Mechanical and thermal properties of ZrSiO4

In order to conduct defueling operations for the decommissioning of the reactor at the Fukushima Daiichi nuclear power plant, an understanding of the physical properties of ZrSiO4 is of extreme importance. ZrSiO4 appears to have formed in the molten core–concrete interaction products at the Fukushima Daiichi nuclear disaster site through a reaction between Zircaloy cladding materials and concrete. Since ZrSiO4 has a high melting point of 2550 K, together with chemical inertness, the material has been widely studied as a refractory material. Various studies on the physical properties of ZrSiO4 have been performed; however, significant differences exist in the data, possibly due to the porosity within the studied samples. In the present study, we have prepared a ZrSiO4 bulk sample with 97.4% of the theoretical density by spark plasma sintering of the ZrSiO4 powder and heat treatment. We have evaluated the thermal and mechanical properties of ZrSiO4 by the measurement of sound velocities, thermal diffusivity, Vickers hardness, and fracture toughness. The Vickers hardness and fracture toughness were found to be 17 ± 3 GPa and 2.1 ± 0.5 MPa m1/2, respectively.