甲基乙烯基硅橡胶和氧化铝的干燥温度对其复合材科导热性能的影响

以Al2O3粉体为导热填料、甲基乙烯基硅橡胶(MVQ)为基体制得MVQ/Al2O3导热复合材料.研究了MVQ和Al2O3的干燥温度对MVQ/Al2O3体系导热性能的影响,并考察了体系的填料网络结构.结果表明,MVQ的干燥温度越高.其小分子挥发分越低,复合材料的导热性能越好.Al2O3的干燥温度越高,其残余水分含量越低;...     

SiC/Al2O3/MVQ导热复合材料的制备与性能研究

分别使用碳化硅(SiC)、氧化铝(Al2O3)和SiC/Al2O3复配物制备了导热甲基乙烯基硅橡胶材料(MVQ),研究了SiC,Al2O3和SiC/Al2O3用量及表面改性对MVQ导热系数和力学性能的影响,结果表明,随导热填料用量的增大,MVQ导热系数增大;同等用量下,SiC/Al2O3/MVQ复合材料的导热性能均优于SiC/MVQ和Al2O3/MVQ;当SiC/Al2O3总用量为50份且SiC/Al2O3质量比为3/1时,复合材料导热系数为0.76 W/mK;随SC/Al2O3用量的增加,拉伸强度与拉断伸长率均降低,邵尔A硬度增大.表面处理后,复合材料导热性能得到进一步改善.     

氧化铝及碳纤维对EPDM/MVQ共混胶性能的影响

选用EPDM/MVQ共混胶为基体,研究了氧化铝、碳纤维/氧化铝对EPDM/MVQ共混胶力学性能、导热性能及导电性能的影响。结果表明,随着氧化铝用量的增加,共混胶的力学性能下降,导热性能增加,电阻变化不大;当氧化铝用量为200份时,复合材料的拉伸强度达到4.5MPa,导热系数达到1.1W/(m·k),选用氧化铝/碳纤维混合填料体系,当氧化铝和碳纤维的用量分别为100份和15份时,复合材料的拉伸强度达到4.8MPa,导热系数达到0.66 W/(m·k)。     

氧化铝的表面改性及其对BR导热性能的影响

采用不同品种偶联剂对氧化铝进行表面湿法改性,制备改性氧化铝/BR复合材料,研究复合材料的物理性能和导热性能.结果表明:硅烷偶联剂KH-550湿法改性氧化铝/BR复合材料的物理性能最佳,硬脂酸湿法改性氧化铝/BR复合材料的导热性能最佳;随着硬脂酸于法改性氧化铝用量的增大,复合材料的硬度、拉断伸长率及导热系数明显增大;在硬脂酸干法改性氧化铝/BR复合材料中加入炭黑N330,复合材料的物理性能提高,导热性能基本不变.     

HDPE和MVQ导热性的影响因素

对高密度聚乙烯（HDPE）、HDPE／导热填料和硅橡胶（MVQ）／导热填料三种材料的导热性能进行了试验研究。总结分析了导热填料种类及含量、温度、结晶度、密度等方面因素对材料导热性能的影响。实验结果表明：HDPE材料的热导率随着结晶度的增大而上升；随着导热填料粒径的增加，HDPE、MVQ材料的热导率增大；材料密度的提高，可提高导热性能。     

Al/Al_2O_3填充PA6复合材料性能研究

以PA6为基体,铝粉和氧化铝粉为填料,利用双螺杆挤出机制备了复合材料,研究了复合材料的力学性能和导热性能。研究结果表明:铝粉和氧化铝粉作为填料复合填充到PA6中,复合材料的力学性能较纯PA6有较大程度降低,导热性能有较大程度提高,当铝粉添加量为30%、氧化铝添加量为20%时,复合材料的力学性能降低最少,导热性能提高最多,导热系数达0.81 W/(m·K)。     

氮化硼纳米片制备及其改性复合材料导热性能研究进展

氮化硼纳米片(BNNSs)是一种二维片状纳米材料,具有较高的导热性和热稳定性.将其作为填料加入聚合物中,可显著提高复合材料的导热性能.基于近年来对BNNSs改性复合材料的导热性能的研究进展,总结了BNNSs的制备和改性方法,介绍了该体系复合材料的导热机理,分析了影响复合材料导热性能的因素,最后对该体系复合材料的导热性能研究进行了展望.     

