Electrochemical and surface analysis of azoles on steel

Magistrsko delo prikazuje študijo korozije nizkolegiranega jekla v 3-odstotni raztopini NaCl in inhibicijo korozije z različnimi azoli. Z elektrokemijskimi metodami smo določili učinkovitost in značilnosti jekla C15 ob prisotnosti uporabljenih korozijskih inhibitorjev. S površinsko analizo smo potrdili, da se azoli adsorbirajo na površino kovinskega vzorca in ga na tak način zaščitijo pred korozijo. S potopitvijo enakih vzorcev nizkolegiranega jekla za 72 ur v 3-odstotno raztopino NaCl in 3-odstotno raztopino NaCl z 0,5- ali 2-odstotnim dodatkom KI za povečanje učinkovitosti korozijskih inhibitorjev smo ugotovili, da je pri vseh pogojih (sobna temperatura ali 70 °C, 1 mM ali 10 mM raztopine korozijskih inhibitorjev, brez ali z dodatkom KI) učinkovit korozijski inhibitor 5 metil-1H-benzotriazol (toliltriazol). Najučinkovitejši korozijski inhibitorji pri vseh potopitvah so bili še benzotriazol, 2-metilimidazol in 2 aminobenzimidazol. Elektrokemijsko smo analizirali najbolj učinkovite korozijske inhibitorje, koncentracije 10 mM v 3-odstotni raztopini NaCl in v 3-odstotni raztopini NaCl z 0,5-odstotnim dodatkom KI. Ugotovili smo, da ima jeklo C15 v kloridnem mediju ob dodatku toliltriazola najbolj pozitiven korozijski potencial, najbolj negativnega pa 2-aminobenzimidazol. Toliltriazol ima tudi v obeh medijih, ne glede na čas izpostavitve, najvišje vrednosti polarizacijske upornosti, torej je najbolj odporen proti enakomerni koroziji med vsemi testiranimi korozijskimi inhibitorji. Z meritvami ciklične polarizacije smo ugotovili, da deluje toliltriazol v obeh medijih kot katodni inhibitor. Z metodo infrardeče spektroskopije s Fourierjevo transformacijo smo na površini vzorcev, ki so bili pri sobni temperaturi 72 ur potopljeni v 3-odstotno raztopino NaCl z dodatkom toliltriazola (10 mM) ter brez ali z 0,5- ali 2-odstotnim dodatkom KI, dokazali prisotnost toliltriazola. Učinkovitost inhibicije korozije s toliltriazolom smo potrdili tudi s 3D profilometrijo, saj je bila povprečna površinska hrapavost vzorcev, potopljenih v raztopine toliltriazola, manjša od hrapavosti vzorcev, potopljenih v 3-odstotno raztopino NaCl brez dodatka korozijskega inhibitorja. Z merjenjem omočitvenih kotov istim vzorcem kot pri prejšnjih površinskih analizah smo ugotovili, da so površine vzorcev hidrofilne.In this study, the corrosion inhibition effectiveness of certain azoles for C15 steel in 3 wt.% NaCl solution was explored. The immersion of steel samples in inhibited solutions after three days was studied. Next, the most effective inhibitors were investigated using different electrochemical techniques. Finally, the binding of azoles on steel surface was confirmed by employing surface analysis. The synergistic effect of the 0.5 wt.% and 2 wt.% addition of KI in inhibited solutions was explored. The most effective corrosion inhibitor was 5 methyl-1H-benzotriazole (tolyltriazole), followed by benzotriazole, 2-methylimidazole, and 2 aminobenzimidazole. The most effective corrosion inhibitors were selected on the basis of immersion tests. For electrochemical measurements, the investigated solutions were 3 wt.% NaCl + 10 mM inhibitor or 3 wt.% NaCl + 10 mM inhibitor + 0.5 wt.% KI. The most positive corrosion potential was obtained for a steel sample in 3 wt.% NaCl solution, inhibited with 10 mM tolyltriazole, and the most negative for a steel sample in 3 wt.% NaCl solution, inhibited with 10 mM 2-aminobenzimidazole. The highest polarisation resistance was obtained for a sample exposed to 3 wt.% NaCl solution, inhibited with tolyltriazole. By employing cyclic polarisation, it was shown that tolyltriazole is a cathodic-type inhibitor. Next, by employing FTIR, the binding of tolyltriazole on the steel surface was confirmed. By employing 3D-profilometry, it was shown that immersion of steel after three days in tolyltriazole-inhibited solution reduces surface roughness in comparison with non-inhibited solution. Using contact angle analysis, it was shown that steel sample surfaces after three days of immersion in tolyltriazole-inhibited solutions with or without the addition of KI are hydrophilic