We present results of a laboratory study of novel electrical resistivity tomography (ERT) sensor ... more We present results of a laboratory study of novel electrical resistivity tomography (ERT) sensor materials, whose performance has been assessed in terms of suitability for long-term geoelectrical monitoring. The study has addressed concerns over the longevity of buried ERT sensors required to support nuclear decommissioning at the Sellafield Site in the UK. Electrodes made from three candidate materials and installed in a bentonite grout were subjected to accelerated measurements and electrochemical analyses were carried out on both pristine and used electrodes after extraction from the laboratory tanks. Electrical contact resistance showed significantly different behaviour for stainless steels compared with platinised titanium. Pt-Ti sensors displayed outstanding properties and their stability under operational conditions was remarkable. Their susceptibility to ERT noise, which was expected to be worse due to their higher nobility, was only marginally greater than that of stainless...
The importance of Co–Ni–P alloy deposits is summarised and recent developments are highlighted. E... more The importance of Co–Ni–P alloy deposits is summarised and recent developments are highlighted. Electroplating and electroless deposition of nanocrystalline Co–Ni–P ternary coatings are considered. Nanostructure, physical and mechanical properties (including corrosion resistance) of various bath types and compositions (including pH and electrolyte additives) as well as plating conditions (including current density, temperature and agitation) are summarised. Applications range from wear and corrosion resistant coatings, particularly as a hard chromium replacement to speciality hydrogen evolution electrodes in water electrolysis. Following this concise review, future research needs are briefly listed.
Abstract In this research, nanocrystalline nickel (14–25 nm) was electrodeposited on rotating cyl... more Abstract In this research, nanocrystalline nickel (14–25 nm) was electrodeposited on rotating cylindrical electrodes in a modified Watts bath. Saccharin was used as a grain refiner. The effect of cathode rotation speed and saccharin concentration on the grain size was studied by transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis. The preferred orientation of deposits progressively changed from a (2 2 0), (2 0 0), and (1 1 1) fiber texture for a saccharin free bath to a (1 1 1) and (2 0 0) double fiber texture for a bath containing 5 g l −1 saccharin. Cathode rotation enhanced the intensity of (1 1 1) peak relative to (1 0 0). The effect of cathode rotation speed, current density, and saccharin concentration on the coating microhardness was investigated. The maximum recorded hardness was 620 HV for 14 nm grain size. The effect of current density and saccharin concentration on morphology was observed by scanning electron microscopy (SEM). The current efficiency changes were studied as a result of saccharin concentration.
The preparation of PbO2 coatings on reticulated vitreous carbon (RVC) has been carried out at con... more The preparation of PbO2 coatings on reticulated vitreous carbon (RVC) has been carried out at constant current from electrolytic baths containing aqueous Pb(II) and methanesulfonic acid (MSA, CH3SO3H). The morphological and structural analysis of the RVC/PbO2 deposits carried out by scanning electron microscopy (SEM) and X-ray diffraction revealed that a thick (100μm), homogeneous, nanostructured β-PbO2 film can be successfully formed. As a result, three-dimensional β-PbO2 structures were obtained, being particularly interesting for their use as anodes in wastewater treatment. The high oxidation ability of these anodes has been verified by the electro-oxidation of Methyl Orange aqueous solutions. Quick decolourisation was achieved, with total colour removal in less than 60min at 600mA due to the production of large amounts of reactive OH radicals from the oxidation of water at high anodic potentials. The progressive mineralisation of the solutions was also ascertained from the total organic carbon (TOC) removal, which was much quicker at a higher applied current. All the coated RVC electrodes exhibited excellent long-term stability and remained unaltered after prolonged electrolyses. In addition, novel PbO2 composite coatings were prepared in the presence of hydrothermally synthesized titanate nanotubes (TiNT). The SEM images showed the presence of TiNT agglomerates along the PbO2 surface, which led to higher anodic current in the cyclic voltammetries carried out with Methyl Orange solutions. It is suggested that TiNT favour the adsorption of the organic molecules, facilitating the contact with the OH radicals and thus accelerating the electro-oxidation process. This was confirmed by the faster TOC removal compared to that yielded by the RVC/PbO2, being 45% instead of 24% at 120min.
