Highly enhancing electromagnetic properties in Fe-Si/MnO-SiO2 soft magnetic composites by improving coating uniformity

Fe-Si/MnO-SiO₂ soft magnetic composites (SMCs) are prepared by sintering ball milled Fe-Si/MnO₂ core–shell structured composites. The correlation between the coating uniformity and electromagnetic properties have been investigated via adjusting ball milling parameters in detail. The results indicate that uniform MnO₂ coating can be transformed into MnO-SiO₂ composite coatings with high insulation due to the high temperature reaction between MnO₂ and Si. Agate ball is more effective than stainless steel ball to improve the uniformity of MnO₂ coating as well as the electromagnetic properties such as significantly higher resistivity, lower core loss and better frequency stability of permeability. Moreover, increasing the ball milling time from 4 h to 24 h can obviously improve the coating uniformity and thus result in the remarkable increase of the resistivity from 2.4 mΩ·cm to 356.9 mΩ·cm. And the core loss and dynamic loss decrease rapidly while the M_s shows a slight decline. When the ball milling time reaches 24 h, the Fe-Si SMCs exhibits superior magnetic properties such as high M_s (181.0 emu/g), very low core loss (361.5 kW/m³ at 100 kHz) and good frequency stability of permeability (65) from 50 Hz to 1000 kHz.     

Improved magnetic properties of iron-based soft magnetic composites with a double phosphate-SiO2 shells structure

Herein a double shells structure was proposed to overcome the drawbacks such as poor heat resistance, incomplete insulation and high core loss coating of iron-based soft magnetic composites (SMCs) with single shell structure. The surface of the iron powder was coated with a double shells structure composed of an inner phosphate coating and an outer SiO₂ coating through phosphating and hydrolysis successively. Subsequently, the effects of different SiO₂ addition amount on the microstructure of iron powder and magnetic properties of SMCs were studied. The introduction of SiO₂ in the double shells structure inhibited the decomposition and failure of phosphating layer after being annealed at a high temperature. The iron powder coated with the phosphate-SiO₂ insulating layer was still effective after annealing in a N₂ atmosphere at 570 °C, achieving the purpose of eliminating residual stress and improving magnetic properties. The optimal process parameters were set at 0.2 wt% phosphoric acid and 0.5 wt% tetraethyl orthosilicate to fabricate the phosphate-SiO₂ double shells. The iron-based SMCs presented excellent magnetic properties with B_s of 1.29 T and P_s of 169.2 W/kg (measured at 1 T and 1 kHz). In addition, the core loss of SMCs introduced with SiO₂ is 83% lower than that of SMCs produced by the phosphating process. This paper provides a feasible method for improving the magnetic properties of SMCs.

     

Mechanosynthesis and magnetic characterization of nanocrystalline manganese ferrites

Manganese ferrites, MnFe₂O_4±δ, synthesized via mechanosynthesis from different manganese sources, MnO, Mn₂O₃ and MnO₂, and mixed with Fe₂O₃, were studied. XRD, SEM and magnetometry were used to characterize the synthesized powders. The MnFe₂O₄ spinel phase appeared after 12 h of milling when MnO and MnO₂ mixed with Fe₂O₃ were used as the precursors and showed the maximum saturation magnetization value (49.77 emu/g). Manganese ferrite did not form when MnO₂ was used. Manganese ferrite obtained from Mn₂O₃ showed the lowest saturation magnetization value. An increase in the milling time promoted the increase in the saturation magnetization values.     

Synthesis and magnetic properties of Ni–SiO2 nanocomposites

Nanocomposite Ni_(1 − x)/(SiO₂)_x soft magnetic materials were synthesized by a simple sol–gel combined hydrogen reduction method. The crystal structure of the particles was determined by X-ray diffraction (XRD). The shapes and sizes of the metal particles embedded in the SiO₂ matrix were determined by transmission electron microscopy (TEM), and magnetic properties were measured by the vibrating samples magnetometer (VSM). The obtained nanocomposite material is composed of nanoparticles coated with a thin SiO₂ layer, and with the content of the silicon increase, the thickness of the silica shells increase and the saturation magnetization decrease. The diameter of Ni particle in the sample is about 30–40 nm. The influence of the Ni content and preparation conditions on the microstructures and magnetic properties were discussed.     

