Preparation method of composite hollow microspheres, composite hollow microspheres prepared by preparation 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 preparation method and application of the composite hollow microspheres. The preparation method comprises the following steps: dissolving a soluble salt of a first metal, a soluble salt of a second metal and an organic auxiliary agent in water, and uniformly mixing to obtain a reaction solution; mixing hollow glass microspheres with the reaction liquid, and performing sol-gel coating to obtain a first intermediate; sequentially carrying out co-pyrolysis and selective reduction on the first intermediate to obtain the composite hollow microspheres, wherein in the soluble salt of the first metal, the first metal is selected from one or more of zinc, aluminum and manganese; in the soluble salt of the second metal, the second metal is selected from one or more of copper, silver, iron, cobalt and nickel. By means of the method, the composite hollow microspheres which are light in weight, stable in structure and good in microwave shielding or absorbing function can be rapidly and efficiently prepared.

Description

Technical Field

[0001] This invention relates to the field of powder 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] With the rapid development of science and technology and the continuous improvement of people's living standards, lightweight materials are increasingly widely used in aerospace, home furnishings, automobiles, electronics, and other fields. Among them, hollow microspheres, with their unique structure, high specific strength, high specific stiffness, and excellent thermal insulation properties, exhibit significant advantages in lightweighting. Firstly, hollow microspheres have a unique structural feature: their interior is hollow, which significantly reduces the mass of the material, resulting in a lower density for the same volume, thus achieving a significant lightweighting effect. Secondly, the enormous potential of hollow microspheres to achieve high specific strength and specific stiffness is also an important advantage for lightweighting. Through reasonable design, weight reduction can be achieved without a significant decrease in mechanical properties, and even superior performance in some aspects. This allows hollow microspheres to maintain sufficient structural strength and stability while achieving lightweighting. Furthermore, the inherent hollow cavity of hollow microspheres also endows them with excellent thermal insulation properties, effectively reducing heat transfer. This characteristic makes hollow microspheres a promising candidate for applications in fields requiring thermal control, such as aerospace, automobiles, electronics, construction, and production equipment.

[0003] Of course, lightweight design must also consider functional requirements. However, the inherent characteristics of certain functional materials limit lightweight design. For example, metals possess numerous advantages in both functional and structural materials due to their excellent electrical and thermal conductivity, high strength, high hardness, and good ductility. However, their inherent high density is a problem to be solved in the lightweighting process. Among them, metal-glass composite hollow microspheres, as a novel lightweight material, have attracted widespread attention due to their unique structure and excellent performance. The hollow structure can reduce the mass of the material, achieving lightweighting, while the composite of metal and glass endows the material with good mechanical properties and chemical stability. Therefore, metal-glass composite hollow microspheres can combine the properties of both metal and glass, and are expected to achieve high specific strength, specific stiffness, and excellent electromagnetic and thermal functions. However, when metal materials are combined with glass and designed into hollow microsphere structures, they still face the challenges of high thermal conductivity and high electrical conductivity due to their inherent characteristics. This limits the application of metal-glass composite hollow microspheres in certain fields, such as thermal insulation and electromagnetic wave absorption. In response to the trend of multifunctional materials, although simple composite microsphere structures can effectively reduce density, they are particularly inadequate in application scenarios that require the coordinated regulation and optimization of two or more functions.

[0004] To further enhance the electromagnetic and thermal properties of metal-glass composite hollow microspheres, researchers have attempted to design and control the conductive and thermally conductive networks of the metal, such as regulating the dispersion and connection states and introducing bubbles. However, single-metal material systems still face numerous challenges in terms of process control and performance optimization. On the other hand, the combination of metals with other materials holds promise for greater performance control, but developing efficient fabrication processes for two- or multi-component composites based on the macroscopic structure of micron-sized hollow microspheres remains extremely difficult. Summary of the Invention

[0005] To address the above problems, the present invention aims to provide a method for preparing composite hollow microspheres, the composite hollow microspheres prepared by this method, and their applications. The method of the present invention can prepare lightweight, structurally stable composite hollow microspheres with good microwave shielding or absorption functions. Furthermore, this method is rapid and efficient, effectively solving the problems of cumbersome steps and low efficiency in current methods for preparing composite magnetic metal hollow microspheres.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] On one hand, the present invention provides a method for preparing composite hollow microspheres, comprising the following steps:

[0008] Dissolve the soluble salt of the first metal, the soluble salt of the second metal, and the organic auxiliaries in water, mix well, and obtain a reaction solution.

