Ceramic honeycomb body for lightweight structures and corresponding production method

Abstract

A honeycomb body made of a composite material for fire-resistant lightweight structures including honeycomb cells having a cross section is provided. The cell walls of the honeycomb cells are produced from a composite material. The composite material has at least one carrier, for example a woven fabric or a laid fabric made of fibers, and a matrix into which the carrier is embedded. The matrix includes a silicon-based ceramic material, of which the proportion by mass in the matrix along the cell walls is at least 30 wt. %. A method for producing such a ceramic honeycomb body and a honeycomb tube as an intermediate product for the same are also provided. A flat semi-finished product as a curable intermediate product for the production of fire-resistant fiber composite lightweight structures, which has a matrix mixture including dispersed silicon particles, is also provided.

Claims

1. A honeycomb body (1) of a composite material for fire-resistant lightweight structures, for use as a core (41) or for producing a core (41) between two cover layers (44) of a lightweight sandwich structure, the honeycomb body (1) comprising honeycomb cells (12) with a cross-section in the L/W plane, cell walls (13) of the honeycomb cells (12) being produced from a composite material, the composite material at least comprising a support, and a matrix, the support being embedded in the matrix, wherein the matrix comprises a silicon-based ceramic material selected from the group consisting of silicon carbide, silicon oxycarbide, silicon nitride, silicon carbonitride and silicon-boron carbonitride, wherein, over the entire height of the cell walls (13) in the T direction perpendicular to the L/W plane, the matrix has a mass fraction of the silicon-based ceramic material of at least 30 wt. %, wherein the mass fraction of the silicon-based ceramic material in the matrix in the central region along the T direction deviates by less than 20 wt. % from the mass fraction of the silicon-based ceramic material in the matrix in the end regions of the height of the cell walls (13), wherein a mass fraction of free carbon in the matrix amounts to at least 1 wt. %.

2. The honeycomb body (1) as claimed in claim 1, wherein a mass fraction of the support in the composite material amounts to 5 wt. % to 80 wt. %.

3. The honeycomb body (1) as claimed in claim 1, wherein the support is produced from fibers.

4. The honeycomb body (1) as claimed in claim 3, wherein the fibers of the support are carbon fibers and/or ceramic fibers.

5. The honeycomb body (1) as claimed in claim 3, wherein a fiber fineness of the support material amounts to between 1 K and 50 K.

6. The honeycomb body (1) as claimed in claim 1, wherein the honeycomb cells (12) are hexagonal with a free diameter in the L/W plane of ? 50 mm.

7. A method for producing a honeycomb body (1), as claimed in claim 1, comprising: providing a support material (21), forming the support material (21) into a support (24) in the form of a honeycomb with honeycomb cells, the cell walls of which are formed from the support material (21), impregnating the support (24) with a carbon-containing matrix mixture (25) which comprises dispersed silicon particles such that the cell walls of honeycomb cells are impregnated with the silicon particle-containing matrix mixture (25) to provide a corresponding honeycomb blank (26), wherein the mass fraction of silicon particles in the matrix mixture (25) amounts to 20 wt. % to 60 wt. %, heating the impregnated honeycomb blank (26) to a pyrolysis temperature and carbonizing the matrix, and heating to a siliconization temperature to liquefy the silicon particles and siliconizing the carbonized matrix to form silicon carbide.

8. The method as claimed in claim 7, wherein the support material (21) is produced in the form of an open-pored air-permeable fiber structure and in particular comprises carbon fibers and/or ceramic fibers.

9. The method as claimed in claim 7, wherein the support material (21) comprises a woven fabric, with a porosity of 2 vol. % to 40 vol. % and/or with a mesh size of 100 to 800 ?m.

10. The method as claimed in claim 7, wherein the silicon particles have a grain size distribution of 0.001 to 1 mm.

11. The method as claimed in claim 7, wherein the matrix mixture (25) comprises at least one precursor for a thermosetting polymer.

