Dynamic Impedance Measurements Research Articles

Degradation of Organic Coatings on Steel Investigated by Dynamic Electrochemical Impedance Spectroscopy

Degradation of the organic coatings on steel has been investigated by the dynamic impedance measurements. The dynamic impedance was displayed on 3-dimension plots, whose axes were real and imaginary components and time. The time variation of the film resistance related to the permeation of water was monitored to discuss the corrosion mechanisms of coated steel.

Analysis on organic film degradation by dynamic impedance measurements

Degradation of the organic coating film on the carbon steel has been investigated by dynamic impedance measurements. Since the permeation of water into the coating progresses in short period after the immersion, the time-stability of the electrode system is not satisfied while measuring the electrochemical impedance. As the result, the impedance spectrum in the low frequency region is distorted with the electrode that does not satisfy the time-stability. In the present paper, a dynamic impedance spectroscopy is applied to the electrode without the time-stability, and the distortion of impedance spectrum in the low frequency region is compensated. The degradation process of the coated metal was analyzed by the curve-fitting of the compensated impedance spectra with the equivalent circuit.

Extended Frequency Bandwidth and Electrical Resonance Tuning in Hybrid Terfenol-D/PMN-PT Transducers in Mechanical Series Configuration

This article addresses the modeling and characterization of hybrid transducers incorporating both ferroelectric and ferromagnetic elements. The complementary electrical and mechanical properties of the two classes of materials can yield transducers with higher performance or enhanced functionality relative to single-element devices. As a template for studying the properties of hybrid architectures, a transducer is considered which consists of a mechanical series arrangement of a PMN-PT stack and a Terfenol-D rod. This configuration exhibits a double resonant frequency response that can be tuned for a variety of applications. We are specifically interested in the development of models and design criteria for achieving broadband electromechanical transduction over the range from 500 Hz to over 6 kHz. To that end, a model is presented which is constructed from three classical, widely available theories: (i) linear mechanical vibrations, (ii) classical electroacoustics, and (iii) linear piezoelectricity and piezomagnetism. Despite the general limitations of linear models when applied to nonlinear materials, the linear formulation is justified in this article by the consideration of biased, low signal regimes in which transducer behavior is quasilinear. The model is applicable to the design and control of high-performance devices, while being mathematically tractable and accurate over the regimes considered. The model also provides a framework which permits extraction of material property information from dynamic impedance measurements – as opposed to quasistatic measurements – that is under conditions similar to those found in transducer operation. The study also shows that it is possible to tune the electrical resonance frequency without fundamentally altering the transducer bandwidth. This result has practical implications in that it allows matching of the transducer response to individual drivers. This could allow for retrofit of an existing hybrid device with a newer, more advanced ferroelectric stack without compromising the device bandwidth.

Measurements Versus Predictions for the Dynamic Impedance of Annular Gas Seals—Part II: Smooth and Honeycomb Geometries

Results are presented from tests conducted using an experimental test facility to measure the leakage and dynamic impedance of smooth and honeycomb straight-bore annular gas seals. The test seals had a 114.3 mm (4.500 in.) bore with a length-to-diameter ratio of 0.75 and a nominal radial clearance of 0.19 mm (0.0075 in.). The honeycomb cell depth for both seals was 3.10 mm (0.122 in.), and the cell width was 0.79 mm (0.031 in.). Dynamic impedance and leakage measurements are reported using air at three supply pressures out to 1.72 Mpa (250 psi), three speeds out to 20,200 rpm, and exit-to-inlet pressure ratios of 40% and 50%. Comparisons to the predictions from the two-control-volume model of Kleynhans and Childs [1] are of particular interest. This model predicts that honeycomb seals do not fit the conventional frequency independent model for smooth annular gas seals. The experimental results verify this new theory. Numerical predictions from a computer program incorporating the new two-control-volume model of Kleynhans and Childs [1] correlate well with both measured seal leakage and dynamic impedances for the honeycomb seals.

The effect of ultrasound on lithium surfaces in propylene carbonate

Ultrasonic irradiation of lithium metal electrodes is demonstrated to erode surface layers and subsequently reduce the interfacial resistance. Dynamic impedance measurements were employed to monitor the erosion and reformation of surface layers formed on lithium electrodes placed in a propylene carbonate electrolyte in the presence and absence of ultrasound, respectively. In the presence of ultrasound a marked decrease in the resistance (ca. 310 Ω cm 2 to 225 Ω cm 2 ) was observed over a 400 s period. Other experiments employing a 50 μm diameter Cu microelectrode showed that ultrasound had a marked effect on both lithium plating and stripping. It was found that the stripping efficiency was reduced from ca. 60% under silent conditions to only ca. 18% in the presence of ultrasound. Subsequent experiments demonstrated that ultrasound efficiently removes lithium from a lithium coated copper microelectrode in the absence of any stripping or plating processes. The results demonstrate that ultrasound, under the conditions reported here, removes lithium from the surface of the microelectrode, increases the voltage required for lithium plating, reduces the interfacial resistance of films formed on lithium within a propylene carbonate electrolyte and decreases the efficiency of the stripping/plating process.

Dynamic quartz crystal impedance measurements of polyvinylferrocene film deposition

Dynamic crystal impedance measurements were used to study the electrochemically-driven deposition of polyvinylferrocene (PVF) films from dichloromethane solutions of PVF onto Au electrodes of a quartz crystal microbalance. Under all the conditions studied, the PVF films were non-rigid, to an extent that depended upon several experimental factors. Films deposited from solutions containing perchlorate salts of tetraalkylammonium salts departed less from rigidity than those deposited under otherwise identical conditions from tetrafluoroborate media. In contrast, the use of different tetraalkylammonium cations, or the use of a potential sweep vs. a potential step from 0 V to the deposition potential (0.7 V), made no significant difference. The departure from rigid characteristics varied with coverage. For the interval of time during deposition that the coverage was 10–160 nmol cm −2 (of monomeric ferrocene units), the films showed no additional departure from rigidity. On the basis that the upper figure corresponds closely to a “monolayer” of terminally attached chains of mean length, we attribute this behaviour to the presence of a dense film, within which chain motion is considerably restrained.

