Tannin as steel corrosion inhibitor

Za zaščito jekel v industriji se vse bolj uveljavljajo zeleni inhibitorji korozije. V diplomski nalogi je v ta namen uporabljena galna kislina (spada med hidrolizirane tanine), da se ugotovi njena inhibicijska učinkovitost. To je bilo doseženo z diferencialno gravimetrično metodo ob spremembi mase pred izpostavitvijo korozijskim medijem in po njej ter z izračunom inhibicije in korozijske hitrosti. Delo je potekalo z vzorci iz nerjavnega jekla (številka: 1.4301), ki jih je bilo potrebno predhodno zbrusiti in očistiti. Za kisli medij so bile izbrane različne koncentracije HCl (0,1 M0,15 M0,25 M0,3 M in 0,5 M), kot inhibitor pa se je uporabila 0,5-, 0,75- in 1-% galna kislina pri izpostavitvenih časih: 4, 8 in 24 ur. Tej metodi je sledila površinska analiza vzorcev s pregledom morfologije površin vzorcev pod svetlobnim mikroskopom in ATR-FTIR (infrardeča spektroskopija s Fourierjevo transformacijo na oslabljeni totalni odboj). Rezultati so pokazali, da je inhibicijska učinkovitost galne kisline največja v 0,25 M HCl, saj pri nižjih koncentracijah ni prišlo do korozije oziroma je bila le-ta minimalna, pri višjih pa je bila inhibicija zanemarljiva, v nekaterih primerih je prišlo celo do negativnih vrednosti inhibicijske učinkovitosti, kar nakazuje na proces aktivacije. Pri izpostavljenosti 0,25 M HCl za 24 ur, je pri 0,5-% galni kislini dosežena več kot 60 % inhibicijska učinkovitost, med tem ko le-ta pri 1-% galni kislini znaša skoraj 87 %. Na podlagi tega se zaključi, da se galna kislina lahko uporabi, v razredčeni raztopini klorovodikove kisline in podobnih kislih medijih, kot uspešen zeleni inhibitor korozije na jeklu.Green corrosion inhibitors are becoming increasingly popular in industry for the protection of steel. In this thesis, gallic acid (a part of hydrolyzed tannin) was used to determine its inhibition effect. This was performed using the mass difference gravimetric method before and after exposure to corrosion media, as well as using the calculations of inhibition and corrosion rate. In the laboratory, stainless steel samples (No. 1.4301) were used, which had to be ground and cleaned beforehand. Different concentrations (0.1 M0.15 M0.25 M0.3 M and 0.5 M) of HCl were used as acidic medium and 0.5 %0.75%and 1 % gallic acid were applied as inhibitors at exposure times of 4, 8 and 24 hours. In addition, the surface of the samples was analyzed with surface morphology inspection under optical microscope and ATR-FTIR (infrared spectroscopy with Fourier transform under attenuated total internal reflection). The results showed that gallic acid in 0.25 M HCl exhibitet the highest value of inhibition efficiency, as no or minimal corrosion occurred at lower HCl concentrations, and at higher HCl concentrations the inhibition was negligible, in some cases even indicating activation processes. In 0.25 M HCl and 24 h exposure, the 0.5% gallic acid achieved an inhibition effect of more than 60 %, while at 1 % gallic acid the inhibition increased to almost 87 %. On this basis, it can be concluded that gallic acid forms a successful green corrosion inhibitor in dilute acidic medium