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Your search keyword '"Lumpkin, Gregory R."' showing total 222 results
Start Over Author "Lumpkin, Gregory R." Publication Year Range Last 50 years Publication Type Academic Journals
222 results on '"Lumpkin, Gregory R."'

39. Profiling hot isostatically pressed canister–wasteform interaction for Pu‐bearing zirconolite‐rich wasteforms.

Author

Dayal, Pranesh, Farzana, Rifat, Zhang, Yingjie, Lumpkin, Gregory R., Holmes, Rohan, Triani, Gerry, and Gregg, Daniel J.

Subjects
HOT pressing, ISOSTATIC pressing, SCANNING electron microscopy, CERAMIC materials, X-ray spectroscopy, STAINLESS steel
Abstract

Zirconolite‐rich full ceramic wasteforms designed to immobilize Pu‐bearing wastes were produced via hot isostatic pressing (HIP) using stainless steel (SS) and nickel (Ni) HIP canisters. A detailed profiling of the elemental compositions of the major and minor phases over the canister–wasteform interaction zone was performed using scanning electron microscopy combined with energy‐dispersive X‐ray spectroscopy (SEM‐EDS) characterization. Bulk sample analyses from regions near the center of the HIP canister were also conducted for both samples using X‐ray diffraction and SEM‐EDS. The sample with the Ni HIP canister showed almost no interaction zone with only minor diffusion of Ni from the inner wall of the canister into the near‐surface region of the wasteform. The sample with the SS HIP canister showed ∼100–120 μm of interaction zone dominated by high‐temperature Cr diffusion from canister materials to the wasteform with the Cr predominantly incorporated into the durable zirconolite phase. We also examined, for the first time, changes to the HIP canister wall thickness caused by HIPing and demonstrated that no canister wall thinning occurred. Instead, in the areas examined, the canister wall thickness was observed to increase (up to ∼20%) due to the compression occurring during the HIP cycle. Further, only sparse formation of (Cr, Mn)‐rich oxide particles were noted within the HIP canister inner wall area immediately adjacent to the ceramic material, with no evidence for reverse diffusion of ceramic materials. Though the HIP canister–wasteform interaction extends to ∼120 μm when using an SS HIP canister for the system investigated, this translates to <<1 vol.% for an industrial scale HIPed wasteform. Importantly, the HIP canister–wasteform interactions did not produce any obviously less durable phases in the wasteform or had any detrimental impact on the HIP canister properties. [ABSTRACT FROM AUTHOR]

Published
2022
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41. Crystal chemistry and ion‐irradiation resistance of Ln2ZrO5 compounds with Ln = Sm, Eu, Gd, and Tb.

Author

Aughterson, Robert D., Lumpkin, Gregory R., Zhang, Zhaoming, Avdeev, Maxim, and Kong, Linggen

Subjects
*RARE earth metals, *NEUTRON diffraction, *SAMARIUM, *X-ray powder diffraction, *ELECTRON diffraction, *TRANSMISSION electron microscopy, *DIFFRACTION patterns, *CRYSTAL structure
Abstract

The previously unattained fabrication of single phase Ln2ZrO5 (Ln = Sm, Eu, Gd, and Tb) compounds via relatively low sintering temperature (1400°C) is achieved in this study using a coprecipitation method. The crystal structures have been investigated by neutron, synchrotron X‐ray powder diffraction, and electron diffraction techniques. While the general long‐range structure may be well described by the defect‐fluorite type structure with Fm3¯$\bar{3}$m symmetry, electron diffraction has highlighted a complex underlying modulated structure that varies between each compound. These compounds have been tested for ion‐irradiation response using in situ 1 MeV krypton ions and transmission electron microscopy characterization. None of the compounds undergo a crystalline to amorphous transition, even holding at 50 K. Both the underlying fluorite and modulated superstructures are little affected by the irradiation. However, some atomic rearrangements are observed in the postirradiated electron diffraction patterns for the Sm2ZrO5 specimen. [ABSTRACT FROM AUTHOR]

Published
2022
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46. Ion irradiation of the Ti[O.sub.2] polymorphs and cassiterite

Author

Lumpkin, Gregory R., Blackford, Mark G., Smith, Katherine L., Whittle, Karl R., Zaluzec, Nestor J., Ryan, Edward A., and Baldo, Pete

Subjects
Ion bombardment -- Usage, Polymorphism (Crystallography) -- Research, Tin ores -- Properties, Earth sciences
Abstract

Thin crystals of rutile, brookite, anatase, and cassiterite were irradiated in situ in the transmission electron microscope using 1.0 MeV Kr ions at 50-300 K. Synthetic rutile and natural cassiterite, with 0.1-0.2 wt% impurities, remain crystalline up to a fluence of 5 x [10.sup.15] ions [cm.sup.-2] without evidence for amorphization at 50 K. Natural brookite and anatase, with 0.3-0.5 wt% impurities, become amorphous at fluences of 8.1 x [10.sup.14] and 2.3 x [10.sup.14] ions [cm.sup.-2], respectively. We have also studied two natural rutile samples containing ~1.7 and 1.2 wt% impurities. These samples became amorphous at 9.2 x [10.sup.14] and 8.6 x [10.sup.14] ions [cm.sup.-2] at 50 K, respectively. Further analyses of the fluence-temperature data for natural brookite, rutile, and anatase give critical amorphization temperatures of 168 [+ or -] 11,209 [+ or -] 8, and 242 [+ or -] 6 K, respectively. Results are briefly discussed with respect to several criteria for radiation resistance, including aspects of the structure, bonding, and energetics of defect formation and migration. Keywords: Ti[O.sub.2] polymorphs, anatase, brookite, rutile, cassiterite, ion irradiation, defect migration DOI: 10.2138/am.2010.3329

Published
2010
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47. The ion irradiation tolerance of the fluorite RE2MO5 (RE = Sm, and Yb, M = Ti, Zr, and Sn) system.

Author

Aughterson, Robert D., Newman, Robin, Ionescu, Mihail, and Lumpkin, Gregory R.

Subjects
FLUORITE, SAMARIUM, TRANSMISSION electron microscopy, YTTERBIUM, GRAZING incidence, TIN, IRRADIATION
Abstract

In the search for novel ceramics for use within nuclear fuel–related applications and nuclear waste-form matrices, a major focus has been on the development of radiation-tolerant materials. Of particular interest in this field have been numerous compounds with either pyrochlore or the related fluorite-type structures. In this study, we look to expand the family of compounds with defect fluorite–type structure. We have fabricated three new compounds; Yb2Sn1.125O5.25, Yb2Sn1.25O5.5, and Yb2Sn1.375O5.75. The compound Yb2Sn1.125O5.25 was determined, via x-ray diffraction, to have the long-range defect fluorite structure, Fm-3 m symmetry, with cell parameter a = 5.17233(1). Further to this, Sm2ZrO5 and Yb2TiO5 compounds were also fabricated and crystal structures characterised. The use of transmission electron microscopy has revealed a much more complex crystal structure than that of the relatively high symmetry fluorite, with the presence of structural modulations being detected. The ion-irradiation response of these compounds was tested via bulk specimen irradiation using 15-MeV gold ions with grazing incidence x-ray diffraction characterisation. The results show that both Sm2ZrO5 and Yb2Sn1.25O5.5 are highly tolerant to ion-irradiation exposure whilst Yb2TiO5 is susceptible to amorphisation. [ABSTRACT FROM AUTHOR]

Published
2022
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