Input stock for use for producing a fibre-ceramic composite

Abstract

The invention relates to an input stock for use for producing a fibre-ceramic composite, the input stock containing 40 wt.% to 55 wt.% inorganic fibres made of SiO2 and / or Al2O3, 40 wt.% to 50 wt.% inorganic oxides, and 5 wt.% to 15 wt.% water, wherein the inorganic oxides contain at least 60 wt.% SiO2 and at most 25 wt.% Al2O3. For this purpose, inorganic fibres are brought into contact with a suspension containing water, ground inorganic oxides and preferably polyvinyl alcohol. At a later point in time, the input stock can be sintered at a temperature of approximately 1000°C, in particular at a temperature from 900 to 990°C. The fibre-ceramic composite produced in this manner contains inorganic fibres and an oxidic ceramic matrix, wherein the inorganic fibres consist of SiO2 and Al2O3, wherein 100% of the the oxidic ceramic matrix consists of inorganic oxides, wherein the proportion of SiO2 is at least 60 wt.% and the proportion of Al2O3 is at most 25 wt.%.

Description

[0001] PRE-MATERIAL FOR USE IN THE MANUFACTURE OF A FIBER-CERAMIC COMPOSITE

[0002] The invention relates to a starting material for use in producing a fiber-ceramic composite, a method for producing such a starting material, the use of such a starting material for producing a fiber-ceramic composite and a fiber-ceramic composite comprising inorganic fibers, in particular oxide and / or mineral fibers, and an oxide ceramic matrix.

[0003] It is known to use inorganic fibers to reinforce ceramics, which significantly improves the mechanical properties of the fiber-ceramic composite and thus its product properties such as ductility, fracture toughness and thermal shock resistance.

[0004] Inorganic fibers used include those made predominantly of AI2O3, which are embedded in a matrix made predominantly of AI2O3 during the production of the fiber-ceramic composite.

[0005] It is also known to provide the fibers and matrix in a composite made from a mixture of Al2O3 and SiO2. However, with such a mixture, a compromise must be found between the properties produced by the respective oxide components.

[0006] Fiber-reinforced ceramics provide a material that eliminates the significant disadvantages of conventional technical ceramics—namely, their low fracture toughness and high temperature sensitivity. Application developments have therefore focused on areas where reliability is required at high temperatures beyond the reach of metals—particularly above 1000 °C—under abrasive, i.e., wear-inducing loads. The following key areas have emerged in developments and applications to date:

[0007] - Heat protection systems for spacecraft exposed to high thermal stresses and vibration loads upon re-entry into the Earth's atmosphere. Components for gas turbines in the area of ​​the hot gases (i.e., in the turbine combustion chamber), the static guide vanes that direct the gas flow, and the actual turbine blades that drive the gas turbine compressor.

[0008] - Components for burner technology and hot gas guides made of oxide composite ceramics.

[0009] - Brake discs for highly loaded disc brakes which are exposed to extreme thermal shock conditions on the friction surface.

[0010] - Components for plain bearings with high corrosion and welding loads.

[0011] A disadvantage of known fiber-reinforced ceramics, however, is that they cause high production costs.

[0012] The object of the invention is therefore to provide a precursor material for a fiber-ceramic composite with an oxide matrix and an oxide and / or mineral fiber, which has optimized properties compared to a known composite, in particular one made of oxides, and which can be produced cost-effectively.

[0013] This object is achieved by a precursor material having the features of claim 1, by a method having the features of claim 12, by the use of a precursor material according to claim 15, and by a fiber-ceramic composite having the features of claim 16. Preferred and advantageous embodiments of the invention are the subject of the dependent claims.

[0014] According to the invention, 100 wt.% of the raw material

[0015] - 40 wt.% to 55 wt.%, in particular 44 wt.% to 50 wt.%, inorganic fibers made of SiCh and / or Al2O3,

[0016] - 40 wt.% to 50 wt.%, in particular 42 wt.% to 48 wt.%, of inorganic oxides and

[0017] - 5 wt.% to 15 wt.%, in particular 7.5 wt.% to 9 wt.%, of water and that 100 wt.% of the inorganic oxides contain at least 60 wt.% SiO2 and a maximum of 25 wt.% AI2O3.

