CN100402417C - A kind of hexagonal boron nitride nanometer microsphere and its synthesis method and application - Google Patents

Abstract

The invention provides a hexagonal boron nitride nanometer microsphere, a synthesis method and an application. The hexagonal boron nitride microsphere has a layered structure and a diameter of 30-150 nanometers. Among them, the amount of hexagonal boron nitride nano-microspheres with a diameter of 30-50 nanometers is more than 60%. The preparation method is as follows: esterify boron oxide and monohydric alcohol to form a mixture of trihydroxy borate and boric acid, bring it into a nitriding furnace with nitrogen or inert gas, and react with excess ammonia at high temperature; Or directly atomize the reaction mixture into micron droplets with an ultrasonic atomizer or a high-speed airflow, then use nitrogen or inert gas to bring it into a nitriding furnace, and react with excess ammonia at high temperature. The product obtained by the reaction is washed with methanol to remove the boron oxide in the product to obtain hexagonal boron nitride nanometer microspheres. The hexagonal boron nitride nanometer microspheres synthesized by the method have high purity, the method is simple, reliable, cheap and suitable for large-scale synthesis. The obtained hexagonal boron nitride microspheres can be used as lubricants.

Description

A kind of hexagonal boron nitride nanometer microsphere and its synthesis method and application

technical field

The invention relates to a method for synthesizing hexagonal boron nitride (h-BN) nanospheres and its application.

Background technique

The solid lubricants commonly used at present mainly include graphite and molybdenum disulfide and a small amount of organic solid lubricants. Usually used under high temperature and high load conditions. However, due to the limitations of the physical and chemical properties of such solid lubricants, their application range is affected to a certain extent. For example, the use temperature of graphite cannot exceed 450°C, the use temperature of molybdenum disulfide cannot exceed 400°C, and so on.

Hexagonal boron nitride has a graphite-like layered structure, its physical and chemical properties are similar to graphite, and its lubricity and thermal conductivity are good. Therefore, it is called "white graphite". The properties of hexagonal boron nitride are: melting point 3000°C (decomposition), specific gravity 2.27; Mohs hardness 2. Hexagonal boron nitride can be used at a temperature of up to 2800°C in inert gas and nitrogen. The use temperature can reach 900-1000℃ in air or oxidizing atmosphere. Due to the good properties of hexagonal boron nitride, there are currently some reports on their application. However, these reported hexagonal boron nitrides are micron-sized powders with irregular shapes. The production process used by these powders is as follows:

1. Borax synthesis method: use borax (Na ₂ B ₄ O ₇ ·10H ₂ O) and ammonium chloride as raw materials, and synthesize hexagonal boron nitride powder by passing ammonia in a reaction furnace at 700-1000°C.

2. Urea method: use boron oxide (B ₂ O ₃ ) or boric acid (H ₃ BO ₃ ) and urea ((NH ₂ ) ₂ CO) as raw materials to synthesize boron nitride at 900-1300°C. But the boron nitride synthesized by this method has hexagonal boron nitride, cubic boron nitride (c-BN) and amorphous boron nitride powder at the same time.

3. Halide synthesis method: boron nitride is synthesized at 600-1000°C with boron halide and ammonia as raw materials. The usual product is both hexagonal boron nitride and cubic boron nitride.

The boron nitride obtained by the above synthesis method is an irregular powder material, and its microscopic morphology is uncontrollable. Moreover, some synthetic processes are more complex, with lower yields and higher costs.

Just because BN is resistant to high temperature, non-toxic and non-polluting. It is expected to be used in high temperature, food and textile and other occasions. Studies have shown that: after adding BN, the wear degree of the lubricating oil sample without adding BN powder is reduced by 50%.

Contents of the invention

The purpose of the present invention is to provide a hexagonal boron nitride nano-microsphere and its synthesis method and application. The hexagonal boron nitride nano-microsphere can be used as an additive for lubricants. The synthesis method is simple, reliable, cheap and suitable for large-scale production. The synthesized hexagonal boron nitride has high purity.

The hexagonal boron nitride nanometer microsphere of the present invention has a layered structure and a diameter of 30-150 nanometers. Wherein the amount of hexagonal boron nitride nanometer microspheres with a diameter of 30-50 nanometers is more than or equal to 60%.

