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Vanadium in Plants
Published in Jörg Rinklebe, Vanadium in Soils and Plants, 2023
Sheikh Mansoor, Tawseef Rehman Baba, Syed Inam ul-Haq, Iqra F. Khan, Sofora Jan, Sadaf Rafiq, Jörg Rinklebe, Parvaiz Ahmad
Vanadium (V) behavior in the soil-plant environment can be comprehended by absorption and translocation of Vanadium by plants. In recent years, owing to the dramatic rise in vanadium mining processes and their harmful effects at elevated levels on plant and human health, many studies have concentrated on vanadium uptake by plants (Del Carpio, Hernández et al. 2018). Vanadium pentoxide (V2O5) is the most commonly existing and usable form of vanadium, along with ammonium metavanadate (NH4VO3), sodium metavanadate (NaVO3) and sodium orthovanadate (Na3VO4). Numerous reports indicate that vanadium transport or translocation and bioaccumulation depend upon its two oxidation states, viz., tetravalent and pentavalent forms, of which the latter is more mobile and more active in the vanadium biogeochemical cycle and exhibits higher toxicity to both plants and animals (Imtiaz, Rizwan et al. 2015; Roychoudhury 2020).
Electrochemical properties and structure of vanadium-based conversion coatings on electro-galvanised steel
Published in Transactions of the IMF, 2018
Chromate conversion coatings have been widely applied for corrosion protection of many metals. However, there has been such great concern about ecological issues regarding these coatings that chromate-free products have been developed.1–6 Among the chromate-free candidates, vanadium has better corrosion resistance and has been used as a corrosion resistant inhibitor for paint or pigmentation systems. It has also been suggested that vanadium-based conversion coatings are attractive as alternatives to chromates. Some studies of the conversion coatings on light metal such as aluminium and magnesium alloys have been reported.7–12 Zou et al. found that a vanadium-based conversion coating on zinc exhibited better corrosion resistance than a chromate conversion coating because hydrated oxides of vanadium, such as V2O5 nH2O and VO(OH)2 mixed with V2O5 and VO2, formed on the surface.13 Yang et al. indicated that the thickness of vanadium-based conversion coatings on magnesium alloy (AZ61) mainly depends on the concentration of the treatment solution and dipping time, but thicker conversion coatings produced higher crack density and led to reduced corrosion resistance.14 Hamdy et al., who studied pre-treatment conditions before vanadium-based conversion coating, showed that a combination of etching and oxide thickening treatment plays an important role in corrosion resistance on aluminium alloys (AA6061 T6).15 A few studies also reported on zinc or galvanised steel.16,17 In most studies, V5+ vanadium compounds such as vanadium pentoxide (V2O5) or sodium metavanadate (NaVO3) were used as raw materials in the treatment solution, and conversion coatings were formed by dipping in the solution bath before rinsing. On the other hand, other coating methods without rinsing after immersing in the treatment bath have been applied for galvanised steel sheets or coil, especially for electro-galvanised steel. The solution dried-in-place on the galvanised steel sheets has been researched over the last 20 years, and vanadium-based treatments have been successfully prepared. The aim of this study is to evaluate the corrosion behaviour of vanadium-based conversion coatings dried-in-place on electro-galvanised steel, especially the differences between conversion coatings treated with solutions including V5+ and V4+. In addition, the effects of pH were studied by adding phosphoric acid to the V5+ solution. The properties of these conversion coatings were investigated by neutral salt spray (NSS) test and electrochemical impedance spectroscopy (EIS). Coating structures were also examined by X-ray photoelectron spectroscopy (XPS).