Steven Thorpe
- Courses6
- Reviews20
- School: University of Toronto
- Campus: St. George Campus
- Department: Materials Engineering
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Location:
Toronto, ON - Dates at University of Toronto: November 2003 - September 2017
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Biography
University of Toronto St. George Campus - Materials Engineering
Experience
Stuart Energy
Vice President Technology
Steven worked at Stuart Energy as a Vice President Technology
University of Toronto
Professor of Materials Science
Steven worked at University of Toronto as a Professor of Materials Science
Education
University of Toronto
Professor of Materials Science
Publications
Microcapillary polarization measurements of friction stir spot welds made in AZ31B magnesium alloy
Materials and Corrosion / WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Microcapillary polarization procedures were optimized to examine the corrosion characteristics of the various microstructural zones developed during friction stir spot welds made in AZ31 magnesium alloy. Tungsten carbide tracing confirmed the location and shape of the stir zone in the weldment. The stir zone was determined to be the noble region while the base metal and the thermo-mechanically affected zone were found to be active. The thermo-mechanically affected zone was found to be most susceptible to localized corrosion attack due to its proximity to the noble stir zone, and the subsequent formation of a macrogalvanic cell. Corrosion rates of individual weld regions were measured.
Microcapillary polarization measurements of friction stir spot welds made in AZ31B magnesium alloy
Materials and Corrosion / WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Microcapillary polarization procedures were optimized to examine the corrosion characteristics of the various microstructural zones developed during friction stir spot welds made in AZ31 magnesium alloy. Tungsten carbide tracing confirmed the location and shape of the stir zone in the weldment. The stir zone was determined to be the noble region while the base metal and the thermo-mechanically affected zone were found to be active. The thermo-mechanically affected zone was found to be most susceptible to localized corrosion attack due to its proximity to the noble stir zone, and the subsequent formation of a macrogalvanic cell. Corrosion rates of individual weld regions were measured.
Part 2 - Impacts of Electrolyte and Reactant Size on Structure Sensitivity in Electrocatalysis: A Geometric Approach
Electrocatalysis, Volume 3, Issue 2, pp 88-95
In previous work performed by the current authors, an in-depth analysis of the current theories relating particle size to electrocatalytic activity was undertaken. In that work, electronic structure effects, geometry and crystallographic orientation effects, territory theory and support structure effects could not account for the structure sensitivity exhibited in the experimental data. This study builds on that previous work and investigates the impact of electrolyte conditions and reactant size on the structure sensitivity of Au nanocatalysts for multiple electrochemical systems. The Fe3+/Fe2+ reaction was studied for multiple reactant sizes in a wide range of electrolyte conditions. There was a clear impact of reactant size on the critical size at which deviation from bulk electrocatalytic performance takes place. These findings were used to develop a geometric model, which could account for the increase in electrocatalytic activity observed below critical nanoparticle diameters.
Microcapillary polarization measurements of friction stir spot welds made in AZ31B magnesium alloy
Materials and Corrosion / WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Microcapillary polarization procedures were optimized to examine the corrosion characteristics of the various microstructural zones developed during friction stir spot welds made in AZ31 magnesium alloy. Tungsten carbide tracing confirmed the location and shape of the stir zone in the weldment. The stir zone was determined to be the noble region while the base metal and the thermo-mechanically affected zone were found to be active. The thermo-mechanically affected zone was found to be most susceptible to localized corrosion attack due to its proximity to the noble stir zone, and the subsequent formation of a macrogalvanic cell. Corrosion rates of individual weld regions were measured.
Part 2 - Impacts of Electrolyte and Reactant Size on Structure Sensitivity in Electrocatalysis: A Geometric Approach
Electrocatalysis, Volume 3, Issue 2, pp 88-95
In previous work performed by the current authors, an in-depth analysis of the current theories relating particle size to electrocatalytic activity was undertaken. In that work, electronic structure effects, geometry and crystallographic orientation effects, territory theory and support structure effects could not account for the structure sensitivity exhibited in the experimental data. This study builds on that previous work and investigates the impact of electrolyte conditions and reactant size on the structure sensitivity of Au nanocatalysts for multiple electrochemical systems. The Fe3+/Fe2+ reaction was studied for multiple reactant sizes in a wide range of electrolyte conditions. There was a clear impact of reactant size on the critical size at which deviation from bulk electrocatalytic performance takes place. These findings were used to develop a geometric model, which could account for the increase in electrocatalytic activity observed below critical nanoparticle diameters.