A kind of preparation method of hexagonal boron nitride microsphere of the present invention, the preparation steps are successively:

1. Weigh the raw materials according to the molar ratio of boron oxide and monohydric alcohol as 1:3, and slowly add boron oxide to the monohydric alcohol several times in the state of stirring until the boron oxide completely reacts with the monohydric alcohol to obtain trihydroxy A clear solution of a mixture of borate ester and boric acid, the monohydric alcohol is methanol or ethanol

2. Bring the mixture solution of trihydroxy borate ester and boric acid obtained in step 1 into the nitriding furnace with nitrogen or inert gas, and react with excess ammonia gas at high temperature. Or the flow of inert gas controls the amount of raw materials entering the reaction furnace, the flow of nitrogen and ammonia depends on the volume of the nitriding furnace, and the reaction temperature is 1000-1400 °C;

3. In the downwind direction of the nitriding furnace airflow, where the temperature is lower, the product is collected to obtain mainly hexagonal boron nitride nanospheres;

The 4th, with the reaction product that step 3 obtains, wash with methanol or distilled water, to remove boron oxide in the product, centrifuge, dry, promptly obtain the hexagonal boron nitride microsphere that diameter is 30-150 nanometer, wherein diameter is 30-50nm hexagonal boron nitride nanospheres≥60%.

Another preparation method of the hexagonal boron nitride microspheres of the present invention, the preparation steps are as follows:

1. Weigh the raw materials according to the molar ratio of boron oxide and monohydric alcohol as 1:3, and slowly add boron oxide to the monohydric alcohol several times in the state of stirring until the boron oxide completely reacts with the monohydric alcohol to obtain trihydroxy The clarified solution of the mixture of borate ester and boric acid, the monohydric alcohol is methanol or ethanol;

2. After the mixture solution of trihydroxyboric acid ester and boric acid obtained in step 1 is atomized into micron droplets by ultrasonic atomization or high-speed air flow, it is then brought into the nitriding furnace with nitrogen or inert gas, and mixed with excess ammonia gas The reaction is carried out at high temperature, and the flow rate of nitrogen or inert gas is used to control the amount of raw materials entering the reaction furnace. The flow rate of nitrogen and ammonia gas depends on the volume of the nitriding furnace, and the reaction temperature is 1000-1400 °C;

3. In the downwind direction of the nitriding furnace airflow, where the temperature is lower, the product is collected to obtain mainly hexagonal boron nitride nanospheres;

The 4th, with the reaction product that step 3 obtains, wash with methanol or distilled water, to remove boron oxide in the product, centrifuge, dry, promptly obtain the hexagonal boron nitride microsphere that diameter is 30-150 nanometer, wherein diameter is 30-50nm hexagonal boron nitride nanospheres≥60%.

The hexagonal boron nitride microspheres of the invention are used as additives for lubricants.

Boron oxide reacts with monohydric alcohol to generate a mixture of trihydroxy borate ester and boric acid. The reaction equation is as follows.

B ₂ O ₃ +3(ROH)→B(OR) ₃ +B(OH)

Under normal circumstances, methanol is the best monohydric alcohol, followed by ethanol, and propanol is not recommended because of its high carbon content, which tends to generate amorphous carbon in the subsequent nitriding reaction and cause too many impurities in the product. The mixture of trihydroxy borate and boric acid, in which trihydroxy borate is volatile, can be brought into the nitriding reaction furnace with nitrogen gas, and react with excess ammonia at a high temperature of 1000-1400°C to form hexagonal nitriding boron and carbon dioxide and water. The reaction equation is as follows:

B(OR) ₃ +NH ₃ →BN+CO ₂ +H ₂ O

It is also possible to directly carry out the esterification reaction of boron oxide and monoalcohol to form a mixture of trihydroxy borate ester and boric acid, atomize it into micron droplets with an ultrasonic atomizer, and then bring it into the nitriding reaction furnace with nitrogen gas. Excess ammonia reacts at a high temperature of 1000-1400°C, namely:

B(OR) ₃ +NH ₃ →BN+CO ₂ +H ₂ O

B(OH)3+NH ₃ →BN+3H ₂ O

The methanol washed product after reaction can still be used as raw material.

The high-resolution TEM morphology of the synthesized hexagonal boron nitride nanospheres is shown in Figure 3. It can be seen from the pictures that the hexagonal boron nitride nanospheres have a perfect layered structure. A complete sphere is formed. Its diameter is 30-150 nanometers. Studies have shown that calcination in air at 800-900 ° C, no signs of oxidation. Under the pressure of 30 MPa, its structure has no change or damage.

