Microwave absorbing material of nitrogen-doped vanadium oxide and preparation method of microwave absorbing material

Abstract

The invention discloses a microwave absorbing material of nitrogen-doped vanadium oxide and a preparation method thereof, the nitrogen-doped vanadium oxide is synthesized by combining a hydrothermal morphology control process with an annealing process for the first time, and the microwave absorbing performance of the nitrogen-doped vanadium oxide is systematically studied. The complex dielectric constant of the sample can be adjusted by adjusting the hydrothermal reduction pH value. When the pH value is 7, selective absorption of electromagnetic waves can be realized by adjusting the thickness of a sample, and the lowest reflection loss can reach 31.57 dB at 4.37 GHz. The reflection loss of the sample with the corresponding thickness in different frequency bands can be lower than 10dB, and the whole frequency range is almost covered. The excellent microwave absorption performance of the microwave absorption material of the nitrogen-doped vanadium oxide is attributed to the improvement of the conductivity in the nitrogen-doped double-phase vanadium oxide, good impedance matching and multiple reflection caused by a unique microstructure of the nitrogen-doped double-phase vanadium oxide. The microwave absorbing material of the nitrogen-doped vanadium oxide can be used as the absorbing requirements of different application scenes, and the corresponding thickness meets the absorbing requirements.

Description

Technical Field

[0001] The invention belongs to the field of microwave absorbing materials, and in particular relates to a nitrogen-doped vanadium oxide microwave absorbing material and a preparation method thereof. Background Art

[0002] In recent years, the field of electromagnetic wave absorbing materials has received extensive attention due to the demand for better electromagnetic interference (EMI) shielding, stealth technology and wireless communication systems. The two parameters that determine electromagnetic wave absorbing materials are complex dielectric constant and complex magnetic permeability. Materials based on complex dielectric constant use dipole polarization as the main absorption mode, which is usually only suitable for absorbing high-frequency electromagnetic waves. Materials based on complex magnetic permeability use magnetic dipole interaction to convert electromagnetic waves into heat energy loss, which is usually only suitable for low frequencies and is limited by their own Curie temperature.

[0003] As a cheap and abundant transition metal oxide on earth, vanadium oxide has aroused great interest among researchers due to its excellent optical and electromagnetic properties. The electrons in the V orbit of vanadium oxide can move along the VV and VO chains, which means that vanadium oxide can provide and receive different numbers of electrons, can become an electron pool or a medium for electron transfer, and can weaken electromagnetic waves through the relaxation effect of dielectric loss. It may be a potential electromagnetic wave absorbing material with excellent effects. In the design of existing microwave absorbing materials, the realization of a wide absorption band and strong absorption performance is still an important challenge.

[0004] Based on the above analysis, the present invention improves the electron mobility efficiency of vanadium oxide by doping nitrogen into vanadium oxide, and controls its microstructure through the synthesis of the precursor to achieve good impedance matching, so that it can selectively absorb electromagnetic waves of different bands by controlling the thickness of the matrix. Summary of the invention

[0005] In view of the above-mentioned shortcomings, the present invention proposes a nitrogen-doped vanadium oxide and a preparation method, which is simple to prepare and low in cost. The thickness can be adjusted according to the scene and functional requirements to achieve selective absorption of electromagnetic waves in different bands, overcoming the problem that absorbers mainly based on dielectric loss are difficult to achieve low-frequency absorption and absorption in different frequency bands.

[0006] The present invention is achieved through the following technical solutions:

[0007] The present invention first discloses a preparation process of a nitrogen-doped vanadium oxide microwave absorbing material, comprising:

[0008] (1) Weighing ammonium metavanadate, guanidine carbonate and glucose, grinding them thoroughly in an agate mortar, adding the obtained mixture into a solvent, stirring and mixing, heating in a water bath, and adjusting the pH to 7 by dropping concentrated hydrochloric acid to obtain a first substance;

[0009] (2) pouring the first substance into the inner lining of the hydrothermal reactor, placing the hydrothermal reactor in an electric constant temperature blast drying oven for heating and heat preservation, taking it out after cooling in the oven, filtering and drying, and obtaining a precursor;

[0010] (3) The precursor is heated to a reaction temperature at a rate of 5° C. / min in a tube furnace, kept at the temperature, and taken out after cooling to obtain a nitrogen-doped vanadium oxide microwave absorbing material; during this period, the mixed gas is continuously introduced.

[0011] Furthermore, in step (1), the mass ratio of ammonium metavanadate, guanidine carbonate and glucose is 16:74:10; and the solvent includes anhydrous ethanol and deionized water.

[0012] Furthermore, the volume ratio of the anhydrous ethanol to deionized water is 3:1.

[0013] Furthermore, in step (1), the stirring speed is 200 r / min, the stirring time is 10 min, and the water bath heating and insulation temperature is 60°C.

[0014] Furthermore, the heating and insulation temperature in step (2) is 180° C., and the heating and insulation time is 4 hours.

