Available from UMI in association with The British Library.; Since 1975, ironwork has been conserved at Portsmouth City Museum by the use of hydrogen reduction. Potentially damaging chlorides are sublimed off at elevated temperatures under a reducing atmosphere. This high temperature has evoked criticism from archaeologists as it will destroy the metallurgical structure of an artefact, losing valuable information on manufacturing methods. To investigate the effect of temperature on metallurgical structure, wrought iron from two sources was carburized and heat treated to form a range of microstructures found in archaeological specimens. These were treated under a reducing atmosphere over a range of temperatures. At 350{dollar}spcirc{dollar}C, the temperature employed for the conservation of land based objects, only fully quenched and lightly tempered structures were affected. The mode of manufacture of an item may still be ascertained after treatment. At 850{dollar}spcirc{dollar}C, conditions used in the conservation of marine artefacts, all traces of the original microstructure is lost along with any carbon present in the material. Addition of methane into the reducing atmosphere will prevent decarburization, however, all metallurgical evidence of steel structures will be destroyed.; The rate of sodium chloride sublimation was examined using thermogravimetry. This was found to be both temperature and gas flow rate dependant. The rate of loss increases with faster flow rates and higher temperatures. The rate of loss is only significant above 802{dollar}spcirc{dollar}C, the melting point of sodium chloride.; The effectiveness of commonly used wash solutions was investigated using rust compacts with a chemical composition similar to that found in corrosion layers on archaeological specimens. All aqueous washing media removed the entire chloride content of the samples after 11 days. Non-aqueous washing failed to remove any chloride during a 161 day trial period. The wetting ability of each solution was determined by measurement of viscosity, surface tension and contact angle. 0.2M dm{dollar}sp{lcub}-3{rcub}{dollar} sodium sesquicarbonate appeared to have the best overall performance.
展开▼
