A geopolymer coating, its method of preparation and use

Abstract

The present application belongs to the technical field of corrosion protection, and particularly relates to a geopolymer coating, a preparation method and application thereof. In the geopolymer material, graphene oxide nanoparticles are incorporated, the hydroxyl groups on the surface of the graphene oxide nanoparticles can not only form hydrogen bonds with the hydroxyl groups in the geopolymer, reduce the pore size of the geopolymer, and establish a high-density polymer network system, but also can form C-O-Fe bonds with the oxide film in the steel through the carboxyl groups of the graphene oxide, improve the interfacial bonding capacity of the coating and the steel, avoid the cracking and peeling of the coating due to the expansion stress of the corrosion products, and establish two lines of defense of the coating and the coating-steel interface for the steel, so that the steel has stable corrosion protection performance.

Description

A geopolymer coating, its preparation method and application Technical Field

[0001] This invention belongs to the field of anti-corrosion technology, specifically relating to a geopolymer coating, its preparation method, and its application. Background Technology

[0002] Geopolymer materials are prepared from industrial byproducts such as fly ash, slag, and metakaolin through alkali activation. They are green, energy-saving, and environmentally friendly inorganic materials. Geopolymer materials possess high early strength, impermeability, and chloride ion curing ability, making them well-suited for preparing anti-corrosion coatings for steel and offering broad application prospects.

[0003] Currently, existing geopolymer coating formulations mainly refine porosity by adding nanomaterials to physically fill the gaps and alleviate the problem of geopolymer shrinkage and cracking. However, as an anti-corrosion coating for steel, the modified materials in existing formulations cannot effectively improve the interfacial bonding between the geopolymer and the steel, causing the coating to easily crack and peel off due to the expansion stress of corrosion products. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a geopolymer coating, its preparation method and application. The geopolymer coating provided by the present invention forms a dense coating with strong bonding ability with steel and has stable anti-corrosion performance.

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

[0006] This invention provides a geopolymer coating, comprising the following components in parts by weight:

[0007] 70-80 parts fly ash, 40-50 parts slag, 25-35 parts metakaolin, 2-4 parts polyvinyl alcohol powder, 6.5-8.5 parts titanium dioxide, 104.0375-104.15 parts graphene oxide dispersion, and 0.5-1 part defoamer.

[0008] Preferably, the graphene oxide dispersion comprises graphene oxide, an alkali activator, and a surfactant.

[0009] Preferably, the alkaline activator comprises an aqueous solution of sodium hydroxide and water glass.

[0010] Preferably, the surfactant comprises a polycarboxylate superplasticizer and / or sodium dodecylbenzenesulfonate.

[0011] Preferably, the mass ratio of sodium hydroxide to water glass is (3.5-4.5):(55-65).

[0012] The present invention also provides a method for preparing the geopolymer coating described in the above technical solution, comprising the following steps:

[0013] Fly ash, slag, metakaolin, polyvinyl alcohol powder and titanium dioxide are first mixed to obtain a solid material;

[0014] The solid material, graphene oxide dispersion, and defoamer are mixed to obtain a geopolymer coating.

[0015] The present invention also provides the application of the geopolymer coating described in the above technical solution or the geopolymer coating prepared by the preparation method described in the above technical solution in steel corrosion protection.

[0016] This invention also provides a method for preparing a geopolymer coating, comprising the following steps:

[0017] Geopolymer coating is applied to the steel surface and dried to obtain a geopolymer coating.

[0018] The geopolymer coating is the geopolymer coating described in the above technical solution or the geopolymer coating prepared by the preparation method described in the above technical solution.

[0019] Preferably, the coating amount of the geopolymer coating is 0.17–0.25 g / cm³. 2 .

[0020] Preferably, the coating is spraying; the diameter of the nozzle used for spraying is 4-6 mm; the spraying pressure is 3-5 MPa; the distance between the nozzle and the steel is 12-18 cm; and the spraying time is 10-15 s.