Graphene (GN) has many beneficial properties that encourage wide applications. Various manufactur... more Graphene (GN) has many beneficial properties that encourage wide applications. Various manufacturing procedures are detailed in the literature but most are unable to produce GN flakes in bulk and usually result in toxic discharges. These techniques are also timeconsuming and involve operations at high temperatures. A 'greener', simpler and a onestep synthesis of the material may be realised by electrochemical oxidation (or reduction) of the graphite host leading to intercalation of ions from the electrolyte (which may be aqueous, organic or an ionic liquid) followed by electrochemical exfoliation. Single-or multi-layered GN flakes can easily be produced in short periods of time, typically within 30 min. This paper reviews the state-of-the-art methods reported in the literature regarding electrochemical synthesis of GN flakes as well as their properties (determined via sophisticated analytical methods such as AFM, TEM, SEM or Raman spectroscopy). This is followed by a discussion on the applications of electrochemically prepared GN flakes. Challenges and opportunities are briefly considered leading to the conclusion that the cathodic intercalation of lithium ions into graphite can produce the highest yield (>70%) of pristine GN flakes in organic electrolytes. Future work is recommended with ternary eutectic melts as electrolytes.
In part 1 of this review, emerging practice to realise nanostructured metallic coatings by electr... more In part 1 of this review, emerging practice to realise nanostructured metallic coatings by electrodeposition, anodising and electrophoresis has been considered. Conventional, aqueous electrolytes may be utilised in some cases if workpiece preparation and process conditions are well controlled. Such coatings can provide wear and corrosion resistance or a catalytic or high active area compared to more conventional coatings. An overview of the principles involved in deploying electrochemical techniques to produce nanostructured surfaces and factors influencing developments in this rapidly emerging field were considered. The strategies, which can be adopted to electrodeposit nanostructured metallic coatings, include grain refinement, application of a pulsed current, inclusion of nanoparticles into the coating and the use of nanoporous templates. In part 2, examples of nanostructured coatings and their properties are illustrated with research findings from the authors' laboratory and the literature. Nanostructured metallic coatings include nanocrystalline, functionally graded, nanocomposite and recently introduced hierarchical structures. The potential uses for these coatings in engineering industries (including tribology and energy conversion) are summarised. Finally, future developments necessary to realise and deploy the coatings in increasingly demanding environments are considered.
This study investigates the removal of Pb(II) using polymer matrix membranes, cellulose acetate/v... more This study investigates the removal of Pb(II) using polymer matrix membranes, cellulose acetate/vinyl triethoxysilane modified graphene oxide and gum Arabic (GuA) membranes. These complexation-NF membranes were successfully synthesized via dissolution casting method for better transport phenomenon. The varied concentrations of GuA were induced in the polymer matrix membrane. The prepared membranes M-GuA2–M-GuA10 were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, atomic force microscope and bio-fouling studies. Thermal stability of the membranes was determined by thermogravimetric analysis under nitrogen atmosphere. Dead end nanofiltration was carried out to study the perm- selectivity of all the membranes under varied pressure and concentration of Pb(NO3)2. The complexation-NF membrane performances were significantly improved after the addition of GuA in the polymer matrix membrane system. M-GuA8 membrane sh...
International Journal of Environmental Science and Technology, 2020
The present study reports the characterization of reverse osmosis (RO) technology at water treatm... more The present study reports the characterization of reverse osmosis (RO) technology at water treatment plant Cogen-2 in paper and Board mills, Pakistan. RO is a commonly used process to obtain de-mineralized water for high-pressure boiler operation in thermal power plants. Scaling and fouling in three-stage RO plants is a major challenge in chemical industry due to the use of raw brackish water in the power plant of paper and board mills. In our study, the feed water quality of RO was changed from soft water to raw water to make it economical. The cleaning frequency was increased three times than normal, which was unsafe for operation and it was required to control scaling and fouling to achieve the desired result. Differential pressures behavior of all stages for 2-month data was observed without acid treatment, and the results of Langelier Saturation Index (LSI) control parameters (temperature, pH, total dissolved solids, calcium hardness, and alkalinity) clearly showed the abnormal...
