Electrolytic Conduction Research Articles

Electrolytic conduction properties of single conical nanopores

Single conical nanopores were fabricated by etching single-ion-irradiated poly(ethylene terephthalate) (PET) films. The etching process was monitored by measuring the transmembrane current. A series of conical nanopores with decreasing tip sizes (decreasing conductivity) were obtained at different maximum etching currents, “ I max ”. Results showed that it was possible to control the tip diameter by terminating etching at a certain I max . The current–voltage characteristic of the nanopores in KCl solution was investigated. The current rectification coefficient, γ = | I ( U - ) / I ( U + ) | , depended significantly on the tip size: a nanopore with small tip diameter could expect a larger γ . γ was also influenced by electrolyte concentration, and reached its maximum at KCl concentration of 0.3 M.

Carbon-fiber-reinforced cement-based sensors

The addition of carbon fibers has proved to be one of the most effective ways of improving the electrical conductivity of ordinary cement pastes. This implies that such materials can be used in strain, temperature, and chemical sensing. The present study was aimed at the development of such sensors. Inexpensive, petroleum-pitch-based, mesophase, high-modulus carbon fibers were used throughout. It was seen that materials with high conductivity could be obtained by reinforcing hydrated cement paste with carbon fibers. Electronic conduction was seen as the dominant mode over electrolytic conduction. Compared with strain, the influence of temperature on the electrical resistivity was found to be insignificant, implying a lack of need for temperature correction. Results also indicate that these sensors can be excellent crack detectors.Key words: carbon-fiber-reinforced cement-based composites, structural health monitoring, sensor, electrical resistivity, compressive strain, temperature, moisture content, chloride concentration, fiber volume fraction, water/cementitious ratio, cracking.

Internal Structure of Open System Pingos, Adventdalen, Svalbard: The Use of Resistivity Tomography to Assess Ground-Ice Conditions

The objectives of this project were to establish the geometry and internal structure of open system pingos in Adventdalen, Svalbard using electrical resistivity tomography. A clear distinction can be made between the electrical properties of the pingos investigated, depending upon whether they are located either above (Innerhytte pingo) or below (Hytte and Longyear pingos) the maximum Holocene marine limit. The resistivity profile at Innerhytte pingo was characterised by high values of resistivity [Formula: see text], indicating either ice-rich frozen bedrock or a lens of massive ground ice. The electrical resistivity of Hytte and Longyear pingos, both developed within fine-grained, saline marine clays, is exceptionally low (predominantly [Formula: see text]) for permanently frozen ground. This is inconsistent with the presence of a body of massive ground ice, and suggests that the internal structures of Longyear and Hytte pingos do not follow the classic model of a plano-convex pingo-core of massive injection ice. Instead, the internal structure of these landforms may be dominated by segregation ice and localised pockets of massive ice within a matrix of partially frozen, fine-grained marine muds. The high salinity of the pore waters and the fine-grained nature of the sediment cause high unfrozen pore water contents, even at temperatures well below [Formula: see text], enabling electrolytic conduction and resulting in apparently anomalously low resistivity measurements. It is therefore concluded that electrical resistivity tomography must be interpreted with care when applied to the characterisation of permafrost in areas of saline marine sediments. Future field monitoring of permafrost landforms and laboratory testing of ice-rich sediments are recommended to improve geophysical interpretation of permanently frozen materials.

Solid state surface and interface spreading: An experimental study

Solid state spreading is experimentally investigated in three types of systems: “ionic salt MX–oxide”, “ionic oxide–ionic oxide”, and “covalent oxide–ionic oxide”, each differing from one another in their nature of chemical bonding (bond ionicity). The novel data obtained in the study clearly show that the mechanisms of solid state spreading are essentially different in these types of systems and depend upon the surface energy and on the type of chemical bonding of the contacting phases. The main factors governing this process are chemical bond ionicity in the mobile, spreading phase and chemical affinity between the mobile phase and the substrate. The mechanism of solid state spreading of an ionic salt over the supporting oxide proceeds via the formation of a non-autonomous interfacial phase (interphase) MX-s. For interfaces of type “covalent, soft oxide | ionic oxide”, the spreading mechanism is complicated. A non-autonomous interphase is first of all formed at the interface. This phase is characterized by bilateral surface activity and mobility. It then spreads over the grain surface of both phases in contact. In the case of the MeWO 4 | WO 3-interface, a MeW- s interphase is formed and exists at elevated temperatures. A set of experimental evidence of MeW- s formation and bilateral movement is obtained. MeW- s possesses rather high electrolytic conduction. The latter is the reason of metacomposite solid electrolyte formation and is a trigger for the field-assisted spreading and a fast electro-surface counter-transfer of MeWO 4 and WO 3.