[0009] Hollow glass microspheres were mixed with the reaction solution and then coated with sol-gel to obtain the first intermediate.

[0010] The first intermediate was subjected to co-pyrolysis and selective reduction in sequence to obtain the composite hollow microspheres;

[0011] Wherein, in the soluble salt of the first metal, the first metal is selected from one or more of zinc, aluminum and manganese;

[0012] In the soluble salt of the second metal, the second metal is selected from one or more of copper, silver, iron, cobalt and nickel.

[0013] Furthermore, the hollow glass microspheres are hollow silicate glass microspheres.

[0014] Furthermore, the density of the hollow glass microspheres is 0.15-0.5 g / cm³. 3 .

[0015] Further, the mass ratio of the soluble salt of the first metal to the water is (0.8-1.2):1. For example, the mass ratio of the soluble salt of the first metal to the water is (0.9-1.2):1, (0.9-1):1, 0.92:1, 1:1, etc.

[0016] Furthermore, the soluble salt of the first metal is selected from the nitrate or organic salt of the first metal.

[0017] Furthermore, the soluble salt of the first metal is selected from zinc nitrate hydrate, etc.

[0018] Further, the mass ratio of the soluble salt of the second metal to the water is (1.7-2.2):1. Exemplary examples include, but are not limited to, (1.75-2.1):1, (1.75-1.95):1, (1.75-1.86):1, (1.75-1.8):1, (1.79-2.1):1, (1.79-1.95):1, (1.79-1.86):1, (1.8-2.1):1, (1.8-1.95):1, 1.75:1, 1.79:1, 1.86:1, 2.1:1, 1.95:1, etc.

[0019] Furthermore, the soluble salt of the second metal is selected from the nitrate of the second metal.

[0020] Furthermore, the soluble salt of the second metal is selected from one or more of hydrated cobalt nitrate, hydrated nickel nitrate, hydrated ferric nitrate, hydrated copper nitrate, and hydrated silver nitrate.

[0021] Furthermore, the soluble salt of the second metal is selected from hydrated cobalt nitrate, or a mixture of hydrated cobalt nitrate and hydrated nickel nitrate in a mass ratio of 25:16 or 15:27, or a mixture of hydrated cobalt nitrate and hydrated ferric nitrate in a mass ratio of 25:19, or a mixture of hydrated cobalt nitrate and hydrated copper nitrate in a mass ratio of 15:27, or a mixture of hydrated cobalt nitrate and hydrated silver nitrate in a mass ratio of 22:21, or a mixture of hydrated cobalt nitrate, hydrated nickel nitrate, and hydrated copper nitrate in a mass ratio of 10:10:23. This condition helps to improve the microwave absorption performance while enhancing the structural stability of the product.

[0022] Furthermore, the mass ratio of the soluble salt of the first metal to the soluble salt of the second metal is (0.45-0.52):1. This helps to obtain composite hollow microspheres with superior structural stability and microwave absorption performance.

[0023] Further, the mass ratio of the organic additive to the water is (0.9-1.3):1. For example, the mass ratio of the organic additive to the water includes, but is not limited to, (0.95-1.2):1, (0.9-1):1, etc.

[0024] Furthermore, the organic additive is selected from one or more of citric acid, glycine, sucrose, starch, cellulose and chitosan.

[0025] Further, the mixing mass ratio of the hollow glass microspheres to the reaction solution is 1:2-1:6. For example, the mixing mass ratio of the hollow glass microspheres to the reaction solution includes, but is not limited to, 1:3-1:6, 1:3-1:5, 1:3-1:4, 1:4-1:6, 1:4-1:5, 1:5-1:6, 1:3, 1:4, 1:5, and 1:6.

