Preparation method of composite hollow microspheres, composite hollow microspheres prepared by method and application of composite hollow microspheres

Abstract

The invention discloses a preparation method of composite hollow microspheres, the composite hollow microspheres prepared by the method and application. The preparation method of the composite hollow microspheres comprises the following steps: dispersing silicate hollow glass microspheres in a nickel salt solution, uniformly mixing, drying, and carrying out heat treatment in an air atmosphere to obtain composite microspheres coated with a metal layer containing nickel and nickel oxide at 550-750 DEG C, and recording the composite microspheres as composite microspheres A, the heat treatment time is 10 to 24 minutes; the composite microspheres A are coated with magnetic metal, and the composite hollow microspheres are obtained. The preparation method is simple and low in cost, use of precious metal is avoided, and the wave-absorbing material with high strength, low density and excellent wave-absorbing characteristic can be prepared by the preparation method.

Description

Technical Field

[0001] This invention relates to the field of powder materials technology. More specifically, it relates to a method for preparing composite hollow microspheres, the composite hollow microspheres prepared by this method, and their applications. Background Technology

[0002] Various forms of electromagnetic wave absorbing or shielding materials have been designed, fabricated, and applied to address the increasingly severe electromagnetic wave threats. Although absorbing materials come in a wide variety of forms and application frequency bands, most traditional absorbing materials are composite systems composed of electromagnetic wave absorbers and matrix materials. The electromagnetic wave absorber introduces conductive, dielectric, or magnetic losses into the composite system, while the matrix plays a crucial role in shaping the composite system, controlling impedance matching, and ensuring the structural stability, cyclicity, and effective integration with the target to be protected. Theoretically, materials with electromagnetic response and loss characteristics can be used as electromagnetic wave absorbers, and their adaptability to different electromagnetic wave frequency bands varies depending on their internal microstructure and physicochemical properties. Among the many candidate materials for electromagnetic wave absorbers, magnetic metals have attracted widespread attention due to their unique conductivity and magnetism. Magnetic metals can have their shape, composition, and crystal structure controlled during chemical synthesis or post-synthesis processing, and they can also be easily composited with other functional materials to prepare high-performance electromagnetic wave absorbers. However, magnetic metals have a significantly higher density than most other types of electromagnetic functional materials, such as oxides, carbon materials, inorganic salts, and polymers. This not only greatly limits their application in fields and equipment where weight is a critical factor, but also does not conform to the general trend of lightweight development of advanced materials and equipment.

[0003] Therefore, researchers generally adopt the method of combining magnetic metals with low-density materials to reduce density. In particular, combining magnetic metals with some conductive or dielectric materials with low intrinsic density can not only reduce density to a certain extent, but also bring richer heterostructures and loss mechanisms, which is conducive to achieving both lightweight and high absorption effects. However, the space for reducing density by relying solely on the design of material chemical composition is limited. To address this issue, constructing hollow structures is an effective way to significantly reduce the density of magnetic metals. In addition, to address the inherent structural instability of hollow structures, researchers have further developed the technique of using high-strength hollow supports to mechanically reinforce the hollow structures of magnetic metals. After years of development, this technique can now construct relatively stable hollow magnetic metal structures using relatively inexpensive high-strength supports. However, to achieve effective combination of high-strength hollow reinforced structures and magnetic metals, these techniques often involve relatively complex preparation processes and the use of expensive precious metal additives (such as palladium). This not only increases the difficulty of process implementation and preparation cycle, but also significantly increases the preparation cost of electromagnetic wave absorbers for hollow magnetic metal structures, which is not conducive to large-scale industrial production and commercialization. Summary of the Invention

[0004] Based on the above facts, one object of the present invention is to provide a novel method for preparing composite hollow microspheres, the composite hollow microspheres prepared by this method, and their applications. This preparation method is simple, low-cost, avoids the use of precious metals, and can produce microspheres with high strength, low density, and excellent wave absorption properties.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] On the one hand, the present invention provides a method for preparing composite hollow microspheres, the method comprising the following steps:

[0007] Silicate hollow glass microspheres are dispersed in a nickel salt solution, mixed, dried, and then heat-treated in an air atmosphere to obtain composite microspheres with a metal layer containing nickel and nickel oxide on the surface, denoted as composite microsphere A. The heat treatment temperature is 550-750℃ and the heat treatment time is 10-24 min.

