Ferromagnetic Powders Research Articles

The Control of Molecular Transport Rate through Liquid Membrane Containing Ferromagnetic Powder under Rotating Magnetic Field

Abstract A novel method with using liquid membrane containing ferromagnetic powder (LM-FP) under rotating magnetic field was proposed for the control of molecular transport rate through the liquid membrane. The rate of phenylglyoxylic acid transport through the LM-FP, (toluene-chloroform mixture containing magnetite powder) increased more than 10 times as compared with the transport rate under non-magnetic field.

Anomalous dielectric permittivity of ammonium perchlorate below 40 K

Polycrystalline NH 4ClO 4 and ND 4ClO 4 samples have anomalously increased dielectric permittivity below ≈ 40 K which depends on measuring voltage, on sample grain size and thermal history. Any sudden change in temperature or bias field provokes an immediate increase in permittivity followed by a slow decrease. The behaviour has analogies with a dipole glass, an incommensurate phase, spin glasses and ferromagnetic powders.

Kinetics of heating of constructional parts of ferromagnetic powders in induction sintering

Kinetics of heating of constructional parts of ferromagnetic powders in induction sintering

Ferromagnetic ultrafine alloy powders by hydrogen reduction of mixed halide vapor and its application to magnetic recording

The authors developed a chemical process to prepare ferromagnetic ultrafine alloy powders using the hydrogen reduction of mixed chloride (FeCl 2 , CoCl 2 , NiCl 2 ) vapor around 1200K. The product is necklace like chain of primary particles. The size distribution of the primary particle is log-normal and the geometric standard deviation is about 1.5±0.1 regardless of the median diameter of 30-110 nm. A washing treatment by polar solvents reduced the residual chlorine from a few percent to less than 10ppm. The partial pressure of chloride mainly affects the primary particle size of the product. Reaction temperature also affects, but the residence time does not. A greater dilution and a higher temperature favor a smaller primary particle and result in a better magnetic property. Degradation of σ s of the product UFP at 60°C and 90%RH is measured and found to be less than 10% in 5 days. The friction factor of the powder layer is 15 to 30% less than that of commercial metallic powder. Samples of floppy disk are made from these powders and evaluated. The overall performance cleared the present standards for high density magnetic recording.

Motion of a ferromagnetic powder during magnetoabrasive polishing

An experimental investigation has been carried out into the distribution of a magnetoabrasive powder in the working zones of a machine with annularly arranged MAP zones. It has been established that in the working zone of the magnetic gap the minimum-density region is located at a distance of one-third of the working gap length from the point of entry into the gap. Qualitative expressions have been obtained reflecting the character of the variation of the velocity components of ferroabrasive particles moving in the course of MAP. Experimental and calculated data have been found to match.

Application of alkoxy-derived ultrafine particles to ceramics.

In manufacturing ceramics by solid-state reactions, properties of powders used play an important role in the manufacturing. By the hydrolysis of metal alkoxides, fine powders with highly homogeneous composition can be produced. This enables the production of ultrafine powders with designed composition and structure. A variety of ceramics can be derived from metal alkoxides. Zirconia (ZrO2) powders with various characteristics are prepared by changing hydrolysis conditions and calcination temperatures. Optoelectronic ceramics PLZT with excellent properties are also manufactured. Because powders derived from metal alkoxides bring about the aggregation by dryng, fluidized forms such as paste, slurry and sol are required. Magnetic fluids are produced by dispersing ferromagnetic fine powders derived from metal alkoxides into the solvent. Solgel process is developed in ceramic manufacturing. Metal alkoxides easily form sols. For example, AlOOH sol is obtained and alumina thin film is fabricated. Alkoxide process is expected as a promising method in manufacturing ceramics.

Transportation of powders using a linear motor device

The theory of linear motors has been formulated for both magnetic and non-magnetic reaction plates and criteria established to assess their performance. The predominant mechanism involved in the transportation of ferromagnetic powders cannot be the same as that in a motor device, because basic calculations show that the induced currents in the particles at 50 Hz are small. Instead, the ferromagnetic particles seem to follow the movement of the travelling magnetic field itself. A study of the phenomena associated with the transportation of powders using linear motor devices has been commenced in a SERC project at Loughborough University of Technology. This paper illustrates the motion of the particles along a linear motor device and also reviews the experimental work done previously, especially that associated with powder cleaning devices. Areas of future research work to be followed are discussed and possible new industrial applications mentioned.

