Xue Guo

Gold nanorods coated by oxygen-deficient TiO2 as an advanced photocatalyst for hydrogen evolution

Gold nanorods coated by oxygen-deficient TiO2 are synthesized by slow hydrolysis followed with high-temperature annealing in a reducing atmosphere. This does not alter the morphology of the nanorods, but produces Ti3+ species and oxygen vacancies in the shell. These nanorods show superior photocatalytic ability in hydrogen generation. The enhanced performance may be attributed to the synergistic effect of Ti3+ species, oxygen vacancies and Au, which effectively enhance light absorption, reduce charge recombination and increase charge-transfer across the interface between the electrolyte and electrode.

Electromagnetic and wave absorbing properties of Fe-doped polymer-derived SiCN ceramics

Fe-doped polymer-derived SiCN ceramics were synthesized by a precursor conversion method with different contents of nano-Fe2O3. The phase composition and microstructure were characterized by XRD, SEM and TEM. The results revealed that α-Fe and graphite phases were generated during the synthetic process. The electromagnetic and wave absorbing properties of the Fe-doped SiCN ceramics were analyzed with different amounts of nano-F2O3 over the frequency range of 2–18 GHz. The existence of α-Fe and graphite phases improved the electromagnetic properties of the materials greatly. The reflectance and electromagnetic attenuation coefficient of Fe-doped SiCN ceramics (15 wt% F2O3) reached −11 dB and 325 at 10.5 GHz, respectively, which indicated that the Fe-doped SiCN ceramics possessed excellent absorbing properties.

Preparation of Zirconium Diboride Powder by Carbon Thermal Reduction Method

Zirconium diboride (ZrB2) powders with no impurities were prepared using zirconium oxide (ZrO2), boron carbide (B4C) and carbon black as raw material by carbon thermal reduction. The phase composition of ZrB2 powders was characterized by X-ray diffraction (XRD) and the micro-morphology was observed by scanning electron microscope (SEM). The effects of B4C content, calcination temperature and holding time were studied on the formation of ZrB2 powders. The results indicated that ZrB2 powders could be successfully synthesized while holding for 1.5 h at 1600 °C in Ar atmosphere. When the content of B4C was 17.7 wt% , there existed the crystal phase of ZrB2 only. The impurities could be easily led in with the increase of content of B4C. ZrB2 powders with the size from 1-5 μm could be obtained eventually and the particle size grew obviously with increase of the holding time.

Graphene platelets enhanced pressureless- sintered B4C ceramics

B4C ceramics with different contents of graphene platelets (GPL) were synthesized by a pressureless process in Ar atmosphere. The influences of GPL on mechanical properties, thermal conductivity and electrical resistivity of the B4C ceramics were investigated. Mechanical properties ran up to optimal condition with hardness of 29.1 GPa, bending strength of 383.9 GPa and fracture toughness of 5.72 MPa m1/2 with 0.8 wt% GPL separately. Thermal conductivity and electrical resistivity reached extreme values of 26.35 W m−1 k−1 and 0.1 Ω cm−1. Performances of the ceramics were mainly affected by the generation of non-functional-GPL and the result indicated that a large amount of non-functional-GPL could contribute to poorer overall performance. Meanwhile, two particular pullout mechanisms concerning toughness enhancing was discussed in detail.

Effect of Molten NaCl on the Synthesis of Ti 3 SiC 2 Powders

Free Ti/Si/C powder mixtures with or without molten salt were heated under vacuum with various schedules. The effect of molten salt during synthesis on the morphology and phase composition of Ti3SiC2 powders were investigated. The combustion powders were analyzed by DSC, XRD, SEM and EDS. The results indicated that the existence of molten salt could promote the reaction process and decrease the synthesis temperature. The Ti3SiC2 powders obtained by molten salt method were uniform and well dispersive. The content of Ti3SiC2 phase was influenced by salt/powders ratio and molding pressure. The appropriate salt/powders ratio and pre-press pressure were 1:1and 100 MPa, respectively.

Microwave Absorbing Performance on Polymer-Derived SiCN Ceramics Doped with Rare Earth Oxides

This study investigated the compositions, dielectric properties, magnetic properties and microwave absorbing properties of polymer-derived SiCN ceramics doped with Dy2O3, Eu2O3, Sm2O3, Y2O3 and Gd2O3 respectively. The complex permittivity and complex permeability were measured at the frequency range of 2–18 GHz. The reflectivity of polymer-derived SiCN ceramics doped with Eu2O3 reaches to the lowest value of −35 dB at 16.4 GHz. While the electromagnetic damping coefficient reaches the maximum value of 653 at 16.1 GHz, which clearly demonstrates that by doping Eu2O3 the wave absorbing performance of polymer-derived SiCN can be enhanced more pointedly than the other samples.

Preparation and Properties of Pressureless-Sintered Porous Si 3 N 4 Ceramics

In this paper, the effect of benzoic acid on the porosity, dielectrical and mechanical properties of porous Si3N4 ceramics prepared by pressureless sintering was investigated. The results showed that the addition of benzoic acid improved the porosity and dielectrical properties of Si3N4 remarkably by pressureless sintering at 1700 ℃ for 60 min. The porosity of sample reached 40.79% with 50 wt% benzoic acid addition and the reflectivity of the sample reached −45 dB at around 12 GHz.