Electroless ternary Ni-W-P alloys containing micron size Al2O3 particles

In the present investigation electroless ternary NiWP-Al₂O₃ composite coatings were prepared using an electroless nickel bath. Second phase alumina particles (1 µm) were used to codeposit in the NiWP matrix. Nanocrystalline ternary NiWP alloys and composite coatings were obtained using an alkaline citrate based bath which was operated at pH 9 and temperature at 88 ± 2 °C. Mild steel was used as a substrate material and deposition was carried out for about 4 h to get a coating thickness of 25 ± 3 µm. Metallographic cross-sections were prepared to find out the coating thickness and also the uniform distribution of the aluminum oxide particles in NiWP matrix. Surface analysis carried out on both the coatings using scanning electron microscope (SEM) showed that particle incorporation in ternary NiWP matrix has increased the nodularity of composite coatings compared to fine nodular NiWP deposits. Elemental analysis of energy dispersive X-ray (EDX) results showed that codeposited P and W elements in plain NiWP deposit were 13 and 1.2 wt.%, respectively. There was a decrease in P content from 13 to 10 wt.% with a marginal variation in the incorporated W (1.01 wt.%) due to the codeposition of aluminum oxide particles in NiWP matrix. X-ray diffraction (XRD) studies carried out on as-plated deposits showed that both the deposits are X-ray amorphous with a grain size of around 3 nm. Phase transformation studies carried out on both the coatings showed that composite coatings exhibited better thermal stability compared to plain NiWP deposits. From the XRD studies it was found that metastable phases such as NiP and Ni₅P₂ present in the composite coatings heat treated at major exothermic peak temperature. Annealed composite coatings at various temperatures revealed higher microhardness values compared to plain NiWP deposits.     

Influence of thermally induced structural transformations on hardness in Fe89.8Ni1.5Si5.2B3C0.5 amorphous alloy

Effect of heat treatment on mechanical behavior of Fe_89.8Ni_1.5Si_5.2B₃C_0.5 amorphous alloy was investigated by measuring microhardness. It was shown that the as-prepared amorphous alloy has an unexpectedly high microhardness. This can be attributed not only to boron dispersed in the alloy, but also to the structure which exhibits aspects of a nanocomposite of nanoparticles dispersed in an amorphous matrix. As the alloy crystallizes at temperatures above 540 °C, microhardness decreases continuously as a function of heating temperature. This is attributed to separation of boron out of the amorphous matrix into nanocrystals of Fe₂B phase. Further decrease in microhardness is attributed to crystallite growth with the accompanying change in the dominant nature of the interfaces from amorphous/crystal to crystal/crystal, and creation of a porous structure. When the crystallization is complete, the alloy exhibits microhardness close to that of a hypothetical mixture of α-Fe and Fe₂B phases of the same composition.     

Investigation of the thermal and magnetic properties of Fe61Co10Zr2 Fe61Co10Zr2.5Hf2.5Me2W2B20 (Me = Y, Nb, W, Ti, Mo, Ni) bulk amorphous alloys obtained by an induction suction method

The microstructure, magnetic properties and thermal stability of Fe₆₁Co₁₀Zr_2.5Hf_2.5Me₂W₂B₂₀ (Me = Y, Nb, W, Ti, Mo, Ni) alloys were investigated. The samples were obtained by an induction suction method as 0.5 mm thickness plates. The microstructure was examined using X-ray diffraction and Mössbauer spectroscopy. It was shown that the investigated samples have amorphous structure throughout the volumes of the samples. The magnetic properties were measured using a Vibrating Sample Magnetometer. The investigated alloys are soft magnetic materials with low coercivity field (from 5.8 A/m to 54 A/m) and high saturation of the magnetization (from 0.87 T to 1.26 T). The studies of thermal stability were performed using a differential scanning calorimeter. It was shown that the addition of respective atoms led to changes of Curie temperature in the range from 497 to 587 K, depending on the composition of the alloys.     

Direct synthesis of Fe3O4 nanopowder by thermal decomposition of Fe-urea complex and its properties

An easy synthesis route of magnetite (Fe₃O₄) nanopowder is developed by using thermal decomposition of Fe-urea complex ([Fe(CON₂H₄)₆](NO₃)₃). The formation of Fe₃O₄ is confirmed from X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurements. The morphological properties and magnetic properties of the Fe₃O₄ are characterized by transmission electron microscopy (TEM) and magnetic measurements, respectively. By an increase in reaction temperature from 200 to 300 °C, the average crystallite size of the Fe₃O₄ nanopowder increases from 37 to 50 nm. Room temperature magnetization hysteresis curves show that the Fe₃O₄ nanopowder possesses ferrimagnetic characteristics. The saturation magnetization of the Fe₃O₄ nanopowder increases from 70.7 to 89.1 emu/g when the reaction temperature increases from 200 to 300 °C.     

