TARGETED CORROSION INHIBITOR FOR MARINE REINFORCED CONCRETE, AND PREPARATION AND APPLICATION THEREOF

Abstract

A targeted corrosion inhibitor for marine reinforced concrete, and a preparation and application thereof. The targeted corrosion inhibitor is a nano silver-loaded nitrite-intercalated layered double hydroxide. The targeted corrosion inhibitor is prepared based on interlayer ion exchangeability of layered double hydroxides and specific recognition of Ag.sup.+ to chloride ions.

Claims

1. A targeted corrosion inhibitor for marine reinforced concrete, wherein the targeted corrosion inhibitor is a nano silver-loaded nitrite-intercalated layered double hydroxide.

2. The targeted corrosion inhibitor of claim 1, wherein the nitrite-intercalated layered double hydroxide is a nitrite-intercalated Ca—Al layered double hydroxide.

3. A method for protecting marine reinforced concrete, comprising: introducing the targeted corrosion inhibitor of claim 1 into the marine reinforced concrete.

4. A method for protecting marine reinforced concrete, comprising: introducing the targeted corrosion inhibitor of claim 2 into the marine reinforced concrete.

5. A method for preparing the targeted corrosion inhibitor of claim 2, comprising: (S1) dissolving sodium carbonate, calcium hydroxide, sodium metaaluminate, silver nitrate and sodium nitrite in boiling water, respectively, to obtain a first solution, a second solution, a third solution, a fourth solution and a fifth solution; (S2) mixing the first solution, the second solution and the third solution followed by pH adjustment to obtain a reaction solution; and stirring the reaction solution; (S3) subjecting the reaction solution to a hydrothermal reaction followed by vacuum filtration to obtain a filter cake; and washing, drying and grinding the first filter cake to obtain a Ca-layered double hydroxide (Ca-LDH); (S4) calcining the Ca-LDH obtained in step (S3) to obtain a Ca-layered double oxide (Ca-LDO); (S5) dissolving the Ca-LDO in the fourth solution followed by pH adjustment, stirring and vacuum filtration to obtain a second filter cake; and washing and drying to the second filter cake to obtain an Ag/Ca-layered double oxide (Ag/Ca-LDO); and (S6) dissolving the Ag/Ca-LDO in the fifth solution followed by stirring at room temperature for 24-48 h, and vacuum filtration to obtain a third filter cake; and washing and drying the third filter cake to obtain the targeted corrosion inhibitor.

6. The method of claim 5, wherein in step (S1), a concentration of the first solution is 0.2-0.5 mol/L; a concentration of the second solution is 1-3 mol/L; a concentration of the third solution is 0.25-1.5 mol/L; a concentration of the fourth solution is 0.1-0.5 mol/L; and a concentration of the fifth solution is 0.5-2.0 mol/L.

7. The method of claim 5, wherein in step (S2), a volume ratio of the first solution to the second solution to the third solution is 2:1:1.

8. The method of claim 5, wherein in step (S3), the hydrothermal reaction is performed at 80-120° C. for 24-48 h.

9. The method of claim 5, wherein in step (S4), the Ca-LDH is calcined at 500-900° C. for 3-6 h.

10. The method of claim 5, wherein in step (S5), a ratio of a weight of the Ca-LDO to a volume of the fourth solution is (0.5-1.0) g:40 mL.

11. The method of claim 5, wherein in step (S6), a ratio of a weight of the Ag/Ca-LDO to the fifth solution is (0.5-1.5) g:200 mL.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] FIG. 1 illustrates X-ray diffraction (XRD) patterns of Ag/Ca—NO.sub.2 LDH prepared in Example 1 and Ag/Ca-LDO prepared in Comparative Example 1;

[0035] FIG. 2 depicts adsorption isotherms of chloride ions on the Ag/Ca—NO.sub.2 LDH prepared in Example 1; and

[0036] FIGS. 3A-3B show electrochemical impedance spectra of reinforcing bars in different groups after 48-h immersion, where FIG. 3A: Nyquist diagram; and FIG. 3B: Bode diagram.

DETAILED DESCRIPTION OF EMBODIMENTS

[0037] The present disclosure will be further described below with reference to the embodiments. It should be noted that the embodiments are merely illustrative of the present disclosure, and not intended to limit the present disclosure. In addition, the technical features in various embodiments of the present disclosure described below can be combined with each other in the absence of contradiction.