12. The method as claimed in claim 7, wherein impregnation is followed by a partial or complete curing step, wherein the honeycomb blank (26) impregnated with the matrix mixture (25) is at least precured by exposure to heat.

13. The method as claimed in claim 7, wherein the support is produced in the form of a honeycomb block (24) by an expansion method comprising the steps of: providing a flat support material (21), applying parallel stripes of an adhesive (22) which extend in the T direction or in the direction of the width of the roll over the width of the roll and are spaced apart from one another at regular distances in the L direction or longitudinal direction of the roll perpendicular to the T direction, cutting the roll into sheets, laying the sheets on one another to form a stack (23), partially or completely curing the adhesive, such that the stack (23) is bonded to form a cohesive block and, expanding the stack in the W direction or in the stack height direction, such that a honeycomb block (24) with honeycomb cells is obtained.

14. The method as claimed in claim 7, wherein the matrix mixture (25) comprises dispersed additives.

15. The method as claimed in claim 7, wherein before or after pyrolysis or after siliconization, the honeycomb body (1) is cut into honeycomb slices (29) transversely to the cell walls of the honeycomb cells.

16. A heat-resistant, lightweight sandwich structure, comprising a core which is bonded to two cover layers of a ceramic fiber composite material, wherein the core comprises the honeycomb body (1) as claimed in claim 1.

17. The honeycomb body (1) as claimed in claim 1, wherein the support is a woven or laid fabric made of fibers.

18. A honeycomb body (1) of a composite material for fire-resistant lightweight structures, for use as a core (41) or for producing a core (41) between two cover layers (44) of a lightweight sandwich structure, the honeycomb body (1) comprising honeycomb cells (12) with a cross-section in the L/W plane, cell walls (13) of the honeycomb cells (12) being produced from a composite material, the composite material at least comprising a support, and a matrix, the support being embedded in the matrix, wherein the matrix comprises a silicon-based ceramic material selected from the group consisting of silicon carbide, silicon oxycarbide, silicon nitride, silicon carbonitride and silicon-boron carbonitride, wherein, over the entire height of the cell walls (13) in the T direction perpendicular to the L/W plane, the matrix has a mass fraction of the silicon-based ceramic material of at least 30 wt. %, wherein the mass fraction of the silicon-based ceramic material in the matrix in the central region along the T direction deviates by less than 20 wt. % from the mass fraction of the silicon-based ceramic material in the matrix in the end regions of the height of the cell walls (13), wherein the support is produced from glass fibers.

19. The honeycomb body (1) as claimed in claim 18 wherein a mass fraction of free silicon in the matrix amounts to at most 15 wt. %.

20. A method for producing a honeycomb body (1), in particular as claimed in claim 18, comprising: providing a support material (21), forming the support material (21) into a support (24) in the form of a honeycomb with honeycomb cells, the cell walls of which are formed from the support material (21), impregnating the support (24) with a matrix mixture (25) which comprises at least one silicon-containing polymer precursor which is, a polycarbosilane, a polycarbosiloxane, a polysiloxane, a polysilazane, a polysilane, a polycarbosilazane, a copolymer with two or more of the above-stated compounds and/or a mixture with two or more of the above-stated compounds, such that the cell walls of the honeycomb cells are impregnated with the matrix mixture (25), to provide a corresponding honeycomb blank (26), heating the impregnated honeycomb blank (26) to a pyrolysis temperature, of ? 1100? C. to form a matrix which contains a silicon-based ceramic material, wherein the support material (21) has a form of an open-pored air-permeable fiber structure and comprises glass fibers.

