Magnesium phosphate inorganic hydrophobic anticorrosive repair coating as well as preparation method and application thereof

Abstract

The invention belongs to the field of coatings, and particularly relates to a magnesium phosphate inorganic hydrophobic anticorrosive repair coating as well as a preparation method and application thereof. The preparation method comprises the following steps: adding an organic silane coupling agent into an ethanol water solution, uniformly stirring, then adding to-be-modified powder, continuously stirring, and after uniformly stirring, cleaning, centrifuging and drying to obtain hydrophobic particles; kH2PO4, a retarder and deionized water are uniformly mixed, then MgO and hydrophobic particles are added, and the magnesium phosphate inorganic hydrophobic anticorrosive repair coating is obtained after uniform stirring. According to the invention, the cohesiveness of the magnesium phosphate cement-based binding material is utilized, hydrophobic slag particles are combined, the surface roughness and surface energy are regulated and controlled, and a durable, fire-resistant and corrosion-resistant magnesium phosphate cement-based hydrophobic coating can be rapidly formed when the coating is brushed on the surface of low-carbon steel at normal temperature.

Description

Technical Field

[0001] This invention belongs to the field of coatings, specifically relating to a magnesium phosphate inorganic hydrophobic anti-corrosion and repair coating, its preparation method, and its application. Background Technology

[0002] Hydrophobic surfaces offer advantages such as antifouling, self-cleaning, and high corrosion resistance, making them widely used in building infrastructure, power control centers, and data processing centers. Currently, hydrophobic coatings are applied to concrete structures such as bridges and buildings to resist external environmental erosion and protect metals from corrosion. However, common hydrophobic coatings suffer from drawbacks such as weak adhesion, easy wear, and poor heat resistance. Therefore, there is a need to develop novel hydrophobic coatings.

[0003] Currently, hydrophobic coatings are divided into organic and inorganic hydrophobic coatings. Organic hydrophobic coatings possess both hydrophobic and hydrophilic functional groups, but they have poor durability and require multiple functional group designs, resulting in higher costs. Inorganic hydrophobic materials struggle to balance hydrophobicity and adhesion, leading to weak adhesion between the coating and the substrate, low surface strength, and poor durability. Summary of the Invention

[0004] To address the shortcomings of existing hydrophobic coatings, such as weak adhesion, easy wear, and poor heat resistance, this invention provides a magnesium phosphate inorganic hydrophobic anti-corrosion and repair coating, its preparation method, and its application. By utilizing the adhesive properties of magnesium phosphate cement-based cementitious materials and combining them with hydrophobic slag particles, the surface roughness and surface energy are controlled. A durable, fire-resistant, and corrosion-resistant magnesium phosphate cement-based hydrophobic coating can be quickly formed on the surface of low-carbon steel at room temperature.

[0005] The technical solution provided by this invention is as follows:

[0006] A method for preparing an inorganic hydrophobic anti-corrosion and repair coating of magnesium phosphate includes the following steps:

[0007] The organosilane coupling agent was added to an ethanol aqueous solution and stirred until homogeneous. Then, the powder to be modified was added and stirred again. After being stirred until homogeneous, the mixture was washed, centrifuged and dried to obtain hydrophobic particles.

[0008] KH2PO4, retarder and deionized water are mixed evenly, then MgO and hydrophobic particles are added and stirred evenly to obtain magnesium phosphate inorganic hydrophobic anti-corrosion and repair coating.

[0009] Furthermore, the powder to be modified is a commercially available slag powder or steel slag powder.

[0010] Furthermore, the retarder is one or more of borax, boric acid, sodium hexametaphosphate, sodium tripolyphosphate, and disodium hydrogen phosphate.

[0011] Furthermore, the ethanol-water solution is prepared from anhydrous ethanol and deionized water, with a volume ratio of anhydrous ethanol to deionized water of 3 to 5:1.

[0012] Furthermore, the organosilane coupling agent is hexadecyltrimethoxysilane or octadecyltrimethoxysilane.

