A metal element doped lithium ion compound wave-absorbing coating and a preparation method thereof

Abstract

The application relates to the technical field of wave-absorbing materials, and particularly discloses a metal element doped lithium ion compound wave-absorbing coating and a preparation method thereof. The lithium ion wave-absorbing material is directly prepared into a plasma spraying slurry after a mixing and grinding of a synthesis raw material (manganese dioxide and a lithium-containing compound) and a doped metal (Fe, Cu, Ni, Al and the like), a wave-absorbing material (i.e. lithium manganate) is synthesized in a spraying process, and a plurality of process steps such as wave-absorbing material preparation, granulation and spraying are concentrated into one, so that the process is simpler, and since the doped metal is mixed with the synthesis raw material first, the doped metal is directly doped in a microcrystal structure of the lithium manganate compound, a wave-absorbing material with better uniformity is formed, and the technical problem that the preparation of the wave-absorbing material, the preparation of the master batch and the preparation of the coating are carried out in steps, the process is complex and loss is prone to occur in the prior art is solved.

Description

Technical Field

[0001] This invention relates to the field of microwave absorbing materials technology, specifically to a lithium-ion compound microwave absorbing coating doped with metal elements and its preparation method. Background Technology

[0002] Radar absorbing materials play a vital role in national security and people's lives. With the rapid development of modern military technology, the research and application of radar absorbing materials have gradually matured. However, with the advancement of technology, traditional absorbing materials can no longer meet today's requirements of being "thin, lightweight, wide, and strong." Existing technology shows that lithium-ion compound absorbing coatings possess both excellent electrical and magnetic loss properties, making them a highly promising absorbing material.

[0003] In existing technologies, lithium ions are generally converted into lithium manganese oxide compounds with a more stable structure, and then doped with metal elements such as iron, nickel, chromium, and copper to improve the microwave absorption performance of lithium manganese oxide compounds. By utilizing the structural stability of lithium manganese oxide compounds, other metal elements are added to enhance their polarization loss. The conductivity and permeability can be controlled by the proportion of other metal elements added, thereby obtaining excellent microwave absorption performance.

[0004] While the aforementioned existing technologies have improved the microwave absorption performance of lithium-ion batteries as microwave absorbing materials, their preparation processes typically involve first preparing lithium manganese oxide, or directly purchasing lithium manganese oxide material, then mixing it with a doped metal compound, grinding it into powder, and using plasma spraying to prepare the microwave absorbing coating. This method, which mixes lithium manganese oxide and the doped metal compound into powder before plasma spraying, suffers from uneven mixing of the lithium manganese oxide and the doped metal compound, hindering further improvements in the performance of the prepared microwave absorbing material. To address this issue, engineers will modify the mixing process of lithium manganese oxide and the doped metal compound. While various grinding methods, such as ball milling, stirring, and ultrasonic dispersion, can improve the uniformity of the mixture of doped metal compounds and lithium manganese oxide to some extent, thus enhancing its microwave absorption performance, the mixing of doped metal compounds and lithium manganese oxide is only a physical mixing. Ions of doped metal compounds are prone to segregation in lithium manganese oxide, and the segregation of doped metal compound ions is difficult to control. This makes it impossible to maintain stable microwave absorption performance of the prepared microwave absorbing coating. Furthermore, the degree of physical mixing has a boundary effect. No matter how fine the powder is or how the mixing method is improved, the degree of mixing cannot be further improved, which in turn prevents further improvement in microwave absorption performance. Summary of the Invention

[0005] The purpose of this invention is to provide a lithium-ion compound microwave absorbing coating doped with metal elements and its preparation method, so as to solve the technical problems mentioned above in the prior art where the doped metal compound microwave absorbing materials are prone to segregation, poor uniformity, and the microwave absorption performance cannot be further improved.

[0006] To solve the above problems, the technical solution adopted by the present invention is as follows: a method for preparing a lithium-ion compound microwave absorbing coating doped with metal elements, characterized by comprising the following steps:

[0007] S1: A metal suspension is formed by adding lithium-containing compounds, manganese dioxide, iron-containing compounds and copper oxide to deionized water, wherein the lithium-containing compounds, manganese dioxide, iron-containing compounds and copper oxide are all powders;

[0008] S2: Add dispersant at 1.5-3% of the solid mass in S1 metal suspension and add deionized water to prepare a composite suspension with a solid content of 30-60%.

[0009] S3: After sonicating the composite suspension for 25-45 minutes, the sonicated composite suspension is sent to a ball mill jar for ball milling for 3.5-5.5 hours to form a composite slurry;

[0010] S4: The substrate, after surface pretreatment with anhydrous ethanol or acetone, is placed in a vacuum chamber and preheated to 115℃-125℃ using a plasma spraying flame.

