Preparation method of alumina fiber reinforced aluminum phosphate composite material with interface layer

Abstract

The invention discloses a preparation method of an alumina fiber reinforced aluminum phosphate composite material with an interface layer, and belongs to the field of ceramic matrix composite materials. In order to solve the problem that reinforcement fibers are corroded by a phosphate matrix, alumina fibers are pretreated mainly by adopting organic aluminum phosphate sol, and on the basis, inorganic aluminum phosphate sol is used as a main matrix for composite molding. The interface layer is formed on the surface of the alumina fiber, so that the fiber can be effectively prevented from being corroded in a low-pH-value environment, meanwhile, the thermal expansion coefficient of the interface layer is close to that of a matrix, and microcracks generated in the thermal cycle process are reduced. The composite material has excellent room-temperature and high-temperature mechanical properties, has high bending strength at room temperature and high temperature, and is suitable for heat insulation in an extreme high-temperature environment.

Description

Technical Field

[0001] The present invention belongs to the field of ceramic matrix composites, and particularly relates to a preparation method of an alumina fiber reinforced aluminum phosphate composite material with an interface layer. Background Art

[0002] With the rapid development of aerospace technology, the temperature and thermal shock received by the external materials of various aircraft are continuously increasing, which requires that aerospace structural materials have higher service temperatures and better wave transmission performance. At present, although the commonly used ceramic matrix wave-transparent composite materials have good high-temperature resistance and high wave transmission performance, their forming processes are complex and the manufacturing costs are high, making it difficult to meet the requirements of high-speed aircraft applications. The continuous fiber reinforced phosphate wave-transparent composite materials have the characteristics of high temperature resistance, oxidation resistance, excellent dielectric properties, low thermal expansion coefficient, and good material structure designability. They are excellent high-temperature resistant and low-dielectric materials. In particular, the phosphate composite materials have good forming processability and low manufacturing costs, and are a type of high-temperature resistant wave-transparent composite materials suitable for the radomes or antenna windows of high-speed aircraft. At present, the common reinforcing fibers in the phosphate composite material system include quartz fibers, alumina fibers, high-silica fibers, etc. Among them, quartz fibers have low cost, good wave transmission performance and process performance, but the normal service temperature is not higher than 800 °C. The alumina fibers represented by Nextel-720 and Nextel-610 fibers have higher service temperatures. The fiber reinforced phosphate composite materials prepared by using alumina fibers as the reinforcement and the lay-up hot pressing process have higher service temperatures, better mechanical strength, and lower manufacturing costs, and have broad application prospects.

[0003] Since the aluminum phosphate sol has certain acidity, it will corrode the high-silica fibers. Especially in a high-temperature environment, the aluminum phosphate matrix will react violently with the surface of the fibers, resulting in strong bonding between the interfaces and a decrease in mechanical properties. Therefore, during the preparation process of the composite material, it is usually necessary to protect the fibers in advance. The commonly used interface layer materials at present include aluminum sol, lanthanum phosphate, etc. Although the introduction of these interface phases can protect the fibers to a certain extent, it will lead to the problem of mismatch in the thermal expansion coefficient with the matrix material. At the same time, the aluminum phosphate matrix itself will also undergo a polymorphic transformation involving a large change in molar volume, which will further lead to defects and microcracks in the material. This limits the application of phosphates as high-temperature engineering ceramic materials. Summary of the Invention

[0004] The purpose of the present invention is to provide a preparation method of an alumina fiber reinforced aluminum phosphate composite material with an interface layer to solve the problem of corrosion of the reinforcing fiber by the phosphate matrix.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing an alumina fiber-reinforced aluminum phosphate composite material with an interface layer, comprising the following steps:

[0007] 1) Weave continuous alumina fibers into a two-dimensional alumina fiber cloth and remove the sizing agent on the fiber surface;

[0008] 2) Prepare an organic aluminum phosphate sol, immerse the alumina fiber cloth with the sizing agent removed in the organic aluminum phosphate sol, perform vacuum defoaming treatment, and then dry to obtain an alumina fiber cloth with an interface layer;

[0009] 3) Prepare an inorganic aluminum phosphate sol, evenly brush the inorganic aluminum phosphate sol on the alumina fiber cloth with an interface layer, scrape off the excess glue solution and then dry to obtain an alumina fiber prepreg;

[0010] 4) Stack the alumina fiber prepregs layer by layer according to the required thickness, scrape off the air bubbles between the layers, place them in a mold for hot pressing, naturally cool to room temperature, and demold to obtain an alumina fiber-reinforced aluminum phosphate composite material with an interface layer.