三维导热高分子复合材料制备方法研究进展

分析了构筑三维导热网络结构在导热高分子复合材料上的应用优势,介绍了构筑三维导热网络结构的不同方法,包括冻干取向法、金属泡沫法、陶瓷泡沫法、3D打印法、静电植绒法、静电纺丝法、碳泡沫法等,概述了不同构筑方法的成型机理,并对不同方法制备的三维导热高分子复合材料的热导率进行了归纳和总结。分析表明,构筑三维导热网络结构对高分子复合材料的导热性能提升具有显著的正向效应。对在构筑三维导热网络结构的同时如何进一步提高复合材料的导热性能进行了展望。     

碳纳米管/纳米氧化铝/天然橡胶复合材料的性能研究

以偶联剂Si69原位改性法制备碳纳米管/纳米氧化铝/天然橡胶(NR)复合材料,对其性能进行探讨。结果表明:复合材料的动态力学性能优异,动态压缩生热较低;碳纳米管与纳米氧化铝并用对提高复合材料导热性能具有协同效应,复合材料的导热性能良好。碳纳米管和纳米氧化铝并用可以解决内部温升造成复合材料寿命缩短的问题。     

导热绝缘硅橡胶的研究

以甲基乙烯基硅橡胶(MVQ)为基体,填充氮化硼(BN)制备了导热绝缘硅橡胶,研究了BN用量及粒径等对MVQ性能的影响。结果表明,随着BN用量的增加,MVQ的导热系数增大;当BN用量小于80份或大于150份时,粒径大小对MVQ热导率的影响不明显;当BN用量为80~150份时,大粒径填充的MVQ具有较好的导热性。采用混合粒径的BN填充MVQ的导热性能优于单一粒径BN填充MVQ的导热性能。填充BN后,MVQ混合体系的电性能变化不大,仍具有较好的绝缘性。     

Graphite trifluoromethylsulfate C12+SO3CF3−

Graphite trifluoromethylsulfate C₁₂SO₃CF₃, a new binary graphite salt is formed by the irreversible solvolysis of C₈SO₃F in a large excess of trifluoromethylsulfuric acid. The salt is identified as a stage one intercalation compound with a C₀ value of 8.12 Å and characterised by microanalysis, epr and ¹⁹F NMR spectroscopy. Both Raman spectra, in the back scattering configuration, and IR spectra, in transmission as well as reflection geometries, are used to support an ionic formulation as C₁₂⁺SO₃CF₃^?.     

Na0.5Bi0.5TiO3–K0.5Bi0.5TiO3–BaTiO3–SrTiO3陶瓷的准同型相界与电性能

采用固相法制备了 Na0.5Bi0.5TiO3–K0.5Bi0.5TiO3–BaTiO3–SrTiO3（NBT–KBT–BT–ST）陶瓷,该体系是按（1–2x）（0.8NBT–0.2KBT）–x（0.94NBT–0.06BT）–x（0.74NBT–0.26ST） （x = 0.10、0.20、0.25、0.30、0.35、0.40、0.45）组合而成的,研究了该系陶瓷的结构与电性能。结果表明：所有样品都处于三方–四方准同型相界区域。该系陶瓷在准同型相界附近表现出了优异的压电性能,压电常数 d33、机电耦合系数 kp和剩余极化强度 Pr随 x 的增加先升高后降低,其中 x=0.35 陶瓷的电性能最佳：d33= 210 pC/N,kp= 0.319,Pr= 39.3 μC/cm2,Ec= 20.2 kV/cm,是一种良好的无铅压电陶瓷候选材料。依据准同型相界组成的线性组合规律来寻找具有优异压电性能的 NBT–KBT–BT–ST 陶瓷准同型相界组成是可行的。     

