Composite alkali activator, method of making and use in geopolymer

Abstract

The present application relates to the field of functional building materials, in particular to a composite alkali activator and a preparation method thereof, a geopolymer composition, a geopolymer and a preparation method and application thereof. The composition comprises 100 parts by mass of metakaolin and slag, 1.5-3 parts by mass of nano-iron oxide, and 0.25-0.75 parts by mass of carbon nanotubes; the mass ratio of the carbon nanotubes to the nano-iron oxide is 1:2-8; and the carbon nanotubes are provided by the composite alkali activator. The geopolymer provided by the present application has excellent electromagnetic shielding efficiency and high-temperature stability.

Description

Technical Field

[0001] This invention relates to the field of functional building materials, specifically to a composite alkali activator and its preparation method, a composition for geopolymers, a geopolymer and its preparation method and application. Background Technology

[0002] With the rapid development of electronic information technology in aerospace, military equipment, and civilian electronics, electromagnetic interference (EMI) has become a key issue affecting equipment reliability and information security. Traditional electromagnetic shielding materials (such as metal matrix composites) have limitations such as high density, poor corrosion resistance, and high processing difficulty, while polymer matrix composites, although lightweight, have insufficient high-temperature resistance (usually below 300℃), making it difficult to meet the requirements of high-temperature operating conditions.

[0003] Geopolymers, as a novel inorganic cementitious material, have shown potential in the field of functional building materials due to their fire resistance (withstanding temperatures above 600°C), low shrinkage, and environmentally friendly properties. Existing research attempts to improve the electromagnetic shielding performance of geopolymers by incorporating conductive fillers (such as carbon fibers and graphene), but the following technical bottlenecks remain: First, there is the challenge of dispersion in alkaline environments. Geopolymer synthesis requires strongly alkaline activators (pH>13), and carbon nanomaterials (CNTs) are prone to agglomeration under high alkalinity, leading to uneven dispersion and interface defects, significantly reducing the efficiency of conductive network construction. Second, there may be high-temperature performance degradation. Most organic dispersants (such as surfactants) decompose and fail in alkaline high-temperature environments, and the filler-matrix interface is prone to debonding under thermal stress, resulting in a significant decrease in the shielding effectiveness and strength of the material after treatment at 600℃. In addition, there is the problem of insufficient broadband shielding effectiveness. The shielding mechanism of a single conductive filler in the low-frequency band of 30 MHz-1.5 GHz is mainly based on reflection, lacking magnetic loss synergy, making it difficult to achieve the high-efficiency shielding requirement of ≥35 dB in the X-band (8.2-12.4 GHz).

[0004] Currently, research on CNTs / geopolymer composites in publicly available technologies mainly focuses on mechanical reinforcement, and there is still a lack of effective solutions for the systematic optimization of their electromagnetic shielding performance, especially in terms of balancing high-temperature stability (strength retention rate at 600℃), broadband shielding effectiveness, and low addition amount (<1.5 wt%). Summary of the Invention

[0005] The purpose of this invention is to provide a geopolymer composite material that combines excellent electromagnetic shielding performance with high-temperature stability.

[0006] To achieve the above objectives, a first aspect of the present invention provides a method for preparing a composite alkali activator, characterized in that the method comprises: (1) Carbon nanotubes, polyvinylpyrrolidone and water are stirred and intermittently ultrasonically dispersed in sequence to obtain a carbon nanotube dispersion; the conditions of the intermittent ultrasonic treatment are controlled so that the temperature of the mixed system during the treatment is ≤35℃; The carbon nanotube dispersion contains 2.0-2.5 wt% carbon nanotubes. (2) The carbon nanotube dispersion and the alkali activator solution are mixed to obtain a composite alkali activator; the modulus of the alkali activator solution is 1.0-1.2, and the alkali equivalent based on sodium oxide is 4-8 wt%. The carbon nanotube content in the composite alkali activator is 0.35-1.05 wt%.

[0007] A second aspect of the present invention provides a geopolymer composition comprising 100 parts by weight of metakaolin and slag, 1.5-3 parts by weight of nano-iron oxide, and 0.25-0.75 parts by weight of carbon nanotubes; wherein the mass ratio of the carbon nanotubes to the nano-iron oxide is 1:2-8. The carbon nanotubes are provided by a composite alkali activator; the composite alkali activator is a composite alkali activator prepared by the method according to the first aspect of the present invention.

