Application of Raman spectroscopy and X-ray diffraction to study the erosion-corrosion of UNS S32205 in mine water A. Moloto a , M.H.E. Seshweni a , S. Aribo a , O.E. Falodun a , O.T. Olalemi b , O.O. Ige a,b , P.A. Olubambi a a Centre for Nanoengineering and Tribocorrosion, School of Mining, Metallurgy and Chemical Engineering, University of Johannesburg, Johannesburg 2094, South Africa b Department of Materials Science and Engineering, Obafemi Awolowo University, Ile-Ife, Osun State, Nigeria article info Article history: Received 30 September 2019 Accepted 10 October 2019 Available online xxxx Keywords: Erosion-corrosion X-ray diffraction Raman spectroscopy Haematite Duplex stainless steel (UNS 32205) abstract Corrosion products play a prominent role in reducing the degradation rate of materials in harsh environ- ments. In this work, the erosion-corrosion behaviour of duplex stainless steel (UNS S32205) in mine water, was characterised using X-ray diffraction and Raman spectrometry. The tests include erosion- corrosion in mine water and erosion in cathodically protected distilled water. X-ray diffraction and Raman spectroscopy were employed to confirm the presence of hydrolysed iron sulphate, chromium oxide, and hydrated iron oxides. The corrosion products were able to explain the effects of pH and flow velocity on the duplex stainless steel performance in the mine water environment. Ó 2020 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the 2nd International Con- ference on Recent Advances in Materials & Manufacturing Technologies. 1. Introduction In recent times, the leading threats in mining and mineral pro- cessing industries are corrosion and erosion-corrosion. The effects of corrosion and erosion-corrosion have caused plants, facilities, and pipes to sudden, rapid, and catastrophic failures in mines [1]. The issues are due to the decline in high-grade ore resources, and the need to tap unviable sources from harsh environments. Another factor is that mine waters are not only highly complex but vary widely in compositions from location to location [2]. Hence, environmental factors like temperature, pressure, soil com- positions, and pH significantly affect the corrosion behavior of materials in mine waters. Efforts have been made to investigate the effect of pH, temperature, flow velocity, and ionic strength on the corrosion performance of materials in mine water [1–4]. Materials selection is one of the choices of minimizing or reduc- ing these problems in the mine environments. Two approaches are often employed: the use of carbon steel and more recently corro- sion resistant materials like stainless steels. In the mining and min- eral processing industries, the use of carbon steel is encouraged due to its cost-effectiveness, and availability. The focus had shifted to stainless steel, which is more corrosion resistant but expensive. In this work, duplex stainless steel is used because of its exclusive benefits. Scheers et al., [3] recommended the use of chromium alloyed steels in mine water with high pH values. The work further stated that the chromium content, the amount of chloride ion in the aqueous environments, and the pH value influenced the corro- sion behaviors of these chromium reinforced steels. The pH of the mine water used in this work is around 11.08 which makes the use of duplex stainless steel appropriate. It is established that the pH significantly affects the electrochemical parameters and most especially the passivation behavior of film-forming materials like stainless steel [3]. In this study, the pH of mine water was moni- tored throughout the erosion-corrosion tests. Several methodologies are used to study the effect of flow velocities on material performance. Earlier studies used equipment like rotating cylinders, rotating disks, and flow pipes to study the behavior of materials in mine water [3–6]. In this study, a rotating cylinder electrode is used because it is well characterized in term of hydrodynamics, and they are less expensive. Recently, the use of X-ray diffraction (XRD) is being employed to study the corrosion products and the sub-surface characteristics of substrates in corrosive media. Aribo et al., [7] studied the sub- surface microstructure modifications induced by work-hardening due to sand impingement on some selected stainless steel. In another study, Feyerl et al., [8] used XRD to assess the corrosion products formed on carbon steel. While, Hango et al. [7] used XRD to examine the microstructures of Hastelloy and Inconel alloy https://doi.org/10.1016/j.matpr.2019.10.175 2214-7853/Ó 2020 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the 2nd International Conference on Recent Advances in Materials & Manufacturing Technologies. Materials Today: Proceedings xxx (xxxx) xxx Contents lists available at ScienceDirect Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr Please cite this article as: A. Moloto, M. H. E. Seshweni, S. Aribo et al., Application of Raman spectroscopy and X-ray diffraction to study the erosion-cor- rosion of UNS S32205 in mine water, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.10.175