Radiation-damage in multi-layered zircon: Mechanical properties

Nanoindentation high-resolution mapping has been used to probe the mechanical properties [elastoplastic factor (S-2/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 similar to 5 to 400 mu m, is due to variations in the U and Th concentrations, resulting in a range of alpha-decay event doses of similar to 3.7x to 7.5x10(18) alpha-decays/g. Thus, this single, zoned zircon crystal can be used to investigate the effects of alpha-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 alpha-decay events. The directly measurable stiffness(2)/load (S-2/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.