Microcapillary Polarization of Friction Stir Welds in AZ31B Magnesium Alloy
Electrochemical Society
Corrosion of friction stir welds made in AZ31B magnesium alloy has been investigated using the microcapillary polarization technique. Various weld regions were examined in both spot and seam welds. The stir zone showed a higher reduction potential than the thermo-mechanically affected zone (TMAZ) and the base metal, due to the dissolution of β-Mg 17 Al12 particles. The absence of second phase particles resulted in elimination of harmful microgalvanic cells between the β-Mg 17 Al12 particles and the α-Mg matrix, and an increased concentration of aluminum in solid solution. The noble stir zone formed a macro galvanic cell with the base metal, which resulted in accelerated corrosion of the TMAZ. No significant variation in the electrochemical response of various weld zones was seen between seam and spot welds.
Microcapillary polarization measurements of friction stir spot welds made in AZ31B magnesium alloy
Materials and Corrosion / WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Microcapillary polarization procedures were optimized to examine the corrosion characteristics of the various microstructural zones developed during friction stir spot welds made in AZ31 magnesium alloy. Tungsten carbide tracing confirmed the location and shape of the stir zone in the weldment. The stir zone was determined to be the noble region while the base metal and the thermo-mechanically affected zone were found to be active. The thermo-mechanically affected zone was found to be most susceptible to localized corrosion attack due to its proximity to the noble stir zone, and the subsequent formation of a macrogalvanic cell. Corrosion rates of individual weld regions were measured.
Part 2 - Impacts of Electrolyte and Reactant Size on Structure Sensitivity in Electrocatalysis: A Geometric Approach
Electrocatalysis, Volume 3, Issue 2, pp 88-95
In previous work performed by the current authors, an in-depth analysis of the current theories relating particle size to electrocatalytic activity was undertaken. In that work, electronic structure effects, geometry and crystallographic orientation effects, territory theory and support structure effects could not account for the structure sensitivity exhibited in the experimental data. This study builds on that previous work and investigates the impact of electrolyte conditions and reactant size on the structure sensitivity of Au nanocatalysts for multiple electrochemical systems. The Fe3+/Fe2+ reaction was studied for multiple reactant sizes in a wide range of electrolyte conditions. There was a clear impact of reactant size on the critical size at which deviation from bulk electrocatalytic performance takes place. These findings were used to develop a geometric model, which could account for the increase in electrocatalytic activity observed below critical nanoparticle diameters.
Microcapillary Polarization of Friction Stir Welds in AZ31B Magnesium Alloy
Electrochemical Society
Corrosion of friction stir welds made in AZ31B magnesium alloy has been investigated using the microcapillary polarization technique. Various weld regions were examined in both spot and seam welds. The stir zone showed a higher reduction potential than the thermo-mechanically affected zone (TMAZ) and the base metal, due to the dissolution of β-Mg 17 Al12 particles. The absence of second phase particles resulted in elimination of harmful microgalvanic cells between the β-Mg 17 Al12 particles and the α-Mg matrix, and an increased concentration of aluminum in solid solution. The noble stir zone formed a macro galvanic cell with the base metal, which resulted in accelerated corrosion of the TMAZ. No significant variation in the electrochemical response of various weld zones was seen between seam and spot welds.
A review of specific conductivities of potassium hydroxide solutions for various concentrations and temperatures
International Journal of Hydrogen Energy, Volume 32, Issue 3, Pages 359-364
This article gives a critical review of the current data on the specific conductivity of aqueous potassium hydroxide (KOH) solutions. Empirical correlations relating concentration to density were developed to compare specific conductivity data given in weight percentage KOH and molarity of KOH. Available data on specific conductivity is related with respect to one another and compared to experimental data. Based on these comparisons, specific sets of reported data were used to develop an equation relating specific conductivity of aqueous KOH to temperature and concentration. This empirical correlation was developed over a molarity range of 0–12 at temperatures of . The correlation has been compared with that proposed by See and White and shows greater accuracy over the concentration range modeled.
Microcapillary polarization measurements of friction stir spot welds made in AZ31B magnesium alloy
Materials and Corrosion / WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Microcapillary polarization procedures were optimized to examine the corrosion characteristics of the various microstructural zones developed during friction stir spot welds made in AZ31 magnesium alloy. Tungsten carbide tracing confirmed the location and shape of the stir zone in the weldment. The stir zone was determined to be the noble region while the base metal and the thermo-mechanically affected zone were found to be active. The thermo-mechanically affected zone was found to be most susceptible to localized corrosion attack due to its proximity to the noble stir zone, and the subsequent formation of a macrogalvanic cell. Corrosion rates of individual weld regions were measured.
