【摘要】迄今为止，在微弧氧化涂层表面上制备Mg-Al水滑石涂层，一般是在高温或低pH值的条件下进行的，这导致水滑石涂层的生长速率远低于微弧氧化涂层的溶解速度，继而限制了复合涂层的耐腐蚀性。在这项研究中，在较低温度（60 ℃）和较高pH值（13.76）的条件下，通过水浴法在微弧氧化涂层上原位生长了一层Mg-Al水滑石涂层，以调控镁合金的降解速率。 微弧氧化涂层与镁合金基体之间具有很高的冶金结合强度，对镁合金具有一定的保护。但是，微弧氧化涂层的多孔结构和微裂纹则是降低耐腐蚀的主要原因。 水滑石是一种纳米结构材料，具有类似三明治的结构，其中二价和三价阳离子包封阴离子。一方面，它可以充当抑制腐蚀的物理屏障。另一方面，它还具有离子交换能力，可以有效地减少腐蚀介质中氯离子对基体的破坏。因此，可以选择水滑石涂层作为顶层来密封多孔微弧氧化涂层。 目前，水滑石的制备大多是在高温或低pH值的制备条件下进行的。但是，这可能会导致微弧氧化涂层溶解速率过快而造成微弧氧化涂层出现严重破坏，导致耐蚀性明显下降。这主要是涉及在水滑石制备过程中，微弧氧化涂层溶解速率和水滑石涂层生长速率之间的平衡性问题。可以分为以下三种方式： 1）如果微弧氧化涂层的溶解速率大于水滑石涂层的生长速率，则微弧氧化/水滑石复合涂层的耐腐蚀性可能会明显降低，即复合涂层耐蚀性反而低于单一微弧氧化涂层。例如，Chen等人（ Appl. Surf. Sci. 463 (2019) 535-544 ）在含有 0.1 M Al(NO 3 ) 3 和 0.6 M NH 4 NO 3 的溶液中，在温度为 95 °C 和pH值为7的条件下，水热处理1 h，在微弧氧化涂覆的镁合金AZ31上制备了Mg-Al水滑石。结果表明，在水滑石制备过程中，低的pH值导致微弧氧化涂层开裂，并且微弧氧化/水滑石复合涂层的自腐蚀电流密度比微弧氧化涂层增加了一个数量级，这表明复合涂层的耐腐蚀性明显降低。 2）如果微弧氧化涂层的溶解速率约等于水滑石涂层的生长速率，则微弧氧化/水滑石复合涂层的耐蚀性可能变化不大。例如，Peng等人（ Sci. Rep. 7 (2017) 8167-8178 ）在含有0.02 M硝酸铝的水溶液中，在温度为 120 °C 和pH值为12.8的条件下，水热处理12 h，在微弧氧化涂覆的镁合金AZ31表面制备了Mg-Al水滑石涂层。结果表明，与微弧氧化涂层相比，复合涂层的自腐蚀电流密度从 9.45×10 -6 A·cm -2 略微降低到 3.92×10-6 A·cm -2 ，这表明耐腐蚀性几乎没有变化。 3）如果微弧氧化涂层的溶解速率小于水滑石涂层的生长速率，则微弧氧化/水滑石复合涂层的耐腐蚀性将得到提高。例如，Jiang等人（ Chem. Eng. J. 373 (2019) 285-297 ）在通过共沉淀和水热的方法在温度为 120 °C 和pH值为11.0的条件下在微弧氧化涂覆的镁合金AZ91表面上制备了Mg-Al水滑石涂层。结果表明，与微弧氧化涂层相比，微弧氧化/水滑石复合涂层的自腐蚀电流密度从 1.27×10 -6 A·cm -2 降低到 1.03×10 -7 A·cm -2 ，这表明耐蚀性明显增强。 如果要获得具有优异耐腐蚀性的微弧氧化/水滑石复合涂层，则微弧氧化涂层的溶解速率必须小于或远小于水滑石涂层的生长速率。因此，水滑石在微弧氧化表面制备的技术难点就是平衡微弧氧化涂层的溶解速率和水滑石涂层的生长速率，这也许可以通过选择合适的制备温度和调节合适的pH值来实现。 结果表明：在低温（ 60 ℃ ）和较高pH（13.76）下，通过原位生长的方法，在微弧氧化涂层表面成功制制备了一层具有纳米片状结构的Mg-Al水滑石涂层。我们发现氢氧化物的形成优先于水滑石，而且氢氧化镁的生长始于金属间化合物或第二相Al-Mn相。EDTA在整个水滑石的生长过程中起到促进Al3+离子沉积的作用，即促进水滑石的生长。电化学结果表明，微弧氧化/Mg-Al水滑石复合涂层的自腐蚀电流密度比基体下降了四个数量级，比微弧氧化涂层下降了两个数量级。