Hengzhi Wang

Study of nanocrystalline TiO2 prepared with raw and modified gelatin dispersants

Nanocrystalline TiO 2 was prepared by the sol-gel method, and raw gelatin and its modified samples crosslinked with formaldehyde acted as dispersers in this method. Transmission electron microscope and X-ray diffractometer measurements showed, using modified gelatin samples, the prepared TiO 2 nanocrystals have smaller particle size and more homogeneous particle distribution at the same calcining temperature. Following Fourier transform IR spectroscope analysis, the dispersion mechanism is considered to be through the bonding of TiO(NO 3 ) 2 . H 2 O with the peptide chains of gelatin by a hydrogen bond.

Usage of ultrafine anatase/TiO2·nH2O powder: photocatalysis and microstructure control for nanocrystalline TiO2

Abstract As a control method, a ultrafine TiO 2 powder (sample A) prepared previously acted as a primary material and was annealed at different temperatures for obtaining nanocrystalline TiO 2 with different microstructures. This process without supplemental heat from gel oxidation has an important effect on the nanocrystalline TiO 2 microstructures. In addition, the photocatalytic efficiency of sample A was evaluated by the methylic orange (pH=6) photocatalytic degradation with this ultrafine powder and the other typical nanocrystalline TiO 2 powders. It was found that only the sample A has an excellent photocatalytic efficiency. The further characterisation by thermal analysis shows that this ultrafine powder consists of anatase phase and non-crystal TiO 2 · n H 2 O. It was explained by the TiO 2 photocatalysis mechanism that the OH − belonging to ultrafine anatase/TiO 2 · n H 2 O powder (sample A) can efficiently promote the purification in low pH medium.

In situ electron microscope study on the formation and morphological evolution of carbon aggregates

Two phenomena were observed when a copper specimen was irradiated by normal electron beam in a transmission electron microscope. One is the growth of the rod-like carbon aggregates normally stemmed from the substrate of specimen, with their unique fir-like shape and pattern caused by the deposition of hydrocarbon molecules. These molecules come from the boiling and evaporating of the diffusion pump oil in the high vacuum system. The other is the evolution of the stacked morphologies from the fir-like to spindle-like, mushroom-like and ball-like. The experimental findings and theoretically analyses lead us to believe that the carbon aggregates go through an evolution process which is governed, to some degree, by the irradiation of electron beam and by the surface tension and the instability of the amorphous carbon. Moreover, during the growing process of the carbon aggregates, the magnitude of electric charges and their distributions on the deposited carbon dominate the side branching and the tip splitting. For the evolution process of the morphologies, the most important driving force is the surface tension of the carbon aggregates under the irradiation of electron beam in a vacuum system.

Fractal carbon trees on polymer and metal substrates in TEM observation

It is well known that the surface of a specimen is easily contaminated by materials in an ordinary vacuum system. This kind of contamination may seriously influence the resolution of the transmission electron microscope (TEM), and grievously limit the study of surface phenomena in materials science by TEM, such as nucleation and growth of new phases at the surface of the specimen, surface diffusion, crystal growth, etc. [1]. The buildup of contaminating material may be controlled or reduced by the employment

A new approach to the determination of Mark-Houwink parameters

Abstract A new approach to determining Mark–Houwink (MH) parameters accurately and conveniently is proposed in this paper. With this method, the MH parameters of a polymer system can be determined by firstly measuring the average retention volumes of several polydisperse samples of the polymer system with a gel permeation chromatography (GPC) and their intrinsic viscosities with a Ubbelohde viscometer, then finding a nonlinear least square function according to the least square principle, and finally deciding the global optimum values of the MH parameters accurately and conveniently by grid search algorithm. With this method, the hard work and possible errors due to fractionation of the polydisperse sample of the polymer can be avoided. In addition, this method has two important advantages over existing analogous methods: one is that, this method uses a GPC chromatogram of a polydisperse sample of the polymer system as a whole instead of dividing it into sections and treating each of the sections as a monodisperse sample, thus, the errors arising from the instrumental spreading effect can be avoided; the other is that, the grid search algorithm is used in this method to find the global optimum values of MH parameters in a short time, thus, the errors and the trouble resulting from the application of a nonlinear regression algorithm can be avoided as well. The polymer systems of polystyrene (PS) in toluene at 25°C and poly(methyl methacrylate) (PMMA) in benzene at 25°C have been selected to demonstrate the applicability of this method. In addition, the computer program can be used to all the cases of determining the MH parameters by this method.