Sunflower Head Extract As Corrosion Inhibitor For The Acid Pickling Of Steel

Acid pickling is widely used to remove the rust and dirt on the surface of metal products.However,the pickling process will lead to the corrosion of metal substrate,resulting in a serious waste of resources and environmental pollution.It is showed that corrosion inhibitor is one of the effective measures to prevent the corrosion of metal substrate.Plant extracts was an efficient,eco-friendly inhibitor due to the properties of rich sources,biodegradable,non-toxic and low cost.Therefore,its proposed the sunflower head extract as the corrosion inhibitor,and the anti-corrosion properties and mechanism of sunflower head pectin/extract were studied in this thesis.The molecular weight of sunflower head pectin?SFHP?was fractionated by MWCO,and the solubility and anticorrosive for carbon steel of different level sunflower head pectin was investigated in pickling solutions?1 mol/L HCl or 0.5 mol/L H₂SO₄?.The results showed that the solubility of sunflower head pectin was increased with decreasing of molecular weight.The anticorrosive for carbon steel in pickling solutions were increased first and then decreased with the decreasing of molecular weight.The sunflower head pectin with the best anticorrosive performance,when the average molecular weight was 3-10 k D.Inhibitors?sunflower head pectin or extract?extracted from the sunflower head by cellulase.Sunflower head pectin with average molecular weight in the range of 3-10 k D was prepared by changing the drying temperature of sunflower head,and sunflower head extract was prepared under the same condition.The results showed that the drying temperature of sunflower head was 150 ?,the average molecular weight of the pectin was about 4.50 k D.Furthermore,the solubility of pectin in the acid pickling mediums reached to 99.45% and99.85%,respectively.The inhibitors were characterized by FTIR.The results showed thatsunflower head pectin contains a large number of anticorrosive functional groups?-OH,-COOH?,and sunflower head extract contains lots of substances with anticorrosive functional groups?benzene,aromatic heterocyclic,double bond?besides pectin.The inhibition performance of sunflower head pectin and extract for carbon steel in 1mol/L HCl and 0.5 mol/L H₂SO₄ were investigated by weight loss,electrochemistry and digital microscope methods.The results showed that the inhibition efficiency of two inhibitors both decreased with increasing ambient temperature,increased with increasing inhibitor concentration.The polarization curve results showed that sunflower head pectin and extract both are mixed-type inhibitor.The inhibition performance of sunflower head extract was better than pectin at the same pickling solutions,and the inhibition performance of inhibitors for carbon steel in 1 mol/L HCl was better than in 0.5 mol/L H₂SO₄.The anticorrosive mechanism of the inhibitors were studied by simulating the adsorption kinetics of the inhibitors and measuring the zero charge potential of the metal in the pickling solution.The results showed that sunflower head pectin and extract in HCl and H₂SO₄ solution were mainly adsorbed by physisorption,accompanied by a degree of chemisorption.Moreover,adding 1 mol/L KCl into the 0.5 mol/L H₂SO₄ solution with and without sunflower head pectin and extract,which demonstrated the synergistic effect of Cl-for inhibitors anticorrosive activity.