Agnieszka Smołka

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.

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.

On the Use of the Scanning Electrochemical Microscopy in Corrosion Research

This paper deals with the basic theory and the usability of Scanning Electrochemical Microscopy (SECM) in corrosion research. The SECM is the in situ method of surface characterization which is based on the scanning of the tested surface using ultramicroelectrode and simultaneous electrochemical testing of the surface. This technique provides an electrochemical imaging of the surface. Key applications of SECM have been demonstrated based on the newest literature data covering the past two years of the active research in the field of corrosion in a nanoscale.

Structure and Resistance to Electrochemical Corrosion of NiTi Alloy

The NiTi alloy (50.6 at.% Ni) passivated for 30 min at 130°C by autoclaving has been studied towards corrosion resistance in aqueous solutions of 3% NaCl, 0.1 M H2SO4, 1 M H2SO4 and HBSS. Structure and thickness of the passive layer (TiO2, rutile) were examined by X-ray reflectivity method and high resolution electron microscopy. Corrosion behavior of this oxide layer was investigated by open circuit potential method and polarization curves. It was found that the corrosion resistance of the passivated NiTi alloy is strongly dependent on the type of corrosive environment. The higher corrosion resistance of the tested samples was revealed in sulfate solutions as compared to chloride ones. The highest resistance to electrochemical corrosion of the NiTi alloy was observed in 0.1 M H2SO4 solution. Susceptibility to pitting corrosion of the tested samples was observed which increased with the concentration rise of chlorine anions in solution. Electrochemical tests for 316L stainless steel carried out under the same experimental conditions revealed a weaker corrosion resistance in all solutions as compared to the highly corrosion resistant NiTi alloy.

Use of Scanning Vibrating Electrode Technique to Localized Corrosion Evaluation

This work presents the basic theory and the usability of the scanning vibrating electrode technique (SVET), especially in the field of corrosion. At present, SVET is to be considered as one of the latest electrochemical testing methods. The essence of determining the current density resulting from corrosion is limited to the measurement of the potential gradient between the two points on the surface of the metal and over it, within the electric field of a local element. SVET has been used to study local, galvanic and intercrystalline corrosion. It is particularly useful in studying the corrosion of alloy steels and welding agents. This paper presents a review of the literature on the newest research in this field.

Effect of Phosphorus on the Structure of Nickel Electrocoatings

The present work deals with the influence of sodium hypophosphite content in the plating bath on the chemical composition and structure of the obtained nickel electrocoatings. Electrodeposition of the Ni-P coatings was conducted under galvanostatic conditions at room temperature from the Watts type bath containing different amounts of sodium hypophosphite (0-30 g dm-3). The chemical and physical characteristics of the obtained Ni-P deposits and comparable Ni coating, were performed using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD) methods. It was found that the addition of sodium hypophosphite as amorphizator to the Ni-plating bath influences both the structure and chemical composition of the obtained Ni electrodeposits. With increase in the content of sodium hypophosphite in the bath, surface morphology of the amorphous Ni-P coatings becomes more developed what is of key-importance for electroevolution of hydrogen on such electrodes.

A Coulometric Method by Local Anodic Dissolution for Measuring the Thickness of Ni/Cu Multi-Layer Electrocoatings

The coulometric or anodic de-plating technique can be used for measuring the thickness of coatings on virtually all substrates such as steel, non-ferrous metals or insulating material bases. This study reports on application of an electrochemical de-plating technique for measuring the thickness of multilayer Ni/Cu coatings electrodeposited on a steel substrate. Principles of a coulometric method by local anodic dissolution according to ISO 2177:2003 have been explained. The phase analysis of the Ni/Cu multi-layer coatings was performed using GIXD technique. The summary of the GIXD diffraction patterns obtained in this experiment indicates that such electrocoating is composed of two sub-layers of nickel and copper.

Characteristics of the Galvanic Baths for Electrodeposition of Nickel Coatings Using the Hull Cell

Electrodeposition of polycrystalline nickel onto carbon steel substrate has been studied from different types of solutions: (bath I) the Watts nickel plating bath, (bath II) the sulfate-chloride nickel plating bath for production of the SUPER Ni coatings, (bath III) the sulfamate nickel plating bath, and (bath IV) the chloride nickel plating bath. A detailed study has been made on the influence of the bath composition on the mass increment and thickness of the deposited Ni coatings. Cathodic current efficiency of the Ni electrodeposition has been also studied. The electrochemical anodic de-plating technique has been used for measuring the thickness of nickel coatings according to ISO 2177:2003. Evaluation of the effect of bath composition on the quality of the galvanic nickel coatings, was carried out using the Hull cell. In a single test, the range of current densities which provided a desired plating characteristic at a given total current, was previewed. Principles of the electroplating process using the Hull cell have also been explained.

Influence of Thermal Treatment on the Structure and the Corrosion Resistance of Zn-Ni Alloy Coatings

Electrolytic Zn-Ni alloy coatings were obtained on the steel substrate under galvanostatic conditions, and then, subjected to thermal treatment in argon atmosphere. The influence of thermal treatment on the surface morphology, phase composition and corrosion resistance of the electrodeposited coatings has been studied. Surface morphology was examined using a scanning electron microscopy. Chemical composition was determined by a X-ray fluorescence spectroscopy. Structural studies were carried out using a X-ray diffraction method. Corrosion resistance tests were carried out in 3% NaCl solution using open circuit potential method and potentiodynamic measurements. It was found that after thermal treatment, the value of polarization resistance increases, the value of the corrosion current decreases, and the value of corrosion potential is shifted towards anodic potentials. This suggests a positive effect of thermal treatment of the Zn-Ni alloy coatings on their corrosion resistance.