[0011] Preferably, the method for removing the sizing agent on the fiber surface in step 1) is: treating in a high-temperature sintering furnace at 500-600 °C for 1 h, or treating in water or acetone at 50-80 °C for 36-48 h.

[0012] Preferably, the method for preparing the organic aluminum phosphate sol in step 2) is: using aluminum nitrate and phosphorus pentoxide with a molar ratio of 1:1-1:2, respectively using ethanol as a buffer solution, and then heating to 70-90 °C and condensing and refluxing for 24-72 h.

[0013] Preferably, the viscosity of the organic aluminum phosphate sol in step 2) is 150-200 mPa·s, and the pH value is 4.8-5.4.

[0014] Preferably, the time for vacuum defoaming treatment in step 2) is 2-4 h, the drying temperature is 60-100 °C, and the drying time is 4-6 h.

[0015] Preferably, the method for preparing the inorganic aluminum phosphate sol in step 3) is: using aluminum hydroxide and phosphoric acid with a molar ratio of 1:1.5-1:3, respectively using deionized water as a buffer solution, and then heating to 90-100 °C and condensing and refluxing for 2-6 h.

[0016] Preferably, the viscosity of the inorganic aluminum phosphate sol in step 3) is 20-45 mPa·s, and the pH value is 2.5-3.5.

[0017] Preferably, the amount of the inorganic aluminum phosphate sol brushed in step 3) is 50%-80% of the mass of the alumina fiber cloth with an interface layer.

[0018] Preferably, in step 3), the drying time is 15 - 18 h and the drying temperature is 25 - 35 °C.

[0019] Preferably, the hot pressing and forming step in step 4) includes: heating from room temperature to 80 - 120 °C over 1 - 2 h, applying a pressure of 2 - 4 MPa after heat preservation for 2 - 4 h; heating to 180 - 240 °C after 3 - 6 h while increasing the pressure to 8 - 10 MPa and maintaining for 2 - 4 h.

[0020] The beneficial effects achieved by the present invention are as follows:

[0021] 1. By using aluminum organophosphate sol to pretreat alumina fibers to form an interface layer, the present invention effectively protects the fibers from being corroded by the aluminum phosphate matrix with a low pH value. At the same time, the coefficient of thermal expansion of the interface layer is similar to that of the matrix, reducing the interface stress during the thermal cycle and significantly limiting the generation of microcracks in the matrix under high-temperature conditions.

[0022] 2. The present invention uses an inorganic aluminum phosphate sol with good fluidity and low curing temperature as the main matrix material, improving the density of the composite material while enhancing its high-temperature performance.

[0023] 3. By reasonably designing the pretreatment and hot pressing and forming processes, the present invention improves the interface bonding performance, ensures uniform adhesion of the interface layer, and enhances the overall mechanical properties and thermal stability of the composite material.

[0024] 4. The preparation and operation processes of the aluminum organophosphate sol and inorganic aluminum phosphate sol used in the present invention are mild and controllable, taking into account both the material properties and the operability of the preparation process, and avoiding the problem of insufficient interface adhesion force that may exist in traditional technologies.

[0025] 5. Compared with the lanthanum phosphate interface layer used in the prior art, the aluminum organophosphate interface layer of the present invention has more excellent anti-corrosion performance and thermal matching properties, and at the same time, the preparation process is simpler and the effect is more stable.

[0026] 6. The alumina fiber-reinforced aluminum phosphate composite material prepared by the present invention has a room-temperature bending strength greater than 210 MPa and a bending strength greater than 180 MPa at 1000 °C, with a high retention rate of high-temperature performance, and is suitable for heat insulation materials and structural materials in extremely high-temperature environments. Description of the Drawings

[0027] Figure 1 is a preparation flow chart of an alumina fiber-reinforced aluminum phosphate composite material with an interface layer.