Electrical Properties of Crustal and Mantle Rocks – A Review of Laboratory Measurements and their Explanation

The electrical properties of rocks and minerals are controlled by thermodynamic parameters like pressure and temperature and by the chemistry of the medium in which the charge carriers move. Four different charge transport processes can be distinguished. Electrolytic conduction in fluid saturated porous rocks depends on petrophysical properties, such as porosity, permeability and connectivity of the pore system, and on chemical parameters of the pore fluid like ion species, its concentration in the pore fluid and temperature. Additionally, electrochemical interactions between water dipoles or ions and the negatively charged mineral surface must be considered. In special geological settings electronic conduction can increase rock conductivities by several orders of magnitude if the highly conducting phases (graphite or ores) form an interconnected network. Electronic and electrolytic conduction depend moderately on pressure and temperature changes, while semiconduction in mineral phases forming the Earth’s mantle strongly depends on temperature and responds less significantly to pressure changes. Olivine exhibits thermally induced semiconduction under upper mantle conditions; if pressure and temperature exceed ~ 14 GPa and 1400 °C, the phase transition olivine into spinel will further enhance the conductivity due to structural changes from orthorhombic into cubic symmetry. The thermodynamic parameters (temperature, pressure) and oxygen fugacity control the formation, number and mobility of charge carriers. The conductivity temperature relation follows an Arrhenius behaviour, while oxygen fugacity controls the oxidation state of iron and thus the number of electrons acting as additional charge carriers. In volcanic areas rock conductivities may be enhanced by the formation of partial melts under the restriction that the molten phase is interconnected. These four charge transport mechanisms must be considered for the interpretation of geophysical field and borehole data. Laboratory data provide a reproducible and reliable database of electrical properties of homogenous mineral phases and heterogenous rock samples. The outcome of geoelectric models can thus be enhanced significantly. This review focuses on a compilation of fairly new advances in experimental laboratory work together with their explanation.

AC impedance spectroscopy: a new equivalent circuit for titania thick film humidity sensors

The variation of the electrical signal with humidity in ceramic sensors is originated by the chemical and physical sorptions of water molecules existing in the atmosphere. The aim of the work described in the present paper is to establish an equivalent electrical circuit for the case of two titania thick-film samples. It is shown, at least for the temperature of 23 °C, that the same type of circuit represents adequately these two samples for various relative humidities. Chemisorption and physisorption are responsible for the different charge transport mechanisms – ion hopping, ion diffusion and electrolytic conduction. Complex impedance data were obtained at the temperature of 23 °C and various relative humidities, in the frequency range 0.1 Hz–40 MHz. The best and simpler circuit representation we found, which gives the best fitting for the Cole–Cole and Bode plots, consists of two RC parallel circuits in series with two constant-phase elements (CPEs). The values of the electrical components are tabled and, as an example, the Cole–Cole and Bode plots fitting obtained for one of our samples, the sample B, for 87.5% RH, in the frequency range 0.1 Hz–40 MHz is shown.

Low‐frequency electrical properties of peat

Electrical resistivity/induced polarization (0.1–1000 Hz) and vertical hydraulic conductivity (Kv) measurements of peat samples extracted from different depths (0–11 m) in a peatland in Maine were obtained as a function of pore fluid conductivity (σw) between 0.001 and 2 S/m. Hydraulic conductivity increased with σw (Kv ∝ σw0.3 between 0.001 and 2 S/m), indicating that pore dilation occurs due to the reaction of NaCl with organic functional groups as postulated by previous workers. Electrical measurements were modeled by assuming that “bulk” electrolytic conduction through the interconnected pore space and surface conduction in the electrical double layer (EDL) at the organic sediment‐fluid interface act in parallel. This analysis suggests that pore space dilation causes a nonlinear relationship between the “bulk” electrolytic conductivity (σel) and σw (σel ∝ σw1.3). The Archie equation predicts a linear dependence of σel on σw and thus appears inappropriate for organic sediments. Induced polarization (IP) measurements of the imaginary part (σ″surf) of the surface conductivity (σ*surf) show that σ″surf is greater and more strongly σw‐dependent (σ″surf ∝ σw0.5 between 0.001 and 2 S/m) than observed for inorganic sediments. By assuming a linear relationship between the real (σ′surf) and the imaginary part (σ″surf) of the surface conductivity, we develop an empirical model relating the resistivity and induced polarization measurements to σw in peat. We demonstrate the use of this model to predict (a) σw and (b) the change in Kv due to an incremental change in σw from resistivity and induced polarization measurements on organic sediments. Our study has implications for noninvasive geophysical characterization of σw and Kv with potential to benefit studies of carbon cycling and greenhouse gas fluxes as well as nutrient supply dynamics in peatlands.

