Early-strength and high-electrothermal geopolymer and preparation method thereof

Abstract

The invention belongs to the technical field of electrothermal materials, and particularly relates to an early-strength and high-electrothermal geopolymer which is at least prepared from three materials, namely metakaolin, carbon fibers and an alkali activator, and a preparation method of the early-strength and high-electrothermal geopolymer comprises the following steps: step 1, adding sodium hydroxide into a sodium silicate solution, stirring the mixture to obtain the alkali activator, and standing at normal temperature for 24 hours; step 2, pouring metakaolin powder and carbon fibers into a crusher, and then quickly stirring to obtain mixed powder; step 3, adding alumina fiber and polyacrylamide into the alkali activator, and stirring and mixing; 4, the mixed powder obtained in the step 2 is added into the prepared alkali activator, slow stirring is conducted firstly, then rapid stirring is conducted, then slurry is poured into a silica gel mold, and bubbles in the slurry are removed through vibration; step 5, maintaining and curing the sample at 60 DEG C; and 6, placing the cured test piece at the temperature of 400 DEG C for 15 minutes. The geopolymer obtained by the invention has the characteristics of early strength and high electric heating.

Description

Technical Field

[0001] The invention belongs to the technical field of electric heating materials, and in particular relates to an early-strength, high-electric heating geopolymer and a preparation method thereof. Background Art

[0002] As energy consumption and environmental problems become increasingly serious, finding efficient and sustainable energy conversion has become an important research topic in the field of modern science and technology. As an efficient way of energy utilization, electrothermal technology has been widely used in road deicing, temperature control, temperature sensors, electrothermal maintenance and other fields due to its advantages of rapid response, easy control and efficient energy conversion.

[0003] Existing electric heating materials include phase change materials, polymer composite materials, building materials, etc. Electric heating building materials are widely used because they can meet the construction and maintenance conditions in cold areas. Most of the existing electric heating building materials are based on ordinary Portland cement, and cement produces a large amount of carbon dioxide during the production process, which can reach 5% of the total carbon emissions. Geopolymer, as a new and green cementitious material, can reduce carbon dioxide produced by 70%-80% during its preparation process compared to cement, and geopolymer has excellent mechanical and durability properties, showing great potential in replacing cement as an electric heating building material.

[0004] In order to bring out the electrothermal properties of geopolymers, conductive fillers are usually added to geopolymers, including carbon fiber, carbon black, graphite, carbon nanotubes, steel fiber, etc. Carbon fiber geopolymers have attracted widespread attention due to their good mechanical properties, durability and electrical conductivity. The prior art has studied the effect of carbon fiber on the cyclic electrothermal properties of geopolymers, and found that carbon fiber geopolymers can form a stable electrothermal cycle at low voltage (3V). However, at high voltage (9V and 12V), the electrothermal performance of the geopolymer is significantly reduced after the first cycle, which is mainly due to the increase in temperature causing the geopolymer gel to shrink and destroy the conductive network.

[0005] Therefore, it is necessary to process the carbon fiber geopolymer to improve its electrothermal performance. To this end, the present invention provides an early-strength, high electrothermal geopolymer and a preparation method thereof. Summary of the invention

[0006] The purpose of the present invention is to provide an early-strength, high-electrical-thermal geopolymer and a preparation method thereof, which can be used to prepare the early-strength, high-electrical-thermal geopolymer.

[0007] The technical solution adopted by the present invention is as follows:

[0008] The invention discloses an early-strength high-electrical-thermal geopolymer, which is prepared from at least three materials: metakaolin, carbon fiber and alkali activator.

[0009] A method for preparing an early-strength, high-electricity and high-thermal geopolymer, the method comprising the following steps:

[0010] Step 1: Add sodium hydroxide to the sodium silicate solution, stir the mixture at a speed of 1000 r / min for 10 min until the sodium hydroxide is completely dissolved to obtain an alkaline activator, and let it stand at room temperature for 24 h;

[0011] Step 2: Pour the kaolin powder and carbon fiber into a pulverizer, and then quickly stir for 3 minutes to obtain a mixed powder;

[0012] Step 3: Add alumina fiber and polyacrylamide to the alkali activator and stir and mix at a speed of 1000 r / min for 10 minutes;

[0013] Step 4: Add the mixed powder obtained in step 2 to the prepared alkali activator, slowly stir at 200 r / min for 2 min, then quickly stir at 500 r / min for 5 min, then pour the slurry into a mold and vibrate to remove bubbles in the slurry;

[0014] Step 5: Curing the sample at 60°C for 24 hours;

[0015] Step 6: Place the cured specimen at 400°C for 15 minutes.