Evolution of coating layers during high-temperature annealing and their effects on magnetic behavior of Fe(Si) soft magnetic composites

Low-loss Fe(Si) soft magnetic composites (SMCs) with atomic-layer-deposition coated layer were successfully prepared in this work. The continuous, compact and uniform Al₂O₃ layer is found to form tight bonding with the powder base. Evolution of the coating layers has been investigated under different annealing temperatures and closely linked to the magnetic performance of the composites. Results indicate that 1100 °C was the optimal annealing temperature, at which the Fe(Si) SMCs showed lowest core loss of 1237 mW/cm³ and the highest permeability of 99.7 simultaneously (100 mT/100 kHz). Integrity of the coating layer ensures the maximum grain growth and stress removal of powder particles at the highest possible temperature, so as to reduce the hysteresis loss. Formation of high resistivity oxides and silicates (Al₂O₃, Fe₂SiO₄ and 3Al₂O₃·SiO₂) after annealing result in a low inter-particle eddy current loss. Besides, high temperature vacuum annealing is helpful to eliminate impurity atoms and decrease the anomalous eddy current loss. The improvement in effective permeability caused by high-temperature annealing is mainly attributed to the relaxation of residual stresses and the reduction of defects. While excessive temperature leads to the decomposition and destruction of the insulation layer, resulting in a significant increase in hysteresis loss, inter-particle and anomalous eddy current loss.     

Micro-structural and tensile strength analyses on the magnesium matrix composites reinforced with coated carbon fiber

Magnesium matrix composites reinforced with SiO₂ coated carbon fibers have been investigated, with an emphasis given on the relation between the material strength and interfacial microstructure. The composites were studied as a function of aluminium (Al) content that is varied between 0 and 9 wt%. The obtained results indicate that the reactivity at the C/Mg–Al interface of the composite can be controlled by varying the Al content. The low Al content in C/Mg–1Al has been completely dissolved in the matrix with no segregation even after solidification, leading to the best mechanical performance. If the Al content is increased to ≥3 wt% (composites such as C/AZ31 and C/AZ91), the SiO₂ coatings are fully depleted due to an extensive formation of carbides at the interface. The precipitates are further identified as Al₂MgC₂ phase that is similar to binary carbide Al₄C₃. SiO₂ coating on the fiber layer prior to fabrication of composite is found to be a promising way to suppress the carbide formation and enable the use of Mg–Al matrix with appropriate Al content.     

Structure and magnetic properties of FeCo-SiO2 nanocomposite synthesized by a novel wet chemical method

A novel soft magnetic nanocomposite with FeCo particles encapsulated by amorphous SiO₂ was synthesized using a co-precipitation combined H₂ reduction method. The saturation magnetization of the (Fe₇₀Co₃₀)₉₀/(SiO₂)₁₀ nanocomposite is as high as 200 emu/g, which is 4-5 times larger than that of traditional spinel ferrites. The frequency dependence of the complex initial permeability is intensely dependent upon the content of SiO₂ insulating phase. With increasing the content of SiO₂ to 10 wt.%, the cut-off frequency is drastically increased to over 1 GHz. The results show that a new high-frequency soft magnetic material with high saturation magnetization (M_s) can be achieved by introducing FeCo/SiO₂ nanocomposite.     

