Polymer-to-ceramic conversion and method of making the same

Abstract

This invention provides a polymer conversion ceramic and its preparation method, relating to the field of polymer conversion ceramic technology. The polymer conversion ceramic, by weight, comprises: 70-90 parts of methylvinyl polysilazane, 5-15 parts of polyacrylonitrile fiber, and 1-6 parts of polysiloxane. Further, the raw material components may also include 1-5 parts of boron oxide, 1-5 parts of metal oxide, 0.3-2 parts of organic peroxide, and / or 2-7 parts of organic solvent. This invention utilizes polyacrylonitrile fiber, which can simultaneously transform into carbon fiber at the high temperature during the ceramization of polysilazane, thereby improving the bonding force of continuous fibers to the ceramic matrix and fully utilizing the reinforcing and toughening effects of continuous fibers.

Description

Technical Field

[0001] This invention belongs to the field of polymer conversion ceramics technology, and relates to a polymer conversion ceramic and its preparation method. Background Technology

[0002] Using polysilazane as a precursor, inorganic ceramics with specific structures and compositions can be converted through a controlled pyrolysis process; these are generally called polymer-converted ceramics (PDCs). However, the inorganic ceramics obtained by this method tend to be brittle, with low impact resistance, fracture toughness, and mechanical damage tolerance, which affects practical applications. Introducing continuous fibers (such as carbon fibers or SiC fibers) into the precursor is an effective way to improve the toughness of PDCs. However, the bonding force between the continuous fibers and the ceramic matrix also affects the effectiveness of the continuous fibers. For example, the shrinkage generated during the thermal decomposition of polysilazane may lead to poor interfacial bonding between the continuous fibers and the ceramic matrix or the formation of microcracks. Continuous fibers may also be damaged due to mechanical stress or chemical action during preparation and pyrolysis, all of which can result in the continuous fibers not fully exerting their effects.

[0003] Therefore, the applicant believes that the existing technology for preparing PDCs with polysilazane as a precursor and continuous fiber reinforcement needs further improvement. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a polymer conversion ceramic and its preparation method.

[0005] The technical solution of the present invention is as follows:

[0006] A polymer conversion ceramic, wherein the raw material components, by weight parts, comprise: 70-90 parts of methylvinyl polysilazane, 5-15 parts of polyacrylonitrile fiber and 1-6 parts of polysiloxane.

[0007] The polysiloxane is selected from polydimethylsiloxane;

[0008] Alternatively, the structure of the polysiloxane is shown in formula (1) below.

[0009] R 1 Me2SiO(SiOMe2) a (SiOMeR 2 ) b SiMe2R 1 (1)

[0010] Among them, R 1 Selected from C1-C4 alkyl, hydroxy, C1-C6 hydroxyalkyl, amino, or C2-C6 aminoalkyl; R 2Selected from C3-C20 alkyl groups containing hydroxyl, epoxy, carbonyl, urea, ester or amide groups, or selected from C1-C4 alkyl groups; a=10-300, b=3-30.

[0011] Preferably, the diameter of the polyacrylonitrile fiber is 1-100 μm.

[0012] Preferably, the values ​​of a and b satisfy: 0.3≤b / a≤0.7.

[0013] Preferably, the raw material components further include 0.3-2 parts of organic peroxide and 2-7 parts of organic solvent, or a combination of two or more of these.

[0014] Preferably, the raw material components further include 1-5 parts of boron oxide and 1-5 parts of metal oxide, or a combination of two or more of these.

[0015] More preferably, the metal oxide is selected from one or a combination of two or more of lead oxide, bismuth oxide, gallium oxide, cerium oxide, cerium oxide and yttrium oxide.

[0016] A method for preparing polymer conversion ceramics according to any of the above embodiments, comprising the steps of:

[0017] The polyacrylonitrile fiber is pre-oxidized to obtain pre-oxidized PAN fiber;

[0018] The pre-oxidized PAN fiber is mixed evenly with the remaining raw material components to obtain a precursor.