21. The method as claimed in claim 20, wherein the support material (21) comprises silicate glass fibers.

22. The method as claimed in claim 20, wherein the matrix mixture (25) comprises polyborazylene.

Description

(1) FIG. 1: shows a perspective view of the principle of an exemplary embodiment of a honeycomb body according to the invention;

(2) FIG. 2: shows a schematic process sequence with pictograms of a production method for a preferred exemplary embodiment of the honeycomb body according to the invention;

(3) FIG. 3: shows a schematic process sequence as a block diagram relating to an exemplary embodiment of a production method for a fiber-reinforced, carbide ceramic sandwich component comprising a honeycomb core; and

(4) FIG. 4: shows a partial view of an exemplary embodiment of a lightweight sandwich structure produced according to the invention, in cross-section perpendicular to the L/W plane.

(5) FIG. 1 shows a block-type honeycomb body 1 with honeycomb cells 12 and the cell walls 13 thereof. The L direction (longitudinal direction), the W direction (width direction) and the T direction are shown by double-headed arrows. The T direction corresponds to the honeycomb height or thickness or the height of the cell walls 13. In this exemplary embodiment, the honeycomb cells 12 are technically hexagonal, i.e. they form a cross-sectionally hexagonal base area in the L/W plane. The honeycomb cells 12 are not shown here true to scale. The honeycomb body 1 is shown in its form subsequent to siliconization. The honeycomb body 1 may optionally subsequently be cut into flat honeycomb slices 29 (FIG. 2) transversely to the T direction.

(6) FIG. 2 shows a process diagram according to an exemplary embodiment of the production method according to the invention for a honeycomb body 1 which is composed of carbon fiber-reinforced SiC. Only the essential steps are shown and described here.

EXEMPLARY EMBODIMENT 1

(7) A roll with a support material 21 is provided in step 210. The woven carbon fiber fabric Tenax? HTA40 200 tex (3K) Style 450-5 Aero is used as the support material 21 in this example. The fabric of the support material 21 is produced using a linen weave. In step 220, mutually parallel stripes 22 of an adhesive are applied, for example with a constant spacing, onto the unrolled support material 21 perpendicular to the L direction or the unrolling direction. An epoxy-phenolic based adhesive is used as the adhesive in this example. The stripes 22 are applied over the entire width of the support material 21. In step 230, the support material 21 is cut into sheets of identical size and, offset relative to one another in the L direction, for example by half the spacing of the adhesive stripes 22, the sheets are set down on one another to form a stack 23. The stack 23 is processed to form a cohesive block by partial or complete curing of the adhesive stripes 22 with exposure to pressure and heat in a press in accordance with a per se known process. In step 240, expansion in the W direction proceeds in per se known manner such that a honeycomb block 24 with technically hexagonal honeycomb cells, i.e. with honeycomb cells which have a hexagonal cross-section in the L/W plane, is obtained. The cell size of the honeycomb cells (cf. FIG. 1) in the L/W plane amounts for example to 9.6 mm. The height of the honeycomb block 24 in the T direction corresponds to the width of the roll of support material 21, and measures for example to 400-500 mm or optionally larger, such as for example 1000 mm. The width of the honeycomb block 24 in the W direction is determined by the expansion step and measures for example 700-900 mm and in further embodiments may also be substantially larger, for example 2440 mm. The length of the honeycomb block 24 in the L direction measures for example 400-600 mm and in further embodiments may also be substantially larger, for example 1220 mm. Before further processing, the honeycomb block 24 has for example a bulk density of approximately 50-60 kg/m.sup.3.

(8) In step 250, the honeycomb block 24 is soaked or impregnated with a matrix mixture 25, in this exemplary embodiment by completely immersing the honeycomb block 24 in a container, in which the matrix mixture 25 is prepared as a bath to a sufficient depth relative to the height of the honeycomb block 24. Other impregnating techniques are likewise possible. The honeycomb block 24 thus forms the support for the matrix applied by impregnation. In this example, the matrix mixture 25 comprises for example phenolic resin precursors dissolved in isopropanol. Bakelite? PF 1145, or Bakelite? PF 0247 DW 01, or also Bakelite? PF 6983 FW 01 from Hexion GmbH, Germany, may for example be used as the phenolic resin. The matrix mixture 25 furthermore comprises dispersed silicon particles of metallic silicon (Si) with a selected grain size distribution, for example in the range from 0.008 to 0.09 mm. The matrix mixture 25 is stirred such that the particles are dispersed. In particular for small particle sizes, however, continuous stirring is not necessary. In this exemplary embodiment, the mass fractions of phenolic resin precursors and silicon in the matrix mixture 25 in each case amount to 33 wt. %. The mass fraction of isopropanol in the matrix mixture 25 in this exemplary embodiment amounts to 30 wt. 8. The matrix mixture furthermore comprises 4 wt. % carbon nanoparticles in this exemplary embodiment.

