Ken Littrell - Academia.edu (original) (raw)

Papers by Ken Littrell

Goldschmidt2021 abstracts

Goldschmidt2021 abstracts

Nature

Single-phase high- and medium-entropy alloys with face-centred cubic (fcc) structure can exhibit ... more Single-phase high- and medium-entropy alloys with face-centred cubic (fcc) structure can exhibit high tensile ductility1,2 and excellent toughness2,3, but their room-temperature strengths are low1-3. Dislocation obstacles such as grain boundaries4, twin boundaries5, solute atoms6 and precipitates7-9 can increase strength. However, with few exceptions8-11, such obstacles tend to decrease ductility. Interestingly, precipitates can also hinder phase transformations12,13. Here, using a model, precipitate-strengthened, Fe-Ni-Al-Ti medium-entropy alloy, we demonstrate a strategy that combines these dual functions in a single alloy. The nanoprecipitates in our alloy, in addition to providing conventional strengthening of the matrix, also modulate its transformation from fcc-austenite to body-centred cubic (bcc) martensite, constraining it to remain as metastable fcc after quenching through the transformation temperature. During subsequent tensile testing, the matrix progressively transforms to bcc-martensite, enabling substantial increases in strength, work hardening and ductility. This use of nanoprecipitates exploits synergies between precipitation strengthening and transformation-induced plasticity, resulting in simultaneous enhancement of tensile strength and uniform elongation. Our findings demonstrate how synergistic deformation mechanisms can be deliberately activated, exactly when needed, by altering precipitate characteristics (such as size, spacing, and so on), along with the chemical driving force for phase transformation, to optimize strength and ductility.

Applied Sciences

In an effort to upgrade and provide a unified and improved instrument control and data acquisitio... more In an effort to upgrade and provide a unified and improved instrument control and data acquisition system for the Oak Ridge National Laboratory (ORNL) small-angle neutron scattering (SANS) instrument suite—biological small-angle neutron scattering instrument (Bio-SANS), the extended q-range small-angle neutron scattering diffractometer (EQ-SANS), the general-purpose small-angle neutron scattering diffractometer (GP-SANS)—beamline scientists and developers teamed up and worked closely together to design and develop a new system. We began with an in-depth analysis of user needs and requirements, covering all perspectives of control and data acquisition based on previous usage data and user feedback. Our design and implementation were guided by the principles from the latest user experience and design research and based on effective practices from our previous projects. In this article, we share details of our design process as well as prominent features of the new instrument control a...

AIP Advances

Paper published as part of the special topic on Chemical Physics, Energy, Fluids and Plasmas, Mat... more Paper published as part of the special topic on Chemical Physics, Energy, Fluids and Plasmas, Materials Science and Mathematical Physics ARTICLES YOU MAY BE INTERESTED IN Ferroelectric and electromechanical properties of poly(vinylidene-fluoridetrifluoroethylene-chlorotrifluoroethylene) terpolymer

Materials & Design

Abstract The bcc ferritic Fe-Ni steels and in particular the commercial 9Ni alloys were developed... more Abstract The bcc ferritic Fe-Ni steels and in particular the commercial 9Ni alloys were developed and widely used at cryogenic temperatures for liquefied natural gas storage. The excellent thermomechanical properties and cryogenic toughness of these materials are closely related to the presence of metastable fcc austenitic phase whose stability increases in the presence of austenitic components (Ni, Cr, Mn, etc.) and with decreasing fcc grain size. Numerous reports are related to quenching and tempering technological procedures improving the cryogenic performance, however, very little attention has been paid to the structural characterization of austenitic minority species except for a few papers revealing rather contradictory results. Using high-energy X-ray diffraction, small-angle neutron scattering and 57Fe Mossbauer spectroscopy we show that the minority austenitic particles in the commercial X8Ni9 steel are enriched in nickel up to 27 ± 6 at.% Ni and have a characteristic size of 620 ± 25 A. The austenitic phase is highly sensitive to mechanical deformation and stress. Disappearance of the fcc grains during the treatment implies a mechanical failure while mechanically-resistant regions are characterized by a higher intensity of the austenitic reflections probably related to the generated texture. The last finding was never reported previously.

