ریخت شناسی ، ترکیب فاز و اثر خوردگی محصولات در آهن شبیه سازی شده باستان شناسی

The immersion corrosion of archaeological iron in solution (0.06mol·L−1 NaCl+0.03mol·L−1 Na2SO4+0.01mol·L−1 NaHCO3) simulating soil water composition was presented. The evolution of archaeological iron from iron to iron oxide and to iron oxy-hydroxides compounds was investigated by scanning electron microscope (SEM) and X-ray diffraction (XRD) analysis. According to the morphology, phase composition, and transformation process, the contributions of each corrosion product to archaeological iron were discussed.

The deterioration of archaeological iron due to corrosion is a well-known problem. -k variety of corrosion products can be formed depending on the species present in their environment (soil, sea water, atmosphere, etc.). To find out the evolution of iron rust is a real challenge since it is difficult to clearly identify the contributions of each corrosion product[ 11. Although the evolution of iron oxides and oxy-hydroxides in different aeration conditions and pH have already been tested[2], their effects on the stability of archaeological iron have not been systematically studied. In addition, at present the most serious problem during restoration of iron artifacts is to find a suitable chemical treatment for their preservation[ 31. Thus, the elucidation of the phase composition of the corrosion layers appears to be very important from the viewpoint of choosing proper chemical reagents to treat archaeological iron objects for their preservation. The main phases constituting the rust layers formed on iron antiquities exposed to soil corrosion are rnagnetite(Fe304), goethite(a-FeOOH), lepidocrocite( y-FeOOH), and akaganeite (0-FeOOH). Generally, iron rusts can be classified into harmful and harmless ones according to the effects on the corrosion of iron[4,5]. Harmless rusts usually do not develop on the iron matrix in the normal environment and do not need to be removed from the iron antiquities. Harmful rusts, on the contrary, are able to accelerate the further corrosion of the metal core in the normal environment and considered to be the main trouble for the iron relics. In this article, scanning electron microscope (SEM) and X-ray diffraction (XRD) will be utilized to investigate the morphology and structure of corrosion product on archaeological iron. Aqueous solution whose composition is mostly the same as that in Chinese soil will be adopted. An attempt was made to distinguish the effects of different kinds of corrosion products on the corrosion evolution of archaeologicaliron by analyzing the transforming process.

1) Corrosion products on the upper surface of the specimen after immersion for 48 days were mainly a-FeOOH, which was grain-like in appearance with loose distribution; while corrosion products on the under surface of the specimen after immersion for 48 days were mainly y-FeOOH, with leprose or petallike shape. (2) Corrosion product of archaeological iron in the solution for 138 days was made up of three layers: a-FeOOH, Fe304 and a little P-FeOOH in the inner layer; y-FeOOH in the middle layer; and a-FeOOH in the outer layer. (3) In the rust of iron antiquities, the layer of a-FeOOH, with the shape like stalactite, is able to prevent the iron matrix suffering from attacks of other environmental factors because of its good continuity and compactness. y-FeOOH has a complicated leprose or petal-like structure; it can decompose to Fe3+ under acidic condition and able to accelerate the corrosion of iron matrix. The molecular structure of P-FeOOH includes chloride element which, if released, will induce the deterioration of iron core. So y-FeOOH and P-FeOOH are harmful rusts to the preservation of iron antiquities. Moreover, iron oxide like Fe203 and Fe304, which are more stable than iron hydroxide, is harmless to iron objects.