PREPARATION OF ULTRAFINE PARTICLE IRON-CARBONIDE CATALYST AND CHARACTERIZATION OF ITS CATALYTICAL BEHAVIOR

Studies on ultrafine particle catalyst have attracted many researchers' attention by its large surface area,higher activity and selectivity.Based on the mechanism of α-Fe and Fe_xC_y as the catalytical active species this paper reports for the first time the preparation method of Fe_3C ultrafine parti- cle catalyst,from highly dispersed amorphous Fe powder and free carbon.The Fe powder and free car- bon,prepared by laser pyrolysis technique,was then treated by washing and heating at high tempera- ture protected with N_2.The catalyst prepared under different experimental conditions was characterazed by means of XRD,electronic diffraction and TEM.It shows that the crystlline grain size is in a range of 1-4nm and composed of Fe_3C and α-Fe.It has been found that the ultrafine particle iron-carbonide catalyst exhibited much higher activity and selectivity to light olefins.At the standard atmosphere and 380℃ reaction temperature,the conversion of CO reached a maximum of 80%.

Effects of Strain Rate and Texture on the Tensile Behavior of Pre-strained NiCr Microwires

The stress–strain behavior and strain rate sensitivity of pre-strained Ni80Cr20（Ni20Cr） were studied at strain rates from 4.8×10^（–4）s^（–1） to 1.1×10^（–1）s^（–1）. Specimens were prepared through cold drawing with abnormal plastic deformation. The texture of the specimen was characterized using electron backscatter diffraction. Results revealed that the ultimate tensile strength and ductility of the pre-strained Ni20Cr microwires simultaneously increased with increasing strain rate. Twinning-induced negative strain rate sensitivity was discovered. Positive strain rate sensitivity was present in fracture flow stress, whereas negative strain rate sensitivity was detected in flow stress values of σ_（0.5%） and σ_（1%）. Tensile test of the pre-strained Ni20Cr showed that twinning deformation predominated, whereas dislocation slip deformation dominated when twinning deformation reached saturation. The trends observed in the fractions of 2°-5°, 5°-15°, and 15°-180° grain boundaries confirmed that twinning deformation dominated the first stage.

The effect of oxidation on physicochemical properties and aqueous stabilization of multiwalled carbon nanotubes：comparison of multiple analysis methods

Surface oxidation can alter physicochemical properties of multiwalled carbon nanotubes(MWCNTs) and influence their aqueous stabilization.Many techniques have been used to characterize the physicochemical properties and aqueous stabilization of MWCNTs.However,the relationship between the change in physicochemical property and the aqueous stabilization of MWCNTs merits more studies,and the multiple characterization techniques have not been well compared.This study systematically and comparatively investigated the effect of oxidation on the physicochemical properties and aqueous stabilization of MWCNTs using multiple analysis methods.Increased surface area,disclosed tube ends,defects on the sidewalls,disruption of the electronic structure,and removal of metal catalysts and amorphous carbon were observed for the oxidized MWCNTs(o-MWCNTs) using the multipoint Brunauer-Emmett-Teller(BET) method,transmission electron microscope observation,Raman spectroscopy,UV-Vis spectroscopy,and thermogravimetric analysis.An oxidation-time-dependent increase in oxygen content of the MWCNTs was verified by the methods of elemental analysis,mass difference calculation,and X-ray photoelectron spectroscopy(XPS).Fourier transform infrared spectroscopy,XPS,and the Boehm titration were employed to study the functionalities on the MWCNT surfaces.Despite the limitations of these techniques,the results indicated that the dramatic increase in carboxyl groups was mainly responsible for the significant increase in oxygen content after the oxidation.The dissociation of the grafted functional groups increased electronegativity of the o-MWCNTs and facilitated the aqueous stabilization of o-MWCNTs through electrostatic repulsions.The oxidation affected the UV-Vis absorbance of MWCNT suspensions.The absorbances at 800 nm of the stabilized MWCNT suspensions had a good correlation with the MWCNT concentrations and could be used to quantify the MWCNT suspensions.The findings of this work are expected to boost the research on carbon nanotubes and their environmental behaviors.