AT527691A1 - Precursor material for a fiber-ceramic composite - Google Patents

Abstract

A precursor material for use in producing a fiber-ceramic composite contains 40 wt.% to 55 wt.% inorganic fibers, 25 wt.% to 45 wt.% inorganic oxides, 1.5 wt.% to 25 wt.% polyvinyl alcohol and 2.5 wt.% to 12.5 wt.% water, wherein the inorganic oxides contain at least 50 wt.% SiO2 and a maximum of 50 wt.% Al2O3.

Description

network.

It is known that inorganic fibers can be used to reinforce ceramics, which improves the mechanical properties of the fiber-ceramic composite and thus its product properties such as ductility, fracture toughness and

Thermal shock resistance can be significantly improved.

As inorganic fibers, for example, those predominantly made of Al2O:3 are used, which are incorporated into a matrix predominantly made of Al2O3;

be embedded.

Furthermore, it is known to provide the fibers and also the matrix in a composite made of a mixture of AlL‚,O3 and SiO;. However, with such a mixture, a compromise must be made between the properties that are determined by the respective oxide

Component can be found.

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—especially above 1000°C—under abrasive, i.e., wear-inducing loads. The following areas have been emphasized:

in developments and applications so far:

— Components for burner technology and hot gas guides made of oxide composite ceramics.

—- Brake discs for highly loaded disc brakes that are exposed to extreme thermal shock conditions on the friction surface.

—- Components for plain bearings with high corrosion and

Welding load.

However, a disadvantage of known fiber-reinforced ceramics is that they entail high production costs. This is due, among other things, to the fact that the corresponding raw material, so-called green bodies, must be sintered at temperatures of approximately 1,300 °C in order to produce a fiber-ceramic composite, so-called white bodies, as the final product that can be installed in the operational state. The high production costs are due in particular to the fact that it was not previously possible to use unsintered components, i.e. green bodies, as the final product, since these were not dimensionally stable and could not be installed in the operational state. Only the sintered white bodies could be installed and

used for insulation purposes.

The object of the invention is therefore to provide a precursor material for a fiber-ceramic composite with an oxidic matrix and an oxidic and/or mineral fiber, which, in comparison to a known material, in particular made of oxides

manufactured composite, not only optimized properties

can also be used as a green body.

This object is achieved by a precursor material having the features of claim 1, by a method having the features of claim 12, and by a

Use of a raw material according to claim 16.

Preferred and advantageous embodiments of the invention are the subject of the subclaims.

Q

According to the invention, 100 wt.% of starting material contains -- 40 wt.% to 55 wt.% inorganic fibers, in particular glass fibers and/or fibers made of basalt, SiO2 and/or Al2O3, -- 25 wt.% to 45 wt.% inorganic oxides, -- 1.5 wt.% to 25 wt.% polyvinyl alcohol (PVA) and -- 2.5 wt.% to 12.5 wt.% water

and that 100 wt.% of the inorganic oxides contain at least 50 wt.

Q

% SLO2 and a maximum of 50 wt.% Al2O3.

An important cost factor in the production of a fiber-ceramic composite, so-called white bodies, is the energy costs for sintering, since known non-sintered green bodies are not dimensionally stable and cannot be used in the assembly. In contrast, the composition of the precursor material according to the invention, which represents the green body, ensures that it is/remains dimensionally stable and can be used as a green body. In the event of a fire, the dimensionally stable green body sinters into a white body in the assembled state and thus provides electrical insulation as well as insulation against temperature and

Fire penetration safe.

Energy costs can be significantly reduced.

Fibres, oxides, polyvinyl alcohol and water do not have to add up to 100% by weight in the raw material, since the raw material may also contain certain percentages by weight of other ingredients, for example

dispersants or defoamers.

The individual weight percentages of fibers, oxides, polyvinyl alcohol, and other ingredients can be adjusted according to requirements. For applications involving high rates of hot particles, for example, a higher proportion (higher weight percentage) of fibers can be selected for better breakdown stability, whereas for applications involving a sacrificial layer in a battery casing, a lower proportion of fibers can be selected, as this reduces the likelihood of abrasive materials. The weight percentages of fibers can be adjusted, particularly by using fibers with different basis weights.

be set.

