Initial Permeability Increase Research Articles

Structural and magnetic properties of nanostructured Li–Ni–Co ferrite prepared by sol–gel method

Li–Ni–Co ferrite samples with compositional formula Li[Formula: see text]Ni[Formula: see text]Co[Formula: see text]Fe[Formula: see text]O4 with [Formula: see text] ranging from 0.00 to 0.1 in steps of 0.02 were prepared by sol–gel method. X-ray diffraction (XRD) analysis confirmed the formation of single phase with spinel structure in all the samples. The lattice constant evaluated from XRD data was found to increase with increase of Co[Formula: see text] substitution and crystallite size was observed in the range of 30–59 nm. The microstructure of the samples was studied by using scanning electron microscopy (SEM). Nanocrystalline nature of ferrites was also confirmed by transmission electron microscopy (TEM). [Formula: see text]–[Formula: see text] measurements were made using a vibrating sample magnetometer and hysteresis parameters such as saturation magnetization and coercivity were obtained for all compositions. The frequency variations of initial permeability and permeability loss showed a dispersive behavior for all compositions and an increase in initial permeability is observed with increase of Co[Formula: see text] substitution. The results obtained and mechanisms involved are discussed in the paper.

Responses of antioxidant defense system of epilithic mosses to drought stress in karst rock desertified areas

Barbula fallax Hedw., Erythrodontium julaceum (Schwaegr.) Par., and Bryum argenteum Hedw. are typical rock mosses growing on rocks in different terrestrial habitats. In this study, B. fallax and E. julaceum, which are epilithic mosses growing in rock desertification in Guizhou, China, were used as ecophysiological mosses in a combination of field investigations and laboratory experiments. We also investigated the reference moss B. argenteum, which is a widely distributed moss in habitats with soil as substrate. Our research focused on the response of the antioxidant defense system of epilithic mosses to drought stress. Most antioxidant defense indicators increased initially, then declined at later stages of drought stress. In contrast, the carotenoid content increased constantly. In addition, there was an initial increase (albeit variable) in relative membrane permeability, with this parameter showing a parabolic trend in all of the epilithic mosses. Among the three species, E. julaceum demonstrated the strongest resistance followed by B. fallax and then by B. argenteum. The epilithic mosses displayed stronger resistance compared to the native mosses; the increase in O 2 -· content and other reactive oxygen species (ROS) at the early stage of drought stress induced the enzymatic and non-enzymatic scavenging systems to sequester ROS. Moreover, the radical scavenging ability and strong drought tolerance was maintained. The long-term growth of bryophyte under drought conditions in a karst environment can help eliminate the intense response of mosses to drought stress as they adapt.

Improvement of the magnetic properties of Li–Zn ferrite by Bi3+ substitution

The effect of Bi-substitution on the physical and magnetic properties of Li0.3Zn0.4BixFe2.3−xO4 ferrites (x = 0.0, 0.02, 0.05 and 0.075), prepared by the standard ceramic method, has been studied. It is found that the saturation magnetization and the initial permeability increase up to x = 0.05 and then decrease. On the other hand, the Curie temperature decreases with increasing x. In addition, the dc electrical resistivity increases with increasing Bi-content (x) which was discussed and explained.

Tuning of magnetoelectric coupling in (1−y)Bi0.8Dy0.2FeO3–yNi0.5Zn0.5Fe2O4 multiferroic composites

