Silver-coated hollow glass microspheres, a preparation method thereof and application thereof in electromagnetic shielding

Abstract

The present application relates to the inorganic nonmetal field, specifically to a kind of silver-coated hollow glass microsphere and its preparation method and application in electromagnetic shielding.The preparation method provided by the present application utilizes alkali activation silane coupling agent and silver nitrate to activate hollow glass microsphere, lays foundation for subsequent silane coupling agent and silver oxalate connection, improves silver-coated coating amount and degree of combination;Adopt sodium oxalate as the precipitant of silver, and the property is stable, transportation is convenient, reduction reaction is also stable, and sodium oxalate is low in cost, easy to obtain.The whole process does not produce waste gas, no resource waste, and the reagent consumed can be recycled;Two kinds of silver ion solution are configured in the preparation process, to avoid the excessive use of silver ion solution, further reduce cost.In addition, the silver-coated hollow glass microsphere obtained by the preparation method provided by the present application is uniformly coated with silver, not only good electromagnetic shielding performance, but also high thermal conductivity.

Description

Technical Field

[0001] This invention relates to the field of inorganic non-metallic materials, specifically to a silver-coated hollow glass microsphere, its preparation method, and its application in electromagnetic shielding. Background Technology

[0002] Hollow glass microspheres are spherical hollow materials made from silicate-borate composites using a special process. Due to their good sphericity, low tap density, and hollow nature, they are widely used for weight reduction in plastics, rubber, cement building materials, and composite materials. Their spherical structure helps prevent edge warping in plastics and rubber, while their hollow structure provides insulation for cement building materials and membrane materials, making them functionally applicable in various fields.

[0003] In recent years, hollow glass microspheres have been vigorously developed and widely applied as an emerging material. When used in thermally conductive materials, they achieve low density and high thermal conductivity after being coated with such materials. In electromagnetic shielding materials, hollow glass microspheres, after being coated with electromagnetic shielding materials, become metal-coated hollow glass microspheres, further enhancing their electromagnetic shielding function on top of their original sound insulation, heat insulation, and lightweight properties. This allows hollow glass microspheres to achieve broader applications in terms of lightweighting, functionality, and low cost.

[0004] CN111377617A describes a two-step process to achieve a uniform and effective silver coating on glass microspheres. This involves activating glass microspheres with alkali and fluoride, followed by surface adsorption using a stannous chloride / HCl mixture. The addition of a silver ammonia solution reduces the silver ammonia with stannous chloride, forming a first silver coating on the microspheres. Excess silver ammonia reacts with a reducing agent to form elemental silver, creating a second coating. However, in practice, the leakage of fluoride and ammonia gas complicates subsequent waste gas treatment, hinders batch production, and the chloride ions in the stannous chloride / HCl mixture consume some silver ions, leading to resource waste and increased costs.

[0005] CN120383890A utilizes polyacrylic acid resin as a carrier, and through the adhesion between polyacrylic acid resin and microspheres, silver is loaded into the polyacrylic acid resin via a silver mirror reaction to achieve silver coating. However, this method results in insufficient density of the silver coating, thus weakening its functionality.

[0006] To address the above issues, a novel silver-coated hollow glass microsphere process is needed to achieve high-performance silver-coated hollow glass microspheres that are low-cost, easy to operate, have good coating performance, and are pollution-free. Summary of the Invention

[0007] In view of this, the technical problem to be solved by the present invention is to provide a silver-coated hollow glass microsphere, a method for preparing the same, and its application in electromagnetic shielding. The preparation method provided by the present invention can obtain silver-coated microspheres with uniform coating. The obtained silver-coated microspheres not only have good electromagnetic shielding performance, but also high thermal conductivity. In addition, the preparation process does not generate waste gas, has no resource waste, and the consumed reagents can be recycled.

[0008] This invention provides a method for preparing silver-coated hollow glass microspheres, comprising the following steps:

[0009] S1) Hollow glass microspheres, silver nitrate solution and alkali-activated silane coupling agent are subjected to the first activation reaction;

[0010] S2) Add silver nitrate solution and sodium oxalate solution to the material obtained in step S1) and heat it simultaneously;

[0011] S3) The material obtained in step S2) is subjected to catalytic reduction and aging under the presence of a catalyst and a reducing agent to obtain silver-coated microspheres.

