Biotemplated synthesis of novel porous SiC

Amorphous silicon carbide with unique porous structures was synthesised from three biological templates (egg shell membrane, butterfly wing and sea urchin skeleton) using liquid phase infiltration with polycarbosilane at atmospheric pressure followed by heating to 1000 °C under N₂. The structure and porosity of the preform was largely reproduced in the final material, although with egg shell membrane the cellular structure of the preform was compromised after infiltration and heating. The SiC yield of the final material was linearly correlated with the number of infiltration steps in the case of egg shell membrane and butterfly wing. Infiltration of the sea urchin shell was unsuccessful.     

MoO3添加对高频MnZn功率铁氧体性能的影响

采用陶瓷工艺制备高频MnZn功率铁氧体材料,研究了MoO3添加对材料微结构和磁性能的影响。用X射线衍射仪(XRD)、扫描电子显微镜(SEM)表征材料结构,用B-H分析仪测试材料磁性能,并对材料功率损耗进行分离。结果表明,适量添加MoO3可以有效改善材料的微观结构,提高致密度,提高材料饱和磁通密度和起始磁导率,降低功率损耗。功耗分离后发现,随着MoO3添加量的增加,磁滞损耗比例下降,涡流损耗所占比例上升。最佳MoO3添加量为0.01 wt%,获得低功耗的MnZn功率铁氧体,100℃、500kHz、50mT条件下功耗为86 kW/m3,起始磁导率约为1928,25℃下的饱和磁通密度为513 mT。     

Upconversion luminescence properties of nanocrystallite MgAl2O4 spinel doped with Ho3+ and Yb3+ ions

The upconversion luminescence spectra of nanocrystallite MgAl₂O₄ doped with 1% of Ho³⁺ and 5% of Yb³⁺ ions after excitation at 980 nm were measured. Influence of excitation regime either continuous or pulse on upconversion mechanisms was shown. For continuous wave (CW) laser excitation upconversion process is due to phonon assisted Excited State Absorption (ESA). For pulse laser excitation upconversion emission is due to Energy Transfer Upconversion (ETU).     

Effect of La2O3 doping on the tunable and dielectric properties of BST/MgO composite for microwave tunable application

Undoped and La₂O₃doped (0.5, 1.0, 2.0, 3.0 wt.%) Ba_0.55Sr_0.45TiO₃/MgO composites were prepared by traditional ceramic processing and their structural, surface morphological, tunable properties and their dielectric properties at low frequency and microwave frequency were systemically examined. The result shows that La₂O₃ dopant has a strong effect on the average grain size. The La₂O₃ doped samples have lower temperature coefficient of capacitance than the undoped. The 0.5 wt.% La₂O₃ doped sample has a little higher tunability than the undoped and the tunability of other doping concentration samples is lower as compared to the undoped. The addition of La₂O₃ decreases the dielectric constant and increases quality factor (Q × f) at microwave frequency. The 0.5 wt.% La₂O₃ doped samples have the best properties among these samples and have a higher tunability, lower dielectric constant and lower dielectric loss tangent at microwave frequency and these properties are very beneficial to the development of the tunable devices application.     

The rock salt oxide Li2MgTiO4: Type I dielectric and ionic conductor

The exploration of the Li–Ti–Mg–O system, using both sol–gel technique and solid state reaction method, allowed a new phase, Li₂MgTiO₄, with disordered rock salt structure (a = 4.159 Å) to be synthesized. The latter is shown to be a good type I dielectric material, with a relative constant of 15 at high frequency and low dielectric loss (tanδ < 10⁻³) over the temperature range −60 to 160 °C. It is also observed that the sintering temperature of this phase is strongly lowered by adopting the sol–gel technique compared to solid state reaction (1150 °C instead of 1300 °C). Finally we show that this phase exhibits cationic conductivity above 400 °C (σ_600 °C = 9 × 10⁻⁵ S cm⁻¹).     

