From Roast to Paints

How to Use Pyrohydrolysis for Inorganic Oxide Prime Material for Ceramics

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Iron Oxides — More than Just a Waste Product of Recycling

The iron oxides that are formed in this process are in the sole form of haematite, that is Fe2O3, with small amounts of FeO (wuestite) or also sometimes Fe3O4 (magnetite). First an unwanted by –product of the recycling process of spent pickling acids in steel industry of normal steel production, it became later on an important product as prime material for the ferrite industry.

In combination with further divalent metals like zinc, manganese, nickel, barium or strontium, and after a thermal treatment to produce certain crystal structures which provide soft or hard magnetic properties. These terms hold for permanent (hard) or demagnetizable (soft) properties which find numerous applications in permanent magnets (hard) or ferrites (soft) for electro devices and for radar applications and many electronic communication systems. Soft ferrites have a lower eddy current loss and higher resistances which enables them to switch magnetic properties very fast, up to 15 000 to 20 000 times a second. Hard ferrites find wide application in permanent magnets, mostly in form of Ba, Ni, Sr-ferrites.

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Manganes containing hard ferrite prime material can also be processed by pyrohydrolysis in a so called co-spray-roasting by combing solutions of FeCl2 with MnCl2, which are made dissolving iron and manganese metal scrap by hydrochloric leach in proper towers. This process is used in some plants in Europe, USA and Asia. Further applications of iron oxides are in food stuff, cosmetics, as catalysts for chemical processing, in toners, plastics and rubbers as well as in inks and paints. Last but not least, not to forget their vast use as fire extinquishers in big scale burnings like fire fighting during forest fires.

Alumina from Pyrohydrolysis — Uncommon, Yet not Unwanted

Alumina (Al2O3) from pyrohydrolytic processes are uncommon and only made when aluminium stripes are being pickled with hydrochloric acid. Starting with fresh hydrochloric acid of 20 wt%, the aluminium is being pickled to produce ( AlCl3)n solutions of a certain polymeric structure which allow high concentrations of Al in solution.