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The paper presents the analysis of two compaction methods for obtaining W/Cu Functional Graded Materials (FGMs) consisting of three layers with the following compositions (% weight): first layer 80 W/20 Cu, second layer 75 W/25 Cu, and third layer 65 W/35 Cu. Each layer composition was obtained using powders obtained through mechanical milling. The two compaction methods were Spark Plasma Sintering (SPS) and Conventional Sintering (CS). The samples obtained after the SPS and CS were investigated from morphological (scanning electron microscopy-SEM) and compositional (energy dispersive X-ray spectroscopy-EDX) points of views. Additionally, the porosities and the densities of each layer in both cases were studied. It was found that the densities of the sample’s layers obtained through SPS are superior to those obtained through CS. The research emphasizes that, from a morphological point of view, the SPS process is recommended for W/Cu-FGMs, having raw materials as fine-graded powders against the CS process.

"The soft magnetic nanocrystalline powders, alloys (Ni3Fe, 79Ni16Fe5Mo, 77Ni14Fe5Cu4Mo, wt. %) and zinc ferrite, were obtained by dry and wet mechanical alloying and reactive milling, followed by different heat treatments. The powders were characterised by X-ray diffraction, scanning electron microscopy, X-ray microanalysis, differential scanning calorimetry, thermomagnetic and magnetic measurements. The X-ray diffraction shown the progressive new phases formation. The crystallite size is between 18-7 nm depending on materials and milling conditions. The particle size is smaller for wet-mechanical alloying comparing with dry-milling. The thermomagnetic measurement shown the Curie temperature of the alloys. The spontaneous magnetisation of the wet-milled and annealed samples is higher than of the molten alloys. Keywords: mechanical alloying; Ni-Fe-X-Y alloys; soft ferrite; magnetisation; XRD; DSC. "

This paper presents findings on the influence of hydrothermal deposition processing parameters (precursor concentration and deposition duration) on the characteristics of ZnO layers deposited on the surface of amorphous Fe-based fibres. The characteristics of the coated fibres, especially the deposited layer, were investigated from structural, morphological, chemical, thermal and magnetic points of view. It was found that the use of a zinc acetate-based solution of 0.05 M concentration and a deposition duration of 24 h leads to a continuous, thin and adherent layer of ZnO on the surface of the fibres. The thickness of the ZnO layer is 450–500 nm, as shown by TEM-EDX investigations. The ZnO coated fibres were used to prepare fibre-based soft magnetic composites via a cold sintering process. The composites obtained are the first reported soft magnetic composites based on amorphous fibres. The coercive field of the cold sintered composites is 3.5 to 8.6 times lower, and the maximum relative permeability is 2.4 times larger, than the best coercive field and the maximum relative permeability reported until now for a crystalline fibre-based soft magnetic composite. The initial relative permeability of cold sintered composites is constant up to the frequency of 1000 Hz.

Fibres-based soft magnetic composites (FSMCs) have been prepared by using Fe fibres of different diameters (65, 125, 250 and 500 μm). The Fe fibres were coated with a 3 μm thick layer of Fe3O4 via the blackening process and subsequently compacted at 700 MPa. The X-ray diffraction analysis (XRD) was used to prove the formation of the Fe3O4 coating on the surface of the fibres. The thickness and the uniformity of the coating were analysed via scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). The DC measurements performed on the composite cores revealed that the saturation induction increase from 1.36 to 1.68 T, the maximum relative permeability increase from 550 to 940, and the coercive field decrease from 796 to 454 A/m as the fibre's diameter increase from 65 to 500 μm. By using thinner fibres (65 and 125 μm), composites with low losses and stable initial relative permeability, in the frequency range 50 Hz–10 kHz, can be obtained. To distinguish between different types of losses dissipated by our compacts, and the influence of the fibre's diameter on the different components of the total losses, a numerical model for loss separation is proposed. The comparative evolution of the AC magnetic characteristics of the FSMCs and powder-based SMCs is presented. According to the presented results, this new type of composites can be successfully used to prepare magnetic cores designated to work in the medium to high-frequency range.