Synthesized silicon-substituted hydroxyapatite coating on titanium substrate by electrochemical deposition

Silicon-substituted hydroxyapaptite (Si-HA) coatings were prepared on titanium substrates by electrolytic deposition technique in electrolytes containing Ca²⁺, PO₄ ³⁻ and SiO₃ ²⁻ ions with various SiO₃ ²⁻/(PO₄ ³⁻ + SiO₃ ²⁻) molar ratios(η_si). The deposition was all conducted at a constant voltage of 3.0 V, with titanium substrate as cathode and platinum as anode, for 1 h at 85°C. The coatings thus prepared were characterized with inductively coupled plasma (ICP), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), field-emission-type scanning electron microscope (FSEM). The results show that the silicon amount in the coatings increases linearly to about 0.48 wt% at first with increasing η_si between 0 and 0.03, then increases slowly to about 0.55 wt% between 0.03 and 0.10 and finally maintains almost at a level around 0.55 wt% between 0.10 and 0.30. The tree-like Si-HA crystals are observed in the coatings prepared in the electrolyte of η_si = 0.20. And the presence of silicon in electrolytes decreases the thickness of the coatings, with effect being more significant as η_si increased. Additionally, the substitution of Si causes some OH⁻ loss and changes the lattice parameters of hydroxyapatite (HA).     

Controllable SiO2 insulating layer and magnetic properties for intergranular insulating Fe-6.5wt.%Si/SiO2 composites

In this study, the intergranular insulating Fe-6.5wt.%Si/SiO₂ soft magnetic composites (SMCs) were prepared successfully using in-situ chemical deposition followed by the spark plasma sintering (SPS) process. The effects of ammonia concentration on the microstructure and magnetic properties of the composites have been studied systematically. The Fe-6.5wt.%Si alloy particles could be well insulated by the uniform SiO₂ insulating layer, and its thickness increases with increasing the ammonia concentration from 0 to 0.02?ml/g. However, further increasing the ammonia concentration to 0.03 and 0.04?ml/g would result in the discontinuous and uneven SiO₂ insulating layer. Correspondingly, the saturation magnetization and effective permeability of the composite compacts first decrease and then increase with increasing the ammonia concentration from 0.00 to 0.04?ml/g, whereas the coercivity and resistivity vary in the opposite tendency. Note that the overall performances such as the frequency stability of effective permeability, higher resistivity and lower total core loss, reach the optimal value for the sample with the ammonia concentration of 0.02?ml/g.     

Photovoltaic performance of dye-sensitized solar cells fabricated with polyvinylidene fluoride–polyacrylonitrile–silicondioxide hybrid composite membrane

Electrospun fibrous membranes of hybrid composites of polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN) and silicon dioxide (SiO₂) (PVdF–PAN–SiO₂) are prepared with different proportions of SiO₂ (3, 5 and 7% w/w). The field emission scanning electron microscopy (FE-SEM) reveals that these membranes have three-dimensional, fully interconnected network structures, which are combined with micropores of fine SiO₂ distribution. The surface roughness of the membranes increases with increasing the SiO₂ content. It is found that 7 wt% SiO₂/PVdF–PAN electrolyte membrane has the highest ionic conductivity (6.96 × 10⁻² S cm⁻¹) due to the large liquid electrolyte uptake (about 570%). As the concentration of SiO₂ nanoparticles increase, the contact angle value also increases, ranging from 135.70° to 140.60° which indicates that the membrane has higher hydrophobicity. The dye sensitized solar cells (DSSCs) are fabricated using the hybrid composite membrane with PVdF–PAN with 7 wt % SiO₂. Its photovoltaic performance exhibits an open circuit voltage (V_oc) of 0.79 V and a short circuit current 11.6 mA cm⁻² at an incident light intensity of 100 mW cm⁻², producing an efficiency of 5.61%. DSSC, using the hybrid composite electrospun membrane which shows more stable photovoltaic performance than other assembled DSSCs.     