[0016] Preferably, in step 1, the purity of sodium hydroxide solid is greater than 96%; in the sodium silicate solution: the SiO2 content is 23%-26%; the Na2O content is 14%-16%; and the rest is water.

[0017] Preferably, the total content of Al2O3 and SiO2 in the metakaolin in step 2 is 94%-97%, and the length of the carbon fiber is 2.5-3.5 mm.

[0018] The technical effects achieved by the present invention are:

[0019] (1) High early strength: The present invention uses alumina fibers and carbon fibers of different sizes to form a multi-gradient fiber interpenetrating network through ratio design. Since the alumina fibers and the geopolymer kaolin reactant have the same aluminum component, the geopolymer gel can nucleate and grow on the alumina fibers, and together with the fiber interpenetrating network, form a three-dimensional rigid skeleton-flexible fiber chain structure, which greatly improves the crack resistance and strength of the geopolymer. In addition, appropriate 60°C temperature curing can promote the dissolution of silicon and aluminum elements in the kaolin and the nucleation and growth of the gel on the alumina fibers, ensuring that the rigid gel skeleton is better formed in the flexible fiber chain. The average compressive strength of the geopolymer obtained in the embodiment and all comparative examples after one day of curing and high temperature treatment exceeded 15MPa, indicating that the geopolymer prepared by the present invention has early strength characteristics.

[0020] (2) Excellent electrothermal performance: Appropriate high-temperature treatment at 400°C will not significantly reduce the early strength of the geopolymer under the joint anti-cracking effect of carbon fiber and alumina fiber. It can better control the shrinkage of the geopolymer gel. The extrusion force generated will overlap the carbon fibers that were originally far apart, thereby making the three-dimensional conductive network denser and the electrothermal cycle stability better.

[0021] By comparing the embodiments and all comparative embodiments, compared with the carbon fiber geopolymer at room temperature, the electrothermal performance of the carbon fiber geopolymer after high temperature treatment is significantly improved, and multiple stable cycles can be performed at a high voltage of 11V. In addition, the temperature of Example 1 can reach 350°C at a voltage of 20V, which is higher than the geopolymer prepared by the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is the preparation process of the early-strength, high-electrical-thermal geopolymer of the present invention;

[0023] Figure 2 is the electron microscope image of HCG2.0 in Example 1;

[0024] Figure 3 middle: Figure 3 a is a resistance diagram of different embodiments and comparative embodiments after high temperature treatment; Figure 3 b is a comparison diagram of the electric heating temperatures of different embodiments and comparative embodiments before and after high temperature treatment;

[0025] Figure 4 middle: Figure 4 a is a graph showing the electrothermal performance of different embodiments and comparative embodiments after high temperature treatment under 11V voltage cycle; Figure 4 b is the temperature variation curves of different embodiments and comparative embodiments in the process of continuously increasing voltage after high temperature treatment; Figure 4 c is a comparison chart of the electrothermal performance of different embodiments and comparative embodiments after high temperature treatment with the prior art. DETAILED DESCRIPTION

[0026] In order to make the purpose and advantages of the present invention more clearly understood, the present invention is specifically described below in conjunction with embodiments. It should be understood that the following text is only used to describe one or several specific embodiments of the present invention, and does not strictly limit the scope of protection of the specific claims of the present invention.

[0027] The geopolymer in the embodiment and comparative embodiment is made from the following raw materials: Table 1 shows the chemical composition of metakaolin, wherein the sum of Al2O3 and SiO2 is 95.918%. The performance parameters of the carbon fiber are shown in Table 2, and the length and diameter are 3 mm and 7 μm respectively. The alkaline activator is made from sodium silicate aqueous solution mixed with sodium hydroxide, and the main chemical composition of the sodium silicate aqueous solution is shown in Table 3, and the purity of sodium hydroxide is >96%. Polyacrylamide and alumina fiber are added to the alkaline activator, and the solid content of polyacrylamide is ≥90%, and the degree of hydrolysis is ≤30%.

