Interdiffusion and reaction between U and Zr

• Published in: Journal of nuclear materials 2018-04, Vol.502 (C), p.42-50
• Main Authors: Park, Y., Newell, R., Mehta, A., Keiser, D.D., Sohn, Y.H.
• Format: Article
• Language: English
• Subjects: Atomic mobilities; Atomic structure; Coefficients; Couples; Dependence; Diffusion; Energy transmission; Interdiffusion; Kinetics; Lattice parameters; Microstructure; Reaction kinetics; Scanning electron microscopy; Solid solutions; Spectroscopy; Tracer diffusion; Transmission electron microscopy; Zirconium
• ISSN: 0022-3115; 1873-4820
• DOI: 10.1016/j.jnucmat.2018.01.063

The microstructural development and diffusion kinetics were examined for the binary U vs. Zr system using solid-to-solid diffusion couples, U vs. Zr, annealed at 580 °C for 960 h, 650 °C for 480 h, 680 °C for 240 h, and 710 °C for 96 h. Scanning and transmission electron microscopies with X-ray energy dispersive spectroscopy were employed for detailed microstructural and compositional analyses. Interdiffusion and reaction in U vs. Zr diffusion couples primarily produced: δ-UZr2 solid solution (hP3) and α′-U at 580 °C; and (γU,βZr) solid solution (cI2) and α′-U at 650°, 680° and 710 °C. The α′-phase was confirmed as a reduced variant of the α-U orthorhombic structure with lattice parameters, a × b × c = 2.65 × 5.40 × 4.75 (Å) with a negligible solubility for Zr at room temperature. Concentration profiles were examined to determine interdiffusion coefficients, integrated interdiffusion coefficients, and intrinsic diffusion coefficients using Boltzmann-Matano, Wagner, and Heumann analyses, respectively. Composition-dependence of interdiffusion coefficients were documented for α-U, δ-UZr2 (at 580 °C) and (γU,βZr) solid solution (at 650°, 680° and 710 °C). U was determined to intrinsically diffuse faster than Zr, approximately by an order of magnitude, in the δ-UZr2 at 580 °C, and (γU,βZr) phases at 650°, 680° and 710 °C. Based on Darken's approach, thermodynamic data available in literature were coupled to estimate the tracer diffusion coefficients and atomic mobilities of U and Zr.