Magnetoelectric composites (1−y)Bi0.8Dy0.2FeO3 (BDFO)–yNi0.5Zn0.5Fe2O4 (NZFO) with y=0.0, 0.1, 0.2, 0.3, 0.4, 0.5 and 1.0 are synthesized by conventional solid state reaction route. The X-ray diffraction analysis confirms the coexistence of orthorhombic perovskite BDFO and spinel NZFO phases with no third phase. Microstructural and surface morphology are studied by Field Emission Scanning Electron Microscopy. Quantitative elemental analysis of the samples is carried out by Energy Dispersive X-ray Spectroscopy. The real part of the initial permeability increases and relative quality peak broadens with the ferrite content in the composites. Dielectric constant, loss tangent, relative quality factor and ac conductivity are measured as a function of frequency at room temperature. The dielectric constant shows usual dielectric dispersion at lower frequencies due to Maxwell–Wagner type interfacial polarization. The complex impedance spectroscopy is used to distinguish between the grain and grain boundary contribution to the total resistance. The modulus study reveals the ease of polaron hopping and negligibly small contribution of electrode effect. The magnetic hysteresis has been studied to know the response of NZFO phase to the applied magnetic field in the composite. The saturation and remanent magnetization are found to increase with increase in NZFO in the composite. The magnetoelectric voltage coefficient, αME is measured as a function of applied dc magnetic field. The tuning of ferrite percentage and dc magnetic field results in highest αME (~66mV/cmOe) for the composite with 40% NZFO at 4.7kOe which is attributed to the enhanced mechanical coupling between the two phases. The incorporation of BDFO and NZFO enhances the multiferroic properties in the present composite which are quite promising from application point of view.

Enhanced multiferroic properties in (1–y)BiFeO3–yNi0.50Cu0.05Zn0.45Fe2O4 composites

Multiferroic composites (1–y)BiFeO3–yNi0.50Cu0.05Zn0.45Fe2O4 (y=0.0, 0.1, 0.2, 0.3 and 0.4) are synthesized by the standard solid state reaction method. The X-ray diffraction analysis affirms the formation of both the component phases and also reveals that there is no chemical reaction between them. From the energy-dispersive X-ray spectroscopy study it is observed that the percentage of the elements in the component phases is well consistent with the nominal composition of the composites. Field Emission Scanning Electron Microscopy analysis shows almost homogeneous mixture of the two phases. The real part of the initial permeability increases (up to 67%) and the loss decreases with the ferrite content in the composites which is important in application point of view. Dielectric constant (ε′), loss tangent and AC conductivity are measured as a function of frequency at room temperature. The highest ε′ is obtained for 0.6BiFeO3–0.4Ni0.50Cu0.05Zn0.45Fe2O4 composite. The dielectric dispersion at lower frequency (<105Hz) is due to the interfacial polarization. The complex impedance spectroscopy is used to correlate between the electrical properties of the studied samples with their microstructures. Two semicircular arcs corresponding to both grain and grain boundary contribution to electrical properties have been observed in all the studied samples. The maximum magnetoelectric voltage coefficient is found to be ∼38mVcm−1Oe−1 for the composite with 80% ferroelectric+20% ferrite phases. The present composite might be a promising candidate as multiferroic materials showing effective electric and magnetic properties.

Dependence of gas shale fracture permeability on effective stress and reservoir pressure: Model match and insights

Although permeability data for different gas shales have been reported previously and attempts have been made to match permeability with empirical correlations, theoretical studies of shale permeability modelling are lacking. In this work, the correlation between fracture permeability and effective stress is established for gas shales through theoretical derivation. This model is able to match the permeability data for different gas shales. The matching results for the gas shale studied show that the model coefficient, fracture compressibility, which decreases as initial shale permeability increases, is strongly affected by the flow directions and varies with the shale’s mineralogical composition. Furthermore, the correlation between fracture permeability and reservoir pressure has also been established. Sensitivity study shows that fracture permeability may decrease significantly with the reservoir pressure drawdown. Moreover, the horizontal fracture permeability drop is found to be significantly affected by the Young’s modulus’ anisotropic ratio (Eh/Ev). The insights gained warrant further theoretical and experimental studies to evaluate shale fracture permeability.