[0018] A key cost factor in the production of a fiber-ceramic composite is the energy costs for sintering. In contrast to known fiber-reinforced ceramics, in which the fibers and matrix in the composite consist of a mixture predominantly of Al2O3 and only a small proportion of SiO2, the advantage of the predominantly SiO2 content provided in the invention lies in the fact that the fibers and matrix can be sintered at relatively low temperatures and thus significantly more cost-effectively, without negatively affecting the mechanical properties and processability.

[0019] Fibers, oxides and water do not have to add up to 100 wt.% in the starting material, since depending on the manufacturing process the starting material can also contain a certain percentage by weight of, for example, polyvinyl alcohol. In addition, the starting material in its storable state can have a film made of, for example, polyethylene or polypropylene, the weight of which can be considered negligible. The lighter the film, the better. The setting of the individual percentages by weight of fibers, oxides and water and, if applicable, polyvinyl alcohol can be selected according to requirements. For example, in the tip of a space rocket, a higher proportion (higher percentage by weight) of fibers can be selected for better mechanical stability, whereas for an application for a sacrificial layer in a battery casing, a lower proportion of fibers can be selected because mechanical stability is then less important in practice.The percentage by weight of fibers can be adjusted in particular by using fibers with different basis weights.

[0020] The percentage by weight of oxides can be selected in particular depending on the desired percentage by weight of fibers and can be adjusted accordingly, for example, by the residence time of the fibers in a matrix bath.

[0021] The weight percentage of water can be selected depending on the desired adhesiveness of the raw material and can be adjusted accordingly during the production of the raw material, for example by the residence time of the fibers in a matrix bath and / or by subsequent pressing of a web of fiber-matrix mixture.

[0022] Within the scope of the invention, the starting material may contain approximately 1 to 1.5 wt.% of polyvinyl alcohol, whereby these weight percentages can be adjusted in the same way as the weight percentages of water.

[0023] In a particularly preferred embodiment, the proportion of SiO2 in the inorganic oxides is at least 65 wt.%, in particular at least 70 wt.%, preferably 72 to 77 wt.%, particularly preferably approximately 73 to 75 wt.%. In a preferred further development of this embodiment, the proportion of Al2O3 is in the range from 15 to 20 wt.%.

[0024] The particular advantage of these designs lies in the balance between temperature stability during processing and mechanical properties. The Al2O3 content ensures temperature stability. This balance means that the precursor material can be sintered without compromising the mechanical stability of the fibers and the load-bearing capacity of the fiber-ceramic composite.

[0025] Within the scope of the invention, the starting material may contain additional inorganic oxides selected from the group consisting of TiO2, Fe2O5, CaO, MgO, K2O, and Na2O. This is advantageous because various types of earthenware, whose composition may vary, can be used as the starting raw material.

[0026] In a further, particularly preferred embodiment, the proportion of SiO2 in the inorganic fibers is at least 60 wt.% and the proportion of Al2O3 is at most 25 wt.%, in particular the proportion of SiO2 is at least 65 wt.%, in particular at least 70 wt.%, for example 85 wt.%, and the proportion of Al2O3 is in the range from 15 to 20 wt.%. If the proportion of SiO2 is similar in both the fibers and the inorganic oxides, there is the advantage that a "size" can be omitted. If, in addition, the proportion of SiO2 is dominant over the proportion of Al2O3, there is the advantage that the matrix mixture can bond particularly well to the fibers.

[0027] Within the scope of the invention, it can also be provided that the proportion of SiO2 in the inorganic fibers is 20 to 30 wt.%, in particular 25 wt.%, and the proportion of AI2O3 is 70 to 80 wt.%, in particular 75 wt.%.

[0028] Within the scope of the invention, the inorganic fibers can be arranged as a woven fabric, a scrim, a nonwoven fabric, a felt, a knitted fabric, a braid, in the form of a winding or as a unidirectional fiber layer.

[0029] In order to improve the storage stability of the precursor material, the precursor material within the scope of the invention can have the form of a flat, rollable web, wherein the top and bottom sides of the web are each formed by a film and the inorganic fibers, the inorganic oxides and the water content are present between the films or wherein the top or bottom side of the web is formed by a film.

