Rock/water interaction in dielectric properties: Experiments with hydrophobic sandstones

Geophysics ◽  
1995 ◽  
Vol 60 (2) ◽  
pp. 431-436 ◽  
Author(s):  
Rosemary Knight ◽  
Ana Abad
Keyword(s):  
Dielectric Constant ◽  
Dielectric Response ◽  
Water Saturation ◽  
Dielectric Behavior ◽  
Partially Saturated ◽  
Water Interaction ◽  
Water Wetting ◽  
Rock Water Interaction ◽  
Air System ◽  
Air Mixing

The dielectric constant of a partially saturated sandstone varies as a function of the level of water saturation. Experimental data indicate that rock/water interaction, at low saturations, has a large effect on the measured dielectric response. To theoretically predict the dielectric constant of the rock/water/air system, this rock/water interaction must be accounted for by including the effect of the water wetting the rock solid. Alternatively, if the rock/water interaction can be eliminated, a three‐component (dry rock, water, and air) mixing law can be used to model the dielectric behavior. In this laboratory study, a chemical treatment is used to change four water‐wet sandstones into hydrophobic sandstones. In three hydrophobic samples the rock/water interaction, seen in the data for the water‐wet samples, is eliminated and the dielectric constant of the partially saturated sandstones can be simply modeled as a dry rock/water/air system. This experimental study illustrates the importance of the chemical state of the rock surfaces in determining the dielectric behavior of sandstones.

Evidence for Antiferroelectric Behavior in KNbO3/KTaO3 Superlattices

2002 ◽  
Vol 720 ◽  
Author(s):  
J. Sigman ◽  
H. M. Christen ◽  
P. H. Fleming ◽  
L. A. Boatner ◽  
D. P. Norton
Keyword(s):  
Phase Transition ◽  
Dielectric Constant ◽  
Temperature Region ◽  
Dielectric Response ◽  
Nonlinear Response ◽  
Structural Phase ◽  
Dielectric Behavior ◽  
Ferroelectric Materials ◽  
Dc Bias ◽  
Superlattice Structures

AbstractThe dielectric response in artificially layered 1x1 KTaO3/KNbO3 perovskite superlattice structures is reported. While KTaO3 and KNbO3 are ferroelectric or paraelectric, respectively, superlattices appear antiferroelectric based on an increase in dielectric constant with applied dc bias. This “positive tunability” in dielectric response occurs at the same temperature region where a structural phase transition is observed. This dielectric behavior is inconsistent with the nonlinear response for either paraelectric or ferroelectric materials. However, an increase in the dielectric constant with applied electric field is consistent with antiferroelectric behavior. The antiferroelectric ordering correlates with cation modulation imposed by the superlattice.

scholarly journals The dielectric constant of sandstones, 60 kHz to 4 MHz

Geophysics ◽  
1987 ◽  
Vol 52 (5) ◽  
pp. 644-654 ◽  
Author(s):  
Rosemary J. Knight ◽  
Amos Nur
Keyword(s):  
Dielectric Constant ◽  
Surface Area ◽  
Dielectric Response ◽  
Water Saturation ◽  
Pore Space ◽  
Strong Dependence ◽  
Complex Impedance ◽  
Volume Ratio ◽  
Electrode Polarization ◽  
Frequency Range

Complex impedance data were collected for eight sandstones at various levels of water saturation [Formula: see text] in the frequency range of 5 Hz to 4 MHz. The measurements were made using a two‐electrode technique with platinum electrodes sputtered onto the flat faces of disk‐ shaped samples. Presentation of the data in the complex impedance plane shows clear separation of the response due to polarization at the sample‐electrode interface from the bulk sample response. Electrode polarization effects were limited to frequencies of less than 60 kHz, allowing us to study the dielectric constant κ′ of the sandstones in the frequency range of 60 kHz to 4 MHz. κ′ of all samples at all levels of saturation shows a clear power‐law dependence upon frequency. Comparing the data from the eight sandstones at [Formula: see text], the magnitude of the frequency dependence was found to be proportional to the surface area‐to‐volume ratio of the pore space of the sandstones. The surface area‐to‐volume ratio of the pore space of each sandstone was determined using a nitrogen gas adsorption technique and helium porosimetry. κ′ also exhibits a strong dependence on [Formula: see text]. κ′ increases rapidly with [Formula: see text] at low saturations, up to some critical saturation above which κ′ increases more gradually and linearly with [Formula: see text]. Using the surface area‐to‐volume ratios of the sandstones, the critical saturation in the dielectric response was found to correspond to water coverage of approximately 2 nm on the surface of the pore space. Our interpretation of the observed dependence of κ′ on both frequency and [Formula: see text] is that it is the ratio of surface water to bulk water in the pore space of a sandstone that controls the dielectric response through a Maxwell‐Wagner type of mechanism.

