Sur les carbonates basiques de fer (III): I. Carbonate basique de fer (III) amorphe

The preparation of a non-stoichiometric basic carbonate of iron (III) is described. The amounts of carbon dioxide and water can vary in large limits, depending on the way the samples are dried. The ratio of Fe₂O₃:CO₂ in a fresh product is nearly one, but decomposition takes place already at room temperature and ambient humidity. When heated slowly, the carbon dioxide is given of in two clear steps, an intermediate product being formed at about 200°C. The basic iron (III) carbonate decomposes between 400° and 500°C to an α-Fe₂O₃ with still a small amount of carbon dioxide. The infrared spectra show that in the freshly prepared products the greater part of the CO ions are linked by two oxygen atoms to two iron atoms, and a smaller part probably only by one oxygen to one iron atom. In the intermediate product, part of the CO^2_₃ ions are linked by two oxygen atoms to one iron atom, or a hydrogenocarbonate group may be formed. The X-ray diagrams taken with Mo K_α rays show only two broad lines.