[0026] Furthermore, the sol-gel coating method includes the following steps:

[0027] The hollow glass microspheres are mixed with the reaction solution and then dried to obtain the first intermediate.

[0028] Furthermore, the total number of times the mixture is dried after mixing is 1-3 times. By repeating the mixing and drying process, the amount of reactant coating in the first intermediate can be well controlled.

[0029] Furthermore, the drying temperature is 10-80℃, preferably 60℃.

[0030] Furthermore, the co-pyrolysis method includes the following steps:

[0031] The first intermediate was placed in a muffle furnace at a temperature of 450-750°C and in an air atmosphere, and held at this temperature for 10-120 minutes.

[0032] The transformation of metals from salts to oxides (oxides of the first metal and oxides of the second metal) was achieved by co-pyrolysis in an air atmosphere.

[0033] Furthermore, the co-pyrolysis temperature is 450-750℃, and the time is 10-120 min.

[0034] For example, the temperature of the co-pyrolysis includes, but is not limited to, 550-650℃, 550-600℃, 600-650℃, 550℃, 600℃, 650℃, etc.

[0035] For example, the co-pyrolysis time includes, but is not limited to, 20-60 min, 20-50 min, 20-40 min, 20-30 min, 30-60 min, 30-50 min, 30-40 min, 40-60 min, 40-50 min, 50-60 min, 60 min, 50 min, 40 min, 30 min, 20 min, etc.

[0036] Furthermore, the selective reduction method includes the following steps:

[0037] The first intermediate after co-pyrolysis is heat-treated in a reducing atmosphere, wherein the reducing atmosphere is a mixture of hydrogen and argon, and the heat treatment temperature is 400-700℃ for 1-24h.

[0038] The oxide of the second metal is reduced to particles of the second metal by selective reduction in a reducing atmosphere.

[0039] Furthermore, the reducing atmosphere is obtained by mixing hydrogen and argon in a volume ratio of 5%:95%.

[0040] For example, the temperature of the heat treatment includes, but is not limited to, 500-700℃, 550-700℃, 600-700℃, 500-600℃, 500-550℃, 550-600℃, 500℃, 550℃, 600℃, 700℃, etc.

[0041] On the other hand, the present invention provides composite hollow microspheres prepared by the preparation method described above.

[0042] Furthermore, the structure of the composite hollow microspheres includes hollow glass microspheres and a composite metal layer coating the surface of the hollow glass microspheres; wherein,

[0043] The composite metal layer contains:

[0044] A continuous phase formed by the oxide of the first metal coated on the surface of the hollow glass microspheres, and

[0045] A second metal particle embedded within the continuous phase, wherein at least a portion of the second metal particle is exposed on the outer surface of the continuous phase.

[0046] Furthermore, the density of the composite hollow microspheres is 0.2-1.5 g / cm³. 3 The average particle size is 10-90 μm.

[0047] Furthermore, by mass percentage, the composite hollow microspheres contain 30-65% hollow glass microspheres, 10-30% oxides of the first metal, and 20-40% particles of the second metal.

[0048] In another aspect, the present invention provides the application of composite hollow microspheres prepared by the preparation method described above, or composite hollow microspheres prepared by the method described above, in the preparation of microwave shielding, absorbing, or thermal control materials.

[0049] Furthermore, the composite hollow microspheres can be used as a microwave absorbing agent.

[0050] Furthermore, as a microwave shielding or absorbing 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.

[0051] The beneficial effects of this invention are as follows:

[0052] The preparation method provided in this invention utilizes the hollow cavity of hollow glass microspheres to reduce the overall density of the composite hollow microspheres; and leverages the supporting effect of the shell of the hollow glass microspheres for sol-gel coating, further obtaining the composite hollow microspheres through co-pyrolysis and selective reduction. This preparation method is rapid and efficient, effectively solving the problems of cumbersome steps and low efficiency in current methods for preparing composite magnetic metal hollow microspheres.