The magnetic, structure and mechanical properties of rapidly solidified (Nd7Y2.5)-(Fe64.5Nb3)-B23 nanocomposite permanent magnet

The Nd₇Y_2.5Fe_64.5Nb₃B₂₃ nanocomposite permanent magnets in the form of rods with 2 mm in diameter have been developed by annealing the amorphous precursors produced by copper mold casting technique. The phase evolution, structure, magnetic and mechanical properties were investigated with X-ray diffractometry, differential scanning calorimetry, electron microscopy, magnetometry and universal uniaxial compression strength techniques. The heat treatment conditions under which the magnets attained maximum magnetic and mechanical properties have been established. The results indicate that magnet properties are sensitive to grain size and volume content of the magnetic phases present in the microstructure. The composite microstructure was mainly composed of soft α-Fe (20-30 nm) and hard Nd₂Fe₁₄B (45-65 nm) magnetic phase grains. The maximum coercivity of 959.18 kA/m was achieved with the magnets annealed at 760 °C whereas the highest remanence of 0.57 T was obtained with the magnets treated at 710 °C. The optimally annealed magnets possessed promising magnetic properties such as _jH_c of 891.52 kA/m, B_r of 0.57 T, M_r/M_s = 0.68, (BH)_max of 56.8 kJ/m³ as well as the micro-Vickers hardness (H_v) of 1138 ± 20 and compressive stress (σ_f) of 239 ± 10 MPa.     

Electromagnetic wave absorption properties of mechanically mixed Nd2Fe14B/C microparticles

Nd₂Fe₁₄B/C microparticles were prepared by a mechanical mixing technique using a weight ratio of 2:1. Paraffin-bonded Nd₂Fe₁₄B/C composites were fabricated using 40 wt% microparticles, and their electromagnetic wave absorption properties were studied and compared with those of the paraffin-bonded Nd₂Fe₁₄B composites in the 2-18 GHz frequency range and for 1-5 mm thickness. The Nd₂Fe₁₄B/C-paraffin composites exhibit dual dielectric resonance in complex relative permittivity (?_r) and essentially flat response in complex relative permeability (μ_r) rather than showing an abrupt change in both ?_r and μ_r as in the Nd₂Fe₁₄B-paraffin composites. The results are ascribed to the increased electrical resistivity in the Nd₂Fe₁₄B/C-paraffin composites and the protection on the magnetic properties of the Nd₂Fe₁₄B microparticles at 2-18 GHz by the presence of the C phase. Large reflection loss (RL) exceeding −10 dB and an optimal RL of −13.2 dB are achieved in the Nd₂Fe₁₄B/C-paraffin composites from 9.6 to 18 GHz at a thickness of 1.4-2.6 mm and at 18 GHz at a thickness of 1.4 mm, respectively.     

Electrodeposition of sol-enhanced nanostructured Ni-TiO2 composite coatings

A novel electroplating method has been developed to produce nanocrystalline metal-matrix nano-structured composite coatings. A small amount of transparent TiO₂ sol was added into the traditional electroplating Ni solution, leading to the formation of nanocrystalline Ni-TiO₂ composite coatings. These coatings have a smooth surface. The Ni nodules changed from traditional pyramid-like shape to spherical shape. The grain size of Ni was also significantly reduced to the level of 50 nm. It was found that the amorphous anatase TiO₂ nano-particles (∼ 10 nm) were highly dispersed in the coating matrix. The microhardness was significantly increased from 320 HV₁₀₀ of the traditional Ni coating to 430 HV₁₀₀ of the novel composite coating with 3.26 wt.% TiO₂. Correspondingly, the wear resistance of the composite coating was improved by ∼ 50%.     

