The effect of electric current assisted annealing was investigated in amorphous Fe40Ni40B20 melt spun ribbons in terms of manipulating the crystallization temperature and phase formation. A specific ...setup was developed, which allows to measure the sample temperature and the electrical resistance in-situ during the annealing process. By employing these simultaneous measurements, the shift of the crystallization temperature was evaluated by employing different electric current modes and current densities. It was found that the onset temperature for crystallization is shifted to lower temperatures when a certain threshold of electric current density is surpassed. Maximum temperature shifts up to 130°C were achieved using direct and alternate current modes, while in pulsed current mode the maximum shift was 100°C. Even though a noticeable change was observed in the crystallization temperature when an electric current is applied during annealing, the nucleated phases were found to be the same as in the samples annealed without current. The reasons for the observed behavior are discussed and compared to propositions found in the literature. It is concluded that the ‘‘hot spots’’ mechanism is in good agreement with the results obtained in this work.
•In-house built set up was developed to detect crystallization temperature.•Electric current annealing decreases the crystallization temperature of Fe–Ni–B.•Different current density and mode affects the onset crystallization temperature.•The mechanism of the observed behavior is related to creation of “hot spots".
The use of multi-stimuli materials is a promising approach for increasing the cooling capacity of magnetic refrigerators. The working body undergoes both a magnetic field and an external compressive ...pressure during cooling. The proposed material must have outstanding magnetocaloric and mechanical properties. The magnetocaloric properties should provide a high adiabatic temperature change value in a limited field range. Mechanical stability at high pressures and adequate geometry are required to ensure high heat transfer values. The compounds La(Fe,Si)13 and their hydrides are the most suitable for the manufacture of such devices. They are able to work at both room and cryogenic temperatures. In the article, we present the results of direct measurements of the magnetocaloric effect and mechanical compression tests of the cast and hydrogenated La(Fe,Si)13Hδ rods. The samples were reinforced with a secondary alpha-iron phase, which ensured their mechanical integrity during hydrogenation and cycle performance. The addition of a secondary alpha-iron phase leads to a decrease in the magnetocaloric effect value. Therefore, we determine the optimal content of the secondary phase, which provides a balance between the caloric and mechanical alloy properties.
•An optimization of La(Fe,Si)13 alloys and their hydrides for multi-stimuli cooling cycle applications has been carried out.•A bundle of 100–300 µm- diameter rods was proposed as the most adequate in the operating frequency range above 3 Hz.•The 15 vol% of α-Fe in the La(Fe,Si)13 alloys provides a balance between the caloric and mechanical alloy properties.
A successful use of the magnetocaloric material in an active magnetic regenerator (AMR) requires its machining into heat exchangers with good mechanical and chemical stability. Most of the ...magnetocaloric materials currently available for room temperature application do not meet those requirements, they are brittle and are susceptible to corrosion. Adhesive-bonding techniques can provide mechanical stability, corrosion protection and net shaped modules in a single step manufacturing process. However, the magnetocaloric properties of the composite materials can be significantly lowered during this process e.g. due to improper adhesion, dilution, and compaction pressure. We report on a comprehensive study of the influence of powder particle size, adhesive type, adhesive concentration and compaction pressure on the magnetocaloric properties of polymer-bonded La(Fe,Mn,Si)13Hx material.
•ΔTad value of bulk La(Fe,Mn,Si)13Hx obtained by direct measurements.•MCE of loose, compacted and polymer bonded powder samples was investigated.•Particle size, compaction pressure, type and amount of adhesive were optimized.•Full dense composite material with preserved magnetocaloric properties was produced.•The new composite material has higher ΔSm and ΔTad values than Gd and La(Fe,Co,Si)13.
La(Fe,Si)13H-based materials are considered to be one of the most promising room-temperature magnetic refrigerants. The intrinsic brittleness and relatively low thermal conductivity in La-Fe-Si-H ...alloys, however, have severely hindered its preparation, shaping and application. To solve this long-standing problem, in this work we propose a novel approach to fabricate stable La-Fe-Si-H blocks and plates by adding extra α-Fe as a reinforcing phase to enhance mechanical integrity. Much better bending strength compared to that in the stoichiometric composition has been observed in our dual phase La-Fe-Si-H magnetic refrigerants. Such novel Fe-rich plates can be exposed to 105 magnetic field cycles without losing mechanical integrity. In addition, a large and reproducible ΔTad of 5.4 K in 1.93 T and a thermal conductivity of 6 W/mK at room temperature have been obtained.
In the dual phase La-Fe-Si-H alloys, materials can be fabricated to the block shape, where the toughening α-Fe guarantees the mechanical integrity and offers significantly enhanced thermal conductivity. Display omitted
•A method of preparation of FeNi L10 phase was proposed.•We applied cycling of oxidation/reduction processes at 320 °C of FeNi nanopowder.•This technique excels at up scaling and the ability to ...control the particle size.•Enhanced diffusion makes the synthesis of Fe-Ni alloys at low temperatures possible.•The influence of the synthesis parameters on physical properties was studied.