FeSiCrB amorphous soft magnetic composites filled with Co2Z hexaferrites for enhanced effective permeability

Z-type Sr₃Co₂Fe₂₄O₄₁ hexaferrites (Co₂Z hexaferrites) were synthesized with sol–gel method and were mechanically mixed with spherical Fe₈₈Si₇Cr_2.5B_2.5 (FeSiCrB) amorphous powders, and then compacted to form toroidal Co₂Z hexaferrites/FeSiCrB amorphous soft magnetic composites (Co₂Z/FeSiCrB SMCs). The compositions, morphology and soft magnetic performance were characterized through SEM, XRD, VSM, EDS, B-H analyzer and impedance analyzer. All results reveal that Co₂Z hexaferrites in Co₂Z/FeSiCrB SMCs should mainly exist in air gaps between spherical FeSiCrB amorphous powders, leading to the increasing density. Saturation magnetization decreases a little for magnetic dilution and coercivity increases for the stronger magnetic interaction of Co₂Z/FeSiCrB SMCs. The introduction of Co₂Z hexaferrites in air gaps increases the conduction area of magnetic circuits and decreases the demagnetization effect, leading to the higher effective permeability of 27.4 for Co₂Z/FeSiCrB SMCs, much higher than 25.0 for FeSiCrB SMCs. Furthermore, Co₂Z/FeSiCrB SMCs present the smaller core loss and more stable DC bias characteristics owing to the insulating Co₂Z hexaferrites.     

Effect of the electronic state of Ti on M-doped TiO2 nanoparticles (M=Zn,Ga or Ge) with high photocatalytic activities: A experimental and DFT molecular study

In the pursuit of environmental sustainability, nanomaterials with specific characteristics that can improve the environment by various methods have been developed. In this work, M-doped TiO₂ microspheres have been synthesized by a colloidal route and doped with 1% in wt. of M (M=Zn, Ga and Ge). The materials were calcined at 400 °C and they were characterized by means X-ray diffraction (XRD) analysis, UV–vis spectroscopy coupled with diffuse reflectance spectroscopy (DRS), N₂ physisorption, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The catalytic activity of the materials was studied by evaluating the photocatalytic degradation of 2,4-dichlorophenoxyacetic acid in an aqueous solution. Moreover the photocatalytic activity of the doped materials were enhanced compared to pristine material, according the next trend:Ge:TiO₂ >Ga:TiO₂ >Zn:TiO₂>TiO_2. The presence of atoms of Zn, Ga or Ge in the structure of TiO₂ was shown by XPS analysis, indeed these results reveal a diminution of the energy levels of the 2p_3/2 and 2p_1/2 electrons from doped materials compared with pristine material, which is evidence for a strong relationship between the doped cation valence of the TiO₂ and the degradation of the 2,4-dichlorophenoxyacetic acid. Theoretical calculations within DFT framework were performed on two models of nanoparticles like-anatase in order to interpret the photocatalytic activity obtained experimentally by means the frontier orbitals (HOMO and LUMO), the morphology and electronic distribution.     

Effect of silicone oil additive on swelling stress alleviation in the metal hydride reactor

Considerable swelling stress associated with hydrogen absorption process caused by metal hydride expansion is extensively observed in a metal hydride tank which is usually designed for hydrogen storage application. Such swelling stress being applied to tank wall may cause potential safety issue such as tank failure. In the present investigation, silicone oil is selected as an additive incorporating into MlNi_4.5Cr_0.45Mn_0.05 alloy in an attempt to alleviate the swelling stress. The results obtained by a self-built direct swelling stress testing apparatus show that the addition of silicone oil can significantly reduce alloy particle swelling stress. The addition of 3 wt% silicone oil is appropriate to acquire efficient swelling stress alleviation. During cycling the maximum swelling stress increases with charging pressure. The formation of silicone oil thin film on the surface of alloy particles, acting as a “cushion” among alloy particles, would reduce particle agglomeration and enhance particle movement during hydrogen absorption and desorption cycling. This is the reason for the observed swelling stress alleviation by silicone oil.     

The wear resistance of Ni alumina and NiAl2O4 alumina nanocomposites

The influence of metallic Ni or NiAl₂O₄ as a reinforcing particle on grain growth and wear resistance in alumina matrix composites was evaluated. Alumina composites with various Ni or NiAl₂O₄ concentrations were prepared by multiple-infiltrations of Ni-nitrate into bisque-fired (necked) alumina green bodies followed by heat treatment and sintering at 1600 °C for 2 h. Sintering in a reducing environment resulted in composites with metallic Ni nanoparticles, while NiAl₂O₄ alumina composites were formed when sintering in air. The addition of Ni or NiAl₂O₄ resulted in a reduction in alumina grain size after sintering. The material response to abrasive wear was estimated by measuring the time to section samples of a defined area using a diamond wafering saw and was compared to the wear resistance of undoped alumina. In both cases, reinforcing alumina with Ni or NiAl₂O₄ particles resulted in a significant increase in wear resistance, correlated to the reduced grain size.