【作者】 季卫刚；

【导师】 张鉴清； 胡吉明；

【作者基本信息】 浙江大学 ， 物理化学， 2007， 博士

【摘要】 在自然环境中,除少数贵金属外,大多数金属都容易发生腐蚀,这会导致金属材料结构的破坏和各种功能的丧失。有机涂层具有低成本、易施工等优点,成为应用最广泛的金属防腐蚀方法。环氧树脂具有粘结力强、耐化学试剂性能好等优点,被广泛用作金属防腐蚀的有机涂层。但环氧涂层的缺点是吸水量大,这限制了它的应用。本文采用含烷氧基的硅烷试剂直接改性环氧涂层,增强了涂层抵御水、离子渗入的能力,提高了涂层与金属基体间的结合力,从而提高涂层的防护能力。这为硅烷试剂在金属防腐蚀领域的应用提供了一条新的思路。主要研究工作包括:（1）直接共混掺杂改性将环氧基丙基三甲氧基硅烷（GPTMS）单体直接掺杂到环氧树脂/聚酰胺涂层中去,采用电化学阻抗谱（EIS）求得涂层电容的变化研究了涂层的吸水情况。结果表明,GPTMS硅烷单体掺杂后,环氧涂层的吸水量显著降低。随共混硅烷量的增加,涂层的饱和吸水量先减小然后增大,5wt%GPTMS掺杂的涂层吸水量最低。采用差示扫描量热法（DSC）研究了环氧树脂/聚酰胺复合物浸泡前后的玻璃转化温度（T_g）。纯坏氧涂层的T_g在浸泡后明显下降,而GPTMS掺杂涂层的T_g在浸泡后却略有增大。这种增大可能是硅烷组分的水解、缩合形成的Si-O-Si结构对涂层结构具有修复作用造成的。通过对环氧复合物粉末在浸泡前后的红外谱图的研究,我们发现对于硅烷掺杂涂层浸泡后1100cm^-1的吸收峰强度略有增强,验证了Si-O-Si的生成。（2）化学改性然而,仅仅极少数硅烷单体可直接用于共混改性环氧涂层,一些长链硅烷如十二烷基三甲氧基硅烷（DTMS）的掺杂甚至会破坏涂层的性能。为解决这个问题,我们通过化学改性的方法把硅烷单体接枝到环氧分子上去。γ-氨基丙基三甲氧基硅烷（γ-APS）可以通过氨基与环氧树脂中的环氧基之间的开环反应接枝到环氧树脂上去。我们发现用1wt%γ-APS改性后涂层的吸水量明显降低,而过量的硅烷会造成涂层固化不完全破坏涂层的性能。同样地,我们发现硅烷改性的涂层在浸泡后T_g略有增加。EIS实验和Machu实验都证明了改性涂层的防护性能比空白涂层有所提高。对于不能和环氧基反应的硅烷单体,我们则借助合适的催化剂,通过环氧树脂的羟基与硅烷的烷氧基反应,把硅烷单体接枝到环氧分子上去。红外光谱的研究发现,改性树脂中对应羟基的吸收减弱而Si-O-C对应的吸收峰明显增强。通过对EIS数据的拟合,我们得到了涂层电容、涂层电阻、涂层/金属界面双电层电容和电荷转移电阻等与涂层金属体系性能及涂层失效过程有关的电化学参数。和纯环氧涂层相比,改性涂层具有较大的反应电阻和较小的界面双电层电容。这表明改性涂层的性能得到提高。Machu实验和沸水实验同样表明改性涂层性能大大提高。GPTMS硅烷化学改性涂层具有最好的防护性能。鉴于此,我们进一步研究了该种硅烷的用量对涂层性能的影响,发现随着硅烷用量的增加,涂层性能随之提高,但当硅烷用量超过化学计量,涂层性能的提高则不再明显。（3）硅烷预聚体（preploymer）改性硅烷单体的水解活性太大,不利于缓蚀作用的长久发挥。我们设想通过对影响硅烷水解、缩合因素的控制,合成出部分水解缩合但仍具有水解活性烷氧基的硅烷预聚体,该预聚体由硅烷单体经不完全水解通过缩聚得到,烷氧基在水渗入时仍可像硅烷单体那样发挥“修复”作用,但由于硅烷已经部分聚合,水解活性降低,这样可能有利于发挥更长期的保护作用。我们分别以甲基三甲氧基硅烷（MTMS）和γ-APS为底物合成出两种不同的硅烷预聚体,并直接掺杂到环氧树脂/聚酰胺涂层体系中去。MTMS硅烷预聚体由于和涂层相容性差,改性涂层性能的提高甚微。而γ-APS预聚体掺杂的涂层性能则大大提高。对涂层电容值及弥散系数（n）演化的分析表明,改性涂层抗水渗入的能力增强,接触角测试也表明预聚体改性涂层的憎水性要优于纯坏氧涂层及单体改性涂层。EIS实验、Machu实验和沸水实验都表明预聚体改性涂层性能大大提高。更多还原