[0021] This invention provides a geopolymer coating, comprising the following components by weight: 70-80 parts fly ash, 40-50 parts slag, 25-35 parts metakaolin, 2-4 parts polyvinyl alcohol powder, 6.5-8.5 parts titanium dioxide, 104.0375-104.15 parts graphene oxide dispersion, and 0.5-1 part defoamer. This invention incorporates graphene oxide into the geopolymer material. The hydroxyl groups of graphene oxide can not only form hydrogen bonds with the hydroxyl groups in the geopolymer, reducing the capillary pore size and establishing a highly dense polymer network system, but also form CO-Fe bonds with the oxide film in the steel through the carboxyl groups of graphene oxide. This improves the interfacial bonding between the coating and the steel, preventing the coating from cracking and peeling due to the expansion stress of corrosion products. It establishes two lines of defense for the steel: the coating itself and the coating-steel interface, giving the steel stable anti-corrosion performance. Attached Figure Description

[0022] Figure 1 shows the actual photos of the coated steel bars after curing in comparative application example 1 and application examples 1-4;

[0023] Figure 2 shows the salt spray test setup;

[0024] Figure 3 shows the adhesion testing device;

[0025] Figure 4 shows the corrosion morphology of uncoated steel bars, comparative application example 1, and coated steel bars obtained from application examples 1 to 4 after salt spray testing. Detailed Implementation

[0026] This invention provides a geopolymer coating, comprising the following components in parts by weight:

[0027] 70-80 parts fly ash, 40-50 parts slag, 25-35 parts metakaolin, 2-4 parts polyvinyl alcohol powder, 6.5-8.5 parts titanium dioxide, 104.0375-104.15 parts graphene oxide dispersion, and 0.5-1 part defoamer.

[0028] Unless otherwise specified, the present invention does not have special requirements on the source of raw materials used, and commercially available products well known to those skilled in the art can be used.

[0029] The geopolymer coating provided by the present invention comprises, by weight, 70-80 parts of fly ash, preferably 72-75 parts. In the present invention, the calcium content of the fly ash is preferably 3-10%, more preferably 5%; the particle size of the fly ash is preferably 1.6-64.3 μm, more preferably 1.98-61.1 μm.

[0030] Based on 1 part by weight of fly ash, the geopolymer coating provided by the present invention comprises 40-50 parts of slag, preferably 42-45 parts. In the present invention, the calcium content of the slag is preferably 40-50%, more preferably 47%; the particle size of the slag is preferably 2.1-49.8 μm, more preferably 2.2-46.8 μm.

[0031] Based on 1 part by mass of fly ash, the geopolymer coating provided by this invention comprises 25-35 parts, preferably 27-30 parts, of metakaolin. In this invention, the metakaolin is preferably obtained by calcining kaolin; the calcination temperature is preferably 600-900℃, more preferably 700-800℃, and the holding time is preferably 30-60 min, more preferably 40-60 min; the particle size of the metakaolin is preferably 0.2-6.3 μm, more preferably 0.22-5.4 μm.

[0032] Based on 1 part by weight of fly ash, the geopolymer coating provided by the present invention comprises 2 to 4 parts, preferably 2.5 to 3 parts, of polyvinyl alcohol powder. In the present invention, the particle size of the polyvinyl alcohol powder is preferably 100 to 110 μm, more preferably 100 to 105 μm; the molecular weight of the polyvinyl alcohol powder is preferably 117,000 to 124,000 Mn, more preferably 117,000 to 122,000 Mn.

[0033] Based on 1 part by weight of fly ash, the geopolymer coating provided by this invention comprises 6.5 to 8.5 parts, preferably 7 to 7.5 parts, of titanium dioxide. In this invention, the particle size of the titanium dioxide is preferably 0.04 to 2.6 μm, more preferably 0.06 to 1.8 μm. The titanium dioxide used in this invention is preferably titanium dioxide powder for architectural coatings, whose main component is rutile titanium dioxide. This titanium dioxide can enhance the mechanical strength, substrate adhesion, and corrosion resistance of the coating.

[0034] Based on 1 part by mass of fly ash, the geopolymer coating provided by the present invention includes 104.0375 to 104.15 parts of graphene oxide dispersion, preferably 104.05 to 104.11 parts.