[0012] This invention first involves a first activation reaction of hollow glass microspheres, silver nitrate solution, and an alkali-activated silane coupling agent. The alkali-activated silane coupling agent is obtained by a second activation reaction of a silane coupling agent under a strong alkali. Specifically, the preparation method of the alkali-activated silane coupling agent of this invention includes the following steps: mixing the silane coupling agent and a strong alkali in water, and then heating the resulting mixed solution to carry out a second activation reaction to obtain the alkali-activated silane coupling agent. The silane coupling agent is selected from one or more of silane coupling agents containing a methoxysilane structure or a silane coupling agent containing an ethoxysilane structure, more specifically from one or more of KH171, KH172, KH540, KH550, monomethyltrimethoxysilane, and KH750; the strong alkali is selected from one or more of sodium hydroxide, potassium hydroxide, and calcium hydroxide.

[0013] In the preparation method of the alkali-activated silane coupling agent of the present invention, the molar ratio of the silane coupling agent to the strong base is 1:(1~3). The concentration of the strong base cation in the system undergoing the second activation reaction is 1 mol / L~3 mol / L, that is, the concentration of the strong base cation in the mixed solution obtained after mixing the silane coupling agent and the strong base in water is 1 mol / L~3 mol / L. The temperature of the second activation reaction of the present invention is 70℃~90℃; the time of the second activation reaction is 0.5 h~1 h.

[0014] This invention utilizes the aforementioned alkali-activated silane coupling agent and silver nitrate to activate hollow glass microspheres, laying the foundation for subsequent in-situ crystallization of silver oxalate on the microsphere surface. Specifically, the silane coupling agent and strong alkali react to generate R-group sodium / potassium / calcium silicate. The R-group sodium / potassium / calcium silicate then reacts with silver nitrate to generate R-group silver silicate. The silanol groups in the R-group silver silicate that did not participate in the reaction can combine with the silanol groups on the microsphere surface during hydrolysis after heating activation. Simultaneously, silver ions also directly combine with the silanol groups on the microsphere surface, thus... Ions grow on the surface of microspheres, a process akin to planting "seeds" on the surface. Subsequently, after co-precipitation of silver nitrate and sodium oxalate, silver ions grow in situ through the silver ions on the "seeds," enabling the generated silver oxalate to tightly bind to the surface of the microspheres. This achieves a core-shell structure assembly of microsphere-silane coupling agent-silver silicate-silver oxalate, resulting in a precursor with a dense coating layer and a more active outermost silver oxalate layer. Consequently, during the subsequent silver coating process after adding a reducing agent, aggregation is not only avoided, but the amount and degree of silver coating are also higher.

[0015] In the first activation reaction step of the present invention, if silver nitrate is not added and only the alkali-activated silane coupling agent is used to activate the hollow glass microspheres, "seeds" will not grow on the surface of the microspheres. This will result in less silver oxalate deposition and insufficient binding during the later deposition, thus leading to a decrease in overall performance.

[0016] In the first activation reaction step of this invention, involving hollow glass microspheres, silver nitrate solution, and an alkali-activated silane coupling agent, if the alkali-activated silane coupling agent is not used, but instead, the unactivated silane coupling agent is directly contacted with the silver nitrate. The disadvantage of this approach is that silver nitrate is acidic, and upon contact with the unactivated silane coupling agent, it causes hydrolysis and cross-linking of the silane coupling agent, resulting in a significant reduction in the subsequent surface activation efficiency of the microspheres.

[0017] This invention involves a first activation reaction of hollow glass microspheres, silver nitrate solution, and an alkali-activated silane coupling agent. Specifically, the hollow glass microspheres and silver nitrate solution are mixed in water, heated to the temperature for the first activation reaction, and then the alkali-activated silane coupling agent is added to initiate the first activation reaction. More specifically, the hollow glass microspheres and silver nitrate solution are mixed in water, heated to the temperature for the first activation reaction, and the alkali-activated silane coupling agent is added while stirring at high speed. After the addition is complete, the first activation reaction is carried out under slow stirring.