[0008] A magnetic metal is coated onto the composite microsphere A to obtain the composite hollow microsphere. The composite hollow microsphere prepared by this method comprises silicate hollow glass microspheres, and sequentially coated onto the silicate hollow glass microspheres with a nickel-containing metal layer and a nickel oxide metal layer, and a magnetic metal layer; wherein,

[0009] The metal layer comprises a continuous phase of nickel oxide and nickel doped in the nickel oxide, wherein the nickel is at least partially exposed on the outer surface of the metal layer.

[0010] In the above preparation method, the resulting composite microsphere A has a structure comprising a continuous phase of nickel oxide and nickel doped in the nickel oxide, with the nickel at least partially exposed on the outer surface of the metal layer. The nickel exposed on the outer surface of the composite microsphere A can further catalyze and assist in the subsequent stable coating of magnetic metals, thereby avoiding the need for expensive precious metal additives such as palladium and silver to assist in achieving magnetic metal coating.

[0011] Meanwhile, during the research process of this invention, it was unexpectedly discovered that dispersing silicate hollow glass microspheres in a nickel salt solution followed by heat treatment can partially oxidize nickel into nickel oxide, an effect that cannot be achieved when dispersed in salt solutions of other metals such as iron, cobalt, and silver. This method is simple, involves few steps, and is low in cost. Furthermore, the heat treatment time has a significant impact on the formation of this structure; if the heat treatment time is too long, the metal content will be too low or even completely converted into oxides.

[0012] Furthermore, the nickel salt solution is obtained by mixing nickel salt, organic carbon source, and water in a mass ratio of 8-12:4:3-5. The mass ratio of nickel salt, organic carbon source, and water in the nickel salt solution affects the composition of the reaction product. Excessive use of organic carbon source results in a smaller coating of nickel and nickel oxide, and a higher proportion of metallic nickel; conversely, insufficient use of organic carbon source results in a larger coating of nickel and nickel oxide, and a lower proportion of metallic nickel—both excessively high and low ratios are unfavorable, but the exact ratio is not crucial.

[0013] Furthermore, the nickel salt is selected from one or a mixture of several nickel nitrates, chlorides, and organic acid salts. When the nickel salt is selected from a mixture of the aforementioned types, they can be mixed in any proportion.

[0014] Furthermore, the organic carbon source is selected from one or more of chitosan, cellulose, citric acid, starch, sucrose, and tartaric acid.

[0015] Furthermore, the drying temperature is 10-70°C.

[0016] Furthermore, the density of the silicate hollow glass microspheres is 0.3-0.6 g / cm³. 3 In the technical solution of this invention, the silicate hollow glass microspheres can be commercially available or prepared according to methods already disclosed in the art.

[0017] Furthermore, the diameter of the hollow portion inside the silicate hollow glass microsphere is 10-70 micrometers.

[0018] Furthermore, the amount of silicate hollow glass microspheres added relative to the nickel salt solution is 0.15-0.7 g / mL.

[0019] Furthermore, in the nickel-containing and nickel oxide-containing metal layer, nickel oxide is a continuous phase and nickel is a dispersed phase, the nickel is doped in the nickel oxide, and the nickel is at least partially exposed on the outer surface of the metal layer.

[0020] Furthermore, the magnetic metal is selected from one or more of iron, cobalt, and nickel, or an alloy of three of them. When the magnetic metal is an alloy of iron, cobalt, and nickel, the alloy may contain phosphorus.

[0021] Furthermore, the method for coating magnetic metal includes the following steps:

[0022] The composite microspheres A are dispersed in a salt solution of a magnetic metal and stirred at 50-80°C for 22-28 minutes. After filtration and drying, the product is obtained.