Journal of The Electrochemical Society

1Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA 2Dep... more 1Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA 2Department of Materials Science and Engineering and A. J. Drexel Nanomaterials Institute, Drexel University, Philadelphia, Pennsylvania 19104, USA 3Department of Chemical and Environmental Engineering, University of California–Riverside, Riverside, California 92521, USA 4ISIS Pulsed Neutron and Muon Source, STFC Rutherford Appleton Laboratory, Harwell Campus, Didcot, Oxfordshire OX11 0QX, United Kingdom 5Chemical Science Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA

Preliminary work has been completed to evaluate the deformation behavior of the Generation II FeC... more Preliminary work has been completed to evaluate the deformation behavior of the Generation II FeCrAl alloy class. The Generation II alloy, C35M, was neutron irradiated within the High Flux Isotope Reactor followed by post-irradiation examination to evaluate the mechanical properties, irradiated microstructure, deformation modes, and deformation microstructure. Complementary characterization techniques were used in this evaluation. It was found that after irradiation to 1.8 dpa at 364°C that the C35M specimen failed in a ductile manner. The observed deformation microstructure showed a high density of line dislocations, dislocation networks, and dislocation pileups. The observed performance and structures are consistent with literature studies on high-Cr FeCr alloys that were thermally aged at 500°C. The observed results suggest that Generation II FeCrAl alloys retain ductility under low-dose, prototypical LWR irradiation conditions.

A novel, cost-effective, and environmentally benign process was developed to produce highly effic... more A novel, cost-effective, and environmentally benign process was developed to produce highly efficient carbon-based adsorbents (CBAs) from paper mill sludge. The production process required chemical activation of sludge using zinc chloride and pyrolysis at 750 C in Nâ gas. The produced CBAs were characterized according to their surface area and pore size distribution using Nâ-BET adsorption isotherm data. Further characterization of the surface and pore structure was conducted using a unified exponential/power law approach applied to small angle neutron scattering (SANS) data. The structural features analyzed by SANS revealed the dependence of porosity with zinc chloride concentration. The presence of inaccessible pores was also determined by contrast-match experiments.

Biochemistry, Jul 1, 2003

Chem Mater, 2002

Small-angle neutron scattering (SANS) and N2-BET analysis were used to characterize the microstru... more Small-angle neutron scattering (SANS) and N2-BET analysis were used to characterize the microstructure of a series of activated carbons produced from paper mill sludge using ZnCl. N-BET and SANS data indicate that the micro- and mesoporous surface areas of the carbons increase with the concentration of ZnCl used in their preparation. Contrast variation SANS studies demonstrate the existence of two

The measurement of the conformation of a Generation-8 Polyamidoamine dendrimer is reported as an ... more The measurement of the conformation of a Generation-8 Polyamidoamine dendrimer is reported as an initial experiment using the Extended Q-range Small Angle Neutron Scattering (EQ-SANS) diffractometer at the Spallation Neutron Source at Oak Ridge National Laboratory (ORNL). The conformation parameters (radius of gyration, thickness of the soft shell etc.) are extracted by model fitting. The results are compared with data collected at the General-Purpose Small Angle Neutron Scattering at the High Flux Isotopic Reactor at ORNL. The comparison shows that the EQ-SANS diffractometer has comparable data statistics and Q resolution with shorter counting time over the measured Q-range.