[0018] In the first activation reaction step of hollow glass microspheres, silver nitrate solution, and alkali-activated silane coupling agent, the concentration of silver ions in the silver nitrate solution is 0.034 mol / L to 0.2 mol / L; the weight ratio of the hollow glass microspheres to the silver nitrate solution is 1:(2.5~3.5), preferably 1:3; the amount of alkali-activated silane coupling agent is based on the number of moles of strong base cations contained in the alkali-activated silane coupling agent, and the ratio of the number of moles of strong base cations contained in the alkali-activated silane coupling agent to the number of moles of silver ions in the silver nitrate solution is (1.0~1.2):1, preferably 1:1.

[0019] In the first activation reaction step of the present invention, which involves hollow glass microspheres, silver nitrate solution, and alkali-activated silane coupling agent, the temperature of the first activation reaction is 70℃~90℃; the time of the first activation reaction is 0.5 h~1 h; the speed of the high-speed stirring is 400 rpm / min~600 rpm / min, preferably 500 rpm / min; and the speed of the slow stirring is 100 rpm / min~200 rpm / min, preferably 150 rpm / min.

[0020] This invention involves a first activation reaction of hollow glass microspheres, silver nitrate solution, and an alkali-activated silane coupling agent, followed by the simultaneous addition of silver nitrate solution and sodium oxalate solution to the resulting material and heating. Specifically, after the first activation reaction, the resulting material is filtered. The resulting filter cake is mixed with water, and then silver nitrate solution and sodium oxalate solution are simultaneously added to the mixture, followed by stirring and heating. The ratio of the filtered filter cake to water is 1:(2~3) based on the weight of the powder in the filter cake:(weight of water in the filter cake + weight of additionally added water). The heating temperature is 70℃~90℃, and the heating time is 4 h~6 h.

[0021] In the step of simultaneously adding silver nitrate solution and sodium oxalate solution to the material obtained in step S1) and heating, the concentration of silver ions in the silver nitrate solution is 0.12 mol / L to 0.36 mol / L; the concentration of sodium ions in the sodium oxalate solution is 0.12 mol / L to 0.36 mol / L; and the ratio of the volume of silver nitrate solution to the volume of sodium oxalate solution to the mass of microspheres in the material obtained in step S1) is (0.9~1.1):(0.9~1.1):1. This invention utilizes oxalate to precipitate silver ions and coat the surface of activated hollow glass microspheres. Oxalate itself has a certain reducing property, and during the precipitation process, a mixed precipitate of silver oxalate and elemental silver will appear. On the one hand, this lays the foundation for silver deposition on the surface of the microspheres during the silver coating process, and the subsequent addition of a reducing agent can further promote the conversion of silver oxalate into elemental silver. On the other hand, the entire process of first depositing silver oxalate on the surface of the microspheres and then carrying out the reduction reaction is slow and does not involve explosive reactions. Therefore, the entire reaction process is easy to control and does not require sophisticated equipment.

[0022] In this invention, silver nitrate solution and sodium oxalate solution are simultaneously added to the material obtained in step S1), and the mixture is heated. The resulting material is then subjected to catalytic reduction and aging under the influence of catalytic and reducing agents to obtain silver-coated microspheres. Specifically, after heating the material obtained in step S1), silver nitrate solution and sodium oxalate solution are simultaneously added to the mixture, the material is filtered, and the resulting filter cake is mixed with water. Catalytic and reducing agents are then added to the mixed material for catalytic reduction and aging. The aged material is then filtered, washed, and dried to obtain silver-coated microspheres. The ratio of the filtered filter cake to water is calculated as follows: (weight of powder in the filter cake: weight of water in the filter cake + weight of additional water added) = 1:(2~3).

[0023] The present invention involves adding catalytic and reducing substances to the mixed material for catalytic reduction. The catalytic reduction temperature is 70℃~90℃; the catalytic reduction time is 25 min~35 min; and the reduction is carried out at a rotation speed of 100 rpm / min~200 rpm / min.

[0024] This invention, after adding catalytic and reducing substances to the mixed material for catalytic reduction, also includes aging the reduced material, specifically static aging. The aging temperature of this invention is 70℃~90℃; the aging time is 10 h~20 h.

