Required Diffusion Time for in-situ Measurement of Diffusion Coefficients in Liquid Alloys by X-ray Fluorescence Analysis

This study establishs a method to determine the diffusion time required for diffusion measurement by using the long capillary technique and through in-situ X-ray fluorescence analysis. A diffusion couple of pure Sn (60 mm height) and Sn90Bi10 (3 mm height) was set to provide stable density layering and maintained at 573 K. The X-ray source was positioned 10 mm above the bottom of the sample. The detected intensity of L beta emission line of Bi (Bi L beta) changed mainly because of the diffusion of Bi in liquid Sn. The apparent diffusion coefficients (Dapp) were calculated by fitting the analytical solution for the diffusion to the temporal distribution of Bi L beta intensity by varying the fitting time range from 0 to tD (diffusion time). The change in Dapp was large at short tD, but decreased with increasing tD. The deviation of Dapp from the value corresponding to the longest tD and the maximum range scale of the confidence interval of Dapp were determined. The largest calculated value is considered to be the systematic error in the diffusion measurement (AD). For the required value of tD, AD becomes less than the acceptable systematic error in the diffusion measurement. The convergent Dapp [(2.16 beta 0.09)beta 10-9 m2/s] agreed with the microgravity reference data in the error range.