Steel hydrophobic coating as well as preparation method and application thereof

Abstract

The invention discloses a steel hydrophobic coating as well as a preparation method and application thereof. The coating comprises the following raw materials in parts by weight: 22-26 parts of monopotassium phosphate, 61-67 parts of magnesium oxide, 5-14 parts of a setting time regulating agent and 2-5 parts of isooctyl triethoxy silane. The preparation method comprises the following steps: mixing 5-14 parts of a setting time regulating agent and 30-34 parts of magnesium oxide to form a mixed solution A; and 2, mixing the solution A with 30-34 parts of magnesium oxide, 22-26 parts of potassium dihydrogen phosphate and 2-5 parts of isooctyl triethoxy silane at normal temperature, and stirring for reaction to obtain the steel hydrophobic coating. The invention also discloses an application of the steel hydrophobic coating in steel corrosion prevention. After the magnesium potassium phosphate gel, the borax and the isooctyl triethoxy silane are added into the raw materials of the coating, the hydrophobicity of the material is greatly improved, the service life is greatly prolonged, and the durability is greatly improved; the coating provides excellent corrosion resistance for the whole soaking period of the steel substrate.

Description

Technical Field

[0001] The present invention belongs to coatings and their preparation methods and applications, and specifically relates to a hydrophobic coating for steel and its preparation method and application. Background Art

[0002] Reinforced concrete has many advantages such as simple structure, low cost, excellent durability, and convenient construction. However, in the atmospheric environment and marine environment, both reinforced concrete structures will be invaded by (Cl - , SO 4 2- , CO 2 ). Especially, chloride ions will damage the passivation film on the surface of steel bars, causing the steel bars to corrode. There are various corrosion problems in marine structures such as marine ships, oil platforms, and port facilities, as well as onshore facilities such as crude oil storage tanks and factory equipment. Long-term corrosion degradation will promote the generation and development of fatigue cracks, and even lead to the ultimate failure of marine structures. According to statistics, the loss of marine corrosion accounts for about 33% of the total corrosion loss. However, as long as effective corrosion management methods are adopted, 25%-30% of the corrosion cost can be saved every year. At the same time, traditional cement concrete is mainly made of cement, sand, aggregates, etc. by mixing with water, and is often used in the fields of construction, civil engineering, transportation, etc. Due to its natural hydrophilicity, cement-based concrete will have problems related to water intrusion such as acid rain erosion, freeze-thaw damage, steel bar corrosion, and shrinkage cracking. At the same time, the evaporation of excess water in cement-based materials will generate pores, resulting in the penetration of external water and erosive ions through capillary absorption or flow through capillary pores under hydrostatic pressure, causing corrosion. Summary of the Invention

[0003] Object of the Invention: In order to overcome the deficiencies in the prior art, the object of the present invention is to provide a hydrophobic coating for steel with a long service life and good durability. Another object of the present invention is to provide a simple and convenient preparation method for the hydrophobic coating for steel. Still another object of the present invention is to provide an application of the hydrophobic coating for steel in steel corrosion prevention.

[0004] Technical Solution: A hydrophobic coating for steel according to the present invention comprises the following raw materials in parts by weight: 22-26 parts of potassium dihydrogen phosphate, 61-67 parts of magnesium oxide, 5-14 parts of setting time regulator, and 2-5 parts of isooctyltriethoxysilane.

[0005] Furthermore, the mass ratio of potassium dihydrogen phosphate to the sum of magnesium oxide and isooctyltriethoxysilane is 1:2.5-3.

[0006] Furthermore, the setting time regulator comprises boric acid solution, water, and sodium silicate.

[0007] Furthermore, the mass percentage of the boric acid solution is 2-5 wt%.

[0008] Furthermore, the average particle size of magnesium oxide is 20 - 30 μm.

[0009] Furthermore, the average particle size of potassium dihydrogen phosphate is 145 - 265 μm.

[0010] Furthermore, after the hydrophobic coating is fully cured, the growth rate of the static water contact angle is at least 190% compared to the coating without the addition of the modified material.

