S. Sathiyanarayanan et al., IN-SITU GRAZING-INCIDENCE X-RAY-DIFFRACTOMETRY INVESTIGATION OF PHASE-CHANGE PROCESSES AT THE SILVER AQUEOUS-HALOGENIDE INTERFACE/, Electrochimica acta, 43(19-20), 1998, pp. 2985-2989
ln-situ grazing incidence X-ray diffractometry has been successfully a
pplied to monitor phase change processes at silver in an aqueous halog
enide interface. Crystalline silver halogenide films and islands equiv
alent to homogeneous films of several nanometers thick could be resolv
ed. Major crystalline orientations independent of pH are AgI (002), Ag
Br (200), AgCl (200). Grain sizes increase with growth time (at fixed
overpotential), but the crystalline percentage decreases with anodic o
verpotential and formation rate. The crystalline portion of the AgX ph
ases is maximum in neutral electrolyte. The amorphous or nanocrystalli
ne phases dominate at high pH. A dissolution-precipitation mechanism i
s valid. A strong pH dependence of the overall generation rate and the
crystalline percentage of the AgX phases has been observed in contras
t to thermodynamic expectations. A mechanistic model involving the mod
ification of silver surfaces covered with specifically adsorbed haloge
nides species by hydroxyl ions is suggested. (C) 1998 published by Els
evier Science Ltd. All rights reserved.