关键词：
ultra high molecular weight polyethylene (UHMWPE);thermal damage;wire drawing
摘要：
Ultra high molecular weight polyethylene (UHMWPE) is a kind of non-polar polymer with a crystalline structure. Its failure appeared usually as a type of wire drawing when it was used as a material of rubbing pairs. By a designed heating test, the thermal damage phenomena of UHMWPE were observed by SEM. Its thermal damage model during the process of wire drawing damage was assumed that when the thermal energy was accepted by the UHMWPE, its volume expanding and its surface melting into a viscous fluid proceeded from its elevated temperature, and then the viscous fluid flowed according with non-Newtonian fluid model; after cooling, the melt re-crystallized and gathered again and at the same time many obvious cavities with phenomena of wire drawing appeared in the re- crystalline polymer. As a result the material of UHMWPE shrank to porosint from the congeries with the small uniform particles.
摘要：
The objective of this study is to develop a novel supported nano-NiO catalysts for tar removal in biomass gasification/pyrolysis, to significantly enhance the quality of the produced gases. For this purpose, the supported nano-NiO/gamma-Al2O3 catalyst was prepared by deposition-precipitation (DP) method. Different analytical approaches such as XRD, BET, TEM and SEM/EDX were used to characterize the synthesized catalysts. The results showed that the prepared nano-NiO/gamma-Al2O3 catalysts had an egg-shell structure with a loading of NiO in catalysts over 12 wt %, and they had also a higher BET surface area over commercial nickel based catalysts. The active components of catalyst were spherical NiO nanoparticles coated on the surface of supports with a size range of 12 similar to 18 nm. Furthermore, the activity of the catalysts to remove tar in the process of biomass pyrolysis was also investigated using a bench-scale combined fixed bed reactor. The experiments demonstrated that the tar yield after adding catalysis was reduced significantly. The tar removal efficiency reached to 99% for catalytic pyrolysis at 800 degrees C, while the gas yield after adding catalysis increased markedly. Meanwhile, the compositions of gas products before and after adding catalysis in the process also changed significantly. The percentages of CO2 and CH4 in the product gas after addign catalysis were obviously reduced whilst those of the valuable H-2 and CO increased sharply. Therefore, using the prepared NiO/gamma-Al2O3 catalyst in biomass gasification/pyrolysis can improve significantly the quality of the produced gas and meanwhile eliminate efficiently the tar generation.
摘要：
Nanocubes, monodispersed nanocrystals and nanospheres of Au have been prepared by a simple reaction between HAuCl<inf>4</inf>4H<inf>2</inf>O, NaOH and NH<inf>2</inf>OHHCl in the presence of gelatin. The role of gelatin and the affection of pH in producing the nanoparticles of Au were discussed. The products were characterized by X-ray powder diffraction, transmission electron microscopy, and UV-visible absorption spectroscopy. The sizes of the monodispersed nanocrystals of Au were estimated by Debye-Scherrer formula according to XRD spectrum.
