XLPE/OMMT纳米复合材料电导和击穿性能

为了研究纳米蒙脱土的分散效果对复合材料电导和击穿性能的影响,采用熔融共混的方法分别制备了无相容剂和以EEA、EVA为相容剂的3种聚合物/蒙脱土纳米复合材料,研究了有机化蒙脱土(organic montmorillonite,OMMT)在聚合物中的层间距变化,对复合材料进行了直流电导–温度和交流击穿场强测试。结果表明:有机化OMMT的分散效果取决于相容剂的极性和有机插层剂的匹配效果;纳米复合材料的体积电导率随温度的升高而增大,其数值大小与不同表面插层剂的插层效率有关;OMMT的加入,改变了聚合物的内部结构,击穿数据分散性明显减小,插层分散的均匀性产生的界面状态是影响纳米复合材料击穿场强的主要因素。     

XLPE/OMMT纳米复合材料水树枝老化特性的研究

通过熔融共混法分别以EEA、EVA为相容剂制备了聚合物/蒙脱土(XLPE/OMMT)纳米复合材料。采用水针法对试样进行水树老化,并通过显微镜观察水树枝形态,研究OMMT用量、两种相容剂和有机插层剂种类对水树枝的影响。结果表明:与纯XLPE相比,添加OMMT的复合材料的水树枝生长长度明显减小,采用EVA作为相容剂可有效提高XLPE/OMMT复合材料的抗水树枝性能,有机插层剂对水树枝的生长长度影响较小。     

交联行为对XLPE/OMMT纳米复合材料结构和介电性能的影响EI北大核心CSCD

为了研究交联行为对纳米复合材料结构和介电性能的影响,采用熔融共混的方法分别制备聚乙烯/有机化蒙脱土(polyethylene/organic montmorillonite,PE/OMMT)和交联聚乙烯/有机化蒙脱土(cross-linked polyethylene/organic montmorillonite,XLPE/OMMT)纳米复合材料。通过小角X射线衍射(X-ray diffraction,XRD)、扫描电子显微镜(scanning electron microscope,SEM)和差示扫描量热法(differential scanning calorimetry,DSC)对试样的性能进行表征。结果表明:OMMT掺杂进入聚合物基体中,层间距将会发生变化,而聚合物的交联会使OMMT的层间距减小;OMMT的异相成核作用使纳米复合材料的结晶形态由球晶变为横穿晶,与交联前相比,XLPE/OMMT试样的非晶区面积增大,结晶度下降。宽频介电谱测试结果表明:复合材料的介电常数随频率的增加而下降,在相同OMMT含量下,XLPE/OMMT纳米复合材料的介电常数高于PE/OMMT。交联影响了OMMT在基体中的分散,使介电频谱由交联前的单峰变为双峰,且峰值增大。随着温度的升高,双峰峰宽加大,松弛时间分布加宽,低频峰在低频段弥散,高频峰移向高频。OMMT含量的增加和交联过程共同导致了OMMT在基体中分散效果变差,界面极化和多元化的基团损耗使介电频谱和温谱发生了明显变化。     

交联行为对纳米复合电介质电导特性和电气强度的影响

为了研究交联行为对纳米复合材料电导特性和电气强度的影响,采用熔融共混法分别制备了聚乙烯/蒙脱土(PE/OMMT)和交联聚乙烯/蒙脱土(XLPE/OMMT)纳米复合材料,研究了有机化蒙脱土(OMMT)在聚合物中的层间距变化和分散状态,对复合材料的体积电阻率和工频电气强度进行了测试。结果表明:OMMT在聚乙烯(PE)基体中的层间距大于在交联聚乙烯(XLPE)中的层间距。当OMMT质量分数为2%时,蒙脱土在聚乙烯中呈现出良好的剥离分散状态。纳米复合材料的体积电阻率随温度升高而减小,其活化能的大小与有机化蒙脱土的插层效率有关。OMMT的加入明显提高了PE的电气强度。而交联后由于三维网状结构的建立,较强的分子间作用力减小了OMMT的层间距,使OMMT的分散均匀性变差,导致交联后复合电介质的电气强度相比交联前有所降低。     

