Electrochemical behavior of polypyrrole-coated AZ31 alloy modified by fluoride anions

Fluoride Coatings on Magnesium Alloy Implants

After several years of research and development, it has been reported that magnesium alloys can be used as degradable metals in some medical device applications. Over the years, fluoride coatings have received increasing research attention for improving the corrosion resistance of magnesium. In this paper, different methods for preparing fluoride coatings and the characteristics of these coatings are reported for the first time. The influence of the preparation conditions of fluoride coatings, including the magnesium substrate, voltage, and electrolyte, on the coatings is discussed. Various properties of magnesium fluoride coatings are also summarized, with an emphasis on corrosion resistance, mechanical properties, and biocompatibility. We screened experiments and papers that planned the application of magnesium fluoride coatings in living organisms. We have selected the literature with the aim of enhancing the performance of in vivo implants for reading and further detailed classification. The authors searched PubMed, SCOPUS, Web of Science, and other databases for 688 relevant papers published between 2005 and 2021, citing 105 of them. The selected time range is the last 16 years. Furthermore, this paper systematically discusses future prospects and challenges related to the application of magnesium fluoride coatings to medical products.

Preparation and Corrosion Performance of PPy/Silane Film on AZ31 Magnesium Alloy via One-Step Cyclic Voltammetry

PPy/silane composite film on a magnesium alloy surface was prepared by one-step cycle voltammetry. The mixed solution of methanol and water was used as the hydrolysis solvent of a γ-(2,3-glycidoxypropyl) trimethoxysilane coupling agent (KH-560). The surface morphology of the PPy/silane film, the electro-polymerization progress of KH-560 and PPy, the influence of the silane coupling agent and the corrosion behavior of the coated AZ31 Mg alloy were all investigated. The results indicated that the PPy/silane film on AZ31 Mg alloy via one-step cyclic voltammetry could provide better corrosion protection for an Mg alloy when the volume fraction of KH-560 in the hydrolysis solution was 15% and the time span of hydrolysis was 24 h with the 5.935 × 10⁻¹⁰ A cm⁻² corrosion current density.

Consolidated Melting Gel Coatings on AZ31 Magnesium Alloy with Excellent Corrosion Resistance in NaCl Solutions: An Interface Study

Magnesium alloys, with a density two-thirds that of aluminum, are very attractive for the industry. However, these alloys are extremely susceptible to corrosion in the presence of aggressive electrolytes such as NaCl solutions. Here, we designed hybrid coatings obtained by the consolidation of organically modified polysilsesquioxanes called "melting gels" for the corrosion protection of AZ31 magnesium alloy in NaCl solutions. The main focus was to study the interaction between coatings and substrate and the influence of the coating thickness on the final properties. Micro-scratch tests, adhesion by tape tests, confocal Raman microscopy, SEM-EDS, and ToF-SIMS indicate good adhesion of coatings based on the interaction of melting gels and substrate. These measurements indicate the presence of the Si-O-Mg bonds between the substrate and coatings. Electrochemical results show very low current densities (10^-13 A cm^-2) without any breakdown potential and impedance values of 10¹⁰ Ω cm².