Dislocation loop imaging using (a) CTEM and (b) STEM-ABF of dislocation loops in neutron irradiat... more Dislocation loop imaging using (a) CTEM and (b) STEM-ABF of dislocation loops in neutron irradiated model Fe-15Cr-3.9Al alloy. Inset in (a) shows TEM acquired [100] zone axis diffraction pattern. Inset in (b) shows expected dislocation loop morphologies. (100 type loops highlighted with red arrows, in-plane with a green arrow, and a /2 111 loops highlighted with blue arrows). .. .. .. . 10 Dislocation structure in unirradiated (a) Fe-10Cr-4.8Al, (b) Fe-12Cr-4.4Al, (c) Fe-15Cr-3.9Al, and (d) Fe-18Cr-2.9Al. STEM-ABF tilted to the [100] zone axis used to image dislocation structures.

Aps March Meeting Abstracts, Mar 1, 1997

ABSTRACT

ABSTRACT The structures of kinetically distinct electron transfer complexes formed between the ph... more ABSTRACT The structures of kinetically distinct electron transfer complexes formed between the photosynthetic reaction center from Rhodobacter sphaeroides R-26, and a water-soluble cytochrome c2 were characterized using small angle neutron scattering, SANS. Reaction center-cytochrome c2 complexes, RC-C, exhibiting predominately single exponential electron transfer kinetics were found to be 1:1 molar complexes, consistent with a low resolution, co-crystal, x-ray structure (Adir et al., 1996), provided that the cofactor separation was adjusted to 14 ± 3 Å. Other RC-C configurations are consistent with SANS data, but are distinguishable by cofactor separation. RC-C preparations exhibiting more complex kinetics were found to have a particle volume markedly greater than that of a 1:1 complex. These results suggest that RC aggregation is associated with the variation in kinetics reported in the literature, and provide evidence that the model for the 1:1 complex in co-crystals is relevant to the solution environment.

Aps March Meeting Abstracts, Mar 1, 2011

The small-angle neutron scattering (SANS) beam line, CG-2, has been in operation since 2007. CG-2... more The small-angle neutron scattering (SANS) beam line, CG-2, has been in operation since 2007. CG-2 has been optimized so that structures from 0.5 to 200 nm can be thoroughly investigated. HFIR's cold source places the flux at CG-2 among the best in the world. Along with high flux, many varied sample environments can easily be integrated into the beam line

Geochimica et Cosmochimica Acta, 2015

We have performed a series of experiments to understand the effects of quartz overgrowths on nano... more We have performed a series of experiments to understand the effects of quartz overgrowths on nanometer to centimeter scale pore structures of sandstones. Blocks from two samples of St. Peter Sandstone with different initial porosities (5.8 and 18.3 %) were reacted from 3 days to 7.5 months at 100 and 200°C in aqueous solutions supersaturated with respect to quartz by reaction with amorphous silica. Porosity in the resultant samples was analyzed using small and ultrasmall angle neutron scattering and scanning electron microscope/backscattered electron (SEM/BSE)based image-scale processing techniques. Significant changes were observed in the multiscale pore structures. By three days much of the overgrowth in the low-porosity sample dissolved away. The reason for this is uncertain, but the overgrowths can be clearly distinguished from the original core grains in the BSE images. At longer times the larger pores are observed to fill with plate-like precipitates. As with the unreacted sandstones, porosity is a step function of size. Grain boundaries are typically fractal, but no evidence of mass fractal or fuzzy interface behavior was observed suggesting a structural difference between chemical and clastic sediments. After the initial loss of the overgrowths, image scale porosity (> ~ 1 cm) decreases with time. Submicron porosity (typically ~25 % of the total) is relatively constant or slightly decreasing in absolute terms, but the percent change is significant. Fractal dimensions decrease at larger scales, and increase at smaller scales with increased precipitation.