The relationship of total dissolved solids measurements to bulk electrical conductivity in an aquifer contaminated with hydrocarbon

A recent conceptual model links higher bulk conductivities at hydrocarbon impacted sites to higher total dissolved solids (TDS) resulting from enhanced mineral weathering due to acids produced during biodegradation. In this study, we evaluated the above model by investigating the vertical distribution of bulk conductivity, TDS, and specific conductance in groundwater. The results showed higher TDS at contaminated locations consistent with the above model. Further, steep vertical gradients in bulk conductivity and TDS suggest vertical and spatial heterogeneity at the site. We observed that at fluid conductivities <40 mS/m, bulk conductivity was inversely related to fluid conductivity, but at fluid conductivities >40 mS/m, bulk conductivity increased with increasing fluid conductivity. However, at fluid conductivities >80 mS/m, bulk conductivities increased without a corresponding increase in fluid conductivity, resulting in a poor correlation between bulk conductivity and fluid conductivity for the contaminated samples. This suggests that electrolytic conductivity was not completely responsible for the observed variability in bulk conductivity. We suggest two possible reasons for the inverse relationship at low fluid conductivity and poor positive correlation at high fluid conductivity: (1) geochemical heterogeneity due to biological processes not captured at a scale comparable to the bulk conductivity measurement and (2) variability in the surface conductivity, consistent with a simple petrophysical model that suggests higher surface conductivity for contaminated sediments. We conclude that biodegradation processes can impact both electrolytic and surface conduction properties of contaminated sediments and these two factors can account for the higher bulk conductivities observed in sediments impacted by hydrocarbon.

The relationship of total dissolved solids measurements to bulk electrical conductivity in an aquifer contaminated with hydrocarbon

A recent conceptual model links higher bulk conductivities at hydrocarbon impacted sites to higher total dissolved solids (TDS) resulting from enhanced mineral weathering due to acids produced during biodegradation. In this study, we evaluated the above model by investigating the vertical distribution of bulk conductivity, TDS, and specific conductance in groundwater. The results showed higher TDS at contaminated locations consistent with the above model. Further, steep vertical gradients in bulk conductivity and TDS suggest vertical and spatial heterogeneity at the site. We observed that at fluid conductivities <40 mS/m, bulk conductivity was inversely related to fluid conductivity, but at fluid conductivities >40 mS/m, bulk conductivity increased with increasing fluid conductivity. However, at fluid conductivities >80 mS/m, bulk conductivities increased without a corresponding increase in fluid conductivity, resulting in a poor correlation between bulk conductivity and fluid conductivity for the contaminated samples. This suggests that electrolytic conductivity was not completely responsible for the observed variability in bulk conductivity. We suggest two possible reasons for the inverse relationship at low fluid conductivity and poor positive correlation at high fluid conductivity: (1) geochemical heterogeneity due to biological processes not captured at a scale comparable to the bulk conductivity measurement and (2) variability in the surface conductivity, consistent with a simple petrophysical model that suggests higher surface conductivity for contaminated sediments. We conclude that biodegradation processes can impact both electrolytic and surface conduction properties of contaminated sediments and these two factors can account for the higher bulk conductivities observed in sediments impacted by hydrocarbon.

Humidity sensing properties of a thick-film titania prepared by a slow spinning process

A ceramic thick film humidity sensor was produced from an emulsion of titania powders by a spin coating technique using a low speed. Electrical measurements were taken between interdigital electrodes obtained by depositing silver paste on the oxide, then cured at 500 °C for 15 min. Different relative humidities of a dynamic atmosphere were obtained by mixing dry and 23 °C saturated synthetic air in convenient proportions. Complex impedance spectra of the titania sensor at various relative humidities (RH) and different temperatures were measured and compared. The humidity sensing behaviour is due to surface water molecules adsorption and capillary condensation. The proposed sensing mechanisms, explaining the registered impedance spectra, are a combination of proton hopping, hydronium electrical drift and diffusion, and electrolytic conduction. In the frequency range 1–400 Hz, resistance and capacitive reactance show variations of three to four-order magnitude over the RH range 10–100%. The curves representing the variations of resistance and capacitive reactance versus RH show clearly the existence of two dominant electrical charge transport mechanisms. A parameter called characteristic humidity is defined to represent the sensitive response of the sensor. It was found that the sensitivity was highly dependent on the frequency. This work also shows that, for the same RH, both resistance and capacitive reactance vary with the atmosphere temperature.

