Fe-14Cr-0.4Ti-0.25Y2O3 ferritic steels were produced by varying the amount of residual process control agent, PCA (ethanol), in the ball-milled powders and changing the spark-plasma-sintering, SPS, ...temperature. Near theoretical density (99.3%), high Vickers hardness (501–920 HV, measured by applying a load of 100 g for 5 s) and fine grain size (26–36 nm), very stable against heating, can be achieved on ODS ferritic steels, consolidated from powders with a low amount of PCA and processing temperature in the range of 1000 °C–1100 °C. Additional grain refinement occurs near α → γ transition which is generated by the reaction of the traces of PCA with the ferritic matrix upon heating. High local temperatures and the evolved thermally activated processes, at the contact points between particles/at the particle surfaces during SPS-consolidation, were demonstrated to be the main factors responsible for improved densities and hardness. The role of PCA in the sintering, thermal and microstructure particularities and its impact on the quality of the final steel was thoroughly analysed throughout the work.
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•Highly dense ultra-fine grained Fe14Cr ODS ferritic steel with high hardness was produced.•Density and Vickers hardness are determined by the amount of residual PCA in MA powders.•PCA dissolved upon heating within the Fe14Cr alloy promoted α → γ transformation.•Rapid cooling from the C- enriched regions caused grain refinement and hardening.•Post SPS treatment - stable nano-sized grains, reduction of (Fe,Cr)2O3 and M7C3.
Abstract
Structural and magnetic properties of Fe oxide nanoparticles prepared by laser pyrolysis and annealed in high pressure hydrogen atmosphere were investigated. The annealing treatments were ...performed at 200 °C (sample A200C) and 300 °C (sample A300C). The as prepared sample, A, consists of nanoparticles with ~ 4 nm mean particle size and contains C (~ 11 at.%), Fe and O. The Fe/O ratio is between γ-Fe
2
O
3
and Fe
3
O
4
stoichiometric ratios. A change in the oxidation state, crystallinity and particle size is evidenced for the nanoparticles in sample A200C. The Fe oxide nanoparticles are completely reduced in sample A300C to α-Fe single phase. The blocking temperature increases from 106 K in A to 110 K in A200C and above room temperature in A300C, where strong inter-particle interactions are evidenced. Magnetic parameters, of interest for applications, have been considerably varied by the specific hydrogenation treatments, in direct connection to the induced specific changes of particle size, crystallinity and phase composition. For the A and A200C samples, a field cooling dependent unidirectional anisotropy was observed especially at low temperatures, supporting the presence of nanoparticles with core–shell-like structures. Surprisingly high M
S
values, almost 50% higher than for bulk metallic Fe, were evidenced in sample A300C.
Abstract Fabrication and extensive characterization of hard-soft nanocomposites composed of hard magnetic low-temperature phase LTP-MnBi and amorphous Fe 70 Si 10 B 20 soft magnetic phase for bulk ...magnets are reported. Samples with compositions Mn 55 Bi 45 + x⋅(Fe 70 Si 10 B 20 ) (x = 0, 3, 5, 10, 20 wt.%) were prepared by spark plasma sintering of powder mixtures. Characterization has been performed by X-ray diffraction, scanning and transmission electron microscopy, magnetometry and 57 Fe Mӧssbauer spectroscopy. It was shown that samples contain crystallized and nanometric LTP-MnBi phases with various elemental compositions depending on the degree of Bi clustering. Complex correlations between starting compositions, processes during fabrication, and functional magnetic characteristics were observed. Unexpected special situations of the relation between microstructure and magnetic coupling mechanisms are discovered. Exchange spring effects of different strengths occur, being very sensitive to morpho-structural and compositional features, which in turn are controlled by processing conditions. An in-depth analysis of related microscopic characteristics is provided. Results of this work suggest that fabrication by powder metallurgy routes, such as spark plasma sintering of hard and soft magnetic powder mixtures, of MnBi-based composites with exchange spring phenomena have a high potential in designing and optimization of suitable materials with tunable magnetic properties towards rare-earth–free permanent magnet applications.
Within the framework of density functional theory, the electronic structure and magnetic properties have been studied for the Ti2FeSn full-Heusler compound. The ferromagnetic state is found to be ...energetically more favorable than paramagnetic and antiferromagnetic states. The spin-polarized results show that Ti2FeSn compound has half-metallic ferromagnetic character with a total spin moment of 2μB and a band gap in the minority spin channel of 0.489 eV, at the equilibrium lattice constant a = 6.342 Ǻ.
► Electronic structure and magnetic properties of Ti2FeSn were investigated. ► The total magnetic moment is 2μB at equilibrium lattice constant (a = 6.342 Ǻ). ► Fully spin polarization for an enlargement of lattice parameter than 6.038 Å.