[0025] The catalyst of this invention is selected from one or more of quaternary ammonium bases, triethylamine, diethylamine, diethylenetriamine, and triethylenetetramine; the quaternary ammonium base includes tetraethylammonium hydroxide, tetramethylammonium hydroxide, etc. The mass of the catalyst of this invention is 5‰~1% of the mass of the microsphere powder in the material obtained in step S2), which ensures the reaction environment for silver reduction and catalyzes the ionization of silver ions to react with the reducing agent. The reducing substance of this invention is selected from one or more of glucose, sodium formate, benzaldehyde, fructose, lactose, and maltose; the amount of the reducing substance added is 0.5~1 times the total amount of silver ions added.

[0026] This invention uses glucose as a reducing agent, allowing reduction and aging to be carried out under alkaline conditions, which can generate a mixed byproduct of organic ammonium oxalate and organic ammonium gluconate. After adding sodium hydroxide in the later stage, sodium oxalate is generated and recrystallized from sodium gluconate to separate the two. Sodium oxalate can be returned to the whole process, reducing costs.

[0027] The present invention also provides silver-coated hollow glass microspheres obtained by any of the preparation methods described above.

[0028] This invention also provides the application of silver-coated hollow glass microspheres obtained by any of the above-described preparation methods in the preparation of electromagnetic shielding materials.

[0029] This invention provides a method for preparing silver-coated hollow glass microspheres and their application in electromagnetic shielding. The preparation method utilizes an alkali-activated silane coupling agent and silver nitrate to activate the hollow glass microspheres, laying the foundation for subsequent bonding of the silane coupling agent and silver oxalate, thus improving the silver coating amount and binding degree. Sodium oxalate is used as the silver precipitant, which is stable, easy to transport, and exhibits stable reaction during reduction. Furthermore, sodium oxalate is inexpensive and readily available. The entire process generates no waste gas, avoids resource waste, and the consumed reagents can be recycled. The preparation process involves two silver ion solutions to avoid excessive use of silver ion solution, further reducing costs. In addition, the silver-coated hollow glass microspheres obtained by the method provided by this invention have uniform silver coating, exhibiting not only good electromagnetic shielding performance but also high thermal conductivity. Attached Figure Description

[0030] Figure 1 This is a low-magnification SEM image of the silver-coated hollow glass microspheres obtained in Example 2 of the present invention.

[0031] Figure 2 This is a high-magnification SEM image of the silver-coated hollow glass microspheres obtained in Example 2 of the present invention.

[0032] Figure 3 This is a SEM image of the microspheres obtained in Comparative Example 1 of this invention;

[0033] Figure 4 This is a SEM image of the microspheres obtained in Comparative Example 2 of this invention;

[0034] Figure 5 This is a SEM image of the microspheres obtained in Comparative Example 3 of this invention;

[0035] Figure 6 This is a SEM image of the microspheres obtained in Comparative Example 4 of this invention. Detailed Implementation

[0036] This invention discloses a silver-coated hollow glass microsphere, its preparation method, and its application in electromagnetic shielding. Those skilled in the art can refer to the content of this document and appropriately modify the process parameters to achieve the desired result. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in this invention. The methods and applications of this invention have been described through preferred embodiments, and those skilled in the art can clearly modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit, and scope of this invention to realize and apply the technology of this invention.

[0037] The present invention will be further described below with reference to the embodiments:

[0038] Example 1

[0039] 1. Take a certain amount of silver nitrate and add water to prepare silver nitrate solution a with a silver ion concentration of 0.034 mol / L and silver nitrate solution b with a silver ion concentration of 0.12 mol / L; take a certain amount of sodium oxalate and add water to prepare sodium oxalate solution c with a sodium ion concentration of 0.12 mol / L.

[0040] 2. Activation of silane coupling agent: Mix silane coupling agent KH550 and sodium hydroxide in water at a molar ratio of 1:1 to prepare a mixed activation solution with a sodium ion concentration of 1 mol / L. Then, activate the solution at 80℃ for 0.5 h to obtain the silane activation solution.

