Measurements of Diffusion Coefficients in Liquid Alloys Using Two Measurement Points of <i>In Situ</i> X-Ray Fluorescence Analysis

The objective of this study is to quantify the improvement of diffusion experiments in liquid alloys by using two measurement points of in situ X-ray fluorescence analysis ( in situ XRF). The impurity diffusion coefficient of Bi in liquid Sn at 573 K was measured by monitoring the temporal change in the Bi concentration at two fixed points using in situ XRF. In the present study, two XRF measurement points were set in order to determine two unknown parameters that corresponded to the diffusion coefficient and the initial concentration at the measurement point just after complete melting. When only one measurement point is set for in situ XRF, the initial concentration is treated as a variable and the obtained impurity diffusion coefficients of Bi deviated by 20-30% from the reliable reference data. By using two measurement points for in situ XRF, the obtained impurity diffusion coefficient of Bi was (2.44±0.08)×10 -9 m 2 s -1 and agreed with the reference data in the reported uncertainty of ±10%.