Sunday, December 27, 2015

Protecting silver cultural heritage objects with atomic layer deposited corrosion barriers [Open Acess]

Many ALD reactors out there are standing idle over the Christmas holidays and maybe this is a good opportunity to sneak into the lab and run some ALD protective coating on your silver silver objects you have at home. Here is an Open Source article from University of Maryland, E-squared Art Conservation Science and The Walters Art Museum on how to protect silver objects by Al2O3 ALD using a Beneq TFS500 reactor.

Protecting silver cultural heritage objects with atomic layer deposited corrosion barriers

Amy E. Marquardt, Eric M. Breitung, Terry Drayman-Weisser, Glenn Gates and R. J. Phaneuf



ALD coatings on silver knives: silver knives a bare, without an ALD coating, b with a 100 nm Al2O3 ALD coating deposited with a 0.5 s TMA pulse/1 s N 2 purge (fast deposition), and c 140 nm Al2O3 ALD coating deposited with a 1 s TMA pulse/4 s N 2 purge (slow deposition). (Heritage Science 2015, 3:37  doi:10.1186/s40494-015-0066-x)

Abstract:

Introduction

Silver, prized throughout history for its luster and shine, develops a black Ag 2 S tarnish layer that is aesthetically displeasing when exposed to atmospheric pollutants. Tarnishing, and subsequent polishing, leads to irreversible material loss and object damage. Currently, nitrocellulose coatings are often used to prevent silver from tarnishing, however non-uniform coatings and degradation over time limit their effectiveness. Atomic layer deposition (ALD) has been explored as a new method for creating dense, uniform, and conformal coatings on 3-dimensional (3D) objects that are more effective than nitrocellulose in preventing silver from tarnishing.

Results

To create high quality ALD coatings on 3D objects, slowing down the ALD process is critical to ensure proper precursor exposure. Non-ideal deposition of organo-oxy-metallic compounds can occur with fast deposition rates that do not allow sufficient flow around 3D objects. The coatings can be removed by dissolving the Al2O3 ALD films in aqueous NaOH. Thicker ALD films prevent defects from occurring on non-ideal surfaces and effectively prevent silver objects from tarnishing under ambient aging conditions

Conclusion

Thick ALD films, deposited with sufficiently long precursor pulse and purge times, may be effective in preventing complex, 3D non-mixed media silver cultural heritage objects from tarnishing. 
Amy, a Ph.D. candidate in the Department of Materials Science and Engineering at University of Maryland, created this video for a Thinkable competition. In it, she explains in a non-technical way how she is is creating and applying ceramic films to silver artifacts to protect them from tarnish. The virtually invisible films are applied using atomic later deposition (ALD) and are only nanometers thick. Amy's technique protects (www.youtube.com)


Thin Film System TFS 500 for ALD research and batch production (www.beneq.com)


Previous posts on Silver protection:

Feb 1, 2014 ... More information on the BENEQ nSILVER coating you can find here and below you can watch a Video on development of silver saving ...
Oct 16, 2014 ... Novel protective coatings for silv