Boron nitride fiber felt and preparation method thereof

Abstract

The present invention discloses a method for preparing a boron nitride fiber felt, comprising the following steps: Step 1: adding boron nitride fiber, a thickener, a dispersant, and a defoaming agent to water, mixing, dehydrating, and drying to form a first preform; Step 2: fully impregnating the first preform with a boron oxide solution, and then drying again to form a second preform; Step 3: heating the second preform to melt the boron oxide, thereby forming a boron oxide-bonded boron nitride fiber felt; Step 4: heat-treating the boron oxide-bonded boron nitride fiber felt under an ammonia and nitrogen atmosphere to obtain a boron nitride fiber felt. The present invention also discloses a boron nitride fiber felt. The boron nitride fiber felt prepared by the present invention has the characteristics of high temperature resistance, corrosion resistance, low dielectric constant, and low thermal conductivity. It can be used as a diaphragm for making thermal batteries, thermal insulation treatment for high-temperature equipment, and can also be used for alloy reinforcement and high-temperature filter materials. The composite material made from it has good wave transmission performance and is an ideal material for aerospace.

Description

Technical Field

[0001] The invention belongs to the technical field of ceramic fiber materials, and particularly relates to a boron nitride fiber felt and a preparation method thereof. Background Art

[0002] In thermal batteries, the performance of the diaphragm determines the battery's interface structure, internal resistance, etc., which directly affects the battery's capacity, cycle and safety performance. The operating temperature of the thermal battery is between 500 and 600°C. The negative electrode material of the battery is Li-Al or Li-B alloy material, and the electrolyte is composed of molten ternary or binary lithium electrolyte. The diaphragm must have the characteristics of chemical stability to the electrode material and electrolyte; and have a certain thickness and porosity to minimize the weight and resistance of the battery; have appropriate mechanical strength to adapt to the stress generated during the battery operation; and have a certain wettability to the molten lithium electrolyte.

[0003] The only materials that are good electrical insulators between 500 and 600°C and can meet the chemical stability requirements for more than one year are the ceramic materials MgO, BN, and BeO. Among these materials, BN is a flexible material that has been obtained in fibrous form and has the processability of a diaphragm. Therefore, it is considered the only material that can be used for thermal battery diaphragms. Boron nitride fiber diaphragm felts in the prior art generally use organic binders. Organic binders decompose at high temperatures, which easily makes the boron nitride fibers separate and unusable, making them unusable for thermal batteries. There are also existing methods in the prior art that use magnesium oxide powder and thermal battery electrolytes to press into sheets to make diaphragms. However, diaphragms made of magnesium oxide powder have disadvantages such as low mechanical strength and easy powder shedding. Therefore, there is an urgent need in the prior art for a high-temperature resistant and high-strength BN fiber felt. Summary of the Invention

[0004] In order to solve the above-mentioned drawbacks of the prior art, the present invention discloses a method for preparing boron nitride fiber felt, and the specific scheme is as follows:

[0005] A method for preparing a boron nitride fiber felt comprises the following steps:

[0006] Step 1: Add boron nitride fiber, thickener, dispersant, and defoamer into water, mix well, dehydrate, and dry to form a first preform;

[0007] Step 2: After fully immersing the first preform in a boron oxide solution, drying it again to form a second preform;

[0008] Step 3: heating the second preform to melt the boron oxide to form a boron nitride fiber felt bonded with boron oxide;

[0009] Step 4: heat-treating the boron oxide-bonded boron nitride fiber felt in an atmosphere of ammonia and nitrogen to obtain a boron nitride fiber felt.

[0010] Furthermore, in step 1, the mass ratio of boron nitride fiber: thickener: dispersant: defoaming agent: water is (1-10): (5-15): (1-5): (1-5): 10000.

[0011] Furthermore, the specific method of mixing and dehydrating in step 1 is:

[0012] The fibers are evenly dispersed by mechanical stirring and then dehydrated through an inclined wire former to form a wet felt.

[0013] Furthermore, the boron oxide solution in step 2 is an ethanol solution of boron oxide, wherein the mass ratio of boron oxide in the ethanol solution of boron oxide is 10%-25%.