[0008] A third aspect of the present invention provides a method for preparing a geopolymer, the method comprising using the components of the composition described in the second aspect, including: (1) Nano-iron oxide, metakaolin and slag are mixed for the first time to obtain a dry mixture; (2) The dry mixture is mixed with the composite alkali activator to obtain slurry I; the composite alkali activator contains carbon nanotubes; (3) The slurry I is subjected to molding and curing treatment in sequence to obtain the geopolymer.

[0009] A fourth aspect of the invention provides a geopolymer prepared by the method described in the third aspect.

[0010] The fifth aspect of the invention provides the application of the geopolymer described in the fourth aspect in electromagnetic shielding materials.

[0011] The technical solution provided by this invention has at least the following advantages: (1) This invention solves the problem of stable dispersion of carbon nanotubes in high alkalinity (pH>13) geopolymer systems through the synergistic effect of carbon nanotubes and nano iron oxide, so that the resulting geopolymer has excellent electromagnetic shielding performance in the 8.2-12.4 GHz frequency band.

[0012] (2) The geopolymer provided by the present invention has excellent high temperature stability and can still maintain high strength after being treated at 600℃, overcoming the defect of insufficient temperature resistance of traditional polymer-based shielding materials.

[0013] (3) The preparation method of the present invention is controllable. Through specific dispersion preparation, step-by-step mixing and stirring processes, the uniform dispersion of filler (especially carbon nanotubes) in strong base matrix and the performance of the resulting geopolymer are effectively guaranteed. The target performance can be achieved without complicated post-heat treatment or surface treatment.

[0014] (4) The geopolymer provided by the present invention, while maintaining its inherent advantages such as fire resistance, low shrinkage and environmental friendliness, achieves a good combination of electromagnetic shielding function and structural strength, and is suitable for high-temperature electromagnetic shielding scenarios such as aerospace and electronic equipment protection. Detailed Implementation

[0015] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0016] The modulus of an alkaline activator solution refers to the molar ratio of silicon dioxide to sodium oxide.

[0017] As previously stated, a first aspect of the present invention provides a method for preparing a composite alkali activator, characterized in that the method comprises: (1) Carbon nanotubes, polyvinylpyrrolidone and water are stirred and intermittently ultrasonically dispersed in sequence to obtain a carbon nanotube dispersion; the conditions of the intermittent ultrasonic treatment are controlled so that the temperature of the mixed system during the treatment is ≤35℃; The carbon nanotube dispersion contains 2.0-2.5 wt% carbon nanotubes. (2) The carbon nanotube dispersion and the alkali activator solution are mixed to obtain a composite alkali activator; the modulus of the alkali activator solution is 1.0-1.2, and the alkali equivalent based on sodium oxide is 4-8 wt%. The carbon nanotube content in the composite alkali activator is 0.35-1.05 wt%.

[0018] Preferably, in step (1), the conditions for the intermittent ultrasonic dispersion treatment include: a single ultrasonic duration of 5-10 min, a single interval of 10-20 s, and a total treatment time of 50-60 min.

[0019] In a preferred embodiment, the intermittent ultrasonic dispersion treatment is carried out in an environment of 0-10°C.

[0020] Preferably, in step (1), the stirring conditions include: a rotation speed of 800-1000 rpm and a stirring time of 50-60 min.

[0021] Preferably, in step (1), the mass ratio of the carbon nanotubes to the polyvinylpyrrolidone is 100:60-80.

[0022] Preferably, in step (2), the alkaline activator in the alkaline activator solution is a combination of sodium silicate and sodium hydroxide.

[0023] More preferably, the modulus of the sodium silicate is 3.3.

[0024] In some embodiments, the alkaline activator solution can be prepared by mixing and dissolving industrial water glass with sodium hydroxide.

[0025] More preferably, in step (1), during the intermittent ultrasonic dispersion process, the control conditions are such that the temperature of the carbon nanotube dispersion is ≤35°C. The inventors have found that, under this preferred condition, the composite alkali activator provided by the present invention exhibits better dispersion stability and can more effectively maintain the structural integrity of the carbon nanotubes, thereby significantly improving the conductivity and mechanical strength of the material in subsequent applications.

[0026] As previously stated, a second aspect of the present invention provides a geopolymer composition comprising 100 parts by weight of metakaolin and slag, 1.5-3 parts by weight of nano-iron oxide, and 0.25-0.75 parts by weight of carbon nanotubes; wherein the mass ratio of the carbon nanotubes to the nano-iron oxide is 1:2-8. The carbon nanotubes are provided by a composite alkali activator; the composite alkali activator is a composite alkali activator prepared by the method according to the first aspect of the present invention.

[0027] In a preferred embodiment, the mass ratio of the carbon nanotubes to the nano-iron oxide is 1:5-7.