[0041] 3. Microbead Activation: A certain amount of microbead powder and silver nitrate solution a are mixed in a weight ratio of microbead powder:silver nitrate solution a = 1:3 and then dispersed in water to obtain a microbead slurry. The microbead slurry is placed in an 80℃ water bath. Then, an equimolar amount of silane activation solution containing sodium ions, obtained in step 2, is slowly added dropwise to the microbead slurry while stirring at high speed. After the addition is complete, slow stirring is started. The reaction is carried out for 2 hours to complete the microbead activation and obtain the activated microbead slurry. The high-speed stirring rate is 500 rpm / min, and the slow stirring rate is 150 rpm / min.

[0042] 4. After the microspheres are activated in step 3, the activated microsphere slurry is filtered to obtain a filter cake. The moisture content of the filter cake is tested, and then water is added to the filter cake for mixing. The ratio of powder weight in the filter cake to water weight in the filter cake plus the weight of the added water is 1:2.5, resulting in a mixed microsphere slurry. The ratio of silver nitrate solution b to sodium oxalate solution c to microsphere powder mass is 1:1:1. Silver nitrate solution b and sodium oxalate solution c are simultaneously and slowly added dropwise to the mixed microsphere slurry while stirring. After the addition is complete, the mixture is kept at 80°C for 4 hours.

[0043] 5. The material obtained in step 4 is washed and filtered to obtain a microsphere filter cake. Then, water is added to the microsphere filter cake for mixing. The weight ratio of the powder in the microsphere filter cake to (weight of water in the filter cake + weight of the added water) is 1:2.5. Tetraethylammonium hydroxide with a mass of 5‰ of the microsphere powder is added, followed by glucose with a molar ratio of 0.5 times the total amount of silver ions. The resulting mixture is placed in an 80°C water bath and stirred at a speed of 100 rpm / min for 30 minutes. After stirring, it is allowed to stand for aging for 10 hours. After aging, the obtained material is filtered, washed, and then dried. The finished product is silver-coated microspheres.

[0044] Example 2

[0045] The experimental procedure in Example 2 differs from that in Example 1 in that:

[0046] In step 1, the concentration of silver nitrate solution a is 0.2 mol / L;

[0047] In step 2, the sodium ion concentration is 3 mol / L.

[0048] Scanning electron microscopy (SEM) was performed on the silver-coated hollow glass microspheres obtained in Example 2, and the results are as follows: Figure 1 and Figure 2 As shown, Figure 1 This is a low-magnification SEM image of the silver-coated hollow glass microspheres obtained in Example 2 of the present invention. Figure 2 This is a high-magnification SEM image of the silver-coated hollow glass microspheres obtained in Example 2 of the present invention.

[0049] Example 3

[0050] The experimental procedure in Example 3 differs from that in Example 2 in that:

[0051] In step 1, the concentration of silver nitrate solution b is 0.36 mol / L, and the concentration of sodium oxalate solution c is 0.36 mol / L;

[0052] In step 5, the amount of tetraethylammonium hydroxide added is 1% of the mass of the microsphere powder.

[0053] Example 4

[0054] The experimental procedure in Example 4 differs from that in Example 3 in that:

[0055] In step 2, the silane coupling agent is methyltrimethoxysilane.

[0056] Example 5

[0057] The experimental procedure in Example 5 differs from that in Example 4 in that:

[0058] In step 2, the strong base is potassium hydroxide;

[0059] The activation time for the mixed activation solution is 1 hour.

[0060] Example 6

[0061] The experimental procedure in Example 6 differs from that in Example 5 in that:

[0062] In step 3, the microsphere slurry is activated at 90℃ for 4 hours, with a high-speed stirring rate of 800 rpm / min and a low-speed stirring rate of 300 rpm / min.

[0063] Example 7

[0064] The experimental procedure in Example 7 differs from that in Example 6 in that:

[0065] In step 4, change "keep warm at 80℃ for 4 hours" to "keep warm at 80℃ for 6 hours".

[0066] Example 8

[0067] The experimental procedure in Example 8 differs from that in Example 7 in that:

[0068] In step 5, the water bath temperature is 90℃, the stirring rate is 200 rpm / min, and the aging time is 20 h.

