Preparation method of boron nitride nanotube reinforced yttrium oxide ceramic

Abstract

The invention discloses a preparation method of boron nitride nanotube reinforced yttrium oxide ceramic, which comprises the following steps of: firstly, adopting a molecular-level mixing technology to obtain uniformly dispersed ceramic, and enhancing the interface strength; and then a ceramic blank with higher density and uniform powder distribution is obtained through a step-by-step dry pressing process. And finally, consolidating the boron nitride nanotube / yttrium oxide blank through a plasma sintering technology, and carrying out in-situ toughening to form the boron nitride nanotube / yttrium oxide composite material. The preparation process is simple, the production efficiency is high, and the prepared ceramic has the advantages of high strength, high density, good insulativity, high temperature resistance and the like.

Description

Technical Field

[0001] The invention relates to the technical field of inorganic ceramic material preparation, and in particular to a method for preparing boron nitride nanotube reinforced yttrium oxide ceramics. Background Art

[0002] Yttria ceramics have excellent heat resistance, corrosion resistance, high temperature stability and high light transmittance. They are widely used in different fields, such as infrared windows, fairings, antenna covers, microwave substrates, insulating brackets, infrared generator shells, infrared lenses, high-performance crucibles for non-ferrous metal smelting, and high-pressure Na lamp light-emitting tubes in infrared guidance.

[0003] Boron nitride nanotubes are tubular analogs of carbon nanotubes, with excellent properties such as low density, high thermal conductivity (350W / mK), chemical stability, oxidation resistance (900℃) and mechanical properties (Young's modulus 1.3TPa, tensile strength 33GPa). In general, carbon nanotubes are easily oxidized above 900℃ in air, which limits their high-temperature applications. In addition, carbon nanotubes can be conductive or semiconductive (depending on chirality and morphology), while boron nitride nanotubes are electrically insulating. Therefore, these superior properties of boron nitride nanotubes make them a good alternative material for composite reinforcement, including insulation and high-temperature structural materials.

[0004] One of the key issues in preparing boron nitride nanotube reinforced ceramics or metal matrix composites is to obtain uniformly dispersed ceramics, so a good mixing process is needed. Currently, molecular-level mixing is the latest method to obtain uniformly dispersed ceramics. After uniform mixing, the performance of boron nitride nanotube reinforced ceramics is greatly improved. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing boron nitride nanotube reinforced yttrium oxide ceramics. The present invention adopts molecular-level mixing technology to obtain uniformly dispersed ceramics and enhance interface strength. We use step-by-step dry pressing technology to make the ceramic body prepared from the composite powder denser and more uniform. Finally, we use plasma sintering technology to consolidate the boron nitride nanotube / yttrium oxide body and in-situ toughen it to form a boron nitride nanotube / yttrium oxide composite material. The preparation process of the present invention is simple and the production efficiency is high. The prepared ceramics can have the advantages of high strength, high density and high temperature resistance.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows: A method for preparing boron nitride nanotube reinforced yttrium oxide ceramics, comprising the following steps:

[0007] Step 1: First, the boron nitride nanotubes are purified in a high-temperature furnace to remove impurities; then, they are added into deionized water under ultrasonic stirring conditions to obtain a boron nitride nanotube aqueous dispersion;

[0008] Step 2: adding yttrium oxide powder, surfactant and dispersant to boron nitride nanotube aqueous dispersion, placing in a planetary ball mill for high-speed ball milling, and then drying the slurry in a drying oven and sieving to obtain boron nitride nanotube / yttrium oxide powder;

[0009] Step 3: quantitatively weigh the boron nitride nanotube / yttrium oxide powder into a steel mold, and place it in a hydraulic press for dry pressing;

[0010] Step 4: The boron nitride nanotube / yttrium oxide ceramic body obtained after demolding is subjected to spark plasma sintering to obtain boron nitride nanotube reinforced yttrium oxide ceramic.

[0011] Preferably, in step 1, the boron nitride nanotube has a diameter of 30-80 nm, a length of 50-200 μm, and a specific surface area of ​​55-80 m 2 / g; the impurity removal process is to heat the muffle furnace from room temperature to 600-700°C at a rate of 1-3°C / min and keep warm for 1-3h; the amount of boron nitride nanotubes added is 1-5mg / ml; and the ultrasonic time is 20-50min.

