1,720,992 research outputs found
Analysis of nickel-aluminium bronze crevice solution chemistry using capillary electrophoresis
No full textA new approach has been developed to simultaneously analyse the evolution of metallic cation and inorganic anion solution concentrations within a crevice micro-environment using capillary electrophoresis. The chemical conditions within a Cortest crevice assembly have been studied when the bold surface of nickel–aluminium bronze was exposed to a bulk 3.5% (0.6 M) NaCl solution. The crevice solution chemistry was assessed intermittently over a period of 6 months. Capillary electrophoresis was used since it is capable of analysing nanolitre solution volumes with widely disparate concentrations of species. A methodology has been optimised for the first time to simultaneously evaluate inorganic anion and metal cation crevice solution composition, without the need for extensive sample pre-treatment. Analyses for chloride and a range of metal cations, including Cu2+, Ni2+ and Fe3+ are presented. <br/
The influence of nickel-aluminium bronze microstructure and crevice colution on the initiation of crevice corrosion
No full textA new mechanistic model has been established for the chemical and electrochemical mechanisms controlling nickel–aluminium bronze crevice corrosion. The crevice corrosion was initially confined to eutectoid regions with slight attack of the copper rich ?-phase within the ?+?III eutectoid. In the presence of high chloride concentrations, copper and aluminium complexes form and the hydrolysis of these complexes leads to the acidification of the crevice solution chemistry. As the crevice solution becomes increasingly acidic the initial protection of the ?-phases due to their higher aluminium contents is lost and become anodic to the ?-phase. The continuous nature of the ?III-phase makes it vulnerable with an 80 ?m depth of attack after only the first month which is accompanied by internal copper redeposited at cathodic sites. Crevice corrosion of copper-based alloys is often reported to be controlled by a copper-ion concentration cell, however, for nickel–aluminium bronze it appears that primarily the crevice corrosion propagation results from a combined action of localised acidification and differential aeration between the bold and occluded zones. This mechanistic understanding provides further insights in to the development of crevice corrosion experienced by nickel–aluminium bronze after long-term exposures to natural seawater for up to 3 years.<br/
The slurry erosion behaviour of high velocity oxy-fuel (HVOF) sprayed aluminium bronze coatings
No full textThis paper investigates the erosion aspects of a novel high velocity oxy-fuel (HVOF) sprayed aluminium bronze coating under sand particle impingement conditions, using a free-jet impingement erosion rig. Erodents at various kinetic energies (0.1–0.8 ?J) and impingement angles (30, 60 and 90°) were used to simulate actual service conditions. Gravimetric measurements, surface profilometry and microscopy techniques were utilised to determine both the erosion rate and the mechanisms of coating failure. The erosion rate of the coating was found to be comparable to bulk 90/10 cupro-nickel (C70600) and about twice that of Marinel and AISI 316L stainless steel. These results suggest that HVOF aluminium bronze coatings are suitable candidates for marine applications. Analysis of the erosion scars suggest that coating erosion occurred by a combination of cutting wear, plastic deformation, and crack propagation at splat boundaries (brittle oxides) leading to the detachment of coating splats, cutting wear was found to be the most dominant. The cutting process was dominated by smaller particle impacts. The number of these particles which cause damage appears to be a function of kinetic energy
Erosion of aluminum based claddings on steel by sand in water
No full textThis paper describes the slurry erosion of a range of HVOF deposited aluminium-based claddings on steel by sand in water. Coatings, approximately 300 ?m thick, of commercially pure aluminium, eutectic aluminium/silicon alloy (12%) and of a novel composite incorporating alumina in this alloy have been tested, both as sprayed and as ground to remove surface roughness as far as possible. Angular silica sand of mean diameter 235 ?m was used at a concentration of 2.5% in tapwater at impingement angles of 90° and 30° and a jet velocity of 27 m/s. Mass loss data and surface structure, as shown by electron microscopy and profilometry, are related to the test conditions, initial surface topography, material hardness and microstructure, especially porosity. They are discussed in terms of the mechanisms of erosion that occur in the different materials, with reference to microcutting and plastic deformation of the surface and to the effects of the alumina inclusions. The consequences of poor flow-out, leading to significant residual porosity of the composite cladding are discussed
Biomimetic inspired marine antifouling coating system assessed using electrochemical techniques
No full textElectrochemical investigation of high velocity oxy-fuel (HVOF) aluminium bronze coatings under slurry erosion in saline environments
No full textEstimation of organic biocide leaching rate using a modified cavity jump diffusion model
No full textEstimation of biocide lifetime in marine antifouling coatings is of great use to improve and develop technologies. An existing model simulating the diffusion of molecules in polymer networks below glass transition temperature was employed to estimate leaching. This model was modified to allow for swelling due to water uptake and to permit evaluation of copolymer binders as well as homopolymers. This enabled prediction of biocide diffusion coefficients in polymeric coatings of various binder types, including pMMA, a pMMA/butylacrylate binder containing rosin, and a trityl copolymer, using usnic acid as a ‘model’ biocide. For comparison with modelling results, coatings fomulated using each binder type were also submitted to static and dynamic seawater immersion. Fluorescence microscopy techniques were used to quantify biocide leaching from these coatings relative to unimmersed coatings. Agreement of the modified diffusion model with experimental data was good for pMMA, reasonable for the rosin-based binder, and poor for the trityl binder. Comparison of predicted and experimental biocide profiles in the binder demonstrated deviation from the expected Fickian mechanism for the pMMA binder, despite the accurate rate prediction. This work demonstrates a first approach to predicting organic biocide diffusion, and highlights the areas for future attention
Electrochemical investigation of high velocity oxy-fuel (HVOF) aluminum bronze coatings under slurry erosion in saline environments
No full textErosion and erosion-corrosion performance of cast and thermally sprayed nickel-aluminium bronze
No full textNickel-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
Corrosion and impressed current cathodic protection of copper-based materials using a bimetallic rotating cylinder electrode (BRCE)
No full textA bimetallic rotating cylinder electrode (having individual electrode areas of 10 cm2 and rotating at 200–1400 rpm) has been used to examine the corrosion and protection characteristics of copper/nickel aluminium bronze and 90–10 copper–nickel/nickel aluminium bronze galvanic couples in filtered seawater at 25 °C. The flow-influenced electrochemistry of the systems was determined using zero resistance ammetry, corrosion potential measurements and a potential step current transient technique. In each case, the galvanic corrosion potential and corrosion rate displayed a Reynolds number dependency where mass transport control of the anodic dissolution reaction partially controlled the reaction rate. Bimetallic impressed current cathodic protection (ICCP) has also been demonstrated for a range of applied protection potentials and Reynolds numbers. A comparison has been made between the directly measured bimetallic ICCP current demand and that determined from independent, single-metal rotating cylinder electrode measurements. In this case, the mixed charge and mass transport controlled rate of oxygen reduction was examined
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