Characterisation of antibacterial silver coatings produced by selective electrolysis on stainless steel

Abstract

Stainless steel surfaces can be made antibacterial by deposition of a functional metal such as copper or silver. Commercially available silver alloyed stainless steels are much too expensive for many applications. A uniform silver layer is effective, but the material no longer looks like stainless steel. Selective electrolytic coating, in which the functional metal is deposited into grain boundaries, gives antibacterial properties without affecting the formability and weldability of stainless steel. Furthermore, the amount of functional material required is low, so the aesthetic appearance of the surface is not changed. Grain boundaries also provide a silver reservoir in the case of wear. Selective deposition was performed on 304L steel using coating baths modified with various additives. Samples deposited for various times at various current densities were characterised by microscopy to determine the location, size and distribution of the silver particles and the silver/iron ratio was determined by EDS analysis. Three coating conditions giving desirable microstructure were identified. The stainless steel retained its appearance even though fine silver particles filled the grain boundaries. Scotch tape tests indicated that 'coating' adhesion was good, with no evidence of debonding. The antibacterial efficiency of the selective silver coatings was found to be significantly better than that of uncoated material and comparable with that of selective copper coated samples.

Keywords:

• STAINLESS STEELS
• ANTIBACTERIAL COATINGS
• SILVER
• COPPER
• ELECTRODEPOSITION
• GRAIN BOUNDARIES