This paper presents the preparation and characterisation of a new type of soft magnetic composites that are prepared from long Fe fibres instead of ferromagnetic particles. The Fe fibres were coated with a polymeric layer and compacted in toroidal shapes. The influence of polymer content and compaction pressure on the AC and DC magnetic properties of the compacts was investigated. The AC magnetic properties of the compacts were determined in the frequency range from 50 to 10 kHz at the flux densities of 0.1 T. It was found that 1 wt% of polymer ensures proper insulation of the fibres, hindering the development of eddy currents. Also, in order to have good magnetic properties, the compaction pressure should not be lower than 600 MPa. The comparison between the fibre-based soft magnetic composite and powder-based soft magnetic composite evidenced the superior magnetic properties of this new class of composites. For example, in the frequency range of 50 Hz–10 kHz, the initial relative permeability of the fibre-based compact is two times larger than the initial relative permeability of the powder-based compacts.

Invar 36 (Fe64Ni36) nanocrystalline powders were successfully obtained by the mechanical alloying process. The mechanically alloyed Invar 36 powders were obtained from both, Fe–Ni elemental and Fe–...

In this work we focus on enhancing the antibacterial activity of ZnO nanoparticles by Mn doping, synthesized using a wet-chemical method. The as-obtained precursor powders were deeply investigated by thermal analyses correlated with the evolved gas analysis (TG-DTA-FT-IR) and by in situ high-temperature XRD to elucidate the thermally induced processes and to understand the manganese doped ZnO nanoparticles formation. The hexagonal wurtzite-type structure and the morphological characteristics of the thermally treated samples have been investigated by X-ray diffraction, and HRTEM. An average particle size ranging between 10 and 29 nm and a polyhedral and spherical morphology with a tendency to form aggregates were evidenced by TEM images. Optical absorption measurements reveal that the band gap of ZnO decreased from 3.19 to 2.99 eV, which confirmed the existence of Zn-O-Mn interaction. The incorporation of the Mn ions into the ZnO lattice has been studied by EPR spectroscopy and also, the generation of reactive oxygen species (ROS) has been evidenced by using the EPR coupled with the spin trapping probe technique. Here, we report that in addition to altering the crystallite size, morphology and optical absorption characteristics of ZnO, the introduction of Mn dopant also improves the antibacterial efficiency against pathogenic microorganisms, namely Escherichia coli and Bacillus cereus.

The aim of this study is to develop core shell microcapsules of bovine serum albumin (BSA) gel with a complex polyelectrolite multilayer shell of natural polysaccharides with opposite charges, pect...

This paper presents a new approach on the wet attrition of some composite WC-10Co powders by using an aqueous medium instead of the classical organic solvent based processing method. The hard metal powders have been characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM), laser particle size analysis (PSA), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis coupled with mass spectrometry (TG-MS). The XRD investigation revealed that no significant changes in the structure of the material occur during milling, while the SEM and PSA analysis highlighted the presence of agglomerates that are formed during the drying of the aqueously processed powders. The observed composite flakes are formed by the sequential cold-welding and fracturing process of the particles. The elemental powders were blended and milled together in an aqueous media (distilled water + corrosion inhibitor) in order to achieve a homogeneous dispersion of the constituents. Prolonged milled durations are resulting in an incremental oxidation process, leading to the formation of CoO(OH). XPS analyses revealed that Co oxidises in depth, as opposed to the sample obtained by classical route, which reveals only superficial oxide. The residual moisture evidenced by TG-MS could also favour the formation of agglomeration and oxide in the powder.

