Controlled release mechanism and inhibition performance of smart inhibitor LDH-NO2 in the reinforced concrete structures
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摘要: 為解決傳統阻銹劑過早失活、過量投放的問題，研究了一種具有控釋、長效、靶向特征的智能阻銹劑LDH-NO2。采用第一性原理計算、物理檢測技術、浸泡實驗和電化學方法研究了智能阻銹劑LDH-NO2的微觀和宏觀控釋規律及緩蝕行為。結果表明：(1) 在氯離子侵蝕或碳化的混凝土環境中，LDH-NO2中的
$ {\text{NO}}_2^ - $ 可快速、自發釋放，1 h內達到釋放平衡，從而及時修復鋼筋的腐蝕損傷；(2) LDH-NO2對碳化環境比氯離子環境更加敏感，其與$ {\text{CO}}_3^{2 - } $ 發生離子交換反應的化學能更大，反應產物的層間距更小、層間作用力更強、穩定性更好；(3) 含氯碳化混凝土環境中，5 g·L?1 LDH-NO2對碳鋼鋼筋的緩蝕效率約99%，使碳鋼鋼筋腐蝕速率下降一個數量級；(4) 相較于傳統阻銹劑NaNO2，智能阻銹劑LDH-NO2可有效延長碳鋼鋼筋的腐蝕起始時間、減少其腐蝕面積、降低其腐蝕程度；(5) LDH-NO2的緩蝕性能主要源于LDH對$ {\text{NO}}_2^ - $ 的釋放，而非其對腐蝕性離子的吸附。因此，智能阻銹劑LDH-NO2在鋼筋混凝環境中具有優異的緩蝕性能和長效性。Abstract: Reinforcement corrosion is one of the most serious problems limiting the durability of concrete structures. Corrosion inhibitors are used as admixtures in the fresh concrete to prolong the service life of the concrete structure, and calcium nitrite is the most extensively tested admixed inhibitor. However, the premature deactivation and overdose of conventional inhibitors limit their application, and one strategy to solve this problem is to use smart inhibitors with controlled release, long-term effects, and targeting performance. In this paper, a smart inhibitor of LDH-NO2 was prepared based on the Zn?Al layered double hydroxide as a shell and the nitrite ions as a core. The first principles calculation, physical detection techniques, immersion test, and electrochemical methods were performed to study the micro- and macro-controlled release mechanism and inhibition property of LDH-NO2. The results show that: (1) The nitrites in LDH-NO2 can release spontaneously in the chloride-contaminated or/and carbonated concrete. The release process reaches equilibrium in 1 h, repairing the corrosion damage of steel reinforcement in time. (2) The LDH-NO2 is much more sensitive in the carbonated concrete than chloride-included concrete, reflected in the greater energy of ion-exchange reaction and the more stable product with thinner interlayer with stronger interlayer force. (3) In the simulated pore solution of chloride-contaminated and carbonated concrete, the corrosion inhibition efficiency of 5 g·L?1 LDH-NO2 on carbon steel reinforcement exceeds 99%, reducing the corrosion rate of carbon steel by one order of magnitude. (4) Compared with the conventional NaNO2 inhibitor, LDH-NO2 effectively prolongs the corrosion initiation time while decreasing the corrosion area of carbon steel reinforcement. (5) The corrosion inhibition performance of LDH-NO2 is mainly due to the release of$ {\text{NO}}_2^ - $ from LDH rather than the corrosive ion adsorption on LDH. Therefore, the smart inhibitor of LDH-NO2 shows excellent corrosion inhibition and a long-term effect in the reinforced concrete environment. -
圖 1 LDHs主體結構的構建.(a) 3R1構型的Zn2Al1(OH)6(NO2)1超胞側視圖；(b) Zn(OH)2的(3×2×1)超胞的俯視圖及其中的(1×1)和(
