Sliding wear resistance of iron aluminides

Room temperature dry sliding wear behaviour of iron aluminides containing 28% aluminium and various amounts of chromium has been investigated using pin on disk wear tester. The aluminides were heat treated to have orderedDO ₃structure. It was found that wear rate of the aluminides increased with the increase of applied normal load and sliding speed. Wear resistance of the aluminides increased with increase in chromium content. SEM observation of the worn surface showed that the microcutting and microploughing were the dominant sliding wear mechanisms.     

Preparation and characterization of bio-functionalized iron oxide nanoparticles for biomedical application

Amine modified iron oxide (Fe₃O₄) nanoparticles were synthesized by thermal decomposition method and were further used to bio-functionalize by grafting of N-hydroxysuccinimide (NHS) ester of folate and ethylenediaminetetraacetate (EDTA). Fe₃O₄ nanoparticles of ~ 22 nm were confirmed from X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies. FT-IR studies indicated two bands at 1515 cm^− 1and 1646 cm^− 1, which can be attributed to carboxylic group and the amide linkage respectively, revealing the conjugation of folate with Fe₃O₄. The conjugation of the chelating agent showed strong C=O stretch and Fe-O vibrations at 1647 and 588 cm^− 1 respectively. The value of saturation magnetization for Fe₃O₄ nanoparticles was found to be 88 emu/g, which further reduced to 18 and 32% upon functionalization with EDTA and NHS ester folate, respectively. These amine modified Fe₃O₄ nanoparticles can also be functionalized with other bifunctional chelators, such as amino acids based diethylene triamine pentaacetic acid (DTPA), and thus find potential applications in radio-labeling, biosensors and cancer detection, etc.     

The origin of hematite nanowire growth during the thermal oxidation of iron

The oxidation of Fe in pure oxygen between 400 °C and 600 °C has been investigated in order to obtain insight into the mechanism of the spontaneous formation of α-Fe₂O₃ nanowires. By varying the oxidation temperature, Fe can be oxidized to form Fe₂O₃/Fe₃O₄/FeO/Fe or Fe₂O₃/Fe₃O₄/Fe layered structure, followed by hematite nanowire growth on the outer layer of hematite (Fe₂O₃). It is observed that Fe₂O₃ nanowires have a bicrystal structure and form directly on the top of the underlying Fe₂O₃ grains. It is shown that the compressive stresses generated by the volume change accompanying the Fe₂O₃/Fe₃O₄ interface reaction stimulate Fe₂O₃ nanowire formation and that the Fe₂O₃ nanowire growth is via surface diffusion of Fe cations supplied from the outward grain boundary diffusion through the Fe₂O₃ layer. This principle of nanowire formation may have broader applicability in layered systems, where the stress gradient in thin layers can be introduced via solid-state interfacial reaction or other means.     

Plasma spheroidization of iron powders in a non-transferred DC thermal plasma jet

In this paper, the results of plasma spheroidization of iron powders using a DC non-transferred plasma spray torch are presented. The morphology of the processed powders was characterized through scanning electron microscopy (SEM) and optical microscopy (OM). The percentages of spheroidized powders were calculated by the shape factors such as the Irregularity Parameter (IP) and Roundness (RN). A maximum of 83% of spheroidization can be achieved. The spheroidization results are compared with the theoretical estimation and they are found to be in good agreement. The phase composition of the spheroidized powder was analyzed by XRD. The effect of plasma jet temperature and plasma gas flow rate on spheroidization is discussed. At low plasma gas flow rates and at high plasma jet temperatures, the percentage of spheroidization is high.     

Wear resistance of Fe-28Al-3Cr intermetallic alloy under wet conditions

Wear behaviour of iron aluminides (Fe-28Al-3Cr at.%) alloy has been investigated under wet conditions using ball on plate sliding wear tester. Wear resistance was examined against tungsten carbide (WC) ball sliding over the iron aluminide plate at room temperature. Wear tests were carried out at 3 N and 5 N load conditions at different sliding frequency of mating ball. The micromechanisms responsible for wear were identified to be microcutting, micropitting, and microcracking of deformed subsurface zones under wet conditions.     