[0028] Figure 2 is a physical diagram of an alumina fiber-reinforced aluminum phosphate flat sample with an interface layer prepared in Example 1.

[0029] Figure 3It is the microscopic morphology diagram of the alumina fiber reinforced aluminum phosphate composite material with an interface layer prepared in Example 1.

[0030] Figure 4 It is the microscopic morphology diagram of the alumina fiber reinforced aluminum phosphate composite material without an interface layer prepared in Comparative Example 1. Specific embodiments

[0031] To make the technical features and advantages or technical effects in the above technical solutions of the present invention more obvious and understandable, the following will be described in detail in conjunction with the drawings.

[0032] Example 1:

[0033] 1. Commercially available continuous alumina fibers (NEXTEL-720, produced by 3M Company, USA) were woven into a two-dimensional alumina fiber cloth according to the eight-harness satin weaving process, treated in a high-temperature sintering furnace at 600 °C for 1 h, and taken out after cooling to room temperature.

[0034] 2. Aluminum nitrate and phosphorus pentoxide were respectively mixed evenly in ethanol according to a molar ratio of 1:1.5, then heated to 85 °C and condensed and refluxed for 48 h, and an organic aluminum phosphate sol (viscosity 201 mPa·s, pH value 5) was obtained after cooling to room temperature. The alumina fiber cloth was put into the sol, and after being vacuum-treated for 3 h with a vacuum pump, the fiber cloth was taken out, and then treated at 80 °C for 4 h to obtain an alumina fiber cloth with an interface layer.

[0035] 3. Aluminum hydroxide and phosphoric acid were mixed evenly according to a molar ratio of 1:3, then heated to 95 °C and condensed and refluxed for 4 h, and an inorganic aluminum phosphate sol (viscosity 21 mPa·s, pH value 2.6) was obtained after cooling to room temperature. Subsequently, 60% of the aluminum phosphate sol was weighed according to the mass of the fiber cloth and evenly coated on the alumina fiber cloth. After scraping off the excess glue solution, it was dried at 35 °C for 16 h to obtain an alumina fiber prepreg.

[0036] 4. Twenty-five layers of alumina fiber prepregs were stacked and placed, and the air bubbles between the layers were scraped off with a scraper and then placed in a mold, and hot pressing was carried out using a hot press. First, it was heated from room temperature to 80 °C in 1 h, kept at this temperature for 2 h and then a pressure of 3 MPa was applied; after 4 h, it was heated to 180 °C, and at the same time the pressure was increased to 10 MPa, and after keeping at this temperature for 3 h, it was naturally cooled to room temperature, and the mold was removed to obtain an alumina fiber reinforced aluminum phosphate composite material with an interface layer and a thickness of 4 mm, as Figure 2-3 shown.

[0037] The alumina fiber reinforced aluminum phosphate composite material with an interface layer prepared was subjected to spline machining and testing, and the average flexural strength at room temperature was measured to be 211 MPa, and the average flexural strength at 1000 °C was 185 MPa.

[0038] Example 2:

[0039] 1. Commercially available continuous alumina fibers (NEXTEL-720, produced by 3M Company, USA) were woven into a two-dimensional alumina fiber cloth according to the eight-harness satin weaving process, and then treated in a high-temperature sintering furnace at 500 °C for 1 h, and taken out after cooling to room temperature.

[0040] 2. Aluminum nitrate and phosphorus pentoxide were respectively mixed evenly in ethanol according to a molar ratio of 1:2, and then heated to 90 °C and condensed and refluxed for 72 h. After cooling to room temperature, an organic aluminum phosphate sol (viscosity 156 mPa·s, pH value 5.1) was obtained. The alumina fiber cloth was put into the sol, and after being vacuum-treated with a vacuum pump for 4 h, the fiber cloth was taken out, and then treated at 60 °C for 6 h to obtain an alumina fiber cloth with an interface layer.

[0041] 3. Aluminum hydroxide and phosphoric acid were mixed evenly according to a molar ratio of 1:1.5, and then heated to 90 °C and condensed and refluxed for 2 h. After cooling to room temperature, an inorganic aluminum phosphate sol (viscosity 43 mPa·s, pH value 3.1) was obtained. Subsequently, 50% of the aluminum phosphate sol was weighed according to the mass of the fiber cloth and evenly coated on the alumina fiber cloth. After scraping off the excess glue solution, it was dried at 25 °C for 18 h to obtain an alumina fiber prepreg.

