| Abstract: | Electron-optical and radiographical examination of a protective iron phosphate layer on iron The protective effect of a novel anticorrosive containing phosphoric acid has been examined for its dependence on mineralogical conditions. The base material contains, intro alia, phosphoric acid, potash mica, organic wetting agents and dyeing agents. Vivianite formation has been precluded by radiographic comparison with natural vivianite and with data quited in technical literature. The scraped protective layer was found to contain, apart from muscovite and α iron, dendritic formations which were observed under the electron microscope and identified, from their diffraction interferences, as cubic form of the potassium iron (III) phosphate leucophosphite documentclass{article}pagestyle{empty}begin{document}$ KFe_2 [OH(PO_4)_2] cdot 2 H_2 O. $end{document} KFe2[OH(PO4)2] · 2 H2O. Precision zone diffraction diagrams of individual dendrites showed ao = 7.75 ± 0.05 Å and the transmission directions [100]X [010]X [202]X, identical to those observed with natural pharmacosiderite, an iron arsenate corresponding to leucophosphite. Natural and synthetic leucophosphite are monoclinic; if Fe3+ is replaced by Al3+, and (PO4)3? by (AsO4)3?, a cubic alumopharmacosiderite is formed. The formation is thereofore interpreted as a cubic modification of leucophosphite, corresponding to pharmacosideriote. A structure comparison shows the epitactic growth of the leucophosphite with [110] and [333] on α iron [100] and [111]. The presence of leucophosphite directly on the iron surface is proved by electron diffraction with grazing incidence of the electron ray. |