The small-angle neutron scattering (SANS) beam line, CG-2, has been in operation since 2007. CG-2... more The small-angle neutron scattering (SANS) beam line, CG-2, has been in operation since 2007. CG-2 has been optimized so that structures from 0.5 to 200 nm can be thoroughly investigated. HFIR's cold source places the flux at CG-2 among the best in the world. Along with high flux, many varied sample environments can easily be integrated into the beam line

Goldschmidt2021 abstracts

Goldschmidt2021 abstracts

Nature

Single-phase high- and medium-entropy alloys with face-centred cubic (fcc) structure can exhibit ... more Single-phase high- and medium-entropy alloys with face-centred cubic (fcc) structure can exhibit high tensile ductility1,2 and excellent toughness2,3, but their room-temperature strengths are low1-3. Dislocation obstacles such as grain boundaries4, twin boundaries5, solute atoms6 and precipitates7-9 can increase strength. However, with few exceptions8-11, such obstacles tend to decrease ductility. Interestingly, precipitates can also hinder phase transformations12,13. Here, using a model, precipitate-strengthened, Fe-Ni-Al-Ti medium-entropy alloy, we demonstrate a strategy that combines these dual functions in a single alloy. The nanoprecipitates in our alloy, in addition to providing conventional strengthening of the matrix, also modulate its transformation from fcc-austenite to body-centred cubic (bcc) martensite, constraining it to remain as metastable fcc after quenching through the transformation temperature. During subsequent tensile testing, the matrix progressively transforms to bcc-martensite, enabling substantial increases in strength, work hardening and ductility. This use of nanoprecipitates exploits synergies between precipitation strengthening and transformation-induced plasticity, resulting in simultaneous enhancement of tensile strength and uniform elongation. Our findings demonstrate how synergistic deformation mechanisms can be deliberately activated, exactly when needed, by altering precipitate characteristics (such as size, spacing, and so on), along with the chemical driving force for phase transformation, to optimize strength and ductility.

Applied Sciences

In an effort to upgrade and provide a unified and improved instrument control and data acquisitio... more In an effort to upgrade and provide a unified and improved instrument control and data acquisition system for the Oak Ridge National Laboratory (ORNL) small-angle neutron scattering (SANS) instrument suite—biological small-angle neutron scattering instrument (Bio-SANS), the extended q-range small-angle neutron scattering diffractometer (EQ-SANS), the general-purpose small-angle neutron scattering diffractometer (GP-SANS)—beamline scientists and developers teamed up and worked closely together to design and develop a new system. We began with an in-depth analysis of user needs and requirements, covering all perspectives of control and data acquisition based on previous usage data and user feedback. Our design and implementation were guided by the principles from the latest user experience and design research and based on effective practices from our previous projects. In this article, we share details of our design process as well as prominent features of the new instrument control a...

AIP Advances

Paper published as part of the special topic on Chemical Physics, Energy, Fluids and Plasmas, Mat... more Paper published as part of the special topic on Chemical Physics, Energy, Fluids and Plasmas, Materials Science and Mathematical Physics ARTICLES YOU MAY BE INTERESTED IN Ferroelectric and electromechanical properties of poly(vinylidene-fluoridetrifluoroethylene-chlorotrifluoroethylene) terpolymer

Materials & Design

Abstract The bcc ferritic Fe-Ni steels and in particular the commercial 9Ni alloys were developed... more Abstract The bcc ferritic Fe-Ni steels and in particular the commercial 9Ni alloys were developed and widely used at cryogenic temperatures for liquefied natural gas storage. The excellent thermomechanical properties and cryogenic toughness of these materials are closely related to the presence of metastable fcc austenitic phase whose stability increases in the presence of austenitic components (Ni, Cr, Mn, etc.) and with decreasing fcc grain size. Numerous reports are related to quenching and tempering technological procedures improving the cryogenic performance, however, very little attention has been paid to the structural characterization of austenitic minority species except for a few papers revealing rather contradictory results. Using high-energy X-ray diffraction, small-angle neutron scattering and 57Fe Mossbauer spectroscopy we show that the minority austenitic particles in the commercial X8Ni9 steel are enriched in nickel up to 27 ± 6 at.% Ni and have a characteristic size of 620 ± 25 A. The austenitic phase is highly sensitive to mechanical deformation and stress. Disappearance of the fcc grains during the treatment implies a mechanical failure while mechanically-resistant regions are characterized by a higher intensity of the austenitic reflections probably related to the generated texture. The last finding was never reported previously.

