Crystallographic Anisotropies in Electrochemical Etching of Pt

Abstract

Single crystal microspheres of Pt are examined by scanning electron microscopy following electrochemical and chemical etching in chloride and cyanide solutions. In all cases, a single major crystal plane is formed which is not the close packed (111) plane. Rates of dissolution and facet formation also vary among planes and with etching conditions. The largest anisotropy occurs with aqua regia where initial attack is exclusively near (210) but only (110) facets are formed. The (111) and (100) planes are attacked in aqua regia only from their edges, but eventually these orientations are transformed completely into (110) facets. Electrochemical chloride etching with a‐c potentials produces large smooth planes near (100), and the (111) plane is attacked readily to form (100) facets. Electrochemical cyanide etching produces the most rapid attack of the (111) orientation to produce facets of (110). Possible mechanisms for these processes and implications for preparation of Pt electrodes are discussed.