此外，由于水滑石涂层的扩散和离子交换行为，微弧氧化/Mg-Al水滑石复合涂层具有较宽的钝化区（ 0.6 V·SCE -1 ）、较高的破钝电位以及阳极区的自愈合现象。这说明高pH值和低制备温度可有效地降低微弧氧化涂层的溶解速率，以匹配水滑石的生长速率，从而制备出具有优异耐腐蚀性的复合涂层。在长时间的浸泡过程中，微弧氧化/Mg-Al水滑石复合涂层保持完好无裂纹，并保持了水滑石的片状结构。而且，纳米片结构的水滑石更有利于钙磷产物的沉积。此外，MTT分析和活/死染色表明，微弧氧化/Mg-Al水滑石复合涂层对于MC3T3-E1成骨细胞具有可接受的生物相容性，且具有更高的细胞存活率。这表明，纳米结构有利于细胞的粘附、生长和扩散。因此，微弧氧化/Mg-Al水滑石复合涂层在整形外科骨植入材料中具有潜在的应用价值。 本研究通过低温和高pH平衡了微弧氧化溶解速率与水滑石的生长速率，得到了耐腐蚀性能优异的复合涂层，而且纳米片状结构有利于钙磷产物的沉积和细胞的生长、扩散、粘附。这为镁合金微弧氧化涂层表面原位生长顶层设计提供了一定的理论指导。 论文“ In vitro degradation and cytocompatibility of a low temperature in-situ grown self-healing Mg-Al LDH coating on MAO-coated magnesium alloy AZ31 ” 发表在《 Bioactive Materials》(5, 2020：364-376) 。第一作者为山东科技大学材料学院硕士研究生李长阳，通讯作者为山东科技大学曾荣昌教授和青岛大学附属医院郅克谦教授。 Fig. 1 Simple flow chart for preparation of the MAO-LDH coating. Fig. 2 Surface morphology images of the (a, c) MAO, and (b, d) MAO-LDH coatings. Fig. 3 (a) Bode and (b) Bode phase angle plots of the ( Ⅰ ) Mg alloy AZ31 substrate, ( Ⅱ ) MAO coating and ( Ⅲ ) MAO-LDH coating. Nyquist plots (c-d) and the corresponding electrical equivalent circuit models (f-h) of all samples. Fig. 4 (a) Potentiodynamic polarization curves and (b) corresponding i corr and E corr of the (Ⅰ) Mg alloy AZ31 substrate, (Ⅱ) MAO coating, and (Ⅲ) MAO-LDH coating. Fig. 5 OD values (a) and Cell viability (b) of MC3T3-E1 cultured in different extracts prepared with the negative control, Mg alloy AZ31 substrate, MAO coating, and MAO-LDH coating for 1, 3 and 5 days. Statistically significant differences ( *P 0.05, **P 0.01.); Fluorescent images (c-f) of MC3T3-E1 after culturing for 24 h in extracts of the (c) negative control, (d) AZ31 substrate, (e) MAO coating and (f) MAO-LDH coating.
