungsmaterial gleichzeitig die Funktion der Kathode übernimmt.
• Fig. 2: Querschnitt einer erfindungsgemäßen Vorrichtung, wobei im Kathodenraum eine Hilfskathode vorgesehen ist.
• Fig. 3: Querschnitt einer erfindungsgemäßen Vorrichtung, wobei im Kathodenraum das Verstärkungsmaterial kontinuierlich zugeführt und entfernt wird und gleichzeitig als Kathode wirkt.
• Fig. 4: Querschnitt einer erfindungsgemäßen Vorrichtung, wobei im Kathodenraum das Verstärkungsmaterial als Kathode wirkt und zwei Anodenräume vorgesehen sind.

The invention will be further illustrated by the following figures:

• Fig. 1 : Cross section of a device according to the invention, wherein the reinforcing material simultaneously assumes the function of the cathode.
• Fig. 2 : Cross section of a device according to the invention, wherein an auxiliary cathode is provided in the cathode compartment.
• Fig. 3 : Cross section of a device according to the invention, wherein in the cathode space, the reinforcing material is continuously supplied and removed and at the same time acts as a cathode.
• Fig. 4 : Cross-section of a device according to the invention, wherein the reinforcing material acts as a cathode in the cathode space and two anode spaces are provided.

The structure of the device and the operation of the method for producing a composite material according to the invention are based on Fig. 1 described. The electrolytic cell 1 is divided by a diaphragm 2 into anode 3 and cathode chamber 4. In the cell 1 is the electrolyte 5. In the anode chamber 3 is a mixture of metal oxide (for example, TiO ₂ ) and Carbon carrier 6 given, for example, oil pitch. In the oxide-carbon mixture 6, a current conductor 7 is used. In the cathode chamber 4 can advantageously be additionally contained an auxiliary anode made of a metal. Due to the anodic dissolution of the metal oxide of the metal oxide carbon anode 7 in a Cl-containing electrolyte, low-value metal chlorides are formed in the electrolyte and are split electrolytically. In this case, the metal is deposited on the cathode 9, the Cl ions are transported under the action of the electric field to the anode 7. At the metal oxide carbon anode 7, the atomic chlorine reacts with the oxide-carbon mixture 6 to form chlorides and CO _x . The chlorides dissolve in the electrolyte 5, dissociate and deposit on the electrodes (for example, 9). In the case exemplified ( Fig. 1 ) The cathode consists of the reinforcing fibers 9, which are held by a holder 8 (cathode) and electrically contacted. Depending on the current density at the cathode 9 and electrolyte selection (Me concentration) Me forms a powder, sponge or dense coating on the reinforcing material 9. According to the invention is preferably used as the cathode 9, a fiber material which is coated with a dense Me layer, the later forms the matrix in a composite material. As the cathode 9, which later serves as a reinforcing material, but can also advantageously an open-cell foam of carbon, a ceramic or a metal are used, then during the electrolysis, the pores are partially or completely filled with the electrolysis product Me.

Furthermore, it corresponds to the idea of the invention, if in the cathode compartment together with the reinforcing material, an auxiliary cathode 10 accordingly Fig. 2 located. This is special makes sense if the reinforcing material 11 is a non-conductor or is present in loose form, for example as a particle or cut fiber. The cathode 10 and reinforcing material 11 are then arranged so that the deposited metal 12 is obtained in the region of the cathode, thereby enclosing or penetrating the reinforcing material.

In Fig. 3 As electrolyte 5, a mixture of LiCl, KCl and CaCl _{2 is} used. This has a melting point of about 430 ° C. The electrolyte 5 is melted in a crucible 13. In the divided by a diaphragm 2 anode space, a mixture of carbon and titanium dioxide powder 6 is given. In the molten salt 5 of the cathode chamber 4 are the reinforcing fibers 9, which are fed continuously via a feed 14 and contacted with the guide 15 and deflected.

