DRY ETCHING AND LASER CLEANING OF ANCIENT-LIKE BRONZES

Bronze alloy specimens, produced to simulate ancient alloys, are used to study the corrosion behaviour in accelerated corrosion conditions. On the coin-like specimens was created artificial ‘bronze disease’. The surface condition after the exposure has been investigated through optical and scanning electron microscopy coupled with EDS as well as X-ray diffraction analytical techniques. Cleaning of the surface was attempted both by dry etching of the bronze patina, using hydrogen plasma at temperatures between 180-190°C and by laser ablation. Laser ablation was performed via Q-switched Nd:YAG laser at 1064 nm wavelength with a pulse duration of 6 ns, repetition rate 1-10 Hz and energy fluence of 0.4-7.7 J/cm2. Then the beam was focused through a lens of f: 10 mm, fixed in position, onto the sample, which was located on an x-y-z micro-adjustable stage, controlled by computer. Deionised water was used, during the laser ablation, as working environment, in order to avoid redeposition of debris and to cool the material. The surface condition of the alloys after the stabilization and cleaning trials was characterized by the analytical methods mentioned above. The performance of the two methods is compared and their advantages and drawbacks are discussed.