Iron-nitride Magnetic Fluid Research Articles

Modeling of plasma chemistry in an atmospheric pressure Ar/NH3 cylindrical dielectric barrier discharge described using the one-dimensional fluid model

The keynote of our research is to study the gas phase chemistry in an atmospheric pressure Ar/NH3 cylindrical dielectric barrier discharge, which is very important to produce the iron-nitride magnetic fluid. For this purpose, a home-made one dimensional fluid model with the Scharfetter-Gummel method has been developed. The equations solved are the particle balances, assuming a drift-diffusion approximation for the fluxes, and the electron energy equation. The self-consistent electric field is obtained by the simultaneous solution of Poisson's equation. The simulations were carried out for the different ammonia concentrations (2%, 3.5%, and 7%), at a voltage of 1 kV, and a driving frequency of 20 kHz. It concluded that the major ion products of Ar are Ar+ and Ar2+. Ar+ is the most important positive ions, followed by Ar2+. It is shown that the NH+ density is smaller than that of the other ammonia ions. The density of NH4+ is more than that of the other ammonia ions when the ammonia concentration increased. The diffuse mode can be established after the discharge was ignited, and the mode changes to filamentary mode with an increase in ammonia concentration.

Study on the magnetic stability of iron-nitride magnetic fluid

The effects of the addition of phenolic antioxidant on the magnetic stability of α-olefinic hydrocarbon synthetic oil based iron-nitride magnetic fluid were studied. It was found that the magnetic stability of α-olefinic hydrocarbon synthetic oil based iron-nitride magnetic fluid, both at room temperature and high temperature (80 °C), could be improved effectively by the addition of phenolic antioxidant. Only 21% magnetic decrease was found for the magnetic fluid with 5 wt.% phenolic antioxidant after exposed to atmosphere environment at room temperature for 12 months. Thus the addition of phenolic antioxidant into α-olefinic hydrocarbon synthetic oil based iron-nitride magnetic fluid is an effective way to improve its magnetic stability.

Preparation of nano-magnetic fluid using plasma technique and its application in safety valves

The magnetic fluid was prepared in a gas–liquid reactor by plasma activation and ionization at atmospheric pressure. Through controlling of discharge parameters, the reduction in time for the technological process was explored; based on the attraction of magnetic fluids by the magnetic field, a sealing device with iron-nitride magnetic fluid was designed and developed. 10,000 h sealing of the safety valve was realized on our sample machine by our client.

Research on the iron-nitride magnetic fluid safety valve for sealing

In order to solve the problems that exist in the spring safety valve, by applying the iron-nitride magnetic fluid developed by our own efforts to the static sealing techniques, we have successfully developed “the magnetic fluid safety valve for sealing” which was accepted as the state patent in 1999 and authenticated as the achievement in the scientific research in 2000. This paper focuses on the existed drawbacks of the spring safety valve now in use, the design principle of the magnetic fluid safety valve for sealing, the testing results of the functional parameters, and the effects of its application.

Study on the Characteristics of an Oscillating Flat Plate in Iron-Nitride Magnetic Fluid.

Iron-nitride magnetic fluid has higher magnetization compared with water-based magnetic fluid W-40 or kerosene-based magnetic fluid HC-50 that are usually used. The effects of magnetic field on oscillation characteristics of a flat plate in iron-nitride magnetic fluid are investigated experimentally and compared with the case of other magnetic fluids especially taking into account the viscous effect. It is clarified that the iron-nitride magnetic fluid has relatively large viscous effect on damping characteristics compared with the commercial magnetic fluids.

ランダムに分散した強磁性体超微粒子の集団的磁性

Collective magnetic properties were studied for randomly dispersed ferromagnetic fine particles with dipolar interactions. The sample was a frozen iron-nitride magnetic fluid containing uniform single-domain particles. The results show divergences of non-linear susceptibility and of relaxation time. These indicate the existence of a spin glass-like phase transition. At lower temperatures, novel aging phenomena were observed as seen in spin glasses.

Phase transitions of iron-nitride magnetic fluids.

Phase transitions of magnetic fluids in the zero field were studied from the viewpoint of static susceptibility and typical relaxation time in order to distinguish between the transitions and the blocking phenomena. We used iron-nitride magnetic fluids containing nearly uniform particles so as to remove the effects of particle-size distribution. In the densest sample, we observed the growth of ferromagnetic fluctuations and, in the diluted samples, a temperature-induced first-order phase transition.

Instability of Magnetic Fluid Surface under Horizontal Non-Uniform Alternating Magnetic Field.

Stability of the surface of a magnetic fluid under a horizontal non-uniform alternating magnetic field is investigated experimentally and analytically. Several modes of interfacial waves of the same frequency as that of the applied magnetic field are observed, and the critical strength of the magnetic field at each frequency were obtained. The linear stability theory shows that the system is destabilized with the increase in the magnetic susceptibility and the gradient of the magnetic field, which is in accord with the experimental result. The iron nitride magnetic fluid, which is newly developed and has very high susceptibility and magnetization, was tested under the same condition as W-35 and HC-50. The small disturbance occurred even at very weak magnetic field, and the steady wave was formed in the uniform magnetic field.

Waves on Magnetic Fluid Surface Excited by Horizontal Non-Uniform Alternating Magnetic Field.