A mixture of Ta and 25 mass% Cu elemental powders was subjected to mechanical alloying in a high-energy ball mill up to 60 h. The results are composite particles formed by nanocrystalline Cu and amorphous Ta phases. Thermal stability of amorphous was investigated by DSC. The XRD, FTIR and EDX analyses of Ta–25 mass% Cu powder milled for 60 h performed after DSC at 800 and 900 °C have revealed large amounts of Ta nitride and Ta oxides even though the milling process was done in Ar atmosphere. This is due to high reactivity of Ta fine particles with oxygen and nitrogen from air. During manipulations of the powder (taking samples from vials and its investigation), the adsorption phenomena on its surface occur, and both surface-adsorbed N2 and O2 are processed with powder and embedded in it. While heating of Ta–25% Cu milled powder in DSC, nitrogen and oxygen diffusion into tantalum is activated, and Ta2N and TaO2/Ta2O5 compound forms.

This study aims to develop new biocompatible hybrid bleaching materials based on titanium dioxide (TiO2), silica dioxide (SiO2) and ascorbic acid (Aa) and to test the characteristics of the bleached teeth, by atomic force microscopy and compressive load at break analyses. The new bleaching agents have similar efficiency with sodium perborate but they are less aggressive towards the tooth than the peroxides. The efficiency of the novel bleaching system consists in lack of side effects, confirmed by mechanical tests.

This paper presents the influence of sintering on the structure, morphology and compressing strength of alumina/nickel composite compacts obtained by spark plasma sintering (SPS). Al2O3/Ni composites were prepared by SPS in argon atmosphere at temperatures in the range of 1000–1200 –C with a holding time of 2, 5 and 10 minutes. The heating rate was 200 C min−1. These composites have been characterised by X-ray diffraction, SEM and EDX. The relative density and compressive strength of the as-obtained compacts were determined. The results showed that the alumina particles are uniformly dispersed in a quasi-continuous Ni network, and there was no sign of phase changes during sintering. The maximum strength of the alumina/nickel composite with a content of 75 vol. − Al2O3 and 25 vol. − Ni was about 240 MPa for the samples sintered at 1200 C for 10 minutes.Special block from the conference RoPM2017 guest edited by Ionel Chicinas, Technical University, Cluj-Napoca.

The preparation and characterisation of soft magnetic composite compacts based on hybrid coated nanocrystalline Fe-Si powder are presented. The Fe-Si powder was prepared by mechanical milling of Fe-Si electrical steels sheets up to 20 h. The hybrid coating consists in an electrically insulating phosphate and a polymer layer that covers the Fe-Si particles. The influence of phosphating duration on the particles surface was investigated by SEM, EDX, XRD, and FTIR investigations. The saturation magnetisation of the powders phosphated for 60 s decreases with 17% as compared to the uncoated powder. The influence of the compaction pressure, as well as the phosphating duration, on initial relative permeability and power losses of the compacts was investigated. It was found that increasing the compaction pressure leads to the increase of the compact's permeability and a decrease of the hysteresis losses. A shorter phosphating duration leads to a partial coating with phosphate of the Fe-Si particles and to compacts with higher density characterised by high magnetic permeability.

This work presents a comparative study on the HITPERM type alloy prepared by wet and dry mechanical alloying. The chosen composition for this study was Fe38.5Co38.5Nb7B15Cu1. The powders were obtained via mechanical alloying starting from elemental Fe, Co, Cu powders and the ferroalloys of Nb and B. Mechanical alloying experiments were done using a high energy planetary ball mill Pulverizette 6 under Ar atmosphere. It was observed that for the powder milled in wet milling conditions, using benzene as process control agent, the alloy amorphisation occurs after 40 h of milling. X-ray diffraction patterns highlighted the alloy amorphisation. In the dry milled powder case, the amorphisation did not occur even after 100 h of milling. The thermal stability and the crystallisation kinetics of the amorphous powders were investigated via differential scanning calorimetry and in-situ high-temperature X-ray diffraction. The powders morphology and chemical homogeneity were studied by scanning electron microscopy and X-ray microanalysis. The saturation magnetisation also reveals a difference between wet and dry milled powders versus milling time. The obtained results concerning the alloy amorphisation and its thermal stability are compared with available data of the literature.

