Evaluation of a.c. conductivity of rubber ferrite composites from dielectric measurements

The effect of frequency, composition and temperature on the a.c. electrical conductivity were studied for the ceramic, Ni1–xZnxFe2O4, as well as the filler (Ni1–xZnxFe2O4) incorporated rubber ferrite composites (RFCs). Ni1–xZnxFe2O4 (where x varies from 0 to 1 in steps of 0×2) were prepared by usual ceramic techniques. They were then incorporated into a butyl rubber matrix according to a specific recipe. The a.c. electrical conductivity (sa.c.) calculations were carried out by using the data available from dielectric measurements and by employing a simple relationship. The a.c. conductivity values were found to be of the order of 10–3 S/m. Analysis of the results shows that sa.c. increases with increase of frequency and the change is same for both ceramic Ni1–xZnxFe2O4 and RFCs. sa.c. increases initially with the increase of zinc content and then decreases with increase of zinc. Same behaviour is observed for RFCs too. The dependence of sa.c. on the volume fraction of the magnetic filler was also studied and it was found that the a.c. conductivity of RFCs increases with increase of volume fraction of the magnetic filler. Temperature dependence of conductivity was studied for both ceramic and rubber ferrite composites. Conductivity shows a linear dependence with temperature in the case of ceramic samples

Dielectric and Conductivity Studies on Cobalt Phthalocyanine Tetramers

Electrically conductive organic and metalloorganic polymers are of great interest and they have applications in electronic, optical, photonic, photoelectric, electrochemical, and dielectric devices. Tetrameric cobalt phthalocyanine was prepared by conventional chemical method. The dielectric permittivity of the tetrameric cobalt phthalocyanine sample was evaluated from the observed capacitance values in the frequency range 100 KHz to 5 MHz and in the temperature range of 300 to 383°K. It is found that the system obeys the Maxwell Wagner relaxation of space charge phenomenon. Further, from the permittivity studies AC conductivity was evaluated. The values of AC conductivity and DC conductivity were compared. Activation energy was calculated. To understand the conduction mechanism Mott’s variable range hopping model was applied to the system. The T 1/4 behavior of the DC conductivity along with the values of Mott’s Temperature (T0), density of states at the Fermi energy N (EF), and range of hopping R and hopping energy W indicate that the transport of charge carriers are by three-dimensional variable range hopping

Composition Dependent Study of AC conductivity in AsSe samples

The room temperature AC conductivity σ(ω) of amorphous AsSe samples with various compositions have been measured in the 103 -106 Hz frequency range. The results indicate that ac conductivity is proportional to n with n=0.89±.01 in the 103 –106 Hz frequency range. Consideration of different models for the frequency –dependent conductivity leads to thermally activated hopping as the most likely process

Short-term effects of human urine fertiliser and wood ash on soil pH and electrical conductivity

The fertiliser value of human urine has been examined on several crops, yet little is known about its effects on key soil properties of agronomic significance. This study investigated temporal soil salinization potential of human urine fertiliser (HUF). It further looked at combined effects of human urine and wood ash (WA) on soil pH, urine-NH_3 volatilisation, soil electrical conductivity (EC), and basic cation contents of two Acrisols (Adenta and Toje series) from the coastal savannah zone of Ghana. The experiment was a factorial design conducted in the laboratory for 12 weeks. The results indicated an increase in soil pH by 1.2 units for Adenta series and 1 unit for Toje series after one week of HUF application followed by a decline by about 2 pH units for both soil types after twelve weeks. This was attributed to nitrification of ammonium to nitrate leading to acidification. The EC otherwise increased with HUF application creating slightly saline conditions in Toje series and non-saline conditions in Adenta series. When WA was applied with HUF, both soil pH and EC increased. In contrast, the HUF alone slightly salinized Toje series, but both soils remained non-saline whenWA and HUF were applied together. The application ofWA resulted in two-fold increase in Ca, Mg, K, and Na content compared to HUF alone. Hence, WA is a promising amendment of acid soils and could reduce the effect of soluble salts in human urine fertilizer, which is likely to cause soil salinity.