[0011] The preparation method of the steel hydrophobic coating described in the present invention includes the following steps:

[0012] Step 1, forming a mixed solution A by mixing 5 - 14 parts of the setting time regulator with 30 - 34 parts of magnesium oxide;

[0013] Step 2, mixing the solution A with 30 - 34 parts of magnesium oxide, 22 - 26 parts of potassium dihydrogen phosphate, and 2 - 5 parts of isooctyltriethoxysilane at room temperature, stirring and reacting to obtain the steel hydrophobic coating.

[0014] Furthermore, in Step 2, the stirring speed is 170 - 180 r / min and the time is 2 - 5 min.

[0015] The application of the steel hydrophobic coating described in the present invention in steel anti-corrosion.

[0016] Furthermore, the steel hydrophobic coating is applied to the surface of the Q235 steel substrate by spraying or brushing, and after curing and refining, a steel hydrophobic coating is formed.

[0017] Preparation principle: For the reaction mechanism of MPC, there are mainly two different theories: sol - gel and solution - diffusion. Among them, the sol - gel theory believes that magnesium oxide and potassium dihydrogen phosphate first dissolve in water respectively to form an aqueous solution of Mg(OH) 2 aqueous solution and KH 2 PO 4 aqueous solution. After the two types of aqueous solutions are mixed with each other, an acid - base neutralization reaction occurs to form a gel body, and at the same time, it promotes the formation of more hydrosols. Finally, the crystal nuclei of the reaction products grow continuously, contact and coalesce with each other, and the gel body is saturated and crystallized to form a crystal structure network with unhydrated magnesium oxide particles as the skeleton and the reaction products of phosphate crystallization as the binder.

[0018] Beneficial effects: Compared with the prior art, the present invention has the following significant features:

[0019] 1. After adding potassium magnesium phosphate cement, borax, and isooctyltriethoxysilane to the coating raw materials, the hydrophobicity of the original materials is greatly increased, and its service life and durability are greatly increased;

[0020] 2. It can be seen from the polarization curve that the corrosion potential remains almost unchanged and is always at a relatively high potential, indicating that during the immersion process, the corrosion driving force of the steel substrate in the 3.5% NaCl solution has not changed, and the coating provides excellent corrosion protection for the steel substrate throughout the immersion cycle. Description of the Drawings

[0021] Figure 1 is the static water contact angle data graph of the present invention without adding hydrophobic modification materials;

[0022] Figure 2 is the static water contact angle data graph of the present invention with 2% mass percentage of hydrophobic modification materials added;

[0023] Figure 3 is the static water contact angle data graph of the present invention with 3% mass percentage of hydrophobic modification materials added;

[0024] Figure 4 is the static water contact angle data graph of the present invention with 4% mass percentage of hydrophobic modification materials added;

[0025] Figure 5 is the static water contact angle data graph of the present invention with 5% mass percentage of hydrophobic modification materials added;

[0026] Figure 6 is the electrochemical polarization curve graph of the present invention with hydrophobic modification materials added;

[0027] Figure 7 is the microscopic morphology graph of the present invention with 3% mass percentage of hydrophobic modification materials added;

[0028] Figure 8 is the microscopic morphology graph of the present invention without adding hydrophobic modification materials. Detailed Description of the Invention

[0029] The materials, reagents, instruments, etc. used in the following examples can be obtained from commercial sources without special instructions. The experimental methods without specific conditions in the examples are usually carried out under conventional conditions or according to the conditions recommended by the manufacturer. The magnesium oxide is dead-burned magnesia (magnesite), with an average particle size of 24.65 μm, a specific surface area of 1489 m 2 / kg, a purity of ≥90.15%, purchased from Nanjing Wanhui Chemical Industry Co., Ltd., with a purity of ≥99%. The average particle size of potassium dihydrogen phosphate is 145 - 265 μm, with a purity of ≥99%. The mass percentage of boric acid liquid is 2%, purchased from Xilong Science Co., Ltd., with a purity of ≥95%. Isooctyltriethoxysilane (TS) is liquid, purchased from Jingchen Technology Co., Ltd., with a purity of ≥99.5%.