The formation of iron oxide/iron composite compacts using mechanically activated and un-activated α-Fe 2 O 3 /Fe powder mixtures in various ratios by reactive spark plasma sintering – SPS is evidenced. Independent on the sintering temperature SPS of activated powders is leading to compacts with a microstructure consisting of iron clusters distributed in a continuous iron oxide matrix. The use of the un-activated powder is resulting in the fragmentation of the iron oxide matrix for several sintering temperatures by coalescence of the iron clusters. The carbon from graphite mould and punches has a significant influence on conserving the Fe/O ratio in compacts. The compact's microstructure and density, phase formation and crystallite size evolution during sintering, sintering mechanism and reactions which occur during sintering are discussed. The results are correlated with the free Gibbs energy of the system at various temperatures. The in-situ high-temperature X-ray diffraction has been performed. It is highlighted that in the case of the un-activated powder up to 1000 °C two or three iron oxides simultaneously coexist. In the temperature range of 550–580 °C in the material are present: α-Fe 2 O 3 , Fe 3 O 4 , and FeO. In the case of activated samples, in the temperature interval 250–530 °C only Fe 3 O 4 is present.

Formation of the Ni2MnSn Heusler alloy by solid state reaction from elemental powders was investigated. The solid state reaction was conducted in a planetary ball mill under argon atmosphere up to 28 h of milling. During the milling, after selected intervals samples were collected and studied by X-ray diffraction to record phase changes. After 16 h of milling a two phase mixture (Ni2MnSn with B2 structure and NiMnSn with C1b structure) was found. Further, the thermal stability of the samples was investigated, and phase precipitation was found. The formed phases are ordered Full Heusler (L21) and Ni3Sn2. The formation temperature and their amount evolution versus temperature and milling time is discussed. An inversion of the formation temperature was found for the L21 and Ni3Sn2 phase, during the DSC study, in relation with the milling time. For the B2 compound a stability range on temperature was identified (from 25 to 300 °C), as well as for the L21 and Ni3Sn2 phases (from 400 to 600 °C) in the case of 28 h milled sample. The milled and annealed sample exhibit nanocrystalline state, formation mechanism under temperature was concluded to be by precipitation.

Fe3O4/Ni3Fe composite powder has been synthetized, starting from Fe, NiO and α-Fe2O3 precursors via mechanosynthesis and annealing, varying the alloy/ferrite ratio. The formation of Fe3O4 is noticed for the composite with low alloy content in the case of the samples milled for 10 h. Formation of Ni3Fe and Fe3O4 does not fully occur after milling for 10 h, in either of the cases and as a consequence, the presence of several intermediate phases can be observed. Annealing at 500 °C for 4 h led to an incomplete reaction between the precursors for the un-milled sample. For the milled and subsequently annealed samples, the complete formation of the composite Fe3O4/Ni3Fe occurs at the milling time of 10 h. The DSC measurements reveal a decrease of the temperature required for the Fe3O4 complete formation upon increasing milling time. The first magnetisation curves reveal a decrease of the magnetisation upon increasing milling time. The value of magnetisation after annealing is higher than the magnetisation value of the milled samples as a result of the complete formation of the ferrite phase and Ni3Fe intermetallic compound.

This paper presents a comparative study regarding the preparation of Fe-based amorphous alloys via mechanical alloying (MA) and rapid quenching (RQ). The obtained samples (powders and ribbons) were characterised by X-ray diffraction (XRD), in-situ high-temperature X-ray diffraction (HT-XRD), differential scanning calorimetry (DSC), thermogravimetry (TG) and vibrating sample magnetometry (VSM). By using elemental powders of Fe, Si and B, it was found that amorphisation cannot be achieved by dry MA or RQ. Wet MA using benzene as process control agent (PCA) led to the alloy amorphisation after 20 h of milling. It was proved that the amorphisation via wet MA is possible due to the extra amount of C atoms provided by the PCA decomposition. Using powders obtained by wet MA or a mixture of Fe, Si, B and C elemental powder, amorphous ribbons were obtained by RQ. During the amorphous samples crystallisation, a mixture of α-Fe(Si) and Fe borides is formed. The magnetic measurements showed that the magnetic characteristics of the samples are strongly influenced by the technique used for their preparation.

