Investigation of synergistic behaviour of non-toxic corrosion inhibitors

Cilj ovog rada bio je ispitati djelovanje smjese netoksičnih korozijskih inhibitora na koroziju čelika. Kao korozijski inhibitori upotrijebljeni su propolis, tanin, škrob, natrij benzoat i polietilen glikol (PEG400) i heksamin. Djelovanje je ispitivano monitoringom korozijske brzine na LPR probi te elektrokemijskom metodom linearne polarizacije. Također, su izmjereni FTIR spektri čisti tvari i sloja s elektrode te su napravljeni pregled površine elektroda SEM-om i EDX analiza. Korozija je ispitivana u otopini 0,5 M NaCl na elektrodama LPR probe izrađenim od čelika AISI 1090 i na elektrodi od čelika X52 5L korištenoj za polarizacijska mjerenja. Nakon 24 sata u otopini inhibitora na elektrodama se stvara kompaktni zaštitni sloj, koji se zadržava i nakon premještanja u otopinu 0,5 M NaCl. Prethodno razvijena smjesa inhibitora koja sadrži 100 ppm propolisa, 2000 ppm tanina, 2000 ppm natrij benzoata modificirana je dodatkom 200 ppm PEG i 400 ppm škroba. U sustavu bez inhibitora, sa formiranim slojem hrđe, brzina korozije iznosi 5,48 mpy u mirnom elektrolitu i 30,18 mpy pri brzini miješanja na magnetskoj miješalici od 90 rpm, dok sustav inhibitora sa formiranim zaštitnim inhibitora daje brzinu korozije od 2,03 mpy u mirnom elektrolitu i od 2,07 mpy pri brzini miješanja od 90 rpm. Miješanjem se povećava efekt djelovanja smjese te formirani zaštitni sloj primarno predstavlja barijeru difuziji kisika. Polarizacijskim mjerenjima utvrđeno je da se dodatkom heksamina, mehanizam inhibicije mijenja iz katodnog u anodni, ali nije zamijećeno značajno povećanje djelotvornosti.The aim of this study was to investigate the effect of non-toxic corrosion inhibitor mixture on steel corrosion. The investigated corrosion inhibitors included: propolis, tannin, starch, sodium benzoate, polyethylene glycol (PEG400) and hexamine. The effect was investigated by monitoring the corrosion rate on the LPR probe and by the use of electrochemical linear polarization method. Also, FTIR spectra of pure substances and the electrode layer was measured followed by SEM electrode surface examination and EDX analysis. Corrosion was tested in 0.5 M NaCl solution on LPR electrode electrodes made of AISI 1090 steel and on X52 5L steel electrode used for polarization measurements. After 24 hours in a solution of inhibitors, a compact protective layer is formed on the LPR electrodes, which is retained even after transfer to a solution of 0.5 M NaCl. The previously developed mixture of inhibitors containing 100 ppm of propolis, 2000 ppm of tannin, 2000 ppm of sodium benzoate was modified by addition of 200 ppm PEG and 400 ppm starch. In the inhibitor-free system, with a rust layer formed, the corrosion rate is 5.48 mpy in a still electrolyte and 30.18 mpy in a mixed electrolyte at a stirring rate of magnetic stirrer equal to 90 rp. In the inhibited system a corrosion rate of 2.03 mpy is obtained in a quiet electrolyte and 2.07 mpy at a stirring rate of 90 rpm. By mixing the electrolyte, the effect of the inhibitor mixture action is increased and the formed protective layer primarily presents a barrier to oxygen diffusion. By polarization measurements it was determined that with the addition of hexamine, the inhibition mechanism changed from cathodic to anodic, but no significant increase in efficacy was observed