[0015] Furthermore, the heating and insulation temperature in step (3) is 600° C., and the heating and insulation time is 3 hours; and the mixed gas is a mixed gas of ammonia and oxygen.

[0016] Furthermore, the flow ratio of ammonia to oxygen is 20:1.

[0017] The invention also discloses a microwave absorbing material of nitrogen-doped vanadium oxide prepared according to any of the above preparation processes.

[0018] The beneficial effects of the present invention are:

[0019] The nitrogen-doped vanadium oxide of the present invention exhibits excellent microwave absorption performance in a wide frequency range, especially when the pH value is 7, selective absorption of electromagnetic waves can be achieved by adjusting the sample thickness, and the minimum reflection loss reaches 31.57 dB. The present invention provides an effective microwave performance modification method and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The electromagnetic wave absorption performance of the sample in Example 1 of the present invention. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0022] Example 1

[0023] Weigh 1.60g of ammonium metavanadate, 7.40g of aminoguanidine carbonate and 1.00g of glucose, put them into a mortar and grind them evenly, then add them to a mixed solution of 38mL of anhydrous ethanol and 12mL of deionized water. After stirring evenly, heat in a 60°C water bath and maintain the temperature. Adjust the pH value of the solution to 7 by adding concentrated hydrochloric acid, and stir at 200rpm for 10 minutes. Pour the mixed solution into the lining of the hydrothermal reactor and react at 180°C for 4 hours. After cooling, filter and dry the precursor. Heat to 600°C in a tubular furnace at a rate of 5°C / min, keep for 3 hours, and then cool to obtain a nitrogen-doped vanadium oxide microwave absorbing material. Ammonia and oxygen mixed gas is continuously introduced during the process (flow rate ratio 20:1). The nitrogen-doped vanadium oxide microwave absorbing material has the ability to selectively absorb electromagnetic waves of 2-18GHZ, and its absorption effect is as follows: Figure 1 As shown. The reflection value of 10dB represents 99% absorption of electromagnetic waves, and the part exceeding 10dB is effective absorption. From the figure, we can see that the products of different thicknesses have corresponding effective absorption widths in different frequency bands, which means that the absorption of electromagnetic waves in different frequency bands can be basically achieved by adjusting the thickness of the sample to meet different usage requirements.

[0024] Example 2

[0025] Weigh 2.56g of ammonium metavanadate, 11.84g of aminoguanidine carbonate and 1.60g of glucose, grind them evenly in a mortar, and add them to a mixed solution of 60mL of anhydrous ethanol and 20mL of deionized water. After stirring evenly, heat in a 60°C water bath and maintain the temperature. Adjust the pH value of the solution to 7 by dropping concentrated hydrochloric acid and stir at 200rpm for 10 minutes. Pour the mixed solution into the lining of the hydrothermal reactor and react at 180°C for 4 hours. After cooling, filter and dry the precursor. Heat to 600°C at a rate of 5°C / min in a tubular furnace, keep it for 3 hours, and then cool it to obtain a microwave absorbing material of nitrogen-doped vanadium oxide. A mixed gas of ammonia and oxygen is continuously introduced during the process (flow rate ratio 20:1).

Claims

1. A process for preparing a microwave absorbing material of nitrogen-doped vanadium oxide, comprising: (1) Weighing ammonium metavanadate, guanidine carbonate and glucose, grinding them thoroughly in an agate mortar, adding the obtained mixture into a solvent, stirring and mixing, heating in a water bath, and adjusting the pH to 7 by dropping concentrated hydrochloric acid to obtain a first substance; (2) pouring the first substance into the inner lining of the hydrothermal reactor, placing the hydrothermal reactor in an electric constant temperature blast drying oven for heating and heat preservation, taking it out after cooling in the oven, filtering and drying, and obtaining a precursor; (3) The precursor is heated to a reaction temperature at a rate of 5° C. / min in a tube furnace, kept at the temperature, and taken out after cooling to obtain a nitrogen-doped vanadium oxide microwave absorbing material; during this period, the mixed gas is continuously introduced.

2. The preparation process according to claim 1, wherein: The mass ratio of ammonium metavanadate, guanidine carbonate and glucose in step (1) is 16:74:10; The solvent includes anhydrous ethanol and deionized water.

3. The preparation process according to claim 2, wherein: The volume ratio of the anhydrous ethanol to deionized water is 3:

1.

4. The preparation process according to claim 1, wherein: The stirring speed in step (1) is 200 r / min and the stirring time is 10 min; The water bath heating and insulation temperature is 60°C.

5. The preparation process according to claim 1, wherein: The heating and insulation temperature in step (2) is 180° C., and the heating and insulation time is 4 hours.

6. The preparation process according to claim 1, wherein: The heating and insulation temperature in step (3) is 600° C. and the heating and insulation time is 3 h; The mixed gas is a mixed gas of ammonia and oxygen.

7. The preparation process according to claim 6, wherein: The flow ratio of ammonia to oxygen is 20:

1.

8. A microwave absorbing material of nitrogen-doped vanadium oxide prepared according to the preparation process of any one of claims 1 to 7.

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