【Abstract】 Most metals, except some noble metals, are prone to corrosion in nature environment, which can result in destruction and function-loss of metallic materials. Organic coatings were widely used for metal protection against corrosion due to their low price and high processibility. Among them, epoxy resin was the one that was most widely used painting component due to its good adhesion with metal substrates and high resistance against organic solvent. However, the high water uptake of epoxy coatings restricts the application in highly humid environment. In this paper, silane agents were directly used to modify epoxy coatings, aiming to improve the protection performance by improving the barrier performance against water permeation of the coatings and increasing the adhesion between metal substrate and polymer coatings, giving a novel method to utilize the silane agents in metal corrosion control. The main contents are listed as follows:（1） Modification by direct incorporation3-glycidoxypropyltrimethoxy silane （GPTMS） were directly incorporated into epoxy/polyamide systems. Coating capacitance, which was measured by electrochemical impedance spectroscopy （EIS）, was employed to calculate the amount of water uptake in epoxy coatings in aqueous solution.The water absorption in epoxy coatings was found to decrease drastically after incorporated with silane component. With the increase of silane content, water uptake of epoxy coatings passes through a minimum, corresponding to 5wt.% of silane incorporation. Differential scanning calormetry （DSC） was used to measure the glass-transition temperature （T_g） of the coatings before and after immersed in water. After water permeation T_g of pure epoxy-polyamide coatings is found to conventionally decrease. However, for silane-incorporated coatings T_g increase slightly after water penetration. The self-repairing effect due to the hydrolysis and condensation of silane agents is proposed to interpret the interesting T_g increase. For GPTMS incorporated coatings, it is found that the relative peak intensity at 1100cm^-1, corresponding to the Si-O-Si bonds, increased slightly after immersion, which was caused by the formation of Si-O-Si bonds.（2） Chemical modificationOur experimental results showed that only few silane monomers gave positive results by the above-mentioned simple direct incorporations. For example, some long-chained silanes （e.g. dodecyl-trimethoxy silane, DTMS） deteriorated the performance of the incorporated organic coatings, due to their poor compatibility with polymeric resins. To overcome this drawback, the silane agents were grafted to epoxy resin molecules by chemical modification.Two main methods were used in chemical modification,γ-amino-propyltrimethoxy silane （γ-APS） can be grafted to epoxy resins via the opening cycle reaction between the amino groups inγ-APS and the epoxide groups in epoxy resins. It was found that the water uptake of epoxy coatings decreased after modified with 1 wt.% content ofγ-APS. whereas excessive amounts of this silane monomer result in the deterioration in performance against water permeation. Similar, the T_g ofγ-APS modified coating was also found to increase slightly. EIS measurement and Machu test demonstrated that the protection performance was improved after modification.Those silanes. which cannot react with the epoxide groups, can be grafted to epoxy resin via the reaction between the alkoxy groups in silane and the hydroxy groups in epoxy resin under the catalysis of organotin compounds. FTIR spectra showed that the absorption intensity of -OH decreased and a new absorption corresponding to the Si-O-C bonds appeared after modification. The parameters related to the protection performance of the coatings, such as coating capacitance （C_c）, coating resistance （R_c）, double layer capacitance (C_dl) and charge transfer resistance (R_ct), were then obtained by fitting of the EIS data. The result indicated an enhancement in protectiveness of silane-modified epoxy coatings against substrate corrosion, which was characterized by higher R_ct and lower C_dl at substrate/electrolyte interface. The results of Machu test and boiling water test were in good accordance with the conclusion derived from EIS measurement. The best performance was observed for coating system modified by GPTMS. Thereby, we further investigate the corrosion performance of GPTMS-modified epoxy coatings with various content of this silane monomer. The result showed that the protection performance was improved with the increase of silane content. But when the amount of silane exceeds the stoichiometric values, only slight improvement in protectiveness can be observed compared with that modified by stoichiometric amount of GPTMS silane monomer.（3） Modification with prepolymers of silanesThe high hydrolysable activity of silane monomer is harmful for long-term protection. By controlling the reaction conditions, we synthesized the prepolymers based on silane monomers. There are residual alkoxy in prepolymer, which can also undergo hydroxylation and condensation to form Si-O-Si structure after water permeation as silane monomer does. The prepolymer has partly condensed which may reduce its hydrolysable activity, and this may guarantee a long-term protection.Two different prepolymers were synthesized, one was based on methyltrimethoxy silane （MTMS） and the other was based onγ-APS silane monomer. They were directly incorporated into the epoxy/polyamide systems aiming to enhance the protection performance. The improvement in protection performance is almost negligible for MTMS prepolymer-incorporated coatings due to the poor compatibility with polymeric resins. Whereas, forγ-APS prepolymer-incorporated coatings, the protection performance of coatings were improved significantly after incorporation. The evolution of C_c values and the dispersion coefficient （n） during the immersion revealed that the barrier performance against water permeation was improved after prepolymer incorporation. The contact angle measurement also showed thatγ-APS prepolymer incorporation improved the hydrophobicity of the epoxy coatings. Machu test and boiling water test also showed an improvement on protection properties forγ-APS prepolymer-incorporated coatings.更多还原