[0023] Furthermore, the magnetic metal salt solution contains a magnetic metal salt, a stabilizer, a reducing agent, a pH adjuster, and water, wherein the concentration of the magnetic metal salt is 10-70 g / L, the concentration of the stabilizer is 30-150 g / L, and the concentration of the reducing agent is 30-80 g / L.

[0024] Furthermore, the addition of the pH adjuster makes the pH of the magnetic metal salt solution 8.0-11.0.

[0025] Furthermore, the salt of the magnetic metal is selected from the sulfate, nitrate or chloride of the magnetic metal.

[0026] Furthermore, the stabilizer is selected from ammonium sulfate and / or potassium sodium tartrate.

[0027] Furthermore, the reducing agent functions to reduce the corresponding metal ions to elemental metals. For example, a suitable reducing agent may be selected from sodium hypophosphite, etc.

[0028] Furthermore, the amount of the composite microsphere A added relative to the salt solution of the magnetic metal is 0.005-0.02 g / mL.

[0029] On another aspect, the present invention provides composite hollow microspheres prepared by the preparation method described above, wherein the structure of the composite hollow microspheres comprises silicate hollow glass microspheres, and a nickel-containing metal layer and a nickel oxide metal layer sequentially coated on the silicate hollow glass microspheres; wherein,

[0030] The metal layer comprises a continuous phase of nickel oxide and nickel doped in the nickel oxide, wherein the nickel is at least partially exposed on the outer surface of the metal layer.

[0031] Furthermore, the composite hollow microspheres prepared by the above method preferably have an apparent density of 0.6-1.45 g / cm³. 3 .

[0032] Furthermore, in the composite hollow microspheres prepared by the above method, the mass fractions of silicate hollow glass microspheres, nickel-containing and nickel oxide-containing metal layers, and magnetic metal layers are 30-60%, 8-30%, and 20-45%, respectively.

[0033] Furthermore, in the nickel-containing and nickel oxide-containing metal layer, the mass fractions of nickel and nickel oxide are 45-55% and 45-55%, respectively.

[0034] In another aspect, the present invention provides the application of the composite hollow microspheres described above in microwave absorption or shielding.

[0035] Furthermore, the composite hollow microspheres can be used as electromagnetic wave absorbers.

[0036] Furthermore, as a microwave absorbing or shielding material, it can be used as one of the following: in the field of military stealth, electromagnetic radiation protection for radio and television transmitters, microwave anechoic chamber materials, and electromagnetic shielding materials in buildings or radio communication equipment.

[0037] The beneficial effects of this invention are as follows:

[0038] In the method for preparing composite hollow microspheres provided in this invention, by controlling the preparation conditions, especially the heat treatment conditions after drying the nickel salt solution containing silicate hollow glass microspheres, a structure containing both nickel and nickel oxide in the intermediate layer was unexpectedly obtained. Furthermore, the nickel is doped into the nickel oxide, and at least partially exposed on the outer surface of the metal layer. This structure facilitates further coating with magnetic metals.

[0039] Furthermore, the composite hollow microspheres prepared by this method achieve high performance and low density, and the method is advantageous for the characteristics of material composition and structure, enabling inexpensive and efficient synthesis. Specifically: First, inexpensive nickel salts and renewable biomass carbon sources are used as raw materials. The assembly of nickel particles onto the surface of a hollow support is achieved through a pyrolysis reaction during sol-gel combustion, resulting in an active hollow support with catalytic magnetic metal reduction activity. Further, the catalytic effect of nickel metal on the reduction process of magnetic metal ions is utilized to achieve the directional assembly of subsequent magnetic metal layers on the surface of the active hollow support. This method has the advantages of being convenient and rapid, and does not require the use of precious metal activators.

[0040] The composite air microspheres prepared by the method of the present invention have low density, high strength and excellent electromagnetic wave absorption properties, and can be further applied as electromagnetic wave absorbers. Attached Figure Description

[0041] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0042] Figure 1 A schematic diagram of the structure of the exemplary composite hollow microsphere is shown.

[0043] Figure 2 A schematic diagram illustrating an exemplary preparation process of the composite hollow microspheres is shown.

