The Role of Phase Combinations on the Corrosion and Passivity Behaviour of High Strength Steels

Literature reports a great deal of contradictory results concerning the effect of microstructure on the corrosion and passivity behaviour of advanced high strength steels. The difficulty in identifying the controlling cause of corrosion results from the inability of disentangling the coupled effects of individual microstructural features in a scientifically rigorous manner, thereby attributing the core behaviour to the wrong sources.The aim of this thesis is to isolate and identify the effect of phases on the electrochemical response of high strength steels. To this end, a combined computational and experimental approach is taken. This work starts by analysing the connection between heat treatment, microstructure, and the resulting corrosion properties. After clarification of this interdependence, a finite element electrochemical model illuminates the corrosion behaviour of idealised two phase ferrite-martensite and ferrite-pearlite systems for different phase volume fraction combinations. The results from the simulations guide the microstructure creation for electrochemical experiments, where employed heat treatments result in ferrite-martensite and ferrite-pearlite microstructures with similar ferrite volume fractions. Potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS) experiments in 0.1M and 0.01M H2SO4 solutions; potentiostatic polarisation, EIS and Mott-Schottky analysis in 0.1M NaOH solutions reveal the corrosion response and passive film barrier properties of the microstructures. Results demonstrate a clear phase dependency for both active and passive conditions, and are further discussed in light of microstructural features of secondary martensite and pearlite phases.Materials Science and Engineerin

Properties of Passive Films Formed on Ferrite-Martensite and Ferrite-Pearlite Steel Microstructures

The effect of ferrite-pearlite and ferrite-martensite phase combinations on the passive layer properties of low carbon steel is investigated in a 0.1 M NaOH solution. Heat treatments were designed to obtain ferrite-pearlite and ferrite-martensite microstructures with similar ferrite volume fractions. Potentiostatic polarisation and electrochemical impedance spectroscopy (EIS) results demonstrated the lower barrier properties of passive films on ferrite-martensite microstructure compared to the ones formed on ferrite-pearlite microstructure. This was attributed to the higher donor density of the passive layer on ferrite-martensite samples, measured with Mott–Schottky analysis. This behaviour was explained by the complex microstructure morphology of the martensite phase that led to the formation of a more defective passive filmTeam Yaiza Gonzalez GarciaTeam Jilt Sietsm

Epidemiology of intra-abdominal infection and sepsis in critically ill patients: "AbSeS", a multinational observational cohort study and ESICM Trials Group Project

PurposeTo describe the epidemiology of intra-abdominal infection in an international cohort of ICU patients according to a new system that classifies cases according to setting of infection acquisition (community-acquired, early onset hospital-acquired, and late-onset hospital-acquired), anatomical disruption (absent or present with localized or diffuse peritonitis), and severity of disease expression (infection, sepsis, and septic shock).MethodsWe performed a multicenter (n=309), observational, epidemiological study including adult ICU patients diagnosed with intra-abdominal infection. Risk factors for mortality were assessed by logistic regression analysis.ResultsThe cohort included 2621 patients. Setting of infection acquisition was community-acquired in 31.6%, early onset hospital-acquired in 25%, and late-onset hospital-acquired in 43.4% of patients. Overall prevalence of antimicrobial resistance was 26.3% and difficult-to-treat resistant Gram-negative bacteria 4.3%, with great variation according to geographic region. No difference in prevalence of antimicrobial resistance was observed according to setting of infection acquisition. Overall mortality was 29.1%. Independent risk factors for mortality included late-onset hospital-acquired infection, diffuse peritonitis, sepsis, septic shock, older age, malnutrition, liver failure, congestive heart failure, antimicrobial resistance (either methicillin-resistant Staphylococcus aureus, vancomycin-resistant enterococci, extended-spectrum beta-lactamase-producing Gram-negative bacteria, or carbapenem-resistant Gram-negative bacteria) and source control failure evidenced by either the need for surgical revision or persistent inflammation.ConclusionThis multinational, heterogeneous cohort of ICU patients with intra-abdominal infection revealed that setting of infection acquisition, anatomical disruption, and severity of disease expression are disease-specific phenotypic characteristics associated with outcome, irrespective of the type of infection. Antimicrobial resistance is equally common in community-acquired as in hospital-acquired infection