(9) As a result of impregnation, a honeycomb blank 26 impregnated with a silicon-containing matrix mixture is obtained. In step 260, the impregnated honeycomb blank 26 is precured at a temperature of 200-300? C., among other things to evaporate the solvent, in this case isopropanol. This results in at least partial crosslinking of the matrix mixture. The matrix mixture may also be completely crosslinked such that it can no longer melt.

(10) In step 270, the precured honeycomb blank 26 is heated in a nitrogen-blanketed pyrolysis furnace 27 to the pyrolysis temperature, 950-1000? C., at atmospheric pressure for approximately 6-8 hours such that the organic constituents of the matrix mixture carbonize and an intermediate product is obtained. This further intermediate product has a support of carbon fibers embedded in a carbon matrix, wherein the matrix has embedded silicon particles.

(11) In step 280, the intermediate product is raised, preferably in the same apparatus as in step 270 and without preceding cooling, to a siliconization temperature in the range from 1400-1550? C. The rate at the temperature is raised in steps 270 and 280 amounts for example to 1-5? C./min. The intermediate product is siliconized for approximately 4-7 hours at a temperature of 1400-1550? ? C. under a slight vacuum (approximately 1-5 mbar) with nitrogen flushing of the pyrolysis furnace. In step 280, the silicon particles in the matrix melt and liquid silicon forms the intended silicon carbide (SiC) with the adjacent carbon atoms of the matrix.

(12) As a result of the siliconization in step 280, a honeycomb body 1 comprising the support of carbon fibers and the silicon carbide-containing matrix is obtained, wherein the fibers of the support are embedded in the matrix or the support and matrix form a ceramic fiber composite material. In this example, the matrix furthermore contains approximately 4 wt. % free carbon. The target bulk density of the honeycomb body is below 400 kg/m.sup.3, in particular below 200 kg/m.sup.3 and may even be 150 kg/m.sup.3.

(13) In step 290, the honeycomb body 1 may be cut for subsequent further processing into slices perpendicular to the cell walls of the honeycomb cells, i.e. perpendicular to the T direction. Honeycomb slices 29 of the desired height with the desired material properties are accordingly produced. Cutting may alternatively also proceed after partial curing in step 260 and before the pyrolysis step 270, such that for example a smaller process chamber may be used for steps 270 and 280.

(14) Exemplary embodiment 2: In a further exemplary embodiment, an open-pored woven carbon fiber fabric preimpregnated with a matrix mixture is used for producing a honeycomb block by the expansion method. The mass fraction of carbon fiber in the preimpregnated fabric is approximately 60 wt. %. In this example, the matrix mixture contains an epoxy resin (for example HexFlow? RTM 6 from Hexcel Corp., USA, or EPIKOTE TM Resin M1-0479-JS or EPONOL? Resin 7035 from Hexion GmbH, Germany) and a dispersed silicon powder in a mass ratio of 1.5 to 1. A honeycomb block is produced by the expansion method as described above according to steps 210, 220, 230 and 240. After the expansion step, the honeycomb block constitutes a partially coated support. In step 250, the expanded honeycomb block is soaked or impregnated with the matrix mixture by immersion in a container into which the matrix mixture has been introduced, wherein an impregnated honeycomb blank is obtained. The steps of pyrolysis 270 and siliconization 280, as well as of cutting 290, are then carried out as described above in relation to the first example.

