Hunting Free and Bound Chloride in the Wrought Iron Rivets from the American Civil War SubmarineH. L. Hunley

The use of subcritical fluids for the stabilisation of archaeological iron: an overview

“…In addition to causing physical damage, the formation of akaganéite may have a direct impact on the chloride extraction effi ciency of traditional desalination techniques [1,4,13,15,32]. These studies have shown that some of the chloride ions are unable to be removed during treatment because they appear to remain locked inside the tunnel-like structure of the akaganéite.…”

“…• Once exposed to air and allowed to dry before treatment, the solubility of the chloride ions drops signifi cantly, directly impacting the effi ciency of immersion treatments [1,4,13,15].…”

“…As part of a collaboration with Clemson University during the development of a long-term conservation plan for the stabilisation treatment of the H.L. Hunley (1864) submarine at the Warren Lasch Conservation Center (WLCC) in Charleston, South Carolina, a new technique for the treatment of chloride-ridden iron was evaluated and compared to the traditional techniques of immersion in sodium hydroxide with and without electrolysis [14][15][16][17][18]. This new technique, known as subcritical water extraction (SWE) or pressurised hot water extraction, was based on prior research carried out with sub-and supercritical fl uids for waste water oxidation and the analysis of extractable material from textile yarns and fabrics [19][20][21].…”

“…All of the techniques are carried out either at room temperature or temperatures up to approximately 60°C. The chloride extraction rate for these treatments varies enormously from one object to another and is dependent on numerous factors including the size of the object, its archaeological context and the nature of the corrosion products at the time of treatment [1,5,6,9,[12][13][14][15].…”

The aluminum-cast Madonna statue of “Tempio Votivo”, Lido di Venezia (Italy): Identification of degradation factors and assessment of a cleaning procedure

“…Notwithstanding the identification of the number of cycles which effectively decreases the released chloride amount, such a water leaching procedure is not easily applicable to the largest fragments of the statue. Moreover, in this experiment the rinsing cycles had a short duration (2 min cycle À1 ) whilst the process of removing chlorides for marine artifacts is often measured in days and years [31]. Therefore, the leaching process might not have been able to remove all the chlorides from the inner layers of the corrosion crust, as well as from the interface with the metal (were they can often be preferentially located, as shown in Fig.…”