Influence of ALD-Al₂O₃ film on anti-scratch and anti-tarnish of silver

We report on atomic layer deposition (ALD) of Al₂O₃ films onto 925 silver and assess their efficiency to prevent metal scratching and tarnishing. Films of five thicknesses (12, 16, 21, 25 and 31 nm) were deposited on the 925 silver. Optical characterization revealed that the colour difference of coated silver increased with film thickness, where the film thickness below 25 nm preserves the lustre of the silver. The tarnishing resistance increased with film thickness, and films thicker than 16 nm were resistant to corrosion in Na₂S solution. The hardness and modulus of the film were 6.4 and 2 times that of 925 silver, respectively. Thicker films enhanced resistance to tarnishing and scratching and also led to a loss of lustre. A thickness of 25 nm was found to have an admirable combined performance. It is promising for applications of ALD process for silver protection.