This paper presents the results of using an aqueous milling media in comparison with traditional milling routes, as well as the influence of the milling media interaction with powder on the morphology and agglomeration behaviour. Hard Metal powders were milled in four milling media, two of them consisting of traditional milling routes and two of them aqueous routes. The aqueous milled powder is larger in size, similar to acetone and exhibits higher hardness as compared to the powder milled using isohexane, acetone, thus lowering the pressability. The pH adjustment of the water leads to soft agglomerates similar to isohexane and acetone. Powder oxidation occurs after the drying process, being more intense in the case of using an aqueous medium. Using N2 atmosphere has inhibited the powder oxidation for the powder milled in traditional media. Using CO2 or by gradual exposure to air the spontaneous oxidation is prevented for aqueous processing.

This study presents the preparation and characterisation of soft magnetic composites (SMCs) in which the powders, that are generally used as the ferromagnetic phase, are replaced by short and thin Fe fibres. The Fe fibres (length of 3–7 mm and thickness of 70–110 μm) were coated with a layer of polymer that represents 1 wt% of the total weight of the fibres. To prepare the toroidal cores, three different mould filling techniques were used with the aim of orienting the fibres with their long axis parallel to the magnetising field. The compaction pressure for the preparation of all compacts was 700 MPa. The fibres used in this study were characterised via scanning electron microscopy (SEM) and vibrating sample magnetometry (VSM). The degree of fibres orientation inside the composite compacts was analysed via energy-dispersive X-ray spectroscopy (EDX). The fibres based composite compacts were analysed in static (DC) and dynamic (AC) magnetisation regime up to the frequency of 10 kHz. The DC and AC magnetisation measurements highlighted that the magnetic characteristics of the compacts increase upon increasing the degree of fibres orientation. A comparison of AC and DC magnetic characteristics of a fibres-based composite and a powder-based composite (prepared in identical conditions) is presented and discussed.

The paper reports on the preparation and characterisation of a new type of soft magnetic composites in which the ferromagnetic particles are replaced by Fe fibres. The fibres were coated via hydrothermal method with a SiO2 layer having a thickness of 150–200 nm. Also, a hybrid coating was developed by adding a supplementary layer of polymer on top of the SiO2 layer. The coated fibres were compacted via cold pressing at the pressure of 700 MPa. Our results indicate that using only SiO2 as the insulating layer leads to compacts characterised by lower hysteresis losses. However, it seems that during compaction, the SiO2 layer is damaged leading to the development of large eddy currents at high frequencies. Conversely, the additional polymer layer manages to prevent the development of excessive eddy currents in the compact, but with a significant increase of the hysteresis losses of the compacts being observed. A significant improvement of the magnetic characteristics of the fibre-based soft magnetic composites can be achieved by an annealing treatment with the condition of maintaining the integrity of the insulating layer, or minimising the diffusion between the fibres and the SiO2 coating during the annealing.

Nanocrystalline/nanosized magnetite - Fe3O4powder was obtained by mechanical milling of well crystallized magnetite obtained by ceramic method starting from stoichiometric mixture of commercial hematite - Fe2O3and iron - Fe powders. The mean crystallites size of the magnetite is decreasing upon increasing the milling time down to 6 nm after 240 minutes of milling. After 30 minutes of milling an undesired hematite phase is formed in the material. The amount of this phase increases upon increasing the milling time. In the early stage of milling (up to 30 minutes) the existence of nanometric particles (mean size below 100 nm) is noticed. The d50median diameter decreases first (up to 5 minutes of milling) and after that, an increase follows for milling times up to 120 minutes. Saturation magnetization decreases upon increasing the milling time and is more difficult to saturate. X-ray diffraction, laser particle size analysis and magnetic measurements have been used for powder characterization.

