Particle Properties of Air Nanobubbles and Their Inhibition Mechanism on Brass Corrosion in Recirculating Cooling Water: Effects of Concentration Ratio and Flow Velocity

The corrosion inhibition performance of air nanobubbles (A-NBs) is expected to address the environmental problems arising from chemical corrosion. In order to regulate the corrosion inhibition performance of A-NBs, the particle characteristics of A-NBs in flowing composite salt solutions are investigated, and the corrosion inhibition effect of A-NBs under different concentration ratios and rotational speed of simulated circulating cooling water is studied. High salt concentrations significantly reduced the particle size, concentration, and zeta-potential value of A-NBs, thus reducing the stability of A-NBs. The flow velocity has a slight effect on A-NBs. The results of the weight loss and electrochemical method showed that A-NBs achieved the highest corrosion inhibition rate of 55% under a concentration ratio of 1.5 and a rotational speed of 100 r min-1. The surface characterization of brass specimens revealed that A-NBs facilitated the formation of Cu2(OH)2CO3 passivation film, calcium carbonate scale film, and a layer of bubbles on the surface of brass, which subsequently mitigated the erosive impact of the fluid. A-NBs can adsorb cations and thus reduce the concentration of corrosive ions. However, the increase in concentration ratio and rotational speed impeded the formation of the bubble layer and passivation film. A-NBs can adsorb free corrosive ions and facilitate the formation of Cu2(OH)2CO3 passivation film, calcium carbonate scale film, and a layer of bubbles on the brass specimens' surface. All of these can prevent the direct contact between the brass surface and corrosive ions, which mitigates the erosive impact of the fluid and realized a remarkable corrosion inhibition. image