Magnetization Processes of (La0.7Pb0.3MnO3)1?x(SiO2)x Composites

The ceramic composites, (La_0.7Pb_0.3MnO₃)_1−x (SiO₂) _x , with diluted magnetic properties are prepared using solid-sate sintering route. Magnetization processes of (La_0.7Pb_0.3MnO₃)_1−x (SiO₂) _x composites are explored in this study. Ferromagnetism is gradually attenuated due to the magnetic dilution induced by the increase of SiO₂ content. Clearly, irreversible behavior is observed in the zero-field cooling and the field cooling (ZFC–FC) curves at a low field of 100 Oe. Saturation magnetization decreases as x increases while ferromagnetic transition temperature remains around 346 K for all composites. All the composites exhibit ferromagnetic hysteresis behavior which can be modeled by the law of the approach to saturation in the form M=M _S(1−a/H). The term a/H expresses the deviation of magnetization from saturation. The smaller factor a for La_0.7Pb_0.3MnO₃-rich samples results in sharper square curve which should be associated with the long-range spin order of ferromagnetic coupling.     

Synthesis and functionalization of SiO2 coated Fe3O4 nanoparticles with amine groups based on self-assembly

The purpose of this research was to synthesize amino modified Fe₃O₄/SiO₂ nanoshells for biomedical applications. Magnetic iron-oxide nanoparticles (NPs) were prepared via co-precipitation. The NPs were then modified with a thin layer of amorphous silica. The particle surface was then terminated with amine groups. The results showed that smaller particles can be synthesized by decreasing the NaOH concentration, which in our case this corresponded to 35 nm using 0.9 M of NaOH at 750 rpm with a specific surface area of 41 m² g^? 1 for uncoated Fe₃O₄ NPs and it increased to about 208 m² g^?1 for 3-aminopropyltriethoxysilane (APTS) coated Fe₃O₄/SiO₂ NPs. The total thickness and the structure of core-shell was measured and studied by transmission electron microscopy (TEM). For uncoated Fe₃O₄ NPs, the results showed an octahedral geometry with saturation magnetization range of (80–100) emu g^?1 and coercivity of (80–120) Oe for particles between (35–96) nm, respectively. The Fe₃O₄/SiO₂ NPs with 50 nm as particle size, demonstrated a magnetization value of 30 emu g^?1. The stable magnetic fluid contained well-dispersed Fe₃O₄/SiO₂/APTS nanoshells which indicated monodispersity and fast magnetic response.     

Studies on the radiopacity of experimental dental composite resins containing admixed SiO2−ZrO2 fillers

To produce radiopaque silica (SiO₂)-based fillers, zirconia (ZrO₂) powders were mechanically added to SiO₂ powders with ZrO₂ content up to 40 wt%. We evaluated the radiopacity of experimental composite resins consisting of (Bis-GMA + TEGDMA + CQ + DMAEMA) monomer mixture (25 wt%) and admixed SiO₂–ZrO₂ fillers (75 wt%), and compared their radiopacity with those of human dentin and enamel. It became confirmed that the radiopacity of experimental composite resins increased linearly with zirconium content, while the composite resin containing 80 wt% SiO₂-20 wt% ZrO₂ filler possessed radiopacity similar to that of human enamel. It was proved that the radiopacity of the composites could be precisely controlled by adjusting ZrO₂ content in SiO₂–ZrO₂ fillers.     

Regulation and control of insulated layers for intergranular insulated Fe/SiO<Subscript>2</Subscript> soft magnetic composites

In this work, the intergranular insulated Fe/SiO₂ soft magnetic composite cores with tunable insulating layer thickness were prepared by a modified Stöber method combined with the spark plasma sintering technology. Most of the conductive Fe particles could be coated uniformly by insulated SiO₂ using the modified Stöber method, and the high compact and intergranular insulated cores could be obtained quickly by the spark plasma sintering process. The intergranular insulated Fe/SiO₂ composite cores exhibited much higher electrical resistivity, lower core loss, better frequency stability of permeability and large higher quality factor than that of raw Fe core without insulated SiO₂. The thickness of SiO₂ insulating layer, electrical and magnetic properties of intergranular insulated Fe/SiO₂ composite cores could be readily controlled by adjusting the tetraethyl orthosilicate concentration. The thickness of SiO₂ insulating layer and resistivity of Fe/SiO₂ composite cores first increased and then dropped with increasing the tetraethyl orthosilicate concentration, while the permeability and core loss changed in the opposite direction. Fe/SiO2 composite core showed the optimal performance when the tetraethyl orthosilicate concentration was 0.135 mol l^?1, which exhibited better frequency stability at high frequencies, much higher electrical resistivity, higher quality factor and lower core loss.     