镁合金腐蚀研究进展(37)—硅烷水解度对水滑石硅烷复合涂层耐蚀性能的影响 水滑石类化合物(LDH)是一类具有层状结构的无机功能材料。LDH的主体层板化学组成与其层板阳离子性质、层板中间阴离子、阴离子交换量和超分子结构等因素密切相关。镁铝碳酸根型水滑石化学通式为：Mg 6 Al 2 (OH) 16 CO 3 ·4H 2 O，具有层间阴离子的可交换性、热稳定性能、组成和结构的可调控性等特点。 有机硅烷的分子结构式一般为:R-Si(OR) 3 (Si-OR为硅烷氧基)。硅烷氧基对无机物具有反应性，也可以与一些有机官能团结合。有机硅烷水解产生的Si-OH一方面可以进行自缩聚形成Si-O-Si网状结构，另一方面能够与水滑石表面的羟基进行结合。因此，Si-OH的浓度势必会影响着有机硅烷与水滑石的结合。 在本工作中，使用共沉淀-水热法合成在镁合金AZ31上制备出镁铝碳酸根水滑石，再用浸渍法在不同配比的硅烷、乙醇和超纯水的混合溶液（3:20:10, 3:15:15和3:10:20）中制备出水滑石/硅烷改性的复合涂层。 图1 涂层结构示意图 Fig. 1 Schematic representation of the coating formation mechanism of the composite coatings. 研究发现，3:10:20比例的溶液具有最高的硅烷水解度，对应制备出的LDH/PMTMS-3涂层具有最好的耐蚀性和表面致密性涂层具有超疏水性能，接触角达150.5°，可以有效地隔绝水溶液的侵蚀。而对于另外两种复合涂层（3:20:10, LDH/PMTMS-1涂层和3:15:15, LDH/PMTMS-2涂层），两者表面均不致密，内层水滑石形貌清晰可见，耐腐蚀性相比于LDH/PMTMS-3涂层较差，但比水滑石涂层或者AZ31基体较好。这两种复合涂层也未达到超疏水效果，接触角分别为120.5°和131.5°。因此，LDH/PMTMS-3涂层作为耐蚀涂层实际应用前景。 该项工作 “Corrosion resistance of Mg(OH) 2 /Mg–Al-layered double hydroxide coatings on magnesium alloy AZ31: influence of hydrolysis degree of silane” 在线发表在 《Rare Metals》(2019). https://doi.org/10.1007/s12598-019-01234-1. 第一作者为研究生姚青松，通讯作者为张芬、曾荣昌。 Fig. 2 FE-SEM of (a) LDH coating, (b) LDH/PMTMS-1 coating, (c) LDH/PMTMS-2 coating and (d) LDH/PMTMS-3 coating Fig. 3 FT-IR spectra of (a) silane solutions: Solution 1 (3:20:10, V / V / V ), Solution 2 (3:15:15, V / V / V ), Solution 3 (3:10:20, V / V / V ); FT-IR spectra of (b) LDH coating, LDH/PMTMS-1 coating, DH/PMTMS-2 coating and LDH/PMTMS-3 coating. 图4 XPS 图谱 Fig. 4 XPS survey scan of (a) LDH/PMTMS-3 coating, (b) Mg peaks, (c) C peaks, (d) O peaks and (e) Si peaks. 图5 极化曲线 Fig. 5 Polarization curves of the (a) AZ31 alloy, (b) LDH coating, (c) LDH/PMTMS-1 coating, (d) LDH/PMTMS-2 coating and (e) LDH/PMTMS-3 coating. 图6 析氢曲线 Fig. 6 (a, b) Hydrogen evolution volume and (a, b) hydrogen evolution rate (HER) as a function of the immersion time for (I) AZ31 alloy, (II) LDH coating, (III) LDH/PMTMS-1 coating , (IV) LDH/PMTMS-2 coating and (V) LDH/PMTMS-3 coating in 3.5 wt. % NaCl solution for 480 h. Fig. 7 Schematic representation of corrosion mechanism of the composite coatings.