[0030] Example 1

[0031] A preparation method of a hydrophobic coating for steel, comprising the following steps:

[0032] (1) Mix 7 parts of boric acid solution with 6 parts of water, add 1 part of water glass and stir well, then add 32 parts of magnesium oxide and stir well to form a mixed solution A.

[0033] (2) Mix solution A with 31 parts of magnesium oxide (the alkaline component of magnesium potassium phosphate cement), 25 parts of potassium dihydrogen phosphate (the acidic component of magnesium potassium phosphate cement), and 2 parts of isooctyltriethoxysilane (TS) at room temperature, and stir and react at 180 r / min for 2 min to obtain a hydrophobic coating for steel, denoted as TS-2.

[0034] Application Example 1

[0035] Apply the hydrophobic coating for steel obtained in Example 1 to steel anti-corrosion. The specific steps are as follows: Spray the product obtained in Example 1 with an anti-corrosion coating thickness of 800 μm on the surface of Q235 steel with dimensions of 150 mm×150 mm×15 mm, and then cure and stand still in an environment of 20±3°C and 90% RH for 300 min.

[0036] Example 2

[0037] A preparation method of a hydrophobic coating for steel, comprising the following steps:

[0038] (1) Mix 6 parts of boric acid solution with 6 parts of water, add 1 part of water glass and stir well, then add 31 parts of magnesium oxide and stir well to form a mixed solution A.

[0039] (2) Mix solution A with 32 parts of magnesium oxide (the alkaline component of magnesium potassium phosphate cement), 23 parts of potassium dihydrogen phosphate (the acidic component of magnesium potassium phosphate cement), and 3 parts of isooctyltriethoxysilane (TS) at room temperature, and stir and react at 180 r / min for 2 min to obtain a hydrophobic coating for steel, denoted as TS-3.

[0040] Application Example 2

[0041] Apply the hydrophobic coating for steel obtained in Example 2 to steel anti-corrosion. The specific steps are as follows: Spray the product obtained in Example 2 with an anti-corrosion coating thickness of 800 μm on the surface of Q235 steel with dimensions of 150 mm×150 mm×15 mm, and then cure and stand still in an environment of 20±3°C and 90% RH for 300 min.

[0042] Example 3

[0043] A preparation method of a hydrophobic coating for steel, comprising the following steps:

[0044] (1) Mix 6 parts of boric acid solution with 6 parts of water, add 1 part of water glass and stir well, then add 30 parts of magnesium oxide and stir well to form a mixed solution A.

[0045] (2) Mix solution A with 30 parts of magnesium oxide (the alkaline component of magnesium potassium phosphate cement), 23 parts of potassium dihydrogen phosphate (the acidic component of magnesium potassium phosphate cement), and 4 parts of isooctyltriethoxysilane (TS) at room temperature, and stir and react at 180 r / min for 2 min to obtain a hydrophobic coating for steel, denoted as TS-4.

[0046] Example 4

[0047] A method for preparing a hydrophobic coating for steel, comprising the following steps:

[0048] (1) Mix 6 parts of boric acid solution with 6 parts of water, add 1 part of water glass and stir well, then add 30 parts of magnesium oxide and stir well to form a mixed solution A.

[0049] (2) Mix solution A with 30 parts of magnesium oxide (the alkaline component of magnesium potassium phosphate cement), 22 parts of potassium dihydrogen phosphate (the acidic component of magnesium potassium phosphate cement), and 5 parts of isooctyltriethoxysilane (TS) at room temperature, and stir and react at 180 r / min for 2 min to obtain a hydrophobic coating for steel, denoted as TS-5.

[0050] Example 5

[0051] A method for preparing a hydrophobic coating for steel, comprising the following steps:

[0052] (1) Mix 2 parts of boric acid solution with 2 parts of water, add 1 part of water glass and stir well, then add 34 parts of magnesium oxide and stir well to form a mixed solution A.

[0053] (2) Mix solution A with 34 parts of magnesium oxide (the alkaline component of magnesium potassium phosphate cement), 26 parts of potassium dihydrogen phosphate (the acidic component of magnesium potassium phosphate cement), and 3 parts of isooctyltriethoxysilane (TS) at room temperature, and stir and react at 170 r / min for 5 min to obtain a hydrophobic coating for steel.