[0019] The precursor is heated to 1000-1500℃ for ceramization to obtain the polymer conversion ceramic.

[0020] Preferably, the process of heating the precursor to 1000-1500℃ includes: heating to a low temperature of 200-400℃ and holding for 0.5-2 hours; then heating to a medium temperature of 400-800℃ and holding for 1-3 hours; and continuing to heat to a high temperature of 1000-1500℃.

[0021] Preferably, when the raw material component contains organic peroxide, the process further includes heating the precursor to no more than 180°C and maintaining it for 10 min to 1 h before ceramization.

[0022] The beneficial effects of this invention are:

[0023] (1) This invention uses polyacrylonitrile fiber (PAN fiber). Within the reaction temperature range of polysilazane to ceramic conversion, PAN fiber is simultaneously converted into carbon fiber, realizing the simultaneous generation of continuous fiber and ceramicization of polysilazane (the formation of ceramic matrix by ceramicization of polysilazane). Moreover, the active groups on the surface of PAN fiber (after oxidation) can react in situ with the ceramicized polysilazane at the interface to form a chemically bonded interface or interface gradient transition layer with good stability, thereby improving the bonding force between carbon fiber as a continuous fiber and ceramic matrix, better exerting the reinforcing and toughening properties of carbon fiber, and the obtained composite PDCs have higher mechanical strength and stronger fracture toughness.

[0024] (2) The addition of polysiloxane in this invention can improve the bonding force between PAN fiber (pre-oxidized PAN fiber) and polysiloxane. Moreover, polysiloxane can also participate in the ceramicization reaction and participate in the formation of ceramic matrix, further improving the bonding force between carbon fiber and ceramic matrix, and further enhancing the performance of composite PDCs. Detailed Implementation

[0025] The technical solution of the present invention will be further explained and described below through specific embodiments.

[0026] On the one hand, the present invention proposes a polymer conversion ceramic PDC, wherein the raw material components, by weight, include: 70-90 parts of methyl vinyl polysilazane, 5-15 parts of polyacrylonitrile fiber and 1-6 parts of polysiloxane;

[0027] The polysiloxane is selected from polydimethylsiloxane;

[0028] Alternatively, the structure of the polysiloxane is shown in formula (1) below.

[0029] R 1 Me2SiO(SiOMe2) a (SiOMeR 2 ) b SiMe2R 1 (1)

[0030] Among them, R 1 Selected from C1-C4 alkyl, hydroxy, C1-C6 hydroxyalkyl, amino, or C2-C6 aminoalkyl; R 2 Selected from C3-C20 alkyl groups containing hydroxyl, epoxy, carbonyl, urea, ester or amide groups, or selected from C1-C4 alkyl groups; a=10-300, b=3-30.

[0031] This invention uses polysilazane as the main component (i.e., precursor) of the ceramic matrix (silicon nitride-based ceramic) and polyacrylonitrile fiber (PAN fiber) as the raw material component. PAN fiber can be simultaneously converted into carbon fiber at the high temperature during the conversion of polysilazane into the ceramic matrix, providing reinforcement and toughening. Furthermore, due to the pre-oxidation of PAN fiber, its surface contains abundant active groups (carbonyl groups, hydroxyl groups, ether bonds, etc.), which can improve the wettability of polysilazane to it. In addition, at the high temperature of the ceramicization reaction, chemical bonding and / or a gradient transition layer can be formed at the interface between the fiber and the ceramic matrix, improving the bonding force between the ceramic matrix and the carbon fiber. This invention has found that adding a small amount of polysiloxane can help improve the mechanical strength and fracture toughness of polymer-converted ceramics, possibly because polysiloxane can further improve the bonding force between the fiber and the ceramic matrix and also participate in the formation of the ceramic matrix.