The method of the present invention has the advantage that the synthesized hexagonal boron nitride nano microspheres have high purity. The hexagonal boron nitride synthesized by other methods is a micron irregular powder. Some methods even synthesize BN with two phases of hexagonal boron nitride and cubic boron nitride, and the purity is low. The method is simple, reliable and suitable for large-scale production.

The hexagonal boron nitride nano microspheres of the invention are applied in lubricants to reduce friction. And because of its small particle size, it has a self-repairing effect on the worn parts. Nano-microspheres are filled on the surfaces of two relatively moving parts, changing sliding friction into rolling friction. Greatly reduced coefficient of friction. Research shows a 17% increase in maximum no-snap bite load.

Description of drawings

Fig. 1 is the schematic diagram of the device for the synthesis of hexagonal boron nitride by trihydroxy borate ester

Figure 2 is a schematic diagram of a device for synthesizing hexagonal boron nitride from boron oxide

Figure 3 is a high-resolution TEM image of the synthesized hexagonal boron nitride nanospheres

The names represented by the serial numbers in the figure: 1 gas valve, 2 flow meter, 3 three-way switch, 4 reaction raw material, 5 tube furnace, 6 corundum tube, 7 tail gas outlet, 8 ultrasonic atomizer

specific implementation plan

Example 1

Step 1. Follow the reaction equation:

B ₂ O ₃ +3(ROH)→B(OR) ₃ +B(OH) ₃

Weigh the raw materials according to the molar ratio of boron oxide and monohydric alcohol as 1:3, and slowly add boron oxide to the monohydric alcohol in fractions under stirring (methanol is the best monohydric alcohol, followed by ethanol, propanol, etc. If the carbon content is too high, it is easy to generate amorphous carbon in the follow-up nitriding reaction and make the product impurities too much. The following are all represented by methanol), until boron oxide is completely reacted with methanol to obtain a clear solution;

Step 2. Connect the synthesis device as shown in Figure 1. Tube furnaces use corundum tubes. Under the condition of ensuring airtightness, turn the switch to the point where the nitrogen gas only leads to the raw material container, and the air in the container is exhausted, and the amount of nitrogen passing through is 5 times the volume of the air in the container; When the nitrogen gas only leads to the reaction furnace, the air is exhausted, and the volume of the nitrogen gas is 5 times the volume of the reaction vessel; continue to pass a small amount of nitrogen gas, so that the temperature of the tube furnace is raised to 1250 °C under the protection of nitrogen gas; close the nitrogen gas, Turn on the ammonia gas, adjust the flow rate of the ammonia gas to 2 liters/minute, and continue to heat up to 1350°C;

Step 3. When the temperature reaches 1350° C., turn on the nitrogen gas, adjust the flow rate to 1 liter/minute, and at the same time, the flow rate of the ammonia gas is correspondingly adjusted to 1 liter/minute, and react for 1 hour (the flow rate is changed with reference to the size of the reaction vessel); After the completion, turn off the ammonia gas, unscrew the tee until the nitrogen gas only leads to the reaction furnace; naturally cool down to below 600°C; collect a large amount of fluffy white granular products in the downwind direction of the tube;

Step 4. The product collected in step 3 is washed twice with methanol, centrifuged, and dried at <120°C to obtain hexagonal boron nitride microspheres with a diameter of 30-150 nanometers, wherein the diameter is 30-50 nanometers Hexagonal boron nitride nanospheres≥60%. Example 2

Step 1. Follow the reaction equation:

B ₂ O ₃ +3(ROH)→B(OR) ₃ +B(OH) ₃

Weigh the raw materials according to the molar ratio of boron oxide and monohydric alcohol as 1:3, and slowly add boron oxide to methanol several times under stirring until the boron oxide completely reacts with methanol to obtain a clear solution;

Step 2 Connect the synthesis device as shown in Figure 2. The tube furnace uses a corundum tube. Under the condition of ensuring airtightness, unscrew the three-way connection so that the nitrogen gas only leads to the raw material container, and the air in the container is exhausted. , the volume of the nitrogen gas is 5 times the volume of the air in the container; then the three-way switch tube is screwed so that the nitrogen gas only leads to the reactor, and the air is exhausted, and the volume of the nitrogen gas is 5 times the volume of the reaction container. ;Continue to pass a small amount of nitrogen, so that the tube furnace is under the protection of nitrogen, and the temperature is raised to 1250°C; turn off the nitrogen, turn on the ammonia, adjust the flow rate of the ammonia to 2 liters/minute, and continue to heat up to 1350°C;

