镇安寺铁牛腐蚀产物及腐蚀机制研究

Study of the corrosion products and mechanism of corrosion of a Zhen’an Temple iron bull

镇安寺铁牛全身腐蚀严重,弄清铁牛腐蚀原因及其影响因素,可为铁牛后续修复和保护提供依据。本研究采用扫描电子显微镜、X射线衍射仪和激光共焦拉曼光谱仪等方法分析了铁牛表面腐蚀产物的形貌、组成、结构及其腐蚀原因。结果表明,铁牛腹部为亚共晶白口铸铁,组织中含有多种相及夹杂物使铁牛耐蚀性能降低;铁牛表面腐蚀产物有严重的分层现象,外层和内层腐蚀产物较为致密,主要成分为α-FeOOH和Fe_(3)O_(4);中间层腐蚀产物较为疏松,主要成分为γ-FeOOH和Fe_(3)O_(4);铁牛耳朵、左脚和尾部腐蚀产物主要含有α-FeOOH、γ-FeOOH、Fe_(3)O_(4)和α-Fe 2O 3等,且α-FeOOH在锈蚀产物中含量最高;不同部位腐蚀产物组成存在明显差异,耳朵处腐蚀产物α-FeOOH和γ-FeOOH含量比(α/γ值)最小,左脚处最大;分析了铁牛腐蚀影响因素和腐蚀机制。

A Zhen’an Temple iron bull has serious corrosion problems;furthermore,the mechanism of corrosion is complex.We tried to clarify the type of corrosion products of the iron bull and the factors influencing the corrosion,in order to provide a basis for its subsequent restoration and conservation.Scanning electron microscopy(SEM),X-ray diffractometry(XRD)and laser confocal Raman spectrometry were used to analyze the phase composition and rust layer structure of the surface corrosion products of the iron bull thus to understand the mechanism of corrosion.The results show that 1)the belly of the iron bull is hypoeutectic white cast iron,and the iron bull structure contains various phases and inclusions,which reduces its corrosion resistance;2)the surface corrosion products of the iron bull exhibit serious delamination;the outer and inner corrosion products are dense,with the main components being goethite and Fe_(3)O_(4);3)the corrosion products in the middle layer are relatively loose,the main components of which are lepidocrocite and hematite;4)the corrosion products of the ear,left foot and tail of the iron bull mainly contain goethite,lepidocrocite,Fe_(3)O_(4) and hematite,etc.;goethite has the highest content in the rust products;5)there are obvious differences in the compositions of the corrosion products of different parts of the iron bull—the ratio of goethite to lepidocrocite of the corrosion products of the ear is the smallest while that of the left foot is the largest.The factors influencing the corrosion and mechanism of corrosion of the iron bull were then analyzed.