Key Engineering Materials Vols. 434-435

Abstract: Carbide slag was used as raw materials for the first time to prepare xonontlite whiskers via a hydrothermal route without special instruments and synthesis conditions. And the effect of pH value of emulsion of carbide slag and hydrothermal conditions on removal rate of impurities, morphology and crystallinity of synthesized xonotlite whiskers were explored using ICP, SEM and XRD techniques. The results indicated that the carbide slag after purification could be used to prepare xonotlite whiskers, and different pH values of emulsion of carbide slag had great impact on the removal rate of impurities and morphology of xonotlite whiskers. Xonotlite whiskers with 20-40 μm in length and 100-500 nm in diameter were hydrothermally synthesized at 230 °C for 15 h with using silicic acid as kiesel material.

Abstract: A process is adopted to grow whiskers on carbon fibers. The whisker growth is carried out in a two-step process. Plasma spraying, electroplating and magnetron sputtering are used to pretreat the surface of carbon fibers and then ZnO whiskers are grown by hydrothermal method. By comparing three different methods of surface pretreatment, it is concluded that magnetron sputtering is most available and has no damage to the carbon fibers. Combining preparation method of the ZnO whiskers, a new process is developed to surface modified of carbon fibers which is expected apply to carbon fiber composites.

Abstract: Zirconia precursor was prepared by adding hydrogen peroxide or ethanol in co-precipitation process from raw materials of ZrOC12•8H2O and ammonia, the zirconia powders were subsequently obtained by calcination of the precursor at 600°C and ball milling. Through the analyzed by TG-DTA, XRD, SEM, the results show that by adding hydrogen peroxide or ethanol in co-precipitation process can reduce the produce of agglomerate. Ethanol and hydrogen peroxide addition on zirconia by co-precipitation for different reaction results were compared and analyzed.

Abstract: A novel nano-iron particulate reinforced polymer-based composite material against electromagnetic pollution was prepared for household appliances. The attenuation, permittivity and various absorbing aspects of the composite materials were investigated. Results indicated that the composite materials exhibit promising effects of microwave absorption. The attenuation was affected by volume fraction of nano-iron powders. A single microwave absorption medium won’t be appreciable, and a combination of different microwave absorption materials is suggested.

Abstract: Pure metal iron nanoparticles are unstable in the air. By a coating iron on nanoparticle surface with gold, these air-stable nanoparticles are protected from the oxidation and retain most of the favorable magnetic properties. However, it is difficult to prepare Fe-core/Au-shell (Fe@Au) nanoparticles under ambient pressure because iron nanoparticles are very easily to be oxidized in the air. In this study, we synthesized Fe@Au nanoparticles by modified reverse micelle method under ambient pressure and investigated them by X-ray diffraction, transmission electron microscopy (TEM), ultraviolet-visible absorption spectra, and magnetic susceptibility measurements. X-ray diffraction analysis shows that the pattern of iron is hidden under the pattern of gold. TEM image reveals that the core-shell structure is obviously observed and the average size of Fe@Au nanoparticles is about 12 nm, with about 8 nm diameter core and 2 nm shell. The absorption band of the Fe@Au nanoparticles shifts to a longer wavelength and broadens relative to that of the pure gold. The magnetic susceptibility of Fe@Au nanoparticles is measured with a SQUID magnetometer and found to be superparamagnetic with a blocking temperature Tb ~25 K.

Abstract: Four kinds of three-dimensional structure of graphane are investigated using first-principles method. It is found that the energy of four different structures has little difference, so the conclusion can be drawn that the four structures are likely to exist synchronously in experiments.

Abstract: Scintillators are ideal candidates used in detectors for X-ray ,γ-ray and high energy ray , and have been widely applied in nuclear medicine , high energy physics ,geologic survey , security inspection and material flaw detection. The high density of HfO2 is an attractive compound for host lattice activated by rare earth for applications as scintillating materials. This paper reported the synthesis of Eu3+ doped HfO2 nanopowders by chemical self-combustion method at low temperature. Analytical grade Eu(NO3)3 and high pure HfOCl2 were used as raw materials. The requisite amount of urea and glycine as the mixed fuel were added to the mixed solution. A little EDTA was used as a complexant. The mixed solution was dried at 200°C, and fired at 450°C. The powders synthesized by self-combustion were then calcined at 800°C to profit the crystal growth and improve the luminescent properties. XRD, TEM were employed to analyze the phase composition and the characteristics of as-obtained powders. The TEM images display typical nano-structured morphology of Eu3+ doped HfO2. Analysis of XRD indicates that Eu3+ doped HfO2 nanopowders are cubic phase. The excitation and emission spectra were analyzed by the fluorescence photometer. There are two peaks in emission spectra .One is at 595nm, and another is at 614nm. The luminescent properties also reveal the structure of cubic phase.

Abstract: A finite element model (FEM) is developed to simulate the temperature distribution in the sample/die/punch assembly during the spark plasma sintering (SPS) process. A thermal–electrical coupled model with temperature dependent thermal and electrical properties is implemented. The simulation studies were conducted using COMSOL and a range of heating-rates and die sizes were considered. Also, both temporary and equilibrium condition during heating process were evaluated in order to express the real temperature development in the sintering. During the spark plasma sintering process, the temperature difference between the sample center and the die surface depend on the heating-rate and die size. The simulation results also revealed that the temperature gradient during the heating process is much bigger than that in the dwelling period. It is necessary to consider the temporary state during the spark plasma sintering process in order to guarantee a well–controlled microstructure, especially in non-conductive ceramic materials.

Abstract: A new technique of flyash utilization was presented and high-purity silica was prepared by alkali leaching. The flyash was added into sodium hydroxide solution, and then the suspension was heated to 115 °C for 30 min. After filtrated, the filtrate was collected and carbon dioxide was imported into the solution. Finally, the silica would precipitate from the solution. The silica was characterized by scanning electron microscopy, X-ray diffraction and X-ray fluorescence spectrometer. The high-purity silica prepared from flyash was qualified for the rubber reinforcing agent used in shoemaking.

Abstract: This paper describes a method of catalyst-assisted pyrolysis of preceramic precursors for the synthesis of Si-based nanostructures. Through tuning the processing conditions, clustered SiOx amorphous nanowires, bundled single-crystalline Si3N4 nanowires, Y-shape and network-like branched single-crystalline Si3N4 nanostructures, aligned single-crystalline Si3N4 nanowires, and so on, have been synthesized. The results reveal that it is a simple and easy-controlling method, and has potential for mass production of nanomateirals of controlled morphology.