[0030] According to the invention, the starting material for use in producing a fiber-ceramic composite is produced in a process comprising the following process steps: a) producing a suspension comprising water and ground, inorganic oxides and preferably polyvinyl alcohol for the subsequent formation of an oxidic ceramic matrix, b) bringing inorganic fibers into contact with the suspension produced according to step a), and c) producing a storage-stable starting material for the fiber-ceramic composite using increased pressure.

[0031] Within the scope of the invention it can be provided that the ground, inorganic oxides for forming the oxidic ceramic matrix are obtained from earthenware. In a preferred embodiment it can be provided that in step b) the fibers in the form of a flat web pass through a container which contains the suspension produced according to step a), and that in step c) the underside and / or the upper side of the flat web, which comprises inorganic fibers, inorganic oxides, a proportion of water and optionally a proportion of polyvinyl alcohol, is covered with a film. The residence time in the container can in particular be used to adjust the percentage by weight of inorganic oxides, water and optionally polyvinyl alcohol. The film enables the water content in the starting material to be kept essentially constant and the web can be stored better.

[0032] According to the invention, the starting material is used to produce a fiber-ceramic composite by carrying out the following process step: d) sintering the starting material at a temperature of approximately 1000 ° C, in particular at a temperature of 900 to 990 ° C, to form an oxide ceramic matrix.

[0033] The matrix according to the invention is sinterable between 900 and 1100 °C. However, in the case of a composite, the weakest link determines the sintering temperature—in this case, the fiber. The mechanical strength of SiO2 fibers drops rapidly at temperatures above 990 °C. However, the invention is characterized by a special balance between temperature stability during production and mechanical properties in the finished composite.

[0034] According to the invention, a fiber-ceramic composite comprising inorganic fibers and an oxide ceramic matrix is ​​proposed, which is characterized in that the inorganic fibers consist of SiO2 and AI2O3 and the oxide ceramic matrix consists of 100% inorganic oxides, wherein the proportion of SiO2 is at least 60 wt.% and the proportion of AI2O3 is at most 25 wt.%.

[0035] The composite according to the invention can be produced at relatively low temperatures and thus significantly more cost-effectively, whereby the mechanical properties and the processability can be optimally adapted to various fields of application for which composites consisting predominantly of AI2O3 and only a small proportion of SiO2 would not be suitable.

[0036] In a preferred embodiment of the composite, it is provided that the proportions of the inorganic fibers and the proportions of the oxide ceramic matrix are in a range between 30 and 70 wt.%, preferably between 40 and 60 wt.%, in particular between 35 and 65 wt.%, based on 100 wt.%.

[0037] The individual weight percentages of fibers and oxides can be selected depending on requirements. For example, in the tip of a space rocket, a fiber content of approximately 65 wt.% can be selected for better mechanical stability. However, for a sacrificial layer in a battery casing, a fiber content of approximately 35 wt.% can be selected, since mechanical stability is then of less practical importance.

[0038] Further details and features of the invention will become apparent from the following description of a preferred embodiment with reference to the drawing, which schematically illustrates a system according to the invention with its essential components. To produce the ceramic matrix, earthenware is ground to a grain size of, for example, 9 pm. The earthenware used can consist of, for example, the following oxides:

[0039] 72% SiO2, 1% TiO2, 18% A12O3, 1% Fe2O3, 5% CaO, 0.50% MgO, 2% K2O, 0.50% Na2O.

[0040] The inorganic fibers used consist of SiO2 or Al2O3. Preferably, the fibers can contain a mixture of Al2O3 and SiO2, with the proportion of Al2O3 being, for example, 75% and the proportion of SiO2 being 25%. The inorganic fibers can be arranged as a woven fabric, nonwoven fabric, felt, knitted fabric, braid, in the form of a winding, or as a unidirectional fiber layer.

[0041] The fibers are continuously unwound from an unwinding unit 1 and guided via guide rollers 2 into a matrix bath. The matrix bath comprises an impregnation tank 3 containing a mixture of water and polyvinyl alcohol, into which the ground stoneware is introduced. The temperature in the matrix bath can be approximately 20 to 40°C. A circulation pump can be provided in the impregnation tank 3 to prevent sedimentation.

