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3. Thermodynamics and kinetics of core-shell versus appendage co-precipitation morphologies: An example in the Fe-Cu-Mn-Ni-Si system

Author

Shu, Shipeng, Wells, Peter B., Almirall, Nathan, Odette, G. Robert, and Morgan, Dane D.

Subjects
Condensed Matter - Materials Science
Abstract

What determines precipitate morphologies in co-precipitating alloy systems? We focus on alloys of two precipitating phases, with precipitates of the fast-precipitating phase acting as heterogeneous nucleation sites for a second phase manifesting slower kinetics. We study a FeCuMnNiSi alloy using the combination of atom probe tomography and kinetic Monte Carlo simulations. It is shown that the interplay between interfacial and ordering energies, plus active diffusion paths, strongly affect the selection of core-shell verses appendage morphologies. Specifically, the ordering energy reduction of the MnNiSi phase heterogeneously nucleated on a pre-existing copper-rich precipitate exceeds the energy penalty of a predominantly Fe/Cu interface, leading to initial appendage, rather than core-shell, formation. Diffusion of Mn, Ni and Si around and through the Cu core towards the ordered phase results in subsequent appendage growth. We further show that in cases with higher primary precipitate interface energies and/or suppressed ordering, the core-shell morphology is favored.

Published
2018
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5. Thermodynamic and kinetic modeling of Mn-Ni-Si precipitates in low-Cu reactor pressure vessel steels

Author

Ke, Huibin, Wells, Peter, Edmondson, Philip D., Almirall, Nathan, Barnard, Leland, Odette, G. Robert, and Morgan, Dane

Subjects
Condensed Matter - Materials Science
Abstract

Formation of large volume fractions of Mn-Ni-Si precipitates (MNSPs) causes excess irradiation embrittlement of reactor pressure vessel (RPV) steels at high, extended-life fluences. Thus, a new and unique, semi-empirical cluster dynamics model was developed to study the evolution of MNSPs in low- Cu RPV steels. The model is based on CALPHAD thermodynamics and radiation enhanced diffusion ki- netics. The thermodynamics dictates the compositional and temperature dependence of the free energy reductions that drive precipitation. The model treats both homogeneous and heterogeneous nucleation, where the latter occurs on cascade damage, like dislocation loops. The model has only four adjustable parameters that were fit to an atom probe tomography (APT) database. The model predictions are in semi-quantitative agreement with systematic Mn, Ni and Si composition variations in alloys character- ized by APT, including a sensitivity to local tip-to-tip variations even in the same steel. The model predicts that heterogeneous nucleation plays a critical role in MNSP formation in lower alloy Ni contents. Single variable assessments of compositional effects show that Ni plays a dominant role, while even small variations in irradiation temperature can have a large effect on theMNSP evolution. Within typical RPV steel ranges, Mn and Si have smaller effects. The delayed but then rapid growth of MNSPs to large volume fractions at high fluence is well predicted by the model. For purposes of illustration, the effect of MNSPs on transition temperature shifts are presented based on well-established microstructure-prop- erty and property-property models., Comment: 51 pages, 12 figures

Published
2017
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7. The DNA of a Converging Diversity: Regional Approaches to Quality Assurance in Higher Education

Author

Council for Higher Education Accreditation and Wells, Peter J.

Abstract

The modernization agendas of higher education systems and institutions around the world are littered with debate over definitions of what is a "quality higher education" often paralyzed by the parallax of multiple stakeholder perspectives. Over the last decade or so there has been a hitherto unprecedented appetite for attempting to clearly define the DNA of quality in higher education. In the process, certain red-herrings have emerged, such as the so called "World-Class Universities" and "University Rankings", but more pragmatic and practical initiatives have also evolved to speak to criteria that are generally held to be important when qualifying an effective higher education system, not merely for the purposes of national trumpet-blowing but in recognition of the immeasurable contribution to economic, political, and cultural development that a strong national higher education system plays. In 2013, are these criteria really so different from nation to nation and from region to region? Is there a convergence towards common principles of evaluating higher education occurring or not? This document examines the evolutions of quality assurance in higher education in four regions of the world (Africa, the Arab Sates, the Asia-Pacific and Europe) and attempts to determine whether or not the diversity of agencies, networks of agencies, their respective guidelines, handbooks and good practices criteria all belong to a common 21st century higher education quality assurance genome. Three annexes are provided: (1) Internal Quality Assurance Criteria; (2) External Quality Assurance Criteria; and (3) Quality Assurance Agency Criteria. A list of references and internet sources is included.

