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Kinetics of face-centered cubic (FCC) phase evolution in equiatomic AlCoCrFeNi alloy has been studied in this work, measuring the phase fraction from X-ray diffraction (XRD). As-cast alloy showed a body-centered cubic (BCC)+B2 structure. Heat treatments performed at different temperatures showed the formation up-to 30 to 35 pct FCC phase between 1073 K and 1373 K. A systematic decrease in hardness from 540 to 390 HV10 with increase in temperature suggested an increase in the FCC volume fraction. Kinetics of FCC evolution were analyzed using the Johnson–Mehl–Avrami–Kolmogorov equation and Arrhenius law to calculate the activation energy for the phase transformation. Furthermore, a time-temperature-transformation diagram was constructed from the isothermal transformation studies. Detailed microstructural investigation suggests faster kinetics of FCC phase formation near dendritic boundaries compared to interdendritic regions. The Kurdjumov–Sachs orientation relationship between FCC and BCC phases suggested a coherent interface between these phases. Results of the present study pave the way to decide on heat treatment practices in AlCoCrFeNi alloy. [ABSTRACT FROM AUTHOR]

The iron nanoparticles coated with oleic acid and drugs such as folic acid/Amoxicillin were synthesized by high energy ball milling and characterized by X-ray diffraction, Transmission electron microscope, zeta potential, dynamic light scattering, Fourier Transform Infra red (FT-IR) measurements, and thermo gravimetric analysis (TGA). FT-IR and TGA measurements show good adsorption of drugs on oleic acid coated nanoparticles. Magnetic measurements indicate that saturation magnetization is larger for amoxicillin coated particles compared to folic acid coated particles. The biocompatibility of the magnetic nanoparticles prepared was evaluated by in vitro cytotoxicity assay using L929 cells as model cells. [ABSTRACT FROM AUTHOR]

Filling the voids of cage forming compounds with loosely bound electropositive elements and by incorporating nano-sized secondary phases are promising approaches to enhance the thermoelectric figure of merit of these materials. Hence, in this work, by combining these two approaches—inserting In into the voids of skutterudite Co4Sb12 as well as dispersing nanoparticles (GaSb)—we have synthesized various samples via ball-milling and spark plasma sintering. InSb as the secondary phase of the matrix, mixed with GaSb, forms the solid solution Ga1−xInxSb. Nanocrystalline grains together with a few larger grains (10–30 μm) are found to be spread in In0.2Co4Sb12. The former is comprised of either InSb, GaSb or Ga1−xInxSb. Because of their identical space group and similar lattice parameters, InSb, GaSb and Ga1−xInxSb could not be detected separately in EBSD. High resolution transmission electron microscopy (HRTEM) was used to resolve different phases, which showed GaSb grains of size ∼10–30 nm and InSb grains of size ∼30–100 nm. Scattering of charge carriers at the interfaces of InSb, GaSb and Ga1−xInxSb as well as the matrix phases increased both the electrical resistivity and Seebeck coefficient. The multi-scale size distribution of grains, of both the matrix phase and the secondary phases, scattered phonons within a broad wavelength range, resulting in very low lattice thermal conductivities. As a result, an enhanced figure of merit of 1.4 was achieved for the (GaSb)0.1 + In0.2Co4Sb12 nanocomposite at 773 K. [ABSTRACT FROM AUTHOR]

In the present work, the concept of mechanically activated annealing (MAA) has been applied to produce nanocrystalline Al0.3CoCrFeNi high-entropy alloys (HEAs) with reduced contamination levels. Phase evolution during conventional mechanical alloying (MA), MAA and subsequent consolidation by spark plasma sintering (SPS) have been studied in detail. Complete alloying is obtained after 15 h of MA, while milling time of 5 h and annealing at 1100 °C for 1 h have been used to achieve alloy formation during MAA. Both the MA–SPS and MAA–SPS routes have shown major FCC phase. The contamination of WC observed during MA was successfully eliminated during MAA, while the volume fraction of Cr7C3 reduced from 20% during MA–SPS to 10% after MAA–SPS. This method can serve as an effective way to produce nanostructured HEAs with minimum contamination. [ABSTRACT FROM AUTHOR]

Dielectric relaxation in sol-gel-derived anatase titanium oxide nanocrystals (6, 9, and 20 nm) has been investigated using impedance spectroscopy in a wide frequency range from 1 Hz to 1 MHz as a function of applied DC bias voltage, ranging from 0 to 4.2 V in a periodic interval of 0.3 V. Under the equilibrium condition, around three order of magnitude variations in the dielectric relaxation time (τ) was observed for the grain size if reduced to 6 nm from 20 nm. An unambiguous evidence for the absence of such a crystallite size effect was experimentally observed in higher biased conditions because of grain boundary Schottky potential barrier height suppression. These experimental results obey the 'grain boundary double Schottky barrier model.' [ABSTRACT FROM AUTHOR]