Reticulated vitreous carbon (RVC) substrates were coated with a composite of PbO 2 and titanate n... more Reticulated vitreous carbon (RVC) substrates were coated with a composite of PbO 2 and titanate nanosheets (TiNS) by anodic electrophoretic depostion. The structure and morphological characteristics of the coating were evaluated by field emission scanning electron microscopy (FESEM) and Raman spectroscopy. The TiNS/PbO 2 /RVC coating contained the anatase phase and showed a well-defined, microporous morphology with hydrophilic character along the length and thickness of the RVC struts. Electrochemical and photocatalytic activity of the coatings facilitated RB-5 dye degradation as a model organic pollutant in wastewater. The electrochemical decolourisation involves the generation of hydroxyl free radicals over the TiNS/PbO 2 /RVC anode composite surface, whereas photocatalytic decolourisation was driven by the synergetic photocatalytic effect imparted by the photoinduced holes and free electron acceptors. The photocatalytic properties of the TiNS/PbO 2 coating were achieved by calcination at 450°C for 60 min in air which converted the titanate phase to anatase and modified its surface area. This enabled 98% electrochemical decolourisation of the RB-5 dye solution (measured by visible absorption at 597 nm) in a time of 60 min.
This paper considers the effects of electrolyte resistivity and inter-electrode gap on the simula... more This paper considers the effects of electrolyte resistivity and inter-electrode gap on the simulated cell potential of an idealized Zn-Ce unit flow cell as a function of the applied current density. The thermodynamic, kinetic and ohmic components of cell potential in a redox flow battery (RFB) are taken into account. This is important in the Zn-Ce RFB, where the positive electrode reaction tends to govern cell performance. The ionic conductivity of methanesulfonic acid (MSA) and typical electrolytes reported in the literature were measured as a function of MSA concentration and temperature. At 50 °C, the ionic resistivity of the positive and negative electrolytes is 3.0 ? cm and 4.8 ? cm respectively, for the most favourable electrolyte composition. The simulated cell potential showed that high surface-area electrodes were beneficial to the cell performance, while electrolytes containing 0.8 mol dm–3 Ce(III) and 1.5 mol dm–3 Zn(II) produced the lowest ohmic drop, which decreased at higher temperatures. The activation overpotential and internal resistance can provide the main potential loss components, depending on electrolyte composition, cell design and electrode materials. The effect of cell geometry on the cell potential was also assessed, larger inter-electrode gaps significantly increasing potential losses.
SUMMARYThe importance of electrode potential measurements in metal finishing is highlighted and t... more SUMMARYThe importance of electrode potential measurements in metal finishing is highlighted and the principles of such measurements are concisely reviewed. Scales for electrode potential are compared and practical determinations are considered.
Since nanofluids increase the thermal conductivity of a fluid mixture compared with the base flui... more Since nanofluids increase the thermal conductivity of a fluid mixture compared with the base fluid, it is important to investigate any damaging effects caused by the presence of the solid particles. Thus, this paper explores the nanofluid synergistic effects produced by the addition of 1 g dm-3 Al 2 O 3 nanoparticles to sea water and compares the performance with the base fluid without nanoparticles. Studies are conducted on carbon steel, using a hydrodynamically smooth-rotating cylinder electrode in turbulent flow at 298 K. The pure corrosion rate and erosion rate of carbon steel in the fluids free of nanoparticles are, respectively, higher (up to 82 %) and lower (ca. 11 %) than in the nanofluids. The synergistic effect of erosion and corrosion in a nanofluid is much higher (up to 237 %) than in the base fluid. These results indicate that the presence of nanoparticles in a flowing fluid could lead to considerable rates of material loss.
