Romarchite and Other Corrosion Phases on Metal Artifacts from the Queen Anne's Revenge (1718)
Dunkle, Stacie E.
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Metal artifacts from the pirate Blackbeardâ s flagship, Queen Anneâ s Revenge (1718), were studied and a preliminary assessment of the corrosion products that have formed on them is presented. Artifacts made of iron, lead, tin, copper, mercury, gold, and silver were recovered from the site with only those made of precious metals displaying no corrosion products. Detailed analysis was conducted of the surfaces of pewter artifacts, made from a tin-rich alloy, revealing corrosion products composed of romarchite (SnO), hydroromarchite (5SnO.2H2O), and abhurite (Sn3O(OH)2Cl2). For comparison, corroded pewter artifacts originating from five other archaeological sites submerged in seawater, dating to between ~1550 and 1733, were analyzed. All of these samples also exhibit abhurite, romarchite, and hydroromarchite, however, some of the artifacts also display cassiterite (SnO2). Textural analysis indicates that abhurite is the first alteration product to arise, followed by romarchite and hydroromarchite and, in some cases, ending with the formation of cassiterite. The absence of cassiterite on many samples demonstrates that, while appearing to be stable under the conditions that were present, the phase has not yet had time to form. Because of the very limited stability field for romarchite, its presence on these artifacts seems to be the result of a kinetic effect, while its universal appearance suggests that it is a required step in the oxidation of pure tin to the final most stable phase of cassiterite. Knowledge of the stability of pewter corrosion products and their effectiveness as agents of passivation can provide insight into the processes of tin corrosion.
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