[0028] Table 1 Main chemical components of metakaolin

[0029]

[0030] Table 2 Carbon fiber performance parameters

[0031]

[0032] Table 3 Main chemical components of sodium silicate aqueous solution

[0033] Main oxide types <![CDATA[SiO2]]> <![CDATA[Na2O]]> <![CDATA[H2O]]> content% 24.87 15 60.13

[0034] like Figure 1 As shown, the preparation method described in the embodiment and the comparative example comprises the following steps:

[0035] Embodiment 1:

[0036] Step 1: Add 85 parts of solid sodium hydroxide to 1415 parts of sodium silicate solution, stir the mixture at a speed of 1000 r / min for 10 minutes until the NaOH is completely dissolved to obtain an alkaline activator, and let it stand at room temperature for 24 hours;

[0037] Step 2: Pour 1000 parts of kaolin powder and 20 parts of carbon fiber into a pulverizer, and then quickly stir for 3 minutes to obtain a mixed powder;

[0038] Step 3: Add 25 parts of alumina fiber and 2 parts of polyacrylamide to the alkali activator and stir and mix at a speed of 1000 r / min for 10 minutes;

[0039] Step 4: Add the mixed powder obtained in step 2 to the prepared alkali activator, slowly stir at 200 r / min for 2 min, then quickly stir at 500 r / min for 5 min, then pour the slurry into a mold and vibrate to remove bubbles in the slurry;

[0040] Step 5: Curing the sample at 60°C for 24 hours to obtain specimen CG2.0;

[0041] Step 6: Place CG2.0 at 400°C for 15 minutes to obtain specimen HCG2.0.

[0042] Comparative Example 2:

[0043] Step 1: Add 85 parts of solid sodium hydroxide to 1415 parts of sodium silicate solution, stir the mixture at a speed of 1000 r / min for 10 minutes until the NaOH is completely dissolved to obtain an alkaline activator, and let it stand at room temperature for 24 hours;

[0044] Step 2: Pour 1000 parts of kaolin powder and 0 parts of carbon fiber into a grinder, and then quickly stir for 3 minutes to obtain a mixed powder;

[0045] Step 3: Add 25 parts of alumina fiber and 2 parts of polyacrylamide to the alkali activator and stir and mix at a speed of 1000 r / min for 10 minutes;

[0046] Step 4: Add the mixed powder obtained in step 2 to the prepared alkali activator, slowly stir at 200 r / min for 2 min, then quickly stir at 500 r / min for 5 min, then pour the slurry into a mold and vibrate to remove bubbles in the slurry;

[0047] Step 5: Curing and curing the sample at 60°C for 24 hours to obtain specimen CG0;

[0048] Step 6: Place CG0 at 400°C for 15 min to obtain specimen HCG0.

[0049] Comparative Example 3:

[0050] Step 1: Add 85 parts of solid sodium hydroxide to 1415 parts of sodium silicate solution, stir the mixture at a speed of 1000 r / min for 10 minutes until the NaOH is completely dissolved to obtain an alkaline activator, and let it stand at room temperature for 24 hours;

[0051] Step 2: Pour 1000 parts of kaolin powder and 5 parts of carbon fiber into a pulverizer, and then quickly stir for 3 minutes to obtain a mixed powder;

[0052] Step 3: Add 25 parts of alumina fiber and 2 parts of polyacrylamide to the alkali activator and stir and mix at a speed of 1000 r / min for 10 minutes;

[0053] Step 4: Add the mixed powder obtained in step 2 to the prepared alkali activator, slowly stir at 200 r / min for 2 min, then quickly stir at 500 r / min for 5 min, then pour the slurry into a mold and vibrate to remove bubbles in the slurry;

[0054] Step 5: Curing the sample at 60°C for 24 hours to obtain a specimen CG0.5;

[0055] Step 6: Place CG0.5 at 400°C for 15 min to obtain specimen HCG0.5.

[0056] Comparative Example 4:

[0057] Step 1: Add 85 parts of solid sodium hydroxide to 1415 parts of sodium silicate solution, stir the mixture at a speed of 1000 r / min for 10 minutes until the NaOH is completely dissolved to obtain an alkaline activator, and let it stand at room temperature for 24 hours;

[0058] Step 2: Pour 1000 parts of kaolin powder and 10 parts of carbon fiber into a pulverizer, and then quickly stir for 3 minutes to obtain a mixed powder;

[0059] Step 3: Add 25 parts of alumina fiber and 2 parts of polyacrylamide to the alkali activator and stir and mix at a speed of 1000 r / min for 10 minutes;

[0060] Step 4: Add the mixed powder obtained in step 2 to the prepared alkali activator, slowly stir at 200 r / min for 2 min, then quickly stir at 500 r / min for 5 min, then pour the slurry into a mold and vibrate to remove bubbles in the slurry;

[0061] Step 5: Curing the sample at 60°C for 24 hours to obtain the sample CG1.0;

[0062] Step 6: Place CG1.0 at 400°C for 15 minutes to obtain specimen HCG1.0.