The effect of thermal conductivity of RIM moulds in kinetics cure

Reaction Injection Moulding (RIM) is a moulding technology used for the production of large size and complex plastic parts. The RIM process is characterized essentially by the injection of a highly reactive chemical system (usually polyurethane) and fast cure, in a mould properly closed and thermally controlled. Several studies show that rapid manufacturing moulds obtained in epoxy resins for Thermoplastic Injection Moulding (TIM) affect the moulding process and the final properties of parts. The cycle time and mechanical properties of final parts are reduced, due to a low thermal conductivity of epoxy materials. In contrast, the low conductivity of materials usually applied for the rapid manufacturing of RIM moulds, increase the mechanical properties of final injected parts and reduce the cycle time. This study shows the effect of the rapid manufacturing moulds material during the RIM process. Several materials have been tested for rapid manufacturing of RIM moulds and the analysis of both, temperature profile of moulded parts during injection and the cure data experimentally obtained in a mixing and reaction cell, allow to determine and model the real effect of the mould material on the RIM process.

An overview of Earth's global electric circuit and atmospheric conductivity

The Earth’s global atmospheric electric circuit depends on the upper and lower atmospheric boundaries formed by the ionosphere and the planetary surface. Thunderstorms and electrified rain clouds drive a DC current (∼1 kA) around the circuit, with the current carried by molecular cluster ions; lightning phenomena drive the AC global circuit. The Earth’s near-surface conductivity ranges from 10−7 S m−1 (for poorly conducting rocks) to 10−2 S m−1 (for clay or wet limestone), with a mean value of 3.2 S m−1 for the ocean. Air conductivity inside a thundercloud, and in fair weather regions, depends on location (especially geomagnetic latitude), aerosol pollution and height, and varies from ∼10−14 S m−1 just above the surface to 10−7 S m−1 in the ionosphere at ∼80 km altitude. Ionospheric conductivity is a tensor quantity due to the geomagnetic field, and is determined by parameters such as electron density and electron–neutral particle collision frequency. In the current source regions, point discharge (coronal) currents play an important role below electrified clouds; the solar wind-magnetosphere dynamo and the unipolar dynamo due to the terrestrial rotating dipole moment also apply atmospheric potential differences. Detailed measurements made near the Earth’s surface show that Ohm’s law relates the vertical electric field and current density to air conductivity. Stratospheric balloon measurements launched from Antarctica confirm that the downward current density is ∼1 pA m−2 under fair weather conditions. Fortuitously, a Solar Energetic Particle (SEP) event arrived at Earth during one such balloon flight, changing the observed atmospheric conductivity and electric fields markedly. Recent modelling considers lightning discharge effects on the ionosphere’s electric potential (∼+250 kV with respect to the Earth’s surface) and hence on the fair weather potential gradient (typically ∼130 V m−1 close to the Earth’s surface. We conclude that cloud-to-ground (CG) lightning discharges make only a small contribution to the ionospheric potential, and that sprites (namely, upward lightning above energetic thunderstorms) only affect the global circuit in a miniscule way. We also investigate the effects of mesoscale convective systems on the global circuit.

A double-Gerdien instrument for simultaneous bipolar air conductivity measurements on balloon platforms

A bipolar air conductivity instrument is described for use with a standard disposable meteorological radiosonde package. It is intended to provide electrical measurements at cloud boundaries, where the ratio of the bipolar air conductivities is affected by the presence of charged particles. The sensors are two identical Gerdien-type electrodes, which, through a voltage decay method, measure positive and negative air conductivities simultaneously. Voltage decay provides a thermally stable approach and a novel low current leakage electrometer switch is described which initiates the decay sequence. The radiosonde supplies power and telemetry, as well as measuring simultaneous meteorological data. A test flight using a tethered balloon determined positive (σ+) and negative (σ−) conductivities of σ+ = 2.77±0.2 fS m−1 and σ− = 2.82±0.2 fS m−1, respectively, at 400 m aloft, with σ+/σ− = 0.98±0.04.