$\sqrt 3$ ×$\sqrt 3 $ )R30°構型；(c)$ {\text{Zn}}_{2}{\text{Al}}_{1}（\text{OH}{）}_{6}^{\text{+}} $ 單胞的俯視圖Figure 1. Structure of LDHs: (a) left view of the Zn2Al1(OH)6(NO2)1 supercell with 3R1 structure; (b) top view of the (3×2×1) supercell of Zn(OH)2 with 3R1 structure; (c) top view of the Zn2Al1(OH)6+ primitive cell
圖 2 幾何優化后LDH-NO2 (a)、LDH-Cl (b)和LDH-CO3 (c)的穩定構象
Figure 2. Different interlayer spaces of LDH-NO2 (a), LDH-Cl (b), and LDH-CO3 (c) after optimization
圖 3 LDH-NO2、LDH-Cl、LDH-CO3的態密度圖(a)和層板投射態密度圖(b) （費米能級被定義為0 eV）
Figure 3. Density of states diagram (a) and projected density of the layer diagram (b) for LDH-NO2, LDH-Cl, and LDH-CO3（Fermi energy level was set to 0 eV）
圖 4 LDH-NO2、LDH-Cl和LDH-CO3中氫鍵的鍵長和鍵角分布
Figure 4. Length and angle distributions of H Bonds for LDH-NO2, DH-Cl, and LDH-CO3
圖 5 LDH-NO2智能阻銹劑的X射線衍射圖譜(a)和掃描電鏡形貌(b)
Figure 5. XRD pattern (a) and SEM morphology (b) of the LDH-NO2 inhibitor
圖 6 混凝土模擬孔隙液中LDH-NO2的亞硝酸釋放動力學曲線.(a)階段性添加腐蝕性離子；(b)直接添加腐蝕性離子
Figure 6. Release kinetic of nitrites from LDH-NO2 in the simulated concrete pore solution: (a) gradual addition of corrosive ions; (b) addition of corrosive ions in the beginning
圖 7 (a)碳鋼鋼筋在含0.17 mol·L?1 NaCl和0.1 mol·L?1 NaHCO3（pH值11.5）的混凝土模擬液中浸泡1 h后的極化曲線；(b)擬合結果
Figure 7. (a) Polarization curves of carbon steel reinforcement after 1 h of immersion in the concrete simulation solution with 0.17 mol·L?1 NaCl and 0.1 mol·L?1 NaHCO3 (pH value of 11.5)；(b) fitting results
圖 8 碳鋼鋼筋在含0.17 mol·L?1 NaCl和0.1 mol·L?1 NaHCO3（pH值11.5）的混凝土模擬液中浸泡16 d后的腐蝕結果. (a)腐蝕起始時間和腐蝕面積；(b)腐蝕形貌
Figure 8. Corrosion behavior of the carbon steel reinforcement after 16 d of immersion in the concrete simulation solution with 0.17 mol·L?1 NaCl and 0.1 mol·L?1 NaHCO3 (pH value of11.5): (a) corrosion initiation time and mass loss; (b) corrosion morphology
圖 9 碳鋼鋼筋在含0.17 mol·L?1 NaCl和0.1 mol·L?1 NaHCO3（pH值11.5）的混凝土模擬液中浸泡1 h后的Nyquist圖和Bode圖：(a, b)添加LDH-NO2阻銹劑；(c, d)添加NaNO2阻銹劑；(e, f)添加LDH-NO3阻銹劑
Figure 9. Nyquist plots and Bode plots of carbon steel reinforcement after 1 h of immersion in the concrete simulation solution with 0.17 mol·L?1 NaCl and 0.1 mol·L?1 NaHCO3 (pH value of 11.5): (a–b) adding LDH-NO2 inhibitor; (c–d) adding NaNO2 inhibitor; (e–f) adding LDH-NO3 inhibitor
圖 10 含氯碳化混凝土模擬液中LDH-NO2、NaNO2和LDH-NO3對碳鋼鋼筋的緩蝕效率
Figure 10. Inhibition efficiency of LDH-NO2, NaNO2, and LDH-NO3 on the carbon steel reinforcement in the chloride-contaminated and carbonated concrete simulation solution
表 1 LDH-NO2、LDH-Cl、LDH-CO3的主要結構參數
Table 1. Main geometrical parameters for hydrotalcites LDH-NO2, LDH-Cl, and LDH-CO3
Species Methods Lattice constant/nm Bond distance/nm Bond angle/(°) a=b c Metal-O O?H A?H* A?O** C?O N?O O?C?O O?N?O LDH-NO2 Calculation 0.3118 2.3939 0.2025 0.0985 0.1716 0.3158 — 0.1261 — 119.041 LDH-Cl Calculation 0.3118 2.3686 0.2062 0.0982 0.2056 0.2988 — — — — Experiment 0.3081 2.3351 0.2054 — — 0.2992 — — — — LDH-CO3 Calculation 0.3118 2.2284 0.2026 0.098 — 0.2814 0.1469 — 120 — Experiment 0.3074 2.2743 0.2034 — — — 0.1170 — 120.01 — Note: * represents the bond length between the interlayer anion and the H atom of the LDH layer；** is the bond length between the interlayer anion and the O atom of the LDH layer. 