[0069] Comparative Example 1

[0070] The difference between Comparative Example 1 and Example 1 is that silver nitrate solution a is not added in step 3.

[0071] The final scanning electron microscope image of the product is as follows Figure 3 As shown, Figure 3 This is a SEM image of the microspheres obtained in Comparative Example 1 of this invention.

[0072] Comparative Example 2

[0073] Compared with Example 1, Comparative Example 2 differs in that step 2 is omitted, and in step 3, the silane coupling agent KH550, in an amount equal to the molar amount of silver ions in the mixed silver nitrate solution, is slowly dripped into the microsphere slurry.

[0074] The final scanning electron microscope image of the product is as follows Figure 4 As shown, Figure 4 This is a SEM image of the microspheres obtained in Comparative Example 2 of this invention.

[0075] Comparative Example 3

[0076] Compared with Example 1, Comparative Example 3 does not activate the microbeads. Instead, after the activated silane coupling agent in step 3 is added, the deposition of silver oxalate is carried out directly in step 4.

[0077] The final scanning electron microscope image of the product is as follows Figure 5 As shown, Figure 5 This is a SEM image of the microspheres obtained in Comparative Example 3 of this invention.

[0078] Comparative Example 4

[0079] The difference between Comparative Example 4 and Example 1 is that no catalyst was added in step 5.

[0080] The final scanning electron microscope image of the product is as follows Figure 6 As shown, Figure 6 This is a SEM image of the microspheres obtained in Comparative Example 4 of this invention.

[0081] Test case

[0082] According to the formulations shown in Table 1, the microbeads obtained in Examples 1 to 8 and Comparative Examples 1 to 4 were prepared into samples:

[0083] Table 1

[0084]

[0085] The specific steps for sample preparation are as follows:

[0086] 1. Thoroughly mix silver-coated hollow glass microspheres with dodecyltriethoxysilane for later use;

[0087] 2. Add the vinyl end silicone oil to the planetary mixer, then add the silver-coated hollow glass microspheres pretreated in step 1. First, stir and disperse at low speed, then vacuum degas for 50 minutes to ensure uniform dispersion, no particles, and no bubbles before discharging.

[0088] 3. After adding hydrogen-containing silicone oil to the material in step 2 and stirring evenly, add isopropanol chloroplatinic acid solution and stir quickly to make it even, then perform vacuum degassing for 10 minutes; finally, pour the mixture into a disc mold, close the mold, heat at 130℃ for 15 minutes, and finally open the mold.

[0089] The samples prepared above were tested for electromagnetic shielding performance according to GB / T30142-2013 and thermal conductivity according to ASTM D5470 standard. The results are shown in Table 2.

[0090] Table 2

[0091]

[0092] The comparative test results showed that the thermal conductivity of the sample prepared with silver-coated hollow glass microspheres in the example was significantly higher than that of the sample prepared with microspheres in the comparative example. Furthermore, the electromagnetic shielding effectiveness improved with increasing silver ion concentration in the system; an appropriate increase in catalyst enhanced the silver coating effect, resulting in better electromagnetic shielding effectiveness; increasing the activation time of the activator on the microspheres improved the electromagnetic shielding effectiveness of the final product; a longer holding time for the mixed deposition of sodium oxalate and silver nitrate resulted in better electromagnetic shielding effectiveness; and a longer reduction time of anions under the action of the catalyst resulted in better electromagnetic shielding effectiveness. The decrease in electromagnetic shielding effectiveness in Comparative Example 1 was mainly due to the cancellation of the bridging effect between anions and the activator during microsphere activation, meaning that growth points for subsequent in-situ growth of sodium oxalate and silver nitrate deposition failed to form on the microsphere surface. Ultimately, this led to a decrease in the amount of silver coating. In Comparative Example 2, no activation solution was prepared; instead, the components of the activation solution were added to the microspheres. This made the mixed system more complex. In addition to hydrolysis, the coupling agent consumed some silver ions, some sodium ions, and some also combined with the microspheres. The conditions became uncontrollable, and the amount of silver ions bound to the surface of the microspheres decreased. In Comparative Example 3, the microspheres were not activated, which meant that there were no attachment points for the growth of silver oxalate crystals on the surface of the microspheres. Even if silver oxalate was deposited later, the effect would be greatly reduced, and the electromagnetic shielding effect would be further reduced. In Comparative Example 4, no catalyst was added, so the conditions for the silver ions to be reduced to elemental silver were not met. As a result, there was very little elemental silver on the surface, and the final effect was also poor.

