IN-SITU GRAZING-INCIDENCE X-RAY-DIFFRACTOMETRY INVESTIGATION OF PHASE-CHANGE PROCESSES AT THE SILVER AQUEOUS-HALOGENIDE INTERFACE/

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.