Molecular Dynamics Simulation of Diffusion Behavior in Liquid Sn and Pb

This study aimed to clarify the effect of a unique structure with a "shoulder,"which represents a hump on the high wave vector side of the first peak of static structure factor, in liquid Sn (liq-Sn) on the self-diffusion behavior through molecular dynamics (MD) simulation. The MD simulations of liq-Sn at 573 K and liquid Pb (liq-Pb) at 773 K were performed for comparison. The former and latter were selected as element with and without shoulder structure and reliable self-diffusion coefficients in liquid have been measured in both elements. The calculated self-diffusion coefficients of liq-Sn and liq-Pb were reproduced as the same order of magnitude with the referred reliable data of diffusion coefficients, which were obtained by experiments on the ground. The microscopic diffusion behavior of liq-Sn is unlike that of the hard-sphere model because the atoms become sluggish in the range that corresponds to the shoulder appearing in the pair distribution function of liq-Sn as well as in the structure factor of liq-Sn based on the local atomic configurations and time-series analyses of individual atoms. Therefore, the velocity autocorrelation function (VACF) converges to zero more rapidly than that of liq-Pb, and it is reproduced by the hard-sphere model. However, the macroscopic diffusion behavior of liq-Sn expressed by the self-diffusion coefficient is the same as that of the hard-sphere model with the non-correlation of the VACF in the long time

液体金属の高精度拡散係数測定と予測式構築

早大学位記番号:新9055早稲田大

Elimination of Systematic Error in Diffusion Measurement Using In-situ X-ray Fluorescence Analysis for Liquid Alloys

The objective of the present study is to quantify and eliminate the error factors in the measurement of diffusion coefficients in liquid alloys by using in-situ X-ray fluorescence analysis (in-situ XRF). Averaging effect, initial mass transport, and matrix effect were investigated. The impurity diffusion coefficient of Bi in liquid Sn was measured at 573 K using a combination of the long capillary technique and in-situ XRF. The apparent diffusion coefficient was obtained as the time-series data by fitting an analytical solution of Fick’s second law to the temporal variation in Bi concentration in the capillary. In the present measurement, matrix effect did not induce a significant error in the measured diffusion coefficient. Averaging effect can be eliminated by convoluting the analytical solution with the distribution of the X-ray fluorescence intensity scanned from the rod sample. Furthermore, the initial mass transport can be eliminated by shifting the point of time origin to the latter time in the temporal variation in the measured concentration by fitting the analytical solution. By performing the above corrections, the systematic error in the measured diffusion coefficient can be reduced