Abstract An Au-coated TiO2 nanotubular array, in the vertically aligned form, was investigated as... more Abstract An Au-coated TiO2 nanotubular array, in the vertically aligned form, was investigated as a highly porous nanostructured electrode for the electrochemical reduction of H2O2 in an acidic sulphate electrolyte at 295 K. The TiO2 nanotubular arrays were formed via a two-stage anodising then nanosized Au particles were sputter deposited onto the surface. The following aspects were studied: (a) the shape evolution of Au particles on the nanotubular array (via surface microstructural imaging), (b) the effect of different degrees of Au loading on the nanotubular array (via voltammetric analysis) and (c) the electrochemical response of an Au–TiO2 nanotubular array compared to a plain, 2-D Au foil. The Au particles could be deposited as a thin 3-D coated layer or as nodular nanostructures on the array. The highly nanoporous structure of the Au–TiO2 electrode led to a large enhancement in the limiting current (enhancement factor up to 6.6) and charge density (enhancement factor up to 8.9) for peroxide reduction compared to a plain Au foil due to the architecture of the ordered, high surface area of the nanotubular array.
Background: Evans’s drop is a classic corrosion experiment that is nearly 100 years old, and it i... more Background: Evans’s drop is a classic corrosion experiment that is nearly 100 years old, and it is analogous to other corrosion systems promoted by O2 gradients. The availability of more robust finite element software packages opens the possibility to reach a deeper understanding of these kind of corrosion systems. Methodology: In order to solve the problem, the model includes the governing mass transport diffusion and migration equation and the material balance in a nonsteady state by the finite element method. This is performed using COMSOL Multiphysics to predict the tertiary current and potential distribution considering the geometry, reaction kinetics, and mass transport for each ionic species. Significant Findings: A simulation of the tertiary current and potential distribution of the Evans’s drop corrosion experiment on an iron surface is presented. An oxygen concentration difference of 0.18 mol m−3 between the center and the drop periphery sets up a potential difference of 6...
We present results of a laboratory study of novel electrical resistivity tomography (ERT) sensor ... more We present results of a laboratory study of novel electrical resistivity tomography (ERT) sensor materials, whose performance has been assessed in terms of suitability for long-term geoelectrical monitoring. The study has addressed concerns over the longevity of buried ERT sensors required to support nuclear decommissioning at the Sellafield Site in the UK. Electrodes made from three candidate materials and installed in a bentonite grout were subjected to accelerated measurements and electrochemical analyses were carried out on both pristine and used electrodes after extraction from the laboratory tanks. Electrical contact resistance showed significantly different behaviour for stainless steels compared with platinised titanium. Pt-Ti sensors displayed outstanding properties and their stability under operational conditions was remarkable. Their susceptibility to ERT noise, which was expected to be worse due to their higher nobility, was only marginally greater than that of stainless...
The importance of Co–Ni–P alloy deposits is summarised and recent developments are highlighted. E... more The importance of Co–Ni–P alloy deposits is summarised and recent developments are highlighted. Electroplating and electroless deposition of nanocrystalline Co–Ni–P ternary coatings are considered. Nanostructure, physical and mechanical properties (including corrosion resistance) of various bath types and compositions (including pH and electrolyte additives) as well as plating conditions (including current density, temperature and agitation) are summarised. Applications range from wear and corrosion resistant coatings, particularly as a hard chromium replacement to speciality hydrogen evolution electrodes in water electrolysis. Following this concise review, future research needs are briefly listed.
Abstract In this research, nanocrystalline nickel (14–25 nm) was electrodeposited on rotating cyl... more Abstract In this research, nanocrystalline nickel (14–25 nm) was electrodeposited on rotating cylindrical electrodes in a modified Watts bath. Saccharin was used as a grain refiner. The effect of cathode rotation speed and saccharin concentration on the grain size was studied by transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis. The preferred orientation of deposits progressively changed from a (2 2 0), (2 0 0), and (1 1 1) fiber texture for a saccharin free bath to a (1 1 1) and (2 0 0) double fiber texture for a bath containing 5 g l −1 saccharin. Cathode rotation enhanced the intensity of (1 1 1) peak relative to (1 0 0). The effect of cathode rotation speed, current density, and saccharin concentration on the coating microhardness was investigated. The maximum recorded hardness was 620 HV for 14 nm grain size. The effect of current density and saccharin concentration on morphology was observed by scanning electron microscopy (SEM). The current efficiency changes were studied as a result of saccharin concentration.