[0013] Furthermore, the molar ratio of KH2PO4 to MgO is 1:3~12.

[0014] Furthermore, the amount of retarder used is 3 to 10 wt% of the total amount.

[0015] The present invention also provides an inorganic hydrophobic anti-corrosion and repair coating of magnesium phosphate, which is prepared by the above preparation method.

[0016] The present invention also provides the application of the above-mentioned magnesium phosphate inorganic hydrophobic anti-corrosion and repair coating in improving the durability, fire resistance and corrosion resistance of concrete or metal surfaces.

[0017] Furthermore, the magnesium phosphate inorganic hydrophobic anti-corrosion and repair coating is placed in a mold to form a shape, or evenly applied to the concrete or metal surface with a thickness of 0.5-2mm, and cured at 20±2℃.

[0018] A method for preparing an inorganic hydrophobic anti-corrosion and repair coating of magnesium phosphate specifically includes the following steps:

[0019] (1) Preparation of hydrophobic particles: Anhydrous ethanol and deionized water are mixed in a volume ratio of 3:1-5:1, and then 3%-15% of hexadecyltrimethoxysilane (HDTMS) or octadecyltrimethoxysilane (ODTMS) or other low surface energy substances are added. The low surface energy substances are substances with a surface energy of < 30 mN / m. Stir for 15-30 min, then add the powder to be modified, and continue stirring for 5-12 h. After the process, wash, centrifuge and dry to obtain hydrophobic particles.

[0020] (2) Preparation of magnesium phosphate cement coating: The raw materials for preparing magnesium phosphate cement coating include MgO, KH2PO4, retarder, deionized water, etc. The magnesium phosphate cement coating is prepared according to the phosphorus / magnesium ratio = 1:3-1:12. The amount of borax is 3-10% of the mass of magnesium oxide, the water-solid ratio is 0.12-0.25, and hydrophobic particles are added. The stirring time is 5-10 min.

[0021] After the coating slurry is prepared, it is placed in a mold to form, or it is evenly applied to the concrete or metal surface with a thickness of 0.5-2mm, and cured at 20±2℃.

[0022] Beneficial effects

[0023] Traditional organic superhydrophobic coatings have poor fire resistance because organic materials are prone to decomposition or combustion at high temperatures. Traditional inorganic hydrophobic coatings have hydrophilic bulk materials. To make the coating hydrophobic, a layer of low surface energy molecules is usually adsorbed on the coating surface. However, this surface layer has poor wear resistance and detaches easily, resulting in poor coating durability. Furthermore, although traditional silicate materials can be hydrophobically modified, their adhesion to the substrate is poor due to the obstruction caused by the hydrophobic groups. Therefore, an intermediate coating layer is needed between the hydrophobic cement and the substrate to enhance adhesion. This method is relatively complex.

[0024] This invention utilizes the phosphate groups in magnesium phosphate cement to form chemical bonds with the matrix, thereby improving adhesion and avoiding the formation of the aforementioned intermediate layer. Simultaneously, hydrophobic silanes form Mg-O-Si-O-Me chemical bonds with the matrix, thus combining hydrophobicity and adhesion. Furthermore, silanes promote the formation of Mg-O-Si-O-Al and RO-Si-O-Mg-PO4 within the magnesium phosphate cement-based coating. 3- - and other chemical bonds enable the magnesium phosphate cement-based coating to form a relatively dense nano-micro roughness structure, ultimately achieving a simple one-step method for preparing durable, fire-resistant, and corrosion-resistant inorganic hydrophobic coatings.