Part 2 - Impacts of Electrolyte and Reactant Size on Structure Sensitivity in Electrocatalysis: A Geometric Approach
Electrocatalysis, Volume 3, Issue 2, pp 88-95
In previous work performed by the current authors, an in-depth analysis of the current theories relating particle size to electrocatalytic activity was undertaken. In that work, electronic structure effects, geometry and crystallographic orientation effects, territory theory and support structure effects could not account for the structure sensitivity exhibited in the experimental data. This study builds on that previous work and investigates the impact of electrolyte conditions and reactant size on the structure sensitivity of Au nanocatalysts for multiple electrochemical systems. The Fe3+/Fe2+ reaction was studied for multiple reactant sizes in a wide range of electrolyte conditions. There was a clear impact of reactant size on the critical size at which deviation from bulk electrocatalytic performance takes place. These findings were used to develop a geometric model, which could account for the increase in electrocatalytic activity observed below critical nanoparticle diameters.
Microcapillary Polarization of Friction Stir Welds in AZ31B Magnesium Alloy
Electrochemical Society
Corrosion of friction stir welds made in AZ31B magnesium alloy has been investigated using the microcapillary polarization technique. Various weld regions were examined in both spot and seam welds. The stir zone showed a higher reduction potential than the thermo-mechanically affected zone (TMAZ) and the base metal, due to the dissolution of β-Mg 17 Al12 particles. The absence of second phase particles resulted in elimination of harmful microgalvanic cells between the β-Mg 17 Al12 particles and the α-Mg matrix, and an increased concentration of aluminum in solid solution. The noble stir zone formed a macro galvanic cell with the base metal, which resulted in accelerated corrosion of the TMAZ. No significant variation in the electrochemical response of various weld zones was seen between seam and spot welds.
A review of specific conductivities of potassium hydroxide solutions for various concentrations and temperatures
International Journal of Hydrogen Energy, Volume 32, Issue 3, Pages 359-364
This article gives a critical review of the current data on the specific conductivity of aqueous potassium hydroxide (KOH) solutions. Empirical correlations relating concentration to density were developed to compare specific conductivity data given in weight percentage KOH and molarity of KOH. Available data on specific conductivity is related with respect to one another and compared to experimental data. Based on these comparisons, specific sets of reported data were used to develop an equation relating specific conductivity of aqueous KOH to temperature and concentration. This empirical correlation was developed over a molarity range of 0–12 at temperatures of . The correlation has been compared with that proposed by See and White and shows greater accuracy over the concentration range modeled.
Influence of Structural, Microstructural and Electrical Properties on Electrocatalytic Performance at the Nanoscale
Electrocatalysis, Volume 2, Issue 1, pp 1-19
In the field of electrocatalysis, significant work has been done over the past few decades on the effect of particle size on electrocatalytic performance. It has been shown in literature that as catalyst particle diameter has decreased into the nanometre scale, four different trends with respect to particle size on electrocatalytic activity have been observed. These four different trends can be classified as either structure sensitive or structure insensitive and are represented by either no change in electrocatalytic activity with respect to particle size, an increase in activity with a decrease in particle size, a decrease in activity with a decrease in particle size or an increase in activity until the catalyst reaches an optimal performance, followed by a decrease in activity with further decreasing of the catalyst size. These changes in electrocatalytic activity have been observed mainly in the mitohedrical region, which is the transition region between atomistic material properties and bulk material properties. To account for these different trends that exist between particle size and electrocatalytic activity, many different theories have been proposed. The purpose of this paper is to highlight and explain these different theories for the reader and to provide a clearer understanding of the current knowledge base with respect to nanoparticle catalysts. In particular, this paper looks at the effects of electronic structure, support structure, particle geometry and microstructure on electrocatalytic performance.
Microcapillary polarization measurements of friction stir spot welds made in AZ31B magnesium alloy
Materials and Corrosion / WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Microcapillary polarization procedures were optimized to examine the corrosion characteristics of the various microstructural zones developed during friction stir spot welds made in AZ31 magnesium alloy. Tungsten carbide tracing confirmed the location and shape of the stir zone in the weldment. The stir zone was determined to be the noble region while the base metal and the thermo-mechanically affected zone were found to be active. The thermo-mechanically affected zone was found to be most susceptible to localized corrosion attack due to its proximity to the noble stir zone, and the subsequent formation of a macrogalvanic cell. Corrosion rates of individual weld regions were measured.
Part 2 - Impacts of Electrolyte and Reactant Size on Structure Sensitivity in Electrocatalysis: A Geometric Approach
Electrocatalysis, Volume 3, Issue 2, pp 88-95
In previous work performed by the current authors, an in-depth analysis of the current theories relating particle size to electrocatalytic activity was undertaken. In that work, electronic structure effects, geometry and crystallographic orientation effects, territory theory and support structure effects could not account for the structure sensitivity exhibited in the experimental data. This study builds on that previous work and investigates the impact of electrolyte conditions and reactant size on the structure sensitivity of Au nanocatalysts for multiple electrochemical systems. The Fe3+/Fe2+ reaction was studied for multiple reactant sizes in a wide range of electrolyte conditions. There was a clear impact of reactant size on the critical size at which deviation from bulk electrocatalytic performance takes place. These findings were used to develop a geometric model, which could account for the increase in electrocatalytic activity observed below critical nanoparticle diameters.