[0044] Figure 3 The SEM image of the composite hollow microspheres in Example 2 is shown. Detailed Implementation

[0045] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments and accompanying drawings, further explains the invention. Similar components in the drawings are indicated by the same reference numerals. Those skilled in the art should understand that the specific description below is illustrative rather than restrictive and should not be construed as limiting the scope of protection of the present invention.

[0046] Performance testing:

[0047] The electromagnetic properties of the products prepared in the above embodiments were tested. The testing methods were as follows: apparent density was obtained by measuring size and weight; porosity was obtained by measuring true density; transmission parameters were tested using a vector network analyzer (test frequency 8-12 GHz, sample thickness 2.5 mm) to analyze shielding performance; electromagnetic parameters were tested using a vector network analyzer (test frequency 2-18 GHz) to analyze absorption performance.

[0048] Example 1

[0049] A glass-nickel-nickel oxide-magnetic metal composite hollow microsphere, the structural schematic diagram of which is shown below. Figure 1 As shown, a schematic diagram of its preparation method is as follows. Figure 2 As shown, the specific solution is as follows:

[0050] 1) Hollow glass microspheres (density 0.31 g / cm³) 3 )(like Figure 2 A) is mixed with treatment solution A containing 10g nickel nitrate, 4g sucrose, and 3g water at a ratio of 0.26g / mL. The mixture is then dried at 60℃ (to obtain...). Figure 2 The structure of B in the figure was treated at 600°C for 0.3 h in air atmosphere, and then dispersed through an 80-mesh sieve to obtain intermediate glass-nickel-nickel oxide hollow microspheres (structure as shown in the figure). Figure 2As shown in C), in the intermediate glass-nickel-nickel oxide hollow microsphere, a layer formed by nickel and nickel oxide covers the surface of the glass hollow microsphere, and in the layer formed by nickel and nickel oxide, nickel oxide is a continuous phase, nickel is dispersed and doped in nickel oxide, and the nickel is at least partially exposed on the outer surface of the layer.

[0051] 2) The above intermediate glass-nickel-nickel oxide hollow microspheres were dispersed at an addition amount of 0.011 g / mL in an aqueous solution B containing 28 g / L cobalt sulfate, 35 g / L sodium hypophosphite, and 65 g / L potassium sodium tartrate, with a pH of approximately 10 (adjusted with ammonia). The mixture was stirred in a water bath at 60°C for 25 min, filtered, and dried to obtain glass-nickel-nickel oxide-magnetic metal composite hollow microspheres (structure as shown). Figure 2 (As shown in D).

[0052] The density of the glass-nickel-nickel oxide-magnetic metal composite hollow microspheres obtained in this embodiment is 0.70 g / cm³. 3 The diameter of the core cavity is 43 micrometers; the mass fractions of the glass sphere, magnetic metal sphere, and nickel-nickel oxide sphere are 43.3%, 34.6%, and 22.1%, respectively; the mass fractions of nickel and nickel oxide in the nickel-nickel oxide sphere are 48.9% and 51.1%, respectively.

[0053] The survival rate is 80.5% at 32MPa; the optimized electromagnetic wave reflection loss is -47.9dB, the effective absorption bandwidth is 4.1GHz; and the electromagnetic shielding effectiveness is 58-72dB.

[0054] Example 2

[0055] The specific preparation scheme for glass-nickel-nickel oxide-magnetic metal composite hollow microspheres is as follows:

[0056] 1) Hollow glass microspheres (density 0.33 g / cm³) 3 Mixed with treatment solution A containing 10g nickel nitrate, 4g starch and 4g water at a ratio of 0.34g / mL; the mixture was then dried at 60℃; and then treated at 550℃ for 0.4h in air atmosphere. After the reaction, the mixture was dispersed through an 80-mesh sieve to obtain intermediate glass-nickel-nickel oxide hollow microspheres. In the intermediate glass-nickel-nickel oxide hollow microspheres, a layer formed by nickel and nickel oxide covers the surface of the glass hollow microspheres. In the layer formed by nickel and nickel oxide, nickel oxide is a continuous phase, and nickel is dispersed and doped in nickel oxide. At least part of the nickel is exposed on the outer surface of the layer.