[0035] In this invention, the graphene oxide dispersion preferably includes graphene oxide, an alkali activator, and a surfactant; the preparation method of the graphene oxide dispersion preferably includes the following steps: mixing graphene oxide, an alkali activator, and a surfactant, and then performing ultrasonic dispersion to obtain the graphene oxide dispersion.

[0036] In this invention, the specific surface area of ​​the graphene oxide is preferably 100–400 m². 2 / g, more preferably 200-400m 2 / g; the number of layers of the graphene oxide is preferably 1 to 2 layers, more preferably 1 layer; the sheet diameter of the graphene oxide is preferably 0.2 to 10 μm, more preferably 0.2 to 5 μm.

[0037] Among various types of engineering materials, graphene oxide stands out as an excellent carbon-based nanomaterial, possessing a high aspect ratio, high specific surface area, and high elastic modulus. Furthermore, the surface of graphene oxide exhibits numerous oxygen functional groups, including hydroxyl (-OH), carboxyl (-COOH), and epoxy (-COOC). These groups facilitate the interaction between graphene oxide and geopolymer gel molecules, as well as the oxide film on the steel surface. This effectively densifies the microstructure of the geopolymer, mitigates its inherent brittleness, and enhances the interfacial bonding between the geopolymer and steel, thereby significantly improving the corrosion resistance of geopolymer-coated steel bars.

[0038] In this invention, the alkali activator preferably comprises an aqueous solution of sodium hydroxide and water glass; the preferred method for preparing the alkali activator is to mix the aqueous solution of sodium hydroxide and water glass and then let it stand; the preferred mass ratio of sodium hydroxide to water glass is (3.5-4.5):(55-65), more preferably (3.5-4):(55-60), and most preferably 4:60; the preferred mass ratio of sodium hydroxide to water in the aqueous solution of sodium hydroxide is (3.5-4.5):(35-45), more preferably 4:40; the preferred modulus of the water glass in the alkali activator is 2-2.3M, more preferably 2-2.2M; the preferred standing time is 18-24h, more preferably 20-24h; the preferred modulus of the alkali activator is 1.3-1.8M, more preferably 1.4-1.5M.

[0039] In this invention, the surfactant preferably comprises a polycarboxylate superplasticizer and / or sodium dodecylbenzenesulfonate, more preferably a polycarboxylate superplasticizer. This invention improves the dispersibility of graphene oxide through surfactants.

[0040] In this invention, the preferred mass ratio of graphene oxide to alkali activator is (0.0375-0.15):104, more preferably (0.05-0.12):104, and most preferably 0.1125:104; the preferred mass ratio of graphene oxide to surfactant is (0.0375-0.15):0.75, more preferably 0.1125:0.75.

[0041] In this invention, the mixing of graphene oxide, alkali activator, and surfactant is preferably carried out by first mixing graphene oxide and alkali activator, followed by adding surfactant and then carrying out second mixing; the first and second mixing are preferably carried out independently in a magnetic stirrer; the speed of the first mixing is preferably 200-800 rpm, more preferably 500-800 rpm; the time of the first mixing is preferably 1-2 min, more preferably 2 min; the speed of the second mixing is preferably 800-1400 rpm, more preferably 1000-1200 rpm; the time of the second mixing is preferably 4-5 min, more preferably 4 min.

[0042] In this invention, the power of the ultrasonic dispersion is preferably 100-400W, more preferably 120-300W, and the time is preferably 60-90min, more preferably 60-80min. This invention uses ultrasonic dispersion to fully separate agglomerated graphene oxide powder, obtaining a graphene oxide dispersion.

[0043] Based on 1 part by weight of fly ash, the geopolymer coating provided by the present invention includes 0.5 to 1 part of defoamer, preferably 0.5 to 0.8 parts. In the present invention, the defoamer is preferably an organosilicon defoamer; the organosilicon defoamer preferably includes a silicone ether mixed defoamer and / or a silicone oil defoamer, more preferably a silicone oil defoamer.

[0044] This invention incorporates graphene oxide into geopolymer materials. The hydroxyl groups of graphene oxide can not only form hydrogen bonds with the hydroxyl groups in the geopolymer, reducing the capillary pore size of the geopolymer and establishing a highly dense polymer network system, but also form CO-Fe bonds with the oxide film in the steel through the carboxyl groups of graphene oxide. This improves the interfacial bonding ability between the coating and the steel, preventing the coating from cracking and peeling off due to the expansion stress of corrosion products. It establishes two lines of defense for the steel: the coating itself and the coating-steel interface, giving the steel stable anti-corrosion performance.