[0053] The composite hollow microspheres provided in this invention utilize the internal hollow cavity to reduce density; the metal doping oxide can change the electronic structure and band structure of the metal shell, thereby regulating its electromagnetic properties; the high thermal resistance and high electrical resistance of the metal oxide can also appropriately disconnect the conductive and thermally conductive network of the metal layer, and combined with the contact regulation between the spheres, low thermal conductivity and high impedance matching can be obtained. Attached Figure Description

[0054] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0055] Figure 1 A schematic diagram of the structure of the three-shell metal-oxide-glass composite hollow microspheres prepared in Example 1 is shown.

[0056] Figure 2 The image shown is a low-magnification SEM image of the three-shell metal-oxide-glass composite hollow microspheres prepared in Example 5.

[0057] Figure 3 The image shown is a high-magnification SEM image of the three-shell metal-oxide-glass composite hollow microspheres prepared in Example 5.

[0058] Figure 4The XRD pattern of the three-shell metal-oxide-glass composite hollow microspheres prepared in Example 5 is shown. Detailed Implementation

[0059] 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.

[0060] Example 1

[0061] The structural schematic diagram of the three-shell metal-oxide-glass composite hollow microsphere (also known as composite hollow microsphere) is shown below. Figure 1 As shown, where, Figure 1 A in the diagram is a structural schematic of the composite hollow microsphere. Figure 1 B in the diagram is a top view of a portion of the surface of the composite hollow microsphere. Figure 1 C represents a side cross-sectional view of a portion of the composite hollow microsphere shell. Specifically:

[0062] Its structure includes hollow glass microspheres (with a glass shell 1) and a composite metal layer 2 covering the surface of the glass shell 1; wherein,

[0063] The composite metal layer 2 includes:

[0064] The continuous phase formed by the oxide 2-1 of the first metal coating the surface of the glass sphere 1, and

[0065] The second metal particle 2-2 is embedded in the continuous phase, wherein at least a portion of the second metal particle 2-2 is exposed on the outer surface of the continuous phase.

[0066] The preparation method of this composite hollow microsphere includes the following steps:

[0067] A density of 0.25 g / cm³ was used. 3 Commercial silicate hollow glass microspheres;

[0068] Weigh 21g of zinc nitrate hydrate, 25g of cobalt nitrate hydrate, 16g of nickel nitrate hydrate, 22g of sucrose and 21g of water, mix them in a beaker, heat in a 55°C water bath to promote dissolution, and stir until completely dissolved to obtain the reaction solution;

[0069] Hollow glass microspheres and reaction solution were mixed at a mass ratio of 1:5, dried at 60°C after thorough mixing, and dispersed. The above process was repeated twice to obtain intermediate A.

[0070] The above intermediate A was transferred to a crucible and then placed in a muffle furnace at 600°C for heat treatment in air atmosphere for 30 min. After the system cooled naturally to room temperature, the heat-treated product was passed through a 120-mesh standard sieve to obtain intermediate B.

[0071] The above intermediate B was heat-treated in an atmosphere with a volume percentage of 5% H2-95% Ar at 500°C for 3 hours to obtain the target product.

[0072] The mass percentages of the glass shell, the oxide of the first metal (zinc oxide), and the second metal particles (cobalt and nickel) in the three-shell metal-oxide-glass composite hollow microspheres prepared according to the above method were 45.5%, 21.8%, and 32.7%, respectively; the density was 0.51 g / cm³. 3 The average particle size is 55.6 micrometers; the isostatic pressure resistance (maximum test pressure with a volume survival rate of over 90%) is 6.2 MPa; the maximum absorption bandwidth is 5.1 GHz (7.3-12.4 GHz), and the maximum reflection loss is -35.4 dB; the thermal conductivity is 0.58 W / m·K.

[0073] Example 2

[0074] The preparation method of the three-shell metal-oxide-glass composite hollow microspheres is as follows:

[0075] A density of 0.28 g / cm³ was used. 3 Commercial silicate hollow glass microspheres;

[0076] Weigh 21g of zinc nitrate hydrate, 25g of cobalt nitrate hydrate, 16g of nickel nitrate hydrate, 12g of citric acid, 13g of glycine and 21g of water, mix them in a beaker, heat in a 55°C water bath to promote dissolution, and stir until completely dissolved to obtain the reaction solution.