[0057] 2) The above intermediate glass-nickel-nickel oxide hollow microspheres were dispersed at an addition amount of 0.01 g / mL in aqueous solution B containing 25 g / L cobalt sulfate, 35 g / L sodium hypophosphite, and 65 g / L potassium sodium tartrate, with pH≈9.5 (adjusted with ammonia). The mixture was stirred in a water bath at 60℃ for 25 min, filtered, and dried to obtain glass-nickel-nickel oxide-magnetic metal composite hollow microspheres. The SEM image is shown below. Figure 3 As shown.

[0058] The density of the glass-nickel-nickel oxide-magnetic metal composite hollow microspheres obtained in this embodiment is 0.68 g / cm³. 3 The diameter of the core cavity is 42.4 micrometers; the mass fractions of the glass sphere, magnetic metal sphere, and nickel-nickel oxide sphere are 47.6%, 34.8%, and 17.6%, respectively; the mass fractions of nickel and nickel oxide in the nickel-nickel oxide sphere are 52.8% and 47.2%, respectively.

[0059] The survival rate at 32MPa is 84.2%; the optimized electromagnetic wave reflection loss is -46.3dB, the effective absorption bandwidth is 3.6GHz, and the electromagnetic shielding effectiveness is 52-63dB.

[0060] Example 3

[0061] The specific preparation scheme for glass-nickel-nickel oxide-magnetic metal composite hollow microspheres is as follows:

[0062] 1) Hollow glass microspheres (density 0.37 g / cm³) 3 Mix the mixture with a treatment solution A containing 10g nickel nitrate, 4g chitosan, and 3g water at a ratio of 0.5g / mL; then dry the mixture at 60°C; then treat it at 700°C for 0.2h in an air atmosphere, and disperse it through an 80-mesh sieve to obtain intermediate glass-nickel-nickel oxide hollow microspheres. In the intermediate glass-nickel-nickel oxide hollow microspheres, a layer formed by nickel and nickel oxide coats the surface of the glass hollow microspheres, and in the layer formed by nickel and nickel oxide, nickel oxide is a continuous phase, nickel is dispersed and doped in nickel oxide, and the nickel is at least partially exposed on the outer surface of the layer.

[0063] 2) The above intermediate glass-nickel-nickel oxide hollow microspheres were dispersed at an addition amount of 0.015 g / mL in an aqueous solution B containing 15 g / L cobalt sulfate, 14 g / L nickel sulfate, 38 g / L sodium hypophosphite, and 70 g / L potassium sodium tartrate, with pH≈9 (adjusted by ammonia). The mixture was stirred in a water bath at 60℃ for 25 min, filtered, and dried to obtain glass-nickel-nickel oxide-magnetic metal composite hollow microspheres.

[0064] The density of the glass-nickel-nickel oxide-magnetic metal composite hollow microspheres obtained in this embodiment is 0.63 g / cm³. 3The diameter of the core cavity is 39.6 micrometers; the mass fractions of the glass sphere, nickel-nickel oxide sphere, and magnetic metal sphere are 57.5%, 27.6%, and 14.9%, respectively; the mass fractions of nickel and nickel oxide in the nickel-nickel oxide sphere are 50.2% and 49.8%, respectively.

[0065] The survival rate is 88.6% at 32MPa; the optimized electromagnetic wave reflection loss is -44.2dB, the effective absorption bandwidth is 3.6GHz, and the electromagnetic shielding effectiveness is 45-59dB.

[0066] Example 4

[0067] The specific preparation scheme for glass-nickel-nickel oxide-magnetic metal composite hollow microspheres is as follows:

[0068] 1) Hollow glass microspheres (density 0.46 g / cm³) 3 Mixed with treatment solution A containing 10g nickel nitrate, 2g sucrose, 2g starch and 3g water at a ratio of 0.22g / mL; the mixture was then dried at 60℃; and then treated at 600℃ for 0.3h in air atmosphere. After the reaction, it was dispersed through an 80-mesh sieve to obtain intermediate glass-nickel-nickel oxide hollow microspheres. In the intermediate glass-nickel-nickel oxide hollow microspheres, a layer formed by nickel and nickel oxide covers the surface of the glass hollow microspheres. In the layer formed by nickel and nickel oxide, nickel oxide is a continuous phase, and nickel is dispersed and doped in nickel oxide. The nickel is at least partially exposed on the outer surface of the layer.