[0038] Unless otherwise specified, the experimental methods used herein are conventional methods, and the experimental materials used herein are commercially available.

Example 1 Preparation of a Targeted Corrosion Inhibitor for Marine Reinforced Concrete

[0039] The targeted corrosion inhibitor was a nano silver-loaded nitrite-intercalated layered double hydroxide, that was, Ag/Ca—NO.sub.2 LDH. The preparation of the targeted corrosion inhibitor was performed as follows.

[0040] (1) Preparation of a Calcium-Aluminum Layered Double Oxide Ca-LDO

[0041] (101) 2.65 g of sodium carbonate was dissolved into 100 mL of boiling distilled water, and was ultrasonicated for 5 min to obtain a first solution; 7.78 g of calcium hydroxide was dissolved into 50 mL of boiling distilled water, and was ultrasonicated for 10 min to obtain a second solution; and 5.56 g of sodium metaaluminate was dissolved into 50 mL of boiling distilled water, and was ultrasonicated for 5 min to obtain a third solution.

[0042] (102) The first solution, and the second solution and the third solution were evenly mixed and adjusted to pH 12 with a 2 mol/L sodium hydroxide solution to obtain a reaction solution. The reaction solution was stirred at room temperature and 1800 r/min for 1 h.

[0043] (103) The reaction solution was transferred into a reaction kettle, and subjected to hydrothermal reaction in an oven at 120° C. for 24 h. The reaction mixture was subjected to vacuum filtration to collect a filter cake, which was rinsed sequentially with deionized water three times, and anhydrous ethanol three times, dried under vacuum at 50° C. for 48 h and ground into 200-mesh particles, so as to obtain a Ca-layered double hydroxide (Ca-LDH), also known as Ca—CO.sub.3 LDH.

[0044] (104) The Ca-LDH was calcined in a muffle furnace at 900° C. for 3 h to obtain a layered double oxide Ca-LDO.

[0045] (2) Preparation of a Nano Silver-Loaded Layered Double Oxide Ag/Ca-LDO

[0046] (201) 1.7 g of silver nitrate was dissolved into 100 mL of boiling distilled water, and was ultrasonicated for 5 min to obtain a fourth solution.

[0047] (202) 40 mL of the fourth solution was added with 1 g of the Ca-LDO, adjusted to pH 9 with aqueous ammonia, stirred at 1800 r/min and 50° C. in a water bath for 24 h, and then subjected to vacuum filtration to collect a filter cake. The filter cake was rinsed sequentially with deionized water three times, and anhydrous ethanol three times, and subjected to vacuum drying in an oven at 50° C. for 24 h to obtain a solid powder Ag/Ca-LDO.

[0048] (3) Preparation of a nano silver-loaded nitrite-intercalated layered double hydroxide Ag/Ca—NO.sub.2 LDH

[0049] (301) 6.9 g of sodium nitrite was dissolved in 200 mL of boiling distilled water, and was ultrasonicated for 5 min to obtain a fifth solution.

[0050] (302) 200 mL of the fifth solution was added with 1 g of the Ag/Ca-LDO, stirred at room temperature and 1800 r/min for 24 h, and then subjected to vacuum filtration to collect a filter cake. The filter cake was rinsed sequentially with deionized water three times, and anhydrous ethanol three times, and subjected to vacuum drying in an oven at 45° C. for 48 h to obtain a solid powder Ag/Ca—NO.sub.2 LDH.

Example 2 Preparation of a Targeted Corrosion Inhibitor for Marine Reinforced Concrete

[0051] The preparation method used herein was basically the same as that adopted in Example 1 except that in step (302), after added with 1 g of the Ag/Ca-LDO, the fifth solution was stirred at room temperature and 1800 r/min for 48 h.

Example 3 Preparation of a Targeted Corrosion Inhibitor for Marine Reinforced Concrete

[0052] The preparation method used herein was basically the same as that adopted in Example 1 except that in step (301), 13.8 g of sodium nitrite was dissolved in 200 mL of boiling distilled water, and was ultrasonicated for 5 min to obtain a fifth solution.