Published
2014

11. Towards the Operational Window for Nitridic and Carbidic Palladium Nanoparticles for Directed Catalysis

Author

Costley‐Wood, Lucy G, primary, Mohammed, Khaled, additional, Carravetta, Marina, additional, Decarolis, Donato, additional, Goguet, Alexandre, additional, Kordatos, Apostolos, additional, Vakili, Reza, additional, Manyar, Haresh, additional, McPake, Erin, additional, Skylaris, Chris‐Kriton, additional, Thompson, Paul, additional, Gibson, Emma K, additional, and Wells, Peter P., additional

Published
2023
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13. Structural selectivity of supported Pd nanoparticles for catalytic NH3 oxidation resolved using combined operando spectroscopy

Author

Dann, Ellie K., Gibson, Emma K., Blackmore, Rachel H., Catlow, C. Richard A., Collier, Paul, Chutia, Arunabhiram, Erden, Tugce Eralp, Hardacre, Christopher, Kroner, Anna, Nachtegaal, Maarten, Raj, Agnes, Rogers, Scott M., Taylor, S. F. Rebecca, Thompson, Paul, Tierney, George F., Zeinalipour-Yazdi, Constantinos D., Goguet, Alexandre, and Wells, Peter P.

Published
2019
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19. Stable amorphous georgeite as a precursor to a high-activity catalyst

Author

Kondrat, Simon A., Smith, Paul J., Wells, Peter P., Chater, Philip A., Carter, James H., Morgan, David J., Fiordaliso, Elisabetta M., Wagner, Jakob B., Davies, Thomas E., Lu, Li, Bartley, Jonathan K., Taylor, Stuart H., Spencer, Michael S., Kiely, Christopher J., Kelly, Gordon J., Park, Colin W., Rosseinsky, Matthew J., and Hutchings, Graham J.

Published
2016
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27. The Character, Stability and Consequences of Mn-Ni-Si Precipitates in Irradiated Reactor Pressure Vessel Steels

Author

Wells, Peter Benjamin

Subjects
Materials Science, Nuclear engineering, Atom Probe Tomography, Irradiation Embrittlement, Reactor Pressure Vessel
Abstract

Formation of a high density of Mn-Ni-Si nanoscale precipitates in irradiated reactor pressure vessel steels could lead to severe, unexpected embrittlement, which may limit the lifetimes of our nation’s light water reactors. While the existence of these precipitates was hypothesized over 20 years ago, they are currently not included in embrittlement prediction models used by the Nuclear Regulatory Commission. This work aims to investigate the mechanisms and variables that control Mn-Ni-Si precipitate (MNSP) formation as well as correlate their formation with hardening and embrittlement.A series of RPV model steels with systematic variations in Cu and Ni contents, two variables that have been shown to have a dominant effect on hardening, were irradiated in a series of test reactor and power reactor surveillance irradiations. Atom probe tomography (APT) measurements show that large volume fractions (fv) of MNSPs form in all the steels irradiated at high fluence, even those containing no added Cu, which were previously believed to have low sensitivity to embrittlement. It is demonstrated that while Cu enhances the rate of MNSP formation, it does not appear to significantly alter their saturation fv or composition. The high fluence MNSPs have compositions consistent with known intermetallic phases in the Mn-Ni-Si system and have fv very near those predicted by equilibrium thermodynamic models. In addition, X-ray diffraction experiments by collaborators shows that these precipitates also have the expected crystal structure of the predicted Mn-Ni-Si phases. Post irradiation annealing experiments are used to measure the hardness recovery at various temperatures as well as to determine if the large fv of MNSPs that form under high fluence neutron irradiation are thermodynamically stable phases or non-equilibrium solute clusters, enhanced or induced by irradiation, respectively. Notably, while post irradiation annealing of a Cu-free, high Ni steel at 425°C results in dissolution of most precipitates, a few larger MNSPs appear to remain stable and may begin to coarsen after long times. A cluster dynamics model rationalizes the dissolution and reduction in precipitate number density, since most are less than the critical radius at the annealing temperature and decomposed matrix composition. The stability of larger precipitates suggests that they are an equilibrium phase, consistent with thermodynamic models. Charged particle irradiations using Fe3+ ions are also used to investigate the precipitates which form under irradiation. Two steels irradiated to a dose of 0.2 dpa using both neutrons and ions show precipitates with very similar compositions. The ion irradiation shows a smaller fv, likely due to the much higher dose rate, which has been previously shown to delay precipitation to higher fluences. While the precipitates in the ion irradiated condition are slightly deficient in Mn and enriched in Ni and Si compared to neutron irradiated condition, the overall similarities between the two conditions suggest that ion irradiations can be a very useful tool to study the susceptibility of a given steel to irradiation embrittlement.Finally, the large fv of MNSPs that are shown to form in all steels, including those low in Cu, at high fluence, even those without added Cu, result in large amounts of hardening and embrittlement. A preliminary embrittlement prediction model, which incorporates MNSPs at high fluence, is presented, along with results from a recent test reactor irradiation to fluences representative of extended lifetimes. This model shows very good agreement with the data.