Magnetoelectric effect of (1−x) Ba0.5Sr0.5Zr0.5Ti0.5O3+(x) Ni0.12Mg0.18Cu0.2Zn0.5Fe2O4 composites

The magnetoelectric composites with chemical compositions (1−x) Ba0.5Sr0.5Zr0.5Ti0.5O3+(x) Ni0.12Mg0.18Cu0.2Zn0.5Fe2O4 (x=20, 40, 60 and 80wt%) was prepared by the conventional solid state reaction method. The presence of a biphase composition was confirmed by X-ray diffraction while the microstructure of the composites was studied by scanning electron microscopy revealing a good mixing of the two phases and a good densification of the bulk ceramics. The dielectric dispersion is observed at lower frequencies due to interfacial polarization arising from the interface of the two phases. At higher frequencies, the dielectric constant is almost constant due to the inability of electric dipoles to follow the first variation of the alternating applied electric field. The dielectric loss shows maxima which are attributed when the hopping frequency of electrons between different ionic sites becomes nearly equal to the frequency of the applied field. The linearity in the log(σAC) vs. log(ω2) plots confirmed the small polaron hopping type of conduction mechanism. The composite materials are found to exhibit an excellent frequency dependence of magnetic properties. In the high frequency range, with increasing ferrite concentration the initial permeability increases and cut-off frequency decreases. An optimal magnetoelectric coupling responding voltage of about 600μVcm−1Oe−1 is obtained for x=20wt% at room temperature.

Electrical and magnetic properties of Fe-based bulk metallic glass with minor Co and Ni addition

The effect of minor Co and Ni alloying on soft magnetic properties and electrical resistivity of Fe75.5C7.0Si3.3B5.5P8.7 (at%) bulk metallic glass has been investigated. Within examined compositional range (Co and Ni up to 4 at%, respectively), the saturation magnetization and electrical resistivity of the alloys continuously decrease with increasing Co or Ni content, while the Curie temperature and initial permeability increase. Comparing the effect of Co and Ni additions, the alloys with Co addition have much higher Curie temperature and saturation magnetization than the alloy with Ni addition. Also, the Co-added alloys show smaller coercivity and larger permeability than the Ni-added alloys. The present results suggest that minor addition of Co can provide better effectiveness to enhance the magnetic softness of Fe-based BMGs than minor Ni addition.

Influence of sintering temperature on electrical and dielectric properties of Mn (1 %) added MgCuZn ferrites

Polycrystalline samples of Mn (1 %) added MgCuZn ferrites have been prepared by conventional solid-state synthesis. Samples have been sintered at different temperatures in the range of 975–1175 °C for 10 h, followed by characterization by X-ray diffraction (XRD) and field emission scanning electron microscope. XRD results reveal that all samples are single phase with spinel structure. Lattice constant increases slightly with increase in sintering temperature. Bulk density and grain size increase with increase in sintering temperature, from 4.61 g/cm3 and 2.2 μm at 975 °C to 4.99 g/cm3 and 8.8 μm at 1175 °C. DC electrical resistivity decreases and dielectric constant and initial permeability increase with an increase in sintering temperature. These results suggest that sintering temperature has a prominent effect on the electrical properties.

Analysis of the complex permeability of NiCuZn ferrites up to 1GHz with regard to Cu content and sintering temperature

Abstract We have studied the frequency dependent permeability of Ni 0.60− x Cu x Zn 0.40 Fe 1.98 O 4 ferrites ( x =0, 0.10, 0.20, 0.30) with regard to the Cu concentration and the undergone heat treatment. To this end, single-phase magnetic ceramics were prepared and characterized in terms of the reversible complex permeability μ ⁎ ( f ) in the 100 kHz to 1 GHz frequency range. The μ ⁎ ( f ) spectra are analyzed into three elementary magnetization processes with changing weight factors as Cu content or sintering temperature T SINT increase. In fact, in addition to the spin rotation relaxation at 150–400 MHz we initially identify the contribution from reversible domain wall bowing rising at 20–80 MHz. For higher Cu content or T SINT , the latter mechanism is suppressed to the benefit of reversible wall displacement in the range below 1 MHz. Concerning particularly the domain wall motion, system dynamics theory and least-squares curve fitting of μ ⁎ ( f ) spectra were employed to distinguish between the high-frequency underdamped resonance (d. wall bowing) and the lower frequency overdamped relaxation dispersions (d. wall displacement). This distinction originates in the microstructural variance between the pinned low-energy domain walls in individual small grains and the cooperative rigid high-energy walls in large grains, respectively. The relevant transition of morphology in NiCuZn ferrites, induced by Cu substitution or by high T SINT , is identified through SEM observation and accords with the experimental results of dilatometry and density measurements. The remarked densification process is reflected on the increase of initial permeability as well. Moreover, on the basis of the recorded B – H loops we derive that the maximum induction B MAX follows the density variation of sintered specimens, contrarily to the coercive field H C which is significantly decreased when magnetic domain walls appear.