The preparation of PbO2 coatings on reticulated vitreous carbon (RVC) has been carried out at con... more The preparation of PbO2 coatings on reticulated vitreous carbon (RVC) has been carried out at constant current from electrolytic baths containing aqueous Pb(II) and methanesulfonic acid (MSA, CH3SO3H). The morphological and structural analysis of the RVC/PbO2 deposits carried out by scanning electron microscopy (SEM) and X-ray diffraction revealed that a thick (100μm), homogeneous, nanostructured β-PbO2 film can be successfully formed. As a result, three-dimensional β-PbO2 structures were obtained, being particularly interesting for their use as anodes in wastewater treatment. The high oxidation ability of these anodes has been verified by the electro-oxidation of Methyl Orange aqueous solutions. Quick decolourisation was achieved, with total colour removal in less than 60min at 600mA due to the production of large amounts of reactive OH radicals from the oxidation of water at high anodic potentials. The progressive mineralisation of the solutions was also ascertained from the total organic carbon (TOC) removal, which was much quicker at a higher applied current. All the coated RVC electrodes exhibited excellent long-term stability and remained unaltered after prolonged electrolyses. In addition, novel PbO2 composite coatings were prepared in the presence of hydrothermally synthesized titanate nanotubes (TiNT). The SEM images showed the presence of TiNT agglomerates along the PbO2 surface, which led to higher anodic current in the cyclic voltammetries carried out with Methyl Orange solutions. It is suggested that TiNT favour the adsorption of the organic molecules, facilitating the contact with the OH radicals and thus accelerating the electro-oxidation process. This was confirmed by the faster TOC removal compared to that yielded by the RVC/PbO2, being 45% instead of 24% at 120min.
Graphene (GN) has many beneficial properties that encourage wide applications. Various manufactur... more Graphene (GN) has many beneficial properties that encourage wide applications. Various manufacturing procedures are detailed in the literature but most are unable to produce GN flakes in bulk and usually result in toxic discharges. These techniques are also timeconsuming and involve operations at high temperatures. A 'greener', simpler and a onestep synthesis of the material may be realised by electrochemical oxidation (or reduction) of the graphite host leading to intercalation of ions from the electrolyte (which may be aqueous, organic or an ionic liquid) followed by electrochemical exfoliation. Single-or multi-layered GN flakes can easily be produced in short periods of time, typically within 30 min. This paper reviews the state-of-the-art methods reported in the literature regarding electrochemical synthesis of GN flakes as well as their properties (determined via sophisticated analytical methods such as AFM, TEM, SEM or Raman spectroscopy). This is followed by a discussion on the applications of electrochemically prepared GN flakes. Challenges and opportunities are briefly considered leading to the conclusion that the cathodic intercalation of lithium ions into graphite can produce the highest yield (>70%) of pristine GN flakes in organic electrolytes. Future work is recommended with ternary eutectic melts as electrolytes.
In part 1 of this review, emerging practice to realise nanostructured metallic coatings by electr... more In part 1 of this review, emerging practice to realise nanostructured metallic coatings by electrodeposition, anodising and electrophoresis has been considered. Conventional, aqueous electrolytes may be utilised in some cases if workpiece preparation and process conditions are well controlled. Such coatings can provide wear and corrosion resistance or a catalytic or high active area compared to more conventional coatings. An overview of the principles involved in deploying electrochemical techniques to produce nanostructured surfaces and factors influencing developments in this rapidly emerging field were considered. The strategies, which can be adopted to electrodeposit nanostructured metallic coatings, include grain refinement, application of a pulsed current, inclusion of nanoparticles into the coating and the use of nanoporous templates. In part 2, examples of nanostructured coatings and their properties are illustrated with research findings from the authors' laboratory and the literature. Nanostructured metallic coatings include nanocrystalline, functionally graded, nanocomposite and recently introduced hierarchical structures. The potential uses for these coatings in engineering industries (including tribology and energy conversion) are summarised. Finally, future developments necessary to realise and deploy the coatings in increasingly demanding environments are considered.
