INHIBITION EFFICIENCY OF STEARIC ACID IN ACIDIC MEDIA

Namen diplomskega dela je bil preučiti inhibicijsko učinkovitost nastale plasti, načeloma hidrofobnega karakterja. V ta namen smo uporabili karboksilno maščobno kislinostearinsko kislino. Feritnemu nerjavnemu jeklu PK2 smo modificirali lastnosti površine s predhodno potopitvijo v etanolno raztopino stearinske kisline. Vse meritve smo izvedli pri sobni temperaturi. Kot korodirni medij smo izbrali klorovodikovo kislino, z naslednjimi koncentracijamic = 0,10,5in 1,0 mol L-1. Ker je bila dosežena zaščita pri višje izbranima koncentracijama minimalna, smo v nadaljevanju izvedli meritve le pri c = 0,1 mol L-1. Prav tako smo izbrali tri različne koncentracije stearinske kislinec = 0,010,05in 0,1 mol L-1. Nižja koncentracija ni bistveno spremenila lastnosti površine v smislu zaščite, medtem ko se je pri višji koncentraciji na površini vzorca ustvarila zdrizasta plast, ki jo je raztopina HCl takoj odplaknila. Iz tega razloga smo uporabili le koncentracijo 0,05 mol L-1. Ker smo želeli inhibicijsko učinkovitost nastale plasti povečati, karakteristike plasti pa izboljšati, smo v etanolno raztopino stearinske kisline dodali še vitamin E v različnih koncentracijah in sicer: w = 0,250,50,751,0 in 2,0 %. Vse izbrane koncentracije vitamina E so dodatno povečale inhibicijsko učinkovitost. Tako pripravljene vzorce smo izpostavili korodirnemu mediju v različnih časovnih intervalih, za 2,5 ure, 4 in 8 ur. Iz podatkov, dobljenih z gravimetrično metodo izgube mase, smo izračunali korozijsko hitrost in inhibicijsko učinkovitost. Glede na rezultate lahko zaključimo, da je stearinska kislina z dodatkom vitamina E uspešno spremeni lastnosti površine (iz hidrofilnega stanja v hidrofobno) in jo relativno dobro zaščiti v izbranem časovnem intervalu. Dolgotrajnejšo zaščito bi dosegli v manj agresivnem korodirnem mediju. Za potrditev hidrofobnosti površine bi bilo potrebno opraviti meritve kontaktnega kota.An objective of the present diploma was to study the inhibition efficiency of the formed layer with hydrophobic nature. In this purpose we used carboxylic fatty acid – stearic acid. With the exposure to the ethanol solution of stearic acid, we wanted to modify the surface of the ferritic stainless steel PK2. All measurements were performed at room temperature. As an acidic medium we used the hydrochloric acid HCl, initially we tested several concentrations (c = 0.1, 0.5 and 1.0 mol L-1), however, we researched in detail only when c = 0.1 mol L-1, since with the other two concentrations the protection was minimal. Further, we have tried with several concentrations of the stearic acid (c = 0.01, 0.05, 0.1 mol L-1). The lowest concentration did not change surface properties significantly, while, at the highest concentration, on the surface of the sample a slimy layer was created, which was washed away by the hydrochloric (HCl) solution. From this reason we used only the concentration of stearic acid of c = 0.5 mol L-1. Because we wanted to increase the inhibition efficiency of the formed layer and improved its characteristics, therefore vitamin E was added vitamin E to the ethanol solution of stearic acid. Vitamin E was added in varying weight percentages (0.25, 0.5, 0.75, 1.0 and 2.0 wt.%). At all chosen concentration of vitamin E the increased of inhibition efficiency was obtained. We exposed steel samples to the corrosive medium for different time interval (2.5, 4 and 8 hours). From the data, collected with the gravimetric method of mass loss, we calculated the corrosion rate and the inhibition efficiency. Regarding the results we can speculated, that the stearic acid with the addition of vitamin E successfully changes the properties of the surface (maybe from hydrophilic to hydrophobic). Moreover, relatively good protection for selected times of exposure was achieved. In less aggressive medium the protection would last longer. To confirm hydrophobic nature of the surface, the contact angle measurement should be performed