Removal of Near-wellbore Formation Damage by Ultrasonic Stimulation

The plugging removal effect under ultrasonic waves and the effect of rock properties, technical parameters, and ultrasonic parameters on the cleaning results were studied using the self-developed dynamic flow apparatus and the artificial cores damaged by in situ fines, inorganic scale, drilling mud, paraffin deposition, and polymer. The experimental results proved that ultrasonic cleaning is the most effective to inorganic scale damage, and the optimum ultrasonic irradiation time is about 80–100 min. In addition, for the five types of damage, the increase of ultrasonic frequency and power drastically improve the permeability recovery rate. The results also indicated that, in in situ fines and inorganic scale experiments, the increase of initial core permeability increases the cleaning effect, and the trend is opposite in drilling mud, paraffin deposition, and polymer experiments.

Increase in initial permeability due to substitution of high spin cations in nanocrystalline Ni–Mg ferrites

In order to increase the permeability, high spin Mn2+ substituted nanocrystalline Ni0.50−xMnxMg0.5Fe2O4 were synthesized by the combustion technique. Mn2+ substitution acts as an accelerator of grain growth and uniform grain distribution in these chemical compositions. Both the real part of initial permeability and the saturation magnetization increase with increasing Mn content up to x=0.30 and they decrease for higher Mn2+ content indicating the possibility of a non-collinear spin arrangement between tetrahedral and octahedral sites. The maximum increase of initial permeability is 54% compared to that of parent composition. The weakening of exchange interaction may be confirmed by increasing lattice parameter and decreasing Néel temperature with increasing Mn2+ content.

Structural and Magnetic Properties of Mn&amp;lt;sub&amp;gt;0.50-x&amp;lt;/sub&amp;gt;Zn&amp;lt;sub&amp;gt;0.50&amp;lt;/sub&amp;gt;Cu&amp;lt;sub&amp;gt;x&amp;lt;/sub&amp;gt;Fe&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt;

Mn0.50-xZn0.50CuxFe2O4 (where x = 0.0 - 0.3) ferrites have been synthesized by auto combustion method. X-ray diffraction patterns reveal that all compositions are of single phase cubic spinel structure. The lattice parameter decreases with the increase in Cu2+ content obeying the Vegard’s law. The bulk density, average grain size, initial permeability, Néel temperature and saturation magnetic induction of Mn0.50-xZn0.50CuxFe2O4 increased with increasing Cu2+content. It is observed that both density and initial permeability increase with increasing sintering temperature. The maximum initial permeability is found to be 1061 which is almost four times greater than that of the parent composition. The resonance frequency of all the samples shifts towards the lower frequency as the permeability increases with Cu2+ content. It is observed from B-H loops of Mn0.50-xZn0.50CuxFe2O4 that coercivity decreases and retentivity increases with Cu2+ content. Possible explanations for the observed magnetic properties with various Cu2+ contents are discussed.

Deformation and failure mechanism of phyllite under the effects of THM coupling and unloading

Although the study of TM (Thermo -Mechanics), HM (Hydraulic — Mechanics) and THM (Thermo — Hydraulic — Mechanics) coupling under a loading test have been under development, rock failure analysis under THM coupling and unloading is an emerging topic. Based on a high temperature triaxial unloading seep test for phyllite, this paper discusses the deformation and failure mechanism of phyllites under the “H↔M, T→H, T→M” incomplete coupling model with unloading conditions. The results indicate that the elastic modulus and initial permeability decrease and the Poisson’s ratio increases with increasing temperature; the elastic modulus decreases and the Poisson’s ratio and initial permeability increase with increasing water pressure. During the unloading process, rock penetrability is small at the initial elastic deformation phase, but the penetrability increases near the end of the elastic deformation phase; mechanisms involving temperature and water pressure affect penetrability differently. Phyllite failure occurs from the initial thermal damage of the rock materials, splitting and softening (which is caused by pore water pressure), and the pressure difference which is formed from the loading axial pressure and unloading confining pressure. The phyllite failure mechanism is a transtensional (tension — shearing) failure.