Within the scope of the invention, the primary material can in particular be 44

Q Q

Contains 100% to 50% by weight of inorganic fibers.

The weight percentage of oxides can be selected in particular depending on the desired weight percentage of fibers and, for example, by the residence time of the fibers

be adjusted accordingly in a matrix bath.

Q Q

Contain 100% to 40% by weight of inorganic oxides.

The weight percentage of water can be selected depending on the desired adhesiveness of the precursor material and adjusted accordingly during the production of the precursor 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. The water is removed in the subsequent drying process.

evaporates.

The weight percentage of polyvinyl alcohol is adjusted in the fiber matrix mixture by adding a PVA-containing solution and ensures the dimensional stability and integrity of the

Green body safe.

Within the scope of the invention, the primary material can in particular be 5

Q

wt.% to 20 wt.% of polyvinyl alcohol.

Any proportions of dispersant and/or defoamer

are preferably between 0.1 wt% and 0.3 wt%,

especially at 0.2 wt%.

In a particularly preferred embodiment, the proportion of SiO2 in the inorganic oxides is at least 65 wt.%, in particular at least 75 wt. In a preferred further development of this embodiment, the proportion of Al2:O3 is in the range of 25 wt.%

up to 35 wt.%.

The particular advantage of these designs with a significantly predominant proportion of SiO2 lies in the balance between temperature stability during processing and mechanical properties. The proportion of Al2:O3s ensures the

Temperature stability. The balance has the effect that

Fiber-ceramic composite may be impaired.

In another particularly preferred embodiment, the proportion of SiO2 in the inorganic oxides is 50 wt.% to 55 wt.%, in particular 51 wt.% to 52 wt.%. In a preferred further development of this embodiment, the proportion of Al2O3 in the

Range from 40 wt% to 49 wt%, preferably 45 wt%

up to 47 wt.%.

The advantages cited for the previously mentioned embodiment also apply to this embodiment with similar proportions of SiO2 and AlO3 or with a slightly predominant proportion of SiO2. However, the previously described balance and the mechanical properties are particularly advantageous in the latter embodiment with a slightly predominant proportion of SiO2. In addition, a more optimal bonding of the inorganic oxides to the fibers takes place and the storability of a film-covered precursor material

improves.

Within the scope of the invention, it can be provided that the starting material contains additional inorganic oxides selected from the group TiO2, Fe2O3s, CaO, MgO, K2O and Na2O. This is advantageous in that various types of earthenware, the composition of which can vary, can be used as the starting raw material.

can be.

In a further, particularly preferred embodiment,

It is intended that the proportion of inorganic fibres

Q

SiO2 at least 60 wt.% and the proportion of Al2O3 maximum 25

Q

% by weight, in particular that the proportion of Si0O2 is at least

Q

65 wt.%, in particular at least 70 wt.%, for example 85

7723

% by weight and the proportion of Al12O3 is in the range of 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 "sizing" can be omitted. If, in addition, the proportion of Si12O2 is dominant over the proportion of Al12O3, there is the advantage that the

Matrix mixture can bind particularly well to the fibers.

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 Al2O: 70 to

80 wt%, in particular 75 wt%.

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

be.

In order to improve the storage life of the precursor material, the precursor material can, within the scope of the invention, 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

The top or bottom of the track is formed by a film.

According to the invention, the primary material is processed in a process

comprising the following process steps:

a) Preparation of a suspension containing water and inorganic oxides and polyvinyl alcohol and preferably a dispersant and/or a defoamer for the subsequent formation of an oxidic

Ceramic matrix,

Application of increased pressure.

Within the scope of the invention, the method used in step a)

Q Q

Suspension 20 wt% to 60 wt% water, in particular 30 wt% to 45 wt% water, 5 wt% to 25 wt% polyvinyl alcohol and 30 wt% to 65 wt% inorganic

Contain oxides, in particular 30 wt.% to 50 wt.%

inorganic oxides.

Within the scope of the invention, it can be provided that the ground, inorganic oxides are used to form the oxidic

Ceramic matrix can be obtained from earthenware.

