Preparation of polyoxometalate ionic liquids (POM‐ILs) coated on metal coins for anticorrosion activity

Abstract

Corrosion is globally a serious problem for metallic structure and materials in recent decades. When there is interaction between acid and metallic structure, a large amount of corrosion produced. Herein, we have synthesized two energetic polyoxometalates (POMs) based ionic liquids by ion exchange method of smaller cations with larger cations tetraalkyl ammonium (CnH2n+1)4N+(n = 7). FT-IR, SEM, Electrochemical Impedance Spectroscopy (EIS), Optical Imaging Microscopy(OIM), Rheological analysis, 1HNMR and TGA techniques were used to characterize the corresponding ionic liquids. Metals can easily be protected by using hydrophobic polyoxometalate-ionic liquids (POM-ILs). At room-temperature the metallic coins were coated with W17@POM-IL andV3W15@POM-IL, comprising of Dawson anions and quaternary tetraheptylammonium cations (Q7). The acid resistant V3W15@POM-IL and W17@POM-IL were used for coating of coins samples. The un-coated coins have shown corrosion with holes production when treated with HCl while POM-ionic liquid coated coins expressed excellent resistant against corrosion and obviously, no cracking was observed. TGA results of W17@POM-IL revealed minimum weight loss of 4.3% and V3W15@POM-IL has maximum weight loss (9.2%) at highest temperature (500 °C). We have analyzed from the results that coins without coating of POM-ILs have demonstrated the weight loss of 14.3% while the coins coated with V3W15@POM-IL and W17@POM-ILs expressed less weight lost with 3.7% and 1.7% respectively. Furthermore, electrochemical impedance measurement (EIS) has charge transfer ratio of 7.03 Ω, 5.23 Ω and 3.78 Ω for W17@POM-IL, V3W15@POM-IL and un-coated coins respectively. Rheological analysis with highest elastic modulus (103 Pa) and viscous modulus (103 Pa) of W17@POM-IL has given best coating properties. Hence, the POM-ILs have variety of applications as coherent, adherent, chemical stability. Comparison of V3W15@POM-IL with W17@POM-IL inferring us that later is best for protection of metal coins against corrosion and damage production with highest thermal stability.