The Diffusion of Uranium into Aluminum

The maximum penetration of uranium into aluminum in the temperature range 200–390°C has been investigated. The maximum values for the penetration coefficient K_T, determined from the relationship K_T = x²/t, are 0.075, 0.50, and 6.1 × 10⁻⁶ in.²/hr at temperatures of 200, 250, and 390°C, respectively; the corresponding activation energy is 14,300 calories per mole. The utility of cathodically vacuum etching specimens to obtain clean metal surfaces prior to the diffusion anneal is demonstrated. Couples prepared in the temperature range investigated, 200–390°C, fracture by the application of tension between the aluminum and the adjacent UAl₃ diffusion zone interface. Subsequent measurement of the maximum UAl₃ peak heights above the initial uranium-aluminum interface assures a maximum value of the penetration coefficient. The investigation provides a necessary basis for interpreting the effect of irradiation on the diffusion rates of uranium into aluminum.