Effect of cooling profile on crystalline phases, oxidation state, and chemical partitioning of complex glasses
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MRS Advances © 2020 Materials Research Society DOI: 10.1557/adv.2020.89
Effect of cooling profile on crystalline phases, oxidation state, and chemical partitioning of complex glasses Authors: J. Marcial,1,2 O. K. Neill,3 M. Newville,4 J. V. Crum,5 J. McCloy,1,2,5 1
School of Mechanical and Materials Engineering, Washington State University, Pullman, WA, USA
2
Materials Science and Engineering Program, Washington State University, Pullman, WA, USA
3
School of Earth and Environmental Sciences, University of Michigan, Ann Arbor, MI, USA
4
CARS, University of Chicago, Chicago, IL, USA
5
Pacific Northwest National Laboratory, Richland, WA, USA
Corresponding author: J. Marcial, email: [email protected]
Abstract: Investigations of the crystallization of aluminosilicate phases within Hanford nuclear waste glasses typically involve subjecting samples to the canister centerline cooling (CCC) schedule. This cooling schedule is representative of the slowest cooling thermal profile which these glasses will experience after the glass is poured into the high level waste (HLW) container. However, few investigations have observed how the crystallization behavior changes by varying the heat treatment schedule. In the present study, three Hanford HLW glasses are subjected to CCC and isothermal heat treatments (IHT) to better understand the evolution of phases and the chemical partitioning due to temperature schedule. Samples were characterized using electron probe microanalysis, X-ray diffraction, micro X-ray fluorescence, and micro X-ray absorption spectroscopy. From IHT, eucryptite and apatite phases were observed which were not observed during CCC. Spatially-resolved measurements demonstrated that the oxidation state of the iron was similar among glass and crystal, and we suggest a mechanism to describe the compositional fluctuations near the crystal-glass interface which influence crystallization.
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INTRODUCTION: Over 200,000 m3 of nuclear waste is currently stored at the Hanford site located in Washington State, USA [1, 2]. This waste will ultimately be vitrified in a joule-heated ceramic-lined melter, where a slurry composed of liquid waste mixed with glass-forming components is discharged into the melter where it undergoes various batch reactions on heating and finally is converted to melt which is discharged into a container where it cools to form glass. The thermal profile which the melt will experience after pouring into stainless steel canisters will depend on the dimensions of the canister, the pour schedule, the initial melt temperature, the melt thermal diffusivity, etc. [3]. Within the center of the canister, the melt is expected to cool slowly from the melter operating temperature (1150°C) to ambient temperature [3]. For the case of some high-level waste (HLW) glasses, this
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