•A continuous microwave processing system for treatment of contaminated soils is demonstrated.•Degree of organic removal was assessed as a function of power and energy input.•Applying the power in a ...single stage was the most energy efficient.•Hydrocarbon removal is higher using two stage heating but required more energy.
A continuous conveyor-belt processing concept using microwave heating was developed and evaluated. Four hydrocarbon-contaminated soils were used as model feedstocks, and the degree of organic removal was assessed against the power and energy input to the process. The findings of this study at scale (150kg/h) are in direct agreement with data obtained in batch laboratory scale experiments, and show that microwave heating processes are fundamentally scalable. It is shown that there is a trade-off between the efficiency of organic removal and the power distribution, and applying the power in a single stage was found to be 20–30% more energy efficient but the overall degree of organic removal is limited to 60%. 75% removal was possible using two processing steps in series, but the organic removal is ultimately limited by the amount of power that can be safely and reliably delivered to the process material. The concept presented in this work is feasible when 75% organic removal is sufficient, and could form a viable industrial-scale process based on the findings of this study.
The electronic and magnetic properties of Ti2CoSi Heusler compound are investigated using density functional calculations. The optimized lattice constant is found to be 6.030Å. The compound is a ...half-metallic ferromagnet with an energy gap in minority spin channel of 0.652eV at equilibrium lattice constant, which leads to a 100% spin-polarization. The obtained total magnetic moment from spin-polarized calculations is 3.0μB for values of lattice constants higher than 5.941Å. The half-metallicity is spoiled for a compressed volume of 4%, suggesting a possible application as pressure sensitive material.
► First-principles calculations investigate the electronic and magnetic properties of Ti2CoSi. ► The total magnetic moment is 3μB for the optimized lattice constant of 6.030Å. ► The half-metallic character is obtained for values of lattice parameter higher than 5.941Å.
Composites of magnetite (Fe3O4) nanoparticles dispersed in a polydimethylsiloxane (PDMS) matrix were prepared by a molding process. Two types of samples were obtained by free polymerization with ...randomly dispersed particles and by polymerization in an applied magnetic field. The magnetite nanoparticles were obtained from magnetic micrograins of acicular goethite (α-FeOOH) and spherical hematite (α-Fe2O3), as demonstrated by XRD measurements. The evaluation of morphological and compositional properties of the PDMS:Fe3O4 composites, performed by SEM and EDX, showed that the magnetic particles were uniformly distributed in the polymer matrix. Addition of magnetic dispersions promotes an increase of thermal conductivity compared with pristine PDMS, while further orienting the powders in a magnetic field during the polymerization process induces a decrease of the thermal conductivity compared with the un-oriented samples. The shape of the magnetic dispersions is an important factor, acicular dispersions providing a higher value for thermal conductivity compared with classic commercial powders with almost spherical shapes.
The influence of the severe plastic deformation
via
high-speed high-pressure torsion (HSHPT) on the structural and magnetic properties of the Zr
13
Co
87
alloys is investigated. Moderate applied ...deformation promotes the growth of the rhombohedral hard magnetic phase leading to the increase of the sample’s hardness and magnetic coercivity. A higher degree of deformation affects the samples morphology leading to a critical value of the grain size under which the exchange coupling of the soft phase is less effective. Additionally, it produces a random alignment of the anisotropy axes, which are both detrimental to the hard magnetic properties.
The half-metallic properties of Ti2CoSn full-Heusler compound is studied within the framework of the density of states theory with the Perdew Burke Ernzerhof generalized gradient approximation (GGA). ...Structural optimization was performed and the calculated equilibrium lattice constant is 6.340Å. The spin up band of compound has metallic character and spin down band is semiconducting with an indirect gap of 0.598eV at equilibrium lattice constant. For the lattice parameter, ranging from 6.193 to 6.884Å the compound presents 100% spin polarization and a total magnetic moment of 3μB.
► Density of states, energy bands and magnetic moments of Ti2CoSn were investigated. ► The calculated equilibrium lattice constant is 6.340Å. ► The compound presents a total magnetic moment of 3μB. ► Fully spin polarization for the lattice parameter interval 6.193–6.884Å.
A quantitative treatment of the effects of magnetic mutual interactions on the specific absorption rate of a superparamagnetic system of iron oxide nanoparticles coated with oleic acid is reported. ...The nanoparticle concentration of the considered ferrofluid samples varied from a very low (0.005) to a medium (0.16) value of the volume fraction, whereas the amplitude of the exciting AC magnetic field ranged from 14-35 kA m−1. It was proved that a direct effect of the interparticle interactions resides in the regime of the modified superparamagnetism, dealing, besides the usual increase in the anisotropy energy barrier per nanoparticle, with the decrease in the specific time constant τ0 of the relaxation law, usually considered as a material constant. Consequently, the increase in the specific absorption rate versus the volume fraction is significantly diminished in the presence of the interparticle interactions compared to the case of non-interacting superparamagnetic nanoparticles, with direct influence on the magnetic hyperthermia efficiency.
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