Influence of Li substitution on structural and magnetic properties of LixNi0.2Mg0.8−2xFe2+xO4

The structural and magnetic properties of polycrystalline LixNi0.2Mg0.8−2xFe2+xO4 (where x=0.00, 0.10, 0.20, 0.30 and 0.40) synthesized by the conventional solid state reaction method is reported. The X-ray diffraction patterns reveal that these compositions are single phase having spinel structure. Lattice constants of the compositions are found to decrease with increasing Li content. The bulk density and average grain diameter are observed to increase with increasing Li content for a fixed sintering temperature and also increase with increasing sintering temperature for a fixed chemical composition. As sintering temperature goes higher, porosity decreases and real part of the initial permeability increases. Increase of initial permeability is more than double (66) compared to parent composition (31). The saturation magnetization at room temperature is found to increase with increasing Li content due to the modification of cations distributions. The observed features of lattice constant, density, microstructure, initial permeability and DC magnetization of the investigated compositions are explained.

Reentrant spin glass behavior and large initial permeability of Co0.5−xMnxZn0.5Fe2O4

A series of polycrystalline ferrites having nominal chemical composition Co0.50−xMnxZn0.5Fe2O4 (0<x<0.4) have been synthesized by the solid-state reaction technique. The XRD analysis confirms single phase cubic spinel structure for all compositions. Lattice constant increases from 0.84195 to 0.84429nm with the increasing Mn content and obeys Vegard's law. The average grain size increases by increasing both Mn content and sintering temperatures. Room temperature saturation magnetization increases for x=0.1 and decreases for increasing Mn content. The coercivity decreases with increasing Mn content due to the decrease of anisotropy constant. A reentrant spin glass behavior of these samples is observed from the zero field cooled magnetization measurements. The real part of the initial permeability increases by increasing both Mn content and sintering temperatures. This is due to the homogeneous grain growth and densification of the ferrites. The highest initial permeability 137 is observed for x=0.4 sintered at 1573K on the other hand, the highest relative quality factor (2522) is obtained for the sample Co0.2Mn0.3Zn0.5Fe2O4 sintered at 1523K. The Mn substituted Co0.50−xMnxZn0.5Fe2O4 ferrites showed improved magnetic properties.

Opposing Effects of the Angiopoietins on the Thrombin-Induced Permeability of Human Pulmonary Microvascular Endothelial Cells

BackgroundAngiopoietin-2 (Ang-2) is associated with lung injury in ALI/ARDS. As endothelial activation by thrombin plays a role in the permeability of acute lung injury and Ang-2 may modulate the kinetics of thrombin-induced permeability by impairing the organization of vascular endothelial (VE-)cadherin, and affecting small Rho GTPases in human pulmonary microvascular endothelial cells (HPMVECs), we hypothesized that Ang-2 acts as a sensitizer of thrombin-induced hyperpermeability of HPMVECs, opposed by Ang-1.Methodology/Principal FindingsPermeability was assessed by measuring macromolecule passage and transendothelial electrical resistance (TEER). Angiopoietins did not affect basal permeability. Nevertheless, they had opposing effects on the thrombin-induced permeability, in particular in the initial phase. Ang-2 enhanced the initial permeability increase (passage, P = 0.010; TEER, P = 0.021) in parallel with impairment of VE-cadherin organization without affecting VE-cadherin Tyr685 phosphorylation or increasing RhoA activity. Ang-2 also increased intercellular gap formation. Ang-1 preincubation increased Rac1 activity, enforced the VE-cadherin organization, reduced the initial thrombin-induced permeability (TEER, P = 0.027), while Rac1 activity simultaneously normalized, and reduced RhoA activity at 15 min thrombin exposure (P = 0.039), but not at earlier time points. The simultaneous presence of Ang-2 largely prevented the effect of Ang-1 on TEER and macromolecule passage.Conclusions/SignificanceAng-1 attenuated thrombin-induced permeability, which involved initial Rac1 activation-enforced cell-cell junctions, and later RhoA inhibition. In addition to antagonizing Ang-1, Ang-2 had also a direct effect itself. Ang-2 sensitized the initial thrombin-induced permeability accompanied by destabilization of VE-cadherin junctions and increased gap formation, in the absence of increased RhoA activity.

