| As a common issue faced by many industries and fields,corrosion would not only cause a lot of economic losses to the country and society,but also threaten human life when it is serious.To inhibit the occurrence of corrosion reaction,pretreatment with protective coatings on the surface of metal is one of the most effective methods.Among these coatings,silane coating posses many advantages like economy,environmental protection,simple operation and beautiful appearance and is widely applied for metal anticorrosion.The traditional silane coating is often prepared through sol-gel method by using silane coupling agent which is prone to phase separation,weak adhesion to metal substrate and poor compactness.Based on the above analysis,this paper proposed a kind of organic-bridged polysilsesquioxane anticorrosion coating which was prepared by organic-bridged silsesquioxane as precursor through sol-gel method.In order to extend the diffusion path of the corrosive matter in the coating,hydroxyl-containing bridged polysilsesquioxane/silica(SiO2)composite anticorrosion coating was fabricated by introducing silica(SiO2)nanoparticles into the coating.In addition,to expand the application field of the coating,the hydrophobic composite coating was obtained by using fluorine-containing silane as modifier.The specific research progress of this work is as follows.(1)For the acid catalyst system,firstly,hydroxy-containing bridged polysilsesquioxane precursor GN was obtained by epoxy-amino ring-opening reaction between glycidoxypropyltrimethoxysilane(GPTMS)and N-(3-trimethoxysilylethyl)ethylenediamine(NTMDA)whose chemical structure was verified by Fourier transform infrared spectroscopy(FT-IR),1H nuclear magnetic resonance spectroscopy(1H NMR)technique.Then the acid catalyzed hydroxyl-containing bridged polysilsesquioxane coating was fabricated by depositing GN sol catalyzed by acetic acid on the surface of Q235 steel sheet through dip-coating technology.And the anticorrosion performance of the coating was evaluated by potentiodynamic polarization curve and electrochemical impedance spectroscopy techniques.As the aging time is different,the ratio of Si-OH and Si-O-Si in the coating structure is different.Thus the influence of aging time on the anticorrosion performance of the coating was investigated.When the aging time is 4 h,the coating's corrosion current obtained by fitting potentiodynamic polarization curve was as low as 21.75 uA·cm-2 and its impedance at the low frequency of 0.01 Hz increased by 1.5 orders of magnitude in contrast to the bare Q235 steel.(2)For the alkali catalyst system,the alkali catalyzed hydroxyl-containing bridged polysilsesquioxane coating was fabricated by depositing GN sol catalyzed by ammonia on the surface of Q235 steel sheet through dip-coating technology.And the anticorrosion performance of the coating was evaluated by potentiodynamic polarization curve and electrochemical impedance spectroscopy techniques.Then the influence of aging time on the anticorrosion performance of the coating was explored.When the aging time is 4 h,the coating's corrosion current obtained by fitting potentiodynamic polarization curve was as low as 16.04 uA·cm-2 and its impedance at the low frequency of 0.01 Hz increased by 2.5 orders of magnitude in contrast to the bare Q235 steel.By comparison,the anticorrosion performance of the alkali catalyzed coating was better than that of the acid catalyzed coating.Therefore,the alkali catalyst system was selected to further improve the anticorrosion performance by the introduction of SiO2 nanoparticles in the subsequent research.(3)For the composite coating system,firstly SiO2 nanoparticles modified by hydroxyl-containing bridged silsesquioxane were introduced into the sol prepared in(2).Then hydroxyl-containing bridged polysilsesquioxane/SiO2 composite coating was obtained by depositing the above composite sol on the surface of Q235 steel sheet through dip-coating technology.And the anticorrosion performance of the coating was evaluated by potentiodynamic polarization curve and electrochemical impedance spectroscopy techniques.As the dispersibility of SiO2 nanoparticles directly affected the anticorrosion performance of the coating,the modification time on the anticorrosion performance of the composite coating was investigated.When the modification time is 2 day,the composite coating's corrosion current obtained by fitting potentiodynamic polarization curve was as low as 2.83 uA·cm-2 and its impedance at the low frequency of 0.01 Hz increased by 3.9 orders of magnitude in contrast to the bare Q235 steel.(4)For the hydrophobic composite coating system,the hydrophobic composite coating by depositing composite sol obtained in(3)modified by fluorine-containing silane on the surface of Q235 steel sheet through dip-coating technology.And the anticorrosion performance of the coating was evaluated by potentiodynamic polarization curve and electrochemical impedance spectroscopy techniques.The influence of the addition of fluorine-containing silane on the hydrophobicity and anticorrosion performance was investigated.When the molar ratio of fluorine-containing silane and hydroxyl-containing bridged polysilsesquioxane was 1:5,the coating was the most hydrophobic with water contact angle of 127°,which is 54° higher than that of the composite coating without the modification of fluorine-containing silane.At the same time,the most hydrophobic coating's corrosion current obtained by fitting potentiodynamic polarization curve was as low as 6.27 uA·cm-2 and its impedance at the low frequency of 0.01 Hz increased by about 2 orders of magnitude in contrast to the bare Q235 steel.By comparision to the composite coating without hydrophobic treatment,the hydrophobicity increased,but the anticorrosion property reduced. |
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