[0012] Preferably, the amount of yttrium oxide powder added in step 2 is 20-50% of the boron nitride nanotube aqueous dispersion, the surfactant is one or more of sodium polyacrylate, hexadecyltrimethylammonium bromide, and sodium dodecylbenzene sulfonate, and the added amount is 0.2-0.8% of the mass of the yttrium oxide powder; the dispersant is ammonium citrate and polyacrylic acid, and the added amount is 0.5-2% of the mass of the yttrium oxide powder; the ball-to-material ratio is (1-3): 1, the ball milling speed is 800-1200rad / s, and the ball milling time is 18-24h; drying at 75-100°C for 18-24h, and passing through an 80-120 mesh sieve.

[0013] Preferably, in step three, the boron nitride nanotube / yttrium oxide powder is quantitatively weighed according to the size of the steel mold, and the hydraulic forming procedure is to first pressurize to 20MPa, 40MPa, and 60MPa at a speed of 0.5-3MPa / s, and maintain the pressure for 30-60s respectively.

[0014] Preferably, in step 4, the specific sintering process is: heating to 800°C at a rate of 1-5°C / min, keeping warm for 1-2h, heating to 1750-1850°C at a rate of 1-3°C / min, and keeping warm for 2-5h.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] (1) The present invention achieves molecular-level mixing of the slurry by using a high-efficiency surfactant combined with a dispersant to form a synergistic effect under high-speed ball milling conditions, thereby obtaining uniformly dispersed boron nitride nanotubes / yttrium oxide powder, thereby enhancing the ceramic interface strength after sintering.

[0017] (2) The present invention uses the step-by-step dry pressing technology to make the ceramic green body prepared from the composite powder have a higher density and more uniformity, thus avoiding the problem of easy cracking of the green body in the traditional dry pressing process.

[0018] (3) The present invention uses plasma sintering technology to consolidate boron nitride nanotubes / yttrium oxide and in-situ phase transformation toughening to form a boron nitride nanotube / yttrium oxide composite material. The toughening mechanism in the composite material is manifested in multiple toughening modes such as crack bridging, boron nitride nanotube pulling out, crack deflection and crack branching, which effectively prevents crack propagation. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a physical picture of the boron nitride nanotube reinforced yttrium oxide ceramic prepared in Example 1. DETAILED DESCRIPTION

[0020] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0021] Example 1

[0022] Step 1: First, the boron nitride nanotubes are heated from room temperature to 600°C at a rate of 1°C / min in a muffle furnace and kept warm for 3 hours to purify and remove impurities; then, 1g of boron nitride nanotubes is added to 1L of deionized water under ultrasonic stirring conditions for 20 minutes to obtain a boron nitride nanotube aqueous dispersion.

[0023] Step 2: Add 201g of yttrium oxide powder, 0.41g of sodium polyacrylate and 1.1g of ammonium citrate to the boron nitride nanotube aqueous dispersion, and then add it to a ball mill for ball milling, with a ball-to-material ratio of 1:1, a ball milling speed of 800rad / s, and a ball milling time of 18h; then place it in a drying oven and dry it at 75°C for 24h, and pass it through an 80-mesh sieve to obtain boron nitride nanotube / yttrium oxide powder.

[0024] Step 3: Weigh 18 g of boron nitride nanotube / yttrium oxide powder into a steel mold and place it in a hydraulic press for dry pressing. The hydraulic pressing procedure is to first pressurize to 20 MPa, 40 MPa, and 60 MPa at a speed of 0.5 MPa / s, and maintain the pressure for 30 seconds respectively.

[0025] Step 4: The boron nitride nanotube / yttrium oxide ceramic body obtained after demolding is subjected to spark plasma sintering. The specific sintering process is: heating to 800°C at a rate of 1°C / min, keeping warm for 1h, heating to 1750°C at a rate of 1°C / min, keeping warm for 2h, and obtaining boron nitride nanotube reinforced yttrium oxide ceramics. The actual sample is shown in Figure 1 shown.

[0026] Example 2

[0027] Step 1: First, the boron nitride nanotubes are heated from room temperature to 650°C at a rate of 2°C / min in a muffle furnace and kept warm for 2.5 hours to purify and remove impurities; then, 2.5 g of boron nitride nanotubes are added to 1 L of deionized water under ultrasonic stirring conditions for 30 minutes to obtain a boron nitride nanotube aqueous dispersion.

[0028] Step 2: Add 303g of yttrium oxide powder, 1.21g of sodium polyacrylate and 3.03g of ammonium citrate to the boron nitride nanotube aqueous dispersion, and then add it to a ball mill for ball milling, with a ball-to-material ratio of 1.5:1, a ball milling speed of 900rad / s, and a ball milling time of 20h; then place it in a drying oven and dry it at 80°C for 22h, and pass it through a 100-mesh sieve to obtain boron nitride nanotube / yttrium oxide powder.

