Impacts of ultrasound on oxide removal - An attempt towards acid-free cleaning.

ABSTRACT

Strong or mid-strong acids are always used to remove oxides from part surfaces in remanufacturing, painting, metallurgical and mineral industries, which is not environmentally benign. In this work, a green cleaning method - ultrasonic (US) cleaning with distilled water is proposed. The impacts of ultrasonic cleaning process parameters including the distance between the sonotrode end surface and the specimen surface, the vibration amplitude, the process time and the concentration of oxalic acid, on the surface oxide removal rate were systematically studied based on a Box-Behnken Design. The results show a significant increase of the oxide removal rate on the specimen surface with the decrease of the distance, the increase of the vibration amplitude, the increase of the process time and the presence of oxalic acid. Based on the experimental results, an empirical model was established to quantitatively describe the effects of these factors on the oxide removal rate. In addition to all the linear factors, the square factors of time and the concentration of oxalic acid as well as the interaction factors among time, driving current and the concentration of oxalic acid are significant on the oxide removal. Compared to the cleaning with acids, a high level removal rate is still achievable with acid-free distilled water even though the process window gets narrower. This study enhances the potential application of US cleaning on oxide removal with a small amount of weak acid or without any acid in the cleaning liquid in industries.