[0069] 2) The above intermediate glass-nickel-nickel oxide hollow microspheres were dispersed at an addition amount of 0.006 g / mL in aqueous solution B containing 30 g / L cobalt sulfate, 15 g / L ferrous ammonium sulfate, 55 g / L sodium hypophosphite, and 85 g / L potassium sodium tartrate, with pH≈10 (adjusted with ammonia). The mixture was stirred in a water bath at 60℃ for 25 min, filtered, and dried to obtain glass-nickel-nickel oxide-magnetic metal composite hollow microspheres.

[0070] The density of the glass-nickel-nickel oxide-magnetic metal composite hollow microspheres obtained in this embodiment is 1.11 g / cm³. 3 The diameter of the core cavity is 18.2 micrometers; the mass fractions of the glass sphere, magnetic metal sphere, and nickel-nickel oxide sphere are 40.7%, 35.0%, and 24.4%, respectively; the mass fractions of nickel and nickel oxide in the nickel-nickel oxide sphere are 49.5% and 50.5%, respectively.

[0071] The survival rate is 93.9% at 32MPa; the optimized electromagnetic wave reflection loss is -60.7dB, the effective absorption bandwidth is 4.6GHz, and the electromagnetic shielding effectiveness is 61-70dB.

[0072] Example 5

[0073] The specific preparation scheme for glass-nickel-nickel oxide-magnetic metal composite hollow microspheres is as follows:

[0074] 1) Hollow glass microspheres (density 0.51 g / cm³) 3 The mixture was mixed with treatment solution A containing 10g nickel nitrate, 4g cellulose and 3g water at a ratio of 0.19g / mL; the mixture was then dried at 60°C; and then treated at 650°C for 0.3h in air atmosphere. After the reaction, the mixture was dispersed through an 80-mesh sieve to obtain intermediate glass-nickel-nickel oxide hollow microspheres. In the intermediate glass-nickel-nickel oxide hollow microspheres, a layer formed by nickel and nickel oxide covers the surface of the glass hollow microspheres. In the layer formed by nickel and nickel oxide, nickel oxide is a continuous phase, and nickel is dispersed and doped in nickel oxide. At least part of the nickel is exposed on the outer surface of the layer.

[0075] 2) The above intermediate glass-nickel-nickel oxide hollow microspheres were dispersed at an addition amount of 0.009 g / mL in an aqueous solution B containing 28 g / L cobalt sulfate, 35 g / L sodium hypophosphite, and 65 g / L potassium sodium tartrate, with pH≈10 (adjusted with ammonia). The mixture was stirred in a water bath at 60℃ for 25 min, filtered, and dried to obtain glass-nickel-nickel oxide-magnetic metal composite hollow microspheres.

[0076] The density of the glass-nickel-nickel oxide-magnetic metal composite hollow microspheres obtained in this embodiment is 1.39 g / cm³. 3 The diameter of the core cavity is 34.8 micrometers; the mass fractions of the glass sphere, magnetic metal sphere, and nickel-nickel oxide sphere are 35.7%, 39.3%, and 25.0%, respectively; the mass fractions of nickel and nickel oxide in the nickel-nickel oxide sphere are 47.1% and 52.9%, respectively.

[0077] The survival rate is 97.4% at 32MPa; the optimized electromagnetic wave reflection loss is -65.8dB, the effective absorption bandwidth is 5.1GHz, and the electromagnetic shielding effectiveness is 68-81dB.