[0025] This invention employs a hydrophobic slag-modified magnesium phosphate cement-based material. The hydrophobic slag hydration reaction generates micro-nano-scale hydration products, constructing a micro-nano roughness microstructure within the coating. Adsorbed molecules on the slag surface provide low surface energy. The combination of these two elements creates overall hydrophobicity in the coating. Simultaneously, the phosphoric acid compounds generated during the hydration reaction chemically bond with the matrix, ensuring adhesion. The neutralization reaction mechanism of the magnesium phosphate cement-based material provides rapid setting characteristics. Its solid-liquid structure provides a continuous anti-corrosion and corrosion-transformation microenvironment for the metal substrate. Therefore, it solves the problem of achieving both adhesion and hydrophobicity in inorganic coatings, realizing a hydrophobic and durable inorganic anti-corrosion and repair coating. Furthermore, the raw material, slag, is a solid waste, representing waste recycling. Attached Figure Description

[0026] Figure 1 The image shows a comparison of the contact angles of ordinary magnesium phosphate cement, magnesium phosphate cement containing 40% ordinary slag, and magnesium phosphate cement containing 40% hydrophobic modified slag. Figure 2 This is a comparison chart of contact angles when the slag contains 40% hydrophobic modified slag and 20% hydrophobic modified slag. Figure 3 A comparison of the surface and cross-sectional contact angles of magnesium phosphate cement containing 40% hydrophobic modified slag. Figure 4 The image shows a comparison of the surface and cross-sectional contact angles of slag magnesium phosphate cement modified with 40% hexadecyltrimethoxysilane and slag magnesium phosphate cement modified with 40% stearic acid. Figure 5The AC impedance spectra are for a 40% ordinary slag magnesium phosphate cement coating and a 40% hydrophobic modified slag magnesium phosphate cement coating. Figure 6 This is a comparison chart of the contact angles of 40% hydrophobically modified slag with the addition of 2wt% nanocellulose and ordinary magnesium phosphate cement. Figure 7 This is a comparison chart of contact angles when the slag contains 40% hydrophobically modified slag and the retarder is either 10% borax or 10% boric acid. Figure 8 The contact angle comparison diagram shows the magnesium-to-phosphorus ratios of 5, 8, and 12 when the slag contains 40% hydrophobic modified slag. Figure 9 The effect of hydrophobic magnesium phosphate cement coating on the properties of different substrates. Detailed Implementation

[0027] Example 1

[0028] Effect of HDTMS modified micropowder on the hydrophobic properties of magnesium phosphate cement coating

[0029] The main steps are as follows:

[0030] (1) Mix 90ml of anhydrous ethanol, 10ml of deionized water and 5ml of HDTMS for 30min, then add 10g of slag or steel slag powder and continue stirring for 12h. After the mixture is finished, wash, centrifuge and dry to obtain hydrophobic slag particles (HDTMS@GBFS).

[0031] (2) Mix 6.8g KH2PO4, 1g borax and 3.4g deionized water for 2 minutes, then add 6g or 10g MgO and 4g or 0g GBFS, and continue stirring for 5 minutes. Then pour the prepared slurry into a mold to form it.

[0032] (3) Mix 6.8g KH2PO4, 1g borax and 3.4g deionized water for 2 minutes, then add 6g or 8g MgO and 4g or 2g HDTMS@GBFS, and continue stirring for 5 minutes. Then pour the prepared slurry into a mold to form it.

[0033] (4) Perform hydrophobicity test on the hydrophobic specimen. Test conditions: break the specimen in the middle, drop deionized water onto the surface or cross-section, and observe the state of the water droplet.

[0034] (5) Figure 1 As shown, water droplets do not form water beads on the surfaces of ordinary magnesium phosphate cement and cement with added ordinary slag, exhibiting hydrophilicity, while magnesium phosphate cement with added hydrophobic slag exhibits hydrophobicity. Figure 2 As shown, with the increase of hydrophobic slag content, the hydrophobic angle increases, and the hydrophobicity improves. Figure 3As shown, the hydrophobic angles of the sample surface and cross-section are similar, indicating that the hydrophobic coating exhibits excellent hydrophobicity overall.