Microcapillary Polarization of Friction Stir Welds in AZ31B Magnesium Alloy
Electrochemical Society
Corrosion of friction stir welds made in AZ31B magnesium alloy has been investigated using the microcapillary polarization technique. Various weld regions were examined in both spot and seam welds. The stir zone showed a higher reduction potential than the thermo-mechanically affected zone (TMAZ) and the base metal, due to the dissolution of β-Mg 17 Al12 particles. The absence of second phase particles resulted in elimination of harmful microgalvanic cells between the β-Mg 17 Al12 particles and the α-Mg matrix, and an increased concentration of aluminum in solid solution. The noble stir zone formed a macro galvanic cell with the base metal, which resulted in accelerated corrosion of the TMAZ. No significant variation in the electrochemical response of various weld zones was seen between seam and spot welds.
A review of specific conductivities of potassium hydroxide solutions for various concentrations and temperatures
International Journal of Hydrogen Energy, Volume 32, Issue 3, Pages 359-364
This article gives a critical review of the current data on the specific conductivity of aqueous potassium hydroxide (KOH) solutions. Empirical correlations relating concentration to density were developed to compare specific conductivity data given in weight percentage KOH and molarity of KOH. Available data on specific conductivity is related with respect to one another and compared to experimental data. Based on these comparisons, specific sets of reported data were used to develop an equation relating specific conductivity of aqueous KOH to temperature and concentration. This empirical correlation was developed over a molarity range of 0–12 at temperatures of . The correlation has been compared with that proposed by See and White and shows greater accuracy over the concentration range modeled.
Influence of Structural, Microstructural and Electrical Properties on Electrocatalytic Performance at the Nanoscale
Electrocatalysis, Volume 2, Issue 1, pp 1-19
In the field of electrocatalysis, significant work has been done over the past few decades on the effect of particle size on electrocatalytic performance. It has been shown in literature that as catalyst particle diameter has decreased into the nanometre scale, four different trends with respect to particle size on electrocatalytic activity have been observed. These four different trends can be classified as either structure sensitive or structure insensitive and are represented by either no change in electrocatalytic activity with respect to particle size, an increase in activity with a decrease in particle size, a decrease in activity with a decrease in particle size or an increase in activity until the catalyst reaches an optimal performance, followed by a decrease in activity with further decreasing of the catalyst size. These changes in electrocatalytic activity have been observed mainly in the mitohedrical region, which is the transition region between atomistic material properties and bulk material properties. To account for these different trends that exist between particle size and electrocatalytic activity, many different theories have been proposed. The purpose of this paper is to highlight and explain these different theories for the reader and to provide a clearer understanding of the current knowledge base with respect to nanoparticle catalysts. In particular, this paper looks at the effects of electronic structure, support structure, particle geometry and microstructure on electrocatalytic performance.
Dependence of catalytic activity on electrode size
Electrochemistry Communications, Volume 9, Issue 9, Pages 2276-2279
This work is an extension on a previous study on the effect of electrode size on catalyst performance. Through these two sets of work, it is shown that there exists a critical electrode size for maximum catalytic activity. Gold nanoelectrode arrays produced by template synthesis and electroless deposition were utilized for all the experimental studies. The comparison of electrocatalytic activity was performed in 0.1 M KOH for the hydrogen evolution reaction. A proposed theory explaining the reasons for the observed change in catalytic performance is introduced in this work.
Microcapillary polarization measurements of friction stir spot welds made in AZ31B magnesium alloy
Materials and Corrosion / WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Microcapillary polarization procedures were optimized to examine the corrosion characteristics of the various microstructural zones developed during friction stir spot welds made in AZ31 magnesium alloy. Tungsten carbide tracing confirmed the location and shape of the stir zone in the weldment. The stir zone was determined to be the noble region while the base metal and the thermo-mechanically affected zone were found to be active. The thermo-mechanically affected zone was found to be most susceptible to localized corrosion attack due to its proximity to the noble stir zone, and the subsequent formation of a macrogalvanic cell. Corrosion rates of individual weld regions were measured.
Part 2 - Impacts of Electrolyte and Reactant Size on Structure Sensitivity in Electrocatalysis: A Geometric Approach
Electrocatalysis, Volume 3, Issue 2, pp 88-95
In previous work performed by the current authors, an in-depth analysis of the current theories relating particle size to electrocatalytic activity was undertaken. In that work, electronic structure effects, geometry and crystallographic orientation effects, territory theory and support structure effects could not account for the structure sensitivity exhibited in the experimental data. This study builds on that previous work and investigates the impact of electrolyte conditions and reactant size on the structure sensitivity of Au nanocatalysts for multiple electrochemical systems. The Fe3+/Fe2+ reaction was studied for multiple reactant sizes in a wide range of electrolyte conditions. There was a clear impact of reactant size on the critical size at which deviation from bulk electrocatalytic performance takes place. These findings were used to develop a geometric model, which could account for the increase in electrocatalytic activity observed below critical nanoparticle diameters.
