e- PRESERVATIONScience 81 FULL PAPER MORANA RTD d.o.o. e- PRESERVATIONScience published by MORANA RTD d.o.o. Charlotte Friederike Kuhn 1 *, Christian Heinrich Wunderlich 2 , Gerhard Eggert 3 , Thomas Schleid 1 ANOTHER BASE, ANOTHER SOLVENT? DESALINATING IRON FINDS WITH TETRAMETHYLAMMONIUM HYDROXIDE SOLUTION 1. Institut für Anorganische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart 2. Landesmuseum für Vorgeschichte Sachsen Anhalt, Richard-Wagner-Straße 9, D-06114 Halle 3. Staatliche Akademie der Bildenden Künste, Am Weißenhof 1, D-70191 Stuttgart corresponding author: kuhn@iac.uni-stuttgart.de received: 24.11.2011 accepted: 31.01.2012 key words: Iron, chloride analysis, corrosion, desali- nation, tetramethylammonium hydroxide e-PS, 2011, 8, 81-85 ISSN: 1581-9280 web edition ISSN: 1854-3928 print edition www.Morana-rtd.com © by M O R A N A RTD d.o.o. The desalination processes commonly applied to improve the corrosion stability of archaeological iron artifacts are based on immersion treatments in aqueous sodium hydrox- ide solutions. Faster and more efficient chloride extraction in solutions based on organic solvents with a lower surface tension can be expected. Furthermore, the danger of new corrosion forming during the subsequent washing out of residual chemicals from the desalinating solution could be minimised, if organic solvents would replace the water, commonly used for this process. Only alkali metal hydroxide (LiOH and NaOH) solutions in organic solvents have been tested so far. Their compara- tively low chloride extraction efficiency was ascribed to the low solubility of the alkali metal hydroxides and the corresponding chlorides in the solvents used. Tetramethylammonium hydroxide (TMAH) is readily soluble in alcohols and has been tested in aqueous and/or methano- lic solutions as an alternative. Neither improved overall chloride extraction efficiency, nor a higher chloride extrac- tion rate could be observed using methanolic solutions. However, aqueous TMAH showed a trend towards higher overall chloride extraction efficiency than the common alkaline treatments. These results could be explained by the different solubility of corrosion products, in particular akaganéite, β-FeO(OH), in the tested solutions. 1 Introduction Excavation of archaeological iron artifacts enables improved access of oxygen to their inner corrosion layers. This causes further oxidation of fer- rous compounds and ions within the corrosion layers and the remaining iron core underneath. Typical damage phenomena are the flaking off of corrosion fragments and the formation of new, powdery corrosion prod- ucts at the metal/corrosion interface. This post-excavation corrosion process is efficiently catalysed by chloride ions, which are attracted from the surrounding soil and accumulate inside the corrosion layers during burial. 1 Experience shows that the corrosion stability of iron artifacts after exca- vation can be significantly improved by extracting chloride ions from their corrosion layers 2 . The common, so-called desalination methods, are based on immersion treatments in aqueous, basic solutions. Usually, sodium hydroxide (NaOH) is used, often with the addition of sodium sul-