[0077] Hollow glass microspheres and reaction solution were mixed at a mass ratio of 1:4, dried at 60°C, and dispersed. This process was repeated twice to obtain intermediate A.

[0078] The above intermediate A was transferred to a crucible and then placed in a muffle furnace at 600°C for heat treatment in air atmosphere for 50 min. After the system cooled naturally to room temperature, the heat-treated product was passed through a 120-mesh standard sieve to obtain intermediate B.

[0079] The above intermediate B was heat-treated in an atmosphere with a volume percentage of 5% H2-95% Ar at 500°C for 5 hours to obtain the target product.

[0080] The three-shell metal-oxide-glass composite hollow microspheres prepared according to the above method contain 51% glass shell, 19.4% oxide (zinc oxide), and 29.6% metal particles (cobalt and nickel) by mass percentage, respectively; and have a density of 0.52 g / cm³. 3 The average particle size is 43.5 micrometers; the isostatic pressure resistance (maximum test pressure with a volume survival rate of over 90%) is 9.9 MPa; the maximum absorption bandwidth is 4.8 GHz (7.6-12.4 GHz); the maximum reflection loss is -33.6 dB; and the thermal conductivity is 0.59 W / m·K.

[0081] Example 3

[0082] The preparation method of the three-shell metal-oxide-glass composite hollow microspheres is as follows:

[0083] Using a density of 0.30 g / cm³ 3 Commercial silicate hollow glass microspheres;

[0084] Weigh 21g of zinc nitrate hydrate, 25g of cobalt nitrate hydrate, 19g of ferric nitrate hydrate, 16g of citric acid, 8g of starch and 21g of water, mix them in a beaker, heat in a 55°C water bath to promote dissolution, and stir until completely dissolved to obtain the reaction solution.

[0085] Hollow glass microspheres and reaction solution were mixed at a mass ratio of 1:6, dried at 60°C, dispersed, and the above process was repeated once to obtain intermediate A.

[0086] The above intermediate A was transferred to a crucible and then placed in a muffle furnace at 600°C for heat treatment in air atmosphere for 30 min. After the system cooled naturally to room temperature, the heat-treated product was passed through a 120-mesh standard sieve to obtain intermediate B.

[0087] The above intermediate B was heat-treated in an atmosphere with a volume percentage of 5% H2-95% Ar at 500℃ for 20 hours to obtain the target product.

[0088] The three-shell metal-oxide-glass composite hollow microspheres prepared according to the above method contain glass shells, oxides (zinc oxide), and metal particles (cobalt and iron) with mass percentages of 58.8%, 17.6%, and 23.5%, respectively; their density is 0.48 g / cm³. 3 The average particle size is 18.7 micrometers; the isostatic pressure resistance (maximum test pressure with a volume survival rate of over 90%) is 38.3 MPa; the maximum absorption bandwidth is 5.4 GHz (6.9-12.3 GHz); the maximum reflection loss is -21.6 dB; and the thermal conductivity is 0.57 W / m·K.

[0089] Example 4

[0090] The preparation method of the three-shell metal-oxide-glass composite hollow microspheres is as follows:

[0091] A density of 0.32 g / cm³ was used. 3 Commercial silicate hollow glass microspheres.

[0092] Weigh 22g of zinc nitrate hydrate, 15g of cobalt nitrate hydrate, 27g of nickel nitrate hydrate, 13g of sucrose, 10g of citric acid and 24g of water, mix them in a beaker, heat in a 55°C water bath to promote dissolution, and stir until completely dissolved to obtain the reaction solution.

[0093] Hollow glass microspheres and reaction solution were mixed at a mass ratio of 1:5, dried at 60°C, dispersed, and the above process was repeated once to obtain intermediate A.

[0094] The above intermediate A was transferred to a crucible and then placed in a muffle furnace at 650°C for heat treatment in air atmosphere for 20 min. After the system cooled naturally to room temperature, the heat-treated product was passed through a 120-mesh standard sieve to obtain intermediate B.