In a preferred embodiment, it can be provided that the fibers in step b) pass through a container in the form of a flat web containing the suspension prepared 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 water content and the proportion of polyvinyl alcohol, is covered with a film. By means of the residence time and a calender, which determines the thickness of the matrix to be applied, the

corresponding weight percentages can be set.

The material can now be shaped using a vacuum furnace, an autoclave, or a hot press. Further sintering of the green body is not necessary. In the event of a fire (thermal runaway), the green body sinters into a white body due to the introduced energy in the form of temperature, thus keeping the affected area of the fire in

limits.

comes .

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 basalt fibers or Si1i02 fibers drops rapidly at temperatures above 990°C. The invention, however, is characterized by a special balance between temperature stability during production and mechanical

Properties in the finished composite.

The individual weight percentages of fibers and oxides can be selected depending on the requirements. For example, in the application area of the tip of a space rocket, a fiber content of approximately 55 wt.% can be selected for better mechanical stability, whereas for the application area of a sacrificial layer of a battery casing, a fiber content of approximately 40 wt.% can be selected.

% by weight, since then the mechanical stability

is of less practical importance.

Further details and features of the invention will become apparent from the following description of a preferred

Embodiment based on the drawing, in which a system according to the invention with its essential components is shown schematically

is shown.

The earthenware used can be made from the following materials:

Oxides consist of:

72% SiO2, 1% T1iO2, 18% Al2Os, 1% FezOs, 5% CaO, 0.50% MgO, 2 5% K2O0, 0.50% Na20.

The inorganic fibers used consist of basalt, SiO2, or Al2:O3s. The inorganic fibers can be arranged as woven fabrics, nonwovens, felts, knitted fabrics, braids, in the form of windings, or as unidirectional fiber layers.

be.

The fibers are continuously unwound from an unwinding unit 1 and guided into a matrix bath via guide rollers 2. 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.

avoid.

The weight percentage of the fibers can be adjusted by the used basis weight of the fibers, e.g. 280 g/m² to 620 g/m². The residence time of the fibers in the matrix bath can be adjusted by the weight percentage of water and

Polyvinyl alcohol can be affected.

The fiber-matrix mixture, which can already be referred to as precursor material after leaving the impregnation tank 3, is guided after the matrix bath through at least one pair of press rollers 4 to exert a contact pressure. The contact pressure presses the suspension into the inorganic fibers, so that the oxides for the formation of the ceramic matrix are introduced into the fibers. In addition, the weight percentages

of water and polyvinyl alcohol.

After the impregnation trough 3 and the pair of press rollers 4, further

Guide rollers 2 are provided, over which the web-shaped

Pre-material for a storage unit 5, for example a roll

for winding up the raw material.

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 upper side 7 or the lower 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 upper side 7 and the lower side 8 of the raw material with a film. In the latter example, the contact pressure generated there further solidifies the raw material, so that even over a longer period of time, storage with appropriate

room temperature is possible.

The raw material can be processed immediately after production or after appropriate storage. First, the foil is removed from the surface of the raw material, and the raw material is placed in several layers in a press mold. The press mold with the raw material is transferred to an oven and heated there for several hours at approximately 70 to 100°C, depending on the further use. The

The mold has been removed. The green body can now be installed.

The inventive precursor material for forming a fiber-ceramic composite in the event of a fire can be used for a range of technical applications. Examples include the production of battery covers and the manufacture of components for aircraft, such as drones. In addition to the specific applications mentioned in the prior art, all applications in which conventional technical ceramics are used or in which metallic

Components or components made of plastic due to corrosion

or high temperatures do not have satisfactory lifetimes

to reach.