[0045] The present invention also provides a method for preparing the geopolymer coating described in the above technical solution, comprising the following steps:

[0046] Fly ash, slag, metakaolin, polyvinyl alcohol powder and titanium dioxide are first mixed to obtain a solid material;

[0047] The solid material, graphene oxide dispersion, and defoamer are mixed to obtain a geopolymer coating.

[0048] In this invention, the first mixing is preferably carried out under stirring conditions; the stirring rate is preferably 30-60 rpm, more preferably 40-60 rpm; the first mixing time is preferably 2-4 min, more preferably 3 min.

[0049] In this invention, the second mixing is preferably carried out under stirring conditions; the stirring rate is preferably 60-100 rpm, more preferably 80-100 rpm; the second mixing time is preferably 4-6 min, more preferably 5 min.

[0050] The present invention also provides the application of the geopolymer coating described in the above technical solution or the geopolymer coating prepared by the preparation method described in the above technical solution in steel corrosion protection.

[0051] This invention also provides a method for preparing a geopolymer coating, comprising the following steps:

[0052] Geopolymer coating is applied to the steel surface and dried to obtain a geopolymer coating.

[0053] The geopolymer coating is the geopolymer coating described in the above technical solution or the geopolymer coating prepared by the preparation method described in the above technical solution.

[0054] In this invention, the preferred coating amount of the geopolymer coating is 0.17–0.25 g / cm³. 2 More preferably, it is 0.17–0.2 g / cm³. 2 The coating method is preferably spraying; the diameter of the nozzle used for spraying is preferably 4-6 mm, more preferably 3-5 mm; the spraying pressure is preferably 3-5 MPa, more preferably 4 MPa; the distance between the nozzle and the steel is preferably 12-18 cm, more preferably 13-15 cm; the spraying time is preferably 10-15 s, more preferably 10-13 s.

[0055] In this invention, the drying is preferably carried out at room temperature; the drying time is preferably 30 to 40 minutes, more preferably 30 minutes.

[0056] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, but they should not be construed as limiting the scope of protection of the present invention.

[0057] Example 1

[0058] (1) Preparation of alkali activator: Dissolve 4g of sodium hydroxide in 40g of deionized water to obtain sodium hydroxide solution, then mix the sodium hydroxide solution with 60g of water glass (modulus 2.2M) to obtain alkali activator with modulus 1.5M and let stand for 24h;

[0059] (2) Preparation of graphene oxide dispersion: Take 0.0375g of graphene oxide and 104g of the above-mentioned alkali activator and stir at 600rpm for 1min in a magnetic stirrer. Then add 0.75g of surfactant (polycarboxylate superplasticizer) and continue stirring at 1000rpm for 4min. Finally, use 120W power ultrasonic dispersion for 60min to obtain graphene oxide dispersion.

[0060] (3) Preparation of geopolymer coating: Weigh 75g fly ash (calcium content of 5%, particle size of 50μm), 45g slag (calcium content of 47%, particle size of 10μm), 30g metakaolin (obtained by calcining kaolin at 800℃ for 60min, with a particle size of 5μm), 3g polyvinyl alcohol powder (molecular weight of 100000Mn), and 7.5g titanium dioxide (particle size of 1μm), pour them into a mixing container and stir evenly at 60rpm for 2min. Then, add 104.0375g graphene oxide dispersion and 0.75g organosilicon defoamer (silicone oil type defoamer) and stir again at 100rpm for 5min to obtain geopolymer coating.

[0061] Example 2

[0062] The difference from Example 1 is that the mass of graphene oxide is 0.075g, while the rest is the same as in Example 1.

[0063] Example 3

[0064] The difference from Example 1 is that the mass of graphene oxide is 0.1125g, and the rest is the same as in Example 1.

[0065] Example 4

[0066] The difference from Example 1 is that the mass of graphene oxide is 0.15g, while the rest is the same as in Example 1.