[0078] Example 6

[0079] The specific preparation scheme for glass-nickel-nickel oxide-magnetic metal composite hollow microspheres is as follows:

[0080] 1) Hollow glass microspheres (density 0.42 g / cm³) 3Mixed with treatment solution A containing 10g nickel nitrate, 4g tartaric acid and 3g water at a ratio of 0.65g / mL; the mixture was then dried at 60℃; and then treated at 600℃ for 0.3h in air atmosphere. After the reaction, the mixture was dispersed through an 80-mesh sieve to obtain intermediate glass-nickel-nickel oxide hollow microspheres. In the intermediate glass-nickel-nickel oxide hollow microspheres, a layer formed by nickel and nickel oxide covers the surface of the glass hollow microspheres. In the layer formed by nickel and nickel oxide, nickel oxide is a continuous phase, and nickel is dispersed and doped in nickel oxide. At least part of the nickel is exposed on the outer surface of the layer.

[0081] 2) The above intermediate glass-nickel-nickel oxide hollow microspheres were dispersed at an addition amount of 0.006 g / mL in an aqueous solution B containing 32 g / L cobalt sulfate, 35 g / L sodium hypophosphite, and 70 g / L potassium sodium tartrate, with a pH of ≈9.5 (adjusted with ammonia). The mixture was stirred in a water bath at 65°C for 25 min, filtered, and dried to obtain glass-nickel-nickel oxide-magnetic metal composite hollow microspheres.

[0082] The density of the glass-nickel-nickel oxide-magnetic metal composite hollow microspheres obtained in this embodiment is 0.87 g / cm³. 3 The diameter of the core cavity is 38.1 micrometers; the mass fractions of the glass sphere, magnetic metal sphere, and nickel-nickel oxide sphere are 47.6%, 42.9%, and 9.5%, respectively; the mass fractions of nickel and nickel oxide in the nickel-nickel oxide sphere are 48.5% and 51.5%, respectively.

[0083] The survival rate is 90.8% at 32MPa; the optimized electromagnetic wave reflection loss is -43.4dB, the effective absorption bandwidth is 3.5GHz, and the electromagnetic shielding effectiveness is 63-74dB.

[0084] Comparative Example 1

[0085] A glass-nickel-nickel oxide-magnetic metal composite hollow microsphere was prepared using the same method as in Example 1, except that the nickel nitrate in step 1) was replaced with either iron nitrate or cobalt nitrate, while the other conditions remained unchanged. During the experiment, it was found that an iron oxide layer (containing no metallic iron) or a cobalt oxide layer (containing no metallic cobalt) was formed on the surface of the glass hollow microsphere in step 1), making it impossible to further achieve magnetic metal coating in subsequent step 2).

[0086] Comparative Example 2

[0087] A glass-nickel-nickel oxide-magnetic metal composite hollow microsphere was prepared using the same method as in Example 1, except that the nickel nitrate in step 1) was replaced with silver nitrate, while the other conditions remained unchanged. During the experiment, a metallic silver layer (containing no silver oxide) was found to form on the surface of the glass hollow microsphere in step 1).

[0088] The prepared composite hollow microspheres are glass-silver-magnetic metal composite hollow microspheres. Their density is 0.74 g / cm³. 3 The diameter of the core cavity is 43 micrometers; the mass fractions of the glass sphere, silver sphere, and magnetic metal are 42.1%, 28.7%, and 29.2%, respectively.

[0089] The survival rate at 32MPa is 79.2%; the optimized electromagnetic wave reflection loss is -43.2dB, the effective absorption bandwidth is 2.2GHz; and the electromagnetic shielding effectiveness is 60-73dB.

[0090] Comparative Example 3

[0091] A glass-nickel-nickel oxide-magnetic metal composite hollow microsphere is prepared in the same way as in Example 1, except that the amount of sucrose added in step 1) is changed to 6g, while the other conditions remain the same.

[0092] The density of the obtained glass-nickel-nickel oxide-magnetic metal composite hollow microspheres is 0.68 g / cm³. 3 The diameter of the core cavity is 43 micrometers; the mass fractions of the glass sphere, magnetic metal sphere, and nickel-nickel oxide sphere are 46.4%, 28.6%, and 25%, respectively; the mass fractions of nickel and nickel oxide in the nickel-nickel oxide sphere are 62.7% and 37.3%, respectively.

