Electroless Copper Plating of Titanium Condenser Tubes for Biofouling Control

摘要

Background: Excellent corrosion resistant titanium is prone to intense biofilm formation leading to biofouling and biomineralization affecting the heat transfer properties of condenser tubes. This work looks into the possibility of using electroless copper (Cu) plating on tube side of titanium (Ti) condenser for biofouling control. Methods: Electroless copper was coated on anodized Ti specimens and annealed at 450℃. Surfaces of annealed Cu coated Ti specimens were characterized using XRD, AFM, SEM and XPS. Antibacterial activity and long term stability of the electroless Cu coating on Ti were studied after exposure of coating specimens to natural seawater for four months. Biofilm community diversity and copper tolerance of microorganisms were analyzed with Denaturing gradient gel electrophoresis (DGGE) and 2-Dimensional electrophoresis (2-DE). Results: Surface analyses of electroless copper coated titanium specimens with AFM and SEM showed reduction in the microroughness of Cu coated Ti surfaces when compared to anodized Ti surface. XPS spectral analysis showed the shift in binding energy inferring the reduction of the hydroxide to metallic copper in Cu 2p_(3/2) peaks. Total viable counts and epifluorescence microscopy analyses showed two orders decrease in bacterial counts on electroless Cu coated Ti specimens when compared to as polished control Ti specimens establishing the antibacterial activity. DGGE analysis inferred the differences in the bacterial diversity among Cu coated and as polished Ti surface biofilms. Distinct protein spots in the 2-DE results of electroless copper coated Ti biofilm protein samples indicated copper accumulating proteins in copper resistant bacterial species of biofilm. Conclusion: Biofouling control due to reduced microroughness of the surface and toxic copper ions was established and inferred the stability of copper coating even after four months exposure to sea water.