[0032] Polysiloxane adopts the structure shown in formula (1) above, through R 2 The value of b / a can adjust the polarity of polysiloxanes, such as R. 2 When polysiloxanes contain highly polar groups such as hydroxyl, epoxy, carbonyl, ester, and amide groups, their polarity can be increased, resulting in a more significant strengthening and toughening effect. The polysiloxanes shown in formula (1) can be prepared using existing technologies, such as ring-opening polymerization of the corresponding siloxane cyclic compound, or hydrosilylation reaction of the corresponding hydrogen-containing silicone oil with an alkenyl compound (such as allyl glycidyl ether), as is well known to those skilled in the art.

[0033] PAN fibers can be formed from single fibers into bundles or woven into a mesh structure, such as PAN fiber woven fabrics. Pre-oxidation of PAN fibers can be carried out at 200-300℃, with no particular limitation on the degree of pre-oxidation, which can be 50-80%; there are also no particular limitations on the stretch ratio, which can be 1.03-1.2 times.

[0034] In some embodiments, the diameter of the polyacrylonitrile (PAN) fibers is 1-100 μm. For example, the diameter of the PAN fibers can be 1 μm, 3 μm, 5 μm, 6 μm, 8 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, or 100 μm. For PAN fibers, pre-oxidation and stretching can be performed, for example, pre-oxidation at 200-300°C, followed by stretching, to improve the mechanical properties and thermal stability of the PAN fibers through molecular chain orientation and structural optimization, before mixing with raw material components such as polysilazane.

[0035] In the above equation (1), a is the average degree of polymerization DP of the -SiOMe2- structure, and b is the degree of polymerization of -SiOMeR. 2- The average degree of polymerization (DP) of the structure. In some embodiments, the values ​​of a and b satisfy: 0.3 ≤ b / a ≤ 0.7. A value of b / a within the above range can yield polysiloxanes with moderate polarity. For example, the value of b / a can be any value or any value between 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, etc., without particular limitation. When R 1 and R 2 Both are methyl groups; therefore, the aforementioned polysiloxane is polydimethylsiloxane.

[0036] In some embodiments, the raw material component further comprises 0.3-2 parts of an organic peroxide and 2-7 parts of an organic solvent, or a combination of two or more of these. The organic peroxide in the raw material component can initiate polymerization at a certain temperature, enabling pre-crosslinking and preliminary shaping. There are no particular limitations on the organic peroxide; examples include cumene peroxide and tert-butyl hydroperoxide. The organic solvent in the raw material component reduces its viscosity, which is beneficial for application and the wetting and penetration of the liquid component into the PAN fiber. There are no particular limitations on the organic solvent; examples include dimethylformamide (DMF), dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), and dimethyl sulfoxide (DMSO).

[0037] In some embodiments, the raw material component further comprises 1-5 parts of boron oxide and 1-5 parts of metal oxide, or a combination of two or more of these. The metal oxide can act as a sintering aid to improve the flowability and sintering density of the raw material component at high temperatures, thereby increasing the hardness of PDCs, or it can refine the grains and improve the fracture toughness of the ceramic. There are no particular requirements for the particle size of the boron oxide and metal oxide; they can be micrometers or smaller, such as 0.1-10 μm.

[0038] In some embodiments, the metal oxide is selected from one or a combination of two or more of lead oxide, bismuth oxide, gallium oxide, cerium oxide, cerium oxide, and yttrium oxide. Boron oxide and metal oxide can further form composite sintering aids for synergistic effects. For example, a combination of boron oxide and lead oxide, or a combination of boron oxide and bismuth oxide, where lead oxide and bismuth oxide provide low-temperature densification, and boron oxide enhances high-temperature stability, further improving the performance of PDCs, such as higher hardness, higher fracture strength, and better fracture toughness.

[0039] On the other hand, the present invention also provides a method for preparing the polymer conversion ceramic described in any of the above embodiments, the steps of which include:

[0040] Polyacrylonitrile fibers are pre-oxidized to obtain pre-oxidized PAN fibers;

[0041] The pre-oxidized PAN fiber is mixed evenly with the remaining raw material components to obtain the precursor;

[0042] The precursor is heated to 1000-1500℃ for ceramization to obtain polymer conversion ceramics.

