Thermal conductivity enhancement of ZnO nanofluid using a one-step physical method

Nano-crystalline Ni has been synthesized by a pulsed wire evaporation (PWE) method, and its abnormal magnetic properties in a magnetic ordered state have been characterized using high and low magnetic fields. It was found that particles with the size ranges from 20 to 80 nm has a mean crystalline size of 40 nm which might influence the magnetic hysterisis behavior. Neutron powder diffraction (NPD) and saturation magnetization results indicate the antiferromagnetic NiO phase in prepared powder exist below the detection limit of 1 wt.%. The shifted hysterisis loop and irreversibility of magnetization in a high field were observed in the magnetic-ordered state of Ni. The initial magnetization curve for Ni is started to overlap the hysterisis loop at applied field of 750 Oe. This irreversibility in a high field can be explained by the non-collinear behavior and the existence of the metastable states of the magnetization at the surface layer (or core) of the particle in the applied magnetic field due to decrease of particle size.

Magnetic properties of nano-size Ni synthesized by the pulsed wire evaporation (PWE) method

Nanocrystalline ZnO powders have been synthesized by means of a novel and simple one-step method of levitational gas condensation. The Zn clusters evaporated from a surface of the levitated liquid Zn droplet and then condensed into nanoparticles of ZnO in a chamber filled with mixtures of Ar and O2 gases. As a result, ZnO was synthesized under an O2 flow rate of 0.1 ≤ V O 2 ( l / min ) ≤ 0.2 . The as-prepared ZnO powders, characterized by transmission electron microscopy and Brunauer–Emmet–Teller analysis, show high specific surface area of 38 m2/g and possess particle size of 30 nm having the web-like pattern with hexagonal structure. From the main peak intensities of X-ray diffraction, the amounts of ZnO and Zn in the sample are found to be 92% and 8%.

Synthesis and characterization of nanoparticles of ZnO by levitational gas condensation

Nanoparticles of γ-Fe 2 O 3 have been prepared by the levitational gas condensation (LGC) method, and their structural and magnetic properties were studied by XRD, TEM and Mossbauer spectroscopy. Fe clusters evaporated from a surface of the levitated liquid Fe droplet and then condensed into nanoparticles of γ-Fe 2 O 3 with particle sizes of 14 to 30 nm in a chamber filled with mixtures of Ar and O 2 gases. From the main peak intensities of XRD and analyses of Mossbauer spectra, the amount of γ-Fe 2 O 3 and α-Fe in the sample is composed of about 93% and 7%, respectively. Mossbauer spectra consist of two sets of six Lorentzian lines corresponding to γ-Fe 2 O 3 and α-Fe. It was found that the phase transition from both γ-Fe 2 O 3 and α-Fe to Fe 3 O 4 , which was evaluated from the results of Mossbauer spectra, strongly depended on the O 2 flow rate. As a result, γ-Fe 2 O 3 was synthesized under the O 2 flow rate of 0.05 ≤ V o2 (l/min) ≤ 0.15, whereas Fe 3 O 4 was synthesized under the O 2 flow rate of 0.15 ≤ V o2 (l/min) ≤ 0.2.

Phase control and Mössbauer spectra of nano γ‐Fe2O3 particles synthesized by the levitational gas condensation (LGC) method

In this paper, we report a facile, an environmental friendly ultrasonic-assisted hydrothermal route for preparation of goethite flower structures using Fe nanopowders at low temperature (85°C). The flower structure consisted of tens of hundreds of nanowires and such structures can further self-assemble with the flake with micro size area. Structural, morphological, and elemental analysis revealed that the products consisted of flower-like structures with high structural uniformity, good crystal quality, and high yields. Influencing factors such as the reaction temperature, pH value, and the deposition time were systematically investigated. A possible formation mechanism was proposed on the basis of the experimental results. Magnetic measurements showed that the as-obtained goethite flowers exhibited weakly ferromagnetic characteristics at room temperature, which were quite different from those of the corresponding bulk materials.

Large-scale synthesis of hierarchical alpha-FeOOH flowers by ultrasonic-assisted hydrothermal route

Nanoparticles of Fe2O3 with a mean particle size of 4–50 nm have been prepared by the pulsed wire evaporation method, and its structural and magnetic properties were studied From the main peak intensity of x-ray diffraction the amount of v-Fe2O3 and ɑ-Fe2O3 in sample is composed about 70% and 30%, respectively The coercivity (53 Oe) and the saturation magnetization (14 emu/g) are about 20% of those of the bulk v-Fe2O3 A quadrupole line on the center of Mossbauer spectrum represents the superparamagnetic phase of v-Fe2O3 with a mean particle size of 7 nm or below

W. W. Kim

Papers

Magnetic nanoparticles of Fe2O3 synthesized by the pulsed wire evaporation method