Thermal etching of silver: Influence of rolling defects

Thermal etching of industrial silver sheets vs. polished silver sheetsEffect of annealing atmosphere on the thermal etching of silver: surface and subsurface characterizationLink between etch pitting and defects induced by rolling.FIB-tomography coupled with EBSD for determining crystal planes of the facets of subsurface pores.FIB-SIMS characterization to probe the gas confined inside subsurface pores.

Silver is well known to be thermally etched in an oxygen-rich atmosphere and has been extensively studied in the laboratory to understand thermal etching and to limit its effect when this material is used as a catalyst. Yet, in many industrial applications the surface of rolled silver sheets is used without particular surface preparation. Here, it is shown by combining FIB-tomography, FIB-SIMS and analytical SEM that the kinetics of thermal etch pitting are significantly faster on rolled Ag surfaces than on polished surfaces. This occurs due to range of interacting phenomena including (i) the reaction of subsurface carbon-contamination with dissolved oxygen to form pores that grow to intersect the surface, (ii) surface reconstruction around corrosion pits and surface scratches, and (iii) sublimation at low pressure and high temperature. A method to identify subsurface pores is developed to show that the pores have {111} and {100} internal facets and may be filled with a gas coming from the chemical reaction of oxygen and carbon contamination.