Nanostructured Materials最新文献

Nanocomposite Pr₂Fe₁₄B/α-Fe magnets with uniform microstructure and enhanced magnetic properties have been synthesized by melt-spinning a Pr₈Fe₈₆B₆ alloy at low wheel speed range. Microstructural and magnetic studies showed that there is an optimum wheel speed (about 16.7 m/s) at which a uniform Pr₂Fe₁₄B/α-Fe structure with fine α-Fe grains (about 10 nm) is developed directly from the melt. Lower speed gives larger grains for both the 2:14:1 and α-Fe, while higher speed leads to the appearance of an amorphous phase which will result in a Pr₂Fe₁₄B/α-Fe structure with larger α-Fe grains after a subsequent crystallization annealing. Magnetic properties obtained under the optimum-quenching followed by a subsequent annealing are M_s = 176.6 emu/g, M_r = 118.2 emu/g, M_r/M_s = 0.67, H_c = 5.4 kOe and (BH)_m = 12.6 MGOe. The coercivity and energy product are about 20% higher than those obtained by crystallization of over-quenched samples due to the refinement of α-Fe size which leads to an enhanced exchange coupling between Pr₂Fe₁₄B and α-Fe.

The analytic expression of the correlation function of Small-Angle Scattering of a quasi-diluted arrangement of homogeneous spheres, the diameters of which are Rayleigh-distributed, is given. Here, the second derivative of the correlation function is exactly proportional to the size distribution density of the diameters of the spheres. This is a fundamental case for the characterization of nanophases in terms of their chord-length distributions.

NiE₂ (E = Se, Te) nanorods were directly synthesized through the reaction of NiCl₂ and selenium or tellurium in an autoclave at 160 ∼ 180°C for 10 ∼ 15 h, using ethylenediamine as a solvent. X-ray powder diffraction patterns and transmission electron microscope images show that the products are cubic NiSe₂ and hexagonal NiTe₂ phase, respectively, in the form of well-crystallized nanorods. A possible mechanism of the formation of NiE₂ nanorods in the solvothermal process is proposed. The solvent ethylenediamine plays an important role in the formation of NiE₂ nanorods.

The preparation, characterization and photocatalytic degradation of phenol pollutant of TiO₂-SiO₂ aerogels were investigated. The aerogels were mostly turned to anatase microcrystalline after supercritical drying in ethanol. Photocatalytic degradation of phenol in water on aerogels shows that the binary aerogels have high efficiency than the commercial TiO₂ and pure TiO₂ aerogel. The photocatalytic activity of the aerogels increased with the SiO₂ content at first but came to a maximum at molar ratio = 1:1.

High pressure magnetron sputtering is a very promising technique for the controlled synthesis of nanocrystalline thin films as well as nanoparticles of various systems. Here we discuss the conditions necessary for the synthesis of nanocrystalline silver both in the thin film and powder forms. The formation of the nanophase material occurs in a relatively high pressure of inert gas and at low substrate temperatures (77–300 K). The mean crystallographic domain size of the nanocrystalline silver thus synthesized was found to lie in the 3–60 nm range. The growth pattern and morphology of the sputter-deposited nano-grains were studied in detail using transmission electron microscopy and atomic force microscopy.

Three kinds of Ti-Al powders, Ti₇₂Al₂₈, Ti₅₇Al₄₃ and Ti₄₈Al₅₂, were mechanically alloyed by a planetary ball mill in atmosphere of argon or hydrogen gases (0.1 MPa) with alloying times up to 30 h. The mechanical alloying (MA) process as well as the phase variations of each powder after subsequent heating at 1173 K were investigated. About 5000 wppm hydrogen, which could be easily removed by a heat treatment at 800 K (heating rate was 20 K/min), was occluded in all powders during MA in the hydrogen atmosphere, whereas the mechanically alloyed powders in the argon atmosphere occluded about 1000 wppm hydrogen. In the hydrogen atmosphere, the titanium powder easily crumbled into finer particles, assisting the diffusion of aluminum into titanium (solid-solid reaction) at an early stage of the MA process and accelerating the formation of an amorphous-like phase at a longer MA process. The phase formation after heat treatment of MA powders at 1173 K could be estimated by the Ti-Al binary phase diagram without the effect of the gas atmosphere.