Exploring the spatial relations between soil physical properties and apparent electrical conductivity

Relations between the apparent electrical conductivity of the soil (ECa) and top- and sub-soil physical properties were examined for two arable fields in southern England (Crowmarsh Battle Farms and the Yattendon Estate). The spatial variation of ECa and the soil properties was explored geostatistically. The variogram ranges showed that ECa varied on a similar spatial scale to many of the soil physical properties in both fields. Several features in the map of kriged predictions of ECa were also evident in maps of the soil properties. In addition, the correlation coefficients showed a strong relation between ECa and several soil properties. A moving correlation analysis enabled differences in the relations between ECa and the soil properties to be examined within the fields. The results indicated that relations were inconsistent; they were stronger in some areas than others. A regression of ECa on the principal component scores of the leading components for both fields showed that the first two components accounted for a large proportion of the variance in ECa, whereas the others accounted for little or none. For Crowmarsh topsoil sand and clay, loss on ignition and volumetric water measured in the autumn had large correlations on the first component, and for Yattendon they were large for topsoil sand and clay, and autumn and spring volumetric water. The cross-variograms suggested strong coregionalization between ECa and several soil physical properties; in particular subsoil sand and silt at Crowmarsh, and subsoil sand and clay at Yattendon. The structural correlations from the linear model of coregionalization confirmed the strength of the relations between ECa and the subsoil properties. Nevertheless, no one property was consistently important for both fields. Although a map of ECa can indicate the general patterns of spatial variation in the soil, it is not a substitute for information on soil properties obtained by sampling and analysing the soil. Nevertheless, it could be used to guide further sampling. (c) 2005 Elsevier B.V. All rights reserved.

In situ calibration of atmospheric air conductivity instruments

A new method of measuring the total conductivity of atmospheric air is described. It depends on determination of the electrical relaxation time of a horizontal wire, mounted between two insulators, which is initially grounded and then allowed to charge freely. The total air conductivity derived is compared with that from an ion mobility spectrometer. Results from the two techniques agreed to within 1.2 fS m(-1). (c) 2006 American Institute of Physics.

An overview of Earth’s global electric circuit and atmospheric conductivity

The Earth’s global atmospheric electric circuit depends on the upper and lower atmospheric boundaries formed by the ionosphere and the planetary surface. Thunderstorms and electrified rain clouds drive a DC current (∼1 kA) around the circuit, with the current carried by molecular cluster ions; lightning phenomena drive the AC global circuit. The Earth’s near-surface conductivity ranges from 10−7 S m−1 (for poorly conducting rocks) to 10−2 S m−1 (for clay or wet limestone), with a mean value of 3.2 S m−1 for the ocean. Air conductivity inside a thundercloud, and in fair weather regions, depends on location (especially geomagnetic latitude), aerosol pollution and height, and varies from ∼10−14 S m−1 just above the surface to 10−7 S m−1 in the ionosphere at ∼80 km altitude. Ionospheric conductivity is a tensor quantity due to the geomagnetic field, and is determined by parameters such as electron density and electron–neutral particle collision frequency. In the current source regions, point discharge (coronal) currents play an important role below electrified clouds; the solar wind-magnetosphere dynamo and the unipolar dynamo due to the terrestrial rotating dipole moment also apply atmospheric potential differences. Detailed measurements made near the Earth’s surface show that Ohm’s law relates the vertical electric field and current density to air conductivity. Stratospheric balloon measurements launched from Antarctica confirm that the downward current density is ∼1 pA m−2 under fair weather conditions. Fortuitously, a Solar Energetic Particle (SEP) event arrived at Earth during one such balloon flight, changing the observed atmospheric conductivity and electric fields markedly. Recent modelling considers lightning discharge effects on the ionosphere’s electric potential (∼+250 kV with respect to the Earth’s surface) and hence on the fair weather potential gradient (typically ∼130 V m−1 close to the Earth’s surface. We conclude that cloud-to-ground (CG) lightning discharges make only a small contribution to the ionospheric potential, and that sprites (namely, upward lightning above energetic thunderstorms) only affect the global circuit in a miniscule way. We also investigate the effects of mesoscale convective systems on the global circuit.