[0042] Due to the basis weight of the fibers used, e.g. 300 g / m 2 or 400 g / m 2 The weight percentage of the fibers can be adjusted. The weight percentage of water and polyvinyl alcohol can be influenced by the length of time the fibers remain in the matrix bath.

[0043] The fiber-matrix mixture, which can already be referred to as precursor material after emerging from the impregnation tank 3, is passed through at least one pair of press rollers 4 after the matrix bath to exert a contact pressure. The contact pressure presses the suspension into the inorganic fibers, so that the oxides for forming the ceramic matrix are introduced into the fibers. In addition, the weight percentages of water and polyvinyl alcohol can be further influenced. The pair of press rollers can be slightly cooled, for example to approx. 15 °C. The distance between the press rollers can be adjusted depending on the basis weight of the fibers used.

[0044] After the impregnation trough 3 and the pair of press rollers 4, further guide rollers 2 are provided, via which the web-shaped raw material is guided to a storage unit 5, for example a roller for winding up the raw material.

[0045] At least one further guide roller 2 can be a supply roll 6 for a removable film (for example siliconized or waxed) in order to cover the top side 7 or the bottom side 8 of the raw material with a film, so that the raw material can be stored more easily. A pair of supply rolls 6 for a removable film can also be provided in order to cover the top side 7 and the bottom side 8 of the raw material with a film. In the latter example, the contact pressure generated there causes the raw material to solidify further, so that storage at appropriate room temperature is possible even over a longer period of time.

[0046] After pressing, the raw material may contain, for example, 44 wt.% of fibers, 47 wt.% of oxides, 8.0 wt.% of water and 0.5 wt.% of polyvinyl alcohol, whereby the weight percentage of film can be neglected.

[0047] The raw material can be processed immediately after production or after appropriate storage. First, the film is removed from the surface of the raw material, and then the raw material is placed in a press mold in several layers. The press mold with the raw material is transferred to a furnace and heated there for several hours at around 30 to 100 °C, depending on the subsequent use. The press mold is then removed, and the pressed layers are placed in a sintering furnace. Sintering takes place at around 900 to 1000 °C for a period of 0.25 to 4 hours, which produces the ceramic matrix and thus the fiber-ceramic composite.

[0048] Within the scope of the invention, for example, 300 to 380 g of matrix mixture comprising oxides, water, and optionally polyvinyl alcohol can be applied to 300 to 400 g of fibers. After sintering, 300 to 400 g of fibers are still present, but the water content and any polyvinyl alcohol content have evaporated, so that, for example, approximately 260 to 320 g of oxides are present.

[0049] An analysis of the fiber-ceramic composite produced according to the exemplary embodiment can show a matrix with a geometric density of 1.65 g / cm 3 , a skeletal density of 2.64 g / cm 3 and an open porosity of 36%.

[0050] The fiber-ceramic composite according to the invention can be used for a range of technical applications. The use in the production of battery covers and the manufacture of components for aircraft, such as drones, is mentioned merely as examples. In addition to the specific applications mentioned in the state of the art, all areas of application are of interest in which conventional, technical ceramics are used, or in which metallic components do not achieve satisfactory service lives due to corrosion or high temperatures.

[0051] In summary, an embodiment of the invention can be described as follows: A starting material for use in producing a fiber-ceramic composite contains 40 wt.% to 55 wt.% inorganic fibers made of SiCb and / or Al2O3, 40 wt.% to 50 wt.% inorganic oxides and 5 wt.% to 15 wt.% water, wherein the inorganic oxides contain at least 60 wt.% SiO2 and a maximum of 25 wt.% Al2O3. For this purpose, inorganic fibers are brought into contact with a suspension containing water, ground inorganic oxides and preferably polyvinyl alcohol. The starting material can be sintered at a later time at a temperature of approximately 1000°C, in particular at a temperature of 900 to 990°C.The fiber-ceramic composite thus produced contains inorganic fibers and an oxide ceramic matrix, wherein the inorganic fibers consist of SiO2 and Al2O3, wherein the oxide ceramic matrix consists of 100% inorganic oxides, wherein the proportion of SiO2 is at least 60 wt.% and the proportion of Al2O3 is a maximum of 25 wt.%.

