Key Engineering Materials Vols. 512-515

Abstract: –Hierarchical flower–like CuS spheres have been synthesized by a facile microwave hydrothermal (MH) method using cetyltrimethylammonium bromide (CTAB) as the surfactant. The as–prepared CuS crystallites under different CTAB contents were characterized by X–ray diffraction (XRD), field–emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). Results show that the CTAB–assisted CuS particles have hierarchical flower–like microstructures that were assembled by thin nanoflakes with thickness of 10~20 nm. The corresponding HRTEM images reveal that these nanoflakes are composed of many nanoparticles with average size of about 7 nm. Moreover, when increasing the CTAB contents from 0 g⁄mL to 0.02 g⁄mL, the as–prepared CuS particles were found to have better dispersion stability with decreased average sizes of the hierarchical flower–like spheres. Comparing with the bulk CuS particles, the related UV–vis absorption spectrum of the as–prepared crystallites exhibits an obvious red shift with the absorption peak at 739 nm.

Abstract: ZrO₂ micro beads are widely used as abrasive media in many areas. This paper introduces a sol-gel process for preparation of ZrO₂ micro beads. First, zirconium nitrate solution and urea were mixed to prepare the sol, then the sol was converted to uniform droplets by vibrating dispersion method. The droplets were emitted from the nozzles into an ammonia solution. Along the way from the nozzle to ammonia solution, the liquid droplets first form spherical shape by their surface tension in air, and were then surface-hardened through ammonia gas. The microspheres complete gelation in the ammonia solution. The gel spheres were treated successively by aging, washing, drying, calcination and sintering to yield ZrO₂ ceramic micro beads. The crystal structure of micro beads was examined by X-ray diffraction (XRD). The microstructure of the micro beads was observed by scanning electron microscopy (SEM). The results indicate that the sol-gel process can be used to prepare ZrO₂ ceramic micro beads with good sphericity and uniform distribution of diameter.

Abstract: Assembled monolayer of silicalite-1 (AMS) microcrystals on Si wafer for carbon nanotube (CNT) growth has been prepared by the rubbing method. Iron oxide (α-Fe2O3, hematite) catalyst films were deposited onto silicate-1 monolayers from a Fe2O3 target by radio frequency (rf)-sputtering. This approach has the potential for producing well-aligned CNTs with controlled diameter from predesigned silicalite-1 templates by catalytic chemical vapor deposition (CCVD). Silicalite-1 monolayer oriented with faces parallel to Si wafer showed only the planes in the forms {0 k 0} lines at (020), (040), (060), (080) and (0100) by XRD. The formation and growth of CNTs by CCVD were achieved on the pores of silicate-1 crystals whereby the pores can be defined as confined spaces (channels, 5.60 Å) in nanometer dimensions acting as a template for a fine dispersion of well-defined Fe2O3 (10-15 nm) particles.

Abstract: Rigid polyurethane foams were prepared using sepiolite nanofibers as main functional fillers. The effect of sepiolite nanofibers on the properties of polyurethane foams was studied systematically. Through characterization by scanning electron microscope, X-ray diffraction and property test, it was found that the thermal insulation effect can be maintained, and the mechanical properties can be improved due to the good interfacial bond between sepiolite nanofibers and rigid polyurethane foams.

Abstract: Black pigment is an important pigment in the ceramic decoration. The traditional black pigment is spinel type matter containing Co, Fe or Cr elements. Carbon black is the best black pigment and is nontoxic. However, carbon black is oxygenated in the ceramic sintering process at atmosphere. Carbon black enclosed in the crystal latter of ZrSiO₄ was reported. However, the content of carbon black is little which decreases the color generation. Carbon black coated with SiO₂ was prepared by sol-gel method using combustion method using SiO₂ sol and black ink as raw materials. The obtained black pigmen_{Subscript text}t was characterized by XRD, TEM and ultraviolet-visible spectrophotometer. The results show that the black pigment does not change its color after calcinations at 1300 °C at atmosphere implying the carbon black is coated completely with SiO₂.

Abstract: Wet foams formed through direct foaming were stabilized using various concentrations of amphiphilic particles that could control pore size and porosity. Microstructures and wet foam stability were tailored by amphiphile concentration, particle concentration, contact angle and pH of the suspension to obtain crack-free porous solid after sintering. The influence of these parameters on the porosity was satisfactorily described in terms of combined effects of the contact angle and particle concentration of the initial suspensions, directly affected by amphiphile concentration. Pores were obtained with sizes of c. a 30 - 300 µm and porosities of over 80%.

Abstract: M-AlN (surface modified aluminum nitride powder) suspensions for aqueous gelcasting were prepared Using NH4PAA as dispersant. The effects of pH value, NH4PAA amount and solid content on the rheological behavior of M-AlN suspensions were investigated. The results showed that low viscosity M-AlN aqueous suspensions with high solid content up to 55vol.% were obtained under the condition that the amount of NH4PAA was 0.9 wt. % of M-AlN powder, and pH value was about at 6.8. In spite of this, these suspensions still show a viscosity lower than 0.12 Pa•s at 100s-1, suggesting a good fluidity which can satisfy the requirement of gelcasting.

Abstract: The porous carbon preforms with fine pore structure has been successfully fabricated by room temperature freezing casting, and the reaction formed SiC with fine mechanical property has prepared successfully by liquid silicon infiltration process. Charcoal powder was used as carbon resource, camphene was used as sublimate vehicle, methyl cellulose was used as pore maker and bonder. The result shows that the homogeneity of the porous carbon preform has been improved largely by adding methyl cellulose ,and the defects of reaction formed silicon carbide has reduced largely also. The density, average flexural strength and Weibull modulus of the best reaction formed silicon carbide prepared in this paper is 2.86 g/cm3, 430.75MPa and 9.29 respectively.

Abstract: The hydrophobic aerogel heating-insulating composite ceramic was fabricated in the way of constant pressure. The properties of the ceramic were attributed through FT-IR and energy spectrum. The microstructure and phase transformation of the insulation composites ceramic was characterized by scanning electron microscopy. The results show that after compositing with aerogel the coefficient of heat conductivity of the heat-insulating ceramic decreases forty-sixty percent and the compressive strength increases a hundred percent. There is little change to the tensile-strength. The holes of the ceramic are full of aero gel particles whose grain size is ten-twenty μm and the distribution of pore size is ten-seventy nm. After heating at 400°C for 12 minutes by quartz lamp on the surface of the ceramic which the thick of it is 8mm, the temperature of the other side increases 10°C .When the thick of the ceramic is 16mm, the temperature of the other side remains unchanged. The ceramic has excellent heating-insulting property.

Abstract: Non-oxide ceramics derived from organo-elemental precursors in the system Si-N-C has attracted much attention for its excellent properties. Typically, the Si-N-C ceramic shows homogeneous elemental distribution, better high-temperature stability and oxidation resistance which making them attractive for applying in various branches of technology. A novel amorphous ceramic is fabricated from precursors mixed by polysilazane (PSZ) and polycarbosilane (PCS). The Si-N-C ceramics (PSZ/PCS=2 (w/w)) are heat-treated between 1200°C and 1500°C in nitrogen to crystallization of microcrystalline α-Si3N4 and nanocrystalline SiC. The obtained Si-N-C ceramics are characterized by density, ceramic yield, porosity, X-ray diffraction and Scanning electron microscope to analyze the crystallization and microstructure. The experimental results indicate that the ratio of PSZ/PCS and the annealing temperature have a big influence on the crystallization behavior.