Single-crystal and textured polycrystalline Nd2Fe14B flakes with a submicron or nanosize thickness

This paper reports on the fabrication, structure and magnetic property optimization of Nd₂Fe₁₄B single-crystal and [0 0 1] textured poly-nanocrystalline flakes prepared by surfactant-assisted high-energy ball milling (HEBM). Single-crystal Nd₂Fe₁₄B flakes first with micron and then with submicron thicknesses were formed via continuous basal cleavage along the (1 1 0) planes of the irregularly shaped single-crystal microparticles during the early stage of HEBM. With further milling, [0 0 1] textured polycrystalline submicron Nd₂Fe₁₄B flakes were formed. Finally, crystallographically anisotropic polycrystalline Nd₂Fe₁₄B nanoflakes were formed after milling for 5-6 h. Anisotropic magnetic behavior was found in all of the flake samples. Nd₂Fe₁₄B flakes prepared with either oleic acid (OA) or oleylamine (OY) as the surfactant exhibited similar morphology, structure and magnetic properties. Both the addition of some low-melting-point eutectic Nd₇₀Cu₃₀ alloy and an appropriate post-annealing can increase the coercivity of the Nd₂Fe₁₄B flakes. The coercivity of Nd₂Fe₁₄B nanoflakes with an addition of 16.7 wt.% Nd₇₀Cu₃₀ by milling for 5 h in heptane with 20 wt.% OY increased from 3.7 to 6.8 kOe after annealing at 450 °C for 0.5 h. The mechanism for formation and coercivity enhancement of Nd₂Fe₁₄B single-crystal and textured poly-nanocrystalline flakes with a submicron or nanosize thickness was discussed.     

High quality TbMnO3 films deposited on YAlO3

High quality thin films of TbMnO₃ were grown by pulsed laser deposition on orthorhombicYAlO₃ (1 0 0). The interface and surface roughness of a 55 nm thick film were probed by X-ray reflectometry and atomic force microscopy, yielding a roughness of 1 nm. X-ray diffraction revealed untwinned films and a small mosaic spread of 0.04° and 0.2° for out-of-plane and in-plane reflections, respectively. This high degree of epitaxy was also confirmed by Rutherford backscattering spectrometry. Using polarized neutron diffraction we could identify a magnetic structure with the propagation vector (0 0.27 0), identical to the bulk magnetic structure of TbMnO₃.     

Computer controlled detonation spraying of WC/Co coatings containing MoS2 solid lubricant

Composite WC/Co + MoS₂ coatings were deposited onto steel substrates by Computer Controlled Detonation Spraying using three spraying modes: very cold, cold and normal. Maximal content of MoS₂ in a sprayed powder was 10 wt.%. Characterization of coatings was made with chemical and phase analyses, microhardness measurement, morphology and microstructure investigation. X-ray diffraction study shows that residual MoS₂ exists only in coatings obtained at very cold and cold spraying modes. At normal spraying mode complete decomposition of the solid lubricant occurs during spraying. From the engineering point of view, the coating applied at the cold mode using a powder containing 10 wt.% MoS₂ is the most promising. Such a coating has microhardness of 650 HV_0.2 and a porosity of 10%.     

Structural and magnetic properties of nanostructured Fe50(Co50)-6.5 wt% Si powder prepared by high energy ball milling

This work investigates the effects of 6.5 wt% Si addition and milling times on the structural and magnetic properties of Fe₅₀Co₅₀ powders. For this purpose, at first the elemental Fe and Co powders were milled for 10 h to produce Fe₅₀Co₅₀ alloy and then Si was added and the new product was milled again for different times. The microstructural and magnetic properties were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM). The results show that the minimum crystallite size of the as-milled powders (∼12 nm) has been achieved after introducing Si and milled for 8 h (total milling time of 18 h). Also an amount of 188 emu/g has been achieved for M_s. This amount of M_s is higher than most of those which have been already reported for M_s of different Fe-Si systems.     

Structural, magnetic and Mössbauer spectral studies of nanocrystalline Ni0.5Zn0.5Fe2O4 ferrite powders

Nanocrystalline Ni_0.5Zn_0.5Fe₂O₄ powders, synthesized by a combustion method are investigated by X-ray diffraction, vibrating sample magnetometry and Mössbauer spectroscopic techniques. We adopt a strategy to systematically control the particle sizes between 4 and 45 nm simply by changing the elemental stoichiometric coefficient, Φ_e, of the combustion mixture. Curie temperature of the superparamagnetic particles of size 4 nm is higher than that of the bulk particles. Interestingly, bigger particles (45 nm) show a comparable room temperature saturation magnetization and exceptionally very high Curie temperature of 833 K, when compared to that of the bulk Ni_0.5Zn_0.5Fe₂O₄ material (563 K).     