[0067] Comparative Example 1

[0068] Weigh 75g of fly ash, 45g of slag, 30g of metakaolin, 3g of polyvinyl alcohol powder, and 7.5g of titanium dioxide, pour them into a mixing container and mix evenly for 2 minutes. Then, add the alkali activator (prepared in Example 1), 0.75g of organosilicon defoamer (silicone oil type defoamer), and 0.75g of water-reducing agent (polycarboxylate water-reducing agent) and mix again for 5 minutes to obtain the coating.

[0069] Comparative Example 2

[0070] 1) Weigh out 50 parts fly ash, 30 parts slag, 20 parts metakaolin, 2 parts redispersible polymer powder, 5 parts titanium dioxide, 40 parts sodium silicate, 2.5 parts sodium hydroxide, 27.5 parts deionized water, 0.37 parts organosilicon defoamer, and 0.5 parts naphthalene-based water-reducing agent by weight.

[0071] 2) Add sodium hydroxide and deionized water to sodium silicate and stir until homogeneous. After cooling to room temperature and aging for 24 hours, an alkaline activator with a modulus of 1.5 is obtained.

[0072] 3) After thoroughly mixing fly ash, slag, metakaolin, redispersible polymer powder, and titanium dioxide powder, place them in a mixing pot. Add the alkali activator and organosilicon defoamer obtained in step 2), and stir at low speed for 2 minutes. The stirring blades' revolution and rotation speeds are 62±5 rpm and 140±5 rpm, respectively. Then add the naphthalene-based water-reducing agent and stir at high speed for 3 minutes. The stirring blades' revolution and rotation speeds are 125±10 rpm and 285±10 rpm, respectively, to obtain the alkali-activated geopolymer coating.

[0073] Application Example 1

[0074] The geopolymer coating prepared in Example 1 was sprayed onto the surface of steel (reinforcing bars and steel plates). The nozzle diameter was 3 mm, the spraying pressure was 4 MPa, the nozzle-to-steel distance was 15 cm, the spraying time was 10 s, and the coating amount was 0.17 g / cm². 2Then, dry at room temperature for 30 minutes to obtain a geopolymer coating.

[0075] Application Example 2

[0076] The difference from Application Example 1 is that the geopolymer coating prepared in Example 1 is replaced with the geopolymer coating prepared in Example 2, and the rest is the same as Application Example 1.

[0077] Application Example 3

[0078] The difference from Application Example 1 is that the geopolymer coating prepared in Example 1 is replaced with the geopolymer coating prepared in Example 3, and the rest is the same as Application Example 1.

[0079] Application Example 4

[0080] The difference from Application Example 1 is that the geopolymer coating prepared in Example 1 is replaced with the geopolymer coating prepared in Example 4, and the rest is the same as Application Example 1.

[0081] Comparative Application Example 1

[0082] The difference from Application Example 1 is that the geopolymer coating prepared in Example 1 is replaced with the coating prepared in Comparative Example 1, and the rest is the same as Application Example 1.

[0083] Performance testing

[0084] (1) Corrosion resistance test

[0085] The coated steel bars / plates obtained from Comparative Application Example 1 and Application Examples 1-4 (as shown in Figure 1, where a is Comparative Application Example 1, b is Application Example 1, c is Application Example 2, d is Application Example 3, and e is Application Example 4) were subjected to salt spray corrosion tests (Figure 2) and adhesion tests (Figure 3). The salt spray test involved spraying the coated steel bars with a 5% sodium chloride solution in a salt spray test chamber for 14 days. The adhesion test used a PosiTestATA-20 adhesion tester to test the coated steel plates before and after immersion in a 5% sodium chloride solution for 14 days at a loading rate of 0.4 MPa / s.

[0086] Figure 1 shows the curing effect of the geopolymer coating. As can be seen from Figure 1, with the increase of graphene oxide content, the coating surface becomes smoother, denser, and thicker. However, due to excessive graphene oxide incorporation, the ribs of the coated steel bars in Application Example 4 become less distinct, and the smoothness decreases.

[0087] The mass loss rate of uncoated steel bars, comparative application example 1, and coated steel bars obtained from application examples 1 to 4 after salt spray corrosion test was tested. The results are shown in Table 1, and the corrosion morphology of coated steel bars after salt spray test is shown in Figure 4.