Fe-Si磁性颗粒/环氧树脂复合材料的冲击和磁学性能

采用双酚A型WSR-615和缩水甘油胺型AG-80环氧树脂为基体,以Fe-Si磁性颗粒为填料,通过热压成型方法制备了高含量磁性Fe-Si颗粒/环氧树脂复合材料。研究了环氧树脂基体的玻璃化温度和冲击强度及Fe-Si磁性颗粒含量对Fe-Si/环氧树脂复合材料的冲击强度和磁化强度的影响及温度敏感性。研究结果表明：随着磁性颗粒含量的增加,Fe-Si/环氧树脂复合材料的冲击强度和磁性能增加。当磁性颗粒体积分数由54 vol%增加到66 vol% 时,Fe-Si/环氧树脂的冲击强度和饱和磁化强度分别由4.03 kJ/m²和162.07 emu/g增加到7.16 kJ/m²和175.04 emu/g。Fe-Si/环氧复合材料在-60 ℃~140 ℃ 范围内的温度敏感性低,符合实际应用对复合材料稳定性的要求。     

Magnetic properties of NiFe2O4 thin films grown on La0.7Sr0.3MnO3-buffered Si substrate

Nickel ferrite NiFe₂O₄ (NFO) thin films have been prepared on a Si substrate (NFO/Si) and La_0.7Sr_0.3MnO₃ (LSMO)-coated Si (100) substrate (NFO/LSMO/Si) by RF magnetron sputtering. The microstructures and magnetic properties of the two films were systematically investigated. X-ray diffraction (XRD) and atomic force microscopy (AFM) revealed that highly (331)-oriented NFO films with a smooth surface were grown on the LSMO/Si substrate. The magnetization of the films was measured at room temperature. It showed a clear hysteresis loop in both samples, with the magnetic field applied in the plane. However, no hysteresis loop is seen with the magnetic field applied perpendicular to the film plane. This indicates the presence of an anisotropy favoring the orientation of the magnetization in the direction parallel to the film plane. A study of magnetization hysteresis loop measurements indicates that the LSMO buffer layer may improve the magnetic properties of NFO thin films, and that the saturation magnetization increases from 4.15 × 10⁴ to 3.5 × 10⁵ A/m.     

Effects of SiO<Subscript>2</Subscript> substitution on wettability of laser deposited Ca-P biocoating on Ti-6Al-4V

Silicon (Si) substitution in the crystal structure of calcium phosphate (CaP) ceramics has proved to generate materials with improved bioactivity than their stoichiometric counterpart. In light of this, in the current work, 100 wt% hydroxyapatite (HA) precursor and 25 wt% SiO₂-HA precursors were used to prepare bioactive coatings on Ti-6Al-4V substrates by a laser cladding technique. The effects of SiO₂ on phase constituents, crystallite size, surface roughness, and surface energy of the CaP coatings were studied. Furthermore, on the basis of these results, the effects and roles of SiO₂ substitution in HA were systematically discussed. X-ray diffraction analysis of the coated samples indicated the presence of various phases such as CaTiO₃, Ca₂SiO₄, Ca₃(PO₄)₂, TiO₂ (Anatase), and TiO₂ (Rutile). The addition of SiO₂ in the HA precursor resulted in the refinement of grain size. Confocal laser microscopy characterization of the surface morphology demonstrated an improved surface roughness for samples with 25 wt% SiO₂-HA precursor compared to the samples with 100 wt% HA precursor processed at 125 cm/min laser speed. The addition of SiO₂ in the HA precursor resulted in the highest surface energy, increased hydrophilicity, and improved biomineralization as compared to the control (untreated Ti-6Al-4V) and the sample with 100 wt% HA as precursor. The microstructural evolution observed using a scanning electron microscopy indicated that the addition of SiO₂ in the HA precursor resulted in the presence of reduced cracking across the cross-section of the bioceramic coating.     

