Corrosion Of Metal Materials In Ionic Liquid Working Fluids

Absorption heat pumps are important energy-saving devices which are driven by industrial waste heat, solar energy and so on. The working fluid in absorption heat pump has the important influence to its service life and performances. The conventional working pairs in absorption heat pump are mainly ammonia-water and lithium bromide-water. However they have great disadvantages of toxicity, corrosion and crystallization respectively. Therefore, it is necessary to seek new working pairs to overcome these problems in application.In recent years, ionic liquids have attracted considerable attention because of their unique properties, such as negligible vapor pressure, thermal stability, low melting temperatures and liquid state over a wide temperature range and good solubility. Excellent properties of ionic liquids make some of them have the possibility used as the absorbent of refrigerant in absorption heat pump.Currently stainless steel, Carbon Steel, copper are the main materials for heat pumps. In this paper, the corrosion behaviors of several metal materials were studied in binary solutions of [EMIM][DEP]+H2O/C2H5OH/CH3OH and [EMIM][DMP]+H2O/C2H5OH/CH3OH. The main woks are as follows:Ionic liquids [EMIM][DEP] and [EMIM][DMP] were synthesized in laboratory. And the structures of the synthetic products were characterized with nuclear magnetic resonance spectrometer.The corrosion behaviors of316L stainless steel in [EMIM][DEP]+H2O/C2H5OH/CH3OH and [EMIM][DMP]+H2O/C2H5OH/CH3OH binary solutions were investigated by scanning electron microscopy (SEM), potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The results indicate that316L shows a obvious surface passivation, a broad passive region and low corrosion current densities in solutions of ionic liquids [EMIM][DEP] and [EMTM][DMP], and316L has better corrosion resistivity than that in LiBr aqueous electrolyte.In order to explain the corrosion mechanism in these working fluids, the Van der Waals volume of ions, hydrogen bonds and interaction energies of ion pairs were calculated based on density functional theory (DFT) in quantum chemistry combined with gradient corrected functional using Gaussian09.The corrosion behavior of20#carbon steel in [EMIM][DEP]+H2O/C2H5OH/CH3OH binary solutions was investigated using same electrochemical measurement instruments. And the influence of pH value on the corrosion was studied. It reveals that imidazolyl cation acts as an corrosion inhibitor which makes20#have good corrosion resistance in the solutions of [EMIM][DEP], and the20#carbon steel has the lowest corrosion rate in [EMIM][DEP] aqueous solution with the pH about10.4.Electrochemical methods were used in exploring the corrosion of T2copper in [EMIM][DEP]+H2O/C2H5OH/CH3OH binary solution and LiBr aqueous solution. The results show that copper is not obviously passivated in [EMIM][DEP] solutions, but the corrosion rate is still lower than that in LiBr aqueous solution.