Low Initial Permeability Research Articles

The effects of Nb 2 O 5 and TiO 2 on electrical and magnetic properties of Mn‐Zn ferrites

Mn-Zn ferrites among iron oxide magnetic materials are widely used for high frequency magnetic core materials because they have low power loss and high initial permeability up to several MHz range. In this paper, the small amount of Nb2O5 and TiO2 were added to the Mn-Zn ferrites to study their effects on electrical and magnetic properties of the Mn-Zn ferrites. The amount of Nb2O5 and TiO2 was in the range of 0 ∼0.02 wt% and 0–0.6 wt% respectively. The effects of additives were studied in view of change in core loss, maximum flux density, specific resistivity, inductance and permeability. Adding both TiO2 (0.6wt%) and Nb2O5 (0.01wt %), the core loss was lowest. It was decreased to 50% at 500 kHz. In this case, the maximum flux density was depressed by only 2%. This means that the additives could drastically decrease the minimum core loss with penalty of a little decrease in magnetic flux density. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Permeability change during experimental fault smearing

Smear sourced from shale or clay is thought to provide an across‐fault barrier to fluid flow in sedimentary rocks. Permeability changes of this phenomenon were investigated using a triaxial testing machine. Experimental specimens consisting of interlayered siltstone (low initial permeability, ∼10−16 m2) and sandstone (high initial permeability, ∼10−13 m2) were subjected to 20, 30, and 40 MPa of effective normal stresses on a precut surface, dividing each specimen at a 30° angle to its axis, at axial shortening velocities between 0.14 and 1.41 μm s−1. Permeability was measured by the oscillation method, and permeability changes categorized in three distinct regimes that corresponded to progressively increasing rock deformation: regime 1, rapid reduction due to compaction of the siltstone layer prior to fault movement; regime 2, constant and minimum permeability while the smear developed; and regime 3, permeability recovery caused by smear thinning and loss of smear continuity. The duration of regime 2 and of smear continuity recorded provide measures of the sealing potential produced by the smear. The shale smear factor SSF, defined as (fault throw)/(thickness of low‐permeability layer), shows that there may be a relation between seal potential and effective normal stress. Both factors in SSF can reach higher values when effective normal stress is 40 MPa than when that is ≥30 MPa.

Electrical and magnetic studies of Ba 3Co 2Fe 23−12 xMn 12 xO 41 Z-type hexaferrites

The electromagnetic and dielectric properties of Mn substituted Ba 3Co 2Fe 23−12 x Mn 12 x O 41 (Z-type) hexaferrites where 0≤ x<0.1 were investigated in this study. The ferrite samples behaved as a semiconductor, and DC resistivity as well as activation energy for electronic conduction increased as the amount of Mn substituted for Fe increased, reaching maximum around x=0.02, and then decreased with further substitution. The behavior of dielectric constant was in an opposite manner to that of the activation energy and DC resistivity. Conduction is explained on hopping of electrons between Fe 2+ and Fe 3+. It was inferred that the initial permeability was sensitively controlled by the substitution of Mn because of magnetostriction compensation. Low-temperature sintered Co 2Z hexaferrite with the substitution of Mn for Fe with low dielectric constant and high initial permeability is suitable for very high frequency (VHF; 300–800 MHz) multilayer chip inductors (MLCI) use.

The use of a modified Petrov-Galerkin method for gas-sold reaction modelling

A new numerical technique for simulating gas-solid reactions including diffusion through the reactant and product layers, reaction on the shrinking surface and internal reaction is presented Some transformations are introduced, and this model can be reduced to dimensionless form including a selfadjoint, singularly perturbed, two-point boundary-value problem and two initial-value problems. A combination of the Petrov-Galerkin finite element method and predictor-corrector method is applied to solve the problem. It is shown that the shrinking-core model including both surface reaction and product layer diffusion can arise for low initial relative permeability and the diffusion-controlled shrinking-core model occurs when the product layer diffusional resistance is large relative to the surface reaction. This method is simple and there is no limit on the range of the parameters. Computed results are numerically evaluated for comparison with results of previous authors.

Respiration in MA-packed, cut carrots

Cut carrot was stored in: (1) bags containing modified air with different oxygen and carbon dioxide content; (2) in bags with different oxygen permeability. Oxygen and carbon dioxide was measured regularly during a storage period of 10 days. Results show that increasing initial oxygen from 5 to 60% delayed anoxia from 3 to 10 days. Only a combination of low initial oxygen (5%) and high permeability bags (1020–1250 cm 3/ (day.Bar.m 2)) could stabilise the oxygen concentration, and only at a low level (5–7% O 2). Respiration of cut carrot has a high dependency of oxygen concentration, as shown by applying a Michaelis-Menten model. In contrast, no dependency of CO 2 was found.

