Mechanochemistry of copper sulphides: phase interchanges during milling

Covellite, CuS and chalcocite, Cu₂S nanoparticles prepared in the explosive manner from elemental precursors were further ball-milled in order to observe additional changes caused by mechanical action. Three phases of chalcocite were interchanging during milling, monoclinic one being major at the equilibrium after 30 min. In the case of covellite synthesis, milling for 15 min brought about a significant diminishment in the content of digenite, Cu_1.8S, impurity. Covellite powder exhibited finer character than chalcocite, as documented by crystallite size, grain size and specific surface area analysis. Finally, the effect of milling speed on the explosive character of the reaction and phase composition of chalcocite was investigated. The most drastic conditions favored the formation of the monoclinic phase with the lowest symmetry and the time and intensity of the explosion was found to depend on the milling speed. The whole process is mechanically driven.     

Thermal coefficients of the expansion and refractive index in YAG

The thermal expansion coefficient and dn/dT are measured by interferometry techniques in undoped YAG below 300 K. The thermal expansion coefficient at 125 K is measured to be 2.70 x 10(-6) K(-1) and dn/dT at 633 nm is 2.5 x 10(-6) K(-1), compared with 7 x 10(-6) K(-1) and 9 x 10(-6) K(-1) for these quantities at 300 K.     

Structural characterization of self-assembled ZnO nanoparticles obtained by the sol-gel method from Zn(CH3COO)2·2H2O

Zinc oxide nanopowders were synthesized by the sol-gel method from an ethanol solution of zinc acetate dihydrate. Detailed structural and microstructural investigations were carried out using x-ray diffraction, Raman spectroscopy, thermogravimetric and differential thermal analyses, as well as high-resolution transmission electron microscopy (TEM) and field-emission scanning electron microscopy. The intermediate compound of the reaction was layered zinc hydroxide acetate that further transforms into hexagonally shaped ZnO crystalline nanoplates (d(m) = 4 nm), which aggregate into larger spherical particles. According to the TEM analysis the ZnO nanoparticles were self-assembled into larger particles with the same orientation, i.e. aligned lattice planes of the particles. A further solvothermal treatment resulted in hexagonal, prismatic ZnO mesocrystals.     

Mechanochemical synthesis and characterization of nanocrystalline BiSe, Bi2Se3 semiconductors

Mechanochemical synthesis of bismuth selenides (BiSe, Bi₂Se₃) was performed by high-energy milling of bismuth and selenium powders in a planetary ball mill. The particle size distribution and the specific surface area of Bi/Se and 2Bi/3Se powder mixtures were analysed at increasing milling time. The products were characterized by X-ray diffraction, differential scanning calorimetry and transmission electron microscopy. The presence of bismuth selenide phases was observed after only 1?min of milling and full conversion into hexagonal BiSe phase (nevskite) and rhombohedral Bi₂Se₃ phase (paraguanajuatite) was reached after 10?min of milling. The nanocrystalline nature of both mechanochemically synthesised bismuth selenides was confirmed and their optical band gap energies were obtained on the basis of the recorded absorption spectra in UV–Vis spectral region.     

The use of de-aggregating agents in ZnSe mechanochemical synthesis

Conventional mechanochemical synthesis of zinc selenide, ZnSe nanoparticles was performed in a planetary ball mill by high-energy milling of zinc (Zn) and selenium (Se) powders with the de-aggregating agents ZnCl₂ and phthalic acid (aromatic dicarboxylic acid, C₈H₆O₄). Physical–chemical and optical properties of the prepared ZnSe nanoparticles were studied and compared. The mechanochemically synthesized products were characterized by X-ray diffraction analysis (XRD) that confirmed the presence of cubic-Stilleite and hexagonal ZnSe phases after 18, 25, 30, 40, 45 and 50 min of milling with various amounts of the added de-aggregating agents. Size of crystallites calculated from XRD patterns was from 20 to 31 nm for cubic ZnSe prepared with ZnCl₂. For ZnSe synthesized with phthalic acid the crystallite size ranged from 16 to 73 nm. Size, phase composition, morphology, and crystallinity of ZnSe nanoparticles were studied by transmission electron microscopy (TEM) and selected area electron diffraction (SAED). Photoluminescence spectra (PL) at room temperature have shown a broad red emission bands, and the presence of de-aggregating agent has altered the intensity of the PL signal as well.     