[0095] The above intermediate B was heat-treated in an atmosphere with a volume percentage of 5% H2-95% Ar at a temperature of 550°C for 9 hours to obtain the target product.

[0096] The three-shell metal-oxide-glass composite hollow microspheres prepared according to the above method have the following mass percentages: glass shell, oxide (zinc oxide), and metal particles (cobalt and nickel) of 62.5%, 14.4%, and 23.1%, respectively; and a density of 0.49 g / cm³. 3 The average particle size is 40.3 micrometers; the isostatic pressure resistance (maximum test pressure with a volume survival rate of over 90%) is 15.4 MPa; the maximum absorption bandwidth is 5.5 GHz (6.8-12.3 GHz); the maximum reflection loss is -16.3 dB; and the thermal conductivity is 0.60 W / m·K.

[0097] Example 5

[0098] The preparation method of the three-shell metal-oxide-glass composite hollow microspheres is as follows:

[0099] A density of 0.37 g / cm³ was used. 3 Commercial silicate hollow glass microspheres.

[0100] Weigh 22g of zinc nitrate hydrate, 41g of cobalt nitrate hydrate, 23g of sucrose and 22g of water, mix them in a beaker, heat in a 55°C water bath to promote dissolution, and stir until completely dissolved to obtain the reaction solution;

[0101] Hollow glass microspheres and reaction solution were mixed at a mass ratio of 1:3, dried at 60°C, dispersed, and the above process was repeated 3 times to obtain intermediate A.

[0102] The above intermediate A was transferred to a crucible and then placed in a muffle furnace at 650°C for heat treatment in air atmosphere for 40 min. After the system cooled naturally to room temperature, the heat-treated product was passed through a 120-mesh standard sieve to obtain intermediate B.

[0103] Intermediate B was heat-treated in an atmosphere of 5% H2 and 95% Ar (volume percentage) at 600°C for 3 hours to obtain the target product, three-shell metal-oxide-glass composite hollow microspheres. A low-magnification SEM image of these microspheres is shown below. Figure 2 As shown, the high-magnification SEM image is as follows: Figure 3 As shown, the XRD pattern is as follows: Figure 4 As shown.

[0104] The three-shell metal-oxide-glass composite hollow microspheres prepared according to the above method contain 47.8% glass shell, 21.5% oxide (zinc oxide), and 30.7% metal particles (cobalt) by mass percentage, respectively; and have a density of 0.73 g / cm³. 3 The average particle size is 40.7 micrometers; the isostatic pressure resistance (maximum test pressure with a volume survival rate of over 90%) is 30.2 MPa; the maximum absorption bandwidth is 4.9 GHz (7.6-12.5 GHz); the maximum reflection loss is -32.7 dB; and the thermal conductivity is 0.65 W / m·K.

[0105] Example 6

[0106] The preparation method of the three-shell metal-oxide-glass composite hollow microspheres is as follows:

[0107] Using a density of 0.40 g / cm³ 3 Commercial silicate hollow glass microspheres;

[0108] Weigh 22g of zinc nitrate hydrate, 15g of cobalt nitrate hydrate, 27g of copper nitrate hydrate, 13g of sucrose, 10g of citric acid and 24g of water, mix them in a beaker, heat in a 55°C water bath to promote dissolution, and stir until completely dissolved to obtain the reaction solution.

[0109] Hollow glass microspheres and reaction solution were mixed at a mass ratio of 1:6, dried at 60°C, dispersed, and the above process was repeated twice to obtain intermediate A.

[0110] The above intermediate A was transferred to a crucible and then placed in a muffle furnace at 650°C for heat treatment in air atmosphere for 20 min. After the system cooled naturally to room temperature, the heat-treated product was passed through a 120-mesh standard sieve to obtain intermediate B.

[0111] The above intermediate B was heat-treated in an atmosphere with a volume percentage of 5% H2-95% Ar at a temperature of 550°C for 15 hours to obtain the target product.