Dielectric relaxation and resistive switching of Bi0.96Sr0.04Fe0.98Co0.02O3/CoFe2O4 thin films with different thicknesses of the Bi0.96Sr0.04Fe0.98Co0.02O3 layer

Bi_0.96Sr_0.04Fe_0.98Co_0.02O₃/CoFe₂O₄(BSFCO/CFO) bilayered thin films with different thicknesses of the BSFCO layer are synthesized on FTO/glass substrates by chemical solution deposition method (CSD). The influence of BSFCO thickness on the microstructure, dielectric relaxation, ferroelectric properties and resistive switching (RS) of the thin films are researched. Strain exists in the prepared thin films and gives rise to structural distortion, which has an effect on charged defects and ferroelectric polarization. Dielectric relaxation that is closely related to the interfacial polarization at the BSFCO/CFO interface is observed, and the dielectric loss peaks along with decreasing intensity shift to high frequency with decreasing strain. The Maxwell-Wagner two-layer model is adopted to investigate the mechanism of dielectric relaxation, and the relaxation time τ is calculated and it shown to be directly proportional to the strain. It is found that the dielectric properties, including low dielectric loss, can be improved by controlling the BSFCO layer thickness. The ferroelectric properties improve with the decreasing strain, the 12-BSFCO/CFO thin film possesses a large P_r ~ 102.9?μC/cm² at 660?kV/cm. The observed resistive switching (RS) behavior is attributed to the interfacial conduction mechanism, it is found that strain-dependent the ferroelectric polarization switching modulates the width of depletion layer and the height of potential barrier at the interface, resulting in the different resistance states.     

High piezoelectric coefficient of Pr2O3-doped Ba0.85Ca0.15Ti0.90Zr0.10O3 ceramics

Pr₂O₃-doped Ba_0.85Ca_0.15Ti_0.90Zr_0.10O₃ (BCTZ-xPr) ceramics were prepared by the conventional solid-state method. A tetragonal phase is only observed in these ceramics, and the introduction of Pr₂O₃ decreases their sintering temperature without affecting negatively the piezoelectric constant. Enhanced ferroelectric properties were obtained in these BCTZ-xPr ceramics. The ceramic with x=0.06 wt% exhibits a good electrical behavior of d₃₃∼460 pC/N, k_p∼47.6%, ε_r∼4638, and tan δ∼0.015 when sintered at a low temperature of ∼1400 °C. As a result, the BCTZ-xPr ceramic is a promising candidate for lead-free piezoelectric ceramics.     

Composite cathodes of La0.9Ca0.1Ni0.5Co0.5O3-Ce0.8Sm0.2O1.9 for solid oxide fuel cells

The mixed ionic and electronic conductors of La_0.9Ca_0.1Ni_0.5Co_0.5O₃-Ce_0.8Sm_0.2O_1.9 (LCNC-SDC) are investigated systematically for potential application as a cathode for solid oxide fuel cells based on a Ce_0.8Sm_0.2O_1.9 (SDC) electrolyte. The electrochemical impedance spectroscopy (EIS) measurements are performed in air over the temperature range of 600-850 °C to determine the cathode polarization resistance. The exchange current densities for oxygen reduction reaction (ORR), determined from the low-field cyclic voltammetry, high-field cyclic voltammetry, and EIS data are systematically investigated. The activation energies (E_a) for ORR determined from the slope of Arrhenius plots are in the range of 102.33-150.73 kJ mol⁻¹ for LCNC-SDC composite cathodes. The experimental results found that LCNC-SDC (70:30) composite cathode has a maximum exchange current density and a minimum polarization resistance of 0.30 Ω cm² for 850 °C among LCNC-SDC composite cathodes.     