[0043] The surface of pre-oxidized PAN fibers contains abundant active groups, which facilitate the wetting and penetration of other raw material components and also promote the formation of a transition layer and / or chemical bonding at the fiber interface at high temperatures, thereby improving interfacial bonding and better leveraging the reinforcing and toughening effects of carbon fibers. Pre-oxidized PAN fibers can also be further stretched, and the mechanical properties and thermal stability of polyacrylonitrile fibers can be improved through molecular chain orientation and structural optimization, ultimately transforming them into carbon fibers to enhance the reinforcing and toughening effects on PDCs.

[0044] In some embodiments, heating the precursor to 1000-1500°C includes: heating to a low temperature of 200-400°C and holding for 0.5-2 hours; then heating to a medium temperature of 400-800°C and holding for 1-3 hours; and continuing to heat to a high temperature of 1000-1500°C.

[0045] For mixing pre-oxidized PAN fibers with the remaining raw material components, the pre-oxidized PAN fibers can be pre-soaked in a solution containing a precursor (polysilazane) at room temperature for a certain time (e.g., 30-60 minutes), drained, and dried at a certain temperature (e.g., 60-100℃) to form pre-impregnated oxidized PAN fibers. The premixed material, after being thoroughly mixed with the remaining raw material components, is then mixed with the pre-impregnated oxidized PAN fibers. Vacuum-assisted impregnation (vacuum-assisted impregnation followed by pressure) can be used to improve the wetting and penetration of the premixed material into the pre-impregnated oxidized PAN fibers, ensuring sufficient wetting and penetration to obtain the precursor. For the high-temperature ceramization of the precursor, it can be carried out in an inert gas atmosphere (such as argon, helium, etc.). The heating can be divided into three stages: The first stage is a low temperature of 200-400℃, held for 0.5-2 hours, with a heating rate of 1-5℃ / min. During this stage, the precursor begins to initially decompose and form an initial ceramic network structure. The second stage is a medium temperature of 400-800℃, held for 1-3 hours, with a heating rate of 2-10℃ / min. During this stage, the precursor begins to thermally decompose and gradually transforms into the target ceramic, and the pre-oxidized PAN fibers begin to carbonize, transforming into carbon fibers. The third stage is a high temperature of 1000-1500℃, held for 1-4 hours, with a heating rate of 2-5℃ / min. During this stage, the precursor is fully ceramized and transformed into PDCs, and the pre-oxidized PAN fibers are fully transformed into carbon fibers, forming a continuous fiber-reinforced composite PDCS. After the ceramization reaction is completed, it can be further cooled to room temperature in an inert gas atmosphere.

[0046] In some embodiments, when the raw material component contains an organic peroxide, the process further includes heating the precursor to no more than 180°C and maintaining it for 10 min to 1 h before ceramization by heating the precursor to 1000-1500°C. Using the above technical solution, the organic peroxide pre-crosslinks and pre-shapes the raw material component, improving the shape stability of the polymer-converted ceramic.

[0047] The technical solution of the present invention will be further described and illustrated below with reference to various embodiments. Unless otherwise specified, the parts mentioned in the following embodiments are parts by weight.

[0048] Example 1

[0049] The raw material components of PDCs include: 80 parts polysilazane (methyl vinyl polysilazane, Mn is 2000 g / mol), 10 parts PAN fiber woven fabric, 3 parts polydimethylsiloxane (DP is 43.8) and 6 parts DMF.

[0050] The PAN fiber bundles used in PAN fiber woven fabrics are pre-oxidized and stretched. Pre-oxidation is carried out at 250-280℃ with a pre-oxidation degree of 65%, followed by stretching with a stretch ratio of 1.05.

[0051] Polysilazane, polydimethylsiloxane and DMF are mixed and stirred until homogeneous to obtain a premix.

[0052] The PAN fiber woven fabric is immersed in the premix, and after vacuum degassing, it is maintained for 60 minutes to allow the premix to fully wet the PAN fibers, thus obtaining the precursor solution.