Claims

Claims: A precursor material for use in the production of a fiber-ceramic composite, wherein the precursor material comprises inorganic fibers, in particular oxide and / or mineral fibers, and inorganic oxides, characterized in that 100 wt.% of the precursor material - 40 wt.% to 55 wt.% inorganic fibers made of SiO2 and / or A12O3, - 40 wt.% to 50 wt.% inorganic oxides and - containing 5 wt.% to 15 wt.% water and that 100 wt.% of the inorganic oxides contain at least 60 wt.% SiO2 and a maximum of 25 wt.% AlO3. Precursor material according to claim 1, characterized in that it contains 44 wt.% to 50 wt.% inorganic fibers of SiO2 and / or AlO3. Precursor material according to claim 1 or 2, characterized in that it contains 42 wt.% to 48 wt.% inorganic oxides. Precursor material according to any one of claims 1 to 3, characterized in that it contains 7.5 wt.% to 9 wt.% water. Precursor material according to any one of claims 1 to 4, characterized in that it contains 1 wt.% to 1.5 wt.% polyvinyl alcohol. Precursor material according to one of claims 1 to 5, characterized in that the proportion of SiO2 in the inorganic oxides is at least 65 wt.%, in particular at least 70 wt.%, preferably 72 to 77 wt.%, particularly preferably 73 to 75 wt.%. I. Precursor material according to one of claims 1 to 6, characterized in that the proportion of AI2O3 in the inorganic oxides is in the range of 15 - 20 wt.%.

8. Precursor material according to one of claims 1 to 7, characterized in that it contains additional inorganic oxides selected from the group consisting of TiO2, Fe2O3, CaO, MgO, K2O and Na2O.

9. Precursor material according to one of claims 1 to 8, characterized in that the proportion of SiO2 in the inorganic fibers is at least 60 wt.% and the proportion of Al2O3 is a maximum of 25 wt.%, in particular that the proportion of SiO2 is at least 65 wt.%, in particular at least 70 wt.%, for example 85 wt.% and the proportion of Al2O3 is in the range of 15 to 20 wt.%.

10. Precursor material according to one of claims 1 to 9, characterized in that the inorganic fibers are arranged as a woven fabric, nonwoven fabric, fleece, felt, knitted fabric, braid, in the form of a winding or as a unidirectional fiber layer. II. Precursor material according to one of claims 1 to 10, characterized in that it has the form of a planar, rollable web, wherein the top (7) and bottom (8) of the web are each formed by a film and the inorganic fibers, the inorganic oxides and the water content are located between the films or wherein the top (7) or the bottom (8) of the web is formed by a film.

12. Method for producing a precursor material according to any one of claims 1 to 11 for use in producing a fiber-ceramic composite comprising the process steps of: a) producing a suspension containing water and ground inorganic oxides and preferably polyvinyl alcohol for the subsequent formation of an oxide ceramic matrix, b) bringing inorganic fibers into contact with the suspension produced according to step a), and c) producing a storage-stable precursor material for the fiber-ceramic composite by applying increased pressure. The process according to claim 9, characterized in that the ground inorganic oxides for the formation of the oxide ceramic matrix are obtained from earthenware.A method according to claim 9 or 10, characterized in that in step b) the fibers pass through a container (3) in the form of a planar web containing the suspension produced according to step a), and that in step c) the underside (7) and / or the top side (7) of the planar web, which comprises inorganic fibers, inorganic oxides, a water content and optionally a polyvinyl alcohol content, is covered with a film. Use of a precursor material according to any one of claims 1 to 11 for producing a fiber-ceramic composite comprising the process step: d) sintering the precursor material at a temperature of about 1000 °C, in particular at a temperature of 950 to 990 °C, to form an oxide ceramic matrix. A fiber-ceramic composite comprising inorganic fibers and an oxide ceramic matrix, characterized in that the inorganic fibers consist of SiCb and Al₂O₃ and that the oxide ceramic matrix consists of 100% inorganic oxides, wherein the proportion of SiO₂ is at least 60% by weight and the proportion of Al₂O₃ is a maximum of 25% by weight. A fiber-ceramic composite according to claim 13, characterized in that the proportions of the inorganic fibers and the proportions of the oxide ceramic matrix are in a range between 30% by weight and 70% by weight, preferably between 40% by weight and 60% by weight, and in particular between 35% by weight and 65% by weight, based on 100% by weight.

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