Evaluation of the Corrosion State of Gray Iron by Optical Sensor Assisted Oxygen Consumption Method

The corrosion rate of gray cast iron samples under different humidity was studied by optical sensor assisted oxygen consumption method. The morphology and structure of the corrosion products on the sample surface were characterized by stereomicroscopy, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results showed that with the increase of ambient humidity, the oxygen consumption rate of gray cast iron samples increased significantly. The oxygen consumption rate at 80% relative humidity was 20 times that at 30%. At all humidity, there were two different kinds of corrosion areas on the samples' surface. One of them was the reddish-brown area dominated by organic acid corrosion products, and the other was the obviously etched pattern area. There were organic acid corrosion products, ferrous oxide (FeO), hydroxyl iron oxide (FeOOH) and iron oxide (Fe₂O₃) in different crystal phases in the both regions. The organic acid product was caused by the free release of fiber humidity control material.