[0053] Under a helium atmosphere, the precursor solution was heated to a low temperature of 350℃ at a heating rate of 3℃ / min and held at that temperature for 1 hour; then heated to a medium temperature of 700℃ at a heating rate of 7℃ / min and held at that temperature for 2 hours; then heated to a high temperature of 1300℃ at a heating rate of 5℃ / min and held at that temperature for 2.5 hours, and then cooled to room temperature to obtain composite PDCs.

[0054] Comparative Example 1

[0055] The difference between this comparative example and Example 1 is that in Example 1, polydimethylsiloxane was replaced with an equal weight of polysilazane, meaning that no polydimethylsiloxane was added in this comparative example. All other steps remain unchanged.

[0056] Comparative Example 2

[0057] The difference between this comparative example and Example 1 is that in Example 1, the PAN fiber woven fabric was replaced with carbon fiber woven fabric. The remaining steps remain unchanged.

[0058] Example 2

[0059] The difference between this embodiment and Embodiment 1 is that in Embodiment 1, polydimethylsiloxane is replaced with an equal weight of polysiloxane (in the above formula (1), R...). 1 It is methyl, R 2 (CH2CHO)CH2O(CH2)3-, a=31.8, b=12.6). The remaining steps remain unchanged.

[0060] Example 3

[0061] The difference between this embodiment and Embodiment 1 is that in Embodiment 1, polydimethylsiloxane is replaced with an equal weight of polysiloxane (in the above formula (1), R...). 1 It is methyl, R 2 The value is CH3OCO(CH2)2- (a=27.4, b=16.2). The remaining steps remain unchanged.

[0062] Example 4

[0063] The difference between this embodiment and Embodiment 2 is that in Embodiment 2, the raw material components also include 3 parts boron oxide (average particle size 1.5 μm) and 3 parts bismuth oxide (average particle size 1 μm), and the high temperature is adjusted from 1300℃ to 1100℃. The remaining steps remain unchanged.

[0064] Example 5

[0065] The difference between this embodiment and Embodiment 2 is that in Embodiment 2, the raw material components also include 3 parts boron oxide (average particle size 1.5 μm) and 3 parts lead oxide (average particle size 0.8 μm), and the high temperature is adjusted from 1300℃ to 1200℃. The remaining steps remain unchanged.

[0066] Example 6

[0067] The raw material components of PDCs include: 70 parts of polysilazane (methyl vinyl polysilazane, Mn is 2000 g / mol), 5 parts of PAN fiber woven fabric, 2 parts of boron oxide (average particle size 1.5 μm), 3 parts of bismuth oxide (average particle size 1 μm), 1 part of the polysiloxane in Example 2 and 5 parts of DMF.

[0068] The fiber bundles of PAN fiber woven fabric are pre-oxidized and stretched. Pre-oxidation is carried out at 250-280℃ with a pre-oxidation degree of 60%, followed by stretching with a stretch ratio of 1.06.

[0069] Polysilazane, boron oxide, bismuth oxide, polysiloxane and DMF are mixed and dispersed to form a premix, and the remaining preparation methods are the same as in Example 4.

[0070] Example 7

[0071] The difference between this embodiment and Embodiment 6 is that in Embodiment 6, the PAN fiber woven fabric was changed from 5 parts to 15 parts, and the polysiloxane was changed from 1 part to 6 parts. The remaining steps remain unchanged.

[0072] Example 8

[0073] The difference between this embodiment and Embodiment 7 is that in Embodiment 7, the polysilazane was changed from 70 parts to 90 parts. The remaining steps remain unchanged.

[0074] Example 9

[0075] The difference between this embodiment and Embodiment 6 is that in Embodiment 6, the raw material components also included 1 part of cumene peroxide. The remaining steps remain unchanged.

[0076] During preparation, before the precursor solution is heated to a low temperature and held at 140°C for 5 minutes, the precursor solution is pre-crosslinked and initially shaped.