[0014] Furthermore, the heating method described in step three is: heating with a hot pressing roller, wherein the pressure is 0.01-0.1 MPa and the temperature is 400° C.-900° C.

[0015] Furthermore, in step three, the proportion of boron oxide in the boron nitride fiber felt combined with boron oxide is 10%-25%.

[0016] Furthermore, the temperature of the heat treatment in step 4 is 600°C-1200°C.

[0017] Furthermore, the thickener in step 1 is one or a combination of hydroxyethyl cellulose, hydroxypropyl methyl cellulose, carboxymethyl cellulose, and polyacrylamide;

[0018] The dispersant is one or a combination of linear alkylbenzene sulfonate sodium, fatty alcohol polyoxyethylene ether sodium sulfate, fatty alcohol polyoxyethylene ether ammonium sulfate, sodium lauryl sulfate, nonylphenol polyoxyethylene ether, diethanolamide stearic acid glycerol monoester, lignin sulfonate, heavy alkylbenzene sulfonate, alkyl sulfonate, fatty alcohol polyoxyethylene ether, cetyltrimethylammonium bromide, and cetyltrimethylammonium chloride;

[0019] The defoaming agent is one or a combination of emulsified silicone oil, higher alcohol fatty acid ester complex, polyoxyethylene polyoxypropylene pentaerythritol ether, polyoxyethylene polyoxypropanolamine ether, polyoxypropylene glycerol ether, polyoxypropylene polyoxyethylene glycerol ether, and polydimethylsiloxane.

[0020] Furthermore, the length of the boron nitride fiber in step 1 is 3 mm to 20 mm.

[0021] The invention also discloses a boron nitride fiber felt, which is prepared by any of the above-mentioned preparation methods.

[0022] The present invention is characterized in that after fully impregnating boron nitride fibers with a boron oxide solution, the boron oxide absorbed in the boron nitride fibers is melted and adhered to the boron nitride fibers to play a bonding role, thereby forming a boron oxide-bonded boron nitride fiber felt. The boron oxide is then converted into boron nitride through heat treatment in an ammonia and nitrogen atmosphere, thereby obtaining a boron nitride-bonded boron nitride fiber felt.

[0023] The boron nitride fiber felt prepared by the present invention has the characteristics of high temperature resistance, corrosion resistance, low dielectric constant, and low thermal conductivity. This is because the boron nitride used for bonding in the present invention is eventually converted into boron nitride. Boron nitride will not be oxidized below 600°C in air atmosphere, and will not melt at 2600°C in an inert atmosphere. It has stable chemical properties, does not react with acids or alkalis, and will not be corroded by molten metals. Boron nitride is also an insulating material with a dielectric constant as low as 4.5. The thermal conductivity of boron nitride fiber is directional, and it is a good conductor of heat in the axial direction but a poor conductor of heat in the radial direction. The fiber felt is a radially stacked material and is a porous material, so it has the characteristics of low thermal conductivity. Therefore, the boron nitride fiber felt prepared by the present invention can be used as a diaphragm for making thermal batteries, a heat insulation treatment for high-temperature equipment, and can also be used for alloy reinforcement and high-temperature filter materials. The composite material made from it has good wave transmission performance and is an ideal material for aerospace. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a photo of the boron nitride fiber felt prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0025] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0026] The present invention discloses a method for preparing a boron nitride fiber felt, comprising the following steps:

[0027] Step 1: Add 1-10 parts of boron nitride fiber, 5-15 parts of thickener, 1-5 parts of dispersant, and 1-5 parts of defoaming agent to 10,000 parts of water, disperse the fibers evenly by mechanical stirring, and then dehydrate through an inclined mesh former to form a wet felt, which is then dried with hot air to form a first preform; wherein the boron nitride fiber is preferably 3mm-20mm short-cut fiber.