The influence of pH and bath composition on the properties of Ni–Co coatings synthesized by electrodeposition

Ni–Co coatings were produced on Cu substrates by electrodeposition from electrolytes with different pH values and different Co²⁺ concentration. The current efficiency increases from 52.1% to 81.2% with the pH increasing from 2.0 to 5.4. It is clearly observed that the content of cobalt in the deposited coatings gradually increases from 9.4% to 19.6% as the pH value varies from 2.0 to 5.4. The Co content in the deposited coatings increases from 16.5% to 72.7% as the molar ratio of CoSO₄/NiSO₄ varying from 1:5 to 1:2 in electrolyte. XRD patterns reveal that the structure of the coatings strongly depends on the Co content in the binary coatings. Both granular and dendritic crystals were investigated by SEM and the different crystallization behaviors were illustrated. The saturation magnetization of the coatings goes up from 96.36 kAm⁻¹ to 136.08 kAm⁻¹ with the pH value increasing from 2.0 to 5.4. The saturation magnetization (M_s) and coercivity (H_c) move up from 144.84 kAm⁻¹ and 15.27 kAm⁻¹ to 175.13 kAm⁻¹ and 125.20 kAm⁻¹ with the increase of Co in the electrolyte, respectively.     

Magnetic properties of NiFe2O4 thin films grown on La0.7Sr0.3MnO3-buffered Si substrate

Nickel ferrite NiFe₂O₄ (NFO) thin films have been prepared on a Si substrate (NFO/Si) and La_0.7Sr_0.3MnO₃ (LSMO)-coated Si (100) substrate (NFO/LSMO/Si) by RF magnetron sputtering. The microstructures and magnetic properties of the two films were systematically investigated. X-ray diffraction (XRD) and atomic force microscopy (AFM) revealed that highly (331)-oriented NFO films with a smooth surface were grown on the LSMO/Si substrate. The magnetization of the films was measured at room temperature. It showed a clear hysteresis loop in both samples, with the magnetic field applied in the plane. However, no hysteresis loop is seen with the magnetic field applied perpendicular to the film plane. This indicates the presence of an anisotropy favoring the orientation of the magnetization in the direction parallel to the film plane. A study of magnetization hysteresis loop measurements indicates that the LSMO buffer layer may improve the magnetic properties of NFO thin films, and that the saturation magnetization increases from 4.15 × 10⁴ to 3.5 × 10⁵ A/m.     

Thin magnetic films of Sm-Co nanocrystallites exploiting spin coating deposition

Thin magnetic films of Sm-Co nanocrystallites on SiO₂ substrate were fabricated using spin coating deposition. In a typical synthesis, precursor of Sm-Co oleate complex was spin coated onto a SiO₂ substrate in the form of precursor films and subsequently they were subjected to reductive annealing at 773 K for 2 h, so as to crystallize Sm-Co phase in the films. It has been found that the reductive annealing temperature (573-773 K) played a critical role on the nucleation and formation of Sm-Co crystalline phases; while the spinning speed (3000-5000 rpm) has a significant effect in controlling the film thickness, which in turn affects the particle diameter, inter-particle distance and packing density of the Sm-Co nanocrystallites. Coercivity values of 27.9, 23.9 and 18.7 kA⋅m^− 1 and magnetization values of 2.89, 2.51 and 2.21 × 10^− 6 A⋅m² were achieved for the Sm-Co films with thicknesses of 345 (3000 rpm), 264 (4000 rpm) and 162 nm (5000 rpm), respectively. Further, these hard magnetic properties could be significantly improved by subjecting the Sm-Co films to post-annealing at 873 K.