Using Al₂O₃/TiO₂ Nano-films To Improve The Scratch And Discoloration Resistance Of 925 Silver Ornaments

Sterling silver(925 silver)is the mainstream material in the fashion jewellery market,but suffers from tarnish and scratches during usage.The alumina and titania films prepared by atomic layer deposition(ALD)are expected to solve the above problems.Unfortunately,current poor understanding of the interplay between ALD alumina/titania film thickness and the colour difference,anti-scratch,and anti-tarnish performances of coated silver,strongly hinders beneficial values of this ALD technique and its widespread application.In this paper,a series of alumina and titania films with a thickness of 5 nm to 30 nm were prepared on the surface of 925 silver using atomic layer deposition technology.Evaluate and compare the differences between the two films by studying their optical,mechanical,and corrosion resistance performances,explore the film and film thickness that can meet the protection requirements of silver jewelry.Finally,the mechanism of the influence of film thickness on the color difference,anti-scratch,and anti-tarnish performance of silver jewelry is revealed.The main conclusions are as follows:(1)As the ALD alumina film becomes thicker,the color difference of 925 silver increases linearly,and 24.8 nm is a critical film thickness that does not affect the appearance of silver jewelry.The thickness of the film determines the corrosion resistance of 925 silver.When the film thickness is increased,the corrosion resistance is enhanced.When the film thickness reaches 15.5 nm,it can resist the corrosion of the sodium sulfide corrosion solution.The mechanical properties of the alumina film are significantly stronger than that of 925 silver,the modulus and hardness are 2 times and 6.4 times of 925 silver,respectively,and the coated 925 silver shows good scratch resistance.A thickness of 25 nm was found to have an admirable combined performance.(2)As the ALD alumina film becomes thicker,the L value of the coated 925 silver decreases,and the a and b values have no change.Obvious yellowing can be observed when the film thickness exceeds 15 nm.The transmittance of films in the visible region shows a trend of decreasing first and then increasing.The corrosion test confirmed that silver sulfide and silver oxide are the main products of 925 silver sulfide corrosion.The impedance spectrum shows that the exposed area of the coated 925 silver is only one tenth of the bare 925 silver.The hardness and elastic modulus of titania film are 4.3 times and 1.9 times that of 925 silver,respectively.(3)The two films have their own advantages.The transmission,color difference,hardness and elastic modulus of the alumina film are superior to the titania film,but the chemical stability is inferior to the titanium dioxide film.The experimental results show that both films have good application prospects.