Structure and Soft Magnetic Properties of Fe-Ti-M (M=Al,Si,Co) Ternary Films

The magnetic and structural properties of sputtered Fe-Al-Ti, Fe-Si-Ti and Fe-Co-Ti ternary films were investigated. Samples were annealed at 673K for one hour. Crystal structures were bcc for the Fe-Si-Ti and Fe-Co-Ti ternary films, and a mixture of bcc and bcc+Fe 2 Ti for the Fe-Al-Ti ternary films. The addition of Ti reduces ?rain sizes to a minimum of about 10 nm. Addition of Al, Si or Ti to Fe reduces the saturation magnetic flux density of Fe-Al-Ti and Fe-Si-Ti films, and addition of Co increases the saturation magnetic flux density of Fe-Co-Ti. Zero-magnetostriction samples were obtained in each ternary system. Low coercivity (under 5 Oe) and high initial permeability (about 1000) were obtained together with zero magnetostriction for Fe-Al-Ti ternary films by adding a small amount of Ti. In the case of Fe-Co-Ti ternary films, low coercivity and high permeability were obtained along with small grain sizes of 10 nm or so. Films with low magnetostriction (? s ≪3×10?6) had a coercivity roughly proportional to the third power of the grain diameter.

Bicomponent vascular grafts consisting of synthetic absorbable fibers: Part II: In vivo healing response.

The objectives of this research were (1) to determine whether the use of partially absorbable vascular grafts would improve their nonthrombogenic performance and whether they are more prone to aneurysmal dilation and subsequent failure in vivo, and (2) to find out the relationships, if any, between these in vivo and the previously reported in vitro data with an emphasis on how the in vitro changes in fabric structure and properties related to these in vivo data. Bicomponent vascular fabrics were made from Dacron and polyglycolic acid (PGA) yarns with a range of composition ratios of the PGA to Dacron. Both woven and single Jersey knit fabrics were made, and implanted in dogs for 4 months. The following findings and relationships were obtained. (1) The bicomponent vascular fabrics resulted in a full-wall healing in the thoracic aorta of dogs. All bicomponent vascular grafts in survived dogs exhibited 100% patency, no thrombus or aneurysmal formation, no hematoma or seroma around the grafts, and no fibrin coagula in the inner capsules. The gross morphology of the regenerated tissues was very similar visually to the adjacent original arterial tissue. Histologically, the luminal surface was lined with a layer of endothelial cells with myofibroblasts, fibroblasts, and collagens underneath. (2) The extent of the full-wall healing depended on the type of fabric structure, the concentration of absorbable yarns, the location of absorbable yarns (for the woven group only), and initial water permeability. It is believed that the concentration effect was related to the level of macrophage activation from the degradation products of the absorbable yarns, while the location effect was attributed to the various types of fabric structure change on the degradation of the absorbable yarns. (3) In general, the knitted group (K), was better than the woven group (W). K3 showed the best in vivo performance in the knitted group. (4) In the woven group, W3 was the best. The incorporation of absorbable yarns in the weft direction of the bicomponent fabrics (W3) resulted in a velourlike, loose and porous fabric surface for facilitating tissue ingrowth. The placement of absorbable yarns in the warp direction (W1), however, did not show this unique surface morphology. Calcification was, however, occasionally observed in the woven samples with low initial water permeability. These observed in vivo performances correlated well with our previously reported in vitro study.

Patterns of Effective Permeability of Leaf Cuticles to Acids.

Plants in the field are frequently exposed to anthropogenic acid precipitation with pH values of 4 and below. For the acid to directly affect leaf tissues, it must pass through the leaf cuticle, but little is known about the permeability of cuticles to protons, or about the effect of different anions on this permeability. We investigated the movement of protons through isolated astomatous leaf cuticles of grapefruit (Citrus X paradisi Macfady.), rough lemon (Citrus limon [L.] Burm. fils cv Ponderosa), and pear (Pyrus communis L.) using hydrochloric, sulfuric, and nitric acids. Cuticles were enzymically isolated from leaves and placed in a diffusion apparatus with pH 4 acid on the morphological outer surface of the cuticle and degassed distilled water on the inner surface. Changes in pH of the solution on the inner surface were used to determine rates of effective permeability of the cuticles to the protons of these acids. Most cuticles exhibited an initial low permeability, lasting hours to days, then after a short transition displayed a significantly higher permeability, which persisted until equilibrium was approached. The change in effective permeability appears to be reversible. Effective permeabilities were higher for sulfuric acid than for the others. A model of the movement of protons through the cuticle is presented, proposing that dissociated acid groups in channels within the cutin are first protonated by the acid, accounting for the low initial effective permeability; then protons pass freely through the channels, resulting in a higher effective permeability.