(15) Further polymer resins which the matrix mixture may contain are for example polyimide resins such as Skybond? 700 from Industrial Summit Technology Corp., USA, or cyanate ester reins, such as for example PT 30 from Lonza AG, Switzerland.

(16) Further variations in material selection for support and matrix are application-dependent and likewise fall within the scope of the invention. FIG. 3 shows a process diagram for an exemplary production method for a fiber-reinforced carbide ceramic sandwich structure comprising a honeycomb core. In step 310, a honeycomb slice which has been produced as described above and two cover layers in the form of a laminate of carbon fiber-reinforced silicon carbide are provided. The laminate layers are produced by impregnating plies of a carbon fiber material, for example woven carbon fabric Injectex G 926 (Hexcel Corp.) or Tenax? HTA40 200 tex (3K) Style 450-5 (from Toho Tenax Europe GmbH, Germany), with a matrix mixture which comprises phenolic resin precursors and dispersed silicon particles, optionally stacking and pressing a plurality of impregnated plies with one another, followed by pyrolysis and siliconization (as above). In step 320, the honeycomb slice is externally provided with an adhesive on the honeycomb uprights and provided on both sides with the laminate layers in order to bond the laminate layers adhesively to the honeycomb slice. The above-stated matrix mixture comprising phenolic resin precursors and dispersed silicon particles may be used as the adhesive. In step 330, the laminate layers and the honeycomb slice are pressed to form a sandwich and then subjected to a pyrolysis step 340 and a siliconization step 350 in a suitable process furnace. This may in principle proceed as described above in relation to FIG. 2, such that the matrix mixture is carbonized and then siliconized between the layers. A heat-resistant lightweight sandwich structure of carbon fiber-reinforced silicon carbide which comprises a honeycomb core between two cover layers is obtained as a result.

(17) In a further exemplary embodiment according to FIG. 3, the cover layers of an unpyrolyzed prepreg material are adhesively bonded to the honeycomb core and pressed to form a sandwich.

(18) The sandwich is then pyrolyzed and siliconized essentially under the above-described conditions. It is also possible, using the matrix mixture, to adhesively bond an unpyrolyzed honeycomb blank in the form of a honeycomb slice to the unpyrolyzed cover layers of a prepreg-material in order to form a sandwich and then to pyrolyze and siliconize the sandwich in order to obtain a fiber-reinforced carbide ceramic sandwich structure.

(19) FIG. 4 shows a portion of a lightweight sandwich structure produced according the process sequence shown in the block diagram according to FIG. 3. The sandwich structure according to FIG. 4 has a honeycomb core 41 with honeycomb cells 42 with cell walls 43 of a carbon fiber-reinforced silicon carbide. The honeycomb core is produced according the method outlined in FIG. 2. The sandwich structure furthermore has two cover layers 44 of a carbon fiber-reinforced silicon carbide which may be provided as described in FIG. 3. The cover layers are bonded to the honeycomb core by an adhesive 45, the adhesive 45 comprising a high, preferably predominant proportion of silicon carbide in the finished sandwich structure.

(20) A lightweight sandwich structure according to FIG. 4 may also be produced with a honeycomb body according to exemplary embodiment 3 (below).

(21) Exemplary embodiment 3:

(22) A roll with a support material 21 is provided in step 210. A woven silica glass or silicate glass fabric is used as the support material 21 in this example. In step 220, mutually parallel stripes 22 of an adhesive are applied, for example with a constant spacing, onto the unrolled support material 21 perpendicular to the L direction or the unrolling direction. An epoxy-phenolic based adhesive is used as the adhesive in this example. The stripes 22 are applied over the entire width of the support material 21. In step 230, the support material 21 is cut into sheets of identical size and, offset relative to one another in the L direction, for example by half the spacing of the adhesive stripes 22, the sheets are set down on one another to form a stack 23. The stack 23 is processed to form a cohesive block by partial or complete curing of the adhesive stripes 22 with exposure to pressure and heat in a press in accordance with a per se known process. In step 240, expansion in the W direction proceeds in per se known manner such that a honeycomb block 24 with technically hexagonal honeycomb cells, i.e. with honeycomb cells which have a hexagonal cross-section in the L/W plane, is obtained. The height of the honeycomb block 24 in the T direction corresponds to the width of the roll of the support material 21.