[0042] 4. Twenty-five layers of alumina fiber prepregs were stacked and laminated, and the air bubbles between layers were scraped off with a squeegee and then placed in a mold, and hot pressing was carried out using a hot press. First, it was heated from room temperature to 90 °C in 2 h, and after holding for 3 h, a pressure of 4 MPa was applied; after another 3 h, it was heated to 200 °C, and at the same time the pressure was increased to 8 MPa. After holding for 4 h, it was naturally cooled to room temperature, and the mold was removed to obtain an alumina fiber-reinforced aluminum phosphate composite material with an interface layer and a thickness of 4 mm.

[0043] The prepared alumina fiber-reinforced aluminum phosphate composite material with an interface layer was subjected to spline machining tests. The test results showed that the average flexural strength at room temperature was 217 MPa, and the average flexural strength at 1000 °C was 181 MPa.

[0044] Example 3:

[0045] 1. Commercially available continuous alumina fibers (NEXTEL-720, produced by 3M Company, USA) were woven into a two-dimensional alumina fiber cloth according to the eight-harness satin weaving process, and then treated in water at 60 °C for 40 h, and taken out after cooling to room temperature.

[0046] 2. Mix aluminum nitrate and phosphorus pentoxide evenly in ethanol according to a molar ratio of 1:1. Then heat to 70 °C and carry out condensation reflux for 24 h. After cooling to room temperature, an organophosphorus aluminum sol (viscosity 168 mPa·s, pH value 5.2) is obtained. Put the alumina fiber cloth into the sol, take out the fiber cloth after vacuum treatment with a vacuum pump for 2 h, and then treat it at 100 °C for 5 h to obtain an alumina fiber cloth with an interface layer.

[0047] 3. Mix aluminum hydroxide and phosphoric acid evenly according to a molar ratio of 1:1.8. Then heat to 100 °C and carry out condensation reflux for 6 h. After cooling to room temperature, an inorganic phosphorus aluminum sol (viscosity 28 mPa·s, pH value 3.4) is obtained. Subsequently, weigh 80% of the phosphorus aluminum sol according to the mass of the fiber cloth and evenly brush it on the alumina fiber cloth. After scraping off the excess glue solution, dry it at 30 °C for 15 h to obtain an alumina fiber prepreg.

[0048] 4. Stack 25 layers of alumina fiber prepregs, use a squeegee to scrape off the air bubbles between layers, then place them in a mold and carry out hot pressing forming with a hot press. First, heat from room temperature to 120 °C in 1.5 h, keep the temperature for 4 h and apply a pressure of 2 MPa; then after 6 h, heat to 240 °C, and at the same time increase the pressure to 9 MPa. After keeping the temperature for 2 h, naturally cool to room temperature and demold to obtain an alumina fiber-reinforced phosphorus aluminum composite material with an interface layer and a thickness of 4 mm.

[0049] Perform spline machining tests on the prepared alumina fiber-reinforced phosphorus aluminum composite material with an interface layer. The test results show that the average flexural strength at room temperature is 220 MPa, and the average flexural strength at 1000 °C is 189 MPa.

[0050] Comparative Example 1:

[0051] 1. Use commercially available alumina fibers (NEXTEL-720, produced by 3M Company, USA) to weave into an alumina fiber cloth according to the eight-harness satin weaving process, treat it in a high-temperature sintering furnace at 600 °C for 1 hour, and take it out after cooling to room temperature.

[0052] 2. Mix aluminum hydroxide and phosphoric acid evenly according to a molar ratio of 1:3. Then carry out condensation reflux reaction at 95 °C for 4 h. After cooling to room temperature, an inorganic phosphorus aluminum sol is obtained. Subsequently, weigh 60% of the phosphorus aluminum sol according to the mass of the fiber cloth and evenly brush it on the alumina fiber cloth. After scraping off the excess glue solution, dry it at 35 °C for 16 h to complete the preparation of the prepreg.