Microcapillary Polarization of Friction Stir Welds in AZ31B Magnesium Alloy
Electrochemical Society
Corrosion of friction stir welds made in AZ31B magnesium alloy has been investigated using the microcapillary polarization technique. Various weld regions were examined in both spot and seam welds. The stir zone showed a higher reduction potential than the thermo-mechanically affected zone (TMAZ) and the base metal, due to the dissolution of β-Mg 17 Al12 particles. The absence of second phase particles resulted in elimination of harmful microgalvanic cells between the β-Mg 17 Al12 particles and the α-Mg matrix, and an increased concentration of aluminum in solid solution. The noble stir zone formed a macro galvanic cell with the base metal, which resulted in accelerated corrosion of the TMAZ. No significant variation in the electrochemical response of various weld zones was seen between seam and spot welds.
A review of specific conductivities of potassium hydroxide solutions for various concentrations and temperatures
International Journal of Hydrogen Energy, Volume 32, Issue 3, Pages 359-364
This article gives a critical review of the current data on the specific conductivity of aqueous potassium hydroxide (KOH) solutions. Empirical correlations relating concentration to density were developed to compare specific conductivity data given in weight percentage KOH and molarity of KOH. Available data on specific conductivity is related with respect to one another and compared to experimental data. Based on these comparisons, specific sets of reported data were used to develop an equation relating specific conductivity of aqueous KOH to temperature and concentration. This empirical correlation was developed over a molarity range of 0–12 at temperatures of . The correlation has been compared with that proposed by See and White and shows greater accuracy over the concentration range modeled.
Influence of Structural, Microstructural and Electrical Properties on Electrocatalytic Performance at the Nanoscale
Electrocatalysis, Volume 2, Issue 1, pp 1-19
In the field of electrocatalysis, significant work has been done over the past few decades on the effect of particle size on electrocatalytic performance. It has been shown in literature that as catalyst particle diameter has decreased into the nanometre scale, four different trends with respect to particle size on electrocatalytic activity have been observed. These four different trends can be classified as either structure sensitive or structure insensitive and are represented by either no change in electrocatalytic activity with respect to particle size, an increase in activity with a decrease in particle size, a decrease in activity with a decrease in particle size or an increase in activity until the catalyst reaches an optimal performance, followed by a decrease in activity with further decreasing of the catalyst size. These changes in electrocatalytic activity have been observed mainly in the mitohedrical region, which is the transition region between atomistic material properties and bulk material properties. To account for these different trends that exist between particle size and electrocatalytic activity, many different theories have been proposed. The purpose of this paper is to highlight and explain these different theories for the reader and to provide a clearer understanding of the current knowledge base with respect to nanoparticle catalysts. In particular, this paper looks at the effects of electronic structure, support structure, particle geometry and microstructure on electrocatalytic performance.
Dependence of catalytic activity on electrode size
Electrochemistry Communications, Volume 9, Issue 9, Pages 2276-2279
This work is an extension on a previous study on the effect of electrode size on catalyst performance. Through these two sets of work, it is shown that there exists a critical electrode size for maximum catalytic activity. Gold nanoelectrode arrays produced by template synthesis and electroless deposition were utilized for all the experimental studies. The comparison of electrocatalytic activity was performed in 0.1 M KOH for the hydrogen evolution reaction. A proposed theory explaining the reasons for the observed change in catalytic performance is introduced in this work.
Localized Corrosion Behaviour in Dissimilar AZ31/AZ80 Friction Stir Welds
ECS Transactions / ©The Electrochemical Society
Corrosion of a dissimilar friction stir weld (FSW) made in AZ31/AZ80 magnesium alloys has been investigated using the scanning reference electrode technique (SRET), and microcapillary polarization technique. The corrosion rate of each of the base metals along with the welded specimen was estimated by mass loss testing and mixed potential theory. The stir zone material in both alloys showed a higher reduction potential than the base metal, due to the dissolution of β-Mg17Al12, and Al-Mn intermetallic particles. The dissimilar welded specimen exhibited a higher corrosion rate compared to either AZ31 or AZ80. The governing corrosion mechanism in dissimilar welds was determined to be different from FSSW joints made with a singular material. The corrosion behaviour of the dissimilar FSW joint was governed by the galvanic coupling of the two alloys, and not by the microstructural evolution that occurred during the welding process.