The surface waves of a magnetic fluid under a horizontal non-uniform alternating magnetic field is investigated experimentally and analytically. While the frequency of the wave on a magnetic fluid is usually the same as that of the applied magnetic field, in the case of the iron nitride magnetic fluid, which is newly developed and has very high susceptibility and magnetization, the frequency of the wave is twice that of the applied magnetic field. This is confirmed by the linear stability theory. The shape of the surface, the motion inside of the fluid and the disturbed magnetic field are presented.

On the chemical stability of iron-nitride magnetic fluids in atmospheric conditions

The chemical stability of iron-nitride magnetic fluids prepared by coating titanium and cobalt has been assessed in an atmospheric condition by means of measurements on their saturation magnetizations and mass changes. The mass changes of both the uncoated and coated iron-nitride magnetic fluids gradually increased on exposing to an atmosphere. Saturation magnetizations of iron nitride magnetic fluids decrease with increasing exposure time, and approach zero after 1008h of exposure time. Such changes are probably caused by an oxidation of iron-nitride particles. The final oxidation form of iron nitride at room temperature is considered to be non-magnetic hematite (α-Fe2O3) rather than ferromagnetic magnetite (Fe3O4) and/or maghemite (γ-Fe2O3). It has been found that cobalt prevents the oxidation of iron-nitride particles in the initial moments of exposure time.

Study on the Characteristics of an Oscillating Flat Plate in Iron-Nitride Magnetic Fluid.

Ion-nitride magnetic fluid has higher magnetization compared with water-based magnetic fluid W 40 or kerosene-based magnetic fluid HC 50 that are usually used. The effects of magnetic field on oscillation characteristics of a flat plate in iron-nitride magnetic fluid are investigated experimentally and are compared with the case of other magnetic fluids especially taking into account the viscous effect. It is clarified that the ion nitride magnetic fluid has relatively large viscous effect on damping characteristics compared with the commercial magnetic fluids.

Phase diagram of am iron-nitride magnetic fluid: effects of temperature and weak magnetic field

The phase diagram is studied for a magnetic fluid with uniform iron-nitride particles. The magnetic properties were measured at various temperatures in weak magnetic fields. The results show a temperature-induced transition. Weak magnetic fields stabilize the state observed at the higher temperatures.

Magnetization curve for iron-nitride fine particle system with random anisotropy

Magnetization curves were measured for a frozen iron-nitride magnetic fluid with uniform particles. The results are compared with calculated curves for the single domain particles with randomly oriented uniaxial easy axes. It is clarified that the magnetization curve for isolated particles shows appreciable deviation from the superparamagnetic superposition in a wide range of temperature above the blocking temperature. This deviation can be attributed to the anisotropy energy on each particle.

Dynamic study of iron-nitride fine particle system: field dependence of the blocking temperature

The AC susceptibility χ′ + iχ″ of frozen iron-nitride magnetic fluids was measured in static fields. The blocking temperature is estimated from the maximum of out-of-phase component χ″ against the frequency of measurement. For a diluted sample, the field dependence of the blocking temperature is explained by the Néel superparamagnetic (blocking) model for an isolated particle. For a dense sample, the blocking temperature is much higher than that for the diluted sample in a zero field and intensively decreases with the power of ⅔ of the magnetic field in the lower field range.

Effects of cooling field on magnetic relaxation on an iron-nitride fine particle system

Effects of the external magnetic field Ha applied during cooling on the magnetic relaxation of a fine particle system are studied. We measured the temperature decay of the residual magnetization and the ac susceptibility for frozen iron-nitride magnetic fluids. It was found that the relaxation time distribution of the diluted sample is independent of Ha and coincides with that expected from the particle diameter distribution, as the superparamagnetic model presents. On the other hand, in the concentrated sample, it is clear that the relaxation time in zero field is widely distributed and depends on Ha.

窒化鉄超微粒子分散系の磁気緩和機構

The effect of magnetic inter-particle interaction on the magnetic relaxation process for a fine particle system was studied. The dc total susceptibility and the ac susceptibility of frozen iron-nitride magnetic fluids with various particle number densities were measured. The relaxation time increases rapidly as the temperature decreases or the inter- particle interaction Jtyp increases. The relaxation seems to be a thermal activation process, and the activation energy tends to be proportional to (kBT/Jtyp)-a in the low-value range of kBT/Jtyp. On the other hand in the range kBT/Jtyp>> 1 the activation energy approaches a constant value deter- mined by the anisotropy energy of isolated particles.

Iron-nitride magnetic fluids prepared by vapor-liquid reaction and their magnetic properties

Abstract A new type metallic magnetic fluids with iron-nitride ϵ−Fe 3 N fine particles dispersed in kerosene were synthesized by a method of vapor-liquid chemical reaction between iron carbonyl and ammonia. The particles are highly uniform in size and well dispersed without agglomeration. The iron-nitride magnetic fluids have high saturation magnetic flux densities up to 2330 G, and have high relative initial permeabilities up to 180. This paper presents the description on the preparative method, crystallographic properties and magnetic properties of the iron-nitride magnetic fluids.

Iron-nitride magnetic fluids prepared by plasma CVD technique and their magnetic properties

A method of preparing a new type of magnetic fluid, which contains iron-nitride fine particles dispersed in toluene, is presented. Magnetic fluids were prepared by plasma CVD reaction of Fe(CO) 5 in N 2. The highest saturation magnetization obtained was 0.022 T. Their crystallographic and magnetic properties are discussed.