50 research outputs found
Modeling of electrochemical oxide film growth -- a PDM refinement
The Point Defect Model (PDM) is known for over 40 years and has brought
deeper insight to the understanding of passivity. During the last decades it
has seen several changes and refinements, and it has been widely used to
analyze growth kinetics of different alloys. Nevertheless, the model has been
based on still unconfirmed assumptions, as constant and potential independent
electric field strength. To overcome this limitation, we introduce a Refined
PDM (R-PDM) in which we replace those assumptions by using additional equations
for charge distribution including new physically valid boundary conditions
based on considering finite dimensions for the defects by introduction of two
defect layer at the film boundaries and by calculating the potential drop at
the surface of the film towards the solution over the compact double layer. The
calculations by the R-PDM show that the original PDM assumptions are only valid
for very specific parameter combinations of oxide film growth and vacancies
transport and cannot generally be taken for granted. We believe our findings of
electric field and potential drop dependency on the external potential to pave
the way for a more realistic description of passive layer formation
Influence of the Chemical Structure and Physicochemical Properties of Chitin- and Chitosan-Based Materials on Their Biomedical Activity
2 Influence of the Chemical Structure and Physicochemical Properties of Chitin-and Chitosan-Based Materials on Their Biomedical Activity
Efecto del catión, del anión y del co-ión sobre la agregación de lÃquidos iónicos en solución acuosa
The aggregation behavior of thirteen 1-alkyl-3-methylimidazolium based ionic liquids in aqueous solution is presented, considering variations of the alkyl side chain length as well as the anionic moiety. Cation and anion molecular volumes are selected as appropriate molecular descriptors. Additionally, the existing relationship between critical micelle concentration (CMC) and electrolyte concentration in solution is established, aiming to clarify ion effects. CMC values were obtained by measuring electrical conductivity and surface tension. It was confirmed that aggregation of ionic liquids in aqueous solution and in presence of inorganic salts is affected by the factors developed in this study
Detection of Bioactive Exometabolites Produced by the Filamentous Marine Cyanobacterium Geitlerinema sp.
Marine cyanobacteria are noted for their ability to excrete metabolites with biotic properties. This paper focuses on such exometabolites obtained from the culture of the marine filamentous cyanobacterium Geitlerinema sp. strain, their purification and subsequent analyses. By this means the recoveries of the active compounds, a prerequisite for properly determining their concentration, are quantified here for the first time. We demonstrate a new procedure using Amberlite XAD-1180 resin in combination with the eluent isopropanol for extraction of the culture media and gas chromatography as simplified chemical analysis. This procedure reduced necessary bacteria cultivation time (from 150 to 21 days) at low volumes of culture media (300 mL) required for identification of two selected bioactive compounds: 4,4′-dihydroxybiphenyl and harmane