Petiti Chiara, Martini Carla, Chiavari Cristina, Vettori Silvia, Welter Jean Marie, Guzmán García Lascurain Paulina, Goidanich Sara
Department of Chemistry, Materials and Chemical Engineering "Giulio Natta", Politecnico di Milano, Piazza Leonardo da Vinci, 32, 20133 Milano, Italy.
Department of Industrial Engineering, University of Bologna, Viale del Risorgimento, 4, 40136 Bologna, Italy.
Materials (Basel). 2023 Mar 3;16(5):2072. doi: 10.3390/ma16052072.
The San Carlo Colossus, known as , is a monument constituted by an internal stone pillar support to which a wrought iron structure is attached. Embossed copper sheets are fixed to the iron structure to give the final shape to the monument. After more than 300 years of outdoor exposure, this statue represents an opportunity for an in-depth investigation of long-term galvanic coupling between wrought iron and copper. Most iron elements of the appeared in good conservation conditions with scarce evidence of galvanic corrosion. In some cases, the same iron bars presented some portions in good conservation conditions and other nearby portions with active corrosion. The aim of the present study was to investigate the possible factors correlated with such mild galvanic corrosion of wrought iron elements despite the widespread direct contact with copper for more than 300 years. Optical and electronic microscopy and compositional analyses were carried out on representative samples. Furthermore, polarisation resistance measurements were performed both on-site and in a laboratory. The results revealed that the iron bulk composition showed a ferritic microstructure with coarse grains. On the other hand, the surface corrosion products were mainly composed of goethite and lepidocrocite. Electrochemical analyses showed good corrosion resistance of both the bulk and surface of the wrought iron, and galvanic corrosion is not occurring probably due to the iron's relatively noble corrosion potential. The few areas where iron corrosion was observed are apparently related to environmental factors, such as the presence of thick deposits and to the presence of hygroscopic deposits that create localized microclimatic conditions on the surface of the monument.
圣卡罗巨像，也被称为 ，是一座由内部石柱支撑构成的纪念碑，其上附着有锻铁结构。压花铜板固定在铁结构上，赋予纪念碑最终形状。经过300多年的户外暴露，这座雕像为深入研究锻铁与铜之间的长期电偶耦合提供了契机。[此处原文未明确提及的某个事物]的大多数铁元素保存状况良好，几乎没有电偶腐蚀的迹象。在某些情况下，同一根铁棒的某些部分保存状况良好，而附近的其他部分则有活性腐蚀。本研究的目的是调查尽管锻铁元素与铜直接广泛接触了300多年，但与之相关的这种轻微电偶腐蚀的可能因素。对代表性样品进行了光学和电子显微镜及成分分析。此外，还在现场和实验室进行了极化电阻测量。结果表明，铁的整体成分显示出具有粗大晶粒的铁素体微观结构。另一方面，表面腐蚀产物主要由针铁矿和纤铁矿组成。电化学分析表明，锻铁的整体和表面都具有良好的耐腐蚀性，电偶腐蚀可能未发生，这可能是由于铁的腐蚀电位相对较高。观察到铁腐蚀的少数区域显然与环境因素有关，例如厚沉积物的存在以及吸湿沉积物的存在，这些吸湿沉积物在纪念碑表面创造了局部微气候条件。