This study investigates the removal of Pb(II) using polymer matrix membranes, cellulose acetate/v... more This study investigates the removal of Pb(II) using polymer matrix membranes, cellulose acetate/vinyl triethoxysilane modified graphene oxide and gum Arabic (GuA) membranes. These complexation-NF membranes were successfully synthesized via dissolution casting method for better transport phenomenon. The varied concentrations of GuA were induced in the polymer matrix membrane. The prepared membranes M-GuA2–M-GuA10 were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, atomic force microscope and bio-fouling studies. Thermal stability of the membranes was determined by thermogravimetric analysis under nitrogen atmosphere. Dead end nanofiltration was carried out to study the perm- selectivity of all the membranes under varied pressure and concentration of Pb(NO3)2. The complexation-NF membrane performances were significantly improved after the addition of GuA in the polymer matrix membrane system. M-GuA8 membrane sh...
International Journal of Environmental Science and Technology, 2020
The present study reports the characterization of reverse osmosis (RO) technology at water treatm... more The present study reports the characterization of reverse osmosis (RO) technology at water treatment plant Cogen-2 in paper and Board mills, Pakistan. RO is a commonly used process to obtain de-mineralized water for high-pressure boiler operation in thermal power plants. Scaling and fouling in three-stage RO plants is a major challenge in chemical industry due to the use of raw brackish water in the power plant of paper and board mills. In our study, the feed water quality of RO was changed from soft water to raw water to make it economical. The cleaning frequency was increased three times than normal, which was unsafe for operation and it was required to control scaling and fouling to achieve the desired result. Differential pressures behavior of all stages for 2-month data was observed without acid treatment, and the results of Langelier Saturation Index (LSI) control parameters (temperature, pH, total dissolved solids, calcium hardness, and alkalinity) clearly showed the abnormal...
Reticulated vitreous carbon (RVC) substrates were coated with a composite of PbO 2 and titanate n... more Reticulated vitreous carbon (RVC) substrates were coated with a composite of PbO 2 and titanate nanosheets (TiNS) by anodic electrophoretic depostion. The structure and morphological characteristics of the coating were evaluated by field emission scanning electron microscopy (FESEM) and Raman spectroscopy. The TiNS/PbO 2 /RVC coating contained the anatase phase and showed a well-defined, microporous morphology with hydrophilic character along the length and thickness of the RVC struts. Electrochemical and photocatalytic activity of the coatings facilitated RB-5 dye degradation as a model organic pollutant in wastewater. The electrochemical decolourisation involves the generation of hydroxyl free radicals over the TiNS/PbO 2 /RVC anode composite surface, whereas photocatalytic decolourisation was driven by the synergetic photocatalytic effect imparted by the photoinduced holes and free electron acceptors. The photocatalytic properties of the TiNS/PbO 2 coating were achieved by calcination at 450°C for 60 min in air which converted the titanate phase to anatase and modified its surface area. This enabled 98% electrochemical decolourisation of the RB-5 dye solution (measured by visible absorption at 597 nm) in a time of 60 min.
