Search results for "Dielectric Spectroscopy"
showing 10 items of 243 documents
Relationships between the Impedance of Oxide Scales on Martensitic and Austenitic Steels and Corrosion Rate in Liquid Lead-Bismuth Eutectic
2004
Abstract The impedance properties (resistance and capacitance) of oxide scales on the martensitic/ferritic steel HT-9 and austenitic stainless steel Type 316L (UNS S31603) were examined during immersion in lead-bismuth eutectic (LBE) using a technique similar to electrochemical impedance spectroscopy. These scales were created by preoxidizing the samples in an air/water vapor environment at 800°C for various times prior to immersion in LBE. Calculation of oxide conductivity for samples immersed in LBE at 200°C for 200 h yielded σHT9 ≈ 4 × 10−7 (Ω × cm)−1 while σ316 ≈ 3 × 10−8 (Ω × cm)−1. The influence of temperature alone gave the anticipated Arrhenius behavior with Ea equal to 0.12 eV, whi…
Dielectric spectroscopy of novel thiol-ene/epoxy thermosets obtained from allyl-modified hyperbranched poly (ethyleneimine) and diglycidylether of bi…
2019
[EN] Dielectric Thermal Analysis (DETA) of a series of new thermoset obtained by click chemistry was performed. The new thermosets were obtained by a dual-curing process consisting in a first photochemical thiol-ene, followed by a thermal thiol-epoxy starting from an allyl-terminated hyperbranched poly(ethyleneimine) (HBPEI) and different proportions of diglycidylether of bisphenol A (DGEBA) and the corresponding stoichiometric proportions of pentaerythritol tetrakis (3-mercaptopropionate, PETMP). The dielectric behaviour was obtained experimentally supressing the conductive effects. Two sub-Tg intramolecular non-cooperative gamma and beta relaxations and an intermolecular cooperative alpha…
Emerging dynamics in surfactant-based liquid mixtures: octanoic acid/bis(2-ethylhexyl) amine systems.
2012
This work focuses on the dynamic phenomena emerging in self-assembled transient intermolecular networks formed when two different surfactants are mixed. In particular, the relaxation processes in liquid mixtures composed by bis(2-ethylhexyl)amine (BEEA) and octanoic acid (OA) in the whole composition range has been investigated by dielectric spectroscopy and Brillouin spectroscopy. A thorough analysis of all the experimental data consistently suggests that, mainly driven by acid-base interactions arising when the two surfactants are mixed, supra-molecular aggregates formation causes the slowing down of molecular dynamics. This, in turn, reflects to longer-range relaxations. These changes ha…
Development of a dielectric spectroscopy technique for the determination of apple (Granny Smith) maturity
2010
Abstract Dielectric measurements of apple were done during its maturity in order to find relations with apple physiological compounds (sugar content, malic acid). An Agilent 85070E open-ended coaxial probe connected to an Agilent E8362B vector network analyzer were used in these experiments. All determinations were made at 30 °C from 500 MHz to 20 GHz. These assays were performed in order to consider the potential use of dielectric spectroscopy for determining the state of fruit maturity. Good correlations among apples Thiault Index with a new defined Dielectric Maturity Index were found. The Dielectric Maturity Index was related to loss factor at two punctual frequencies (0.5 GHz and dipol…
Electrical impedance spectroscopy of ionic liquid 1-ethyl-3-methylimidazolium methanesulfonate (ECOENG™ 110)
2011
Abstract Ionic liquid “ECOENG™ 110”, a promising electrolyte for electrochemical devices, was investigated by impedance spectroscopy. Metallic electrodes (Pt, Cu, Ag, and Mo) as well as carbon were used for the electrochemical characterization. The dependences of the real and imaginary impedance, polarization resistance and electrochemical capacity of the double layer on the electrode potential were investigated using electrical equivalent circuits of R1(QR2) and R1[Q(R2W)] types.
Hydrogel-supported protein-tethered bilayer lipid membranes: a new approach toward polymer-supported lipid membranes
2011
Polymer-supported bilayer lipid membranes offer great opportunities for the investigation of functional membrane proteins. Here we present a new approach in this direction by introducing a thin hydrogel layer as a soft ‘cushion’ on indium–tin oxide (ITO), providing a smooth, functional surface to form the protein-tethered BLM (ptBLM). ITO was used as a transparent electrode, enabling simultaneous implementation of electrochemical and optical waveguide techniques. The hydrogel poly(N-(2-hydroxyethyl)acrylamide-co-5-acrylamido-1-carboxypentyl-iminodiacetate-co-4-benzoylphenyl methacrylate) (P(HEAAm-co-NTAAAm-co-MABP)) was functionalized with the nickel chelating nitrilotriacetic acid (NTA) gr…
Structure of doped polyaniline - dielectric spectroscopy measurements
1993
The role of doping reagents (residual water and acid anions) in determining the electric properties of a chemically synthesized polyaniline (PANI) was studied using a dielectric spectroscopy method. Dependencies of dielectric losses and susceptibility of PANI as the functions of temperature (-100÷+100°C) and electric field frequency (0.3÷30000 Hz) were examined at it was shown the role of water acts as a doping impurity similar to acid anions. The model is proposed to explain the role of water in terms of adsorption of H 2 O molecules at nitrogen sites of PANI chain and their dissociation
Local electrochemical impedance measurements on inclusion-containing stainless steels using microcapillary-based techniques
2009
MnS inclusions are good precursor sites for pitting corrosion of stainless steel. The objective of this paper was to quantify the passive properties of resulfurized stainless steel after immersion in chloride media. This was done by combining microcapillary techniques with electrochemical impedance spectroscopy and numerical analysis (specific equivalent circuit). It was shown that sulfur species produced in the electrolyte during the dissolution of inclusions react with the native passive film to CrS and FeSO 4 . Local electrochemical impedance spectroscopy measurements provided data describing the behaviour of the affected matrix at the microscale. For example, the value of the charge tra…
Electrochemical capacitance spectroscopy and capacitive relaxation of the changeover process in iron hexacyanoferrate molecular compound
2010
Abstract In this work it was proposed the use electrochemical capacitance spectroscopy (ECS) to evaluate the storage process during changeover in FeHCF compound. The approach is equivalent to electrochemical impedance spectroscopy (EIS) albeit from such analysis it was possible to focus attention on the capacitive and dielectric relaxation instead of the dispersive relaxation related to charge transfer. From such approach it was possible to obtain complementary information on the role played by [Fe 2+ (CN) 6 ] 4− vacancies during the changeover process. It was observed that Fe 3+ (NC) 5 OH − clusters located in these vacancies mediate an electronic and ionic coupled trapping/detrapping proc…
Li-ion diffusion in Li_{x}Nb_{9}PO_{25}$
2013
Abstract Wadsley–Roth phase Li x Nb 9 PO 25 has been studied as a potential candidate for anode material of Li-ion batteries. Its crystal structure, which consists of ReO 3 -type blocks of NbO 6 octahedra connected with PO 4 tetrahedra, provides a good stability and performance during Li + insertion/removal. Li-ion chemical diffusion coefficient ( D chem ) in Li x Nb 9 PO 25 was determined by means of potentiostatic intermittent titration technique and electrochemical impedance spectroscopy. Different data treatments (classical Warburg equation or the model of an electrode system with ohmic potential drop and/or slow kinetics of the interfacial Li + ion transfer across the electrode/electro…