镁铝水滑石的制备及其涂层耐腐蚀性能的研究

目的 为了提高水性工业涂料的防腐蚀性能，常常会添加以含锌为主的防腐填料。然而，随着环保要求越来越高，以及欧盟限锌令的颁布，片层无锌镁铝水滑石(MgAl-LDHs)有望用于涂料中替代含锌填料。方法 采用共沉淀法合成无锌水滑石复合填料，并将其进行硅烷偶联剂表面改性，最后添加到丙烯酸树脂中，制备了水滑石防腐涂料。研究了不同制备工艺与水滑石结构之间的关系，以及不同添加量对涂料腐蚀性能的影响。结果 通过对比实验可以看出，当Mg∶Al(物质的量比)=2∶1，滴定终点pH值为11，能制备出相对完美的具有片层形貌、结晶度高、结构完整的镁铝水滑石;FTIR以及悬浮性测试表明，当MgAl-LDHs被KH570成功改性后，实现了表面亲水到疏水的转变，有效增加了与树脂的相容性;电化学考评发现，添加5%(质量分数)MgAl-LDHs的涂层240 h后防腐性能最好，塔菲尔电流密度最低为6.35 μA/cm²，容抗弧曲率半径最大;同时，耐盐雾试验证明，添加5%(质量分数)MgAl-LDHs涂层的耐腐蚀性能同样最佳，与电化学测试结果相匹配。结论 当MgAl-LDHs的添加量为5%(质量分数)时，涂层的防腐蚀性能最佳。MgAl-LDHs作为颜填料，能有效改善水性工业涂料防腐性能。

Preparation of Magnesium-aluminium Hydrotalcite and Corrosion Resistance of Its Composite Coatings

In order to improve the corrosion resistance of waterborne industrial coatings, anti-corrosion fillers containing zinc are often added. However, with the increasing environmental requirements and the European Union''s zinc restriction decree, lamellar zinc-free magnesium aluminum hydrotalcite (MgAl-LDHs) is expected to be used to replace zinc-containing fillers in coatings. Hydrotalcite (LDHs) has a layered structure, as well as features such as ion exchangeability, thermal stability, modifiable compositional structure, and recoverability. In this paper, the Zn-free hydrotalcite composite filler was synthesized by co-precipitation method, which is a commonly used method at present. The surface of the filler was modified by silane coupling agent, and finally added to the acrylic resin to prepare an anticorrosive coating. The relationship between different preparation process and the structure of hydrotalcite was explored to study the effect of MgAl-LDHs content on corrosion resistance of composite coating and determine the optimal content of MgAl-LDHs by analyzing the effect of MgAl-LDHs on the corrosion resistance of the composite coating. The crystal structure and phase composition of hydrotalcite were analyzed by X-Ray Diffraction (XRD). The surface morphology, particle size and dispersion of the filler were observed by scanning electron microscope (SEM). Fourier transform infrared spectroscopy (FTIR) was used to determine the active functional groups present in the hydrotalcite, which was beneficial to surface modification and improved the interaction between the filler and the resin. The corrosion rate and anti-corrosion effect of fillers on the coating were evaluated by Tafel polarization curve and electrochemical impedance spectroscopy. In addition, the salt spray resistance of the coating was tested. In this work, the BGB 2300 tinplate steel (80 mm×25 mm×0.28 mm) was used as the metal substrate, and the D012 acrylic acid coating was rolled on the surface of the metal substrate. The test samples of the D012 acrylic acid coating/BGB 2300 tinplate steel system was put it into a salt spray resistant box. The test samples were divided into 3 cycles:24, 72, 96 h. The macro morphology of the acrylic acid coating surface. Through comparative experiments, it can be found that when n(Mg2+)∶n(Al3+)=2∶1 and the titration endpoint pH=11, relatively perfect Mg-Al hydrotalc with lamellar morphology, high crystallinity and complete structure could be prepared. The results of FTIR and suspension test showed that when MgAl-LDHs were successfully modified by KH570, the surface was transformed from hydrophilic to hydrophobic, which effectively increased the compatibility with the resin. The electrochemical test results show that the coating with 5wt.% hydrotalcite has the best anti-corrosion performance after soaking for 240 h. The lowest Tafel current density is 6.35 μA/cm2, and the curvature radius of the resistance arc is the largest. At the same time, the salt spray resistance test shows that the coating with 5wt.% filler also has the best corrosion resistance, which is consistent with the electrochemical test results. MgAl-LDHs, as a new type of zinc-free pigment filler, can effectively improve the anti-corrosion performance of the coating, and has a broad application prospect in the future.