Result of research concerning the influence of milling conditions on the amorphisation of the Fe75Si20B5 (at.%) alloy is presented. Amorphous powder of Fe75Si20B5 (at.%) was prepared by dry and wet mechanical alloying (MA) route starting from a mixture of Fe, Si and B elemental powders. The mixture was wet/dry milled up to 50 hours. Benzene, oleic acid and ethanol were used as process control agents (PCA) in order to investigate the influence of their chemical composition on the powder amorphisation. The evolution of the powder crystalline structure, thermal stability and magnetic properties were investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetry (TG) as well as magnetic measurements versus temperature and field. It is proved that the chemical composition of the PCA (especially the carbon content) plays an important role in the amorphisation process induced by wet MA.

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Nanocrystalline Fe-10 wt% Si powders has been obtained by mechanical alloying. The synthesis conditions as well as their influence on the structural and magnetic properties of this soft magnetic alloy have been investigated in the light of several experimental techniques (X-ray diffraction, neutron diffraction, DSC, magnetic measurement, SEM). By X-ray diffraction (XRD) investigations have been highlighted that Fe-Si alloy is formed after 4 h of mechanical milling and the mean crystallite size is down to 14 nm (8 h milled sample). The heat treatment leads to the formation of the Fe 3 Si compound with DO3-type superstructure for low milling times. The saturation magnetisation of the as-milled powders decreases in the first 4 h of milling due to the formation of the Fe-Si alloy. The behaviour of the saturation magnetisation versus milling time and annealing was explained by the different magnetic moment of iron atoms in Fe 3 Si structure. The Curie temperature decreases from 770 °C (the Curie temperature for pure iron) to about 650 °C after 8 h of milling.

The composite/nanocomposite powders of Mn0.5Ni0.5Fe2O4/Fe type were synthesized starting from nanocrystalline Mn0.5Ni0.5Fe2O4 (D = 7 nm) (obtained by ceramic method and mechanical milling) and commercial Fe powders. The composites, Mn0.5Ni0.5Fe2O4/Fe, were milled for up to 120 min and subjected to heat treatment at 600 °C and 800 °C for 2 h. The manganese-nickel ferrite/iron composite samples were subjected to differential scanning calorimetry (DSC) up to 900 °C for thermal stability investigations. The composite component phases evolution during mechanical milling and heat treatments were investigated by X-ray diffraction technique. The present phases in Mn0.5Ni0.5Fe2O4/Fe composite are stable up to 400–450 °C. In the temperature range of 450-600 °C, the interdiffusion phenomena occurs leading to the formation of Fe1−xMnxFe2O4/Ni–Fe composite type. The new formed ferrite of Fe1−xMnxFe2O4 type presents an increased lattice parameter as a result of the substitution of nickel cations into the spinel structure by iron ones. Further increases of the temperature lead to the ferrite phase partial reduction and the formation of wustite-FeO type phase. The spinel structure presents incipient recrystallization phenomena after both heat treatments (600 °C and 800 °C). The mean crystallites size of the ferrite after heat treatment at 800 °C is about 75 nm. After DSC treatment at 900 °C, the composite material consists in Fe1−xMnxFe2O4, Ni structure, FeO, and (NiO)0.25(MnO)0.75 phases.

Commercially, iron (α-Fe) and hematite (α-Fe2O3) powders were used for the synthesis of composite powders of Fe2O3/Fe type by mechanical milling. Several ratios of Fe2O3/Fe were chosen for the composite synthesis; the atomic percent of oxygen in the starting mixtures ranged from 21 to 46 %. The Fe2O3/Fe composite samples with various Fe/O ratios were milled for different milling times. The milled composite samples were subjected to the heat treatments in argon up to 900 °C. During the heat treatment at temperatures that do not exceed 550 °C, Fe3O4/Fe composite particles are formed by the reaction between the Fe2O3 and Fe. Further increase of the heat treatment up to 700 °C leads to the reaction of the Fe3O4/Fe composite component phases, resulting thus in the formation of FeO/Fe composite. The heat treatment up to 900 °C of the Fe2O3/Fe leads to the formation of a composite of FeO/Fe3O4/Fe independent of the milling time and Fe2O3/Fe ratios. The onset temperatures of the Fe3O4 and FeO formations decrease upon increasing the milling time. Another important aspect is that, in the case of the same milling time but with a large amount of iron into the composite powder the formations temperatures of Fe3O4 and FeO are also decreasing. The influence of the mechanical activation time, heat treatment temperature, and Fe/O ratio on the formation of the (Fe3O4, FeO)/Fe composite from Fe2O3+Fe precursor mixtures was studied by differential scanning calorimetry and X-ray diffraction techniques.

