Ein dem Malachit ähnliches basisches Eisenkarbonat als Korrosionsprodukt von Stahl

A basic ferrous carbonate similar to malachite as a corrosionproduct of steel A formerly unknown basic ferrous carbonate is described, which was found on the cone of a hot water valve (temperature 180°C) together with siderite and magnetite. According to analysis the formula is Fe_1,8²⁺Fe_0,2²⁺(OH)_2,2CO₃ or “Fe₂(OH)₂CO₃” with some amorphous ferric oxidehydrate. The unit cell of said compound is orthorhombic: a = 9,39₀Å; b = 24,53 Å; c = 3,21₂ Å; Z = 8 aspect p* ab. The measured density: 3,59 g · cm^?3. An infrared spectrum was taken and the frequencies of absorption coordinated tentatively with vibrations between 800–500 cm^?1. Thermal analysis in oxygen leads to a stepwise exothermic decomposition and oxidation in course of which above 197°C an intermediate metastable compound (ferric oxidecarbonate “Fe₂O₂CO₃”) is topotactically formed. The unit cell of this compound is orthorhombic: a = 9.23 Å; b = 12,18 Å; c = 5,94 Å. Also in this case an infrared spectrum was taken and bonds coordinated. Above 360°C further decomposition leads the formation of hematite. Decomposition in argon starts at 300°C. The reaction is endothermic and the product magnetite. A structural relationship exists between “Fe₂(OH)₂CO₃” and malachite and also to siderite. In this latter case we assume epitaxial relations.