[0112] The three-shell metal-oxide-glass composite hollow microspheres prepared according to the above method have mass percentages of glass shells, oxides (zinc oxide), and metal particles (cobalt and copper), respectively, of 41.2%, 23.8%, and 35%; and a density of 0.92 g / cm³. 3 The average particle size is 42.1 micrometers; the isostatic confining pressure resistance (maximum test pressure with a volume survival rate of over 90%) is 33.8 MPa; the maximum absorption bandwidth is 6 GHz (7.1-13.1 GHz); the maximum reflection loss is -46.8 dB; and the thermal conductivity is 0.67 W / m·K.

[0113] Example 7

[0114] The preparation method of the three-shell metal-oxide-glass composite hollow microspheres is as follows:

[0115] A density of 0.45 g / cm³ was used. 3 Commercial silicate hollow glass microspheres;

[0116] Weigh 22g of zinc nitrate hydrate, 22g of cobalt nitrate hydrate, 21g of silver nitrate hydrate, 22g of sucrose and 24g of water, mix them in a beaker, heat in a 55°C water bath to promote dissolution, and stir until completely dissolved to obtain the reaction solution;

[0117] Hollow glass microspheres and reaction solution were mixed at a mass ratio of 1:6, dried at 60°C, dispersed, and the above process was repeated 3 times to obtain intermediate A.

[0118] The above intermediate A was transferred to a crucible and then placed in a muffle furnace at 600°C for heat treatment in air atmosphere for 40 min. After the system cooled naturally to room temperature, the heat-treated product was passed through a 120-mesh standard sieve to obtain intermediate B.

[0119] The above intermediate B was heat-treated in an atmosphere with a volume percentage of 5% H2-95% Ar at 700°C for 9 hours to obtain the target product.

[0120] The mass percentages of glass shells, oxides (zinc oxide), and metal particles (cobalt and silver) in the three-shell metal-oxide-glass composite hollow microspheres prepared according to the above method were 32.7%, 28.1%, and 39.2%, respectively; the density was 0.49 g / cm³. 3The average particle size is 39.6 micrometers; the isostatic pressure resistance (maximum test pressure with a volume survival rate of over 90%) is 42.9 MPa; the maximum absorption bandwidth is 5.7 GHz (7-12.7 GHz); the maximum reflection loss is -52.8 dB; and the thermal conductivity is 0.71 W / m·K.

[0121] Example 8

[0122] The preparation method of the three-shell metal-oxide-glass composite hollow microspheres is as follows:

[0123] A density of 0.15 g / cm³ was used. 3 Commercial silicate hollow glass microspheres;

[0124] Weigh 22g of zinc nitrate hydrate, 10g of cobalt nitrate hydrate, 10g of nickel nitrate hydrate, 23g of copper nitrate hydrate, 13g of sucrose, 4g of chitosan, 6g of cellulose and 24g of water, mix them in a beaker, heat in a 55°C water bath to promote dissolution, and stir until completely dissolved to obtain the reaction solution.

[0125] Hollow glass microspheres and reaction solution were mixed at a mass ratio of 1:5, dried at 60°C, dispersed, and the above process was repeated once to obtain intermediate A.

[0126] The above intermediate A was transferred to a crucible and then placed in a muffle furnace at 550°C for heat treatment in air atmosphere for 60 min. After the system cooled naturally to room temperature, the heat-treated product was passed through a 120-mesh standard sieve to obtain intermediate B.

[0127] The above intermediate B was heat-treated in an atmosphere with a volume percentage of 5% H2-95% Ar at 550°C for 18 hours to obtain the target product.

[0128] The three-shell metal-oxide-glass composite hollow microspheres prepared according to the above method have the following mass percentages: glass shell, oxide (zinc oxide), and metal particles (cobalt, nickel, and copper) of 62.5%, 15%, and 22.5%, respectively; and a density of 0.23 g / cm³. 3 The average particle size is 61 micrometers; the isostatic confining pressure resistance (maximum test pressure with a volume survival rate of over 90%) is 3.2 MPa; the maximum absorption bandwidth is 5.3 GHz (7.2-12.5 GHz); the maximum reflection loss is -15.2 dB; and the thermal conductivity is 0.56 W / m·K.