[0028] Preferably, the mass ratio of the metakaolin to the slag is 70:30.

[0029] According to a preferred embodiment, the average diameter of the nano-iron oxide particles is 20-22 nm.

[0030] This invention first mixes a carbon nanotube dispersion with a composite alkali activator having a specific modulus and a specific alkali equivalent to obtain a composite alkali activator, and then applies it as a whole to a geopolymer composition. This simplifies the process of introducing carbon nanotubes into geopolymers, and the composite alkali activator pre-stabilizes the carbon nanotubes, preventing them from agglomerating during subsequent stirring and curing. As a result, the final geopolymer composite material exhibits superior and stable conductivity and higher mechanical strength.

[0031] As previously described, a third aspect of the present invention provides a method for preparing a geopolymer, the method being carried out using the components of the composition described in the second aspect, comprising: (1) Nano-iron oxide, metakaolin and slag are mixed for the first time to obtain a dry mixture; (2) The dry mixture is mixed with the composite alkali activator to obtain slurry I; the composite alkali activator contains carbon nanotubes; (3) The slurry I is subjected to molding and curing treatment in sequence to obtain the geopolymer.

[0032] The present invention does not impose any particular restrictions on the first mixing operation in step (1). Those skilled in the art can make the selection based on the technical means known in the art, as long as the components in the dry mixture can be mixed evenly. The present invention will not elaborate further here, and those skilled in the art should not understand it as a limitation of the present invention.

[0033] Preferably, in step (2), the second mixing operation includes: first mixing at a stirring speed of R1 for time t1, and then mixing at a stirring speed of R2 for time t2; wherein, The stirring speed of R1 is 150-300 rpm, and the time of t1 is 2-3 min; The stirring speed of R2 is 1000-1500 rpm, and the time t2 is 2-3 min. The inventors have found that under this preferred condition, it is possible to ensure that the materials are uniformly mixed and fully wetted, efficiently break up lumps, optimize the rheological properties of the slurry, and thus improve the final uniformity and overall performance of the material.

[0034] Preferably, in step (3), the conditions for the maintenance treatment include: a temperature of 35-45℃ and a time of 72h.

[0035] As previously described, the fourth aspect of the present invention provides a geopolymer prepared by the method described in the third aspect.

[0036] Preferably, the geopolymer has an electromagnetic shielding effectiveness of ≥35 dB in the 8.2-12.4 GHz frequency band.

[0037] As previously stated, the fifth aspect of the present invention provides the application of the geopolymer described in the fourth aspect in electromagnetic shielding materials.

[0038] The present invention will be described in detail below through embodiments. Unless otherwise specified, the raw materials and equipment used in the following embodiments are commercially available products.

[0039] Nano iron oxide: average particle diameter 20 nm, purchased from McLean Company; Polyvinylpyrrolidone: weight average molecular weight 58,000, purchased from Maclean's; Carbon nanotubes: Carboxylated multi-walled carbon nanotubes, purchased from Shenzhen Suiheng Graphene Technology Co., Ltd. Sodium silicate, industrial water glass, with a modulus of 3.3.

[0040] Preparation Example 1 The composite alkali activator is prepared using the following steps: (1) Dissolve polyvinylpyrrolidone in water, add carbon nanotubes, stir at 25°C and 1000 rpm for 60 min, then intermittently sonicate in an ice-water bath for 60 min, with a single sonication duration of 5 min and a single interval of 5 s, for a total treatment time of 60 min, to obtain a carbon nanotube dispersion; control the conditions so that the temperature of the mixing system during the treatment is ≤35°C; in the carbon nanotube dispersion, the content of carbon nanotubes is 2.44 wt%, and the content of polyvinylpyrrolidone is 1.97 wt%; (2) Mix 123.48g of industrial water glass with a modulus of 3.3, 23.85g of sodium hydroxide and 60.504g of deionized water to prepare an alkaline activator solution with a modulus of 1.2 and an alkaline equivalent of 8wt% based on sodium oxide. (3) The carbon nanotube dispersion obtained in step (1) is mixed with the alkali activator solution obtained in step (2) to obtain a composite alkali activator, named M1; in the composite alkali activator, the content of carbon nanotubes is 0.7wt%.

[0041] Comparative Preparation Example 1 The same process as in Preparation Example 1 was used, except that in step (1), the temperature of the mixture during the process was controlled to be 45°C.

[0042] All other process parameters were the same as in Preparation Example 1, and the resulting composite alkali activator was named DM1.

