Thermal etching of sodium chloride III. Etching of non-cubic surface

Previous work on the thermal etching of (100) surfaces of NaCl single crystals is extended to the other surface orientations by using polycrystalline samples. The results obtained with (110), (111), (520) and (144) surfaces are used to corroborate the correctness of the mechanisms proposed in a previous paper to explain the thermal etching in air of (100) surfaces; it is also shown that these mechanisms are only dependent on crystal structure and not on the surface orientation.When such surfaces were treated with wet silk, concentrated HC1, and Moran's reagent, a very different behaviour was observed for each orientation. The reactivity is very sensitive to crystallographic orientation, being very low in the case of the (144) surface.