[0129] Test method:

[0130] Density and strength testing of three-spherical shell metal-oxide-glass composite hollow microspheres:

[0131] Density was tested using Archimedes' principle. Strength was evaluated using isostatic pressing, and the test was conducted in accordance with the patent "A method for determining the isostatic pressing strength of hollow glass microspheres" (201410196976.0).

[0132] The thermal conductivity of the three-spherical shell metal-oxide-glass composite hollow microspheres was tested using a thermal constant tester.

[0133] Electromagnetic performance testing of three-shell metal-oxide-glass composite hollow microspheres:

[0134] Coaxial rings were prepared by mixing three-spherical shell metal-oxide-glass composite hollow microspheres with paraffin wax. The rings had an inner diameter of 3 mm, an outer diameter of 7 mm, and a thickness of 2 mm. Electromagnetic parameters were then tested using a vector network analyzer to analyze their electromagnetic performance. The effective absorption bandwidth was found to be in the frequency range with a reflection loss ≤ -10 dB.

[0135] 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: Dissolve the soluble salt of the first metal, the soluble salt of the second metal, and the organic auxiliaries in water, mix well, and obtain a reaction solution. Hollow glass microspheres were mixed with the reaction solution and then coated with sol-gel to obtain the first intermediate. The first intermediate was subjected to co-pyrolysis and selective reduction in sequence to obtain the composite hollow microspheres; Wherein, in the soluble salt of the first metal, the first metal is selected from one or more of zinc, aluminum and manganese; In the soluble salt of the second metal, the second metal is selected from one or more of copper, silver, iron, cobalt and nickel.

2. The preparation method according to claim 1, characterized in that, The mass ratio of the soluble salt of the first metal to the water is (0.8-1.2):1; and / or The mass ratio of the soluble salt of the second metal to the water is (1.7-2.2):1; and / or The mass ratio of the organic additive to the water is (0.9-1.3):

1.

3. The preparation method according to claim 1, characterized in that, The mixing mass ratio of the hollow glass microspheres to the reaction solution is 1:2 to 1:

6.

4. The preparation method according to claim 1, characterized in that, The sol-gel coating method includes the following steps: The hollow glass microspheres were mixed with the reaction solution and then dried to obtain the first intermediate. Preferably, the total number of times the mixture is dried after mixing is 1-3 times; Preferably, the drying temperature is 10-80℃.

5. The preparation method according to claim 1, characterized in that, The co-pyrolysis method includes the following steps: The first intermediate was placed in a muffle furnace at a temperature of 450-750°C and in an air atmosphere, and held at this temperature for 10-120 minutes.

6. The preparation method according to claim 1, characterized in that, The selective reduction method includes the following steps: The first intermediate after co-pyrolysis is heat-treated in a reducing atmosphere, wherein the reducing atmosphere is a mixture of hydrogen and argon, and the heat treatment temperature is 400-700℃ for 1-24h.

7. Composite hollow microspheres prepared by the preparation method according to any one of claims 1-6.

8. The composite hollow microspheres according to claim 7, characterized in that, The composite hollow microspheres comprise hollow glass microspheres and a composite metal layer coating the surface of the hollow glass microspheres; wherein, The composite metal layer contains: A continuous phase formed by the oxide of the first metal coated on the surface of the hollow glass microspheres, and A second metal particle embedded within the continuous phase, wherein at least a portion of the second metal particle is exposed on the outer surface of the continuous phase.

9. The composite hollow microspheres according to claim 7 or 8, characterized in that, The density of the composite hollow microspheres is 0.2-1.5 g / cm³. 3 The average particle size is 10-90 μm; Preferably, the composite hollow microspheres contain 30-65% hollow glass microspheres, 10-30% oxides of a first metal, and 20-40% particles of a second metal, by mass percentage.

10. The application of the composite hollow microspheres prepared by the preparation method according to any one of claims 1-6 or the composite hollow microspheres according to any one of claims 7-9 in the preparation of microwave shielding, absorbing or thermal control materials.

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