[0029] Step 3: Weigh 20g of boron nitride nanotube / yttrium oxide powder into a steel mold and place it in a hydraulic press for dry pressing. The hydraulic pressing procedure is to first pressurize to 20MPa, 40MPa, and 60MPa at a speed of 1MPa / s, and maintain the pressure for 50s respectively.

[0030] Step 4: The boron nitride nanotube / yttrium oxide ceramic body obtained after demolding is subjected to spark plasma sintering. The specific sintering process is: heating to 800°C at a rate of 2°C / min, keeping warm for 2h, heating to 1775°C at a rate of 2°C / min, keeping warm for 3h, to obtain boron nitride nanotube reinforced yttrium oxide ceramics.

[0031] Example 3

[0032] Step 1: First, the boron nitride nanotubes were heated from room temperature to 675°C at a rate of 3°C / min in a muffle furnace and kept warm for 3 hours to purify and remove impurities; then, 3.5 g of boron nitride nanotubes were added to 1 L of deionized water under ultrasonic stirring conditions for 40 minutes to obtain a boron nitride nanotube aqueous dispersion.

[0033] Step 2: Add 403g of yttrium oxide powder, 2.41g of sodium polyacrylate and 6.05g of ammonium citrate to the boron nitride nanotube aqueous dispersion, and then add it to a ball mill for ball milling, with a ball-to-material ratio of 2:1, a ball milling speed of 1000rad / s, and a ball milling time of 22h; then place it in a drying oven and dry it at 90°C for 23h, and pass it through a 100-mesh sieve to obtain boron nitride nanotube / yttrium oxide powder.

[0034] Step 3: Weigh 25 g of boron nitride nanotube / yttrium oxide powder into a steel mold and place it in a hydraulic press for dry pressing. The hydraulic pressing procedure is to first pressurize to 20 MPa, 40 MPa, and 60 MPa at a speed of 2 MPa / s, and maintain the pressure for 60 seconds respectively.

[0035] Step 4: The boron nitride nanotube / yttrium oxide ceramic body obtained after demolding is subjected to spark plasma sintering. The specific sintering process is: heating to 800°C at a rate of 3°C / min, keeping warm for 1.5 hours, heating to 1800°C at a rate of 3°C / min, keeping warm for 4 hours, to obtain boron nitride nanotube reinforced yttrium oxide ceramics.

[0036] Example 4

[0037] Step 1: First, the boron nitride nanotubes are heated from room temperature to 700°C at a rate of 2°C / min in a muffle furnace and kept warm for 2 hours to purify and remove impurities; then, 5g of boron nitride nanotubes are added to 1L of deionized water under ultrasonic stirring conditions for 50 minutes to obtain a boron nitride nanotube aqueous dispersion.

[0038] Step 2: Add 508g of yttrium oxide powder, 4.07g of sodium polyacrylate and 10.17g of ammonium citrate to the boron nitride nanotube aqueous dispersion, and then add it to a ball mill for ball milling, with a ball-to-material ratio of 3:1, a ball milling speed of 1200rad / s, and a ball milling time of 24h; then place it in a drying oven and dry it at 100°C for 24h, and pass it through a 120-mesh sieve to obtain boron nitride nanotube / yttrium oxide powder.

[0039] Step 3: Weigh 28g of boron nitride nanotube / yttrium oxide powder into a steel mold and place it in a hydraulic press for dry pressing. The hydraulic pressing procedure is to first pressurize to 20MPa, 40MPa, and 60MPa at a speed of 3MPa / s, and maintain the pressure for 50s respectively.

[0040] Step 4: The boron nitride nanotube / yttrium oxide ceramic body obtained after demolding is subjected to spark plasma sintering. The specific sintering process is: heating to 800°C at a rate of 1.5°C / min, keeping warm for 2 hours, heating to 1850°C at a rate of 1.5°C / min, keeping warm for 5 hours, to obtain boron nitride nanotube reinforced yttrium oxide ceramics.

[0041] Comparative Example

[0042] Step 1: Weigh 20g of yttrium oxide powder into a steel mold and place it in a hydraulic press for dry pressing. The hydraulic pressing procedure is to first pressurize to 20MPa, 40MPa, and 60MPa at a speed of 0.5MPa / s, and maintain the pressure for 30s respectively.

[0043] Step 2: The yttrium oxide ceramic body obtained after demolding is subjected to spark plasma sintering. The specific sintering process is: heating to 800°C at a rate of 3°C / min, keeping warm for 1.5h, heating to 1800°C at a rate of 3°C / min, keeping warm for 4h, to obtain yttrium oxide ceramics.

[0044] Effect verification:

[0045] The density, hardness and wear rate of the boron nitride nanotube reinforced yttrium oxide ceramic materials obtained in the above-mentioned Examples 1, 2, 3 and 4 were tested according to the following standards. The test results are shown in Table 1.