Humidity sensing properties of a thick-film titania prepared by a slow spinning process

A ceramic thick film humidity sensor was produced from an emulsion of titania powders by a spin coating technique using a low speed. Electrical measurements were taken between interdigital electrodes obtained by depositing silver paste on the oxide, then cured at 500°C for 15min. Different relative humidities of a dynamic atmosphere were obtained by mixing dry and 23°C saturated synthetic air in convenient proportions. Complex impedance spectra of the titania sensor at various relative humidities (RH) and different temperatures were measured and compared. The humidity sensing behaviour is due to surface water molecules adsorption and capillary condensation. The proposed sensing mechanisms, explaining the registered impedance spectra, are a combination of proton hopping, hydronium electrical drift and diffusion, and electrolytic conduction. In the frequency range 1–400Hz, resistance and capacitive reactance show variations of three to four-order magnitude over the RH range 10–100%. The curves representing the variations of resistance and capacitive reactance versus RH show clearly the existence of two dominant electrical charge transport mechanisms. A parameter called characteristic humidity is defined to represent the sensitive response of the sensor. It was found that the sensitivity was highly dependent on the frequency. This work also shows that, for the same RH, both resistance and capacitive reactance vary with the atmosphere temperature.

Crosshole IP imaging for engineering and environmental applications

Induced polarization (IP) imaging is a promising tool in engineering and environmental studies. Application of this technique for near‐surface investigations has previously been limited by incomplete understanding of the physicochemical controls on the IP response, together with a lack of appropriate methods for data inversion. As laboratory studies have shown, description of IP in terms of complex electrical conductivity enables access to various structural characteristics pertinent to practical issues such as subsurface lithology definition, hydraulic permeability estimation, or hydrocarbon contaminant mapping. In particular, analysis in terms of real and imaginary conductivity components offers improved lithological characterization, since surface polarization effects are separated from electrolytic and surface conduction effects. An Occam‐type IP inversion algorithm based on complex algebra is described which accounts for these advances in IP interpretation by directly solving for complex conductivity. Results from crosshole applications at two case study sites demonstrate the suitability of the IP imaging approach for subsurface characterization. In the first case study, the imaging results correlate with the observed complex sequence of Quaternary sediments at a waste disposal site. Characterization of the polarizability of these sediments offers significant value in lithological differentiation. In the second case study, the results of IP imaging at a hydrocarbon‐contaminated site illustrate the potential of the method in environmental studies. The hydrocarbon location is clearly evident from the IP image, and a markedly different response is observed at an uncontaminated region of the site. By adopting empirical structural–electrical relationships, images of textural and hydraulic properties are estimated as a step toward improved quantitative characterization. The success of the method for these contrasting applications supports further investigation into understanding the physical and chemical processes that control observed IP.

Investigation of a Bronze Age plankway by spectral induced polarization

AbstractThe induced polarization (IP) method was developed originally for ore exploration. The transition from electronic to electrolytic conduction causes strong polarization effects in ores. However, other porous materials also exhibit polarization effects. They are caused by electrochemical processes at the internal interface between the pore fluid and the mineral grains. Although these effects are one to two orders smaller in size, modern IP equipment is able to resolve these phenomena. Spectral induced polarization (SIP) investigates the polarization effect in a wide frequency range. As a SIP measurement has an identical setup to conventional resistivity survey, a multichannel geoelectrical instrument (SIP‐256) was developed that is able to measure both apparent resistivity and the polarization effect using a multi‐electrode array.The Federsee bog near Lake Konstanz with its optimal preservation conditions is of international importance for archaeology. Pile dwelling settlements dating back to the eneolithicum have been revealed. Wood samples of a Bronze Age plankway (1500–1400 BC) were collected and investigated. The astonishing result of the laboratory measurements was that the samples showed a remarkable polarization effect in the classic frequency range of IP. Wood therefore can be regarded as a polarizable material. As a consequence a SIP survey was performed in order to investigate the plankway. The SIP survey was carried out in a frequency range from 1 to 60 Hz, where the maximum polarization effect in the laboratory was observed. Two profiles were measured, one parallel and one perpendicular to the plankway. In contrast to the result of the resistivity measurement, the plankway could be identified by weakly increased polarization effects. Copyright © 2002 John Wiley &amp; Sons, Ltd.