Comparative Example 1 Preparation of Ag-Loaded Calcium-Aluminum Layered Double Oxide Ag/Ca-LDO

[0053] The prepared method used herein was basically the same as the steps (1)-(2) adopted in Example 1.

Comparative Example 2 Preparation of Layered Double Hydroxide Ca—NO.SUB.2 .LDH

[0054] 23.62 g of Ca(NO.sub.3).sub.2.4H.sub.2O and 18.75 g of AlNO.sub.3.9H.sub.2O were dissolved into 200 mL of boiling distilled water, and were ultrasonicated for 5 min to obtain a solution A. 13.8 g of NaNO.sub.2 and 12 g of NaOH were dissolved in 100 mL of boiling distilled water, and were ultrasonicated for 5 min to obtain a solution B. The solution A and the solution B were mixed, stirred at room temperature for 24 h, and then subjected to vacuum filtration to collect a filter cake, which was rinsed sequentially with deionized water three times and anhydrous ethanol three times, and subjected to vacuum drying in an oven at 45° C. for 48 h to obtain a solid powder Ca—NO.sub.2 LDH.

Experimental Example 1 X-Ray Diffraction (XRD) Analysis

[0055] Structures of the Ag/Ca—NO.sub.2 LDH prepared in Example 1, the Ag/Ca-LDO prepared in Comparative Example 1, a precursor Ca—CO.sub.3 LDH and a precursor Ca—NO.sub.2 LDH prepared in Comparative Example 2 were analyzed by XRD. In FIG. 1, Ag/Ca-LDO and Ag/Ca—NO.sub.2 LDH showed an obvious characteristic diffraction peak of Ag, indicating that Ag ions were successfully loaded. Compared with Ag/Ca-LDO, the Ag/Ca—NO.sub.2 LDH prepared in Example 1 showed an obvious characteristic diffraction peak of LDH in a Ca—NO.sub.2 LDH structure, indicating that based on a structure memory effect of the Ag/Ca-LDO, the Ag/Ca—NO.sub.2 LDH, that was, the nano silver-loaded nitrite-intercalated layered double hydroxide, was successfully prepared.

Experimental Example 2 Evaluation of Chloride Ion Binding Capacity

[0056] A saturated solution of calcium hydroxide with pH of 12.5 was used as a simulated concrete pore solution. The saturated solution was respectively added with sodium chloride solutions of different concentrations at 5, 10, 20, 40 and 80 mmol/L, to obtain test solutions. 0.5 g of the Ag/Ca—NO.sub.2 LDH prepared in Examples 1-3 and 0.5 g of the Ag/Ca-LDO of Comparative Example 1 were added into 50 mL of each test solution, placed into a sealed bottle with a capacity of about 100 mL, and continuously stirred for 24 h. A Langmuir model and a Freundlich model were used for fitting.

[0057] According to adsorption isotherms of chloride ions shown in FIG. 2, the measured experimental data was more in line with the Langmuir model. It was obtained through the fitting that a saturated adsorption capacity of the Ag/Ca—NO.sub.2 LDH prepared in Example 1 to chloride ions in the simulated concrete pore solution was 4.207 mmol/g; a saturated adsorption capacity of the Ag/Ca—NO.sub.2 LDH prepared in Example 2 to chloride ions in the simulated concrete pore solution was 4.103 mmol/g; a saturated adsorption capacity of the Ag/Ca—NO.sub.2 LDH prepared in Example 3 to chloride ions in the simulated concrete pore solution was 4.089 mmol/g; and a saturated adsorption capacity of the Ag/Ca-LDO prepared in Comparative Example 1 to chloride ions in the simulated concrete pore solution was 4.59 mmol/g. The chloride binding capacity of the Ag/Ca—NO.sub.2 LDH was a little less than that of the Ag/Ca-LDO, but was still desirable.