[0043] Comparative Preparation Example 2 The same procedure as in Preparation Example 1 was used, except that in step (2), 127.64 g of industrial water glass with a modulus of 3.3, 16.89 g of sodium hydroxide, and 38.1 g of deionized water were mixed to prepare an alkali activator solution with a modulus of 1.5 and an alkali equivalent of 8 wt% based on sodium oxide. In the composite alkali activator, the content of carbon nanotubes was 0.7 wt%.

[0044] All other process parameters were the same as in Preparation Example 1, and the resulting composite alkali activator was named DM2.

[0045] Example 1 Geopolymers are prepared using the following steps: (1) 300g of metakaolin and slag were dry-mixed for 5min, and then mixed with nano-iron oxide to obtain a dry mixture; in the dry mixture, the mass ratio of metakaolin to slag was 7:3; based on the sum of the masses of metakaolin and slag, the amount of nano-iron oxide was 3wt%; (2) Place the dry mixture in a mixing pot, add the composite alkali activator M1, stir at 150 rpm for 2 min, then increase the speed to 1500 rpm and continue stirring for 2 min to obtain slurry I; the composite alkali activator contains carbon nanotubes; in the slurry I, the mass ratio of the carbon nanotubes to the nano iron oxide is 1:6; (3) Inject the slurry I into the coating mold and seal the surface; after curing at 40±1℃ for 72h, demold to obtain the geopolymer, named S1.

[0046] Example 2 The same process as in Example 1 was used, except that the amount of nano-iron oxide was 2 wt%, based on the sum of the masses of the metakaolin and the slag; and the mass ratio of the carbon nanotubes to the nano-iron oxide in the slurry I was 1:8.

[0047] All other process parameters were the same as in Example 1, and the resulting geopolymer was named S2.

[0048] Example 3 The same process as in Example 1 was used, except that the amount of nano-iron oxide was 1.5 wt%, based on the sum of the masses of the metakaolin and the slag; and the mass ratio of the carbon nanotubes to the nano-iron oxide in the slurry I was 1:2.

[0049] All other process parameters were the same as in Example 1, and the resulting geopolymer was named S3.

[0050] Example 4 The same process as in Example 1 was used, except that the dry mixture was placed in a mixing pot, the composite alkali activator was added, and the mixture was stirred at 1500 rpm for 4 minutes to obtain the slurry I.

[0051] All other process parameters were the same as in Example 1, and the resulting geopolymer was named S4.

[0052] Comparative Example 1 The procedure was the same as in Example 1, except that carbon nanotubes and nano-iron oxide were not added. Specifically: (1) Mix 300g of metakaolin and slag dry for 5 minutes to obtain a dry mixture; in the dry mixture, the mass ratio of metakaolin to slag is 7:3; (2) Mix 123.48g of industrial water glass with a modulus of 3.3, 23.85g of sodium hydroxide and 60.504g of deionized water to prepare an alkaline activator solution with a modulus of 1.2 and an alkaline equivalent of 8wt% based on sodium oxide. (3) Place the dry mixture obtained in step (1) into a mixing pot, add the alkali activator solution obtained in step (2), stir at 150 rpm for 2 min, then increase the speed to 1500 rpm and continue stirring for 2 min to obtain slurry I; the mass ratio of alkali activator solution to dry mixture is 0.69:1; (4) Inject the slurry I into the coating mold and seal the surface; after curing at 40±1℃ for 72h, demold and the resulting geopolymer is named D1.

[0053] Comparative Example 2 The procedure was the same as in Example 1, except that the amount of nano-iron oxide used was 1.5 wt%, based on the sum of the masses of the metakaolin and the slag; and carbon nanotubes were not added. Specifically: (1) 300g of metakaolin and slag were dry-mixed for 5min, and then mixed with nano-iron oxide to obtain a dry mixture; in the dry mixture, the mass ratio of metakaolin to slag was 7:3; based on the sum of the masses of metakaolin and slag, the amount of nano-iron oxide was 1.5wt%; (2) Mix 123.48g of industrial water glass with a modulus of 3.3, 23.85g of sodium hydroxide and 60.504g of deionized water to prepare an alkaline activator solution with a modulus of 1.2 and an alkaline equivalent of 8wt% based on sodium oxide. (3) Place the dry mixture obtained in step (1) into a mixing pot, add the alkali activator solution obtained in step (2), stir at 150 rpm for 2 min, then increase the speed to 1500 rpm and continue stirring for 2 min to obtain slurry I; the mass ratio of alkali activator solution to dry mixture is 0.68:1; (4) Inject the slurry I into the coating mold and seal the surface; after curing at 40±1℃ for 72h, demold and the resulting geopolymer is named D2.

