Disinfestation of historical buildings – corrosion evaluation of four fumigants on standard metals

This study aims for providing adapted solutions for disinfestation of cultural buildings and collections in place of the use of methyl bromide, ozone depleting substance recently forbidden. It reports on a two-step corrosion test assessing the corrosive activity (corrosivity) of alternative fumigants. Four candidate fumigants are investigated: sulfuryl fluoride (SF), dimethyl disulfide (DMDS), phosphine (PH3) and cyanogen (EDN) in conjunction with five standard metals: silver (Ag), tin (Sn), iron (Fe), lead (Pb) and copper (Cu). The applied procedure is detailed including the fumigation protocol and the description of a specific electrochemical twin cells device. The surface evolution of metallic coupons after fumigation treatments and after hygrothermal ageing (35 °C, 95% RH) is compared to a blank reference series (indoor atmosphere). Results from colorimetry and electrochemical (linear sweep voltammetry) measurements, completed by Raman spectroscopy investigation show that each fumigant differently affects metals both in amplitude (amount of surface species) and in composition (nature of corrosion products). Sulfuryl fluoride (SF) can be recommended for cultural heritage but care has to be taken in presence of Pb, Sn and Cu. DMDS is also a good alternative candidate, however, it affects greatly Cu coloration and promotes Pb corrosion. Phosphine (PH3) is dramatic for Cu and has to be avoided while the efficient biocide EDN increases corrosion of Ag and Cu even if low color variation is observed. It is strongly recommended for selecting the fumigant to properly identify the metallic artefacts prior fumigation.