Synthesis of nanocrystalline nickel-zinc ferrite (Ni0.8Zn0.2Fe2O4) thin films by chemical bath deposition method

The nickel-zinc ferrite (Ni_0.8Zn_0.2Fe₂O₄) thin films have been successfully deposited on stainless steel substrates using a chemical bath deposition method from alkaline bath. The films were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), static water contact angle and cyclic voltammetry measurements. The X-ray diffraction pattern shows that deposited Ni_0.8Zn_0.2Fe₂O₄ thin films were oriented along (3 1 1) plane. The FTIR spectra showed strong absorption peaks around 600 cm⁻¹ which are typical for cubic spinel crystal structure. SEM study revealed compact flakes like morphology having thickness ∼1.8 μm after air annealing. The annealed films were super hydrophilic in nature having a static water contact angle (θ) of 5°.The electrochemical supercapacitor study of Ni_0.8Zn_0.2Fe₂O₄ thin films has been carried out in 6 M KOH electrolyte.The values of interfacial and specific capacitances obtained were 0.0285 F cm⁻² and 19 F g⁻¹, respectively.     

Nanocrystalline Zr3Al made through amorphization by repeated cold rolling and followed by crystallization

The intermetallic compound Zr₃Al is severely deformed by the method of repeated cold rolling. By X-ray diffraction it is shown that this leads to amorphization. TEM investigations reveal that a homogeneously distributed debris of very small nanocrystals is present in the amorphous matrix that is not resolved by X-ray diffraction. After heating to 773 K, the crystallization of the amorphous structure leads to a fully nanocrystalline structure of small grains (10-20 nm in diameter) of the non-equilibrium Zr₂Al phase. It is concluded that the debris retained in the amorphous phase acts as nuclei. After heating to 973 K the grains grow to about 100 nm in diameter and the compound Zr₃Al starts to form, that is corresponding to the alloy composition.     

Synthesis and characterization of polypropiolate sodium (PPNa)-Fe3O4 nanocomposite

Polypropiolate sodium (PPNa)-Fe₃O₄ nanocomposites were successfully synthesized by the precipitation of Fe₃O₄ in the presence of sodium polypropiolate and followed by reflux route. Structural, morphological, electrical and magnetic properties evaluation of the nanocomposite were performed by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), thermal gravimetric analysis (TGA), vibrating scanning magnetometry (VSM) and conductivity measurements. Crystalline phase was identified as magnetite with an average crystallite size of 7 ± 3 nm as estimated from X-ray line profile fitting. Particle size estimated from TEM, by log-normal fitting, is ∼9 ± 1 nm. FT-IR analysis shows that the binding of PPNa on the surface of iron oxide is through bidentate linkage of carboxyl group. TGA analysis showed the presence of 20% PPNa around 80% magnetic core (Fe₃O₄)…PPNa-Fe₃O₄ nanocomposite show superparamagnetic characteristics at room temperature. It is found that the a.c. conductivity of the nanocomposites obeys the well-known power law of frequency in which it also depends on temperature. Additionally, its d.c. conductivity showed that two operating regions of the activation energy. Both real and imaginary parts of either permittivity exhibit almost the same attitudes which are the indication of the same ability in the stored energy, and dissipation of energy within the PPNa and PPNa-Fe₃O₄ nanocomposites.     

Structure and mechanical properties of TiAlSiN/Si3N4 multilayer coatings

TiAlSiN/Si₃N₄ multilayer coatings which have different separate layer thicknesses of TiAlSiN or Si₃N₄ were deposited onto glass sheets, single-crystal silicon wafers and polished WC-Co substrates by reactive magnetron co-sputtering. The morphology, crystalline structure and thickness of the as-prepared multilayer coatings were characterized by TEM, SEM, XRD and film thickness measuring instrument. The mechanical properties of the coatings were evaluated by a nanoindenter. The effects of monolayer thickness on the microstructure and properties of TiAlSiN/Si₃N₄ multilayer coatings were explored. The coatings showed the highest hardness when the thickness of Si₃N₄ and TiAlSiN monolayers was 0.33 nm and 5.8 nm, respectively. The oxidation characteristics of the coatings were studied at temperatures ranging from 700 °C to 900 °C for oxidation time up to 20 h in air. It was found that the coatings displayed good oxidation resistance.     