Microcapillary polarization measurements of friction stir spot welds made in AZ31B magnesium alloy
Materials and Corrosion / WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Microcapillary polarization procedures were optimized to examine the corrosion characteristics of the various microstructural zones developed during friction stir spot welds made in AZ31 magnesium alloy. Tungsten carbide tracing confirmed the location and shape of the stir zone in the weldment. The stir zone was determined to be the noble region while the base metal and the thermo-mechanically affected zone were found to be active. The thermo-mechanically affected zone was found to be most susceptible to localized corrosion attack due to its proximity to the noble stir zone, and the subsequent formation of a macrogalvanic cell. Corrosion rates of individual weld regions were measured.
Part 2 - Impacts of Electrolyte and Reactant Size on Structure Sensitivity in Electrocatalysis: A Geometric Approach
Electrocatalysis, Volume 3, Issue 2, pp 88-95
In previous work performed by the current authors, an in-depth analysis of the current theories relating particle size to electrocatalytic activity was undertaken. In that work, electronic structure effects, geometry and crystallographic orientation effects, territory theory and support structure effects could not account for the structure sensitivity exhibited in the experimental data. This study builds on that previous work and investigates the impact of electrolyte conditions and reactant size on the structure sensitivity of Au nanocatalysts for multiple electrochemical systems. The Fe3+/Fe2+ reaction was studied for multiple reactant sizes in a wide range of electrolyte conditions. There was a clear impact of reactant size on the critical size at which deviation from bulk electrocatalytic performance takes place. These findings were used to develop a geometric model, which could account for the increase in electrocatalytic activity observed below critical nanoparticle diameters.
Microcapillary Polarization of Friction Stir Welds in AZ31B Magnesium Alloy
Electrochemical Society
Corrosion of friction stir welds made in AZ31B magnesium alloy has been investigated using the microcapillary polarization technique. Various weld regions were examined in both spot and seam welds. The stir zone showed a higher reduction potential than the thermo-mechanically affected zone (TMAZ) and the base metal, due to the dissolution of β-Mg 17 Al12 particles. The absence of second phase particles resulted in elimination of harmful microgalvanic cells between the β-Mg 17 Al12 particles and the α-Mg matrix, and an increased concentration of aluminum in solid solution. The noble stir zone formed a macro galvanic cell with the base metal, which resulted in accelerated corrosion of the TMAZ. No significant variation in the electrochemical response of various weld zones was seen between seam and spot welds.
A review of specific conductivities of potassium hydroxide solutions for various concentrations and temperatures
International Journal of Hydrogen Energy, Volume 32, Issue 3, Pages 359-364
This article gives a critical review of the current data on the specific conductivity of aqueous potassium hydroxide (KOH) solutions. Empirical correlations relating concentration to density were developed to compare specific conductivity data given in weight percentage KOH and molarity of KOH. Available data on specific conductivity is related with respect to one another and compared to experimental data. Based on these comparisons, specific sets of reported data were used to develop an equation relating specific conductivity of aqueous KOH to temperature and concentration. This empirical correlation was developed over a molarity range of 0–12 at temperatures of . The correlation has been compared with that proposed by See and White and shows greater accuracy over the concentration range modeled.
Influence of Structural, Microstructural and Electrical Properties on Electrocatalytic Performance at the Nanoscale
Electrocatalysis, Volume 2, Issue 1, pp 1-19
In the field of electrocatalysis, significant work has been done over the past few decades on the effect of particle size on electrocatalytic performance. It has been shown in literature that as catalyst particle diameter has decreased into the nanometre scale, four different trends with respect to particle size on electrocatalytic activity have been observed. These four different trends can be classified as either structure sensitive or structure insensitive and are represented by either no change in electrocatalytic activity with respect to particle size, an increase in activity with a decrease in particle size, a decrease in activity with a decrease in particle size or an increase in activity until the catalyst reaches an optimal performance, followed by a decrease in activity with further decreasing of the catalyst size. These changes in electrocatalytic activity have been observed mainly in the mitohedrical region, which is the transition region between atomistic material properties and bulk material properties. To account for these different trends that exist between particle size and electrocatalytic activity, many different theories have been proposed. The purpose of this paper is to highlight and explain these different theories for the reader and to provide a clearer understanding of the current knowledge base with respect to nanoparticle catalysts. In particular, this paper looks at the effects of electronic structure, support structure, particle geometry and microstructure on electrocatalytic performance.
Dependence of catalytic activity on electrode size
Electrochemistry Communications, Volume 9, Issue 9, Pages 2276-2279
This work is an extension on a previous study on the effect of electrode size on catalyst performance. Through these two sets of work, it is shown that there exists a critical electrode size for maximum catalytic activity. Gold nanoelectrode arrays produced by template synthesis and electroless deposition were utilized for all the experimental studies. The comparison of electrocatalytic activity was performed in 0.1 M KOH for the hydrogen evolution reaction. A proposed theory explaining the reasons for the observed change in catalytic performance is introduced in this work.