Synthesis and characterization of silicon oxide nanoparticles using an atmospheric DC plasma torch

An atmospheric pressure DC plasma torch reactor was employed using Hexamethyldisiloxane (HMDSO) and oxygen reactants in nitrogen carrier gas to produce silicon oxide nanoparticles and nanoparticle agglomerates with the diameters in the ranges of 8–14?nm and 130–260?nm, respectively. The mean sizes of primary nanoparticles and nanoparticle agglomerates as well as their surface properties are studied by varying the process conditions. In general the mean sizes of primary nanoparticles and nanoparticle agglomerates decrease with the increase of the plasma torch power, the increase of the oxygen concentration, and the decrease of the HMDSO concentration. Under those conditions, the more completely-oxidized silicon oxide clusters are formed and aggregate into the compact, densely-packed, and small-size primary silicon oxide nanoparticles, which further agglomerate into the densely-packed, small nanoparticle agglomerates. The hydrophilic and white nanoparticle powder with a low BET surface area can be thus obtained. Under the opposite processing conditions, the loosely-packed, low density and large-size carbon-containing silicon oxide nanoparticles and nanoparticle agglomerates can be obtained with hydrophobic surface, high BET surface areas, and gray color.     

Corrosion of carbon-alloyed iron aluminides

The corrosion behaviour of two carbon-alloyed intermetallics of composition Fe-28.1Al-2.1C and Fe-27.5Al-3.7C has been studied and compared with that of binary intermetallics. Potentiodynamic polarization studies indicated that the intermetallics exhibited active-passive behaviour in an acidic solution of pH = 1, whereas they exhibited stable passivity in a buffer solution of pH 8.4. Corrosion rates were also obtained by immersion testing. The variation of corrosion rate as a function of time was similar for both the intermetallics. The variation in corrosion rate as a function of time has been explained based on the observed potentiodynamic polarization behaviour. Scanning electron microscopy of corroded surfaces indicated that the carbon-alloyed intermetallics were susceptible to galvanic corrosion, due to the presence of carbides.     

Ultra-fast boriding of nickel aluminide

In this study, we explored the possibility of ultra-fast electrochemical boriding of nickel aluminide (Ni₃Al) in a molten borax electrolyte. Electrochemical boriding was performed at 950 °C for 15 min and at current densities ranging from 0.1 to 0.5 A/cm². The boride layers formed on the test samples were 50 to 260 μm thick depending on the current density. The mechanical, structural, and chemical characterization of the boride layers was carried out using a Vickers micro-hardness test machine, optical and scanning electron microscopes, and a thin film X-ray diffractometer. The hardness of boride layer was in the range from 800 to 1200 ± 50 HV depending on the load and the region from which the hardness measurements were taken. X-ray diffraction studies confirmed that the boride layers were primarily composed of Ni₃B, Ni₄B₃ and Ni₂₀AlB₁₄ phases. Structurally, the boride layer was very homogenous and uniformly thick across the borided surface area.     

Controlled synthesis of alumina nanoparticles using inductively coupled thermal plasma with enhanced quenching

Synthesis of alumina nanoparticles in an Ar-O₂ inductively coupled radio frequency (rf) plasma controlled by axial quench gas injection was investigated. The flow and temperature fields for various quench gas flow rates in the plasma reactor, as well as the corresponding quench rates, were predicted using a renormalization group (RNG) k-ε turbulence model. Nanosize alumina particles were synthesized from the vapor phase by oxidation of aluminum in the plasma. The collected products were characterized by means of field emission scanning electron microscopy (FE-SEM), dynamic light scattering (DLS), and BET surface area analysis. The dependences of particle size and shape on the injection position and the flow rate of the quench gas were discussed.     

Synthesis of Mn-Al alloy nanoparticles by plasma arc discharge

Alloy nanoparticles in the Mn-Al system were prepared by the plasma arc discharge method. The influence of process parameters on the vaporization rate, composition, particle size, and magnetic properties of the as-produced nanoparticles was investigated. The Mn content was found to be higher in the nanoparticles than in the corresponding mother alloy, although the difference diminished with the reaction time. With increasing H₂ content in the reaction gas, both vaporization rate and particle size increased. With 30 at.% Mn, the average particle diameter in pure Ar was 35.2 nm, whereas that in an atmosphere with Ar:H₂ = 60:40 was 95.4 nm. With the addition of a small amount of carbon, ε-phase nanoparticles were synthesized. After heat treatment in a vacuum for 30 min at 400-600 °C, the nonmagnetic ε-phase was transformed into the ferromagnetic τ-phase and a very high coercivity of about 446 kA/m was achieved.     

Synthesis and spectroscopic investigations of Mn3O4 nanoparticles

Trimanganese tetraoxide (Mn₃O₄) nanoparticles have been synthesized via hydrothermal process. Nevertheless, homogeneous nanoparticles of Mn₃O₄ with platelet lozange shape were obtained. The crystallite size ranged from 40 to 70 nm. The Mn₃O₄ product was investigated by X-ray diffraction, transmission electron microscopy (MET), and impedance spectroscopy. Electrical conductivity measurements showed that the as-synthesized Mn₃O₄ nanomaterial has a conductivity value which goes from 1.8 10⁻⁷ Ω⁻¹ cm⁻¹ at 298 K, to 23 10⁻⁵ Ω⁻¹ cm⁻¹ at 493 K. The temperature dependence of the conductivity between 298 and 493 K obeys to Arrhenius law with an activation energy of 0.48 eV.     