[0035] Example 2

[0036] Effects of different low surface energy modified slags on the hydrophobic properties of magnesium phosphate cement coatings

[0037] The main steps are as follows:

[0038] (1) Mix 90ml of anhydrous ethanol, 10ml of deionized water and 5ml of HDTMS for 30min, then add 10g of slag powder and continue stirring for 12h. After the mixture is finished, wash, centrifuge and dry to obtain hydrophobic slag particles (HDTMS@GBFS).

[0039] (2) Mix 25g of anhydrous ethanol and 0.5g of stearic acid (SA) at 50°C until the stearic acid is completely dissolved. Then add 5g of slag powder and continue stirring for 2 hours. After the mixture is finished, wash, centrifuge and dry to obtain hydrophobic slag particles (SA@GBFS).

[0040] (3) Mix 6.8 KH2PO4, 1g borax, and 3.4g deionized water for 2 minutes, then add 6g MgO and 4g ODTMS@GBFS or SA@GBFS, and continue stirring for 5 minutes. Then pour the prepared slurry into a mold to form it.

[0041] (4) Perform hydrophobicity test on the hydrophobic specimen. Test conditions: break the specimen in the middle, drop deionized water onto the surface, and observe the state of the water drop.

[0042] (5) Figure 4 As shown, HDTMS-modified slag magnesium phosphate cement exhibits better hydrophobicity, while SA-modified slag magnesium phosphate cement shows no obvious contact angle and poor hydrophobicity. This is because HDTMS is firmly bonded to slag through covalent bonds, and the resulting hydrophobic structure can stably exert its modifying effect; while stearic acid only has a weak physical or ionic adsorption bond with slag, and it will quickly dissociate and be coated by hydration products in the magnesium phosphate cement system, causing the hydrophobic sites to completely fail and ultimately failing to impart hydrophobicity to the magnesium phosphate cement.

[0043] Example 3

[0044] The effect of HDTMS-modified slag on the resistivity of magnesium phosphate cement coating

[0045] The main steps are as follows:

[0046] (1) Polish the surface of the steel sheet with 1200# and 1500# Sic sandpaper respectively, rinse the surface with deionized water, rinse the surface with ethanol, and clean the surface with ethanol for three minutes in an ultrasonic cleaner to remove surface impurities. Dry it with hot air and set it aside.

[0047] (2) Mix 90ml of anhydrous ethanol, 10ml of deionized water and 5ml of HDTMS for 30min, then add 10g of slag or steel slag powder and continue stirring for 12h. After the mixture is finished, wash, centrifuge and dry to obtain hydrophobic slag particles (HDTMS@GBFS).

[0048] (3) Mix 6.8g KH2PO4, 1g borax and 3.4g deionized water for 2 minutes, then add 6g MgO and 4g HDTMS@GBFS, and continue stirring for 5 minutes. Then spread evenly onto the treated steel sheet.

[0049] (4) Electrochemical tests were performed on the coated steel sheet. Test conditions: The sample was placed in NaCl solution (3.5wt%) for electrochemical impedance spectroscopy.

[0050] (5) Figure 5 As shown, the resistivity of ordinary slag magnesium phosphate cement coating is 1188 Ω·cm. 2 The resistivity of the hydrophobic slag magnesium phosphate cement coating is 2903 Ω·cm. 2 The hydrophobic magnesium phosphate cement coating of slag has a higher resistivity. This is because the hydrophobic modification causes an air layer to form between the coating and the solution, thereby increasing its resistivity.

[0051] Example 4

[0052] Effects of polymers on the hydrophobicity and toughness of magnesium phosphate cement coatings

[0053] The main steps are as follows:

[0054] (1) Mix 90ml of anhydrous ethanol, 10ml of deionized water and 5ml of HDTMS for 30min, then add 10g of slag or steel slag powder and continue stirring for 12h. After the mixture is finished, wash, centrifuge and dry to obtain hydrophobic slag particles (HDTMS@GBFS).