One-step solvothermal approach for preparing soft magnetic hydrophilic PFR coated Fe3O4 nanocrystals

The hydrophilic phenol formaldehyde resin coated Fe₃O₄ nanocrystals are prepared via a novel one-step solvothermal approach at 160 °C for 6-9 h without inert gas protection. Water-glycol mixture is used as solvent in common air surrounding. FeSO₄·7H₂O, hexamethylenetetramine and phenol are used as resource materials without any others additives or surfactants. The transmission electronic microscope images show the samples are composed of sphere-like particles with sizes about 10-20 nm. The X-ray diffraction data indicate cube-phase Fe₃O₄ nanocrystals are obtained at given conditions. Fourier transform infrared spectra further reveal the samples are consisted of Fe₃O₄ and PFR. Without modified pH and added surfactants, the solubility of the obtained sample is over 1% in water, which is far more than its solubility in toluene. Room-temperature hysteresis loop indicate that the as-obtained nano-crystals possess soft magnetic properties with high saturated mass magnetization (50.6 emu/g) and negligible coercivity.     

Preparation and characteristics of Fe3O4@YVO4:Eu bifunctional magnetic-luminescent nanocomposites

A facile direct precipitation method has been developed for the synthesis of bifunctional magnetic-luminescent nanocomposites with Fe₃O₄ nanoparticles as the core and YVO₄:Eu³⁺ as the shell. Transmission electron microscopy (TEM) images revealed that the obtained bifunctional nanocomposites had a core-shell structure and a spherical morphology. The average size was ∼150 nm, and the thickness of the shell was ∼15 nm. The X-ray diffraction (XRD) patterns showed that a cubic spinel structure of Fe₃O₄ core and a tetragonal phase of YVO₄ shell were obtained. Fourier transform infrared (FT-IR) spectra confirmed that the YVO₄:Eu³⁺ had been successfully deposited on the surface of Fe₃O₄ nanoparticles. Photoluminescence (PL) spectra indicated that the nanocomposites displayed a strong red characteristic emission of Eu³⁺. Magnetic measurements showed that the obtained bifunctional nanocomposites exhibited superparamagnetic behavior at room temperature. Therefore, the bifunctional nanocomposites are expected to develop many potential applications in biomedical fields.     

Boride coatings on steel using shielded metal arc welding electrode: Microstructure and hardness

In the present study, shielded metal arc welding electrodes were produced for making boride coatings and low-carbon steel plates were surfaced with single-pass bead on-plate welds. The effects of the boron content in the electrode shield on the microstructure and hardness of the coatings were investigated. After deposition, microstructural analyses including metallographic examination, wavelength-dispersive X-ray (WDX), X-ray and microhardness measurements of the coatings were evaluated. From the results, it was seen that different boron contents formed primary and eutectic Fe₂B, and consequently had an effect on the hardness of the coating. As the amount of boron which was transferred from the electrode shield to the coating increased, the microstructure of the coating changed from the eutectic structure (α-Fe + F₂B) to primary Fe₂B with the eutectic of Fe₂B plus martensite, and the hardness increased. The present study has therefore shown that the shielded metal arc welding electrodes produced here for the first time can be used effectively and economically to produce boride coatings on SAE 1020 steel.     

Preparation of Ni0.5Zn0.5Fe2O4/SiO2 nanocomposites and their adsorption of bovine serum albumin

The magnetic nanocomposites of (1 − x)Ni_0.5Zn_0.5Fe₂O₄/xSiO₂ (x = 0-0.2) were synthesized by the citrate-gel process and their absorption behavior of bovine serum albumin (BSA) was investigated by UV spectroscopy at room temperature. The gel precursor and resultant nanocomposites were characterized by FTIR, XRD, TEM and BET techniques. The results show that the single ferrite phase of Ni_0.5Zn_0.5Fe₂O₄ is formed at 400 °C, with high saturation magnetization and small coercivity. A porous, amorphous silica layer is located at the ferrite nanograin boundaries, with the silica content increasing from 0 to 0.20, the average grain size of Ni_0.5Zn_0.5Fe₂O₄ calcined at 400 °C reduced from about 18-8 nm. Consequently, the specific surface area of the nanocomposites ascends clearly with the increase of silica content, which is largely contributed by the increase in the thickness of the porous silica layer. The Ni_0.5Zn_0.5Fe₂O₄/SiO₂ nanocomposites demonstrate a better adsorption capability than the bare Ni_0.5Zn_0.5Fe₂O₄ nanoparticles for BSA. With the increase of the silica content from 0 to 0.05 and the specific surface area from about 49-57 m²/g, the BSA adsorption capability of the Ni_0.5Zn_0.5Fe₂O₄/SiO₂ nanocomposites calcined at 400 °C improve dramatically from 22 to 49 mg/g. However, with a further increase of the silica content from 0.05 to 0.2, the specific surface area increase from about 57-120 m²/g, the BSA adsorption for the nanocomposites remains around 49 mg/g, owing to the pores in the porous silica layer which are too small to let the BSA protein molecules in.