Hydrothermal synthesis of magnetite nanoparticles via sequential formation of iron hydroxide precipitates

A novel method for preparing fine magnetite nanoparticles without using any additives and organic solvents has been developed. In this method, a sequential precipitates formation method, ferrous and ferric hydroxides are not coprecipitated but sequentially formed in an alkaline solution, and then the resulting suspension is subjected to a hydrothermal treatment. The obtained magnetite nanoparticles were characterised through scanning electron microscopy observation and X-ray diffraction analysis, and the particle size and magnetic properties were measured with a dynamic light scattering particle size analyser and a superconducting quantum interference device magnetometer, respectively. In order to prepare fine magnetite nanoparticles with a uniform size, both the formation sequence of ferrous and ferric hydroxide precipitates and the supersaturation of ferric hydroxide in the solution were essential. The ferromagnetic magnetite nanoparticles with a median size 8.5?nm were relatively easily obtained in the formation process in which a ferric sulphate solution was rapidly poured into a suspension of ferrous hydroxide particles prepared beforehand using ferric chloride and sodium hydroxide, whereas the median size of magnetite nanoparticles prepared via conventional coprecipitation route was 38.6?nm.     

Synthesis, characterization and magnetoresistance properties study of magnetite thin films by electroless plating in aqueous solution

Polycrystalline half-metallic Fe₃O₄ films with 1 μm in thickness were synthesized on glass substrates directly by electroless plating in aqueous solution at 90 °C without heat treatment. The films have single pure spinal phase structure and the well-crystallized columnar grains grow perpendicularly to the substrates, as revealed by XRD, XPS and SEM. At room temperature, the films exhibit negative magnetoresistance (MR) ratio of about −5.1%, which is ascribed to intergranular tunneling of spin polarized electrons of Fe₃O₄. The resistivity R of the films with 1 μm in thickness at room temperature is about 5.2 × 10⁻¹ Ω cm. The cation distribution and the arrangement of the magnetic moments of the plated Fe₃O₄ ferrite thin films are different from that of the bulk materials, which is likely to be one of the reasons for the modification of R and MR properties.     

Influence of carbon precursors on thermal plasma assisted synthesis of SiC nanoparticles

Nanosized SiC was synthesized by solid state method using silicon and carbon powders followed by non-transferred arc thermal plasma processing. X-ray diffraction (XRD) analysis revealed that activated carbon has highest reactivity while graphite has lowest activity in the crystallization of SiC through solid state method. The reactivity was dependent on surface area of carbon source and activated carbon with highest surface area (590.18 m² g⁻¹) showed highest reactivity, whereas graphite with least surface area (15.69 m² g⁻¹) showed lowest reactivity. The free silicon content was decreased with increasing reaction time as well as carbon mole ratio. Scanning electron microscope (SEM) study showed that the shape and size of synthesized SiC depends on the shape and size of carbon source. SiC nanoparticles within 500 nm were formed for carbon black while bigger particles (∼5 μm) were formed for activated carbon and graphite. Plasma processing of these solid–solid synthesized SiC resulted into the formation of well dispersed, ultrafine SiC nanoparticles (30–40 nm) without any structural modification. Thermal plasma processing resulted into the increase in crystallite size of SiC.     

Effect of nitrogen-hydrogen mixed plasma on nitridation process of iron nanoparticles

Fe₃O₄ nanoparticles coated with an oleic acid as a surfactant were reduced and nitrided by hydrogen plasma and nitrogen-hydrogen mixed plasma generated by 13.56 MHz Radio-Frequency. Fe₃O₄ nanoparticles could be reduced to α-Fe nanoparticles with small average grain size about 35 nm and with little carbonization by hydrogen plasma treatment. In the nitrogen-hydrogen mixed plasma treatment, it was clarified that the mixture of hydrogen with ratio of 10-30% to nitrogen accelerated nitridation of α-Fe nanoparticles. This effect was derived by generating exited species with higher activity such as NH ions and its radicals. Furthermore, it was also revealed that nitridation behavior strongly depended on average grain size of as-prepared α-Fe nanoparticles. In the plasma nitridation of α-Fe nanoparticles with average grain size of 35 nm, the nitridation was easily promoted with lower input power. This could be attributed to large surface energy of nanoparticles because nanoparticles had wide surface area than bulk materials.     