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表 2 LDH-NO2、LDH-Cl、LDH-CO3層間空間中各原子的分數坐標
Table 2. Fractional coordinates of atoms in the interlayer spaces for hydrotalcites LDH-NO2, LDH-Cl, and LDH-CO3
Atomic positions LDH-NO2 LDH-Cl LDH-CO3 Interlayer N(0.62, 0.55)
O(0.48,0.51)
O(0.91,0.71)Cl(0.5, 0.5) C(0.75, 0.5)
O(0.61, 0.50)
O(0.75, 0.22)
O(0.89, 0.78)Layer Al(0.5, 0.5)
H(0.64, 0.64)
H(0.96, 0.65)Al(0.5, 0.5) Al(0.75, 0.5)
H(0.53, 0.34)
H(0.68, 0.03)
H(0.81, 0.62)
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表 3 LDH-NO2、LDH-Cl、LDH-CO3的Mulliken電荷布居
Table 3. Atomic populations of LDH-NO2, DH-Cl, and LDH-CO3
Species Zn/e Al/e O/e H (far from anion)/e H (near anion)/e Anion
(inter)/eLayer 1.160 1.750 ?0.930 0.410 — — LDH-NO2 1.070 1.710 ?0.935 0.4175 0.375 ?0.670 LDH-Cl 1.070 1.710 ?0.933 0.420 0.360 ?0.670 LDH-CO3 1.107 1.715 ?0.930 0.413 0.400 ?1.59
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表 4 LDH-NO2和Cl?、
$ {\text{CO}}_3^{2 - } $ 發生離子交換反應所涉及的各物相的總能Table 4. Thermodynamic potentials for species involved in the ions exchange reaction of LDH-NO2 with Cl? and
$ {\text{CO}}_3^{2 - } $ Species Thermodynamic Potentials/eV Species Thermodynamic Potentials/eV $ {\text{NO}}_2^ - $ ?1148.29 LDH-NO2 ?7561.55 Cl? ?426.37 LDH-Cl ?6851.32 $ {\text{CO}}_3^{2 - } $ ?1451.21 LDH-CO3 ?7164.32
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表 5 碳鋼鋼筋在含不同阻銹劑環境中的交流阻抗譜擬合值
Table 5. Fitting data for the electrochemical impedance spectrum of carbon steel reinforcement in the simulated concrete pore solution with different inhibitors
Inhibitors Dosage /
(g·L? 1)Rs /
(Ω·cm2)Qc /
(${ {\text{Ω} }^{ - 1} } \cdot {\text{c} }{ {\text{m} }^{ - 2} } \cdot { {\text{s} }^{ {n_{\text{c} } } } }$)nc Rc /
(Ω·cm2)Qf /
(${ {{\Omega } }^{ - 1} } \cdot {\text{c} }{ {\text{m} }^{ - 2} } \cdot { {\text{s} }^{ {n_{\text{f} } } }}$)nf Rf /
(Ω·cm2)Blank 0 22 3.82×10? 4 0.85 18 1.37×10? 4 0.95 1170 LDH-NO2 1 21 2.81×10? 4 0.84 121 1.93×10? 4 0.89 1603 5 20 7.95×10? 5 0.89 54 5.15×10? 5 0.88 6999 10 20 1.24×10? 4 0.82 61 1.93×10? 5 0.91 11995 NaNO2 0.108 31 3.12×10? 4 0.78 1788 9.49×10? 3 0.95 518 0.540 45 1.36×10? 4 0.84 2290 8.85×10? 4 0.64 2851 1.080 26 1.05×10? 4 0.86 5160 4.24×10? 4 0.72 8139 LDH-NO3 1 23 1.29×10? 4 0.92 19 1.62×10? 4 0.91 1104 5 22 1.23×10? 4 0.90 17 1.90×10? 4 0.89 1169 10 19 1.46×10? 4 0.88 25 1.73×10? 4 0.87 1583
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