Bio-mechanochemical synthesis of silver nanoparticles with antibacterial activity

By using a bio-mechanochemical approach combining mechanochemistry (ball milling) and green synthesis for the first time, silver nanoparticles (Ag NPs) with antibacterial activity were successfully synthesized. Concretely, eggshell membrane (ESM) or Origanum vulgare L. plant (ORE) and silver nitrate were used as environmentally friendly reducing agent and Ag precursor, respectively. The whole synthesis took 30?min in the former and 45?min in the latter case. The photon cross-correlation measurements have shown finer character of the product in the case of milling with Origanum. UV–Vis measurements have shown the formation of spherical NPs in both samples. TEM study has revealed that both samples are composites of nanosized silver nanoparticles homogenously dispersed within the organic matrices. It has shown that the size and size distribution of the silver nanoparticles is smaller and more uniform in the case of eggshell membrane matrix implying lower silver mobility within this matrix. The antibacterial activity was higher for the silver nanoparticles synthesized with co-milling with Origanum plant than in the case of milling with eggshell membrane.     

Microstructure Development in Low-Antimony Oxide-Doped Zinc Oxide Ceramics

The grain growth of ZnO ceramics sintered with low additions of Sb₂O₃ (<500 ppm of Sb) was investigated. Additions of Sb<250 ppm resulted in a coarse-grained microstructure with large ZnO grains (55–70 μm), much larger than the grain size of ZnO ceramics without any Sb₂O₃ addition (45 μm). The addition of 500 ppm of Sb resulted in a fine-grained microstructure with an average ZnO grain size of about 12 μm. The results are explained by an inversion-boundary (IB) -induced grain-growth mechanism. The grain-growth exponent has a value of about 2 as long as the grains containing IBs grow at the expense of IB-free grains. It increases to about 4 after the IB-containing grains impinge on each other, and achieves values above 10 for additions of 500 ppm of Sb when IBs nucleate in nearly all the ZnO grains so that grains with IBs prevail in the microstructure at an early stage in the grain-growth process.     

Preparation and analytical electron microscopy of a SiC continuous-fiber ceramic composite

Continuous-fiber-reinforced SiC/SiC-based matrix composite materials, to be used in the first-wall blanket of a fusion reactor, were prepared by the infiltration of SiC cloth with SiC-based suspensions of various chemical compositions. The compositions were tailored with respect to the calculated activation in a fast-neutron flux. Liquid-phase sintering was used for material densification, using different sintering aids, such as Al₂O₃, Y₂O₃, P₂O₅, AlN, etc. The microstructures of the differently prepared materials were studied with scanning and transmission electron microscopy and microanalysis. This paper was presented at the International Symposium on Manufacturing, Properties, and Applications of Nanocrystalline Materials sponsored by the ASM International Nanotechnology Task Force and TMS Powder Materials Committee on October 18–20, 2004 in Columbus, OH.     

Microstructural Development in SnO2-Doped ZnO–Bi2O3 Ceramics

The effects of adding small quantities of SnO₂ to the basic ZnO–Bi₂O₃ varistor composition were studied in terms of phase reactions, microstructural development, and the formation of inversion boundaries. Scanning and transmission electron microscopy studies showed that the inversion boundaries, triggered by the addition of SnO₂, cause anisotropic grain growth in the early stages of sintering. ZnO grains that include inversion boundaries grow exaggeratedly, at the expense of normal grains, until they dominate the microstructure. Higher additions of SnO₂ lead to an increase in number of grains with inversion boundaries and to a more fine-grained microstructure. The increasing amount of secondary phases is also related to a higher level of SnO₂ addition; however, the influence of these phases on ZnO grain growth is subordinate to the role of inversion boundaries.     

Measurement of aerosol-particle trajectories using a structured laser beam

What is believed to be a new concept for the measurement of micrometer-sized particle trajectories in an inlet air stream is introduced. The technique uses a light source and a mask to generate a spatial pattern of light within a volume in space. Particles traverse the illumination volume and elastically scatter light to a photodetector where the signal is recorded in time. The detected scattering waveform is decoded to find the particle trajectory. A design is presented for the structured laser beam, and the accuracy of the technique in determining particle position is demonstrated. It is also demonstrated that the structured laser beam can be used to measure and then correct for the spatially dependent instrument-response function of an optical-scattering-based particle-sizing system for aerosols.