Mechanism of powellite crystallite expansion within nano-phase separated amorphous matrices under Au-irradiation

Patel, Karishma B. and Schuller, Sophie and Lampronti, Giulio I. and Farnan, Ian (2020) Mechanism of powellite crystallite expansion within nano-phase separated amorphous matrices under Au-irradiation. Physical Chemistry Chemical Physics, 22 (27). pp. 15616-15631. ISSN 1463-9076 DOI https://doi.org/10.1039/D0CP02447C

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Abstract

A fundamental approach was taken to understand the implications of increased nuclear waste loading inthe search for new materials for long-term radioisotope encapsulation. This study focused on theformation and radiation tolerance of glass ceramics with selectively induced CaMoO4as a form to trapthe problematic fission product molybdenum. Several samples were synthesised with up to 10 mol%MoO3within a soda lime borosilicate matrix, exhibiting phase separation on the nano scale according tothermal analysis, which detected two glass transition temperatures. It is predicted that these two phasesare a result of spinodal decomposition with Si–O–Ca–O–Si and Si–O–Ca–O–B units, with the latterphase acting as a carrier for MoO3. The solubility limit of molybdenum within this matrix was 1 mol%,after which crystallisation of CaMoO4occurred, with crystallite size (CS) increasing and cell parametersdecreasing as a function of [MoO3]. These materials were then subjected to irradiation with 7 MeV Au3+ions to replicate the nuclear interactions resulting froma-decay. A dose of 3�1014ions per cm2wasachieved, resulting in 1 dpa of damage within a depth ofB1.5mm, according to TRIM calculations.Glasses and glass ceramics were then analysed using BSE imaging, XRD refinement, and Raman spectro-scopy to monitor changes induced by accumulated damage. Irradiation was not observed to cause anysignificant changes to the residual amorphous network, nor did it cause amorphisation of CaMoO4based on the relative changes to particle size and density. Furthermore, the substitution of Ca2+toform water-soluble Na2/NaGd–MoO4assemblages did not occur, indicating that CaMoO4is resilientto chemical modification following ion interactions. Au-irradiation did however cause CaMoO4latticeparameter expansion, concurrent to growth in CS. This is predicted to be a dual parameter mechanismof alteration based on thermal expansion from electronic coupling, and the accumulation of defectsarising from atomic displacements.

Item Type:	Article
Uncontrolled Keywords:	2020AREP; IA76
Subjects:	03 - Mineral Sciences
Divisions:	03 - Mineral Sciences 07 - Gold Open Access 12 - PhD
Journal or Publication Title:	Physical Chemistry Chemical Physics
Volume:	22
Page Range:	pp. 15616-15631
Identification Number:	https://doi.org/10.1039/D0CP02447C
Depositing User:	Sarah Humbert
Date Deposited:	14 Dec 2020 15:03
Last Modified:	14 Dec 2020 15:03
URI:	http://eprints.esc.cam.ac.uk/id/eprint/4938

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