Solubility, permeation, and capturing of impurity oxygen in Au/Ag: A comparative investigation from first-principles

• Gold (Au) and silver (Ag) are often used as the ideal jewelry materials.
• Oxygen (O) is a common impurity significantly affecting on the purification.
• A comparative analysis on the O behaviors in Au and Ag is systematically given.
• The diffusivity and permeation of O in Au/Ag agree well with the experiments.

Here we present a comparative analysis on the behaviors of impurity O in Au and Ag based on first-principles calculations. In both Au and Ag, O prefers to occupy the tetrahedral site with a higher solution energy of 1.00 eV in Au and lower value of −0.02 eV in Ag, respectively. This leads to that the interstitial O concentration in Ag is obviously higher than that in Au. The diffusion energy barrier of O in Au is 0.05 eV, which is far less than 0.58 eV in Ag, thus resulting in that the O diffusivity in Au is notably higher than that in Ag. However, due to the lower O concentration in Au, the O permeability (Φ=D·SΦ=D·S, D and S are the diffusivity and concentration, respectively.) in Au is obviously lower than that in Ag. Our theoretical results for both diffusivity and permeability are in quantitative agreement with the experimental data. In both Au and Ag, the On–vacancy (OnV) clusters are demonstrated to be easily formed. In Au, One vacancy can accommodate up to 5 O atoms, slightly lower than 6 O atoms in Ag. At the same time, we demonstrate that O2 molecule in a single vacancy is energetically unable in both metals. These research results can provide a very useful reference for the refinement of Ag/Au as noble metal in industry.

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