Studies on adhesion characteristics and corrosion behaviour of vinyltriethoxysilane/epoxy coating protective system on aluminium

The corrosion stability of vinyltriethoxysilane/epoxy coating protective system on aluminium is strongly related to the strength of bonds forming at the metal/organic coating interface. This article is a study of adhesion, composition, electrochemical and transport properties of epoxy coatings electrodeposited on bare aluminium and aluminium pretreated by vinyltriethoxysilane (VTES) during exposure to 3% NaCl. The VTES film was deposited on aluminium surface from 2% vinyltriethoxysilane solution during 30 s. From the values of adhesion strength (pull-off test), time dependence of pore resistance and coating capacitance of epoxy coating (impedance measurements) and diffusion coefficient of water through epoxy coating (gravimetric liquid sorption measurements), the influence of VTES sublayer on the corrosion stability of the electrodeposited epoxy coating was shown.The work discusses the role of the VTES pretreatment in the enhanced adhesion and corrosion stability of epoxy cataphoretic coating. The electrochemical results showed that the aluminium pretreatment by VTES film improved barrier properties of epoxy coating (greater pore resistance and lower coating capacitance). The lower value of diffusion coefficient of water through epoxy coating indicates the lower porosity, while the smaller adhesion reduction points to better adhesion of epoxy coating on aluminium pretreated by VTES film. The composition of the deposited coatings investigated by XPS enabled the clarification of the bonding mechanism.     

恒电流库仑分析法测定乙烯基三乙氧基硅烷

建立了恒电流库仑分析法测定乙烯基三乙氧基硅烷(VTES)含量的方法. 探讨了电解液、反应时间、极化电位、溶剂等因素对测定的影响. 结果表明, 选用V(甲酸)∶V(KBr (2 mol/L))∶V(乙醇)＝6∶1∶3为电解液, 极化电位为200 mV, VTES与溴的四氯化碳溶液反应30 min, 甲醇为VTES的溶剂时测定结果最佳. 该方法用于样品VTES的测定, 加标回收率为98.4%～102.7%, 相对标准偏差为1.7%.     

铑催化吲哚与乙烯基三乙氧基硅烷的C—H烯基化反应

研究了铑催化N-嘧啶吲哚与乙烯基三乙氧基硅烷的C—H烯基化反应. 在以二氯（五甲基环戊二烯基）合铑(Ⅲ)二聚体{[RhCp*Cl₂]₂(Cp*: 五甲基环戊二烯基)}为催化剂, Cu(OAc)₂为氧化剂, AgF为添加剂, 1,2-二氯乙烷为溶剂及反应温度为90 ℃条件下, 以42%~88%的收率得到末端吲哚乙烯衍生物. 动力学同位素效应实验结果为K_H/K_D=5.7∶1, 表明C—H键断裂可能是反应过程中的决速步骤. 竞争性实验结果表明, 含有供电子取代基的底物比吸电子取代基的底物反应活性高, 反应可能经历亲电性C—H键活化过程. 推测了可能的反应机理, 主要包括配位、 C—H键活化、 转金属化、 还原消除和氧化等步骤. 将此方法应用于一种δ-咔啉衍生物的制备.