[en] Thinned samples of as-cast and sintered Nd-Fe-B magnets have been observed by transmission electron microscopy during in-situ heat treatments. Strip-like contrast was observed in the Nd₂Fe₁₄B phase. A transition from cubic to hexagonal Nd₂O₃ occurs at about 200 C

[en] Mass transfer coefficient of water in a porous material (baked clay) is determined by gamma ray attenuation (from a Cs135 source) and thermal shock. Water content is found higher by thermal shock, difference obtained between the two methods is discussed. 7 refs

[en] Transmission electron microscopy was performed on the μ phase in the Fe-Nd-Al system. The structure of μ consists of a long period stacking of planes, typical of polytypism. These basal planes exhibit a diffraction pattern with a six-fold symmetry, characteristic of a two-dimensional hexagonal structure (a=1.65 nm). A 12R type stacking sequence was recognized, with c=15 nm. (orig.)

[en] ⁵⁷Fe Mossbauer spectroscopy and electron microprobe analysis are used to determine the Al-distribution in the Nd-Fe-Al-B alloys; Mossbauer spectroscopy gives the Al distribution between the J₂ and K₂ sites of Nd₂Fe₁₄ B-like-phase; microprobe analysis gives the composition of both matrix and minor phases and their evolution with sintering

[en] The bulk magnetic compound Sm₂(Fe_0.5Co_0.5)₁₇ was nitrided by two different processes: gaseous nitrogenation and fluidized bed nitrogenation. The nitrogen distribution was investigated by scanning electron microscopy, X-ray diffraction and chemical analysis. The cross-sectional nitrogen distribution differed according to the nitrogenation process: (1) nitrogen mainly diffuses along microcracks present in the samples with the gaseous nitrogenation, while it forms a nitrided layer parallel to the surface with the fluidized bed process, (2) the nitriding kinetics is controlled by diffusion (parabolic rate law) for the fluidized bed nitrogenation, whereas it is accelerated in the gaseous process. (orig.)

[en] In Nd-Fe-B permanent magnets, the cubic Nd- rich phase (a = 0.52 nm) is very important both to the development of coercivity and to sintering mechanism. Transmission electron microscopy shows that this Nd-rich phase is not stable under the electron irradiation. The analysis of the decomposition reaction, leading to the formation of cubic Nd₂O₃ and NdO, proves that the Nd-rich phase can be classed as a NdO compound which is supersaturated with Oxygen and stabilized with Iron. Taking into account the existence of a liquid miscibility gap in the Nd-Fe-B-O quaternary system, a model is proposed to explain its formation

[en] An eutectic Fe-Nd(-Al) alloy was investigated, where a 3-phase equilibrium Nd₅Fe₁₇+μ+Nd was found. Their stability is discussed for different heat-treatments. The evolution of the microstructures with a continuously variable cooling rate is studied. (orig.)

[en] X-ray diffraction, Moessbauer effect and magnetisation investigations have been performed on sputtered Fe₄₀(Al₂O₃)₆₀ thin films. Ultrafine Fe particles of nanometer size in an amorphous Al₂O₃ matrix have been formed by annealing in the temperature range from 100 deg. C to 500 deg. C. Their particle sizes, however, show a rather wide distribution. Moessbauer spectra are constituted of both paramagnetic and ferromagnetic contributions. The paramagnetic contribution is associated with small grains of Fe, whereas the magnetic component is contributed by large iron grains. This assumption is supported by the ZFC- and FC-measurements, in which the 'blocking' temperatures of 60 and 90 K were evidenced for as-deposited and 200 deg. C-annealed films, respectively

[en] The nitriding of bulk Sm₂(Fe_0.5Co_0.5)₁₇ compound was carried out by two different processes: fluidized bed and gaseous nitrogenation. It was investigated by X-ray diffraction and Moessbauer spectrometry. The site occupancy of iron atoms in Sm₂(Fe_0.5Co_0.5)₁₇ was determined, showing a full 6c site filling. The Moessbauer hyperfine parameters increase upon nitrogenation; an enhancement up to 50 kOe is noticed for the hyperfine field. Due to modifications of the sample's surface conditions, the time dependence of the nitrogen surface concentration differed according to the nitrogenation process, evidencing that the nitriding kinetics is controlled by an interfacial reaction for gaseous nitrogenation, and by diffusion for the fluidized-bed process. (orig.)

[en] The primary solidification of iron in Nd-Fe-B alloys is detrimental to the magnetic properties of sintered magnets; around the composition of the ferromagnetic φ phase (Nd₂Fe₁₄B) some fluctuations of the composition and/or production processes control this solidification. A microstructural study of as-cast alloys by means of metallography, electron probe, and Moessbauer spectroscopy showed, besides the main φ phase, some amounts of α-Fe dendrites and intergranular precipitates of Nd_1.1Fe₄B₄ and of an Nd-rich phase. Following our observations, the boundary separating the primary crystallization field of Fe and φ can be more precisely defined. The optimal composition avoiding iron precipitation can be found