Dynamic impedance measurements on a thin-film poly-3-methylthiophene electrode: Memory effects and space charge formation

A new procedure for measuring electrochemical impedance spectra directly during potential cycling is presented. The method consists in taking a series of impedance-potential curves at different potential modulation frequencies. Then the impedance values at desired electrode potentials are sampled, and corresponding dynamic impedance spectra are reconstructed. The method was applied to a thin-film poly-3-methylthiophene/vbPt (P3MT/vbPt) electrode in an acetonitrile solution. The results suggested that undoping of the polymer at negative potentials gave rise to development of a space-charge region within the film that hindered the polymer doping process unless flat-band conditions were reached. Such behavior could account for a well-known memory effect observed in conducting polymers. Moreover, our data provide further evidence that illumination of a P3MT electrode at negative potentials results in photoelectrochemical undoping of the polymer.

Dynamic force and impedance measurement in statically loaded structures

A method is investigated to measure relatively low dynamic forces and impedance in statically loaded structures by means of thin elastic layers and built-in piezo-electric transducers. The elasticity theory equations being solved for two regions of the layer, a pressure distribution is achieved and the condition minimising pressure non-uniformity is determined. Computation and experimental results are shown.

Closure to “Discussion of ‘Investigation of Adsorbed Hydrogen on Platinum Electrode by Means of Dynamic Impedance Measurement’ [T. Ohsaka, Y. Sawada, T. Yoshida, and K. Nihei (pp. 1339–1345, Vol. 123, No. 9)

not Available.

Discussion of “Investigation of Adsorbed Hydrogen on Platinum Electrode by Means of Dynamic Impedance Measurement” [T. Ohsaka, Y. Sawada, T. Yoshida, and K. Nihei (pp. 1339–1345, Vol. 123, No. 9)

not Available.

Mechanical properties and microstructure of sintered PVC powder. II. Permeability and porous structure

Static and dynamic air-flow impedance measurements were conducted with thin specimens of a variously sintered PVC powder. The results were interpreted by a statistical theory that expresses the parameters of a quasihomogeneous acoustic absorber in terms of porosity averages of channel radius and orientation. The low-frequency behavior of the air-flow impedance is determined by the porosity, a structure factor, and three different average channel radii that are related by inequalities. The latter could be established from general statistical considerations and were confirmed in most cases by experiment. Photomicrographs of sections through sintered powder layers were analyzed by stereological techniques in terms of specific surfaces. The channel radii derived from such measurements compared favorably with the average acoustic channel radii.

Investigation of Adsorbed Hydrogen on Platinum Electrode by Means of Dynamic Impedance Measurement

Adsorbed hydrogen phenomena on a platinum electrode were investigated by an impedance method which draws potentiodynamically the in‐phase and quadrature components of electrode admittance. The kinetic behavior of hydrogen adsorbed on platinum was examined in full with the complex capacitance representation. The kinetic experimental results were well explained on the basis of the proposed equivalent circuit which was composed of the pseudocapacitance, Warburg impedance, and ohmic component associated with the adsorption‐desorption process of adsorbed hydrogen, together with the reaction resistance due to the Volmer reaction.

Static and dynamic acoustic impedance measurements in infant ears.

Tympanometry and acoustic reflex threshold data are reported for a series of presumable normal infants ranging in age from 55 to 132 days. In general, tympanograms displayed single peaks between +/- 50 mm H2O. Susceptance tympanograms with a 660-Hz probe frequency were sometimes characterized by monotonically increasing susceptance as ear canal pressure was changed from -200 to +200 mm H2O. Static values of acoustic conductance, susceptance, admittance, resistance, reactance, impedance, and phase angle were computed from tympanograms using the values of ambient and +200 mm H2O (0/+200 procedure) and maximum and minimum tympanometric values (MAX/MIN procedure). Comparison of the data from the two computational procedures suggested that the MAX/MIN procedure produces means and standard deviations of static values which are more manageable for establishing confidence limits with which to evaluate potentially pathological subjects. The MAX/MIN procedure resulted in lower mean values of conductance and susceptance for infant subjects relative to previously reported adult data using a similar computational procedure. Acoustic reflex thresholds were clearly present in all testable infants at coupler sound pressure levels similar to adult data, suggesting that the relations between reflex thresholds and hearing sensitivity demonstrated in adult subjects are similarly applicable to infant subjects. Mild sedation to induce sleep without altering the reflex would make acoustic reflex threshold measurement a useful procedure for screening large numbers of infants.

Anodic dissolution of Ni in 1 N H 2SO 4 studied by dynamic impedance measurements

The anodic dissolution of 99·999% Ni in 1 N H 2SO 4 has been studied by dynamic impedance measurements using a lock-in-amplifier. The method allows the simultaneous dynamic recording of I/ V and impedance curves. The capacitance/potential curve shows two distinct maxima in the transpassive region at about 1400 mV(nhe). In this region the I/ V curve displays only a monotonic increase of I with V. The potential range at which the two C p maxima occur has been studied as a function of the velocity of the potential change (0·1 V/h < d V/d t < 20 V/h) and of pH (0·3 < pH < 5·3). The results lead to the conclusion that the first maximum at less noble potential is due to a subsequent oxidation of the passive layer and the second maximum is due to an irreversible adsorption reaction.