Abstract: The ZnO/TiO2 composite films were deposited over glass using spin coating technique by sol-gel process. Single-walled carbon nanotubes (SWNTs) were used to modify the ZnO/TiO2 films successfully in this paper. The structure and composition of the ZnO/TiO2 composite and SWNTs doped ZnO/TiO2 composite were characterized by X-ray diffraction (XRD). The morphology of samples was characterized by scanning electron microscopy (SEM). The photocatalytic activity was investigated by photocatalytic degradation of aqueous methyl orange under ultraviolet (UV) radiation. The UV-vis absorption spectra of the ZnO/TiO2 films and SWNTs doped ZnO/TiO2 films in the wavelength region 200~800 nm were obtained. The results indicate that the SWNTs addition can decrease the grain size of ZnO/TiO2, which can enhance the photocatalytic activity. UV-vis absorption spectra of SWNTs-ZnO/TiO2 showed obvious blue shifts compared with ZnO/TiO2. The optimal amount of doping SWNTs is 1% according to this research. The enhanced mechanism of the SWNTs for the photocatalytic activity in ZnO/TiO2 films was analyzed in this article.
Abstract: With the development of technology, composites are used more broadly, especially at different temperature. So it is very important to research the mechanical properties of composites at different temperature. Three dimensional braided composites are new composites with high performances, in which fiber-tows are interlacing in space with multi-direction and pass through the thickness to form a no-laminated and integrated structure. However researches on the mechanical properties of three dimensional braided composites are almost at room temperature. In this paper, the tensile and bending strengths of three dimensional braided composites (TR-30s carbon fiber/epoxy) at 23 oC and 150 oC are researched respectively. The results indicate that the effect of temperature on the tensile strength and bending strength of 3D braided composites is obviously different. The average tensile strength of 3D braided composites at 150 oC is almost the same as that at 23 oC. However the average bending strength of 3D braided composites at 150 oC is mush lower than that at 23 oC. This means that the effect of temperature on different mechanical properties is different and application temperature should be taken care of when 3D braided composites bear different kind of loads.
Abstract: Many investigations have been conducted on compressive strength of lightweight aggregate concretes (LWAC), but there are few experimental studies on the relationship between compressive strength, bond strength and elastic modulus of LWAC. In this paper, the specimens of twenty kinds of LWACs with different mix proportions were made. Properties of compressive strength, bond strength and modulus of elasticity of the LWACs were tested. Based on the testing resulting, equations for relationship between bond strength and compressive strength of the LWAC were established. For LWAC modulus of elasticity, the experimental results of this study can fit well with predicted equation of ACI 318
Abstract: The reaction mechanism of an Al-TiO2 system is discussed. Thermodynamic analysis indicates that the reaction between Al and TiO2 can occur spontaneously due to the negative Gibbs free energy of the Al-TiO2 reaction system. When the reinforcement volume fraction is 30%, there is an endothermic peak and an exothermic peak in the DSC curve. But when the reinforcement volume fraction increases to 100%, there are two independent exothermic peaks and the height of them increases obviously. With increasing the heating rate, the ignite temperature becomes higher and all the peaks move to the higher temperature direction. The reactions between Al and TiO2 consist of two steps: first, Al reacts with TiO2 to form the stable α-Al2O3 particles and the active Ti atoms; second, the active Ti atoms react with Al to form Al3Ti.
Abstract: Carbon Nanotubes /AZ31 alloy composites were fabricated by joining preform of CNTs during melting under the protection of Ar. Composites were prepared by means of equal channel angular pressing ( ECAP) by Bc route in the die with the intersecting angle of 90°. Effects of the pressing passes on the microstructure and the mechanical properties of composites during ECAP were investigated; The fractographs were observed and analyzed via scanning electron microscope (SEM). The results indicate that a great deal of ultra-fine grains appear in CNTs/AZ31 Alloy Composites just after one pass of ECAP; With the increase of pass number, the proportion of ultra-fine grain increases. With 4 pressing passes, the grains are effectively refined to a mean size of 2 μm. And with increasing in the pressing passes, elongation of the composites is increased and the tensile strength is decreased as a result of the refinement of grain size. CNTs were broken under high shearing stress, and the particle distribution in the matrix alloy was homogeneous.