镁合金表面自愈合钼酸根水滑石涂层 Self-healing molybdate intercalated hydrotalcite coating on Mg alloy 曾荣昌 山东科技大学 Rong-Chang Zeng Shandong Uniersity of Science and Technology 我们采用共沉积和水热法在镁合金AZ31表面制备了钼酸根水滑石涂层，这种涂层具有纳米层状结构、离子交换和自愈合（ self-healing ）功能，有望成为一类对环境刺激发生响应的智能涂层（ smart coating ）。研究结果发表在《 Journal of Materials Chemistry A》(2014, 2, 13049–13057 ) 。 Abstract A molybdate intercalated hydrotalcite (HT-MoO 4 2- ) coating with a nanosized lamellar structure was synthesized on AZ31 Mg alloy by a combination of the co-precipitation and hydrothermal processes. The characteristics of the coatings were investigated by SEM, EPMA, XRD, EDS and FT-IR. The corrosion resistance of the coatings was assessed by potentiodynamic polarization, electrochemical impedance spectrum, and hydrogen evolution. The results indicated that the HT- MoO 4 2- coating, characterized by interlocking plate-like nanostructures, ion-exchange and self-healing ability, has a potential to be a “smart” coating capable of responding to stimuli from the environment. Self-healing mechanism The self-healing process of the HT-MoO 4 2- coating in the corrosive medium is demonstrated on the cross-sectional views of the coatings (Fig. 1). Fig. 1a and b show the cross-sectional views of the coatings before and after 144 h of immersion, respectively. Fig. 1c and d designate the magnitude morphologies and their corresponding EDS spectra of the original and the immersed coating, respectively. It was revealed in Fig. 10b that the coating contained two layers: the newly formed outer layer and the thinned inner HT-MoO 4 2- coating after 144 h of immersion in NaCl solutions. It is also found that the coating morphology has been changed. The non-uniform hexagonal flakes of the HT-MoO 4 2- coating (Fig. 1c) were changed into round and bar-like particles (Fig. 1d). The EDS spectrum in the inset of Fig. 1d indicates that the main component of the outer coating is Mg(OH) 2 . Fig. 1 The self-healing process of the HT-MoO 4 2- coating demonstrated on the cross-sectional views. The XRD patterns of the original HT- MoO 4 2- coated sample and the samples after different immersion times are shown in Fig. 2a. Obvious Mg(OH) 2 peaks appeared on the immersed samples, in addition to those of the HT- MoO 4 2- layer. and the Mg substrate. With the extended immersion time, it can be seen from Fig. 2 that the intensity of Mg(OH) 2 peaks increased, while the intensity of HT- MoO 4 2- peaks decreased, the peak at 22.5 nearly disappeared after the immersion of 12 days. But, it can be seen that the peaks of the HT- MoO 4 2- coating on AZ31 Mg substrate still existed after a 12 days immersion test, which indicated that the HT- MoO 4 2- coating had a good corrosion resistance. The peaks position of (003) were shied to a large angle of approximately 0.2 (Fig. 2b), indicating that the chloride ions were intercalated by ion exchange. Fig. 2(a) XRD patterns of the original HT-MoO 4 2- coated sample and immersed sample with different time. (b) Detail XRD patterns of (003). The dissolution reaction of the Mg(OH) 2 film on the Mg alloy surface in chloride solution can be given as follows: Mg(OH) 2 + Cl - → Mg(OH)Cl + OH - (1) Mg(OH)Cl + Cl - → MgCl 2 + OH - (2) The ion-exchange reaction of the HT-MoO 4 2- coating on the Mg alloy in chloride containing solution can be expressed as follows (Fig. 3): HT-MoO 4 2- +2 Cl - → HT-2Cl - + MoO 4 2- (3) Anodic reaction: Mg → Mg 2+ + 2e (4) Cathodic reaction: 2 H 2 O + 2e - → 2OH - + H 2 ↑ (5) The total reaction: Mg + 2 H 2 O → Mg(OH) 2 + H 2 ↑ (6) The released MoO 4 2- ions can produce the following reactions : MoO 4 2- + 8 H + + 3e - → Mo 3+ + 4 H 2 O (7) At the same time, Mo 3+ ions also consume the OH - ions and create the formation of Mo(OH) 3 . The Mo(OH) 3 compound is quite unstable and has a tendency which can transform into more stable compounds: Mo(OH) 3 + OH - → Mo(OH) 4 (8) MoO 4 2- may react with the dissolved Mg 2+ to form a protective deposition film. The deposition of MoO 4 2- can inhibit the expansion and spreading of pitting corrosion. The probable reaction can be given as follows Mg 2+ + MoO 4 2- → (9) Fig. 3 Corrosion protection mechanism of the HT-MoO 4 2- coating. Conclusions (1) Based on the ion exchange, the released MoO 4 2- ions lead to the formation of a diffusion boundary layer. (2) In the diffusion boundary layer, the released MoO 4 2- ions greatly impair the adsorption of Cl - on the surface of the coating. Also, the released MoO 4 2- with the ability for oxidation and deposition can effectively reduce the damage of pitting corrosion to the substrate. (3) In the HT- MoO 4 2- coating, the coexistence of HT- MoO 4 2- and HT-2Cl can effectively block the penetration of aggressive ions, the corrosion pits can thus be healed by the Mg(OH) 2 layer and inhibit MoO 4 2- . This article has been published on Journal of Materials Chemistry A (2014, 2, 13049–13057).
标签: 水滑石