[0054] Comparative Example 1

[0055] The remaining steps of this comparative example are the same as those of Example 1, and the only difference is that: the isooctyltriethoxysilane (TS) liquid is omitted and an equal mass of dead-burned magnesium oxide is added, that is, 0 part of octyltriethoxysilane (TS) liquid and 72 parts of dead-burned magnesium oxide are used in step (1), and the prepared paste is denoted as KB.

[0056] Comparative Example 2

[0057] The remaining steps of this comparative example are the same as those of Example 1, and the only difference is that: 6 parts of octyltriethoxysilane (TS) liquid. It was found that the fluidity of the material was too large and it could not be effectively added.

[0058] The coatings obtained in Examples 1 to 4 and Comparative Example 1 were sprayed on the surface of Q235 steel according to the method of Application Example 1, and test blocks of 150 mm × 150 mm × 15 mm were made in the order of standard numbers KB, TS-2, TS-3, TS-4, and TS-5, and the static water contact angle was detected on a static water contact angle tester. It can be seen from Table 1 that as the TS content increases, the static water contact angles of each group of specimens gradually increase. This is because the TS molecules in the coating hydrolyze into silanols under alkaline conditions with the hydration products of portland cement, calcium silicate hydrate (C—S—H) and Ca(OH) 2 The surface chemical bonds are hydrolyzed into silanols, and the two hydroxyl groups of TS and the silanols react with the hydroxyl groups on the surface of the hydration products, and stable Si—O—Si chemical bonds are formed on the cement surface through Si—O bonds. The hydroxyl groups on the surface of the cement particles react and are bonded to the surface of the magnesium oxychloride cement particles through stable Si—O—Si bonds. At the same time, the surface with a double fractal structure formed by a sub-millimeter grid structure and nano-scale needle-like phases becomes rougher, and —CH 3 and —CH 2 groups can effectively reduce the surface energy. Thus, it shows that after modification, the magnesium phosphate cement has obtained strong surface hydrophobicity.

[0059] Table 1 Static water contact angle data of the coatings

[0060] Number Left hydrostatic contact angle Right hydrostatic contact angle Lifting rate KB 41.03° 40.6° 0 TS-2 79.15° 79.61° 194％ TS-3 103.08° 93.17° 242.50％ TS-4 107.48° 105.77° 262％ TS-5 114.71° 118.08° 287.50％

[0061] Electrochemical polarization curve test:

[0062] The coatings of Examples 1 to 4 and Comparative Example 1 were sprayed on the surface of the steel according to the method of Application Example 1, and after setting, they were immersed in a NaCl solution with a mass concentration of 3.5 ± 0.3%.

[0063] As Figures 1 to 5 , for the static water contact angle diagrams of the modified magnesium phosphate cement coatings without and with 2%, 3%, 4%, and 5% isooctyltriethoxysilane (TS) added, it can be seen that as the amount of the modified material increases, the left and right static water contact angles of the coating show an increasing trend.

[0064] As Figure 6 , an obvious passivation zone appears in the polarization curve after adding 2% TS; while under the same immersion time, only an over-passivation zone exists in the polarization curves with other TS contents. As the TS content increases, the corrosion potential of the coating after immersion changes little. It can be seen from Figure 1 that the modified magnesium phosphate cement coating with 3% isooctyltriethoxysilane (TS) added has the strongest corrosion resistance, and the corrosion potential is basically stable at about -0.6 V.

[0065] As Figure 7, after the crystals in TS were polarized, no obvious crystal structure damage or erosion was found, and there were no obvious voids. It can also be found from the figure that there are fine particles on the crystal surface. This is because the polymer material isooctyltriethoxysilane (TS) forms a polymer film on the crystal surface, thus preventing water molecules from invading the interior of the crystal and causing corrosion and damage. Compared with the KB group as Figure 8 , there is no polymer film on the surface, so its resistance differs by an order of magnitude from that of the modified potassium magnesium phosphate cement material.

[0066] The electrochemical fitting results of the coating materials in Examples 1 to 3 are shown in Table 2. It can be seen from Table 2 the polarization resistance R p , corrosion potential E coor , corrosion current I coor , anodic slope B of the polarization curve a and cathodic slope B of the polarization curve c of the numerical values and their variation laws.