(23) In step 250, the honeycomb block 24 is soaked or impregnated with a matrix mixture 25, in this exemplary embodiment by completely immersing the honeycomb block 24 in a container, in which the matrix mixture 25 is prepared as a bath to a sufficient depth relative to the height of the honeycomb block 24. Other impregnating techniques are likewise possible. The honeycomb block 24 thus forms the support for the matrix applied by impregnation. The matrix mixture 25 comprises in this example a functionalized polysiloxane, for example an alkoxysilane (for example Silmer TMS, 50 to 700 series, from Siltech, such as Silmer TMS C50 or Di-50). In this example, the matrix mixture comprises no solvent. A solvent, for example isopropanol, may however be used for adjusting viscosity. The preferred residence time in the dip bath amounts to 2 to 5 minutes.

(24) As a result of impregnation, a honeycomb blank 26 impregnated with a matrix mixture is obtained. In step 260, the impregnated honeycomb blank 26 is precured at a temperature of 150-200? ? C. in a circulating air oven, among other things to evaporate the solvent, in this case isopropanol. This results in at least partial crosslinking of the matrix mixture. Depending on the bulk density to be achieved, this step may optionally be repeated a number of times.

(25) In step 270, the precured honeycomb blank 26 is heated to the pyrolysis temperature, approximately 400-600? ? C., such that the siloxane chains of the matrix mixture are converted into Sioc ceramics. Pyrolysis is then continued at 800-900? C.

(26) As a result, a honeycomb body 1 comprising the support of carbon fibers and the silicon oxycarbide matrix is obtained, wherein the fibers of the support are embedded in the matrix or the support and matrix form a ceramic fiber composite material.

(27) Step 280 (see exemplary embodiment 1 or 2) is omitted here.

(28) In step 290, the honeycomb body 1 may be cut for subsequent further processing into slices perpendicular to the cell walls of the honeycomb cells, i.e. perpendicular to the T direction. Honeycomb slices 29 of the desired height with the desired material properties are accordingly produced. Cutting may alternatively also proceed after partial curing in step 260 and before the pyrolysis step 270, such that for example a smaller process chamber may be used for steps 270 and 280.

Ceramic honeycomb body for lightweight structures and corresponding production method

LIST OF REFERENCE SIGNS

(29) FIG. 1 L Longitudinal direction of the honeycomb body W Width direction of the honeycomb body T Honeycomb height or thickness or height of the cell walls of the honeycomb cells 1 Honeycomb body 12 Honeycomb cells 13 Cell walls FIG. 2 21 Support material 22 Adhesive stripes 23 Stack 24 Honeycomb block 25 Matrix mixture 26 Honeycomb blank 27 Pyrolysis furnace 29 Honeycomb slice Process steps: 210 Providing a roll of support material 220 Applying adhesive to the support material 230 Cutting the support material, stacking and adhesively bonding the sheets to form a block 240 Expanding the block 250 Immersing the honeycomb block in the matrix mixture 260 Precuring the honeycomb blank 270 Pyrolysis or carbonization 280 Siliconization 290 Cutting the honeycomb body into honeycomb slices FIG. 3 Method steps: 310 Providing the honeycomb slice and cover layers 320 Placing the adhesive and arranging the honeycomb slice between the cover layers 330 Pressing the cover layers and honeycomb slice to form a sandwich 340 Pyrolysis 350 Siliconization FIG. 4 41 Honeycomb core 42 Honeycomb cells 43 Cell walls 44 Cover layers 45 Adhesive