Fe-Ti-M (M=Al, Si, Co) 合金薄膜の構造と軟磁気特性

The magnetic and structural properties of sputtered Fe-Al-Ti, Fe-Si-Ti, and Fe-Co-Ti ternary films were investigated. The samples were annealed at 673 K for one hour. The crystal structures were bcc for the Fe-Si-Ti and Fe-Co-Ti ternary films, and a mixture of bcc and bcc+Fe2Ti for the Fe-Al-Ti ternary films. The addition of Ti reduces the grain size to a minimum of about 10 nm. Addition of Al, Si, or Ti to Fe reduces the saturation magnetic flux density for Fe-Al-Ti and Fe-Si-Ti films, and addition of Co increases the saturation magnetic flux density for Fe-Co-Ti. Zero magnetostriction samples were obtained for each ternary system. Low coercivity (less than 5 Oe) and high initial permeability (about 1000) were obtained with zero magnetostriction for Fe-Al-Ti ternary films by adding a small amount of Ti. For Fe-Co-Ti ternary films, low coercivity and high permeability were obtained with a small grain size of about 10 nm. For films with low magnetostriction (λs<3×10-6), the coercivity was roughly proportional to the third power of the grain diameter.

Perturbation analysis of gas—solid reactions—I. Solid of low initial permeability

A general model for gas—solid reactions considering both internal and external reaction, and accounting for the effect of local internal conversion at the shrinking core surface, is analyzed here by a perturbation procedure for low initial relative permeability. It is shown that the shrinking core model including both surface reaction and product layer diffusion can arise only in this limit. Prior approaches considering only internal reaction have yielded only the diffusional control limit of the shrinking core model. The perturbation procedure shows that the shrinking core surface is always accompanied by a narrow reaction zone in which internal reaction occurs even for low initial permeability. The effect of this reaction zone on the overall conversion is found to be significant, with errors in the shrinking core model predictions as large as 12%, even when the ratio of the effective diffusivity in the core to that in the completely converted solid is only 0.06. One-term perturbation corrections to the shrinking core model, valid for all internal pore structures, are developed analytically.

Microbial selective plugging and enhanced oil recovery

The ability of indigenous populations of microorganisms in Berea sandstone to improve the volumetric sweep efficiency and increase oil recovery by in situ growth and metabolism following the injection of nutrients was studied. Cores of differing permeabilities connected in parallel without crossflow and slabs of sandstone with differing permeabilities in capillary contact to allow crossflow were used. The addition of a sucrosenitrate mineral salts medium stimulated the growth and metabolism of microorganisms in the sandstone systems. This resulted in a preferential decrease in permeability in the core or slab with the higher initial permeability, diverted flow into the lower-permeability core or slab and improved the volumetric sweep efficiency. Injectivity into the slab with the lower initial permeability in the crossflow system increased during subsequent nutrient injections. Thus, microbial selective plugging does occur in laboratory systems that have the complex flow patterns observed in petroleum reservoirs without losing the ability to inject fluids into the formation. In situ microbial growth and metabolism increased oil recovery 10 to 38% of the original oil in place. Biogenic gas production accompanied oil production, and much of the gas was entrained within the produced oil suggesting that gas production was an important factor leading to increased oil recovery. Quantitation of the amount of phospholipid in the core confirmed that microbial growth preferentially occurred throughout the core with the higher initial permeability. These data showed that in situ microbial growth in the high-permeability regions improved not only the volumetric sweep efficiency but also the microscopic oil displacement efficiency.

ChemInform Abstract: Initial Magnetization Behavior of Rapidly Quenched Neodymium‐Iron‐Boron Magnets

Initial magnetization and demagnetization data are reported for three forms of rapidly solidified Nd-Fe-B permanent magnet materials: melt-spun ribbons, hot pressed magnets, and die upset magnets. In all three materials the results are consistent with domain wall pinning at grain boundary phases as the coercivity mechanism. Optimally quenched ribbons are comprised of randomly oriented single domain Nd2Fe14B grains, and both initial magnetization and demagnetization are controlled by strong domain wall pinning at grain boundaries. Maximum coercivity is accompanied by a low initial permeability. Coercivity is reduced in overquenched ribbons by partial retention of a magnetically soft amorphous or very finely crystalline microstructure. Coercivity decreases in underquenched ribbons because wall pinning weakens as the grain size increases above optimum. Correlation of magnetization and demagnetization behaviors suggests that maximum coercivity in ribbons is largely determined by the resistance to domain wall formation in grains smaller than the single domain particle limit. Grain size is much less important in the aligned die upset magnets. Domain walls are initially free to move until they become strongly pinned at grain edges, and complete magnetization requires an applied field greater than the coercive field. Hot pressed magnets show a mixture of ribbon and die upset behavior.