Claims (1)

Patent claims: Precursor material for use in producing a fiber-ceramic composite, wherein the precursor material comprises inorganic fibers, in particular oxidic and/or mineral fibers, and inorganic oxides, characterized in that 100 wt.% precursor material —- 40 wt.% to 55 wt.% inorganic fibers, in particular glass fibers and/or fibers made of basalt, SiO>» and/or AlL12O3, —- 25 wt% to 45 wt% inorganic oxides, —- 1.5 wt% to 25 wt% polyvinyl alcohol and —- Contains 2.5% to 12.5% water by weight and that 100 wt.% of the inorganic oxides contain at least 50 wt.% SiO2 and a maximum of 50 wt.% AlO2. Precursor material according to claim 1, characterized in that it contains 44% to 50% by weight of inorganic fibers. Precursor material according to claim 1 or 2, characterized in that it contains 30 wt.% to 40 wt.% contains inorganic oxides. Precursor material according to one of claims 1 to 3, characterized in that it contains 5 wt.% to 20 wt.%, in particular 10 wt.% to 15 wt.% of polyvinyl alcohol contains. Precursor material according to one of claims 1 to 4, characterized in that in the inorganic oxides the proportion of SiO2; 50 wt.% to 55 wt.%, in particular 51 wt.% to 52 wt.%, or at least 65 wt.%, in particular at least 75% by weight. 14 Precursor material according to one of claims 1 to 5, characterized in that in the inorganic oxides the proportion of Al2:O3 is in the range from 40 wt.% to 49 wt.%, preferably at 45 wt.% to 47 wt.%, or in the range of 25 wt% - 35 wt%. Precursor material according to one of claims 1 to 6, characterized in that it contains additional inorganic oxides selected from the group Ti0O2, Fe2O5, CaO, MgO, K2O and Na2O. Precursor material according to one of claims 1 to 7, characterized in that in the case of the inorganic fibers of the Q Proportion of SiO2; at least 60 wt.% and the proportion of AlO3 is at most 25 wt.%, in particular that the proportion of SiO2 is at least 65 wt.%, in particular at least 70 Q % by weight, for example 85 % by weight and the proportion Q of Al2:O3 is in the range of 15 to 20 wt.%. Precursor material according to one of claims 1 to 8, characterized in that the inorganic fibers are arranged as a woven fabric, scrim, nonwoven, felt, knitted fabric, braid, in the form of a winding or as a unidirectional fiber layer are. Precursor material according to one of claims 1 to 9, characterized in that it has the form of a flat, rollable web, wherein the upper side (7) and underside (8) 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 upper side (7) or the underside (8) of the web is formed by a film. 12. 13. 14. 15 Precursor material according to one of claims 1 to 10, characterized characterized in that it contains a proportion of 0.1 - 0.3 wt.%, in particular 0.2 wt.%, of dispersant and/or a proportion of 0.1 - 0.3 wt.%, in particular 0.2 wt.- %, of defoamer. Method for producing a precursor material according to one of claims 1 to 11 for use in producing a fiber-ceramic composite comprising the Process steps: a) preparing a suspension containing water and inorganic oxides and polyvinyl alcohol and preferably a dispersant and/or a defoamer for the subsequent formation of an oxide ceramic matrix, b) bringing inorganic fibers into contact with the suspension prepared according to step a) and c) Production of a storage-stable precursor material for the fiber-ceramic composite using increased Pressure. Method according to claim 12, characterized in that in step a) a suspension containing 20 wt.% to 60 Q Q % by weight water, in particular 30% by weight to 45% by weight Q Q Water, 5 wt% to 25 wt% polyvinyl alcohol and 30 Q Q wt.% to 65 wt.% inorganic oxides, in particular 30 Q Q wt.% to 50 wt.% inorganic oxides. Process according to claim 12 or 13, characterized in that the ground, inorganic oxides for forming the oxide ceramic matrix of earthenware be obtained. 16. 16 Method according to one of claims 12 to 14, characterized in that in step b) the fibers in the form of a flat web pass through a container (3) which contains the suspension produced according to step a), and in that in step c) the underside (7) and/or the upper side (7) of the flat web, which comprises inorganic fibers, inorganic oxides, a proportion of water and a proportion of polyvinyl alcohol, is covered with a film is covered. Use of a precursor material according to one of claims 1 to 11 for producing a fiber-ceramic composite comprehensively the process step: d) Sintering the precursor material at a temperature of approximately 1000°C, in particular at a temperature of 950 to 990°C, to form an oxide ceramic matrix in the installed operating condition of the raw material.