Corrosion behavioer of stainless steels in pfosphate buffer saline solution : master thesis

Praćenjem vremenske promjene potencijala otvorenog strujnog kruga, primjenom linearne i cikličke polarizacije te elektrokemijske impedancijske spektroskopije ispitana je anodna i spontana korozija različitih vrsta nehrđajućeg čelika (AISI 304L, AISI 316L i 2205 DSS) u slanoj otopini fosfatnog pufera (PBS, pH = 7.4) pri 37 °C (tj. simuliranoj fiziološkoj otopini u ljudskom organizmu). Nakon anodne i spontane korozije, površine ispitivanih uzoraka snimljene su pomoću svjetlosnog i pretražnog elektronskog mikroskopa (SEM) uz EDS analizu. Utvrđeno je da otpornost materijala prema anodnoj koroziji raste redom: AISI 304L AISI 316L 2205 DSS. Naime, istim se redom povećava mogućnost repaivacije i otpornost na lokalnu koroziju. Korozijska otpornost uzoraka čelika na potencijalu otvorenog strujnog kruga posljedica je formiranja prirodnog oksidnog filma dvoslojne strukture, koji se sastoji od unutarnjeg barijernog i vanjskog poroznog sloja. Unutarnji barijerni sloj je jako tanak velikog otpora, dok je vanjski porozni sloj deblji i znatno manjeg otpora. Koroziju uzoraka čelika sprječava unutarnji barijerni sloj i to redom: AISI 304L < AISI 316L < 2205DSS. Svjetlosni mikroskop i SEM/EDS analiza nakon anodne i spontane korozije pokazuju oštećenja na AISI 304L i AISI 316L površini, dok je površina 2205 DSS čelika uglavnom neoštećena korozijom.Anodic and spontaneous corrosion of different types of stainless steel (AISI 304L, AISI 316L and 2205 DSS) in phosphate-buffered saline solution (PBS, pH = 7.4) at 37 °C (i.e., in simulated physiological solution in the human body) were examined using open circuit potential measurements, linear and cyclic polarization, and electrochemical impedance spectroscopy methods. After the anodic and spontaneous corrosion, the surface of the tested samples was investigated by light and scanning electron microscopy (SEM) with EDS analysis. It has been established that the anodic corrosion resistance of the examined materials inecreases in the order: AISI 304L < AISI 316L < 2205 DSS. Namely, the possibility of repassivation and the resistance to local corrosion increases in the same order. The corrosion resistance of steel samples at open circuit potential is a consequence of forming a natural oxide film with a bi-layer structure and consists of an inner barrier and an outer porous layers. The inner barrier layer has a small thickness and extremely high resistance, while the outer porous layer is much thicker but also has significantly lower resistance. The inner barrier layer mainly prevents corrosion of examined steel samples in order: AISI 304L < AISI 316L < 2205 DSS. Light microscopy and SEM/EDS analysis after anodic and spontaneous corrosion showed damage on the AISI 304L and AISI 316L surface, while the surface of 2205 DSS was almost undamaged by corrosion