Non-Destructive Evaluation of Engineering Properties of Asphalt Mixtures

2013 ◽  
Vol 723 ◽  
pp. 428-433
Author(s):  
Chieh Min Chang ◽  
Jian Shiuh Chen
Keyword(s):  
Dielectric Constant ◽  
Dielectric Response ◽  
Asphalt Mixture ◽  
Dielectric Behavior ◽  
Engineering Properties ◽  
Asphalt Pavements ◽  
Electromagnetic Devices ◽  
High Dielectric ◽  
Non Destructive ◽  
Coaxial Probe

The measurement of dielectric response has gained importance because it can be used for non-destructive monitoring of asphalt pavements. The open-ended coaxial probe technique was selected to investigate the dielectric response of the dense-graded asphalt mixture. The effects of material properties such as density on dielectric response were examined. Results indicated that density have a significant influence on dielectric behavior of asphalt mixture. The dielectric constant was shown to increase with increasing density of the asphalt mixture, whereas a high density resulted in low voids that contributed to a relatively high dielectric constant. These findings could be used to enhance the accuracy of non-destructive electromagnetic devices applied in the pavement field.

Influence of Ca-Doping on Structural, Magnetic and Dielectric Properties of Ba3Co2-xCaxFe24O41 Hexaferrite Powders

2015 ◽  
Vol 241 ◽  
pp. 226-236 ◽  
Author(s):  
Neha Solanki ◽  
Rajshree B. Jotania
Keyword(s):  
Dielectric Constant ◽  
Dielectric Properties ◽  
Sol Gel ◽  
Calcium Content ◽  
Combustion Method ◽  
Dielectric Behavior ◽  
Dielectric Parameters ◽  
Ca Doping ◽  
Auto Combustion ◽  
Magnetic And Dielectric Properties

Influence of Ca substitution on structural, magnetic and dielectric properties of Ba3Co2-xCaxFe24O41(where x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0), prepared by Sol-Gel auto-combustion method, has been investigated in present studies. The obtained powder was sintered at 950 oC for 4 hrs. in the static air atmosphere. Structural analysis of Ca-doped Ba3Co2-xCaxFe24O41powders revealed pure Z-type hexaferrite phase at low temperature. The frequency dependent dielectric constant (Єʹ) and magnetic properties such as remanent magnetization (Mr), saturation magnetization (Ms) and coercivity (Hc) were studied. It is observed that coercivity increased gradually with increase in calcium content. The real dielectric constant (Єʹ) and dielectric loss tangent (tan δ) were studied in the frequency range of 20Hz to 2MHz. The dielectric parameters for all samples show normal dielectric behavior as observed in hexaferrites. Contents of Paper

COMPARATIVE STUDY OF DIELECTRIC BEHAVIOR OF Mn0.4Zn0.6Fe2O4 NANOFERRITE BY CITRATE PRECURSOR METHOD

2008 ◽  
Vol 22 (16) ◽  
pp. 2537-2544 ◽  
Author(s):  
PREETI MATHUR ◽  
ATUL THAKUR ◽  
M. SINGH
Keyword(s):  
Particle Size ◽  
Dielectric Constant ◽  
Comparative Study ◽  
Average Particle Size ◽  
Dielectric Behavior ◽  
Average Particle ◽  
Oxidizing Agent ◽  
Precursor Method ◽  
Citrate Precursor ◽  
Citrate Precursor Method

In the present work, comparative study of the dielectric behavior of Mn 0.4 Zn 0.6 Fe 2 O 4 ferrite synthesized with and without H 2 O 2 (hydrogen peroxide) has been presented. The dc resistivity has been improved by the citrate precursor method as compared to the ceramic method, and it is further improved by the addition of H 2 O 2, which acts as a strong oxidizing agent. We have shown by means of X-ray diffraction that the resulting ferrite is made up of nanocrystallites and the average size of these nanocrystallites–calculated by Scherrer's formula–depends on the polarizer. The average particle size was found to be ~70 nm with H 2 O 2 and ~88 nm without H 2 O 2. The particle size is further confirmed by scanning electron microscopy. Both the results are found to be in good agreement. The decrease in dielectric constant and dielectric loss factor by addition of oxidizing agent is justified by inverse proportionality between the resistivity and dielectric constant. Possible mechanisms contributing to these processes have been discussed.

