Preparation and electrochemical study of cerium-silica sol-gel thin films

被引:174
作者
Garcia-Heras, M
Jimenez-Morales, A
Casal, B
Galvan, JC
Radzki, S
Villegas, MA
机构
[1] CSIC, Ctr Nacl Invest Met, E-28040 Madrid, Spain
[2] Univ Carlos III Madrid, Madrid 28911, Spain
[3] CSIC, Inst Ciencia Mat, E-28040 Madrid, Spain
[4] Marie Curie Sklodowska Univ, PL-20031 Lublin, Poland
关键词
thin films; chemical synthesis; X-ray diffraction; electrochemical reactions; thermal analysis;
D O I
10.1016/j.jallcom.2004.03.047
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
Design and development of suitable multilayered systems for delaying corrosion advance in metals requires that both the alteration mechanisms of the metal and the behaviour and properties of the protective coatings be known. Coatings prepared by the sol-gel method provide a good approach as protective layers on metallic surfaces. This kind of coatings can be prepared from pure chemical reagents at room temperature and atmospheric pressure, with compositions in a very wide range of environmentally non-aggressive precursors. Sol-gel coatings based on siloxane bonded units were prepared starting from an organic-inorganic hybrid system. The precursors were gamma-methacryloxypropyltrimethoxysilane (MAP) and tetramethoxysilane (TMOS). Cerium nitrate hexahydrate in three different concentrations was added. Cerium salts may perform a similar protective effect to that carried out by the well-known lead oxides and chromium salts, even though in this case a negative environmental impact is not expected. Application of coatings upon pure zinc substrates and common glass slides were performed by spinning. Coated samples were heat treated at 40degreesC for 6 days. Optical measurements (UV-Vis absorption and diffuse reflectance spectroscopies) pointed out that the coatings were colourless and transparent, reducing the diffuse reflectance of the metallic surface up to similar to60%. Optical and scanning electron microscopies (SEM) allowed observation of the texture and microstructure of the coated samples, both before and after the corrosion tests were carried out. Likewise, the remaining sols were kept to gelify at 60degreesC for 4 days and then powdered to obtain suitable samples for analysing them by other characterisation techniques (Fourier transformed infrared, FTIR and differential thermal analysis, DTA). Electrochemical measurements were performed by impedance spectroscopy. This technique was used to clarify the anticorrosive protection role of cerium ions incorporated into the hybrid sol-gel network. The effect of cerium concentration on the impedance spectra was analysed, as well as the system behaviour against the corrosive medium (0.6 M NaCl aqueous solutions), as a function of exposure time. From the electrochemical point of view, the sol-gel films behave as a conversion coating on the metallic surface. (C) 2004 Elsevier B.V. All rights reserved.
引用
收藏
页码:219 / 224
页数:6
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