Kurikka V. P. M. Shafi

Sonochemical preparation of nanosized amorphous Fe-Ni alloys

Nanosized amorphous alloy powders of Fe20Ni80, Fe40Ni60, and Fe60Ni40 were prepared by sonochemical decomposition of solutions of volatile organic precursors, Fe(CO)5 and Ni(CO)4 in decalin, under an argon pressure of 100 to 150 kPa at 273 K. Magnetic susceptibility of Fe40Ni60 and Fe60Ni40 indicates blocking temperatures of 35 K and a magnetic particle size of about 6 nm. Thermogravimetric measurements of Fe20Ni80 give Curie temperatures of 322 °C for amorphous and 550 °C for crystallized forms. Differential scanning calorimetry exhibits an endothermic transition at 335 °C from a combination of the magnetic phase transition and alloy crystallization. The Mossbauer spectrum of crystallized Fe20Ni80 shows a sextet pattern with a hyperfine field of 25.04 T.

Sonochemical preparation and characterization of nanosized amorphous Co–Ni alloy powders

Nanosized amorphous alloy powders of Co20Ni80 and Co50Ni50 have been prepared by sonochemical decomposition of solutions of volatile organic precursors, Co(NO)(CO)3 and Ni(CO)4 in decalin, under an argon pressure of 100 to 150 kPa, at 273 K. The amorphous nature of these particles was confirmed by various techniques, such as SEM, TEM, SAED, and XRD. A transmission electron micrograph of the heated Co20Ni80 sample showed near uniform particles with sizes less than 10 nm. Magnetic measurements indicated that the as-prepared amorphous CoNi alloy particles were superparamagnetic. The observed magnetization, measured up to a field of 15 kG, of the annealed Co20Ni80 sample (54 emu g–1) was significantly lower than that for the reported multidomain bulk particles (75 emu g–1), reflecting the ultrafine nature of our sample. Thermogravimetric measurements of Co20Ni80 with a permanent magnet yielded a glass transition temperature of 338 °C for the amorphous form, and a Curie temperature of 565 °C for the crystallized form. The differential scanning calorimetry showed crystallization temperatures of 400 °C for Co20Ni80 and 365 °C for Co50Ni50 amorphous samples.

Use of functionalized WS2 nanotubes to produce new polystyrene/polymethylmethacrylate nanocomposites

Multiwall WS2 nanotubes of 40 ‐ 50 nm diameter were functionalized with n-octadecyl phosphonic acid by sonication in toluene and blended with mixtures of polystyrene (PS) and polymethylmethacrylate (PMMA) to form new nanocomposite (NC) materials. The surface and domain structures were studied by atomic force microscopy (AFM), scanning transmission X-ray microscopy (STXM) and transmission electron microscopy (TEM) for various levels of loading of nanotubes up to 20 wt%. Phase-separated domain size and surface roughness of the nanocomposite films were found to be dramatically reduced relative to the pure homopolymer blend and good dispersal of the nanotubes in the blend matrix was attained. q 2003 Published by Elsevier Science Ltd.

Sonochemical approach to the preparation of barium hexaferrite nanoparticles

Abstract A new method, via. the sonochemical decomposition of the solutions of organic precursors, for the synthesis of nanostructured crystalline single phase BaFe12O19 particles is proposed. Nanosized amorphous precursor powders for BaFe12O19, were prepared by the sonochemical decomposition of the solutions of Fe(CO)5 and Ba[OOCCH(C2H5)C4H9]2 in decane, under air at 273 K. The amorphous nature of these particles was confirmed by various techniques, such as SEM, TEM, SAED, and XRD, and the magnetic measurements indicated the superparamagnetic nature. The XRD of the heated sample of this confirmed the formation of single phase BaFe12O19, and the TEM micrograph revealed near uniform platelets with sizes less than 50 nm. The observed magnetization measured upto a field of 1.5 kG of the nanocrystalline BaFe12O19 sample ( 48 emu g−1) was significantly lower than that for the reported multidomain bulk particles ( 72 emu g−1), reflecting the ultrafine nature of the sample.