成型方式对XLPE/OMMT纳米复合材料介电性能的影响

为了研究压制成型法和挤出成型法对纳米复合材料介电性能的影响,分别采用两种成型方式制备了交联聚乙烯/有机化蒙脱土（XLPE/OMMT）纳米复合材料。探讨了不同复合材料中有机化蒙脱土的层间距变化对复合材料电阻-温度特性、介电常数和介质损耗以及电气强度的影响。结果表明：成型加工过程中的力场作用会影响OMMT的插层分散效果;挤出成型过程中的拉伸应力使试样中OMMT片层沿拉伸方向进行取向,形成了规整排列单元,载流子的迁移运动受到阻碍,从而改善了试样的电阻-温度特性;聚合物分子链段的运动受限于取向的片层间,使试样中偶极子的极化率降低,使得介电常数和介质损耗因数减小;同时,OMMT的有效插层与聚合物形成的杂化结构使电子产生漫反射现象,延长了电子运动路径,提高了挤出成型试样的电气强度。     

交联度对交联聚乙烯/有机化蒙脱土纳米复合材料拉伸性能和介电性能的影响

为了研究交联度对纳米复合材料拉伸性能和介电性能的影响，通过调控交联时间，制备了不同交联度的交联聚乙烯/有机化蒙脱土（XLPE/OMMT）纳米复合材料。采用X射线衍射（XRD）测试判断蒙脱土的插层分散状态和试样聚集态结构的变化，利用扫描电子显微镜（SEM）观察试样的结晶形态，并对其拉伸性能、电导-温度特性、介电常数、介质损耗及击穿场强进行了测试。结果表明：交联形成的三维网状结构抑制了晶体生长，且晶体尺寸和结晶度随交联度的增加而不断减小；剥离分散的OMMT在XLPE/OMMT中充当了物理交联点，与交联键共同作用，提高了纳米复合材料的拉伸强度，且不断完善的交联网络，使复合材料的弹性模量增大，韧性增强。纳米复合材料的电导率随温度升高而增大，其活化能的大小与交联度和OMMT的界面区域有关。完善的交联网络和均匀分布的界面区，增加了势垒，提高了复合材料的活化能。交联度的增加，形成较强的分子间作用力，阻碍了偶极子和侧基的转向极化，使介电常数和介质损耗角正切值减小；OMMT的加入和交联结构的完善，共同提高了复合材料的击穿场强；但过度交联会影响OMMT在基体中的分散程度，使OMMT片层发生微重排，进而导致...     

热老化对XLPE/OMMT纳米复合材料微观结构和力学性能的影响

采用熔融共混的方法制备了交联聚乙烯/有机化蒙脱土（XLPE/OMMT）纳米复合材料,通过小角X射线衍射（XRD）、差示扫描量热法（DSC）、扫描电子显微镜（SEM）、傅里叶变换红外光谱（FTIR）和力学性能测试对试样热老化前后的性能进行表征。结果表明：老化前质量分数为0.5%的OMMT可在基体中达到最佳分散状态,填料掺杂量增多时会团聚;OMMT与XLPE基体仅有较少的化学键联系,两者主要以物理缠结的形式共存;OMMT片层的空间位阻效应使纳米复合材料的结晶度下降。老化后仅有XLPE/OMMT-0.5%试样的层间距减小,结晶度升高;随OMMT掺杂量的增加,层间距会因XLPE分子链断裂和OMMT在基体中的热重排而增大,晶体结构完善性变差,晶体尺寸分布变宽,结晶度显著降低;受热氧反应和热裂解反应的影响,分子链结构破坏严重。老化后XLPE/OMMT-0.5%的力学性能仅小幅度降低,当OMMT质量分数超过0.5%时,材料力学性能劣化严重,变脆变硬。     

蒙脱土/环氧树脂-氰酸酯复合材料介电性能研究

采用十八烷基三甲基氯化铵作为插层剂改性钠基蒙脱土,制得有机蒙脱土(OMMT),通过OMMT与环氧树脂共同改性氰酸酯(CE),制备了有机蒙脱土/环氧树脂-氰酸酯(OMMT/EP-CE)复合材料,研究不同含量OMMT条件下复合材料的微观结构与动态力学性能和介电性能。结果表明:适量的OMMT均匀分散在EP-CE基体树脂中,OMMT的存在弱化了微裂纹的传播,复合材料呈现出凹凸不平的"鱼鳞"状断面形貌。当OMMT质量分数为5%时,复合材料30℃下的储能模量达到最大值3 400 MPa,比EP-CE基体提升了126.7%;随着OMMT含量的增加,复合材料的介电常数呈现先减小后增大的趋势,当OMMT的质量分数为5%时,OMMT/EP-CE复合材料100 Hz下的介电常数为3.23,介质损耗因数为0.002 2,电气强度达到28.2 kV/mm,相比未掺杂OMMT的基体提升了38.9%。     