Ni~(2+)-Fe~(3+)-C_7H_7SO_3~--LDHs催化剂的制备

以尿素为沉淀剂,柠檬酸钠为络合剂,采用均相沉淀法制备Ni~(2+)-Fe~(3+)-CO_3~(2-)-LDHs。以制备的Ni~(2+)-Fe~(3+)-CO_3~(2-)-LDHs为前驱体,分别与Na Cl和对甲苯磺酸钠进行离子交换反应得到Ni~(2+)-Fe~(3+)-C_7H_7SO_3~--LDHs新型催化剂,成功实现对甲苯磺酸根负载Ni~(2+)-Fe~(3+)-LDHs。研究表明,Ni~(2+)-Fe~(3+)-C_7H_7SO_3~--LDHs为介孔材料,比表面积为165.6 m~2·g~(-1),平均孔径为14.7 nm,较大比表面积和空隙结构增强了其吸附性能和催化活性。     

ZrO2/SiO2- and La2O3/Al2O3-supported platinum catalysts for CH4/CO2 reforming

Surface-phase ZrO₂ on SiO₂ (SZrOs) and surface-phase La₂O₃ on Al₂O₃ (SLaOs) were prepared with various loadings of ZrO₂ and La₂O₃, characterized and used as supports for preparing Pt/SZrOs and Pt/SLaOs catalysts. CH₄/CO₂ reforming over the Pt/SZrOs and Pt/SLaOs catalysts was examined and compared with Pt/Al₂O₃ and Pt/SiO₂ catalysts. CO₂ or CH₄ pulse reaction/adsorption analysis was employed to elucidate the effects of these surface-phase oxides.

The zirconia can be homogeneously dispersed on SiO₂ to form a stable surface-phase oxide. The lanthana cannot be spread well on Al₂O₃, but it forms a stable amorphous oxide with Al₂O₃. The Pt/SZrOs and Pt/SLaOs catalysts showed higher steady activity than did Pt/SiO₂ and Pt/Al₂O₃ by a factor of three to four. The Pt/SZrOs and Pt/SLaOs catalysts were also much more stable than the Pt/SiO₂ and Pt/Al₂O₃ catalysts for long stream time and for reforming temperatures above 700 °C. These findings were attributed to the activation of CO₂ adsorbed on the basic sites of SZrOs and SLaOs.     

Photocatalytic activity of Cu2O/TiO2, Bi2O3/TiO2 and ZnMn2O4/TiO2 heterojunctions

Cu₂O/TiO₂, Bi₂O₃/TiO₂ and ZnMn₂O₄/TiO₂ heterojunctions were studied for potential applications in water decontamination technology and their capacity to induce an oxidation process under VIS light. UV–vis spectroscopy analysis showed that the junctions-based Cu₂O, Bi₂O₃ and ZnMn₂O₄ are able to absorb a large part of visible light (respectively, up to 650, 460 and 1000 nm). This fact was confirmed in the case of Cu₂O/TiO₂ and Bi₂O₃/TiO₂ by photocatalytic experiments performed under visible light. A part of the charge recombination that can take place when both semiconductors are excited was observed when a photocatalytic experiment was performed under UV–vis illumination. Orange II, 4-hydroxybenzoic and benzamide were used as pollutants in the experiment. Photoactivity of the junctions was found to be strongly dependent on the substrate. The different phenomena that were observed in each case are discussed.     

Preparation and characterization of Cr2O3-TiO2-Al2O3-V2O5 green pigment

Green pigments with high near infrared reflectance based on a Cr₂O₃-TiO₂-Al₂O₃-V₂O₅ composition have been synthesized. Cr₂O₃ was used as the host component and mixtures of TiO₂, Al₂O₃ and V₂O₅ were used as the guest components. TiO₂, Al₂O₃, and V₂O₅ were mixed into 39 different compositions. The spectral reflectance and the distribution of pigment powder were determined using a spectrophotometer and a scanning electron microscope, respectively. It was found that a pigment powder sample S9 with a Cr₂O₃-TiO₂-Al₂O₃-V₂O₅ composition of 80, 4, 14 and 2 wt%, respectively, gives a maximum near infrared solar reflectance of 82.8% compared with 49.0% for pure Cr₂O₃. The dispersion of pigment powders in a ceramic glaze was also studied. The results show that the pigment powder sample S9 is suitable for use as a coating material for ceramic-based roofs.