Electromagnetic shielding properties of amorphous alloy shields for cathode ray tubes

Because of the excellent soft magnetic properties of the amorphous alloy Fe40Ni38Mo4B18 (2826MB), we have made funnel-shaped shields for cathode ray tubes by combining the amorphous ribbons and ferromagnetic powders via resin transfer molding composite technology. The electromagnetic shielding properties of shields were improved by increasing the thickness of ribbons and the weight percentage of ferromagnetic powders. For a shield with six-layer ribbons, the maximum magnetic shielding effectiveness obtained near the applied magnetic field 2 Oe (dc and ac 60 Hz) was about 25–27 dB, and the magnetic shielding factors were improved to 27–30 dB by adding the ferromagnetic powders. After the field annealing of shields, the magnetic shielding effectiveness increased and the maximum values of 35–40 dB were shifted near the applied magnetic field 0.2 Oe. The electric field shielding effectiveness over the broadband spectrum 10 kHz–18 GHz was in the range 50–80 dB.

Theory of the magnetic reactions occurring in abrasive machining with a ferromagnetic powder

An examination is made of the existing methods of calculation for the analysis of the magnetic interactions in magnetoabrasive polishing. An error in the approach to the problem is pointed out which has resulted in calculated values of forces being much smaller than experimental. The superposition method is employed for calculating the magnetization intensity of a magnetoabrasive powder particle and cylindrical ferromagnetic work placed in a magnetic powder medium. Formulas are derived for calculating the forces acting on a spherical powder particle during the MAP of a cylindrical part made of a ferromagnetic material.

High-temperature bend testing of sintered materials in exploratory investigations

i. E.G. Konovalov and G. S. Shulev, Finish Machining of Parts with Ferromagnetic Powders in a Magnetic Field [in Russian], Nauka i Tekhnika, Minsk (1967). 2. Yu. M. Baron, "Physical principles of operation of magnetoabrasive materials," in: Magnetoabrasive Materials and Their Methods of Testing [in Russian], Institute of Materials Science, Academy of Sciences of the Ukrainian SSR, Kiev (1980), pp. 10-17. 3. V.N. Bakul', Yu. I. Nikitin, A. N. Bakalenko, and B. V. Pogorelyi, "Classification of diamond grinding powders according to grain shape on a vibrating table," in: Synthetic Diamonds [in Russian], Vol. 1 (1973), pp. 5-9. 4. M.D. Krymskii, "Materials for magnetoabrasive polishing," Inventor's Certificate No. 831599, Byull. Izobret., No. 19 (1981). 5. M.D. Krymskii, "Method of preparation of magnetoabrasive powder," Inventor's Certificate No. 835643, Byull. Izobret., No. 21 (1981). 6. G. S. Shulev, "Method of abrasive machining of parts," Inventor's Certificate No. 165651, Byull. Izobret., No. 19 (1964). 7. V.I. Zhdanovich and B. I. Chernoglaz, "Investigation of the pressure of ferromagnetic powder on the work surface in magnetoabrasive machining," Tr. SKB-3, Minsk, Vol. 5 (1971), pp. 15-19. 8. M.D. Krymskii, "Distribution and densification of magnetoabrasive powder in the working gap of the machine," in: Magnetoabrasive Materials and Their Methods of Testing [in Russian], Institute of Materials Science, Academy of Sciences of the Ukrainian SSR, Kiev (1980), pp. 92-96. 9. M.D. Krymskii, O. A. Katrus, Yu. I. Nikitin, and V. D. Belik, "Comminution of composite magnetoabrasive materials," Poroshk. Metall., No. 9, 82-85 (1982).

Ferromagnetic resonance condition and powder pattern analysis for dilute, spherical, single-domain particles of cubic crystal structure

A resonance condition containing the anisotropy parameters K 1 K 2, and K 3 is presented and tested as a means of generating FUR powder patterns for dilute suspensions of spherical, single-domain magnetic particles of cubic crystal structure.

Mössbauer study ofCo0.99557Fe0.005S2in external magnetic fields: Magnetic structure of CoS2and the quadrupole splitting of the FeS2-CoS2-NiS2system

The M\"ossbauer effect of $^{57}\mathrm{Fe}$-doped ferromagnetic Co${\mathrm{S}}_{2}$ was measured at 4.2 K in external magnetic fields up to 40 kOe. Ferromagnetic powder spectra were analyzed by taking into account the effect of the ferromagnetic moment. The hyperfine field induced by the ferromagnetic moment is -16 kOe when the moment lies along the principal axis of the electric field gradient and -7 kOe when the moment is perpendicular to it. The sign of the electric field gradient is negative at the $^{57}\mathrm{Fe}$ nucleus. Using these results, we conclude that the spectrum at zero external field is explicable from the collinear magnetic structure with a [111] easy direction of Co spins. The quadrupole splitting is negative in the Fe${\mathrm{S}}_{2}$-Co${\mathrm{S}}_{2}$-Ni${\mathrm{S}}_{2}$ system. The quadrupole splitting changes around the metal-semiconductor phase boundary because of a delocalization of ${e}_{g}$ electrons in the metallic region. The absolute value in the low-resistivity region is smaller than that in high-resistivity regions by about 0.1 mm/sec.

