A double-layer mechanism for the complex-ion embrittlement of silver chloride

A mechanism for the complex-ion embrittlement of AgC1 is proposed which involves the adsorption-induced formation of charge double layers, initially at the surface and subsequently ahead of propagating cracks. Since the predominant charge carriers in AgCl at room temperature are Frenkel defects, such double-layer regions will contain a high concentration, of these defects. It is suggested that, under specific environmental conditions, the hardening resulting from their presence may be sufficient to cause surface embrittlement, and that failure may then occur by the repeated formation and rupture of such hardened layers. Experimental evidence in support of this hypothesis is presented. For example, the surface microhardness of AgCl is shown to be significantly increased when the specimen is immersed in an environment containing complexes of high charge. In addition, when polycrystalline specimens are stressed in such environments, the activation energy for the failure process over the temperature range 30-100°C is in good agreement either with that for the motion of silver interstitials, Ag i + , or silver vacancies, Ag v − depending on whether the sign of the charge on the adsorbing complexes is negative or positive, respectively.