Surface characterization study of the thermal decomposition of Ag2CO3

The changes in chemical states and composition of the surface region of a Ag2CO3 powder at various stages during thermal decomposition have been examined using X-ray photoelectron spectroscopy (XPS) and ion scattering spectroscopy (ISS). The near-surface region of the as-received powder consists primarily of Ag2CO3 although some hydrocarbon and alcohol contaminants also are present. A 155 degrees C anneal results in partial decomposition of Ag2CO3 to Ag metal and oxides and reduces the amounts of the C contaminants. An anneal at 170 degrees C causes further decomposition of the Ag2CO3 to Ag metal, Ag2O, and AgO. ISS data indicate that at 205 degrees C oxygen migrates more rapidly to the outermost atomic layer than it desorbs, resulting in an increased oxygen concentration. The AgO species undergoes further decomposition to Ag2O during a 340 degrees C anneal treatment. Between 340 and 430 degrees C the Ag2O decomposes, leaving only Ag metal and subsurface oxygen in the near-surface region of the sample. These results are consistent with temperature-programmed reaction (TPR) data which exhibit a CO2 peak at 260 degrees C and an O-2 peak at 420 degrees C. Both the XPS and TPR data indicate that the thermal decomposition of these species are activated since their decompositions occur at temperatures much higher than predicted by equilibrium thermodynamic calculations.