Step 3. When the temperature reaches 1350°C, turn on the nitrogen gas and adjust the flow rate to 1 liter/min. At the same time, adjust the flow rate of the ammonia gas to 1 liter/min. Turn on the ultrasonic atomizer and react for 1 hour; after the reaction is completed, Turn off the ammonia gas, turn the three-way switch until the nitrogen gas only leads to the reaction furnace, and naturally cool down to below 600°C; in the downwind direction of the tube, a large number of fluffy white granular products are collected;

Step 4. The product collected in step 3 is washed twice with methanol, centrifuged, and dried at <120°C to obtain hexagonal boron nitride microspheres with a diameter of 30-150 nanometers, wherein the diameter is 30-50 nanometers Hexagonal boron nitride nanospheres≥60%.

Characterization: The XRD test of the product shows that the product is hexagonal boron nitride. High-resolution TEM images show its good layered structure, see Figure 3.

Claims (4)

1. a hexagonal nanometer boron nitride microsphere is characterized in that this microballoon is a laminate structure, and diameter is the 30-150 nanometer, and wherein diameter is hexagonal nanometer boron nitride microsphere amount 〉=60% of 30-50 nanometer.

2. the preparation method of the described hexagonal nanometer boron nitride microsphere of claim 1 is characterized in that preparation process is followed successively by:

1st, be to take by weighing raw material at 1: 3 by the mol ratio of boron oxide and monohydroxy-alcohol, under the state that stirs, divide several slowly to join in the monohydroxy-alcohol boron oxide, complete and the monohydroxy-alcohol reaction until boron oxide, obtain the settled solution of trihydroxy-boric acid fat and mebor, described monohydroxy-alcohol is methyl alcohol or ethanol;

2nd, the settled solution of the mixture that step 1 is obtained, with nitrogen or rare gas element volatile trihydroxy-boric acid fat is brought in the nitriding furnace, at high temperature react with excess of ammonia gas, enter the material quantity of Reaktionsofen with the flow control of nitrogen or rare gas element, the flow of nitrogen and ammonia is decided on the volume of nitriding furnace, and temperature of reaction is 1000-1400 ℃;

3rd, at the following wind direction of nitriding furnace air-flow, product is collected in the temperature lower, obtains being mainly hexagonal nanometer boron nitride microsphere;

4th, the reaction product that step 3 is collected, remove boron oxide in the product with methyl alcohol or distilled water wash, centrifugation then, oven dry, promptly obtaining diameter is the hexagonal boron nitride microballoon of 30-150 nanometer, and wherein diameter is 30-50 nano-hexagonal boron nitride nanometer ball amount 〉=60%.

3. the preparation method of the described hexagonal nanometer boron nitride microsphere of claim 1 is characterized in that preparation process is followed successively by:

1st, be to take by weighing raw material at 1: 3 by the mol ratio of boron oxide and monohydroxy-alcohol, under the state that stirs, divide several slowly to join in the monohydroxy-alcohol boron oxide, complete and the monohydroxy-alcohol reaction until boron oxide, obtain the settled solution of trihydroxy-boric acid fat and mebor, described monohydroxy-alcohol is methyl alcohol or ethanol;

2nd, the settled solution of the mixture that step 1 is obtained, behind ultrasonic atomizatio or high-speed gas atomization one-tenth micron droplet, utilize nitrogen or rare gas element to bring in the nitriding furnace again, at high temperature react with excess of ammonia gas, enter the material quantity of Reaktionsofen with the flow control of nitrogen or rare gas element, the flow of nitrogen and ammonia is decided on the volume of nitriding furnace, and temperature of reaction is 1000-1400 ℃;

3rd, at the following wind direction of nitriding furnace air-flow, product is collected in the temperature lower, obtains being mainly hexagonal nanometer boron nitride microsphere:

4th, the reaction product that step 3 is collected is with methyl alcohol or distilled water wash, to remove the boron oxide in the product, centrifugation, oven dry, promptly obtaining diameter is the hexagonal boron nitride microballoon of 30-150 nanometer, wherein diameter is 30-50 nano-hexagonal boron nitride nanometer ball amount 〉=60%.

4. the application of the described hexagonal nanometer boron nitride microsphere of claim 1 is characterized in that being used for lubricant additive.

Images