[0067] Table 2 Fitting results of the polarization curves of the coatings

[0068]

[0069] It can be seen from the data in Table 2 that after adding TS with proportions of 2%, 3%, 4%, and 5% of the total gel material, the specific changes in the corrosion potential E corr , corrosion current density I corr and polarization resistance R p of the coating can be seen. Among them, the corrosion potential E corr of the coating represents the corrosion state of the environment where the coating is located. The smaller the corrosion potential, the stronger the corrosion of the coating. The corrosion current density I corr of the coating represents the ability of the coating to prevent the charge in the corrosion solution from passing through the coating and transferring to the metal substrate, reflecting the anti-permeability ability and internal defect situation of the coating. The larger the corrosion current density, the weaker the anti-charge transfer ability of the coating. The polarization resistance R p directly reflects the protection ability of the coating for the metal substrate. The larger the polarization resistance, the better the anti-corrosion performance of the coating. And B a and B c are the parameters for calculating the polarization resistance R p . The polarization resistance R p of the coating is significantly improved compared with KB throughout the immersion period. During the immersion process, the TS molecules in the coating react with the hydration products of portland cement, calcium silicate hydrate (C—S—H) and Ca(OH) 2The surface chemical bonds are hydrolyzed into silanols under alkaline conditions. Two hydroxyl groups of TS and the hydroxyl groups on the surface of the silanols react with the hydroxyl groups on the surface of the hydration product, forming stable Si—O—Si chemical bonds on the cement surface through Si—O bonds. This results in a decrease in the surface energy of the coating, thereby preventing water molecules from invading the interior of the magnesium phosphate coating and causing corrosion. When soaked for 28 days, the higher the content of TS, the more positive the corrosion potential E coor of the coating. Among them, the R p value of TS-5 is the largest, which is about 864% higher than that of the blank group, indicating that adding about 5% of isooctyltriethoxysilane (TS) to the coating will have a better inhibitory effect on the anodic reaction and make the corrosion resistance stronger.

[0070] In the above examples, Example 4 is the optimal example.

Claims

1. A hydrophobic coating for steel, characterized in that: The invention comprises the following raw materials in parts by weight: 22 to 26 parts of potassium dihydrogen phosphate, 60 to 68 parts of magnesium oxide, 5 to 14 parts of a setting time regulator, and 2 to 5 parts of isooctyl triethoxy silane.

2. A hydrophobic coating for steel according to claim 1, characterized in that: The mass ratio of the potassium dihydrogen phosphate to the sum of magnesium oxide and isooctyltriethoxysilane is 1:2.5-3.

3. A hydrophobic coating for steel according to claim 1, characterized in that: The coagulation time regulator includes boric acid solution, water and water glass.

4. A hydrophobic coating for steel according to claim 1, characterized in that: The mass percentage of the boric acid solution is 2-5 wt %.

5. A hydrophobic coating for steel according to claim 1, characterized in that: The average particle size of the magnesium oxide is 20 to 30 μm.

6. A hydrophobic coating for steel according to claim 1, characterized in that: The average particle size of the potassium dihydrogen phosphate is 145 to 265 μm.

7. A hydrophobic coating for steel according to claim 1, characterized in that: After the coating is completed and fully cured, its static water contact angle reaches more than 100°.

8. A method for preparing a hydrophobic coating for steel according to any one of claims 1 to 7, characterized in that: The following steps are involved: Step 1, 5 to 14 parts of a setting time regulator and 30 to 34 parts of magnesium oxide form a mixed solution A; Step 2: Mix solution A with 30 to 34 parts of magnesium oxide, 22 to 26 parts of potassium dihydrogen phosphate, and 2 to 5 parts of isooctyltriethoxysilane at room temperature, and stir to react to obtain a hydrophobic coating for steel.

9. The method for preparing a hydrophobic coating for steel according to claim 7, characterized in that: In the step 2, the stirring speed is 170-180 r / min, and the stirring time is 2-5 min.

10. Use of the steel hydrophobic coating according to claim 1 in steel corrosion protection.

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