FeNi L10 (tetrataenite) phase has great perspectives for hard magnetic materials production. In this paper we report on synthesis of this phase in chemically co-precipitated FeNi nanopowder by means of a thermal treatment procedure which includes cycling oxidation and reduction processes at 320 °C. The presence of the FeNi L10 phase in the samples was confirmed by magnetic measurements and differential scanning calorimetry analysis.
The reactive crucible melting method is known to be an efficient and low-cost bulk combinatorial synthesis technique to search for new phases. In this work, we tested this technique by investigating ...the Fe-Sn binary system. For high-throughput characterization, this synthesis technique was combined with energy dispersive x-ray spectroscopy as well as magneto-optical Kerr microscopy. The latter was used for identification of desired phases with uniaxial magnetic anisotropy. Reliability of the reactive crucible method was evaluated by comparison of the phase composition forming in the reactive crucible with phases appearing in conventionally melted samples and with the phases represented in the reported Fe-Sn phase diagram. It was found that the Fe5Sn3 phase, existing in the equilibrium phase diagram at 800 °C and forming in conventionally melted alloys, does not exist in the diffusion zone of the reactive crucible. The problem of ‘missing phases’ is discussed. In addition, we have shown that the anisotropy energy obtained by quantitative analysis of the uniaxial domain structure of Fe3Sn2 phase, gives the value of 1 MJ/m3, whereas K1 evaluated by conventional magnetometry is ∼ 0.07 MJ/m3 only, by this demonstrating how erroneous the assessment of K1 from domain structure can be. Finally, a new unit cell is proposed for Fe5Sn3 phase, which is commensurately modulated by the orthorhombic unit cell with lattice parameters of a = 4.221 Å, b = 7.322 Å, c = 5.252 Å and the space group Pbcm(α00)0s0 with a modulation vector of q = (½,0,0).
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Hydrogenated La(Fe,Mn,Si) 13 -based alloys have an excellent magnetocaloric properties, but poor mechanical and chemical stability. This hinders their direct machining and implementation in an active ...magnetic regenerator (AMR). In this paper, we show how machinability and corrosion protection of the particles can be improved by a hot-dip coating. To avoid the loss of hydrogen during the coating process, a low melting temperature eutectic Bi-Sn-In alloy was selected as a metal binder. The coated particles were used to build a packed bed regenerator as an array of fixed particles, avoiding such negative effects as sedimentation, segregation, and channel deformation. Similarity theory, combined with unsteady heat transfer approach was applied in order to calculate the optimal operation frequency and to estimate the maximal cooling power of the magnetocaloric regenerators. Two different geometries of heat exchangers were theoretically compared: stacked flat plate/channel structure and packed bed of equidimensional spherical particles. It is shown that, operating at low frequency, the same amount of magnetocaloric material can expel bigger amount of heat, when formed as packed bed heat exchangers. The metal-bonded packed bed regenerator made from La(Fe,Mn,Si) 13 H x powder was tested in a home-build versatile testing device in a magnetic field change of 10 kOe. The maximal achievable temperature span as a function of both parameters-hot end temperature and length of regenerator-was explored. The largest thermal span of 8 K was produced by the regenerator with 40 mm length.
Metal-filled carbon nanocomposites containing 20wt% of metallic FeCo nanoparticles were synthesized by means of infrared heating of precursors (polyacrylonitrile – iron acetylacetonate - cobalt ...acetate). This fabrication approach shows promise for making radiation-absorbent materials in short one-step process with ability to control the size of nanoparticles and attune the composition of the metallic components. In this work the magnetic behavior of reaction products obtained at different stages of the synthesis have been investigated in detail. We report on the influence of the annealing temperature on evolution of the structure, chemical composition, size, surface morphology, spontaneous magnetization and coercivity of the FeCo nanoparticles.
•A method of preparation of FeCo metal-filled carbon nanocomposites was proposed.•Proposed method is based on infrared heating of the precursors.•This technique excels at up scaling and the ability to control the particle size.•Usage of IR radiation leads to significant reduction of process time and temperature.•The influence of the synthesis parameters on physical properties was studied.
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The remanence and coercivity of arc melted Mn70Ga30 can be substantially improved by cold rolling. For best performance the rolled material should be annealed at T=730K in the presence of a magnetic ...field of 1T. The so-obtained magnet has a remanence of 0.239T and a coercivity of 1.24T at room temperature. The underlying reason for the high coercivity and remanence is the increase of the content of a metastable ferrimagnetic D022 phase at the expense of the normally stable anti-ferromagnetic D019. Magnetic field significantly increases the nucleation rate of the ferromagnetic D022 phase that leads to grain size refinement and as a consequence of improving remanence and coercive field.
•Alternative synthesis method for D022 phase formation in Mn–Ga is developed.•Effect of cold rolling and annealing on magnetic properties of Mn70Ga30 is examined.•Small magnetic fields are sufficient to accelerate nucleation of the D022 phase.
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