Corrosion Improvement of Surgical Grade Stainless Steel by Sol-Gel Hybrid Coatings Containing SiO2 Nanoparticles and Glass-ceramic Particles

S. CERÉ; S. PELLICE; W. H. SCHREINER; M. APARICIO; A. DURÁN; J. BALLARRE,

Niza, Francia

Congreso; 61st Annual Meeting of the International Society of Electrochemistry; 2010

International Society of Electrochemistry

Among the materials used as orthopaedic devices, metals are the most used due to their excellent mechanical and structural properties. Nevertheless they are no able to make a natural bonding with the existing bone, and it is necessary to fix them with external devices or acrylic cement. Besides, they present the possibility of particle release to the surrounding area that can lead to the final removal of the prosthesis. The protection of 316L stainless steel used in permanent implants applying a hybrid organic-inorganic sol-gel coating is one of the ways to improve the surface condition of metals. The coatings have a double goal: to act as a barrier to corrosion reaction and, to be a potential holder for different kind of functional particles. This work presents the synthesis of coatings made by the sol-gel method of tetraethoxysilane (TEOS), methyl-triethoxysilane (MTES) and different amount of silica nanoparticles used as precursors applied onto AISI 316L by dip coatings. A two layered system is used. The addition of SiO2 colloidal particles to the sol (10 or 30% in weight in the inner layer) is thought to give films with bigger thickness, improve the mechanical properties and to act as reinforcement and protection to corrosive processes. The coating with 10% SiO2 particles presented better corrosion resistance than the coatings with 30%. Probably the inner 30% layer has higher roughness and is less homogeneous than the one with 10%, and when the second layer with 10% SiO2 is deposited, the system reaches the critical thickness of the film in the valley-peak zone, creating defects after the deposition. This was not found in the 10% SiO2 coatings because the second layer is deposited on one with similar characteristics, with high continuity and easily joinable with the first one. The electrochemical behavior of the coatings containing silica nanoparticles could be explained considering the reactions that took place into the defects in the coatings. There is an OH-release as a common cathodic reaction en slightly basic aqueous media in presence of oxygen, which indicates the local basification of the medium. The silica nanoparticles present in the coatings can react with the OH-leading to silicate formation. These silicates can react with Na+ and K+ cations present in the SBF, creating soluble silicates that conduct to the progressive deterioration of the film or with Ca2+ or Fe3+, Cr3+ ions creating insoluble voluminous compounds that could contribute to the progressive filled of the coatings defects.