[0063] Comparative Example 5:

[0064] Step 1: Add 85 parts of solid sodium hydroxide to 1415 parts of sodium silicate solution, stir the mixture at a speed of 1000 r / min for 10 minutes until the NaOH is completely dissolved to obtain an alkaline activator, and let it stand at room temperature for 24 hours;

[0065] Step 2: Pour 1000 parts of kaolin powder and 15 parts of carbon fiber into a pulverizer, and then quickly stir for 3 minutes to obtain a mixed powder;

[0066] Step 3: Add 25 parts of alumina fiber and 2 parts of polyacrylamide to the alkali activator and stir and mix at a speed of 1000 r / min for 10 minutes;

[0067] Step 4: Add the mixed powder obtained in step 2 to the prepared alkali activator, slowly stir at 200 r / min for 2 min, then quickly stir at 500 r / min for 5 min, then pour the slurry into a mold and vibrate to remove bubbles in the slurry;

[0068] Step 5: Curing the sample at 60°C for 24 hours to obtain specimen CG1.5;

[0069] Step 6: Place CG1.5 at 400°C for 15 min to obtain specimen HCG1.5.

[0070] In the present invention:

[0071] The average compressive strength of the geopolymers obtained in the examples and all comparative examples after one-day curing and high-temperature treatment exceeds 15 MPa, indicating that the geopolymers prepared in the present invention have early strength characteristics.

[0072] The electrothermal temperatures of HCG2.0 in Example 1 at a voltage of 9V are increased by 111°C, 110°C, 96°C and 36°C respectively compared with HCG0 in Comparative Example 2, HCG0.5 in Comparative Example 3, HCG1.0 in Comparative Example 4 and HCG1.5 in Comparative Example 5. This is because the high temperature causes the geopolymer to shrink and produce more carbon fiber conductive paths, thereby improving the electrothermal performance of the geopolymer. HCG2.0 in Example 1 can undergo multiple electrothermal cycles at a voltage of 11V and remain stable. In addition, the electrothermal temperature of HCG2.0 in Example 1 reaches 350°C at a voltage of 20V, which exceeds the electrothermal temperature of geopolymers prepared by prior art.

[0073] In summary, the present invention provides an early-strength, high-electrothermal geopolymer and a preparation method thereof, which solves the technical problems that the geopolymer exhibits unstable electrothermal performance during the circulation process and the maximum achievable electrothermal temperature is low.

[0074] The above is only a preferred embodiment of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principles of the present invention, and these improvements and modifications should also be considered as the protection scope of the present invention. The structures, devices and operating methods not specifically described and explained in the present invention shall be implemented according to the conventional means in the art unless otherwise specified and limited.

Claims

1. An early-strength, high-electricity and high-thermal geopolymer, characterized by: The invention is prepared from at least three materials: metakaolin, carbon fiber and alkali activator.

2. A method for preparing an early-strength, high-electricity and high-thermal geopolymer, characterized in that: The preparation method is used to prepare the early-strength, high-electrical-thermal geopolymer described in claim 1, and the preparation method comprises the following steps: Step 1: Add 150-250 parts of solid sodium hydroxide to 1200-1600 parts of sodium silicate solution, stir the mixture at a speed of 1000 r / min for 10 minutes until the NaOH is completely dissolved to obtain an alkaline activator, and let it stand at room temperature for 24 hours; Step 2: Pour 800-1200 parts of kaolin powder and carbon fiber into a pulverizer, and then quickly stir for 3 minutes to obtain a mixed powder; Step 3: Add 20-30 parts of alumina fiber and 1-3 parts of polyacrylamide to the alkali activator, and stir and mix at a speed of 1000 r / min for 10 minutes; Step 4: Add the mixed powder obtained in step 2 to the prepared alkali activator, slowly stir at 200 r / min for 2 min, then quickly stir at 500 r / min for 5 min, then pour the slurry into a mold and vibrate to remove bubbles in the slurry; Step 5: Curing the sample at 60°C for 24 hours; Step 6: Place the cured specimen at 400°C for 15 minutes.

3. The method for preparing an early-strength, high-electricity and high-thermal geopolymer according to claim 2, characterized in that: In step 1, the purity of sodium hydroxide solid is greater than 96%; in the sodium silicate solution: the SiO2 content is 23%-26%; the Na2O content is 14%-16%; and the rest is water.

4. The method for preparing an early-strength, high-electricity and high-thermal geopolymer according to claim 2, characterized in that: The total content of Al2O3 and SiO2 in the metakaolin in step 2 is 94%-97%, and the length of the carbon fiber is 2.5-3.5 mm.

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