RESUMO
The decommissioning of contaminated metal equipment in nuclear facilities may produce a wide range of radioactive waste. For metallic equipment like the primary loop, the radioactivity is mainly located in the oxide surface. Laser decontamination was performed on 304 stainless steel specimens with a stable isotope Cs contamination layer. Laser melting was used to create oxide layer on the surface of polished specimen for enhancing the penetration of Cs+ ion. The interaction between laser and matter (contamination, oxide and substrate) was studied by the stratification theory considering the difference in the thickness of contamination layer. At higher pulse duration (τp = 5ns), laser decontamination is mainly caused by thermal effects. The metal near oxide layer melts and vaporizes to form a molten pool and crater. For short pulse duration (τp = 1ns), the removal of surface contaminations mainly depends on thermal effect and stress wave, CsCl particles were removed by vaporization; however, oxide layer was stripped from the substrate in the form of solid fragment. For ultra-short pulse duration (τp = 150ps), the oxide layer has been partially ablated. Most of the heat absorbed by γ (austenite) is used for heating and evaporation to form porous structure, while the great mass of heat absorbed by M (martensite) is used for thermal diffusion. Therefore, the M regions only form a dynamic molten pool on its surface without vaporization.
RESUMO
Paint layer was stripped from the 2024 aluminium alloy aircraft skin by either 1000 grit sandpaper or laser with 150 ps pulse width while the laser paint stripping (LPS) process was recorded by a high-speed camera. The surface and cross-section morphologies, chemical compositions and chemical valences of obtained the paint stripping samples were also characterise. The corrosion resistance was determined by the Potentiodynamic Polarization Curve (PPC). On mechanical paint stripping (MPS) samples, a large amount of scratches remained. Surface roughness increased and the oxide film was removed completely. The trace of the laser scan was observable on the surface of LPS samples. Recrystallisation occurred on the LPS surface and eventually formed arrayed micro and sub-micro structures. The oxide film is mainly composed of Al2O3 with a thickness about 2.10 µm. The corrosion current density of mechanical and LPS samples are 3.66 ×10-2 mA·cm-2 and 6.66×10-5 mA·cm-2, respectively. Comparing to MPS which removed all the oxide film and damaged the substrate metal, LPS only damaged the oxide film mildly without damaging metal substrate. The remaining oxide film contributes to a higher corrosion resistance of the LPS sample.