[0054] Comparative Example 3 The procedure was the same as in Example 1, except that the carbon nanotubes in the composite alkali activator were 0.7 wt%; no nano-iron oxide was added; and the amount of carbon nanotubes used was 0.5 wt% based on the sum of the masses of the metakaolin and the slag.

[0055] All other process parameters were the same as in Example 1, and the resulting geopolymer was named D3.

[0056] Comparative Example 4 The same procedure as in Example 1 was used, except that the composite alkali activator was replaced with DM1 instead of M1; the mass content of carbon nanotubes in slurry I remained unchanged.

[0057] All other process parameters were the same as in Example 1, and the resulting geopolymer was named D4.

[0058] Comparative Example 5 The same procedure as in Example 1 was used, except that the composite alkali activator was replaced with DM2 instead of M1; the mass content of carbon nanotubes in slurry I remained unchanged.

[0059] All other process parameters were the same as in Example 1, and the resulting geopolymer was named D5.

[0060] Test case The performance test data of the examples and comparative examples are shown in Table 1.

[0061] The testing methods for electromagnetic shielding effectiveness are: vector network analyzer method and coaxial method.

[0062] The test method for compressive strength is as follows: refer to GB / T 17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)".

[0063] The test method for compressive strength retention rate is as follows: refer to GB / T 17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)".

[0064] Table 1

[0065] As can be seen from the results in Table 1, the geopolymer provided by this invention forms a complete "conductive-magnetic loss" network, exhibiting excellent electromagnetic shielding effectiveness and high-temperature stability.

[0066] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A composition for use with geopolymers, characterized in that, The composition comprises 100 parts by weight of metakaolin and slag, 1.5-3 parts by weight of nano-iron oxide, and 0.25-0.75 parts by weight of carbon nanotubes; the mass ratio of carbon nanotubes to nano-iron oxide is 1:2-8. The carbon nanotubes are provided by a composite alkali activator; the composite alkali activator is a product prepared by a method comprising the following steps: (1) Carbon nanotubes, polyvinylpyrrolidone and water are stirred and intermittently ultrasonically dispersed in sequence to obtain a carbon nanotube dispersion; the conditions of the intermittent ultrasonic treatment are controlled so that the temperature of the mixed system during the treatment is ≤35℃; The carbon nanotube dispersion contains 2.0-2.5 wt% carbon nanotubes. (2) The carbon nanotube dispersion and the alkali activator solution are mixed to obtain a composite alkali activator; the modulus of the alkali activator solution is 1.0-1.2, and the alkali equivalent based on sodium oxide is 4-8 wt%. The carbon nanotube content in the composite alkali activator is 0.35-1.05 wt%.

2. The composition according to claim 1, characterized in that, In step (1), the conditions for the intermittent ultrasonic dispersion treatment include: the duration of a single ultrasonic treatment is 5-10 min, the interval between treatments is 5-20 s, and the total treatment time is 50-60 min; And / or, the intermittent ultrasonic dispersion treatment is carried out in an environment of 0-10°C.

3. The composition according to claim 1, characterized in that, In step (1), the stirring conditions include: a rotation speed of 800-1000 rpm and a stirring time of 50-60 min.

4. The composition according to any one of claims 1-3, characterized in that, In step (1), the mass ratio of the carbon nanotubes to the polyvinylpyrrolidone is 100:60-80; And / or, in step (2), the alkaline activator in the alkaline activator solution is a combination of sodium silicate and sodium hydroxide.

5. The composition according to claim 1, characterized in that, The mass ratio of the metakaolin to the slag is 70:

30.

6. A method for preparing geopolymers, characterized in that, This method is performed using any of the components in the composition according to any one of claims 1-5, comprising: (1) Nano-iron oxide, metakaolin and slag are mixed for the first time to obtain a dry mixture; (2) The dry mixture is mixed with the composite alkali activator to obtain slurry I; the composite alkali activator contains carbon nanotubes; (3) The slurry I is subjected to molding and curing treatment in sequence to obtain the geopolymer.

7. The method according to claim 6, characterized in that, In step (2), the second mixing operation includes: first mixing at a stirring speed of R1 for time t1, and then mixing at a stirring speed of R2 for time t2; wherein, The stirring speed of R1 is 150-300 rpm, and the time of t1 is 2-3 min; The stirring speed of R2 is 1000-1500 rpm, and the time t2 is 2-3 min; And / or, in step (3), the conditions for the curing treatment include: a temperature of 35-45°C and a time of 72 hours.

8. The geopolymer prepared by the method of claim 6 or 7.

9. The application of the geopolymer of claim 8 in electromagnetic shielding materials.

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