Radiation-damage in multi-layered zircon: Mechanical properties

Abstract

Nanoindentation high-resolution mapping has been used to probe the mechanical properties [elastoplastic factor (S2/P, where S is the contact stiffness and P is the load), indentation hardness (H), and elastic modulus (E)] of a natural, highly zoned zircon (ZrSiO4). The zoning, on a scale of ∼ 5 to 400 μm, is due to variations in the U and Th concentrations, resulting in a range of α-decay event doses of ∼ 3.7× to 7.5 × 1018 α-decays/g. Thus, this single, zoned zircon crystal can be used to investigate the effects of α-decay radiation-damage on mechanical properties. The results also illustrate how multilayered ceramics accommodate volume expansion and change in mechanical properties as a function of radiation dose. Further, the detailed investigation of fractures in the lesser damaged, higher crystalline domains provides a better understanding of crack propagation in the initially crystalline material due to the strain induced by heterogeneous damage distribution. This is an important consideration in designing materials for the immobilization of plutonium from dismantled nuclear weapons, as plutonium decays by α-decay events. The directly measurable stiffness2/load (S2/P) provides a useful estimate of the degree of radiation-damage. The evolution of E provides experimental evidence for the predicted second percolation transition that denotes the end of percolation of the crystalline fraction.

Crystal chemistry and thermodynamic properties of zircon structure-type materials

“…Metamict zircon-type materials experience softening in both elastic moduli and hardness, and an increase in dissolution rate (Ewing et al 1982). Again, several review papers have summarized the radiation effects on zircon structure-type materials from the structural and energetic perspectives, and we recommend these papers to the reader (Meldrum et al 1997a(Meldrum et al , 2000Ewing et al 2003;Ewing 2007;Geisler et al 2007;Weber and Ewing 2013;Beirau et al 2019;Weber et al 2019).…”

“…; Ewing 2007;Geisler et al 2007;Weber and Ewing 2013;Beirau et al 2019;Weber et al 2019), how the Pb daughter product is incorporated in the crystal structure is the subject of much debate, which has major implications on how geologic processes are dated(Watson et al 1997;Kramers et al 2009; view, in an eight-fold coordination environment, Pb 4+ (0.94 Å) is similar in size to parent U…”

Influence of indentation size and spacing on statistical phase analysis via high-speed nanoindentation mapping of metal alloys

“…The difference between the H/E ratio and the H and E maps is more pronounced for the DSS sample. Therefore, it can be derived that, although H and E represent different mechanical phenomena, they are interrelated in such a way that the corresponding H/E ratio for each phase reveals more reliable and comparable values [29], similar to S 2 /P. Hence, H/E ratio offers better resolution to discriminate the mechanical response of the constitutive phases of DSSs, in which the austenitic phase demonstrates a higher H/E ratio compared with the ferritic phase.…”