Journal of The Electrochemical Society

1Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA 2Dep... more 1Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA 2Department of Materials Science and Engineering and A. J. Drexel Nanomaterials Institute, Drexel University, Philadelphia, Pennsylvania 19104, USA 3Department of Chemical and Environmental Engineering, University of California–Riverside, Riverside, California 92521, USA 4ISIS Pulsed Neutron and Muon Source, STFC Rutherford Appleton Laboratory, Harwell Campus, Didcot, Oxfordshire OX11 0QX, United Kingdom 5Chemical Science Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA

Preliminary work has been completed to evaluate the deformation behavior of the Generation II FeC... more Preliminary work has been completed to evaluate the deformation behavior of the Generation II FeCrAl alloy class. The Generation II alloy, C35M, was neutron irradiated within the High Flux Isotope Reactor followed by post-irradiation examination to evaluate the mechanical properties, irradiated microstructure, deformation modes, and deformation microstructure. Complementary characterization techniques were used in this evaluation. It was found that after irradiation to 1.8 dpa at 364°C that the C35M specimen failed in a ductile manner. The observed deformation microstructure showed a high density of line dislocations, dislocation networks, and dislocation pileups. The observed performance and structures are consistent with literature studies on high-Cr FeCr alloys that were thermally aged at 500°C. The observed results suggest that Generation II FeCrAl alloys retain ductility under low-dose, prototypical LWR irradiation conditions.

A novel, cost-effective, and environmentally benign process was developed to produce highly effic... more A novel, cost-effective, and environmentally benign process was developed to produce highly efficient carbon-based adsorbents (CBAs) from paper mill sludge. The production process required chemical activation of sludge using zinc chloride and pyrolysis at 750 C in Nâ gas. The produced CBAs were characterized according to their surface area and pore size distribution using Nâ-BET adsorption isotherm data. Further characterization of the surface and pore structure was conducted using a unified exponential/power law approach applied to small angle neutron scattering (SANS) data. The structural features analyzed by SANS revealed the dependence of porosity with zinc chloride concentration. The presence of inaccessible pores was also determined by contrast-match experiments.

Biochemistry, Jul 1, 2003

Chem Mater, 2002

Small-angle neutron scattering (SANS) and N2-BET analysis were used to characterize the microstru... more Small-angle neutron scattering (SANS) and N2-BET analysis were used to characterize the microstructure of a series of activated carbons produced from paper mill sludge using ZnCl. N-BET and SANS data indicate that the micro- and mesoporous surface areas of the carbons increase with the concentration of ZnCl used in their preparation. Contrast variation SANS studies demonstrate the existence of two

The measurement of the conformation of a Generation-8 Polyamidoamine dendrimer is reported as an ... more The measurement of the conformation of a Generation-8 Polyamidoamine dendrimer is reported as an initial experiment using the Extended Q-range Small Angle Neutron Scattering (EQ-SANS) diffractometer at the Spallation Neutron Source at Oak Ridge National Laboratory (ORNL). The conformation parameters (radius of gyration, thickness of the soft shell etc.) are extracted by model fitting. The results are compared with data collected at the General-Purpose Small Angle Neutron Scattering at the High Flux Isotopic Reactor at ORNL. The comparison shows that the EQ-SANS diffractometer has comparable data statistics and Q resolution with shorter counting time over the measured Q-range.

