Laser irradiation-an effective means to create an anti-tarnishing surface on purple gold substrate

摘要

Purple gold (PG) has emerged as a colored gold product for use in decorating jewelry items. However, PG possesses little chemical stability in the ambient environments and undergoes noticeable decolorizing in a few months. This work uses the 4th harmonic Nd:YAG laser as a new measure instead of conventional coating technique to generate an anti-tarnishing layer on PG. The laser beam brings about instant melting at the irradiated surface of PG and re-solidification of the melt leads to a dense overlaying thin layer, of which the structure is contingent on the laser parameters and thermodynamic properties of the treated surface. This thin layer possesses very different properties from the non-irradiated surface. An investigation of laser-irradiation effect by varying its scanning speed and scanning repetitions were carried out to determine an optimal treatment condition. In conjunction with this investigation, scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive X-ray (EDX) were employed as well. The dependence of surface morphology and composition on the setting of parameters has been discovered through this work.