Study of Nd-Fe-B Alloys with Nonstoichiometric Nd Content in Optimal Magnetic State

Characterization of two rapid-quenched Nd-Fe-B alloys with nonstoichiometric Nd content in the optimized magnetic state was carried out using the X-ray diffractometry (XRD), (57)Fe Mossbauer spectroscopic phase analysis (MS), electron microscopy (TEM), high resolution TEM (HREM) and Superconducting Quantum Interference Device (SQUID) magnetometer. The experimental results demonstrate the fundamental difference in the structure and magnetic properties of the two investigated alloys in the optimized magnetic state. The Nd-Fe-B alloy with the reduced Nd content (Nd(4.5)Fe(77)B(18.5)) was found to have the nanocomposite structure of Fe(3)B/Nd(2)Fe(14)B and partly alpha-Fe/Nd(2)Fe(14)B, with mean grain size below 30 nm. On the other side, the overstoichiometric Nd(14)Fe(79)B(7) alloy has almost a monophase structure with the dominant content of the hard magnetic phase Nd(2)Fe(14)B (up to 95 wt. %) and a mean crystallite size about 60 nm, as determined by XRD and TEM analysis. The results of magnetic measurements on SQUID magnetometer also suggest the nanocomposite structure of the Nd-low alloy and nanocrystalline decoupled structure of the Nd-rich alloy after the optimal heat treatment.open

Volumetric and thermodynamic properties of binary mixtures of p-cymene with alpha-pinene, limonene and citral at atmospheric pressure and temperatures up to 323.15 K

An experimental analysis of density, refractive index, speed of sound and the viscosity at atmospheric pressure and temperatures T = (288.15 to 323.15) K has been carried out for the three binary systems, i.e. (p-cymene + alpha-pinene), (p-cymene + limonene) and (p-cymene + citral). Excess molar volumes, viscosity deviations, deviations in isentropic compressibility and excess Gibbs free energy of activation of viscous flow were calculated from experimental data. The results were fitted employing Redlich-Kister polynomial equation. Also, partial molar volumes, excess partial molar volumes and partial molar volumes at infinite dilutions were calculated to elucidate the non-ideal behavior of investigated mixtures. Furthermore, Prigogine-Flory-Patterson (PFP) model was successfully applied for the correlation of excess molar volumes of examined binary mixtures. The results of excess molar volume correlations show very good agreement with experimental measurement

Nanocomposite permanent magnetic materials Nd-Fe-B type: The influence of nanocomposite on magnetic properties

The influence on the magnetic properties of nanocristalline ribbons and powders has character of microstructure, between others – the grain size volume of hard and soft magnetic phases and their distribution. Magnetic properties of ribbons and powders depend mainly on their chemical composition and parameters of their heat treatment [1]. Technology of magnets from nanocristalline ribbon consists of the following process: preparing the Nd-Fe- B alloy, preparing the ribbon, powdering of the ribbon, heat treatment of the powder and finally preparing the magnets. Nanocomposite permanent magnet materials based on Nd-Fe- B alloy with Nd low content are a new type of permanent magnetic material. The microstructure of this nanocomposite permanent magnet is composed of a mixture of magnetically soft and hard phases which provide so called exchange coupling effect

Thermomagnetic Analysis of Nanocrystalline Nd4.5Fe77B18.5 Alloy

Changes in the phase composition and crystallite size of a rapid quenched Nd4.5Fe77B18.5 alloy, caused by thermomagnetic measurements (TM) have been studied using XRD methods of phase analysis. crystallite size and lattice microstrain determination. Structural changes in regard to optimal magnetic state were additionally analyzed by TEM. Magnetic properties in optimal magnetic state and after TM were observed using room temperature SQUID measurements. The obtained experimental results suggest the Fe3B/Nd2Fe14B and partly alpha-Fe nanocomposite structure of the alloy in the optimized magnetic state. with mean crystallite size (< 30nm). After TM. an increased amount of alpha-Fe phase, presence of different oxide and Fe-B phases as well as growth of crystallites are found to be the main reasons for the observed quality loss of hard magnetic properties.close4