Localized Corrosion Behaviour in Dissimilar AZ31/AZ80 Friction Stir Welds
ECS Transactions / ©The Electrochemical Society
Corrosion of a dissimilar friction stir weld (FSW) made in AZ31/AZ80 magnesium alloys has been investigated using the scanning reference electrode technique (SRET), and microcapillary polarization technique. The corrosion rate of each of the base metals along with the welded specimen was estimated by mass loss testing and mixed potential theory. The stir zone material in both alloys showed a higher reduction potential than the base metal, due to the dissolution of β-Mg17Al12, and Al-Mn intermetallic particles. The dissimilar welded specimen exhibited a higher corrosion rate compared to either AZ31 or AZ80. The governing corrosion mechanism in dissimilar welds was determined to be different from FSSW joints made with a singular material. The corrosion behaviour of the dissimilar FSW joint was governed by the galvanic coupling of the two alloys, and not by the microstructural evolution that occurred during the welding process.
Part 1 - Structure-Sensitivity of Nanoparticle Catalysts: Relating Current Theories to Experimental Data
Electrocatalysis, Volume 3, Issue 1, pp 68-74
This work investigates the current theories that have been used to explain the particle size effect on electrocatalytic activity. In particular, this work focuses on electronic structure effects, geometric shape effects, crystallographic orientation effects, support structure effects, and the concept of territory theory. To investigate these theories, gold and nickel–phosphorus nanowire arrays have been used as model systems for electrocatalytic testing of the hydrogen evolution reaction in basic medium. In this study, the current particle size effect theories cannot adequately account for the observed structure-sensitive trends that are exhibited in the aforementioned systems. This work systematically looks at each of these different theories and discusses new possible factors that could serve as a foundation for a new theory on structure-sensitive catalysis.
Microcapillary polarization measurements of friction stir spot welds made in AZ31B magnesium alloy
Materials and Corrosion / WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Microcapillary polarization procedures were optimized to examine the corrosion characteristics of the various microstructural zones developed during friction stir spot welds made in AZ31 magnesium alloy. Tungsten carbide tracing confirmed the location and shape of the stir zone in the weldment. The stir zone was determined to be the noble region while the base metal and the thermo-mechanically affected zone were found to be active. The thermo-mechanically affected zone was found to be most susceptible to localized corrosion attack due to its proximity to the noble stir zone, and the subsequent formation of a macrogalvanic cell. Corrosion rates of individual weld regions were measured.
Part 2 - Impacts of Electrolyte and Reactant Size on Structure Sensitivity in Electrocatalysis: A Geometric Approach
Electrocatalysis, Volume 3, Issue 2, pp 88-95
In previous work performed by the current authors, an in-depth analysis of the current theories relating particle size to electrocatalytic activity was undertaken. In that work, electronic structure effects, geometry and crystallographic orientation effects, territory theory and support structure effects could not account for the structure sensitivity exhibited in the experimental data. This study builds on that previous work and investigates the impact of electrolyte conditions and reactant size on the structure sensitivity of Au nanocatalysts for multiple electrochemical systems. The Fe3+/Fe2+ reaction was studied for multiple reactant sizes in a wide range of electrolyte conditions. There was a clear impact of reactant size on the critical size at which deviation from bulk electrocatalytic performance takes place. These findings were used to develop a geometric model, which could account for the increase in electrocatalytic activity observed below critical nanoparticle diameters.
Microcapillary Polarization of Friction Stir Welds in AZ31B Magnesium Alloy
Electrochemical Society
Corrosion of friction stir welds made in AZ31B magnesium alloy has been investigated using the microcapillary polarization technique. Various weld regions were examined in both spot and seam welds. The stir zone showed a higher reduction potential than the thermo-mechanically affected zone (TMAZ) and the base metal, due to the dissolution of β-Mg 17 Al12 particles. The absence of second phase particles resulted in elimination of harmful microgalvanic cells between the β-Mg 17 Al12 particles and the α-Mg matrix, and an increased concentration of aluminum in solid solution. The noble stir zone formed a macro galvanic cell with the base metal, which resulted in accelerated corrosion of the TMAZ. No significant variation in the electrochemical response of various weld zones was seen between seam and spot welds.