• <TiO₂> + <C> + 2{Cl} = (TiCl₂) + {CO₂}
• <TiO₂> + 2<C> + 2{Cl} = (TiCl₂) + 2{CO}
• <TiO₂>+<C> + 4{Cl} = {TiCl₄} + {CO₂}
• <TiO₂>+ 2<C> + 4{Cl} = {TiCl₄} + 2{CO}

The chlorine ions of the electrolyte are transported to the anode 7 under the action of the electric field. At the anode 7, chlorine reacts with the TiO ₂ -carbon mixture to form Ti-chlorides and CO and CO ₂ according to the reactions listed below.

• <TiO ₂ > + <C> + 2 {Cl} = (TiCl ₂ ) + {CO ₂ }
• <TiO ₂ > + 2 <C> + 2 {Cl} = (TiCl ₂ ) + 2 {CO}
• <TiO ₂ > + <C> + 4 {Cl} = {TiCl ₄ } + {CO ₂ }
• <TiO ₂ > + 2 <C> + 4 {Cl} = {TiCl ₄ } + 2 {CO}

The Ti chlorides formed dissolve in the electrolyte 5 and are converted by the dissolved in the electrolyte 5 Ca at the cathode to Ti and CaCl ₂ . CaCl ₂ dissociates into 2Cl ^- and Ca ²⁺ . The anode current density is adjusted so that predominantly TiCl ₂ forms. On the side of the cathode 9, in particular TiCl _{2 is} again converted together with Ca ²⁺ into Ti and CaCl ₂ . The Ti forms a tight coating on the reinforcing fiber 9 connected as a cathode. Through the discharge 16, the titanium-coated fiber is continuously removed from the process.

In Fig. 4 The crucible 13 contains two anode chambers 3 containing mixtures of carbon and different metal oxides 6. By applying suitable potentials between the anode chambers 3 and the cathode 9, the deposition rate of the different metals can be adjusted so as to be able to produce a metal alloy as matrix material.

Claims (12)

1. A process for producing a metal/reinforcement material composite material, comprising the steps of contacting a conductive anode containing carbon and at least one metal oxide electrolytically with a cathode in the zone of which said reinforcement material is present as an electrolyte in a salt melt and said metal is cathodically deposited with inclusion of said reinforcement material, wherein an electrolytic cell is divided by the membrane into anode and cathode compartments, characterized in that a reinforcement material in the form of fibers, particles and/or an open-cell foam is employed, and that said metal is deposited on the reinforcement material formed as a cathode.
2. The process according to claim 1, characterized in that an essentially inorganic, especially completely inorganic, anode is employed.
3. The process according to claim 1 or 2, characterized in that an anode containing a flux, especially a chloride and/or fluoride, especially CaCl₂, is employed.
4. The process according to any of claims 1 to 3, characterized in that a metal oxide selected from oxides of the refractory metals and/or light metals, especially the metals Al, Mg, Ti, Ni, Nb, W and/or Zr, is employed.
5. The process according to any of claims 1 to 4, characterized in that a reinforcement material of metal, carbon and/or ceramics, especially of SiC, is employed.
6. The process according to any of claims 1 to 5, characterized in that a reinforcement material that has not been pretreated is employed with the metal oxide.
7. The process according to any of claims 1 to 6, characterized in that a reinforcement material that will chemically react with the metal produced is employed.
8. The process according to any of claims 1 to 7, characterized in that said composite material is subjected to a pressing process, optionally in combination with a heat treatment, subsequently to the electrolysis.
9. The process according to any of claims 1 to 8, characterized in that said cathode material and/or anode material is continuously supplied and removed.
10. An electrolytic cell for producing a composite material consisting of a metal matrix and a reinforcing material, comprising at least one anode compartment and at least one cathode compartment, which is separated from said anode compartment by a membrane, characterized in that said anode includes a conductive anode containing carbon and at least one metal oxide, wherein a reinforcement material in the form of fibers, particles and/or an open-cell foam is provided as the electrolyte in a salt melt.
11. The cell according to claim 10, characterized in that said cathode consists of said reinforcement material.
12. The cell according to claim 10 or 11, characterized in that means for continuously supplying and removing the material are present in the anode and/or cathode compartments.

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