B. Łosiewicz

Structure of Low Temperature Nitrided/Oxidized Layer Formed on NiTi Shape Memory Alloy

Structure of the nitride-oxide surface layers, formed using glow discharge technique at low temperature (between 200 and 380°C) changing the parameters of the process, was examined applying X-ray diffraction as well as transmission electron microscopy. The phase analysis was supported by results obtained from XPS measurement. Obtained results have shown that low temperature nitriding/oxiding produced the thin layers (18 ÷ 30 nm in thickness), which consist of titanium nitride and oxide phase. Low amount of the nickel-titanium oxide was also identified in the layer produced at higher temperature. Decrease of nitriding/oxidizing temperature below 300oC cause that between nitride-oxide surface layer and NiTi alloy did not create the intermediate layer of Ni3Ti phase. The results were verified and confirmed by observation carried out using high resolution electron microscopy. The corrosion properties of such coatings were tested in the physiological Tyrod’s solution using the cyclic potentiodynamic polarization method.

Application of EIS to Study the Corrosion Resistance of Passivated NiTi Shape Memory Alloy in Simulated Body Fluid

The NiTi shape memory alloy passivated for 90 min by autoclaving has been studied towards corrosion performance in the Tyrode’s simulated body fluid using open circuit potential and EIS measurements. The surface morphology and thickness of the oxide layer was determined by XRR. The HREM was used to observe the cross-section of the thin foil and to confirm the amorphous state of the TiO2 layer and its thickness. Electrochemical measurements revealed a good corrosion resistance at the beginning of long-term (20 days) immersion. It was found that with the increase of immersion time, the corrosion resistance of the surface deteriorated after nearly 1 day of immersion due to occurence of pitting corrosion. The EIS method was used to detailed study on the electrolyte | passive layer interfacial properties. Equivalent electrical circuit for the pitting corrosion on the passivated NiTi alloy has been applied.

Structure and electrochemical corrosion resistance of the passivated Fe-40at.%Al binary alloy in sulfuric acid solution

The electrochemical corrosion resistance of the passivated Fe-40at.%Al binary alloy has been investigated in sulfuric acid at 25°C. Structural investigations were conducted by XRD method and confirmed a single phase material of the ordered B2 structure. Electrochemical corrosion behavior was determined using potentiodynamic polarization and EIS methods. Anodic polarization measurements revealed a passive behavior of the tested electrode. Detailed characteristics of the Fe-40at.%Al electrode | passive film | solution interface as a function of the electrode potential in the fully passive range of 0.5  E  1.5 V, was investigated. The impedance behavior was determined by a highly doped n-i-n structure (n-type semiconductor – insulator – n-type semiconductor).

Localized Electrochemical Impedance Spectroscopy for Studying the Corrosion Processes in a Nanoscale

This work deals with localized electrochemical impedance spectroscopy (LEIS) which is an improved technique of the commonly used electrochemical impedance spectroscopy (EIS). Thanks to modern structural solutions, the LEIS technique ensures local impedance measurement. Therefore, it is used in the research into point corrosion, such as the pitting corrosion, and in the research into protective coatings or into alloys including alloy steels. This review paper presents the basic theory and the usability of the LEIS based on the literature on the newest research in the field of corrosion.

Effect of Polarization Scan Rate on the Pitting Potential of the Self-Passivated NiTi Shape Memory Alloy in a Simulated Body Fluid

The pitting potential, Epit, of the passive layer on the implant alloy can be treated as an accelerated laboratory test to assessment a susceptibility to pitting corrosion of metallic biomaterials in simulated body fluids. This study deals with an evaluation of Epit of the self-passivated TiO2 layer formed on the surface of the NiTi implant alloy as a function of the scan rate of polarization. Cyclic potentiodynamic studies were performed in Ringer’s solution at 37°C. It was found out that the more noble value of Epit in the range of 0.99-2 V was registered at a given polarization scan rate that ranged from 0.16 to 2 mV s-1, the lower susceptibility of the self-passivated NiTi implant alloy to the initiation of pits was detected.

Electrochemical Characterization of Nickel-Phosphorus Based Coatings Containing Cobalt

The Ni-P, Ni-Co-P and Ni-P+Co coatings were obtained in galvanostatic conditions at the current density of jdep= -200 mA cm-2. A stereoscopic microscope was used for surface morphology characterization of the coatings. The X-ray diffraction (XRD) method was used to determine phase composition of the coatings and the atomic absorption spectrometry (AAS) was applied to specify their chemical composition. The behavior of the obtained coatings was investigated in the process of hydrogen evolution reaction (HER) from 5 M KOH using steady-state polarization and electrochemical impedance spectroscopy (EIS) methods. It was found that introduction into Ni-P amorphous matrix powder of cobalt produced porous electrode materials which could be used for the HER.

The Influence of Current Density of Electrodeposition on the Electrochemical Properties of Ni-Mo Alloy Coatings

The Ni-Mo alloy coatings with a high content of Mo up to 44.5 at.%, were prepared by galvanostatic electrodeposition in the range of deposition current density, jdep, from-30 to-240 mA cm-2 from the nickel plating bath containing potassium pyrophosphate, nickel chloride, sodium molybdate, and sodium bicarbonate. Investigations of hydrogen evolution reaction (HER) were carried out in 5 M KOH solution at room temperature using steady-state polarization and electrochemical impedancy spectroscopy (EIS) measurements. It was found that for the Ni-Mo alloy coatings, the increase in their catalytic properties towards the HER with the increase in the value of jdep of the coatings, was due to the intrinsic activity.

Structure of Electrodeposited Zinc Oxide Films on NiTi Shape Memory Alloy for Biomedical Applications

In this study, the electrosynthesis method of the zinc oxide films on NiTi shape memory alloy substrate from zinc acetate solution, has been studied. The optimum conditions for production of the ZnO thin films were found at a voltage of 20 V for 60 s. Experimental data were presented on the deposition process, structure and composition of the ZnO thin films. It was found that depending on the deposition parameters, the structure of the obtained zinc oxide films varies from amorphous to coarse-grained. It was ascertained that the examined electrosynthesis of the ZnO films appears as a useful method for the surface modification of the NiTi alloy towards biomedical applications.

The Role of Ni(II) Ion Adsorption onto TiO2 in the Electrodeposition of Composite Ni-P+TiO2 Coatings

This study reports on Ni (II) ion adsorption onto TiO2 powder of different concentration in suspension baths developed for electrodeposition of composite Ni-P+TiO2 coatings. The experimental results were modeled with the Langmuir, Freundlich and Temkin adsorption isotherms. It was found that the best fit of Ni (II) ion adsorption data was obtained using the Langmuir isotherm. The study also revealed that adsorption of the nickel ions is a function of TiO2 adsorbent dose in bath. The role of Ni (II) ion adsorption onto TiO2 adsorbate in the elctrodeposition process of composite Ni-P+TiO2 coatings was discussed.

Application of the Scanning Kelvin Probe Technique for Characterization of Corrosion Interfaces

This paper deals with the basic theory and the usability of the scanning Kelvin probe (SKP) being a non-destructive, non-contact method for testing the condition of the surface of conductor, semiconductor and dielectric samples. This technique is based on the electron work function (EWF) characteristic of various test substances and depends, inter alia, on the sample surface condition. During measurement, the so-called surface potential distribution map containing information about EWF value is registered. Key applications of SKP and its various modifications to characterization of corrosion interfaces, have been presented based on the newest literature data covering the past two years of the active research in the field of corrosion in a nanoscale.