[0077] Example 10

[0078] The difference between this embodiment and Embodiment 6 is that in Embodiment 6, the PAN fiber woven fabric was pre-soaked and impregnated with a polysilazane solution (the polysilazane, ethylene glycol dimethyl ether solution in Embodiment 6, with a concentration of 5%). The remaining steps remain unchanged.

[0079] Performance testing

[0080] Bending strength: Three-point bending method, span 20 mm.

[0081] Fracture toughness: Tested according to the method of GB / T 1449-2025, single-sided notched beam method.

[0082] Vickers hardness: 1kg load.

[0083] The results are shown in Table 1 below.

[0084] Table 1

[0085]

[0086] Therefore, as shown in Table 1 above, compared with the direct use of carbon fiber, the use of PAN fiber in this invention can significantly improve the mechanical strength and fracture toughness of composite PDCs. Furthermore, the added polysiloxanes can further enhance the mechanical strength and fracture toughness of composite PDCs, especially polysiloxanes with polar side chains, which exhibit a more pronounced improving effect. The addition of boron oxide and metal oxides can significantly improve density and fracture toughness while lowering the high-temperature ceramization temperature.

[0087] As described above, the basic principles, main features, and advantages of the present invention have been shown and described. Those skilled in the art should understand that the present invention is not limited to the above embodiments, which are merely preferred embodiments and should not be construed as limiting the scope of the invention. All equivalent changes and modifications made in accordance with the scope of the patent and the description should still fall within the scope of the present invention. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A polymer conversion ceramic, characterized in that, The raw material components, by weight, include: 70-90 parts methyl vinyl polysilazane, 5-15 parts polyacrylonitrile fiber, and 1-6 parts polysiloxane; The polysiloxane is selected from polydimethylsiloxane; Alternatively, the structure of the polysiloxane is shown in formula (1) below. R 1 Me2SiO(SiOMe2) a (SioMeR 2 ) b SiMe2R 1 (1) Among them, R 1 Selected from C1-C4 alkyl, hydroxy, C1-C6 hydroxyalkyl, amino, or C2-C6 aminoalkyl; R 2 Selected from C3-C20 alkyl groups containing hydroxyl, epoxy, urea, ester or amide groups, or selected from C1-C4 alkyl groups; a=10-300, b=3-30.

2. The polymer conversion ceramic according to claim 1, characterized in that, The diameter of the polyacrylonitrile fiber is 1-100 μm.

3. The polymer conversion ceramic according to claim 1, characterized in that, The values ​​of a and b satisfy: 0.3 ≤ b / a ≤ 0.

7.

4. The polymer conversion ceramic according to claim 1, characterized in that, The raw material components also include 0.3-2 parts of organic peroxide and 2-7 parts of organic solvent, or two of them.

5. The polymer conversion ceramic according to claim 1, characterized in that, The raw material components also include 1-5 parts of boron oxide and 1-5 parts of metal oxide, or one or two of them.

6. The polymer conversion ceramic according to claim 5, characterized in that, The metal oxide is selected from one or more of lead oxide, bismuth oxide, gallium oxide, cerium oxide, cerium oxide, and yttrium oxide.

7. A method for preparing a polymer conversion ceramic according to any one of claims 1-6, characterized in that, step include: The polyacrylonitrile fiber is pre-oxidized to obtain pre-oxidized PAN fiber; The pre-oxidized PAN fiber is mixed evenly with the remaining raw material components to obtain a precursor. The precursor is heated to 1000-1500℃ for ceramization to obtain the polymer conversion ceramic.

8. The method for preparing polymer conversion ceramics according to claim 7, characterized in that, The process of heating the precursor to 1000-1500℃ includes: heating to a low temperature of 200-400℃ and holding for 0.5-2 hours; then heating to a medium temperature of 400-800℃ and holding for 1-3 hours; and continuing to heat to a high temperature of 1000-1500℃.

9. The method for preparing polymer conversion ceramics according to claim 7, characterized in that, When the raw material component contains organic peroxide, before the precursor is heated to 1000-1500°C for ceramization, the process further includes: heating the precursor to no more than 180°C and maintaining it for 10 min-1 h.

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