Agnieszka Krząkała

Application of plasma electrolytic oxidation to bioactive surface formation on titanium and its alloys

In this work, a review of the literature concerning the surface modification of implants composed of titanium and titanium alloys by plasma electrochemical oxidation (PEO), also known as micro-arc oxidation (MAO), is presented. The application of this process allows for the formation of oxide layers with different porosities on implants. Moreover, it is possible to enrich these oxide layers with species contained in solutions used for anodising, yielding suitable surface chemical properties. Anodising titanium implants in solutions containing compounds of calcium and phosphorous leads to the formation of bioactive layers and significantly reduces the time required for the osseointegration of implant to bone. Studies of the PEO process with respect to titanium implants have been conducted by a large number of research centres, and their results have been applied to the production of a new generation of titanium implants.

Surface characterisation of Ti–15Mo alloy modified by a PEO process in various suspensions

This paper reports on the surface modification of a Ti-15Mo alloy by plasma electrolytic oxidation (PEO). This process was carried out in solutions of 0.1M Ca(H2PO2)2 with various concentrations of tricalcium phosphate (Ca3(PO4)2), wollastonite (CaSiO3), or silica (SiO2) using voltages of up to 350V. The surface microstructure (SEM, cross-section of coating), roughness and chemical composition (energy-dispersive X-ray spectroscopy, thin layer X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectroscopy) of the porous oxide layers were investigated. The concentration of powder added to the solution changed the chemical composition and morphology of PEO coatings on the Ti-15Mo alloy surface. Calcium and phosphorous compounds were detected in the coatings formed on the substrate by the PEO process at 300V.

Modification of niobium surfaces using plasma electrolytic oxidation in silicate solutions

Herein, a study of the plasma electrolytic oxidation (PEO) of niobium in an anodising bath composed of potassium silicate (K2SiO3) and potassium hydroxide (KOH) is reported. The effects of the K2SiO3 concentration in the bath and the process voltage on the characteristics of the obtained oxide layers were assessed. Compact, barrier-type oxide layers were obtained when the process voltage did not exceed the breakdown potential of the oxide layer. When this threshold was breached, the morphology of the oxide layer changed markedly, which is typical of PEO. A significant amount of silicon, in the form of amorphous silica, was incorporated into the oxide coatings under these conditions compared with the amount obtained with conventional anodising. This surface modification technique led to an improvement in the corrosion resistance of niobium in Ringer’s solution, regardless of the imposed process conditions.

Formation of bioactive coatings on Ti–13Nb–13Zr alloy for hard tissue implants

In an attempt to increase the bioactivity of a vanadium-free titanium alloy, Ti–13Nb–13Zr, the plasma electrolytic oxidation (PEO) process for surface modification was utilised. Select samples were subjected to further treatment, either thermal or alkali. The morphology, chemical composition, and phase composition of the treated Ti–13Nb–13Zr alloy were investigated using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). It was observed that during the anodic process under sparking discharge conditions, the simultaneous incorporation of calcium and phosphorus in the forming oxide layer occurs. The resulting layers were porous and exhibited the typical morphology for layers formed during the PEO process. After the alkali treatment of samples oxidised at 150 V, a gel-like titanate layer was formed. The bioactivity investigations in simulated body fluid (SBF) solution indicated that after anodising at 150 V and following alkali treatment the Ti–13Nb–13Zr alloy exhibits osteoinductive properties. The approach presented here may be applied for fabricating Ti–13Nb–13Zr-based implants for hard tissue regeneration.

Stripping of copper coatings from steel in Cr(VI)-free commercial bath

In this work the electrochemical characteristics of copper and steel in chromate, cyanide, and phosphate baths as well as in a commercial bath (ENSTRIP S-180), in the absence of chromium and cyanides were determined. Average rates of copper coatings stripping from steel in the above mentioned baths and the baths influence on the morphology of steel surfaces were described. It was found that the commercial bath ENSTRIP S-180 could be successfully used for stripping of copper coatings from steel elements.

Characterization of Electrophoretically Deposited Chitosan Coatings on Ti13Zr13Nb Alloy for Biomedical Applications

The chitosan (CH) coatings on a Ti13Zr13Nb alloy substrate were obtained by electrophoretic deposition (EPD). The EPD yield was investigated under different deposition conditions. The microstructure of the CH coatings obtained by cataphoresis was studied by scanning electron microscopy and the chemical composition was examined using EDAX. The functional groups and formed phases were analyzed using Fourier transform infrared spectroscopy and X-ray diffraction, respectively. It was found that the CH coating thickness and porosity can be controlled by time and voltage used for the EPD process. It was ascertained that the studied EPD of the natural biopolymer, chitosan, in aqueous solution is applicable for the surface modification of the Ti13Zr13Nb implants to develop novel bioactive coatings.

Microplasma Oxidation of Magnesium Alloy AZ91D by Impulse Current

In this work the results of investigations on thickness distribution of conversion coatings on magnesium alloy AZ91D obtained by plasma electrolytic oxidation (PEO) in sodium silicate solution are presented. The morphology and chemical composition as well as thickness distribution of obtained coatings, with special respect to hard to reach points are shown. Also the corrosion resistance of obtained alloy samples is determined.