[0093] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing silver-coated hollow glass microspheres, characterized in that, Includes the following steps: S1) Hollow glass microspheres, silver nitrate solution and alkali-activated silane coupling agent are subjected to the first activation reaction; S2) Add silver nitrate solution and sodium oxalate solution to the material obtained in step S1) and heat it simultaneously; S3) The material obtained in step S2) is subjected to catalytic reduction and aging under the presence of a catalyst and a reducing agent to obtain silver-coated hollow glass microspheres.

2. The method for preparing silver-coated hollow glass microspheres according to claim 1, characterized in that, In step S1), the alkali-activated silane coupling agent is obtained by a second activation reaction of the silane coupling agent under strong alkali conditions; The silane coupling agent is selected from one or more of silane coupling agents containing a methoxysilane structure or a silane coupling agent containing an ethoxysilane structure. The strong base is selected from one or more of sodium hydroxide, potassium hydroxide, and calcium hydroxide.

3. The method for preparing silver-coated hollow glass microspheres according to claim 2, characterized in that, The molar ratio of the silane coupling agent to the strong base is 1:(1~3); The concentration of the strong base cation in the system undergoing the second activation reaction is 1 mol / L to 3 mol / L.

4. The method for preparing silver-coated hollow glass microspheres according to claim 2, characterized in that, The temperature of the second activation reaction is 70℃~90℃; the time of the second activation reaction is 0.5 h~1 h.

5. The method for preparing silver-coated hollow glass microspheres according to claim 1, characterized in that, In step S1), the concentration of silver ions in the silver nitrate solution is 0.034 mol / L to 0.2 mol / L; The weight ratio of the hollow glass microspheres to the silver nitrate solution is 1:(2.5~3.5); The amount of the alkali-activated silane coupling agent is based on the number of moles of strong base cations contained in the alkali-activated silane coupling agent, and the ratio of the number of moles of strong base cations contained in the alkali-activated silane coupling agent to the number of moles of silver ions in the silver nitrate solution is (1.0~1.2):

1. In step S2), the concentration of silver ions in the silver nitrate solution is 0.12 mol / L to 0.36 mol / L; The sodium ion concentration in the sodium oxalate solution is 0.12 mol / L to 0.36 mol / L; The ratio of the volume of the silver nitrate solution to the volume of the sodium oxalate solution to the mass of the microspheres in the material obtained in step S1) is (0.9~1.1):(0.9~1.1):

1.

6. The method for preparing silver-coated hollow glass microspheres according to claim 1, characterized in that, In step S1), the temperature of the first activation reaction is 70℃~90℃; the time of the first activation reaction is 0.5 h~1 h; In step S2), the heating temperature is 70℃~90℃; the heating time is 4 h~6 h. In step S3), the aging temperature is 70℃~90℃; the aging time is 10 h~20 h.

7. The method for preparing silver-coated hollow glass microspheres according to claim 1, characterized in that, In step S3), the catalyst is selected from one or more of quaternary ammonium base, triethylamine, diethylamine, diethylenetriamine, and triethylenetetramine; The reducing agent is selected from one or more of glucose, sodium formate, benzaldehyde, fructose, lactose, and maltose.

8. The method for preparing silver-coated hollow glass microspheres according to claim 1, characterized in that, In step S3), the mass of the catalyst is 5‰ to 1% of the mass of the microsphere powder in the material obtained in step S2), and the amount of reducing substance added is 0.5 to 1 times the total amount of silver ions added.

9. Silver-coated hollow glass microspheres obtained by any of the preparation methods described in claims 1 to 8.

10. The application of silver-coated hollow glass microspheres obtained by any of the preparation methods according to claims 1 to 8 in the preparation of electromagnetic shielding materials.

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