Study On The Hydrolysis Process And Stability Of Silane Solution In Surface-treatment Process Of Metals

Silane surface treatment has great advantages such as low cost, environmentalprotectiion, high efficiency, compared with other traditional surface treatmenttechnology (i.g., phosphate).It is one of development direction of industry of the metalsurface treatment.The water soluble mixtures of bis-[trimethoxysilylpropyl]amine (BAS) andvinyltriacetoxysilane (VTAS) were choose as raw materials. Hydrolysis conditionswere optimized and the influencing mechanisms of different factors on stability ofsilane solution were studied. The hydrolysis degree of BAS was calculated byspectrophotometer method.Si-OH in silane solutions was characterized by FourierTransform infrared spectroscopy. The corrosion resistance of silane film was measuredby CuSO4drop test and dynamic polarization curves, and themorphology of silane filmwas characterized by scanning electron microscopy.In this paper, three methods were used to prepare silane solution:directpreparation,dilution of silane solution and mixing of silane solution with differentconcentration,and the corrosion resistance of silane films were discussed.The resultsindicate that Concentration of solution is a key factor affecting the property of thesilane solution and the hydrolysis degree of silane.The activity of solution (i.e.,hydrolysis degree of BAS and the content of Si-OH) prepared by direct preparationand the corrosion resistance of silane film prepared are better than the others.So, directpreparation is the best hydrolysis process to prepared silane working solution.The influences of impurity ions on the stability of silane solution were alsoinvestigated. The results show that:(1) gel appears in silane solution under highconcentration of impurity ions. The influence order of impurities on silane solution isNaOH>NaNO2>CaCl2>MeCl2>NaCl>FeCl3. For NaOH, NaNO2and FeCl3, changingpH of silane solution results in the formation of gel. The coagulation value of NaCl is0.102mol/L, and the coagulation value of CaCl2and MeCl2are0.068mol/L.(2)Cations has more obvious influence on the corrosion resistance of the silane film(Fe3+>Mg2+/Ca2+> Na+),while the influence of anion is not obvious.(3) Theaccumulation of Fe3+is responsible for the invalidation of silane solution and the dropof corrosion resistances of silane film in the cycle experiment.It is because that theparticle size distribution of silane range from68.06nm to615.10nm in the2%silane solution, and it is belong to heterogeneous colloids dispersed system.The influence ofimpurity ions in solution is electrostatic interactions. In other words, impurity ions onlypromote the polymerization of silane in solution. The charge and concentration ofimpurity ions are higher,the greater harmful effect on the stability of silane solution.