Sintering Temperature Dependent Permeability of Nanocrystalline &lt;i&gt;Ni&lt;sub&gt;0.20&lt;/sub&gt;Cu&lt;sub&gt;0.30&lt;/sub&gt;Zn&lt;sub&gt;0.50&lt;/sub&gt;Fe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;4&lt;/sub&gt;&lt;/i&gt; Ferrite

The spinel ferrite of Ni0.20Cu0.30Zn0.50Fe2O4 was studied at room temperature using X-ray diffraction pattern prepared by auto combustion technique. The analysis of the XRD patterns showed that the sample has a single phase cubic spinel structure. The bulk density, average grain size and initial permeability increase with increasing sintering temperature up to a optimum temperature. Beyond that temperature all those properties decreases. The value of relative quality factor decreases with increasing sintering temperature. The DC magnetization measurement showed that at room temperature the sample is in ferrimagnetic state. The number of Bohr magneton, n(?B), Néel temperature, TN, and the field at which saturation occurs were also calculated and possible explanation for the observed characteristics of microstructure, initial permeability, DC magnetization, and Néel temperature of the studied sample are presented.DOI: http://dx.doi.org/10.3329/jbas.v35i1.7972Journal of Bangladesh Academy of Sciences, Vol.35, No.1, 67-75, 2011

Magnetic properties and DC electrical resistivity studies on cadmium substituted nickel–zinc ferrite system

Polycrystalline Ni0.65−xCdxZn0.35Fe2O4 ferrites with x varying from 0.00 to 0.20 in steps of 0.04 have been prepared by conventional ceramic route. Calcination and sintering of samples were performed at 950 and 1250°C for 4 and 2h, respectively. The prepared samples were characterized by powder X-ray diffraction. The observed modifications in structure and increase in lattice constant are attributed to the difference in ionic radius of substituted Cd2+ ion and displaced Ni2+ ion. The room temperature specific saturation magnetization and Curie temperature are observed to decrease continuously with decrease in cadmium content and are attributed to the decline of A–B exchange interaction. The monotonic increase in initial permeability and decrease in magnetic loss are observed with cadmium concentration. An increase in dc electrical resistivity is observed up to x=0.12 of cadmium followed by a continuous decrease. The variation of electrical resistivity with temperature was measured in the temperature range of RT–140°C and the corresponding activation energies for conduction obtained from the logρ vs 1/T graphs.

Carbon dioxide plasticization and conditioning effects in thick vs. thin glassy polymer films

Recent studies have shown that thin glassy polymer films undergo physical aging more rapidly than thick films. This suggests that thickness may also play a role in the plasticization and conditioning responses of thin glassy films in the presence of highly-sorbing penetrants such as CO2. In this paper, a carefully designed systematic study explores the effect of thickness on the CO2 plasticization and conditioning phenomena in Matrimid®, a polyimide commonly used in commercial gas separation membranes. Thin films are found to be more sensitive than thick films to CO2 exposure, undergoing more extensive and rapid plasticization at any pressure. The response of glassy polymers films to CO2 is not only dependent on thickness, but also on aging time, CO2 pressure, exposure time, and prior history. Finally, thin films experiencing constant CO2 exposure for longer periods of time exhibit an initial large increase in CO2 permeability, which eventually reaches a maximum, followed by a significant decrease in permeability for the duration of the experiment. Thick films, in contrast, do not seem to exhibit this trend for the range of conditions explored.