Li Fanqing

Boehmite sol properties and preparation of two-layer alumina membrane by a sol-gel process

A two layer ultrafiltration alumina membrane was prepared by a sol-gel process using boehmite sol as precursor. The sol was prepared by hydrolysation of aluminium tri-sec-butoxide. Sol properties, such as viscosity as a function of concentration and acidity, were investigated by using capillary viscometry, transmission electron microscopy and laser scattering photometry etc. The viscosity increased with an increase in concentration and a decrease in pH, while the particle shape and size of the sol were mainly determined by pH. The membrane prepared by a dipping procedure was characterized by both scanning electron microscopy and transmission electron microscopy. The results showed that the membrane thickness and surface morphology were affected by the dipping time, the viscosity and the temperature.

Preparation of asymmetric Ni/ceramic composite membrane by electroless plating

Abstract Although a lot of work has been done on electroless nickel coating, work on preparing asymmetric nickel membranes on porous ceramic supports is rarely reported. In this work, microfiltration nickel membranes are prepared on porous alumina supports with electroless plating. A new approach technique, sol–gel process is used to activate the alumina supports. The coated membranes were investigated by means of scanning electron microscopy and gas permeation test. Membrane thickness and amount of nickel increase with plating time. Membrane pore size decreases greatly as electroless coating is processed for 15 min. After 15-min coating the pore size decreases slightly. For a 90-min electroless plated membrane, the thickness reaches 4.5 μm and the mean pore radius is 0.13 μm with a narrow distribution.

Preparation and electron spin resonance effect of nanometer-sized Mn2O3

Abstract Nanometer-sized manganic oxide (Mn 2 O 3 ) has been prepared for the first time by a chemical liquid homogeneous precipitation (CLHP) method. Transmission electron micrographs and X-ray powder diffraction patterns show that the average particle sizes are in the range of 9–50 nm. From the electron spin resonance (ESR) patterns of 9 nm manganic oxide particle, we can observe hyperfine structure (Six absorption peaks of ESR) of Mn 2+ ion adding the Mn 3+ ion signal.

Growth of Bi2Sr2CaCu2O8 single crystals from Bi-rich melts

Abstract High-quality Bi 2 Sr 2 CaCu 2 O 8 single crystals with dimensions up to 15x4x0.05 mm 3 were grown from the starting composition Bi 2+ x Sr 2 CaCu 2 O y , where x =0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6 and 0.7. Different amounts of Bi 2 O 3 in excess are included in each crystal growth run to act as flux for the growth and the optimum concentrations of the flux amount have been found. Structure characterization of a high-quality 2212 free crystal of 5x1.8x0.02 mm 3 was conducted by the (00 l ), ( h 00) and (0 k 0) X-ray diffractions, using a rotating anode diffractometer, and the back-reflection Laue photograph. It is found that melting incongruency is the main problem encountered in the growth of large and pure-phase single crystals from Bi 2 O 3 -rich melts and we have shown that, for x =0.8, crystals of 2212 phase and crystals of 2201 phase coexisting with CuO are obtained from the two segregated parts of the Bi-rich melts.

The structural characteristics of Bi-based 2212 phase whiskers

Abstract We have succeeded in studying the structural characteristics of a single thread of Bi-based 2212-phase whisker by X-ray diffraction. It is found that the structural characteristics of a single thread of whisker coincide with those of a 2212-phase single crystal. The single thread of whisker is a 2212 plate-like single crystal and is stacked in a layered structure. There are a number of low-angle boundaries in the BC-plane, but few in the AB-plane of the whisker.

Plasma environment during hot cathode direct current discharge plasma chemical vapor deposition of diamond films

The plasma characteristics have been investigatedin situ by using optical emission spectroscopy (OES) and the Langmuir probe during hot cathode direct current discharge plasma chemical vapor deposition of diamond films. The changes of atomic H and CH radical in the ground state have been calculated quantitatively according to the results of OES and the Langmuir probe measurement as discharge current density varied. It is shown that atomic H and CH radicals both in the ground state and in the excited state increase with the enhancement of the discharge current density in the plasma. The electron density and CH emission intensity increase linearly with the enhancement of discharge current densities. The generation of different carbon-containing radicals is related to the elevation of electron temperature. Combining the growth process of diamond films and the diagnostic results, it is shown that atomic H in the excited state may improve the diamond growth efficiently, and the increase of electron temperature and density plays an important role in the increase of the deposition rate of diamond films.

Study on the cathode deposit produced in the process of carbon arc discharge

The cathode deposit produced by carbon arc discharge was studied by scanning electron microscopy, high resolution electron microscopy, x-ray diffraction and Raman spectroscopy. The results indicate that the stacking of hexagonal carbon layer in the discharged graphite is different from the ABAB stacking sequence in graphite, and that carbon nanotube is a kind of graphite-like micro-crystal with a low-dimensional structure.

Microstructure and luminescence properties of GaxIn1-xP/GaAs heterostructure

The GaxIn1-xP/GaAs heterostructures with different x values have been investigated by photoluminescence (PL), energy dispersive spectrum (EDS), and transmission electron microscopy (TEM). Experimental results suggested that the composition of epitaxial layers evidently affected the microstructure of the heterostructures. When x value was close to 0.5, the defects in the epitaxial layer decreased, and the lattice match between film and substrate approached optimum. Meanwhile, the heterostructure provided a high luminescence efficiency.