Published
2016

28. Future CO2 emissions from shipping: four-scenarios using a multi-level perspective – a proposed methodology

Author

Wells Peter, Pettit Stephen, Abouarghoub Wessam, Haider Jane, and Beresford Anthony

Subjects
Social Sciences
Abstract

Previous work by Pettit et al (2017) drew on Socio-technical Transitions Theory (STT) to contextualise recent developments in the technological and operational eco-efficiency of ships which may ameliorate sustainability issues in shipping. Within STT the Multi-Level Perspective (MLP) is a framework used to explain the permeation of innovations into society (Geels, 2014). The framework has three levels: Landscape; Regime and Niche. In order to develop a better understanding of changes that may take place in the future, this paper uses the MLP to assess the broad range of challenges facing the shipping industry with respect to future CO2 emissions at each of the three levels. The framework is applied to four scenarios for global shipping in order to understand the potential range of outcomes for CO2 emissions. The four scenarios are: ‘Business as Usual’; ‘Managed Transition’; ‘Chaotic Transition’; and ‘Managed Degrowth’. It is contended that changes in the shipping industry alone are unlikely to lead to large-scale changes in its CO2 emissions. Under ‘Business as Usual’ conditions, CO2 emissions will continue to rise as the changes required at all three levels, but primarily at the regime level, will have limited impact. Under the other three scenarios, it is suggested that there is room for optimism that CO2 emissions will decline over time.

Published
2018
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30. Tracking the solid-state incorporation of Sn into the framework of dealuminated zeolite beta, and consequences for catalyst design

Author

Navar, Ricardo, primary, Tarantino, Giulia, additional, Beynon, Owain T., additional, Padovan, Daniele, additional, Botti, Luca, additional, Gibson, Emma K., additional, Wells, Peter P., additional, Owens, Alun, additional, Kondrat, Simon A., additional, Logsdail, Andrew J., additional, and Hammond, Ceri, additional

Published
2022
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31. Controlling the Production of Acid Catalyzed Products of Furfural Hydrogenation by Pd/TiO 2

Author

Tierney, George F., primary, Alijani, Shahram, additional, Panchal, Monik, additional, Decarolis, Donato, additional, de Gutierrez, Martha Briceno, additional, Mohammed, Khaled M. H., additional, Callison, June, additional, Gibson, Emma K., additional, Thompson, Paul B. J., additional, Collier, Paul, additional, Dimitratos, Nikolaos, additional, Corbos, E. Crina, additional, Pelletier, Frederic, additional, Villa, Alberto, additional, and Wells, Peter P., additional

Published
2021
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34. Investigation of MoO x/Al 2 O 3 under cyclic operation for oxidative and non-oxidative dehydrogenation of propane

Author

Matam, Santhosh K., Moffat, Caitlin, Hellier, Pip, Bowker, Michael, Silverwood, Ian P., Catlow, C. Richard A., Jackson, S. David, Craswell, James, Wells, Peter P., Parker, Stewart F., and Gibson, Emma K.

