Study on the superhydrophilic modification and enhanced corrosion resistance method of aluminum alloy distillation desalination tubes

Abstract

In low temperature multi-effect distillation (LT-MED) seawater desalination system, the (super-)hydrophilic surface modification of aluminum alloy distillation desalination tube is effective in improving the performance of the desalination system and reducing the cost. However, the poor corrosion resistance of desalination tubes under (super-)hydrophilic surface modification is a bottleneck that limits the application of desalination tubes. This research breaks this technical bottleneck and proposes a simple, economical and industrially applicable method that jointly enhances hydrophilicity and corrosion resistance on aluminum alloy distillation desalination tubes. This method combines a concentrated anodizing electrolyte, pyrophosphoric acid, with an eco-friendly corrosion inhibitor, Na2MoO4, and prepares a superhydrophilic anodic oxide film with substantially enhanced corrosion resistance. The research shows that the concentration of Na2MoO4 in electrolyte plays a crucial role in the corrosion resistance of the superhydrophilic anodic oxide films: under the condition of ensuring the superhydrophilic surface of aluminum alloy (contact angle <5°), as Na2MoO4 concentration (0– 0.5 mol/L) increases, the higher the concentration of Na2MoO4 in the electrolyte, the better the corrosion resistance of the prepared superhydrophilic anodic oxide film. When adding 0.5 mol/L Na2MoO4 to 70 wt% pyrophosphoric acid electrolyte, compared with the superhydrophilic anodic oxide film without the addition of Na2MoO4, the prepared superhydrophilic film has its corrosion potential increased by 0.451 V, corrosion current density reduced by nearly four times, and corrosion inhibition efficiency increased from 25 % to 80 %. This research reveals the mechanism by which the corrosion inhibitor Na2MoO4 enhances the corrosion resistance of superhydrophilic anodic oxide film through adsorption of the porous layer, thickening of the barrier layer and Mo(+VI) incorporating. This paper provides a new idea and method for developing aluminum alloy desalination tubes with both stable superhydrophilicity and excellent corrosion resistance.