A review of specific conductivities of potassium hydroxide solutions for various concentrations and temperatures
International Journal of Hydrogen Energy, Volume 32, Issue 3, Pages 359-364
This article gives a critical review of the current data on the specific conductivity of aqueous potassium hydroxide (KOH) solutions. Empirical correlations relating concentration to density were developed to compare specific conductivity data given in weight percentage KOH and molarity of KOH. Available data on specific conductivity is related with respect to one another and compared to experimental data. Based on these comparisons, specific sets of reported data were used to develop an equation relating specific conductivity of aqueous KOH to temperature and concentration. This empirical correlation was developed over a molarity range of 0–12 at temperatures of . The correlation has been compared with that proposed by See and White and shows greater accuracy over the concentration range modeled.
Influence of Structural, Microstructural and Electrical Properties on Electrocatalytic Performance at the Nanoscale
Electrocatalysis, Volume 2, Issue 1, pp 1-19
In the field of electrocatalysis, significant work has been done over the past few decades on the effect of particle size on electrocatalytic performance. It has been shown in literature that as catalyst particle diameter has decreased into the nanometre scale, four different trends with respect to particle size on electrocatalytic activity have been observed. These four different trends can be classified as either structure sensitive or structure insensitive and are represented by either no change in electrocatalytic activity with respect to particle size, an increase in activity with a decrease in particle size, a decrease in activity with a decrease in particle size or an increase in activity until the catalyst reaches an optimal performance, followed by a decrease in activity with further decreasing of the catalyst size. These changes in electrocatalytic activity have been observed mainly in the mitohedrical region, which is the transition region between atomistic material properties and bulk material properties. To account for these different trends that exist between particle size and electrocatalytic activity, many different theories have been proposed. The purpose of this paper is to highlight and explain these different theories for the reader and to provide a clearer understanding of the current knowledge base with respect to nanoparticle catalysts. In particular, this paper looks at the effects of electronic structure, support structure, particle geometry and microstructure on electrocatalytic performance.
Dependence of catalytic activity on electrode size
Electrochemistry Communications, Volume 9, Issue 9, Pages 2276-2279
This work is an extension on a previous study on the effect of electrode size on catalyst performance. Through these two sets of work, it is shown that there exists a critical electrode size for maximum catalytic activity. Gold nanoelectrode arrays produced by template synthesis and electroless deposition were utilized for all the experimental studies. The comparison of electrocatalytic activity was performed in 0.1 M KOH for the hydrogen evolution reaction. A proposed theory explaining the reasons for the observed change in catalytic performance is introduced in this work.
Localized Corrosion Behaviour in Dissimilar AZ31/AZ80 Friction Stir Welds
ECS Transactions / ©The Electrochemical Society
Corrosion of a dissimilar friction stir weld (FSW) made in AZ31/AZ80 magnesium alloys has been investigated using the scanning reference electrode technique (SRET), and microcapillary polarization technique. The corrosion rate of each of the base metals along with the welded specimen was estimated by mass loss testing and mixed potential theory. The stir zone material in both alloys showed a higher reduction potential than the base metal, due to the dissolution of β-Mg17Al12, and Al-Mn intermetallic particles. The dissimilar welded specimen exhibited a higher corrosion rate compared to either AZ31 or AZ80. The governing corrosion mechanism in dissimilar welds was determined to be different from FSSW joints made with a singular material. The corrosion behaviour of the dissimilar FSW joint was governed by the galvanic coupling of the two alloys, and not by the microstructural evolution that occurred during the welding process.
Part 1 - Structure-Sensitivity of Nanoparticle Catalysts: Relating Current Theories to Experimental Data
Electrocatalysis, Volume 3, Issue 1, pp 68-74
This work investigates the current theories that have been used to explain the particle size effect on electrocatalytic activity. In particular, this work focuses on electronic structure effects, geometric shape effects, crystallographic orientation effects, support structure effects, and the concept of territory theory. To investigate these theories, gold and nickel–phosphorus nanowire arrays have been used as model systems for electrocatalytic testing of the hydrogen evolution reaction in basic medium. In this study, the current particle size effect theories cannot adequately account for the observed structure-sensitive trends that are exhibited in the aforementioned systems. This work systematically looks at each of these different theories and discusses new possible factors that could serve as a foundation for a new theory on structure-sensitive catalysis.
Effect of electrode size on catalytic activity
Electrochemistry Communications
In the field of catalyst research, synthesis innovations have allowed for the production of nanoparticle catalysts less than 2 nm in size. With this decrease in catalyst size, new questions have arisen with respect to the overall effect of size on catalytic activity. It is generally accepted that as catalyst particles decrease in size, the surface area to volume ratio of the catalyst is increased, resulting in higher catalytic performance. This paper introduces a novel technique for producing electrode structures with specific catalyst sizes. Through the use of electrochemical impedance spectroscopy and chronoamperometry, these different electrode sizes are compared with respect to the hydrogen evolution reaction. From this work, it is shown that for the given reaction, there exists a critical size at which catalytic activity begins to increase. A proposed explanation for the observed change in catalytic performance is introduced.