The nanocrystalline/nanosized mixed manganese–nickel spinel ferrite ${\rm Mn}_{0.5}{\rm Ni}_{0.5}{\rm Fe}_{2}{\rm O}_{4}$ was successfully synthesized by the classical ceramic method followed by mechanical milling. The refinement of the crystallite size is obtained by increasing the milling time up to 120 min. The particles size distribution performed on the milled powder showed a fine ferrite powder. The Neel temperature of ${\rm Mn}_{0.5}{\rm Ni}_{0.5}{\rm Fe}_{2}{\rm O}_{4}$ decreases by increasing the milling time as a result of the structural disorder and it is larger when compared with the manganese ferrite one and lower when compared with the nickel ferrite one. The saturation magnetization of the spinel structure was found to be 2.42 $\mu_{B}$ and it is close to the theoretical one 2.5 $\mu_{B}$ . The saturation magnetization and spontaneous magnetization decrease by increasing milling time. The spontaneous magnetization is reduced more drastically when compared with the saturation magnetization. One of the major causes is assumed to be the spin canted effect induced at the particles surface by milling process.

Soft magnetic composite of ${\rm Fe}/{\rm Fe}_{3}{\rm O}_{4}$ type was synthesized by mechanical milling and reactive sintering starting from a mixture of Fe and ${\rm Fe}_{2}{\rm O}_{3}$ commercial powders. During mechanical milling, the Fe and ${\rm Fe}_{2}{\rm O}_{3}$ phases start to react after 120 min. A composite powder of ${\rm Fe}/{\rm Fe}_{2}{\rm O}_{3}$ type results after 60 and 120 min of milling. The composite powder obtained by milling was pressed in toroidal shape at 100 up to 300 MPa. The green composite compacts $({\rm Fe}/{\rm Fe}_{2}{\rm O}_{3})$ were sintered at 1100 $^{\circ}{\rm C}$ for 6 h, resulting in ${\rm Fe}/{\rm Fe}_{3}{\rm O}_{4}$ like sintered composite compacts having an amount of FeO phase. The microstructure analysis shows an iron matrix that embeds iron oxide clusters. The magnetic measurements in dc current indicate the positive influence of the increased applied pressure on the magnetic permeability and saturation induction characteristics. The investigations in dc revealed that the milling time has almost no influence on the magnetic characteristics of the sintered composite compacts. ac investigations showed that the magnetic permeability decreases upon increasing the testing frequency. The total losses increase significantly by increasing the frequency due to the excessive increase in eddy currents at higher frequencies.

International audience; The spark plasma sintering technique is used to prepare composite compacts starting from nanocrystalline Supermalloy and iron powder. The sintered compacts are investigated by X-ray diffraction, scanning electron microscopy, X-ray microanalysis, electrical resistivity and DC magnetic measurements. It is found that iron addition leads to an enhanced sintering process, the relative density of the compacts increases upon increasing iron content. The mean crystallite size of Supermalloy increases from 19 to 27±2 nm with increasing the iron content from 0% to 50 wt% (for identical sintering conditions). The interface created during the sintering process between iron and Supermalloy particles has a wide range of chemical composition including that corresponding to Rhometal like alloys. This leads to an increase of the electrical resistivity and coercivity of the compacts. The saturation induction and maximum relative permeability increase by 58% and 143% respectively, when the iron content increases up to 50 wt%.