The use of ultrasound radiation for the preparation of magnetic fluids

Ultrasound radiation has been used for the preparation of amorphous metals, amorphous alloys, amorphous metal oxides and amorphous metal nitrides. In all these cases, the cavitation phenomenon that leads to high temperatures and high pressures was utilized to synthesize the above-mentioned materials as powders having nanometer-sized particles. In this report, we describe the preparation of magnetic fluids formed by the application of ultrasound radiation. Three different systems in which stable magnetic fluids were formed are described. They represent (1) a cobalt colloidal solution in decalin stabilised by oleic acid, (2) a colloidal dispersion of amorphous metallic iron in a polymeric matrix. (3) a Fe 2 O 3 colloidal solution in hexadecane stabilised by oleic acid.

Preparation and magnetic properties of nanosized amorphous ternary Fe-Ni-Co alloy powders

Nanosized amorphous alloy powders of Fe 25 Ni 13 Co 62 , Fe 38 Ni 23 Co 39 , Fe 40 ,Ni 24 ,Co 36 , and Fe 69 Ni 9 Co 22 were prepared by sonochemical decomposition of solutions of volatile organic precursors, Fe(CO) 5 , Ni(CO) 4 , and Co(NO)(CO) 3 in decalin, under an argon pressure of 100 to 150 kPa at 273 K. The amorphous nature of these particles was confirmed by various techniques, such as scanning electron microscopy, transmission electron microscopy, electron microdiffraction, and x-ray diffractograms. Magnetic measurements indicated that the as-prepared amorphous Fe–Ni–Co alloy particles were superparamagnetic. The observed magnetization measured up to a field of 1.5 kG of the annealed Fe–Ni–Co samples (75–87 emu g −1 ) was significantly lower than that for the reported multidomain bulk particles (175 emu g −1 ), reflecting the ultrafine nature of our sample.

Nanoparticle-induced light emission from multi-functionalized silicon

It has been the vision and challenge of device physicists to add optical functionality to silicon. Here we demonstrate, for the first time, a aplug and playo approach in which sonochemically synthesized amorphous Fe2O3 nanoparticles [2] are incorporated onto device quality Si wafers, leading to multiple light emission and multiple functionality (magnetic, metallic, semiconducting, insulating, and optical) all in one. On annealing the Si wafer treated with Fe2O3 nanoparticles, the Fe 3+ is reduced by the silicon, and desorbs as SiO, resulting in the formation of magnetic nanoparticles, consisting predominantly of Fe. More importantly, these samples exhibit multiple light emissions at 1.57, 1.61, and 1.65 lm, which are crucial wavelengths for optical fiber communications. The Fe nanoparticles self-assemble on patterned Si wafers, preferentially nucleating at reactive centers in step-bunched regions. The field of nanotechnology has been gaining increasing momentum in recent years with the advent of novel materials, experimental techniques and methodologies. The main motivation behind this quest is the observation that materials exhibit unique properties when their size is reduced to the quantum regime. In the area of semiconductors, this can lead to novel device architectures and concepts. Indeed, nanoparticles have already been applied in a variety of fields. The main challenges in this field are to control the properties of nanostructures such as size, spatial distribution as well as the functionality itself. One route to achieving this goal is to externally synthesize the nanostructures of desired functions and size, and to incorporate them in the semiconductor in a spatially controlled manner. However, from the technology viewpoint, it is highly desirable that the nanostructures possess multiple functionalities. This requires designing and controlling chemical transformations during manufacturing. In what follows, we show that multiple functionalizations of Si wafers, leading to light emitting property, are possible by using amorphous Fe2O3 nanoparticles through oxidation± reduction reactions. Fabrication of functional nanostructures on semiconducting wafers is essential for realizing nanodevices. Amorphous iron oxide nanoparticles were synthesized by ultrasonic decomposition of the volatile precursor (Fe(CO)5) solution in decane. In short, a decane solution of 0.5 M Fe(CO)5 was sonicated at 273 K for 3 h, under oxygen atmosphere, using a high intensity ultrasonic probe (Sonics, Model VC 601, 1.25 cm Ti horn, 20 kHz, 100 W/cm). In this route, nanoparticles of nearly spherical shape with reasonably uniform size distribution could be prepared in gram quantities. The nanoparticles were suspended in ethanol using an ultrasonic bath, and a drop of the suspension was placed on a Si wafer, which was precleaned by chemical etching. After evaporation of the ethanol, the sample was loaded into the ultra high vacuum (UHV) chamber and annealed to various temperatures. The nature of the surface species was characterized in-situ by photoelectron spectroscopy. Samples were transferred to the molecular beam epitaxy (MBE) chamber where evaporation of Si was carried out by using an electron beam. The samples were examined, outside the chamber, by a variety of techniques. Figure 1 shows an atomic force microscopy (AFM) image of a planar Si(111) which was treated with the nanoparticles and subsequently annealed in UHV at 850 C. As can be seen, the particles are of uniform size and nucleate preferentially at