Abstract

A MoOx/Al2O3 catalyst was synthesised and tested for oxidative (ODP) and non-oxidative (DP) dehydrogenation of propane in a reaction cycle of ODP followed by DP and a second ODP run. Characterisation results show that the fresh catalyst contains highly dispersed Mo oxide species in the +6 oxidation state with tetrahedral coordination as [MoVIO4]2− moieties. In situ X-ray Absorption Spectroscopy (XAS) shows that [MoVIO4]2− is present during the first ODP run of the reaction cycle and is reduced to MoIVO2 in the following DP run. The reduced species are partly re-oxidised in the subsequent second ODP run of the reaction cycle. The partly re-oxidised species exhibit oxidation and coordination states that are lower than 6 but higher than 4 and are referred to as MoxOy. These species significantly improved propene formation (relatively 27% higher) in the second ODP run at similar propane conversion activity. Accordingly, the initial tetrahedral [MoVIO4]2− present during the first ODP run of the reaction cycle is active for propane conversion; however, it is unselective for propene. The reduced MoIVO2 species are relatively less active and selective for DP. It is suggested that the MoxOy species generated by the reaction cycle are active and selective for ODP. The vibrational spectroscopic data indicate that the retained surface species are amorphous carbon deposits with a higher proportion of aromatic/olefinic like species.

Published
2020

36. Reviews

Author

Harrison, Stephen H., Roby, John, Polk, II, Harding, Morgan, Courtney, Allaire, Bernard, Muhammad, Allison, Allen, Rebecca, Perttula, Timothy K., Swanepoel, Natalie, Mandzy, Adrian, Beaman, Jr., Thomas E., Mullins, Paul R., Wells, Peter S., Mazow, Laura B., Pendery, Steven R., Rodning, Christopher B., Pykles, Benjamin C., Valentino, Alicia, Edwards, Megan E., Courtney, Paul, Hoover, Robert L., Vasalech, Crystal M. B., Podgorny, Irina, Roberts, Joseph, Haecker, Charles M., Moyer, Teresa S., and Rothschild, Nan A.

Published
2011
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37. Co3O4/TiO2catalysts studied in situduring the preferential oxidation of carbon monoxide: the effect of different TiO2polymorphsElectronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d2cy01699k

Author

Nyathi, Thulani M., Fadlalla, Mohamed I., Fischer, Nico, York, Andrew P. E., Olivier, Ezra J., Gibson, Emma K., Wells, Peter P., and Claeys, Michael

Abstract

Co3O4nanoparticles were supported on different TiO2polymorphs, namely, rutile, anatase, and a 15 : 85 mixture of rutile and anatase (also known as P25), viaincipient wetness impregnation. The Co3O4/TiO2catalysts were evaluated in the preferential oxidation of CO (CO-PrOx) in a H2-rich gas environment and characterised in situusing PXRD and magnetometry. Our results show that supporting Co3O4on P25 resulted in better catalytic performance, that is, a higher maximum CO conversion to CO2of 72.7% at 200 °C was achieved than on rutile (60.7%) and anatase (51.5%). However, the degree of reduction (DoR) of Co3O4to Co0was highest on P25 (91.9% at 450 °C), with no CoTiO3detected in the spent catalyst. The DoR of Co3O4was lowest on anatase (76.4%), with the presence of TixOy-encapsulated CoOxnanoparticles and bulk CoTiO3(13.8%) also confirmed in the spent catalyst. Relatively low amounts of CoTiO3(8.9%) were detected in the spent rutile-supported catalyst, while a higher DoR (85.9%) was reached under reaction conditions. The Co0nanoparticles formed on P25 and rutile existed in the fcc and hcp crystal phases, while only fcc Co0was detected on anatase. Furthermore, undesired CH4formation took place over the Co0present in the P25- and rutile-supported catalysts, while CH4was not formed over the Co0on anatase possibly due to encapsulation by TixOyspecies. For the first time, this study revealed the influence of different TiO2polymorphs (used as catalyst supports) on the chemical and crystal phase transformations of Co3O4, which in turn affect its activity and selectivity during CO-PrOx.

Published
2023
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50. The Future of Ocean Governance and Capacity Development : Essays in Honor of Elisabeth Mann Borgese (1918-2002)

Author

Werle, Dirk, Boudreau, Paul R., Brooks, Mary R., Butler, Michael J.A., Charles, Anthony, Coffen-Smout, Scott, Griffiths, David, McAllister, Ian, McConnell, Moira L., Porter, Ian, Rolston, Susan J., Wells, Peter G., Werle, Dirk, Boudreau, Paul R., Brooks, Mary R., Butler, Michael J.A., Charles, Anthony, Coffen-Smout, Scott, Griffiths, David, McAllister, Ian, McConnell, Moira L., Porter, Ian, Rolston, Susan J., and Wells, Peter G.

Published
2018
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