Transparent semiconductor CuAlO2 in nanodimension was prepared by mechanical alloying of Cu2O and α-Al2O3 powders in toluene medium. The formation of single phase CuAlO2 with an average crystallite size of 45 nm was confirmed by x-ray diffraction analysis. The nanocrystalline nature of CuAlO2 was confirmed by atomic force microscopy. Frequency-dependent dielectric property measurements and the relaxation behavior were studied using impedance spectroscopy. Dielectric relaxation time estimated from the modulus curves was found to be decreasing with increase in temperature. The existence of stretched exponent parameter β<1 in the present nanocrystalline CuAlO2 implies non-Debye type relaxation behavior in this material. [ABSTRACT FROM AUTHOR]

The nanocrystalline Pb0.92Nd0.08(Zr0.53Ti0.47)0.98O3 (PNZT) has been synthesized by high-energy ball milling (mechanical alloying). X-ray diffraction studies shows that these compounds are tetragonal. Detailed studies of impedance and dielectric properties of PNZT as a function of temperature (and frequency) showed the high permittivity of 10 626 at 10 kHz at the Curie temperature (TC), broadening of permittivity peak, lowering of TC, decrease in conductivity, and increase in relaxation time with the decrease in crystallite size. [ABSTRACT FROM AUTHOR]

The nanocrystalline Gd-doped lead titanium zirconate (PGZT) with the composition Pb[sub 0.92]Gd[sub 0.08](Zr[sub 0.53]Ti[sub 0.47])[sub 0.98]O[sub 3] has been synthesized by a combination of high-energy ball milling [mechanical alloying (MA)] and sintering. PGZT prepared by MA followed by high-temperature sintering has a higher dielectric constant compared to that of the conventional technique. PGZT shows a nonrelaxor ferroelectric behavior but has diffuse ferroelectric–paraelectric phase transition. The activation energy of the material was found sensitive to its crystallite size. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A systematic study on the formation and the stability of Al[sub 70]Cu[sub 20]Fe[sub 10] quasicrystalline alloy has been carried out through mechanical alloying. The influence of the milling parameters, sequence of additive elements, and heat treatment on the formation of icosahedral phase has been investigated through x-ray diffraction analysis and transmission electron microscopy. A combination of milling and heat treatment of Al[sub 70]Cu[sub 20]Fe[sub 10] composition resulted in the formation of a single icosahedral phase (i-phase) quasicrystal with face-centered structure. We present evidence that suggests the i phase is of a nanoquasicrystalline nature. From the present investigations, we propose an i-phase formation mechanism in Al–Cu–Fe system. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In this paper, influence of additives on structural properties of Tantalum (Ta) doped PZT ceramics, prepared by solid-state oxide and mechanical activation (MA) routes, has been studied. The Fourier transformation infrared spectroscopy (FTIR) studies, are done to understand the structural interactions, confirmed that the wave number and bond energy decreases with the increase in Ta content accompanied by decrease in grain size. FTIR spectrum becomes broader in nanocrystalline Ta-PZT. The fraction of tetragonal phase decrease along with reduction in grain size as the Ta content increase. The remnant polarisation and coercive field also follows the similar trend on Ta doping. It is seen that infrared spectroscopy results corroborate the structure and ferroelectric properties of PZT materials. [ABSTRACT FROM AUTHOR]

The present investigation deals with the processing of [(Fe0.5Co0.5)0.75B0.2Si0.05]96Nb4 bulk metallic glass (BMG) using different techniques. The maximum plate thickness for the amorphous phase formation has been found to be 1.25 mm using a conventional BMG casting technique (forced infiltration casting). For enhancing the dimension, an alternate processing route was employed to produce the BMG in the form of compacts. In this case, the dimensions are not restricted by the glass forming ability of the alloy. The process involved the preparation of amorphous ribbons using a melt spinner followed by high energy ball milling to crush the ribbons into very fine particles. The powder was then compacted in the form of pellets using spark plasma sintering technique. Density achieved was almost near to theoretical density (99%). The density was found to increase with a decrease in the particle size of glassy powder, which could be achieved by increasing the duration of high energy ball milling. The maximum densification occurred when the holding temperature was within undercooled liquid regime (∆Tx). Further increase of temperature beyond crystallization temperature (Tx) resulted in decreasing the compact density. [ABSTRACT FROM AUTHOR]