[0046] Density test: Archimedes drainage method is used for testing.

[0047] Hardness test: Use a hardness tester to test. The hardness test complies with GB / T 4100-2015.

[0048] Wear test: The test is carried out using a wear tester in accordance with EN ISO 26424-2016.

[0049] Table 1 Performance test results of the boron nitride nanotube reinforced yttrium oxide ceramics prepared in Examples 1-4 and the yttrium oxide ceramics prepared in the comparative example

[0050] Example <![CDATA[Density (g / cm 3 )]]> Hardness (HV) <![CDATA[Wear rate (mm 3 / N m)]]> Example 1 5.0 1785 <![CDATA[5.92×10 -9 ]]> Example 2 4.98 1782 <![CDATA[6.02×10 -9 ]]> Example 3 4.95 1802 <![CDATA[6.49×10 -9 ]]> Example 4 4.96 1789 <![CDATA[6.5×10 -9 ]]> Comparative Example 4.91 1720 <![CDATA[1.23×10 -8 ]]>

[0051] As shown in Table 1, the density of the boron nitride nanotube reinforced yttrium oxide ceramics prepared by the present invention exceeds 4.95 g / cm 3 The wear rate is 6.5×10 -9 mm 3 / N m or less, the hardness value exceeds 1700, and the performance is better than that of the control example, indicating that boron nitride nanotube reinforced yttrium oxide ceramics have higher density, hardness and wear resistance.

[0052] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with the technical field within the technical scope disclosed by the present invention and within the spirit and principle of the present invention should be covered by the protection scope of the present invention.

Claims

1. A method for preparing boron nitride nanotube reinforced yttrium oxide ceramics, characterized in that: The following steps are involved: Step 1: First, the boron nitride nanotubes are purified in a high-temperature furnace to remove impurities; then, they are added into deionized water under ultrasonic stirring conditions to obtain a boron nitride nanotube aqueous dispersion; Step 2: adding yttrium oxide powder, surfactant and dispersant to boron nitride nanotube aqueous dispersion, placing in a planetary ball mill for high-speed ball milling, and then drying the slurry in a drying oven and sieving to obtain boron nitride nanotube / yttrium oxide powder; Step 3: quantitatively weigh the boron nitride nanotube / yttrium oxide powder into a steel mold, and place it in a hydraulic press for dry pressing; Step 4: The boron nitride nanotube / yttrium oxide ceramic body obtained after demolding is subjected to spark plasma sintering to obtain boron nitride nanotube reinforced yttrium oxide ceramic.

2. The method for preparing a boron nitride nanotube reinforced yttrium oxide ceramic according to claim 1, characterized in that: In step 1, the boron nitride nanotube has a diameter of 30-80 nm, a length of 50-200 μm, and a specific surface area of ​​55-80 m 2 / g; the impurity removal process is to heat the muffle furnace from room temperature to 600-700°C at a rate of 1-3°C / min and keep the temperature for 1-3h. The amount of boron nitride nanotubes added is 1-5mg / ml; and the ultrasonic time is 20-50min.

3. The boron nitride nanotube reinforced yttrium oxide ceramic and the preparation method thereof according to claim 1, characterized in that: In step 2, the amount of yttrium oxide powder added is 20-50% of the boron nitride nanotube aqueous dispersion, the surfactant is one or more of sodium polyacrylate, hexadecyltrimethylammonium bromide, and sodium dodecylbenzene sulfonate, and the added amount is 0.2-0.8% of the mass of the yttrium oxide powder; the dispersant is ammonium citrate and polyacrylic acid, and the added amount is 0.5-2% of the mass of the yttrium oxide powder; the ball-to-material ratio is (1-3): 1, the ball milling speed is 800-1200 rad / s, and the ball milling time is 18-24h; drying at 75-100°C for 18-24h, and passing through an 80-120 mesh sieve.

4. The method for preparing a boron nitride nanotube reinforced yttrium oxide ceramic according to claim 1, characterized in that: In step three, the boron nitride nanotube / yttrium oxide powder is quantitatively weighed according to the size of the steel mold, and the hydraulic forming procedure is to first pressurize to 20MPa, 40MPa, and 60MPa at a speed of 0.5-3MPa / s, and maintain the pressure for 30-60s respectively.

5. The method for preparing a boron nitride nanotube reinforced yttrium oxide ceramic according to claim 1, characterized in that: In step 4, the specific sintering process is: heating to 800°C at a rate of 1-5°C / min, keeping warm for 1-2h, heating to 1750-1850°C at a rate of 1-3°C / min, and keeping warm for 2-5h.

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