Dislocation loop imaging using (a) CTEM and (b) STEM-ABF of dislocation loops in neutron irradiat... more Dislocation loop imaging using (a) CTEM and (b) STEM-ABF of dislocation loops in neutron irradiated model Fe-15Cr-3.9Al alloy. Inset in (a) shows TEM acquired [100] zone axis diffraction pattern. Inset in (b) shows expected dislocation loop morphologies. (100 type loops highlighted with red arrows, in-plane with a green arrow, and a /2 111 loops highlighted with blue arrows). .. .. .. . 10 Dislocation structure in unirradiated (a) Fe-10Cr-4.8Al, (b) Fe-12Cr-4.4Al, (c) Fe-15Cr-3.9Al, and (d) Fe-18Cr-2.9Al. STEM-ABF tilted to the [100] zone axis used to image dislocation structures.

Aps March Meeting Abstracts, Mar 1, 1997

ABSTRACT

ABSTRACT The structures of kinetically distinct electron transfer complexes formed between the ph... more ABSTRACT The structures of kinetically distinct electron transfer complexes formed between the photosynthetic reaction center from Rhodobacter sphaeroides R-26, and a water-soluble cytochrome c2 were characterized using small angle neutron scattering, SANS. Reaction center-cytochrome c2 complexes, RC-C, exhibiting predominately single exponential electron transfer kinetics were found to be 1:1 molar complexes, consistent with a low resolution, co-crystal, x-ray structure (Adir et al., 1996), provided that the cofactor separation was adjusted to 14 ± 3 Å. Other RC-C configurations are consistent with SANS data, but are distinguishable by cofactor separation. RC-C preparations exhibiting more complex kinetics were found to have a particle volume markedly greater than that of a 1:1 complex. These results suggest that RC aggregation is associated with the variation in kinetics reported in the literature, and provide evidence that the model for the 1:1 complex in co-crystals is relevant to the solution environment.

Aps March Meeting Abstracts, Mar 1, 2011

The small-angle neutron scattering (SANS) beam line, CG-2, has been in operation since 2007. CG-2... more The small-angle neutron scattering (SANS) beam line, CG-2, has been in operation since 2007. CG-2 has been optimized so that structures from 0.5 to 200 nm can be thoroughly investigated. HFIR's cold source places the flux at CG-2 among the best in the world. Along with high flux, many varied sample environments can easily be integrated into the beam line

Geochimica et Cosmochimica Acta, 2015

We have performed a series of experiments to understand the effects of quartz overgrowths on nano... more We have performed a series of experiments to understand the effects of quartz overgrowths on nanometer to centimeter scale pore structures of sandstones. Blocks from two samples of St. Peter Sandstone with different initial porosities (5.8 and 18.3 %) were reacted from 3 days to 7.5 months at 100 and 200°C in aqueous solutions supersaturated with respect to quartz by reaction with amorphous silica. Porosity in the resultant samples was analyzed using small and ultrasmall angle neutron scattering and scanning electron microscope/backscattered electron (SEM/BSE)based image-scale processing techniques. Significant changes were observed in the multiscale pore structures. By three days much of the overgrowth in the low-porosity sample dissolved away. The reason for this is uncertain, but the overgrowths can be clearly distinguished from the original core grains in the BSE images. At longer times the larger pores are observed to fill with plate-like precipitates. As with the unreacted sandstones, porosity is a step function of size. Grain boundaries are typically fractal, but no evidence of mass fractal or fuzzy interface behavior was observed suggesting a structural difference between chemical and clastic sediments. After the initial loss of the overgrowths, image scale porosity (> ~ 1 cm) decreases with time. Submicron porosity (typically ~25 % of the total) is relatively constant or slightly decreasing in absolute terms, but the percent change is significant. Fractal dimensions decrease at larger scales, and increase at smaller scales with increased precipitation.

The small-angle neutron scattering (SANS) beam line, CG-2, has been in operation since 2007. CG-2... more The small-angle neutron scattering (SANS) beam line, CG-2, has been in operation since 2007. CG-2 has been optimized so that structures from 0.5 to 200 nm can be thoroughly investigated. HFIR's cold source places the flux at CG-2 among the best in the world. Along with high flux, many varied sample environments can easily be integrated into the beam line