Aleksey D. Lisenkov

Self-healing protective coatings with “green” chitosan based pre-layer reservoir of corrosion inhibitor

A new type of corrosion protective self-healing coating is reported in the present study. The coating is constituted by a chitosan-based pre-layer deposited onto the metal surface and a barrier hybrid film. The chitosan film doped with cerium ions serves as a reservoir for the corrosion inhibitor. The cerium ions form a complex with the functional groups of chitosan macromolecules providing a prolonged release of the active agent on demand. The developed bi-layer protective coating was applied to aluminium alloy 2024, which is widely used in the aeronautical industry. The results obtained from electrochemical impedance spectroscopy clearly demonstrate a superior corrosion protection when the coating with the cerium-doped biopolymer pre-layer is used. The localized electrochemical study in micro-confined defects showed a well-defined self-healing ability of the developed coating system.

Nanostructured LDH-container layer with active protection functionality

Self-healing protective coatings based on different types of nanocontainers of corrosion inhibitors have been recently developed and reported as promising solutions for many industrial applications. Layered double hydroxide (LDH) nanocontainers are among the most interesting systems since they confer the delivery of inhibitors on demand under action of corrosion-relevant triggers such as the presence of corrosive anions or local change of pH. In this paper, we report for the first time a new approach based on formation of a nanostructured LDH-container layer directly on the metal surface as a result of conversion reaction with a metal (aluminium alloy 2024) surface. The methodology allows the formation of a spatially differentiated LDH structure preferentially on surface sites located at active intermetallics. The LDH container layer loaded with vanadate ions provides an efficient active corrosion protection and can be used as a functional layer in self-healing coating systems.

Active corrosion protection coating for a ZE41 magnesium alloy created by combining PEO and sol–gel techniques

An active protective coating for ZE41 magnesium alloy was produced by sealing an anodic layer, loaded with 1,2,4-triazole, with a sol–gel film. An anodic oxide layer was formed using PEO in a silicate–fluoride alkaline solution. This thin (1.8 μm) porous PEO layer was impregnated with corrosion inhibitor 1,2,4-triazole and sealed with a silica-based sol–gel film modified with titanium oxide. For the first time it was demonstrated that this relatively thin PEO-based composite coating revealed high barrier properties and provided superior protection against corrosion attack during 1 month of continuous exposure to 3% NaCl. A scanning vibrating electrode technique showed a sharp decrease (100 times) of corrosion activity in micro defects formed in the 1,2,4-triazole doped composite coating, when compared to blank samples.

Deposition of hydroxyapatite–incorporated TiO2 coating on titanium using plasma electrolytic oxidation coupled with electrophoretic deposition

A porous hydroxyapatite (HA)–incorporated TiO2 coating has been deposited on the titanium substrate using a plasma electrolytic oxidation coupled with electrophoretic deposition (PEO-EPD). Potassium titanium(IV) oxalate is decomposed by micro arcs generated on the anode producing TiO2 while HA particles have been simultaneously deposited on anode during EPD process. Hydroxyapatite and TiO2 particles have been coagulated into roundish conglomerates with the average diameter in a range of 200–600 nm. The microstructure, as well as elemental and phase composition of the coatings have been examined by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), glow discharge optical emission spectroscopy (GDOES), fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). XRD has showed that the coatings are composed mainly of HA, rutile and anatase phases. The composition and surface morphologies are not strongly dependent on the applied voltages. The amount of HA deposited into the coating increases with increasing the applied voltage. The wear resistance of PEO-EPD coatings has been assessed using tribological tests. The bioactivity of the obtained coatings has been investigated in a simulated blood fluid.

Photocatalytic Deposition of Hydroxyapatite onto a Titanium Dioxide Nanotubular Layer with Fine Tuning of Layer Nanoarchitecture

A new effective method of photocatalytic deposition of hydroxyapatite (HA) onto semiconductor substrates is proposed. A highly ordered nanotubular TiO2 (TNT) layer formed on titanium via its anodization is chosen as the photoactive substrate. The method is based on photodecomposition of the phosphate anion precursor, triethylphosphate (TEP), on the semiconductor surface with the following reaction of formed phosphate anions with calcium cations presented in the solution. HA can be deposited only on irradiated areas, providing the possibility of photoresist-free HA patterning. It is shown that HA deposition can be controlled via pH, light intensity, and duration of the process. Energy-dispersive X-ray spectroscopy profile analysis and glow discharge optical emission spectroscopy of HA-modified TNT prove that HA deposits over the entire TNT depth. High biocompatibility of the surfaces is proven by protein adsorption and pre-osteoblast cell growth.

A copper-deficient tetragonal phase derived from chalcopyrite CuGaS2.

Direct synthesis of CuGaS(2) from elemental ingredients in a two-zone furnace resulted in a macroseparation of Cu-rich and Ga-rich regions over the crystallization volume. In the Cu-rich parts of the ingot, a near-stoichiometric CuGaS(2) chalcopyrite phase (I42d) and copper sulfides were found. In the Ga-rich part, along with a chalcopyrite phase with some Cu deficiency, a new tetragonal phase I4m2 with composition close to Cu(5)Ga(9)S(16) and the crystal lattice parameters a = 3.7777(2) Å, c = 5.2483(4) Å was revealed. It was concluded that this Cu-deficient chalcopyrite-like phase is not an ordered defect compound (ODC). As opposed to the systems Cu-Ga-Se and Cu-Ga-Te, in a system based on sulfur, the ODC phenomenon is unlikely to occur.

Encapsulation of Al and Ti-Al alloy 1-D nanorods into oxide matrix by powerful pulsed discharge method

AbstractEncapsulated metal nanostructures were prepared using the powerful pulsed discharge method. Metal nanorods were obtained in porous titania and alumina matrix by direct electrodeposition from 1-ethyl-3-methylimidazolium chloride-based ionic liquids. The deposition process was characterized by cyclic voltammetry. Morphology of the encapsulated structures was studied by scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) for morphological and elemental analysis. It was found that the most efficient method for electrodeposition of pure aluminum into titania nanotubes is the potential cycling method, while for deposition of the Al-Ti alloy in alumina pores a pulsed method with three different steps is preferable. Closing the titania nanotubes was found to be possible both with empty and metal-filled pores, whereas in alumina matrix this procedure can be performed only when pores are filled with a conductive material. The obtained results throw light on the mechanism of porous film encapsulation under high-voltage pulses and allow preparing encapsulated nanostructures in the oxide films. Graphical abstractᅟ