[0011] S5: Using argon as the spraying gas, hydrogen as the auxiliary gas, and nitrogen as the powder feeding gas, the composite slurry in S3 is introduced into the plasma through a peristaltic pump. The powder in the composite slurry is loaded into the plasma flame in a molten or semi-molten state using plasma spraying equipment to spray the substrate in S4, forming a microwave absorbing coating.

[0012] The beneficial effects of this implementation plan are as follows:

[0013] 1. In existing technologies for preparing lithium-ion compound microwave absorbing coatings, a lithium-ion compound microwave absorbing material (i.e., lithium manganese oxide compound) is first prepared or lithium manganese oxide material is directly purchased, and then mixed with a doped metal compound. Mixing methods include physical mixing methods such as ball milling, stirring, and ultrasonic dispersion. After mixing, plasma spraying is used for coating. The drawback is that the crystal lattice of lithium manganese oxide is fixed during mixing. No matter how finely the lithium manganese oxide material and the doped metal compound particles are pulverized, it is impossible to achieve the degree of ion-to-ion contact mixing, thus limiting the performance of the lithium-ion microwave absorbing material. This application directly mixes the raw materials for preparing lithium-ion compounds (manganese dioxide and lithium-containing compounds) with a doped metal compound to prepare a plasma spraying slurry, which is then subjected to plasma spraying. During the spraying process, manganese dioxide and the lithium-containing compound undergo a high-temperature solid-state reaction to form lithium manganate. At this time, the doped metal compound, due to the high temperature, becomes molten and is involved in the entire reaction, existing between the manganese dioxide and the lithium-containing compound. It participates in the lattice formation process of lithium manganate, thus the doped metal compound is directly embedded in the newly formed lithium manganate lattice. Compared with existing technologies, the raw material prepared by doping other metals into the microcrystalline structure of the lithium manganate compound has better uniformity. Problems such as poor uniformity are eliminated, and its microwave absorption performance is further improved, achieving an excellent performance of 50% absorption loss rate across the entire wavelength band.

[0014] 2. In existing technologies, the mixing of lithium manganese oxide with other doped metal compounds is a physical mixture. During spraying, the lithium manganese oxide absorbing material undergoes interpenetration in a molten or semi-molten state. However, the interpenetration of metals is limited by segregation laws, making it difficult to control the segregation of the doped metal compounds in the absorbing material. Furthermore, the doped metal compounds continue to segregate during the later use of the absorbing material after the reaction, resulting in unstable performance. This application, however, does not use a mixture of lithium manganese oxide and doped metal compounds. Instead, it uses manganese dioxide, a lithium-containing compound, and the doped metal compound for ultrasonic treatment. In the ball milling process, manganese dioxide undergoes a high-temperature solid-state reaction with lithium-containing compounds during spraying to produce lithium manganese oxide. At this time, because the doped metal compound is mixed in the manganese dioxide and lithium-containing compounds, it is involved in the entire reaction and participates in the lattice formation process of lithium manganese oxide. Therefore, the doped metal compound is directly embedded in the lattice of the newly formed lithium manganese oxide. This method of doping the metal compound into the microcrystalline structure of the lithium manganese oxide compound restricts the doped metal compound to the lattice, so it is not affected by segregation or is only minimally affected after preparation. Compared with the existing technology, it has better stability in later use.

[0015] 3. In this application, a plasma spraying slurry is directly prepared from synthetic raw materials, and then a microwave absorbing coating is generated by high-temperature solid-state reaction during the spraying process. The steps are simple, the spraying speed is fast, the coating structure is dense, and it is easier to mass-produce high-quality and high-performance microwave absorbing coatings. According to experimental testing, this application can achieve an excellent performance of 50% absorption loss rate across the entire wavelength band.

[0016] Furthermore, the lithium-containing compound, manganese dioxide, iron-containing compound, and copper oxide in S1 are composed of the following components in parts by weight: 10-15 parts lithium-containing compound, 10-20 parts manganese dioxide, 5-15 parts iron-containing compound, and 2-8 parts copper oxide.

[0017] Furthermore, the addition ratio of the lithium-containing compound, manganese dioxide, iron-containing compound, and copper oxide is based on an elemental ratio of Li:Mn:Fe:Cu of 1:1.4:0.4:0.2.

[0018] Furthermore, the metal suspension in S1 also includes powdered nickel oxide and aluminum hydroxide, the content of which is consistent with that of copper oxide.

[0019] Furthermore, the lithium-containing compound in S1 includes lithium carbonate and lithium hydroxide.

[0020] Furthermore, the iron-containing compounds in S1 include ferric oxide and ferric chloride.

[0021] Furthermore, the process parameters of the plasma spraying equipment are set as follows: spraying power: 30-150kW, atomization pressure: 0.5-1.5MPa, feeding speed: 5-20rad / min, spraying distance: 80-200mm.

