Evaluación del estado de conservación del patrimonio arqueológico subacuático mediante las velocidades

Abstract

This paper presents the results of the comparative study of the conservation status of the guns and anchors of two shipwrecks belonging to the French navy, Fougueux and Bucentaure sunken, respectively, on 22th and 23th October of 1805, after Battle of Trafalgar (Cádiz, Spain). Some of these large iron objects were selected in both sites as witnesses or white, to know their current condition and to estimate the prospects of remaining in the medium, as dictated by the UNESCO in the Convention on the Protection of Underwater Cultural Heritage. In the first phase were carried out partial de-concretion task which allowed to conduct in situ measurements of pH and corrosion potential Ecorr, following the method patented by the author. These data allowed to determine the degree of stability of each object and make a prediction about its future condition. The prediction was made by applying the linear relationship between the logarithm of the corrosion rate (Vcorr) and the corrosion potential of iron in seawater (Ecorr) log Vcorr = M�Ecorr + C, where M and C are parameters of the linear fit. In a second phase, a method of in situ protection based on the use of cathodic protection with zinc anodes was proposed. Application of these sacrificial anodes has moved the iron corrosion potential toward the immunity area of Pourbaix diagram. On the other hand, it has been observed an increase in pH, which shows that the flow of electrons inside the object causes a decrease in the levels of acidity in the solution trapped in the metal-concretion interface due to hydrogen evolution process.