Committee Members:

Dr. Preet M. Singh, Advisor

Dr. Hamid Garmestani

Dr. Joshua Kacher

Effect Of Vanadium on High Temperature Corrosion of Alloy Steel

Abstract: Vanadium modified 9 Cr alloys (Grade 91) are commonly used at high temperature processes in industries. However, their corrosion performance needs to be further evaluated in order to consider them a vital alternative for corrosion application. This research was focused on the performance of this material at high temperature corrosion. Three materials were selected to undergo some experiment, namely T22, T9, and T91. Small squared samples were extracted from each of these materials to be tested at 4 different temperatures for 1 week. The gases used were air and SO2. The experiments were carried out in Thermogravimetric Analyzer (TGA) which is an equipment that helps study high temperature corrosion. The TGA results for air showed that the corrosion resistance of T9 and T91 was better than T22 under tested conditions. The oxidation kinetics were identified to be following the parabolic rate law and the activation energies were calculated. X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), and Energy Dispersive X-ray Spectroscopy (EDS) were used to gain better understanding about the scale properties and dominant phases. The main compounds identified in the corrosion scale were wüstite (FeO), magnetite (Fe3O4), hematite (Fe2O3), and chromia (Cr2O3). SEM/EDS images proved that the scale is getting thicker as temperature increases in air. In addition, the oxide scale formed at lower temperatures tends to be non-adhesive and easy to come off, while at higher temperatures remains adhesive and attached to the base material. XRD, SEM, and EDS analysis did not show any oxides or spinels that vanadium played a major role in, during the oxidation process. This suggests that vanadium contribution to the oxidation and sulfidation process is not significant and might be absent in some cases.