Surface and electrochemical corrosion analysis of niobium oxide film formed in various wet media

Niobium metal has a wide range of applications in medical devices, nuclear applications, and solar cells. Therefore, niobium corrosion behavior and oxide film formation mechanisms are of great interest. Steady-state polarization and a.c transient techniques were employed to determine the effective capacitance, oxide film thickness, and the corrosion behavior of niobium through the time-constant distribution. In this report, we describe a cost-effective wet chemical method of surface treatment of niobium metal for the study of the metastable oxide film (Nb2O5) formed in different media such as NaCl, NaOH, HCl, and H2SO4 solutions. The investigations confirmed a time-dependent formation and dissolution of a protective oxide layer in all the tested media at different potentials, however, recommends short immersion time ( 1 h for NaCl and NaOH. The work developed a new understanding of the niobium corrosion behavior through effective capacitance and film morphology

Further studies into the flow corrosion cathodic mass transfer kinetics of copper and nickel-aluminium bronze wall-jet electrodes

This work has investigated the corrosion performance and mass transfer of oxygen on copper and nickel-aluminium bronze surfaces within a wall-jet flow cell assembly. Limiting currents of the dissolved oxygen mass-transfer kinetics as a function of volume flow rate at a wall-jet electrode were examined for copper and nickel-aluminium bronze in a 3.5 wt.% NaCl solution. Mass transfer kinetics for the reduction process studied was compared with rotating disc and cylinder electrode data. The wall-jet electrode mass transfer coefficients for commercially pure copper and cast nickel-aluminium bronze were determined to be 0.01-0.06 cm s–1 and 0.01-0.05 cm s–1, respectively

Electro-mechanical interactions during erosion-corrosion

This study aims to understand the physical processes invoked when solid particle erosion occurs in a corrosive media. The literature on wear-corrosion shows some effort has been placed in qualifying the interactions between erosion and corrosion leading to ‘synergistic’, ‘additive’ and ‘antagonistic’ terms. These terms are difficult to quantify experimentally with multiple experiments being required and generate considerable errors often suggesting these interactive terms are negligible. Hence the current work seeks to investigate these interactions, the errors associated with their measurement and gain understanding of the processes involved by careful examination of microstructural and mechanical property changes of surfaces subjected to erosion-corrosion. Cast nickel-aluminium bronze / NaCl solution has been chosen to study as this system has been studied at Southampton for several years. In situ electrochemical, gravimetric and topographical analyses have been evaluated and discussed using microstructural and hardness measurements

Galvanic corrosion performance of high strength copper-nickel alloys in seawater

High strength copper-nickel (Cu-Ni-Mn-Al-Nb) alloys are widely used for marine applications due to their excellent resistance to seawater corrosion, high inherent resistance to biofouling and ease of fabrication. However, in-service experience has shown that these alloys may encounter variable performance worldwide due to local environmental conditions. In particular, the corrosion performance of high strength Cu-Ni alloys may be affected by the seawater environmental factors, which may include: biofouling, temperature, salinity, pH and dissolved oxygen content. This study reports an investigation into the galvanic corrosion performance between two wrought high strength copper-nickel alloys, with nickel contents of 15 and 19 %, regarding the influence of surface oxide films / deposits and biofouling. X-ray photoelectron spectroscopy was used to study the composition of the corrosion product films. Analyses of galvanic currents, coupled and decoupled potentials routinely monitored for seawater immersion over a period of 2 years are presented

Erosion and erosion–corrosion performance of cast and thermally sprayed nickel–aluminium bronze

Nickel–aluminium bronze (NAB) is widely used for propulsion and seawater handling systems in naval platforms. It is selected because of its attractive combination of toughness and shock resistance but it has inherent susceptibility to selective phase corrosion (SPC) and erosion–corrosion. In order to extend the life of NAB components, modern coating techniques are being considered in order to confer improved wear and corrosion resistance, as well as a method of providing cost effective refurbishment. This paper presents research into erosion and erosion–corrosion of both “as-cast” and thermally sprayed NAB. The synergistic effects based on mass loss measurements and electrochemical techniques obtained from pure erosion (E), flow corrosion (C) and erosion–corrosion (T) experiments are presented under a range of energies that relate to maritime operating conditions. The influence of synergy was found to be dependent on flow energy and could be either beneficial or detrimental. Comparison of the erosion performance with that of the erosion–corrosion performance both coating and cast surfaces demonstrate a propensity for negative synergy. However, vulnerability at high energies to positive synergy was seen for the coating. The results of this work assist with material selection for controlled or reduced material loss in marine vessels