[0022] Furthermore, the dispersant in S2 may be selected from one or more of ammonium polyacrylate, polyvinyl alcohol, or polyamide. Attached Figure Description

[0023] Figure 1 This is a graph showing the microwave absorption performance of the microwave absorbing material in Embodiment 1 of the present invention. Detailed Implementation

[0024] The following detailed description illustrates the specific implementation methods:

[0025] Example 1

[0026] The doped metal compounds in Example 1 are ferric oxide and copper oxide, and the lithium-containing compound is lithium carbonate.

[0027] Step 1: Mix powdered lithium carbonate, manganese dioxide, ferric oxide and copper oxide into a metal mixture according to the molar ratio of Li:Mn:Fe:Cu of 1:1.4:0.4:0.2. Add the metal mixture to deionized water to form a metal suspension.

[0028] By directly and thoroughly mixing the raw materials (manganese dioxide and lithium-containing compounds) with the doped metal compounds (Fe, Cu, Ni, Al, etc.), the doped metal compounds are fully mixed with the raw materials during the plasma spraying process to generate the microwave absorbing material (lithium manganese oxide). As a result, the doped metal compounds are directly incorporated into the microcrystalline structure of the lithium manganese oxide compound during the doping process, leading to better uniformity.

[0029] Step 2: Add ammonium polyacrylate at 1.5% of the solid mass of the metal mixture, and finally add deionized water to prepare a composite suspension with a solid content of 30%.

[0030] The addition of dispersant ammonium polyacrylate makes the prepared suspension less prone to sedimentation. If the suspension settles, the separation of the doped metal compound from the synthetic raw material will affect the uniformity of the later stage. Therefore, the use of dispersant can improve the doping effect in the later stage, thereby improving the uniformity of the microwave absorbing coating after spraying.

[0031] Step 3: Sonicate the composite suspension for 25 minutes, then transfer it to a ball mill jar for ball milling for 3.5 hours. After that, remove the slurry and place it in a sealed container for later use.

[0032] The ultrasonic process further disperses the various metal compound particles in the composite suspension, enhances the ball milling effect, and further reduces the size of the synthetic metal and doped metal compound particles, thus further improving the degree of mixing.

[0033] Step 4: Clean the surface of the substrate with anhydrous ethanol, place the cleaned substrate into a vacuum chamber, and then preheat the substrate to 115°C using a plasma spraying flame.

[0034] Preheating the substrate improves the bonding strength between the microwave absorbing coating and the substrate.

[0035] Step 5: Argon is selected as the spraying gas, hydrogen as the auxiliary gas, and nitrogen as the powder feeding gas for spraying. The spraying power is set to 30KW, the atomization pressure to 0.5MPa, the feed rate to 5rad / min, and the spraying distance to 80mm. Spraying begins by introducing the slurry into the plasma through a peristaltic pump. The powder in the slurry is loaded into the plasma flame and is in a molten or semi-molten state. While reacting under high temperature, it is sprayed onto the substrate surface at high speed through the nozzle. It grows and reacts on the substrate surface to form a metal element-doped lithium-ion compound microwave absorbing coating with a coating thickness of 0.75mm.

[0036] Since this scheme does not directly add lithium manganese oxide as the microwave absorbing material, but instead prepares a plasma spraying slurry by combining manganese dioxide, the raw material for synthesizing lithium manganese oxide, with lithium carbonate, the lithium-ion compound microwave absorbing coating is prepared by a high-temperature solid-state reaction between the raw material manganese dioxide and lithium carbonate during the preparation process. Therefore, the added doped metal compound is directly embedded in the crystal structure of lithium manganese oxide, and there are no problems such as poor uniformity of raw materials after the reaction is complete.

[0037] Because the doped metal compound and the absorbing material have good uniformity in this scheme, the absorption performance is greatly improved. The absorption performance data are as follows: Figure 1 As shown:

[0038] according to Figure 1 The data above shows that this solution can achieve an absorption loss rate of 50% across the entire frequency band, which far exceeds the performance of microwave absorbing coatings that are simply sprayed with lithium manganese oxide.

[0039] Example 2

[0040] The doped metal compounds in Example 2 are ferric chloride and copper oxide, and the lithium-containing compound is lithium hydroxide.

[0041] Step 1: Mix powdered lithium hydroxide, manganese dioxide, ferric oxide and copper oxide into a metal mixture according to the molar ratio of Li:Mn:Fe:Cu of 1.5:2:0.8:0.4. Add the metal mixture to deionized water to form a metal suspension.

[0042] Step 2: Add ammonium polyacrylate at 2% of the solid mass of the metal mixture, and finally add deionized water to prepare a composite suspension with a solid content of 45%.