[0053] 3. Stack 25 layers of prepreg laminates, scrape off the air bubbles between layers using a squeegee and place them in a mold, then perform hot pressing using a hot press. First, heat from room temperature to 80 °C over 1 h, apply a pressure of 3 MPa after holding for 2 h; then heat to 180 °C after 4 h while increasing the pressure to 10 MPa, hold for 3 h and then cool naturally to room temperature to obtain an alumina fiber-reinforced aluminum phosphate composite without an interface layer with a thickness of 4 mm, as Figure 4 shown.

[0054] After performing spline machining tests on the prepared alumina fiber-reinforced aluminum phosphate composite without an interface layer, the average flexural strength at room temperature was measured to be 206 MPa, and the average flexural strength at 1000 °C was 147 MPa.

[0055] Although the present invention has been disclosed above in embodiments, it is not intended to limit the present invention. Any appropriate modifications or equivalent replacements made by those of ordinary skill in the art to the technical solutions of the present invention shall be covered within the protection scope of the present invention. The protection scope of the present invention shall be defined by the claims.

Claims

1. A method for preparing an alumina fiber reinforced aluminum phosphate composite material with an interface layer, characterized in that: The following steps are involved: 1) Weaving continuous alumina fibers into two-dimensional alumina fiber cloth and removing the impregnant on the fiber surface; 2) preparing an organic aluminum phosphate sol, immersing the alumina fiber cloth from which the impregnant has been removed in the organic aluminum phosphate sol, performing a vacuum degassing treatment, and then drying to obtain an alumina fiber cloth with an interface layer; 3) preparing an inorganic aluminum phosphate sol, and evenly applying the inorganic aluminum phosphate sol on the alumina fiber cloth with the interface layer, scraping off excess glue, and drying to obtain an alumina fiber prepreg; 4) The alumina fiber prepreg is stacked according to the required thickness, and after the bubbles between the layers are scraped off, it is placed in a mold for hot pressing, naturally cooled to room temperature, and demolded to obtain an alumina fiber reinforced aluminum phosphate composite material with an interface layer.

2. The preparation method according to claim 1, characterized in that The method for removing the wetting agent on the fiber surface in step 1) is: treating in a high-temperature sintering furnace at 500-600° C. for 1 hour, or treating in water or acetone at 50-80° C. for 36-48 hours.

3. The preparation method according to claim 1, characterized in that: The preparation method of the organophosphate aluminum sol in step 2) is: aluminum nitrate and phosphorus pentoxide in a molar ratio of 1:1 to 1:2 are respectively treated with ethanol as a buffer, and then heated to 70 to 90° C. and condensed and refluxed for 24 to 72 hours.

4. The preparation method according to claim 1 or 3, characterized in that: The viscosity of the organoaluminum phosphate sol in step 2) is 150-200 mPa·s, and the pH value is 4.8-5.

4.

5. The preparation method according to claim 1, characterized in that: In step 2), the vacuum defoaming treatment time is 2 to 4 hours, the drying temperature is 60 to 100° C., and the drying time is 4 to 6 hours.

6. The preparation method according to claim 1, characterized in that: The preparation method of the inorganic aluminum phosphate sol in step 3) is: aluminum hydroxide and phosphoric acid with a molar ratio of 1:1.5 to 1:3 are respectively used as a buffer with deionized water, and then heated to 90 to 100° C. and condensed and refluxed for 2 to 6 hours.

7. The preparation method according to claim 1 or 6, characterized in that: The viscosity of the inorganic aluminum phosphate sol in step 3) is 20-45 mPa·s, and the pH value is 2.5-3.

5.

8. The preparation method according to claim 1, characterized in that: The amount of inorganic aluminum phosphate sol applied in step 3) is 50% to 80% of the mass of the alumina fiber cloth with the interface layer.

9. The preparation method according to claim 1, characterized in that: In step 3), the drying time is 15 to 18 hours and the drying temperature is 25 to 35°C.

10. The preparation method according to claim 1, characterized in that: The hot pressing step in step 4) includes: heating to 80-120° C. at room temperature for 1-2 hours, keeping warm for 2-4 hours, and then applying a pressure of 2-4 MPa; heating to 180-240° C. after 3-6 hours, and pressurizing to 8-10 MPa at the same time, and maintaining for 2-4 hours.

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