[0028] The thickener is one or a combination of hydroxyethyl cellulose, hydroxypropyl methyl cellulose, carboxymethyl cellulose and polyacrylamide;

[0029] The dispersant is one or a combination of linear alkylbenzene sulfonate (LAS), fatty alcohol polyoxyethylene ether sodium sulfate (AES), fatty alcohol polyoxyethylene ether ammonium sulfate (AESA), sodium lauryl sulfate (K12 or SDS), nonylphenol polyoxyethylene (10) ether (TX-10), diethanolamide (6501) stearic acid glycerol monoester, lignin sulfonate, heavy alkylbenzene sulfonate, alkyl sulfonate (petroleum sulfonate), fatty alcohol polyoxyethylene ether, cetyltrimethylammonium bromide, and cetyltrimethylammonium chloride;

[0030] The defoaming agent is one or a combination of emulsified silicone oil, higher alcohol fatty acid ester complex, polyoxyethylene polyoxypropylene pentaerythritol ether, polyoxyethylene polyoxypropanolamine ether, polyoxypropylene glycerol ether, polyoxypropylene polyoxyethylene glycerol ether, and polydimethylsiloxane.

[0031] Step 2: After fully immersing the first preform in a boron oxide solution, hot air drying is performed again to form a second preform; wherein the boron oxide solution is preferably an ethanol solution of boron oxide, wherein the mass ratio of boron oxide in the ethanol solution of boron oxide is 10-25%.

[0032] Step 3: The second preform is heated by hot pressing rollers to melt the boron oxide, forming a boron oxide-bonded boron nitride fiber mat. The hot pressing rollers are applied at a pressure of 0.01-0.1 MPa and a heating temperature of 400°C-900°C. The boron oxide content of the boron oxide-bonded boron nitride fiber mat is 10%-25%.

[0033] Step 4: feeding the boron oxide bonded boron nitride fiber felt into a high-temperature furnace and heat-treating it in an atmosphere of ammonia and nitrogen to obtain a boron nitride bonded boron nitride fiber felt, wherein the heat treatment temperature is 600° C.-1200° C.

[0034] The present invention is carried out by fully impregnating boron nitride fibers with a boron oxide solution, and then melting the boron oxide at a high temperature under a certain pressure. The boron oxide absorbed in the boron nitride fibers is melted and adheres to the boron nitride fibers to play a bonding role, thereby forming a boron oxide-bonded boron nitride fiber felt. The boron oxide is then converted into boron nitride through heat treatment in an ammonia and nitrogen atmosphere, thereby obtaining a boron nitride-bonded boron nitride fiber felt.

[0035] Example 1

[0036] 10 parts of 6mm boron nitride fiber, 15 parts of carboxymethyl cellulose, 5 parts of fatty alcohol polyoxyethylene ether ammonium sulfate (AESA), and 5 parts of polyoxyethylene polyoxypropanolamine ether are added to 10,000 parts of water, and the fibers are evenly dispersed by mechanical stirring. The wet felt is then dehydrated through an inclined wire former to form a wet felt, and then hot-air dried to form a first preform.

[0037] After the first preform is fully immersed in the ethanol solution of boron oxide, hot air drying is performed again to form a second preform;

[0038] The second preform is heated by a hot pressing roller to melt the boron oxide, thereby forming a boron nitride fiber felt bonded with boron oxide; wherein the pressure of the hot pressing roller is 0.1 MPa and the heating temperature is 400°C.

[0039] The boron oxide bonded boron nitride fiber felt is fed into a high-temperature furnace and heat-treated in an atmosphere of ammonia and nitrogen to obtain a boron nitride bonded boron nitride fiber felt, wherein the heat treatment temperature is 1200°C.

[0040] Example 2

[0041] 1 part of 3 mm boron nitride fiber, 5 parts of hydroxypropyl methylcellulose, 1 part of sodium fatty alcohol polyoxyethylene ether sulfate (AES), and 1 part of a higher carbon alcohol fatty acid ester complex are added to 10,000 parts of water, the fibers are evenly dispersed by mechanical stirring, and then dehydrated through an inclined wire former to form a wet felt, which is then dried with hot air to form a first preform;

[0042] After the first preform is fully immersed in the ethanol solution of boron oxide, hot air drying is performed again to form a second preform;

[0043] The second preform is heated by a hot pressing roller to melt the boron oxide, thereby forming a boron nitride fiber felt bonded with boron oxide; wherein the pressure of the hot pressing roller is 0.01 MPa and the heating temperature is 900°C.

