Search results for "Dielectric Spectroscopy"
showing 10 items of 243 documents
A kinetic interpretation of a negative time constant in impedance equivalent circuits for the dissolution/passive transition
2007
Abstract A theoretical impedance function is proposed for the active/passive transition of nickel in an acid sulphate medium. It is considered that passivating species progressively covers the electrode surface. This approximated model predicts the appearance of negative time constants in the impedance spectra when coverage coefficient θ values for passive species are greater than 0.5.
Alternating current electrogravimetry of copper electrodissolution in a sulfuric acid solution
2017
Abstract Copper electrodissolution processes have been studied by means of electrochemical impedance spectroscopy and ac-electrogravimetry (mass impedance). During ac-electrogravimetry acquisition, mass decreases or increases due to the electrodissolution or the electrodeposition of copper, respectively. As a result, this continuous mass drift makes impossible obtaining a true ac-electrogravimetry response unless a numerical correction was applied. It has been compared the electrochemical behavior of copper layers previously treated and other freshly deposited on the gold electrode of the quartz crystal microbalance. The simultaneous analysis of both impedance functions has allowed separati…
The phase situation and ferroelectric properties in the mixed crystals [4-NH2PyH][SbCl4(1−x)Br4x]
2008
Abstract The group of mixed crystals of general formula: [4-APyH][SbCl4(1−x) Br4x] with x ranging from 0 to 1 was studied by means of differential scanning calorimetry, dilatometry and dielectric spectroscopy. The ferroelectric properties are preserved for mixed crystals with replacement fraction, x, less than 0.30. Moreover, such a substitution of the chlorine atoms by the bromine ones significantly lowers the temperature of the structural phase transition shifting it from 240 K for pure [4-APyH][SbCl4] to about 185 K for the mixed crystals richer in bromine. The dielectric relaxation process exhibited by the mixed crystal with x = 0.90 in the radio-frequency region was analyzed and the ac…
Molecular scale structure and dynamics at an ionic liquid/electrode interface.
2017
After a century of research, the potential-dependent ion distribution at electrode/electrolyte interfaces is still under debate. In particular for solvent-free electrolytes such as room-temperature ionic liquids, classical theories for the electrical double layer are not applicable. Using a combination of in situ high-energy X-ray reflectivity and impedance spectroscopy measurements, we determined this distribution with sub-molecular resolution. We find oscillatory charge density profiles consisting of alternating anion- and cation-enriched layers at both cathodic and anodic potentials. This structure is shown to arise from the same ion-ion correlations dominating the liquid bulk structure.…
Structural and conductivity studies in LiFeP 2 O 7 , LiScP 2 O 7 , and NaScP 2 O 7
2000
Structural studies of LiScP2O7 by Rietveld refinement confirm that this material is isostructural with LiFeP2O7 studied previously. However, NaScP2O7 shows a structure different from the structural types of the basic group of NaIMIIIP2O7 known thus far. Systematic ranges for the six structural types of AIMIIIP2O7 are presented in terms of ion radii sums and ratios. The framework of LiMP2O7 (M=Sc, Fe) has rather wide tunnels running along the crystallographic c-axis. This feature has determined our interest to check the ion conductivity in AIMIIIP2O7 (A=Li, Na; M=Sc, Fe). The bulk conductivity, however, is low in these compounds, 10−6–10−7 S/cm at 300 °C, as determined by impedance spectrosc…
Application of microwaves dielectric spectroscopy for controlling pork meat (Longissimus dorsi) salting process
2010
Abstract Salting treatment is a common operation in the production of high quality meat products, one of its main problems is the difficulty to control the simultaneous water and salt fluxes into the product and control the protein fibers transformation throughout process. Dielectric properties of salted porcine meat are strongly related to its structure and composition. Thus, dielectric properties measurement appears as a promising method for controlling on-line the salting process in meat industry. Dielectric spectroscopy studies have been performed on raw and salted Longissimus dorsi pork samples. Dielectric spectra were measured in the frequency range from 500 MHz to 20 GHz by an Agilen…
Evaluation of the electrochemical anion recognition ofNO3−-imprinted poly(Azure A) inNO3−/Cl−mixed solutions by ac-electrogravimetry
2016
Abstract During the reversible electrochemical reactions of the intrinsically conducting polymer (ICP) films, ions are inserted in them to balance the inner charge site of the polymer. For this reason, doped ICP films with anions or cations can be good candidates for the electrochemical removal of contaminant ions from wastewater. In this work, a polymer of a phenothiazine derivative (poly(Azure A or PAA)) was electrosynthesized by cyclic voltammetry in aqueous solutions using nitrate ions as a structural template. After that, PAA film was repeatedly cycled in identical conditions in a monomer-free solution. The electrochemical anion recognition of the nitrate-imprinted poly(Azure A) ( N O …
An approach to the electrochemical activity of poly-(phenothiazines) by complementary electrochemical impedance spectroscopy and Vis–NIR spectroscopy
2010
Abstract The electroactivity of two poly-(phenothiazine), the poly-(Azure A) and the poly-(Methylene Blue), has been compared in this work. The spectroelectrochemical results prove clearly the existence of two electroactive moieties integrated in the polymeric lattice, the phenothiazine ring (detected by changes of absorbance at 590 and 685 nm) and the newly formed covalent links which fixes the monomers in the backbone of the polymer (detected by changes of absorbance at 460 and 875 nm). Differences in the electrochemical response of both polymers are due to differences in this covalent link. However in both polymers, the charge balance during electrochemical reactions takes place by the e…
Charge transport in electrically responsive polymer layers
2007
The processes of charge transport in the conducting polymer electrochromic films have been studied by means of spectral-electrochemical method, impedance spectroscopy and cyclic voltametry measurements. It has been shown that charge transport during the coloration-bleaching processes is not symmetric phenomenon. By means of impedance spectroscopy the effective diffusion coefficients for anode and cathode charge transport have been measured. The higher rate of charge transport in the bleaching process as compared to coloration is considered in the frame of conformation rebuilding of conducting polymer chains.
Electrochemical and spectroscopic study on thiolation of polyaniline
2013
Abstract Polyaniline (PANI) is a conducting polymer, easily synthesized and lucrative for many electrochemical applications like ion-selective sensors and biosensors. Thiolated molecules, including biological ones, can be bound by nucleophilic attachment to the polyaniline backbone. These covalently bound thiols add functionality to PANI, but also cause changes in the electrochemical properties of PANI. Polyaniline studied in this work was electropolymerized on glassy carbon electrodes. 2-Mercaptoethanol (MCE) and 6-(ferrocenyl)hexanethiol (FCHT) were used as the thiols to form functionalized films. The films were characterized by cyclic voltammetry (CV), ex situ FTIR and Raman spectroscopi…