ON THE DIELECTRIC BEHAVIOR OF LiCo3/5Fe2/5VO4 CERAMICS

2010 ◽  
Vol 24 (07) ◽  
pp. 665-670
Author(s):  
MOTI RAM
Keyword(s):  
Activation Energy ◽  
Dielectric Constant ◽  
Frequency Dependence ◽  
Chemical Method ◽  
Arrhenius Plot ◽  
Dielectric Behavior ◽  
Tangent Loss ◽  
Low Frequencies ◽  
Different Temperatures ◽  
Tan Δ

The LiCo 3/5 Fe 2/5 VO 4 ceramics has been fabricated by solution-based chemical method. Frequency dependence of the dielectric constant (εr) at different temperatures exhibits a dispersive behavior at low frequencies. Temperature dependence of εr at different frequencies indicates the dielectric anomalies in εr at Tc (transition temperature) = 190°C, 223°C, 263°C and 283°C with (εr) max ~ 5370, 1976, 690 and 429 for 1, 10, 50 and 100 kHz, respectively. Frequency dependence of tangent loss ( tan δ) at different temperatures indicates the presence of dielectric relaxation in the material. The value of activation energy estimated from the Arrhenius plot of log (τd) with 103/T is ~(0.396 ± 0.012) eV.

Numerical Modeling of Multi-Frequency Complex Dielectric Permittivity Dispersion of Sedimentary Rocks

Geophysics ◽  
2021 ◽  
pp. 1-69
Author(s):  
Artur Posenato Garcia ◽  
Zoya Heidari
Keyword(s):  
Numerical Simulation ◽  
Dielectric Permittivity ◽  
Numerical Simulations ◽  
Dielectric Response ◽  
Water Saturation ◽  
Pore Scale ◽  
Simulation Results ◽  
Wet Rocks ◽  
Permittivity Measurements ◽  
The Impact

The dielectric response of rocks results from electric double layer (EDL), Maxwell-Wagner (MW), and dipolar polarizations. The EDL polarization is a function of solid-fluid interfaces, pore water, and pore geometry. MW and dipolar polarizations are functions of charge accumulation at the interface between materials with contrasting impedances and the volumetric concentration of its constituents, respectively. However, conventional interpretation of dielectric measurements only accounts for volumetric concentrations of rock components and their permittivities, not interfacial properties such as wettability. Numerical simulations of dielectric response of rocks provides an ideal framework to quantify the impact of wettability and water saturation ( Sw) on electric polarization mechanisms. Therefore, in this paper we introduce a numerical simulation method to compute pore-scale dielectric dispersion effects in the interval from 100 Hz to 1 GHz including impacts of pore structure, Sw, and wettability on permittivity measurements. We solve the quasi-electrostatic Maxwell's equations in three-dimensional (3D) pore-scale rock images in the frequency domain using the finite volume method. Then, we verify simulation results for a spherical material by comparing with the corresponding analytical solution. Additionally, we introduce a technique to incorporate α-polarization to the simulation and we verify it by comparing pore-scale simulation results to experimental measurements on a Berea sandstone sample. Finally, we quantify the impact of Sw and wettability on broadband dielectric permittivity measurements through pore-scale numerical simulations. The numerical simulation results show that mixed-wet rocks are more sensitive than water-wet rocks to changes in Sw at sub-MHz frequencies. Furthermore, permittivity and conductivity of mixed-wet rocks have weaker and stronger dispersive behaviors, respectively, when compared to water-wet rocks. Finally, numerical simulations indicate that conductivity of mixed-wet rocks can vary by three orders of magnitude from 100 Hz to 1 GHz. Therefore, Archie’s equation calibrated at the wrong frequency could lead to water saturation errors of 73%.

scholarly journals Dielectric Properties of the System GdCo1-xFexO3Synthesized by Chemical Route (x = 0.10, 0.20)

2006 ◽  
Vol 3 (4) ◽  
pp. 313-328
Author(s):  
K. D. Mandal ◽  
L. Behera
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Dielectric Constant ◽  
Chemical Method ◽  
Perovskite Oxides ◽  
Space Charge Polarization ◽  
Dielectric Behavior ◽  
Dielectric Parameters ◽  
Chemical Route ◽  
Scanning Electron

The perovskite oxides GdCo1-xFexO3(x = 0.10, 0.20) were prepared by chemical method. The dielectric behavior of compositions with x = 0.10 and 0.20 in the system GdCo1-xFexO3was studied in the temperature range 300-500 K. It is observed that dielectric constant increases with increasing Fe2+ions concentration. The frequency dependence of dielectric constant in these materials indicates that space charge polarization contributes significantly to their observed dielectric parameters. A uniform distribution of grains is observed from the microstructure by Scanning electron microscopy.

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