[0044] The boron oxide bonded boron nitride fiber felt is fed into a high-temperature furnace and heat-treated in an atmosphere of ammonia and nitrogen to obtain a boron nitride bonded boron nitride fiber felt, wherein the heat treatment temperature is 600°C.

[0045] Example 3

[0046] 5 parts of 10 mm boron nitride fiber, 10 parts of hydroxyethyl cellulose, 3 parts of linear alkylbenzene sulfonate (LAS), and 3 parts of emulsified silicone oil are added to 10,000 parts of water, the fibers are evenly dispersed by mechanical stirring, and then dehydrated by an inclined wire former to form a wet felt, which is then dried with hot air to form a first preform;

[0047] After the first preform is fully immersed in the ethanol solution of boron oxide, hot air drying is performed again to form a second preform;

[0048] The second preform is heated by a hot pressing roller to melt the boron oxide, thereby forming a boron nitride fiber felt bonded with boron oxide; wherein the pressure of the hot pressing roller is 0.05 MPa and the heating temperature is 600°C.

[0049] The boron oxide bonded boron nitride fiber felt is fed into a high-temperature furnace and heat-treated in an atmosphere of ammonia and nitrogen to obtain a boron nitride bonded boron nitride fiber felt, wherein the heat treatment temperature is 900°C.

[0050] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in this field can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. These modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and description of the present invention.

Claims

1. A method for preparing a boron nitride fiber felt, characterized in that: The steps include: Step 1: Add boron nitride fiber, thickener, dispersant, and defoamer into water, mix well, dehydrate, and dry to form a first preform; Step 2: After the first preform is fully immersed in a boron oxide solution, it is dried again to form a second preform; the boron oxide solution in step 2 is an ethanol solution of boron oxide, wherein the mass ratio of boron oxide in the ethanol solution of boron oxide is 10%-25%; Step 3: heating the second preform to melt the boron oxide to form a boron oxide-bonded boron nitride fiber felt; in step 3, the mass ratio of boron oxide in the boron oxide-bonded boron nitride fiber felt is 10%-25%; Step 4: heat-treating the boron oxide-bonded boron nitride fiber felt in an atmosphere of ammonia and nitrogen to obtain a boron nitride fiber felt; the heat-treating temperature in step 4 is 600° C.-1200° C.

2. The preparation method according to claim 1, wherein: In step 1, the mass ratio of boron nitride fiber: thickener: dispersant: defoaming agent: water is (1-10): (5-15) (1-5): (1-5): 10000.

3. The preparation method according to claim 1, wherein: The specific method of mixing and dehydrating in step 1 is: The fibers are evenly dispersed by mechanical stirring and then dehydrated through an inclined wire former to form a wet felt.

4. The preparation method according to claim 1, wherein: The heating method described in step three is: heating with a hot pressing roller, wherein the pressure is 0.01MPa-0.1MPa and the temperature is 400℃-900℃.

5. The preparation method according to claim 1, wherein: The thickener in step 1 is one or a combination of hydroxyethyl cellulose, hydroxypropyl methyl cellulose, carboxymethyl cellulose, and polyacrylamide; The dispersant is one or a combination of linear alkylbenzene sulfonate sodium, fatty alcohol polyoxyethylene ether sodium sulfate, fatty alcohol polyoxyethylene ether ammonium sulfate, sodium lauryl sulfate, nonylphenol polyoxyethylene ether, diethanolamide stearic acid glycerol monoester, lignin sulfonate, heavy alkylbenzene sulfonate, alkyl sulfonate, fatty alcohol polyoxyethylene ether, cetyltrimethylammonium bromide, and cetyltrimethylammonium chloride; The defoaming agent is one or a combination of emulsified silicone oil, high carbon alcohol fatty acid ester complex, polyoxyethylene polyoxypropylene pentaerythritol ether, polyoxyethylene polyoxypropanolamine ether, polyoxypropylene glycerol ether, polyoxypropylene polyoxyethylene glycerol ether, and polydimethylsiloxane.

6. The preparation method according to claim 1, wherein: The length of the boron nitride fiber in step 1 is 3 mm to 20 mm.

7. A boron nitride fiber felt, characterized in that: The method is prepared by any one of claims 1 to 6.

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