[0088] Table 1 Mass loss rate of coated steel bars

[0089]

[0090] As shown in Table 1, the mass loss rate of the coated steel bars formed by the geopolymer coating prepared in this invention is much lower than that of the comparative application example 1 and the uncoated steel bars. The coated steel bars in application example 3 have the lowest mass loss rate, at 0.44%, which is 69.2% lower than that of the comparative application example 1. This indicates that graphene oxide and geopolymer form a highly dense polymer network, which improves the density of the coating, reduces pore connectivity, and thus slows down the transport and penetration of chloride ions.

[0091] As shown in Figure 4, after 14 days of salt spray treatment, the rust diffusion of the coated steel bars in Example 3 was not obvious, and the degree of corrosion was relatively mild.

[0092] The adhesion of the coated steel plates obtained in Comparative Application Example 1 and Application Examples 1-4 before and after immersion in salt solution was tested, and the results are shown in Table 2.

[0093] Table 2 Adhesion of Coated Steel Sheets / MPa

[0094] Group Comparison Application Example 1 Application Example 2 Application Example 3 Application Example 4 Before Soaking 1.82 1.89 2.02 2.18 2.15 After Soaking 1.18 1.39 1.60 1.78 1.64 surface

[0095] As shown in Table 2, before immersion, Application Example 3 exhibited the highest adhesion, representing a 19.8% improvement compared to Comparative Application Example 1. After immersion, Application Example 3 showed the lowest adhesion loss rate at 18.3%. In contrast, Comparative Application Example 1 had an adhesion loss rate of 35.2%, meaning Application Example 3's adhesion loss rate was 48% lower than Comparative Application Example 1. This is because the oxygen-containing functional groups of graphene oxide form hydrogen bonds with the hydroxyl iron oxide protective film on the steel, enhancing the interfacial bonding ability and effectively resisting the expansion stress of corrosion products, thus preventing coating cracking and further diffusion of corrosion products.

[0096] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A geopolymer coating, characterized in that, The preparation method is as follows: (1) Preparation of alkali activator: Dissolve 4g of sodium hydroxide in 40g of deionized water to obtain sodium hydroxide solution, then mix the sodium hydroxide solution with 60g of water glass with a modulus of 2.2M to obtain alkali activator with a modulus of 1.5M and let it stand for 24h; (2) Preparation of graphene oxide dispersion: Take 0.1125g of graphene oxide and 104g of the above alkali activator and mix them in a magnetic stirrer at 600rpm for 1min, then add 0.75g of polycarboxylate superplasticizer and continue stirring at 1000rpm for 4min, and finally, use 120W power ultrasonic dispersion for 60min to obtain graphene oxide dispersion; (3) Preparation of geopolymer coating: Weigh 75g of fly ash with a calcium content of 5% and a particle size of 50μm, 45g of slag with a calcium content of 47% and a particle size of 10μm, 30g of metakaolin, 3g Polyvinyl alcohol powder with a molecular weight of 100,000 and 7.5g of titanium dioxide with a particle size of 1μm were poured into a mixing container and stirred at 60rpm for 2min. Then, 104.1125g of graphene oxide dispersion and 0.75g of silicone oil-type defoamer were added and stirred again at 100rpm for 5min to obtain the geopolymer coating. Metakaolin was obtained by calcining kaolin at 800℃ for 60min, and the particle size of the metakaolin was 5μm.

2. The application of the geopolymer coating of claim 1 in steel corrosion protection.

3. A method for preparing a geopolymer coating, characterized in that, The process includes the following steps: applying a geopolymer coating to the steel surface and drying it to obtain a geopolymer coating. The geopolymer coating is the geopolymer coating of claim 1.

4. The preparation method according to claim 3, characterized in that, The coating amount of the geopolymer coating is 0.17~0.25 g / cm³. 2 .

5. The preparation method according to claim 3, characterized in that, The coating is spraying; the diameter of the nozzle used for spraying is 4~6mm; the spraying pressure is 3~5MPa; the distance between the nozzle and the steel is 12~18cm; and the spraying time is 10~15s.

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