Low-temperature, carbon-free reduction of iron oxide

Abstract We report here that iron oxide can be reduced completely to elemental iron, through a carbon-free and low-temperature reaction. Nanoparticles of Fe 2 O 3 are completely reduced, resulting in the formation of nanoparticles of Fe, on the surfaces of Si or Ge, at ∼740 and ∼440 °C respectively. We show that this phenomenon is due to the oxygen atoms changing the bonding partner from Fe to Si or Ge, followed by the desorption of the respective monoxides. Therefore, the reduction temperature is dictated by the desorption temperatures of SiO or GeO molecules. The nanoparticles thus formed are magnetic and are of uniform size and shape. On graphite surfaces, however, Fe 2 O 3 retains the original stoichiometry even after annealing at higher temperatures.

Self-organization in ferrofluids prepared by sonochemical radiation method

Abstract We report on the sonochemical synthesis and aging of ferrofluids consisted of nanosized particles. TEM study reveals that nanoparticles in fresh liquids are round-shaped and have almost uniform particle size distribution centered around 10 nm. During aging, magnetic nanoparticles organize themselves in clusters of different shape, which depends mainly on the magnetic nature of metals in a particular ferrofluid. Magnetization measurements demonstrate the change of magnetic signal, as compare to the fresh ferrofluids.

Sonochemical Synthesis of Amorphous Bimetallic Fe-Ni Alloys

The amorphous alloys often called metallic glasses or glassy metals, obtained by rapid quenching of the melt lack the long range order of their crystalline counterparts and are of great importance in modern technology because of their unique electronic, magnetic and corrosion resistant properties1–4. Ferromagnetic amorphous alloys containing Fe and Co show excellent magnetic properties equivalent or superior to the conventional soft magnetic materials and they have already being used in magnetic storage media and power transformer core5. The acoustic cavitation, i.e., the formation, growth and implosive collapse of a bubble in liquid generate transient localized hot spot; a temperature of 5000 K with submicrosecond life time and a pressure of 1800 atm is achieved with cooling rate > 109K6–8. This extremely rapid cavitational cooling rate is much faster than that obtained by other conventional techniques like spalt quenching or roller quenching 9. Suslick et al have employed this sonochemical method for the preparation of nanosized amorphous metallic powders of Fe, Co and their alloys, and metal carbide, Mo2C10–14..The important criterion for achieving the good sonochemical yield is that the precursor should be volatile, because the primary sonochemical reaction site is the vapor inside the cavitation bubbles15. Secondly, the solvent vapor pressure should be lower at the sonochemical temperature since the solvent vapor inside the bubble reduces the collapse efficiency. Our group have prepared amorphous Ni and Fe2O3 and also showed that one could control the particle size of the amorphous iron by varying the precursor, Fe(CO)5 concentration in decalin16–18. The present study is a part of our ongoing project on the synthesis and characterization of nanosized amorphous metals and alloy particles.