Metal tapes using ultra fine powder prepared by gas evaporation method

In the last decade, investigations of ultrafine powders prepared by the gas evaporation method have been carried out in Japan. Metals were evaporated in inert gases such as Xe or He or Ar. Ultra fine particles of 50 to 2000 A in diameter were precipitated like soot. The basic magnetic charcterstics have already been reported in previous papers. The coercive force of ferromagnetic fine powders can be controlled by changing the constituents of the alloy up to 2500 Oe. Resistance heating, plasma jet, induction heating or LASER have been examined as evaporation heat sources. Viedo and Audio tapes were tested in Fuji Photo Film Co.,Ltd.. One of the typical tapes gave 12.8 dB higher output level at 5 MHz and 10.0 dB better C/N at 4.5 MHz compared with commercially available highest quality tape. Reduction of the saturation magnetization of the tape is 0% after being kept in the condition that 60°c, 90% R.H. for one week. Still frame is more than 30 minutes.

Stimulated polarization echoes with long decay times in ferromagnetic powders

Stimulated polarization echoes with decay time, T 1, exceeding one minute at room temperature have been detected in powders of ferromagnetic materials.

Radiofrequency echoes from piezoelectric powder

Echoes of mechanical origin following a two or more pulse excitation, analogous to those observed from normal metals or ferromagnetic powders, were observed from powder of Rochelle salt. Echoes were excited by rf pulses of electric field intensity (e1,e2) ≳ 800 V/cm and varied approximately as e1e22. The echo amplitude was strongest in the ferroelectric region and the relaxation time of the echo gradually decreased with temperature.

Non-reciprocal transmission in artificial dielectrics using ferromagnetic powders

A detailed analysis of the non-reciprocal transmission property of artificial dielectrics containing ferromagnetic metal particles has been made assuming a tensor permeability which involves the Landau-Lifshiftz form of damping for these particles. Corrections have also been applied to the results for the case when the absorption curve departs from lorentzian lineshape due to a field-dependent loss term. It is shown that the optimum non-reciprocal behaviour for these materials can be realized using metals with high saturation magnetization and low ferromagnetic resonance loss. A steady Faraday rotation as high as 32 deg cm−1 at an average figure of merit of 6 deg dB−1 may be realized over the entire X-band with a suitable choice of particle size. The ratio of the attenuation constants appropriate for the two circular polarizations is found to have a maximum value of 11 for metals like nickel, permalloy, etc which have a relaxation time of the order of 10−9 s. A higher value of the ratio would be feasible for metals with a larger relaxation time.

Surface strengthening of ferromagnetic powders for electromagnetic powder clutches

1. Optimum conditions have been determined for the deposition of protective nickel and nickel-phosphorus coatings on the particles of atomized iron powder and for the subsequent heat treatment of the powder designed to produce nickel- and phosphorus-rich surface diffusion layers. 2. It has been established that nickel and nickel-phosphorus coatings in the form of 10–15Μ thick diffusion layers decrease the oxidation of atomized iron powder in air and water vapor atmospheres at 300–500‡C by a factor of 2 to 6. Maximum surface strengthening is induced by the deposition of a nickel-phosphorus coating. 3. It is shown that aluminized iron powders could prove useful as ferromagnetic powders for EPC; the possibility has been established of producing iron powders aluminized to a depth of 10–15Μ.

Preparation and Properties of Ultra Fine Metal Powders

Ultra fine metal powders of less than 0.1 µm in diameter can be produced in Ar, He or He+H2 gaseous atmosphere by using the gas evaporation method with several heating methods. Three heating methods, that is, plasma jet, open arc and high frequency induction, have been tested to heat the surface of molten metal and alloy by the authors for producing ultra fine powders. Operating conditions of the ultra fine metal powder apparatus, the relation between the mean particle size of ultra fine Ni powder and the operating condition of the plasma jet, the similar data for ultra-fine Cu powder produced by an induction heating method and magnetic properties of ferromagnetic material powders are described.

Preferred Orientations of Commercial Magnetic Recording Tapes

The ferromagnetic powders dispersed in coating surfaces of commercial broadcast video tapes were exa-mined using X-ray diffraction and Mossbauer technique. X-ray diffraction of the coatings showed the presence of preferred orientation having [110] parallel to an alignment direction on the plane of the tape surface. For the majority of particles examined the easy direction was also parallel to the above direction. These results are compared with those obtained by electrical conductivity measurements.

An apparatus for the manufacture of very fine ferromagnetic powders

An apparatus for the manufacture of very fine ferromagnetic powders