The role of copper in the thermal conductivity of thermoelectric oxychalcogenides: do lone pairs matter?

Understanding the underlying mechanisms that suppress thermal conduction in solids is of paramount importance for the targeted design of materials for thermal management and thermoelectric energy conversion applications. Bismuth copper oxychalcogenides, BiOCuQ (Q = Se, Te), are highly crystalline thermoelectric materials with an unusually low lattice thermal conductivity of approx. 0.5 Wm-1K-1, a value normally found in amorphous materials. Here we unveil the origin of the unusual thermal transport properties of these phases. First principles calculations of the vibrational properties combined with analysis of in-situ neutron diffraction data, demonstrate that weak bonding of copper atoms within the structure leads to an unexpected vibrational mode at low frequencies, which is likely to be a major contributor to the low thermal conductivity of these materials. In addition, we show that anharmonicity and the large Grüneisen parameter in these oxychalcogenides are mainly related to the low frequency copper vibrations, rather than to the Bi3+ lone pairs.

Evaluation of the pH and electrical conductivity in milk from jersey cows during the first month of lactation

In order to assess the influence of the colostrum period on pH and, electrical conductivity, we collected 418 milk samples from 127 Jersey cows. The samples were collected from healthy udders that did not present any bacterial growth in the microbiological examination. They were divided into eight groups as follows < 1/2 day; 1/2 and 1 degrees day; 2 degrees day; 3 degrees day; 4 degrees and 5 degrees day; 6 degrees and 7 degrees day; 8 degrees to 15 degrees day; 16 degrees to 30 degrees days of lactation. The samples were collected before milking and the following analyses were conducted: pH, electrical conductivity. In the first 24 hours of lactation, there was an reduction in electrical conductivity value, associated with an increase in pH value. We observed that transition of secretion from colostrum to milk, occurs during the first week of lactation; from 6(rd) day of lactation for pH value and 3(th) day for electrical conductivity value. We recommend the use the following figures as normal ranges for the first 24 hours of lactation (colostrum period): pH <= 6,51 and electrical conductivity <= 6,33 mS/cm; while for the interval between 2(nd) and 7(th) days of lactation (transition from colostrum to milk) we suggest the use of the values as normal ranges: pH <= 6,66 and electrical conductivity <= 5,93 mS/cm.

Magnetic resonance and conductivity study of gelatin-based proton conductor polymer electrolytes

This work report results from proton nuclear magnetic resonance (NMR), continuous-wave (CW-EPR) and pulsed electron paramagnetic resonance (P-EPR) and complex impedance spectroscopy of gelatin-based polymer gel electrolytes containing acetic acid. cross-linked with formaldehyde and plasticized with glycerol. Ionic conductivity of 2 x 10(-5) S/cm was obtained at room temperature for samples prepared with 33 wt% of acetic acid. Proton ((1)H) line shapes and spin-lattice relaxation times were measured as a function of temperature. The NMR results show that the proton mobility is dependent on acetic acid content in the plasticized polymer gel electrolytes. The CW-EPR spectra, which were carried out in samples doped with copper perchlorate, indicate the presence of the paramagnetic Cu(2+) ions in axially distorted sites. The P-EPR technique, known as electron spin echo envelope modulation (ESEEM), was employed to show the involvement of both, hydrogen and nitrogen atoms, in the copper complexation of the gel electrolyte. (C) 2009 Elsevier Ltd. All rights reserved.

NMR and conductivity study of gelatin-based polymer electrolytes

Nuclear Magnetic Resonance spectroscopy (NMR) and complex impedance spectroscopy have been used to study gelatin-based polymer electrolytes plasticized with glycerol and containing lithium perchlorate. The studied samples were prepared with salt concentration of 7.9 wt% and 10.3 wt%. Ionic conductivity of about 10(-5) S/cm was obtained at room temperature for both samples. Lithium (Li-7) and proton (H-1) lineshapes and spin-lattice relaxation times were measured as a function of temperature. The Li-7 NMR relaxation results indicate that the ionic mobility in this system is comparable to those found in other plasticized polymer electrolytes.