Fabrication and humidity sensing properties of nanostructured TiO 2–SnO 2 thin films

Nanostructured TiO 2–SnO 2 thin films have been prepared using a sol–gel process and the humidity sensing properties of the films were investigated. The films possess nano-sized grains and nanoporous structure. The TiO 2–20 wt.% SnO 2 film exhibits the highest sensitivity for the humidity, which shows over three orders change in the resistance during the relative humidity (RH) variation from 20 to 90%. The high humidity sensitivity is due to the protonic and electrolytic conduction between hydroxyl ions and water molecules adsorbed on the film surfaces with capillary nanopores.

Electrochemical Treatment of Pyrrhotite-rich Tailings–a Laboratory Study

Many sulphide minerals are semiconductors and are therefore amenable to electrochemical manipulation. Large scale massive sulphide bodies can act as solitary electrodes in electrochemical cells. In mill tailings, however, sulphide minerals occur as silt- to sand-sized particles. The present study was conducted to determine if the same in-situ electrochemical treatment system used for sulphide bodies might work on a tailings deposit that is greater than 75% pyrrhotite. The objective was achieved by determining two key factors: (1) the mechanism of charge transfer within tailings: electronic vs electrolytic and (2) where cathodic reductions reactions occur, ie., on the surface or within the tailings body. Results showed that electronic conduction predominated over electrolytic conduction in the tailings sample. Most of the reduction reactions took place at the outer surface of the tailings mass rather than within the tailings matrix. This study confirmed that the identified tailings deposit behaves as a single conductive body and is therefore a potential site for installation of an in-situ electrochemical treatment system.

Comparative study on micromorphology and humidity sensitive properties of thin-film and thick-film humidity sensors based on semiconducting MnWO 4

Based on our experience of developing thick-film MnWO 4 humidity sensors, a thin-film humidity sensor with nano-sized MnWO 4 grains has been fabricated using the sol–gel technique. The thin-film sensor shows smaller humidity sensitivity than that compared to a thick-film sensor. However, it exhibits a fast response to humidity change and also has a very low temperature coefficient within the temperature range of 20–60°C. The absence of capillary pores in the well defined thin-films makes water condensation, and hence electrolytic conduction, impossible. The physically adsorbed multi-layered water molecules on the surface of the thin sensing film play a dominating role for the humidity sensing mechanism. Studies on thin-film sensors based on MnO and WO 3 indicate that the W +6 sites in the hubnerite material contribute strongly to the humidity sensing mechanism.

Electrolytic conduction of silver metaphosphate glass until dielectric breakdown

Ac/dc bias was applied to gold- or silver-electroded AgPO3 glass samples at ∼150 °C. Dielectric breakdown took place with bias fields of ∼700 V/cm. Depth profiles of silver, gold, oxygen, and phosphorus were measured from the electrode surfaces by x-ray photoelectron spectroscopy. Electrolytic conduction of silver and others and field-induced injection of gold ions into glass from the gold anode were found.

Direct Electrowinning of Lead from Galena Concentrate Anode

Abstract Extraction of lead directly from galena anode has the advantage of eliminating a number of process steps as well as pollution. But inherent problems remain in using powder galena as an electrode. In the preceding years some important developments have taken place. Different electrolytes have been tested and reactions established. Compact anode fabrication has been possible. It has also been possible to identify specific instances of bed conduction and electrolytic conduction in case of suspended anode. Electrolyte as well as bed conditions suitable for electronic conduction that leads to electrolytic dissolution of lead from suspended galena anode have also been established. This paper critically analyses these aspects and presents some investigations examining the effect of temperature and current density in the overall process.

High‐resolution electromagnetic images of conducting zones in an upthrust crustal block

A high‐resolution, controlled‐source, electromagnetic survey in the Kapuskasing region, over exposed deep crustal material upthrust along ramp‐and‐flat geometry faults, reveals a shallow weakly‐conductive layer (5,000–10,000 Ω·m) within a resistive host (50,000–100,000 Ω·m). This layer, at ≈1 km depth, correlates spatially with a zone of enhanced reflectivity, and coincident breaks in both conductivity and reflectivity suggest that a high‐angle fault zone offsets the layer. The cause(s) of this enhanced conductivity is conjectural until this unit is drilled, but the two probable candidates are: (1) electrolytic conduction in saline‐filled porous rocks, or (2) ionic conduction along connected grain‐boundary films of graphite. Or both conduction mechanisms may be operating with the graphite interconnectivity provided by the brines.

Teaching conductometry: Another perspective

A presentation of the concepts of electrolytic conduction in a way that avoids the drawbacks of the typical, historical presentation.