This paper considers the effects of electrolyte resistivity and inter-electrode gap on the simula... more This paper considers the effects of electrolyte resistivity and inter-electrode gap on the simulated cell potential of an idealized Zn-Ce unit flow cell as a function of the applied current density. The thermodynamic, kinetic and ohmic components of cell potential in a redox flow battery (RFB) are taken into account. This is important in the Zn-Ce RFB, where the positive electrode reaction tends to govern cell performance. The ionic conductivity of methanesulfonic acid (MSA) and typical electrolytes reported in the literature were measured as a function of MSA concentration and temperature. At 50 °C, the ionic resistivity of the positive and negative electrolytes is 3.0 ? cm and 4.8 ? cm respectively, for the most favourable electrolyte composition. The simulated cell potential showed that high surface-area electrodes were beneficial to the cell performance, while electrolytes containing 0.8 mol dm–3 Ce(III) and 1.5 mol dm–3 Zn(II) produced the lowest ohmic drop, which decreased at higher temperatures. The activation overpotential and internal resistance can provide the main potential loss components, depending on electrolyte composition, cell design and electrode materials. The effect of cell geometry on the cell potential was also assessed, larger inter-electrode gaps significantly increasing potential losses.
SUMMARYThe importance of electrode potential measurements in metal finishing is highlighted and t... more SUMMARYThe importance of electrode potential measurements in metal finishing is highlighted and the principles of such measurements are concisely reviewed. Scales for electrode potential are compared and practical determinations are considered.
Since nanofluids increase the thermal conductivity of a fluid mixture compared with the base flui... more Since nanofluids increase the thermal conductivity of a fluid mixture compared with the base fluid, it is important to investigate any damaging effects caused by the presence of the solid particles. Thus, this paper explores the nanofluid synergistic effects produced by the addition of 1 g dm-3 Al 2 O 3 nanoparticles to sea water and compares the performance with the base fluid without nanoparticles. Studies are conducted on carbon steel, using a hydrodynamically smooth-rotating cylinder electrode in turbulent flow at 298 K. The pure corrosion rate and erosion rate of carbon steel in the fluids free of nanoparticles are, respectively, higher (up to 82 %) and lower (ca. 11 %) than in the nanofluids. The synergistic effect of erosion and corrosion in a nanofluid is much higher (up to 237 %) than in the base fluid. These results indicate that the presence of nanoparticles in a flowing fluid could lead to considerable rates of material loss.
Abstract An Au-coated TiO2 nanotubular array, in the vertically aligned form, was investigated as... more Abstract An Au-coated TiO2 nanotubular array, in the vertically aligned form, was investigated as a highly porous nanostructured electrode for the electrochemical reduction of H2O2 in an acidic sulphate electrolyte at 295 K. The TiO2 nanotubular arrays were formed via a two-stage anodising then nanosized Au particles were sputter deposited onto the surface. The following aspects were studied: (a) the shape evolution of Au particles on the nanotubular array (via surface microstructural imaging), (b) the effect of different degrees of Au loading on the nanotubular array (via voltammetric analysis) and (c) the electrochemical response of an Au–TiO2 nanotubular array compared to a plain, 2-D Au foil. The Au particles could be deposited as a thin 3-D coated layer or as nodular nanostructures on the array. The highly nanoporous structure of the Au–TiO2 electrode led to a large enhancement in the limiting current (enhancement factor up to 6.6) and charge density (enhancement factor up to 8.9) for peroxide reduction compared to a plain Au foil due to the architecture of the ordered, high surface area of the nanotubular array.
Background: Evans’s drop is a classic corrosion experiment that is nearly 100 years old, and it i... more Background: Evans’s drop is a classic corrosion experiment that is nearly 100 years old, and it is analogous to other corrosion systems promoted by O2 gradients. The availability of more robust finite element software packages opens the possibility to reach a deeper understanding of these kind of corrosion systems. Methodology: In order to solve the problem, the model includes the governing mass transport diffusion and migration equation and the material balance in a nonsteady state by the finite element method. This is performed using COMSOL Multiphysics to predict the tertiary current and potential distribution considering the geometry, reaction kinetics, and mass transport for each ionic species. Significant Findings: A simulation of the tertiary current and potential distribution of the Evans’s drop corrosion experiment on an iron surface is presented. An oxygen concentration difference of 0.18 mol m−3 between the center and the drop periphery sets up a potential difference of 6...
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Papers by Frank C Walsh