Atmospheric Corrosion of Ag and Cu with Ozone, UV and NaCl

Ag and Cu are both used for electronics and are susceptible to atmospheric corrosion. They are also good corrosivity monitors used to evaluate aggressiveness of the environment. Unfortunately, laboratory exposure testing does not always represent field environments very well. Discrepancies between lab and field exposure tests are not uncommon. For example, Ag does not corrode in salt spray exposure during ASTM B117 test, while it corrodes everywhere outdoor. This suggests that new laboratory exposure test for Ag needs to be designed and studied.A full factorial experiment was carried out with three factors: ozone, UV intensity and relative humidity (RH). NaCl was loaded by fast evaporation of NaCl/ethanol solution before exposure. After exposure, corrosion products were identified by XRD and quantified by galvanostatic reduction technique. For lab exposure samples, AgCl was identified as the only corrosion product in high RH (87%) environments, while Ag2O and AgO formed as well during exposures at low RH. This result derived a qualitative prediction on corrosion behavior of Ag in field. It predicts that less stable silver compounds such as oxide and sulfate are possible corrosion products in field even silver chloride is the dominant corrosion product forming in field. This prediction was confirmed by analysis of field exposed Ag samples. By quantification of corrosion products, it is determined that UV has two contravening effects on atmospheric corrosion of Ag: photolysis of ozone to generate stronger oxidizing species such as atomic O and photodecomposition of Ag corrosion products by UV radiation.Following its success in Ag corrosion research, the environment of UV, ozone and NaCl was extended to study Cu corrosion. It is determined that UV alone can double Cu corrosion rate by generation of electron-hole pairs in n-type cuprous oxide. It is also found that ozone alone is not as aggressive on Ag as on Cu because protection of naturally formed cuprous oxide. With the addition of NaCl, corrosion rate of Cu increases dramatically because of the breakdown of the naturally formed cuprous oxide by NaCl. To mimic corrosion behavior of metals in real field, a new environment chamber that generated constant deposition of NaCl was invented. With this novel environment chamber, the kinetics of Cu corrosion with constant deposition of NaCl in synthetic air with high and low CO2 and UV was studied. Cu2O and Cu2(OH)3Cl were both dominant corrosion products after exposure. 0.1 M Na2CO3 instead of 0.1M KCl was used as supporting electrolyte for reduction of Cu2O and Cu2(OH)3Cl, because it can clearly differentiate reduction of Cu2O and Cu2(OH)3Cl. With quantification of Cu2O and Cu2(OH)3Cl respectively, it is found UV has strong effect on formation of Cu2O but little on Cu2(OH)3Cl. It is also determined that localized corrosion of Cu dominates at the beginning of Cu corrosion and then uniform corrosion takes over.

Name thesis:degree_name

Doctor of Philosophy

Level thesis:degree_level

doctoral

Discipline thesis:degree_discipline

Materials Science and Engineering

Grantor dc:publisher

The Ohio State University

Year dc:date

2013

Author dc:creator

• Lin, Huang

Contributors dc:contributor

• Frankel, Gerald

• Mechanical Engineering

Statement dc:rights

• unrestricted
• This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws.

Language dc:language

English

Repository record dc:identifier

http://rave.ohiolink.edu/etdc/view?acc_num=osu1357309228

OAI identifier oai:identifier

oai:etd.ohiolink.edu:osu1357309228