[0043] Step 3: After sonicating for 30 minutes, the slurry is then placed in a ball mill jar for ball milling for 4 hours. The slurry is then removed and placed in a sealed container for later use.

[0044] Step 4: Place the substrate, which has undergone surface pretreatment with anhydrous ethanol, acetone, etc., into the vacuum chamber, and then preheat the substrate to 120°C using a plasma spraying flame.

[0045] Step 5: Argon is selected as the spraying gas, hydrogen as the auxiliary gas, and nitrogen as the powder feeding gas for spraying. The spraying power is set to 45KW, the atomization pressure to 1.5MPa, the feed rate to 10rad / min, and the spraying distance to 200mm. Spraying begins by introducing the slurry into the plasma through a peristaltic pump. The powder in the slurry is loaded into the plasma flame and is in a molten or semi-molten state. While reacting under high temperature, it is sprayed onto the substrate surface at high speed through the nozzle. It grows and reacts on the substrate surface to form a metal element-doped lithium-ion compound microwave absorbing coating with a coating thickness of 0.8mm.

[0046] Example 3

[0047] The difference between Example 3 and Examples 1 and 2 is that, in addition to iron compounds and copper oxide, the doped metal compound also includes powdered nickel oxide and aluminum hydroxide, and the content of nickel oxide and aluminum hydroxide is the same as that of copper oxide.

[0048] The above descriptions are merely embodiments of the present invention, and common knowledge regarding specific structures and characteristics is not elaborated upon here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the structure of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method for preparing a lithium-ion compound microwave absorbing coating doped with a metal element, characterized in that: Includes the following steps: S1: A metal suspension is formed by adding a lithium-containing compound, manganese dioxide, and a doped metal compound to deionized water, wherein the lithium-containing compound, manganese dioxide, and the doped metal compound are all powders. S2: Add dispersant at 1.5-3% of the solid mass in S1 metal suspension and add deionized water to prepare a composite suspension with a solid content of 30-60%. S3: After sonicating the composite suspension for 25-45 minutes, it is then sent to a ball mill jar for ball milling for 3.5-5.5 hours to form a composite slurry; S4: The substrate, which has undergone surface pretreatment with anhydrous ethanol and acetone, is placed in a vacuum chamber and preheated to 115℃-125℃ using a plasma spraying flame. S5: Using argon as the spraying gas, hydrogen as the auxiliary gas, and nitrogen as the powder feeding gas, the composite slurry in S3 is introduced into the plasma by a peristaltic pump. The powder in the composite slurry is loaded into the plasma flame in a molten or semi-molten state and sprayed onto the substrate in S4 to form a microwave absorbing coating.

2. The method for preparing a lithium-ion compound microwave absorbing coating doped with metal elements according to claim 1, characterized in that: The doped metal compound is an iron-containing compound and copper oxide. The lithium-containing compound, manganese dioxide, iron-containing compound and copper oxide in S1 are composed of the following components by weight: 10-15 parts lithium-containing compound, 10-20 parts manganese dioxide, 5-15 parts iron-containing compound and 2-8 parts copper oxide.

3. The method for preparing a lithium-ion compound microwave absorbing coating doped with metal elements according to claim 2, characterized in that: The lithium-containing compound, manganese dioxide, iron-containing compound, and copper oxide are added in a ratio of 1:1.4:0.4:0.2 based on the molar ratio of Li:Mn:Fe:Cu.

4. The method for preparing a lithium-ion compound microwave absorbing coating doped with metal elements according to claim 2, characterized in that: The metal suspension in S1 also includes powdered nickel oxide and aluminum hydroxide, the content of which is the same as that of copper oxide.

5. The method for preparing a lithium-ion compound microwave absorbing coating doped with metal elements according to claim 1, characterized in that: The lithium-containing compound in S1 includes lithium carbonate and / or lithium hydroxide.

6. The method for preparing a lithium-ion compound microwave absorbing coating doped with metal elements according to claim 2, characterized in that: The iron-containing compounds include ferric oxide and / or ferric chloride.

7. The method for preparing a lithium-ion compound microwave absorbing coating doped with metal elements according to claim 1, characterized in that: When the plasma spraying equipment is used for spraying, the process parameters are set within the following range: spraying power: 30-150kW; atomization pressure: 0.5-1.5MPa; feeding speed: 5-20rad / min; spraying distance: 80-200mm.

8. The method for preparing a lithium-ion compound microwave absorbing coating doped with metal elements according to claim 1, characterized in that: The dispersant in S2 is selected from one or more of ammonium polyacrylate, polyvinyl alcohol, or polyamide.

9. A lithium-ion compound microwave absorbing coating doped with a metal element, characterized in that: The microwave absorbing coating is prepared by the preparation method according to any one of claims 1 to 8.

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