Dielectric properties of ZnNb2O6/epoxy composites

The dielectric properties of epoxy composites with various contents of ZnNb₂O₆ filler were investigated at microwave frequencies. Increasing frequency from 1 GHz to 9 GHz did not affect the composites’ dielectric constants but increased their dielectric losses; both of which depended on ZnNb₂O₆ content and showed typical values of 9.63 and 0.019, respectively, at 9 GHz in the composite with 0.6 volume fraction ZnNb₂O₆. The results were compared with theoretical models and shown to be well described by the EMT model.     

Oxygen permeation properties and surface modification of acceptor-doped CeO2/MnFe2O4 composites

The preparation and oxygen permeation properties of the (Ce_0.8Pr_0.2)O_2−δ − x vol% MnFe₂O₄ composites, where x = 0 to 35, have been investigated. The samples were prepared by the Pechini method. In the case of Ce_0.8Pr_0.2O_2−δ, an oxygen flux density of 6 μmol⋅cm⁻²⋅s⁻¹ (L = 0.0247 cm) and the maximum methane conversion of 50% were attained at 1000^∘C. Unlike composites consisting of Gd-doped CeO₂ and MnFe₂O₄, the oxygen permeability of the (Ce_0.8Pr_0.2)O_2−δ – x vol% MnFe₂O₄ composites was almost constant regardless of the volume fraction of MnFe₂O₄; however, the optimum volume fraction of MnFe₂O₄ was determined to be 5 to 25 in the context of the chemical and mechanical stabilities under methane conversion atmosphere. In addition, the surface modification of the (Ce_0.8Gd_0.2)O_2−δ – 15 vol% MnFe₂O₄ composite was performed by using the FePt nanoparticles. The catalyst loading of 2.8 mg/cm² on the both side of the 0.3 mm-thick (Ce_0.8Gd_0.2)O_2−δ – 15vol% MnFe₂O₄ composite increased the oxygen flux density from 0.30 to 0.76 μmol⋅cm⁻²⋅s⁻¹ in the case of He/air gradients; however, the effect seems to be reduced in the case of high oxygen flux density caused by a large pO₂ gradient. Moreover, the Langmuir-Blodgett film of the FePt nanoparticles were successfully prepared on the tape-cast (Ce_0.8Gd_0.2)O_2−δ – 15vol% MnFe₂O₄ composite. Hydrophobic treatments for the surface of the composite were crucial to achieve high transfer ratio for the deposition of the LB film.     

SiO_2包覆片状羰基铁粉的制备及电磁性能

采用机械球磨法使羰基铁粉片状化,以正硅酸乙脂(TEOS)为硅源,通过St?ber法制备二氧化硅(Si O_2)包覆的片状羰基铁粉。通过扫描电子显微镜、能谱、红外光谱、X射线衍射等手段研究了Si O_2包覆的羰基铁粉的结构特性,并讨论了Si O_2包覆对其热性能、电磁和微波吸收性能的影响。结果表明,Si O_2包覆羰基铁粉的抗氧化性能显著提高。与未包覆羰基铁相比,包覆后羰基铁粉的介电常数急剧下降,在1~6GHz波段内具有较好的吸波效果。当厚度为3.4 mm时,在2 GHz处的最小反射损耗可以达到-25.6 d B。     

Preparation and properties of SiO2 aerogel and fabric composite based on polyurethane

ABSTRACT

The thermal insulation composite were prepared by blending aqueous polyurethane and modified SiO₂ aerogel, and then coating to the surface of fabric. The influence of the content of SiO₂ aerogel and polyurethane, crosslinking temperature and the particle size of SiO₂ aerogel on thermal insulation rate of the composite fabric were detail analysis, the heat insulation, breathable, IR, SEM surface morphology of the composite fabric were evaluated. The thermal insulation rate of the SiO₂ aerogel composite fabric is 28.97%, which is twice that of the original fabric. SiO₂ aerogel composite fabric will have a wide range of application in the thermal insulation clothing, curtains, shoe materials, industrial equipment and building insulation, etc.     

Effect of Sn/Zn ratio on structure and photoluminescence properties of SnO2@ZnO composites

ABSTRACT

The SnO₂@ZnO composites, with Sn/Zn molar ratio (Sn/Zn–ratio) from 4:1 to 8:1, were successfully prepared via two–step hydrothermal method. The microstructure and morphology of the as–prepared Sn/Zn–ratio–dependence SnO₂@ZnO composites were investigated. Furthermore, a reasonable growth mechanism of SnO₂@ZnO composites was proposed and the results indicated that the dispersity of SnO₂ nanowires on the ZnO nanorods surface was obviously influenced by the Sn/Zn–ratio. The photoluminescence (PL) properties of the Sn/Zn–ratio–dependence SnO₂@ZnO composites were investigated. The results showed the opposite intensity change of ultraviolet (UV) and visible emission while the Sn/Zn–ratio increased. In addition, the possible emission mechanisms were also discussed that the UV emission is attributed to free–exciton recombination at the near–band edge and the potential difference between SnO₂ and ZnO result in the visible emission.     

基于氧化铝/羰基铁粉的复合贴片吸波与导热特性分析

分别以羰基铁粉和氧化铝粉作为功能填料、丁腈橡胶作为基材制备了系列复合吸波贴片,对样品的微观形貌、电磁参数以及热导率进行了测试表征,分析了羰基铁粉和氧化铝粉用量比例调整对复合贴片吸波与导热性能的影响.结果表明,随着羰基铁粉含量减小、氧化铝粉含量相应增大,复合贴片的复介电常数和复磁导率实部、虚部总体上均呈减小的趋势;反射损耗峰的位置移向高频,衰减系数均随频率的升高逐渐增大,同一频率下羰基铁粉含量越高的样品衰减系数越大;复合贴片的热导率呈先上升后下降的趋势;考察的样品均表现出宽带强吸收特性,样品热导率的相对较高值为～1.66 W/(m?K).通过两种填料的粒径和体积分数匹配设计进行界面特性优化,可有效调控复合贴片的电磁参数、减小界面热阻,实现对复合贴片吸波与导热性能的兼顾提升.     

Enhanced dielectric properties of bismuth titanate/silver composites

Bismuth titanate (BiT) based composites containing silver particles are fabricated by a solution chemical process. Incorporation of silver particles does not result in unwanted reaction phase. SEM micrographs reveal fine silver particles distribute at BiT grain boundaries and into larger BiT plate-like grains. With the addition of silver, the dielectric constant increases up to ∼10 times higher than that of pure BiT ceramic, which can be attributed to the effective electric fields developed around the dispersed metal particles and the percolation effect. Additionally, the dielectric losses are significantly reduced by incorporating silver particles, and the values of BiT/Ag composites are lower than 0.5%. The dielectric properties of BiT/Ag composites are nearly frequency independent in the measured frequency range (1 kHz to 1 MHz).     

Ba 3 Co 2 Fe 24 O 41 /polyimide composites with magnetic and dielectric properties

Ba3Co2Fe24O41(Co2Z)/polyimide(PI) composites were synthesized via in-situ polymerization process, using the micron-sized Co2Z particles prepared by the solid-state reaction. X-ray diffractometer...