Corrosion resistance of Fe80B13.5Si4.5C2 metallic glass in sulphate and chloride solutions

Metallic glasses, widely used because of their characteristic internal structure and properties are the subject of many research papers, both theoretical and practical. The present study analyses corrosion of the metallic glass Fe80B13.5Si4.5C2 in neutral and acidic solutions. At ambient temperature the material in the for of tape segments was etched for 4 and ca 20 h in neutral mediums, in which the corrosion rate is not high. Two series of measurements, respectively, were carried out in acidic mediums (in which the corrosion rate - Vcorr was considerable) for shorter periods of time - 1h and 2 h or 4 h. The metallic glass corrosion rate was determined using the gravimetric method, at the same time the dissolution rate was Vdiss.Fe determined for the main component of the alloy - i.e. iron. Visual observations both sides of the tape surface (dull and shiny) were carried out using the optic microscope; additionally, X-ray microanalysis were carried out using the scanning microscope. The data concerning the corrosion rate point to the fact that in neutral solutions the corrosion process is accompanied by the generation of sparingly soluble corrosion products. The accumulation of coloidal gels on the material surface is greater in 5% Na2SO4 solution than in 5% NaCl solution. It is connected both with the corrosion rate and its change in time in either medium. In acidic mediums the corrosion process is not accompanied by the generation of insoluble products. The corrosion rate is high, it is a few times higher in H2SO4 solutions than in HCl, where a study corrosion process can be observed. The measurements of iron dissolution rate show that at slow corrosion rate for metallic glass, the percentage of iron in the total mass decrease is lower than the nominal one. It can be accounted for by the fact that the outer layers of the material are enriched by the light components of the alloy. At the same time, during long-time etching at a slow corrosion rate the lowered percentage of iron can be explained by selective dissolution of light elements and their diffusion from the inside of the material towards its surface. (author)