Corrosion, erosion and erosion–corrosion performance of plasma electrolytic oxidation (PEO) deposited Al2O3 coatings

Electrolytic plasma techniques have been used to surface modify 6082 aluminium alloy to a depth of 100 ?m. Potentiodynamic polarisations and electrochemical impedance spectroscopy (EIS) have been made under static conditions in order to evaluate the corrosion performance of both unsealed and sealed PEO coatings. The erosion and erosion–corrosion performance of the unsealed PEO Al2O3 coating has also been assessed for a range erodent kinetic energies which varied between 0.016 and 7.1 ?J. The erosion and erosion–corrosion tests were carried out using subangular sand particles ranging in size from 135 to 235 ?m. Scanning electron microscopy (SEM) was used to investigate the coating microstructure and the coating/substrate interface. The analyses show that the PEO Al2O3 coatings studied in this investigation had a pore/crack network to the Al alloy substrate, which compromised the corrosion performance and ultimately the erosion–corrosion performance

Erosion and erosion-corrosion performance of cast and thermally sprayed nickel-aluminium bronze

Nickel-Aluminum Bronze (NAB) is widely used for propulsion and seawater handling systems in naval platforms. It is selected because of its attractive combination of toughness and shock resistance but it has inherent susceptibility to selective phase corrosion and erosion-corrosion. In order to extend the life of NAB components, modern coating techniques are being considered in order to confer improved wear and corrosion resistance, as well as a method of providing cost effective refurbishment. This paper presents research into erosion and erosion-corrosion of both "as cast" and thermally sprayed NAB. The synergistic effects based on mass loss measurements obtained from pure erosion (E), flow corrosion (C) and erosion-corrosion (T) experiments are presented under a range of energies that relate to maritime operation conditions. The influence of synergy was found to be dependent on flow energy and could be either beneficial or detrimental. The results of this work assist with material selection for controlled or reduced material loss in marine vessels

The corrosion of nickel–aluminium bronze in seawater [in A Century of Tafel’s Equation: A Commemorative Issue of Corrosion Science]

Nickel–aluminium bronze (NAB) alloys show good corrosion resistance under marine conditions. The corrosion behaviour of cast and wrought NAB alloys is illustrated in this work through a range of electrochemical techniques including open-circuit potentiometry with time, oxygen reduction voltammetry, NAB dissolution voltammetry, potential step (or flow step) current transients and linear polarisation resistance. The galvanic coupling of NAB to stainless steel or copper is examined by zero resistance ammetery. The importance of using controlled flow working electrodes is illustrated by the use of a rotating disc electrode, a rotating cylinder electrode and a bimetallic (NAB/copper–nickel) rotating cylinder electrode. In addition to controlling the hydrodynamics, such electrodes allow charge transfer data to separate from those of mass transport control under mixed kinetic control. Longer term seawater immersion trials on planar coupons coupled to titanium or cupronickel are also reported. The relative contributions of erosion and corrosion attack are considered using a wall-jet electrode and the corrosion characteristics of NAB are compared to those of copper and copper–nickel in chloride media

Brucella endocarditis – A series of five case reports

Endocarditis due to brucellosis is considered a rare occurrence involving native, congenital and prosthetic valves. The diagnosis needs high degree of suspicion in culture negative endocarditis especially in those with history of exposure to farm animals. A positive culture in a susceptible patient confirms the diagnosis with 91% sensitivity. An early diagnosis and prompt treatment with appropriate antibiotics can restore the valve structural integrity with minimal damage. Here we present a series of five cases of culture proven Brucella endocarditis (four native valves, one prosthetic valve) and this report discusses the diagnostic and management issues involved