Investigation of the Effects of Reburial on Metals

Institution
Western Australian Museum
C/o Shipwreck Galleries Western Australian Maritime Museum
47-49 Cliff Street FREMANTLE WA 6160 AUSTRALIA

Co-ordinator
B. App. Sci., MPhil Vicki Richards. vicki.richards@museum.wa.gov.au
Dr Ian MacLeod. ian.macleod@museum.wa.gov.au

Aim
Aim The aim of this sub-project is to investigate the corrosion of metals buried in the marine environment. The corrosion of reburied and exposed modern metal coupons and archaeological metals will be examined and compared over time. This study will ascertain the effect of reburial on the deterioration of archaeological metals commonly found on underwater cultural heritage sites.

Methodology
The sacrificial metals will consist of standard corrosion coupons of known metal composition. The standard corrosion coupons utilized will be mild steel, cast iron (grey), brass, copper and bronze. The iron and non-ferrous metals will need to be mounted separately to prohibit galvanic and proximity corrosion. Therefore, seven units for each alloy group will be prepared to allow recovery and analysis after 1, 2, 3, 6, 12, 24 and 48 years. Each unit will consist of three sets of metal samples mounted at three different depth intervals (totally exposed, just below the sediment and buried 50cm in the sediment). Each set of metal samples will be secured with cable ties to three perforated high density polyethylene plates, attached to a high density polyethylene rod at the specified depth intervals. The units will then be buried on the Marstrand harbour site. In addition, three sets of metal samples will be appropriately stored in the laboratory to be used as controls. Control samples will be analysed prior to burial, after six years and after 48 years.

Analyses
The extent of corrosion of the metals will be monitored by weight change and a combination of optical emission spectroscopy and wet chemical analysis utilizing inductively coupled atomic emission spectrometry (ICP-AES) and standard Leco techniques. The associated corrosion products will be examined by scanning electron microscopy (SEM) and identified by x-ray diffraction (XRD) analysis.

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