[0093] The survival rate at 32MPa is 78.6%; the optimized electromagnetic wave reflection loss is -32.5dB, the effective absorption bandwidth is 2.4GHz; and the electromagnetic shielding effectiveness is 57-73dB.

[0094] Comparative Example 4

[0095] A glass-nickel-nickel oxide-magnetic metal composite hollow microsphere is prepared in the same way as in Example 1, except that the treatment time at 600°C in air atmosphere in step 1) is changed to 0.6 h, while the other conditions remain the same.

[0096] The density of the obtained glass-nickel-nickel oxide-magnetic metal composite hollow microspheres is 0.69 g / cm³. 3 The diameter of the core cavity is 43 micrometers; the mass fractions of the glass sphere, magnetic metal sphere, and nickel-nickel oxide sphere are 44.8%, 37.9%, and 17.3%, respectively; the mass fractions of nickel and nickel oxide in the nickel-nickel oxide sphere are 35.6% and 64.4%, respectively.

[0097] The survival rate at 32MPa is 79.0%; the optimized electromagnetic wave reflection loss is -38.3dB, the effective absorption bandwidth is 2.5GHz; and the electromagnetic shielding effectiveness is 50-62dB.

[0098] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A method for preparing composite hollow microspheres, characterized in that, Includes the following steps: Silicate hollow glass microspheres are dispersed in a nickel salt solution, mixed, dried, and then heat-treated in an air atmosphere to obtain composite microspheres with a metal layer containing nickel and nickel oxide on the surface, denoted as composite microsphere A. The heat treatment temperature is 550-750℃ and the heat treatment time is 10-24min. The composite hollow microspheres are obtained by coating the composite microspheres A with magnetic metal.

2. The preparation method according to claim 1, characterized in that, The nickel salt solution is obtained by mixing nickel salt, organic carbon source and water in a mass ratio of 8-12:4:3-5.

3. The preparation method according to claim 1, characterized in that, The organic carbon source is selected from one or more of chitosan, cellulose, citric acid, starch, sucrose, and tartaric acid.

4. The preparation method according to claim 1, characterized in that, The density of the silicate hollow glass microspheres is 0.3-0.6 g / cm³. 3 .

5. The preparation method according to claim 1, characterized in that, The amount of silicate hollow glass microspheres added relative to the nickel salt solution is 0.15-0.7 g / mL.

6. The preparation method according to claim 1, characterized in that, In the nickel-containing and nickel oxide-containing metal layer, nickel oxide is a continuous phase and nickel is a dispersed phase. The nickel is doped in the nickel oxide, and the nickel is at least partially exposed on the outer surface of the metal layer.

7. The preparation method according to claim 1, characterized in that, The magnetic metal is selected from one or more of iron, cobalt, and nickel, or an alloy of three of them.

8. The preparation method according to claim 1 or 7, characterized in that, The method for coating magnetic metal includes the following steps: The composite microspheres A were dispersed in a salt solution of a magnetic metal and stirred at 50-80°C for 22-28 minutes. After filtration and drying, the product was obtained. Preferably, the magnetic metal salt solution comprises a magnetic metal salt, a stabilizer, a reducing agent, a pH adjuster, and water, wherein the concentration of the magnetic metal salt is 10-70 g / L, the concentration of the stabilizer is 30-150 g / L, the concentration of the reducing agent is 30-80 g / L, and the concentration of the pH adjuster is such that the pH value of the magnetic metal salt solution is 8-11. Preferably, the amount of the composite microsphere A added relative to the salt solution of the magnetic metal is 0.005-0.02 g / mL.

9. The composite hollow microspheres prepared by the preparation method according to any one of claims 1-8, characterized in that, The composite hollow microspheres comprise silicate hollow glass microspheres, and sequentially coated with a nickel-containing metal layer and a nickel oxide metal layer, and a magnetic metal layer; wherein, The metal layer comprises a continuous phase of nickel oxide and nickel doped in the nickel oxide, wherein the nickel is at least partially exposed on the outer surface of the metal layer.

10. The application of the composite hollow microspheres as described in claim 9 in microwave absorption or shielding.

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