Abstract: TiNP/2014Al composite was prepared by powder metallurgy method with a reinforcement volume fraction of 15%. High strain rate superplastic deformation behavior of the TiNP/2014Al composite was investigated by tensile tests conducted at 818 K with different strain rates range from 1.7×100 to 1.7×10-3 s-1, DSC, OM, TEM and SEM. It is shown that a maximum elongation of 351% is achieved at 818 K and 3.3×10-1 s-1. The curve of value can be divided into two stages with the variation of strain rate and the critical strain rate is 10-1 s-1. Plastic deformation of the TiNP/2014Al composite at 818 K and 3.3×10-1 s-1 is conducted at an almost constant maximum value of flow stress. High strain rate superplastic deformation mechanism of the TiNP/2014Al composite deformed at 818 K with the strain rate of 3.3×10-1 s-1 is grain boundary sliding accommodation mechanism plus liquid phase helper accommodation mechanism.
Abstract: Zr-Al-O-N composites were prepared in N2 atmosphere at 1600oC with Ca-PSZ and Al powders as raw materials. Phase composition of the composites and formation reaction mechanism were investigated by XRD and SEM analyses. With Al content increaseing from 1% to 50%, phase composition of the composites were changed step by step. The results showed that phase compositions of the composites are related to Al content.
Abstract: Preliminary study on the preparation and performance of vapor grown carbon fibers (VGCF) reinforced cement composites was carried out. VGCF were prepared from de-oiled asphalt (DOA) by chemical vapor deposition (CVD). Results demonstrated that compressive strength and electrical conductivity of VGCF reinforced cement could be significantly enhanced with very low fiber content. The resistivity decreased and compressive strength increased of cement-matrix composites with weight fraction of VGCF increasing from 0 to 0.6% fiber in the paste. The fiber content of 0.4% by mass of cement was recommended, which yielded the resistivity of 1.49×103Ωcm. That was two orders of magnitude lower than that for the same paste without VGCF (3.25×105Ωcm). Furthermore, the compressive strength increased by 28.8% as the VGCF content increases from 0 to 0.4% by mass of cement.
Abstract: To investigate the causations why the tensile performance index of carbon fiber composite in use is generally under that offered by the manufacturer, the tests on the tensile characteristics of the carbon fiber monolayer and those of the gumming carbon fiber monolayer were carried out in this paper. Based on the test results and mixed principle of the relation between strength of composite and each of the components, the influencing factors on the drop in tensile performance index of the carbon fiber composite in use were analyzed. It is concluded that all kinds of the defects could reduce the local strength of composite materials. Internal defects of the composite, possible load eccentricity in the test, size effect of the composite sample, and tensile properties of the resin may be the primary influencing factors.
Abstract: To investigate the role of nano-Al2O3, WC–Al2O3–8wt%Co hard metals was mixed with 0-1.2 wt% nano-Al2O3 and prepared by conventional sintering (CS) for 2 h at 1440°C to see whether the addition of Al2O3 could improve densification behaviour, the microstructure and mechanical properties of the samples. The results showed that the use of Al2O3 nanoparticles as dispersions could reduce the porosity of WC-Co alloy and decrease the relative density; it could also inhibit the growth of the grains of WC-Co hardmetal to enhance the hardness and transverse rupture strength of the alloy in a proper range. The influence of Al2O3 content on the magnetic properties including coercive force and saturated magnetic intensity of the WC–Al2O3–8wt%Co hardmetals manifested the additive of nano-Al2O3 have effect on the WC grain growth inhibition and the formation of decarbonization phase in the alloy.