Investigations Of Some Pyrazolo-pyrimidine Derivatives As Corrosion Inhibitors On Copper In Sulfuric Acid Solution

As an excellent metal,copper has been highly applied in modern industry.The study of the corrosion process in H₂SO₄ solution and the inhibition action of pyrazolo-pyrimidine derivatives for copper provide theoretical and practical significance to select efficient inhibitor in in the actual industry.Pyrazolo-pyrimidine derivatives are new green inhibitors,they have unique characteristics which are low toxicity,low vapor pressure,multiple adsorption sites and good designability.Therefore,pyrazolo-pyrimidine derivatives have been researched as inhibitors over the years.In this paper,five pyrazolo-pyrimidine derivatives were chosen as the corrosion inhibitors.They were 4-amino pyrazolo-pyrimidine?APP?,4-hydroxy pyrazolo-pyrimidine?HPP?,4-mercapto pyrazolo-pyrimidine?MPP?,3-bromine-4-amino pyrazolo-pyrimidine?Br-APP?and 3-Iodine pyrazolo-pyrimidine?I-APP?.Potentiodynamic polarization,electrochemical impedance spectroscopy?EIS?,scanning electronic microscope?SEM?analysis,x-ray photoelectron spectroscopy analysis?XPS?and quantum chemical calculations analysis method were applied to evaluate their inhibition effect for copper in 0.5 M H₂SO₄ solution.The conclusions received from the research are displayed as follows:?1?The potentiodynamic polarization curves indicated the current density reduced and the inhibited efficiency augmented with the concentration gained.At the same time,the reaction mechanism of cathode hydrogen evolution did not alter as the addition of inhibitors.All the variations of E_corr were less than 85 mV,which manifested these organics were mixed-type inhibitors.?2?The EIS results suggested that the diameter R_ctt changed larger with the increasing concentration of the test inhibitor.Therefore,the resistance during the corrosion reaction increases and the corrosion inhibition efficiency increases,which indicating the corrosion inhibitor molecules gradually adsorbed on the metal surface,replacing the previous water molecules on the metal surface,thus forming a protective film,effectively inhibiting the corrosion of copper by sulfuric acid.?3?X-ray photoelectron spectroscopy analysis showed that all corrosion inhibitors were adsorbed on the surface of metallic copper,and they also formed covalent bonds with the copper surface to enhance the adsorption of corrosion inhibitors and copper,thereby increasing corrosion inhibition efficiency.?4?The adsorption analysis showed that the five inhibitors on the copper in 0.5 M H₂SO₄ solution obeyed the Langmuir isotherm model.The adsorption on the metal was a spontaneous process,and the process contained physisorption and chemisorption.?5?From quantum chemical calculations,we found that occupied molecular orbital of LUMO(E_LUMO)were higher and molecular orbital of HOMO(E_HOMO)were lower,the difference value??E?got smaller.Thus,the adsorption force between pyrazolo-pyrimidine and metal got stronger,and the ability against corrosion augments.In conclusion,that the five pyrazolo-pyrimidine derivatives presented good inhibition for copper in 0.5 M H₂SO₄ solution.The inhibition effect of these pyrazolo-pyrimidine derivatives follows:MPP>HPP>APP,I-APP>Br-APP>APP.