[0055] (2) Mix 6.8 KH2PO4, 1g borax, 0.12g nanocellulose, and 3.4g deionized water for 2 minutes, then add 6g MgO and 4g HDTMS@GBFS, and continue stirring for 5 minutes. Then pour the prepared slurry into a mold to form it.

[0056] (3) Perform hydrophobicity test on the hydrophobic specimen. Test conditions: break the specimen in the middle, drop deionized water onto the surface, and observe the state of the water droplet.

[0057] (4) Figure 6 As shown, the hydrophobic slag-modified magnesium phosphate cement sample with 2 wt% nanocellulose still exhibits hydrophobicity, but the contact angle is smaller than that of the control group. This is because the strong hydrophilicity of nanocellulose itself directly enhances the overall hydrophilicity of magnesium phosphate cement, thereby inhibiting hydrophobic properties. However, due to the small amount added, the overall hydrophobicity is not completely lost.

[0058] Example 5

[0059] The effect of retarder type on the hydrophobicity of magnesium phosphate cement coating

[0060] The main steps are as follows:

[0061] (1) Mix 90ml of anhydrous ethanol, 10ml of deionized water and 5ml of HDTMS for 30min, then add 10g of slag or steel slag powder and continue stirring for 12h. After the mixture is finished, wash, centrifuge and dry to obtain hydrophobic slag particles (HDTMS@GBFS).

[0062] (2) Mix 6.8g KH2PO4, 1g borax or boric acid, and 3.4g deionized water for 2 minutes, then add 6g MgO and 10g HDTMS@GBFS, and continue stirring for 5 minutes. Then pour the prepared slurry into a mold to form it.

[0063] (3) Perform hydrophobicity test on the hydrophobic specimen. Test conditions: break the specimen in the middle, drop deionized water onto the surface, and observe the state of the water droplet.

[0064] (4) Figure 7 As shown, both hydrophobic slag-modified magnesium phosphate cement exhibited hydrophobicity when borax or boric acid was used as a retarder. The sample with added borax showed a larger hydrophobic angle and better hydrophobicity. This is because borax's gentle regulation prevents uncontrolled hydration and protects hydrophobic sites from being buried; while boric acid exacerbates the acidity of the slurry, often damaging hydrophobic functional groups.

[0065] Example 6

[0066] Effect of magnesium-to-phosphorus ratio on the hydrophobicity of magnesium phosphate cement coating

[0067] The main steps are as follows:

[0068] (1) Mix 90ml of anhydrous ethanol, 10ml of deionized water and 5ml of HDTMS for 30min, then add 10g of slag or steel slag powder and continue stirring for 12h. After the mixture is finished, wash, centrifuge and dry to obtain hydrophobic slag particles (HDTMS@GBFS).

[0069] (2) Weigh 6g MgO, 4g HDTMS@GBFS, and 1g borax. Then weigh KH2PO4 according to the magnesium-to-phosphorus molar ratios of 5:1, 8:1, and 12:1. Weigh deionized water according to a water-to-cement ratio of 0.2. Mix KH2PO4, borax, and deionized water for 2 minutes, then add MgO and HDTMS@GBFS and continue stirring for 5 minutes. Finally, pour the prepared slurry into a mold to form the slurry.

[0070] (3) Perform hydrophobicity test on the hydrophobic specimen. Test conditions: break the specimen in the middle, drop deionized water onto the surface, and observe the state of the water droplet.

[0071] (4) Figure 8 As shown, hydrophobic slag enables cements with different magnesium-to-phosphorus ratios to exhibit hydrophobicity, with larger hydrophobic angles and better hydrophobicity at magnesium-to-phosphorus ratios of 5 and 8. This is because as the magnesium-to-phosphorus ratio increases, more unreacted MgO is produced, leading to an overall increase in hydrophilicity. However, a high magnesium-to-phosphorus ratio also results in poorer slurry rheology, making the hydrophobic slag more prone to agglomeration and uneven dispersion, thus affecting overall hydrophobicity.