Initial Magnetization Behavior of Rapidly Quenched Neodymium-Iron-Boron Magnets

ABSTRACTInitial magnetization and demagnetization data are reported for three forms of rapidly solidified Nd-Fe-B permanent magnet materials: melt-spun ribbons, hot pressed magnets, and die upset magnets. In all three materials the results are consistent with domain wall pinning at grain boundary phases as the coercivity mechanism. Optimally quenched ribbons are comprised of randomly oriented single domain Nd2Fe14B grains, and both initial magnetization and demagnetization are controlled by strong domain wall pinning at grain boundaries. Maximum coercivity is accompanied by a low initial permeability. Coercivity is reduced in overquenched ribbons by partial retention of a magnetically soft amorphous or very finely crystalline microstructure. Coercivity decreases in underquenched ribbons because wall pinning weakens as the grain size increases above optimum. Correlation of magnetization and demagnetization behaviors suggests that maximum coercivity in ribbons is largely determined by the resistance to domain wall formation in grains smaller than the single domain particle limit. Grain size is much less important in the aligned die upset magnets. Domain walls are initially free to move until they become strongly pinned at grain edges, and complete magnetization requires an applied field greater than the coercive field. Hot pressed magnets show a mixture of ribbon and die upset behavior.

Quench rate dependence of the initial magnetization in rapidly solidified neodymium-iron-boron ribbons

The quench rate dependence of the magnetization process is reported for rapidly solidified Nd-Fe-B ribbons. In optimally quenched ribbons, where the Nd 2 Fe 14 B grain size is less than the estimated single domain particle size, moment reversal during both magnetization and demagnetization is controlled by strong domain wall pinning at grain boundaries. Maximum coercivity is accompanied by a low initial permeability. Coercivity is reduced in overquenched ribbons by partial retention of a magnetically soft amorphous or very finely crystalline microstructure. Coercivity decreases in underquenched ribbons because wall pinning weakens as the grain size increases above optimum. Magnetization and demagnetization behaviors remain strongly correlated in underquenched ribbons, suggesting that maximum coercivity may be largely determined by the resistance to domain wall formation within grains smaller than the single domain particle limit.

Influence of Conditions of Preparation on the Properties of Nickel-Zinc-Ferrite

Studies on the influence of various fabrication parameters viz., calcination temperature, grinding period, sintering temperature and soaking time, on the initial a.c. permeability and Q-factor of Nickel-Zinc-Ferrite (Ni0.3Zn0.7 Fe2O4 samples, were made with a view to develop ferrite cores, for use at high frequencies. A higher calcination temperature, a lower sintering temperature and a shorter soaking period have been found desirable to attain reasonably high density coupled with a low initial permeability and high Q. Repeated calcinations interspaced with wet grinding resulted in further improvement of the properties.

Factors affecting the sensitivity of gamma-level ring-core magnetometers

A theoretical and experimental analysis has been made of the geometrical and magnetic factors affecting the sensitivity of the ring-core magnetometer first introduced by Geyger in 1961. Using a drive-to-pickup transfer function derived from an assumed dynamic hysteresis loop and a given dc input signal, the second-harmonic output voltage was derived for both current-source and voltage-source driving conditions. Results of the analysis, which were confirmed by experiment, show the following. 1) When a single, diametrically wound (solenoid-type) pickup winding is used with a ring-core sensor, simultaneous minimization of both fundamental and second-harmonic feedthrough can be achieved by a simple rotational adjustment. This optimization is possible only with a circular core. 2) Sensitivity can be increased by increasing frequency, number of pickup turns, dynamic differential permeability, cross-sectional area, and effective sensor length, and by decreasing the dc initial permeability (μ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> ). 3) The dominant factor affecting the sensitivity is the demagnetizing term <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\mu_{0}K = \mu_{0}l^{-1.72} (4A/\pi)^{0.86}</tex> , which determines the entrance attenuation of the dc signal to be measured. Highest sensitivity is obtained when <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\mu_{0}K</tex> is small, which requires a low initial permeability, since a large dimensional ratio <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">l/A^{1/2}</tex> is usually not attainable. When the demagnetizing term is not small, the sensitivity advantages of the other factors are negated by the input signal attenuation. Power considerations show that increasing sensitivity by raising area, length, or frequency results in increased power consumption. However, increasing sensitivity by using a pickup coil with a larger number of turns or by a sensor core with lower initial permeability can be achieved without additional power.