Experimental Example 3 Electrochemical Analysis

[0058] A saturated solution of calcium hydroxide with pH of 12.5 was used as a simulated concrete pore solution. A 3.5 wt % NaCl solution was added to the simulated concrete pore solution, and was stirred for evenly mixing, so as to obtain an electrolyte solution to simulate a corrosion of chloride salts in seawater. 100 mL of the electrolyte solution was taken for later use. The Ag/Ca—NO.sub.2 LDH prepared in Example 1 was added into the electrolyte solution according to an addition amount of 1 g/L, and was marked as an Ag/Ca—NO.sub.2 LDH group. The Ag/Ca-LDO prepared in Comparative Example 1 was added into the electrolyte solution according to addition amount of 1 g/L, and was marked as an Ag/Ca-LDO group. The simulated concrete pore solution (electrolyte) without any corrosion inhibitor was used as a reference group. Q235 carbon steel bars (f10 mm*5 mm) were subjected to a pretreatment before a corrosion test. Specifically, the Q235 carbon steel bars were ultrasonicated using anhydrous ethanol to remove surface impurities, and a copper wire was welded to a side of each Q235 carbon steel bar after the Q235 carbon steel bars were dried. Each Q235 carbon steel bar was then sealed in a polyvinyl chloride (PVC) pipe using an epoxy resin. After the epoxy resin was completely cured, an exposed surface of each Q235 carbon steel bar was polished with a sandpaper (400-3000 mesh), and then washed with anhydrous ethanol. The Q235 carbon steel bars were then immersed into the simulated concrete pore solution of a blank group for passivation for 14 days. Passivated Q235 carbon steel bars were than immersed into the Ag/Ca—NO.sub.2 LDH group, the Ag/Ca-LDO group and the reference group for 48 h, respectively. A CHI660E electrochemical workstation (CH Instruments Ins., US) was used to perform an electrochemical impedance test, and a three-electrode system was adopted, in which each Q235 carbon steel bar was used as a working electrode; a platinum sheet was used as an auxiliary electrode; and a saturated calomel electrode was used as a reference electrode).

[0059] FIGS. 3A-3B showed electrochemical impedance spectra of Q235 carbon steel bars that had been immersed in each group for 48 h. FIG. 3A was a Nyquist diagram of the electrochemical impedance spectra; and FIG. 3B was a Bode diagram of the electrochemical impedance spectra. The Nyquist diagram was composed of an imaginary part of impedance and a real part of the impedance, and a corrosion performance of each Q235 carbon steel bar was determined according to a radius of a capacitive resistance arc that a larger radius of the capacitive resistance arc indicated a higher corrosion resistant of the Q235 carbon steel bar. In the Bode diagram, a phase angle was used to determine the corrosion of the Q235 carbon steel bar that a larger phase angle indicated a higher corrosion resistant of the Q235 carbon steel bar. As shown in FIGS. 3A-3B, the Q235 carbon steel bar immersed in the reference group had a small radius of the capacitive resistance arc and a small phase angle, indicating that without adding a corrosion inhibitor, the Q235 carbon steel bar would corrode quickly under corrosion of Cl.sup.− and a polarization resistance would decrease rapidly. With the addition of the Ag/Ca-LDO prepared in Comparative Example 1, the Q235 carbon steel bar showed a larger radius of the capacitive resistance arc than that in the reference group. With the addition of the Ag/Ca—NO.sub.2 LDH prepared in Example 1, the Q235 carbon steel bar showed a much larger radius of the capacitive resistance arc and phase angle than those in the reference group and the Ag/Ca-LDO group, indicating that the Ag/Ca—NO.sub.2 LDH provided herein can significantly improve the corrosion resistance of reinforcing bars, and had a much better performance than that of the Ag/Ca-LDO.

[0060] Accordingly, the targeted corrosion inhibitor provided herein is a nano silver-loaded nitrite-intercalated layered double hydroxide. Based on inter-layer ion exchangeability of the layered double hydroxides and specific recognition of Ag.sup.+ to chloride ions, the targeted corrosion inhibitor provided herein can release nitrite for inhibiting corrosion while binding the infiltrating chloride ions, so as to provide the reinforcing bar with a double protection effect. In addition, since the targeted corrosion inhibitor is isomeric with a hydration product of the cement, the targeted corrosion inhibitor has no adverse effect on the concrete matrix and has excellent anti-corrosion performance.

[0061] The embodiments provided herein are illustrative of the present disclosure, and not intended to limit the present disclosure. Variations, replacements and modifications made by those skilled in the art without departing from the spirit of the present disclosure should fall within the scope of the present disclosure defined by the appended claims.