Generation of Si:H nanoparticles by a combination of pulse plasma and hydrogen gas pulses

Si:H nanoparticles have been generated from 3 nm to 500 nm in count mean diameter (CMD) using a plasma chemical vapor deposition (CVD) system. In the present work, the nanoparticles are synthesized using cold plasma in order to get monodispersed size distribution with a combination of square wave modulated RF pulse plasma and a hydrogen gas pulse for better control of their size. The size of synthesized nanoparticles was measured by scanning mobility particle sizer (SMPS). The synthesis was carried out using pulse plasma with on-time of 1 s and off-time of 4 s. During 1 s on-time of plasma we added hydrogen gas pulses varying from 0.1 s to 0.9 s. Our results show that by utilizing dual pulse plasma and by controlling hydrogen gas pulse on-time we achieved smaller diameter Si nanoparticles. Hence, it is easier to generate smaller nanoparticles which generally have quantum effect and be utilized for various applications especially in solar cell application.     

Characteristic analysis of Fe3O4 nanoparticles modified by oleic acid and undecylenic acid

Carbonization of magnetic polymer microspheres is one of the methods for the preparation of magnetic carbon materials. Fe₃O₄ magnetic particle characteristics considerably influence the magnetic content and size distribution of magnetic polymer microspheres. The characteristics of Fe₃O₄ nanoparticles modified by oleic acid (OA) and undecylenic acid (UA) were analyzed by X-ray diffraction, Fourier transform infrared, scanning electron microscopy, dynamic laser light scattering, thermogravimetry/differential thermogravimetry, vibrating sample magnetometer, and water contact angle. Fe₃O₄ nanoparticles modified by OA and UA are nearly spherical and exhibit superparamagnetism. Fe₃O₄ particle size and saturation magnetization are slightly influenced by the OA and UA composition. OA and UA both are chemically adsorbed onto Fe₃O₄ as bidentate chelates. OA shows easier adsorption onto Fe₃O₄ than UA. OA groups have an expanded arrangement on OA@Fe₃O₄, whereas UA groups have a condensed arrangement on UA@Fe₃O₄. Particle lipophilicity decreases and particle clustering increases with decreasing OA content and increasing UA content on OA-UA@Fe₃O₄ nanoparticles.     

Processing of bovine hydroxyapatite (HA) powders and synthesis of calcium phosphate silicate glass ceramics using DC thermal plasma torch

In the present work, hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) was prepared from bovine bones with calcination method (up to 850 °C).The calcinated hydroxyapatite was powdered (30-40 μm) using a mechanical grinder; the particles were highly irregular in shape with sharp edges, angular, rounded, circular, dentric, porous and fragmented morphologies. The irregular shaped calcinated hydroxyapatite was plasma processed to produce spherical powders for thermal spray coating applications. More over; calcium phosphate silicate glass ceramics was produced by plasma melting of ball milled hydroxyapatite-borosilicate glass (50 wt.%) mixture. The samples were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffractometer (XRD) and energy dispersive X-ray analysis (EDX). The morphology was determined using scanning electron (SEM) and optical microscopy (OM). The microhardness, density and porosity measurements for the synthesized samples were made.     

Synthesis of nano-sized Al doped TiO2 powders using thermal plasma

High quality nano-sized Al doped TiO₂ powders were prepared using a DC plasma jet. Titanium tetrachloride (TiCl₄) and aluminum chloride (AlCl₃) were fed into the plasma flame as starting materials, and the ratio of Al to TiO₂ was varied from 1 to 8 wt.%. We investigated the effect of process parameters on phase composition, particle size, and optical property by using XRD, SEM/EDX, TEM, UV/Vis spectroscope. The powders collected at the reaction tube were dominated by anatase. The size of synthesized powder decreased by increasing the amount of Al because doped Al species inhibited the particle growth. For the optical property, the absorption band of synthesized powders shifted from the UV region to the visible region according to the increase of the amount of Al dopant.     

Synthesis of WS2 and MoS2 fullerene-like nanoparticles from solid precursors

Inorganic fullerene-like WS₂ and MoS₂ nanoparticles have been synthesized using exclusively solid precursors, by reaction of the corresponding metal oxide nanopowder, sulfur and a hydrogen-releasing agent (NaBH₄ or LiAlH₄), achieved either by conventional furnace heating up to ∼900 °C or by photothermal ablation at far higher temperatures driven by highly concentrated white light. In contrast to the established syntheses that require toxic and hazardous gases, working solely with solid precursors permits relatively safer reactor conditions conducive to industrial scale-up.