[0072] Example 7

[0073] Influence of hydrophobic magnesium phosphate cement coating on the properties of different substrates

[0074] The main steps are as follows:

[0075] (1) Polish the magnesium alloy surface with 1200# and 1500# Sic sandpaper respectively, rinse the surface with deionized water, rinse the surface with ethanol, and clean the surface with ethanol for three minutes in an ultrasonic cleaner to remove surface impurities. Dry it with hot air and set it aside.

[0076] (2) Mix 90ml of anhydrous ethanol, 10ml of deionized water and 5ml of HDTMS for 30min, then add 10g of slag or steel slag powder and continue stirring for 12h. After the mixture is finished, wash, centrifuge and dry to obtain hydrophobic slag particles (HDTMS@GBFS).

[0077] (3) Mix 6.8g KH2PO4, 1g borax and 3.4g deionized water for 2 minutes, then add 6g MgO and 4g HDTMS@GBFS, and continue stirring for 5 minutes. Then evenly apply it to the treated magnesium alloy.

[0078] (4) Electrochemical tests were performed on the coated magnesium alloy. Test conditions: The sample was placed in a NaCl solution (3.5 wt%) for Tafel testing. Results Figure 9 As shown, the results indicate that the applied coating significantly improves the corrosion resistance of magnesium alloys. In the Tafel curve, the corrosion current density of the coated sample is significantly reduced, indicating that the coating is corrosive to ions (such as Cl-).- The penetration of ) constitutes an effective physical barrier.

Claims

1. A method for preparing a magnesium phosphate inorganic hydrophobic anticorrosive repair coating, characterized in that, Includes the following steps: The organosilane coupling agent was added to an ethanol aqueous solution and stirred until homogeneous. Then, the powder to be modified was added and stirred again. After stirring until homogeneous, the mixture was washed, centrifuged and dried to obtain hydrophobic particles. KH2PO4, retarder and deionized water are mixed evenly, then MgO and hydrophobic particles are added and stirred evenly to obtain magnesium phosphate inorganic hydrophobic anti-corrosion and repair coating.

2. The preparation method of the magnesium phosphate inorganic hydrophobic anti-corrosion and repair coating according to claim 1, characterized in that, The powder to be modified is slag powder or steel slag powder.

3. The preparation method of the magnesium phosphate inorganic hydrophobic anti-corrosion and repair coating according to claim 1, characterized in that, The retarder is one or more of borax, boric acid, sodium hexametaphosphate, sodium tripolyphosphate, and disodium hydrogen phosphate.

4. The preparation method of the magnesium phosphate inorganic hydrophobic anti-corrosion and repair coating according to claim 1, characterized in that, The ethanol-water solution is prepared from anhydrous ethanol and deionized water, with a volume ratio of anhydrous ethanol to deionized water of 3 to 5:

1.

5. The preparation method of the magnesium phosphate inorganic hydrophobic anti-corrosion and repair coating according to claim 1, characterized in that, The organosilane coupling agent is hexadecyltrimethoxysilane or octadecyltrimethoxysilane.

6. The preparation method of the magnesium phosphate inorganic hydrophobic anti-corrosion and repair coating according to claim 1, characterized in that, The molar ratio of KH2PO4 to MgO is 1:3~12.

7. The preparation method of the magnesium phosphate inorganic hydrophobic anti-corrosion and repair coating according to claim 1, characterized in that, The amount of retarder is 3 to 10 wt% of the total amount.

8. A magnesium phosphate inorganic hydrophobic anti-corrosion and repair coating, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the magnesium phosphate inorganic hydrophobic anti-corrosion and repair coating according to claim 8 in improving the durability, fire resistance and corrosion resistance of concrete or metal surfaces.

10. The application according to claim 9, characterized in that, Magnesium phosphate inorganic hydrophobic anti-corrosion and repair coating is placed in a mold to form a shape, or it is evenly applied to the concrete or metal surface with a thickness of 0.5-2mm, and cured at 20±2℃.

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