纳米复合高导热绝缘材料及其绝缘结构研究

通过异丙醇水溶液的冻融循环结合球磨工艺制备了h-BNNSs,采用微波等离子体对h-BNNSs表面进行功能化处理得到AF-BNNSs,并与甲基丙烯酸反应制备了Vi-BNNSs单体。利用此单体与纳米SiO_2杂化的乙烯基有机硅改性环氧树脂复配制备了纳米改性高导热绝缘漆;利用AF-BNNSs与有机化蒙脱土(OMMT)改性环氧树脂复合制备了一种纳米改性少胶带胶黏剂,并用该胶黏剂制备了一种纳米改性高导热少胶云母带。通过SEM、TEM、HRTEM、AFM等测试手段对h-BNNSs进行了表征,并对纳米改性高导热绝缘漆、纳米改性高导热少胶云母带及由此组合形成的绝缘结构进行了性能测试。结果表明:制备的h-BNNSs具有单层或少层的结构;由功能化h-BNNSs制备的导热绝缘材料及其组成的绝缘系统基本符合6 kV级高压电机的技术要求。     

环氧树脂/有机蒙脱土纳米复合材料的制备与表征

分别采用熔融插层法与溶液插层法制备了环氧树脂/有机化蒙脱土纳米复合材料,并对不同工艺条件下制备的复合材料结构进行了表征。用X射线衍射法(XRD)测试了有机化蒙脱土在被插层前后片层间距的变化,用扫描电子显微镜(SEM)观察了复合材料冲击断面相态结构与蒙脱土在有机相中的分散情况。结果表明环氧树脂分子插入到经有机化改性的蒙脱土片层中,蒙脱土在环氧树脂固化过程中剥离成纳米级颗粒,无序的分散在环氧树脂基体中,且溶液插层法更有利于蒙脱土片层的剥离。通过热重分析(TGA)测试发现,溶液插层法制备的试样中残留的溶剂对复合材料的热性能影响很大。     

Erosion resistance and mechanical properties of silicone nanocomposite insulation

The results of erosion resistance, tensile strength, elongation at break, hardness, and thermal stability measurements are presented for silicone nanocomposites prepared using various nano and micro silica and alumina fillers in a two-part silicone rubber (SiR) matrix. The fillers are used to improve the erosion resistance of SiR, which is necessary for outdoor insulation housing applications. Good dispersion of the fillers is achieved using Triton/sup TM/, a common surfactant. An optimal surfactant concentration imparts good erosion resistance to the nanocomposites in laser heating tests without adverse effects, but excess surfactant has a negative impact on the mechanical properties of the silicone. Thermal gravimetric analysis demonstrated that nano fumed silica imparts better heat resistance to silicone than natural nano silica or nano alumina fillers. Fourier transform infrared spectroscopy analysis of the nanofillers indicated a significantly higher concentration of silanol groups in the nano fumed silica filler than in micro silica. The influence of the increased number of silanol groups on the erosion resistance of the nanocomposites and their mechanical properties is discussed.     

膨胀型阻燃剂聚丙烯阻燃复合材料的研究

采用乳液共混法制备了三聚氰胺/多聚磷酸铵/季戊四醇磷酸酯改性膨胀型阻燃剂(Mo_IFR),用双螺杆挤出机将Mo_IFR和未改性的三聚氰胺/多聚磷酸铵/季戊四醇磷酸酯膨胀型阻燃剂(Un_IFR)分别与聚丙烯(PP)共混制备了PP/Mo_IFR和PP/Un_IFR阻燃复合材料,研究了PP/Un_IFR与PP/Mo_IFR的力学性能、结晶性能和断面形貌。结果表明,随着阻燃剂用量的增加,PP/Mo_IFR与PP/Un_IFR的缺口冲击强度和拉伸强度下降,弯曲强度提高;但是,PP/Mo_IFR缺口冲击强度和拉伸强度的下降幅度比PP/Un_IFR的缺口冲击强度和拉伸强度的下降幅度要小得多,而PP/Mo_IFR的弯曲强度提高的幅度比PP/Un_IFR的弯曲强度提高的幅度大。PP/Un_IFR的冲击断面显示是脆性断裂,而PP/Mo_IFR的冲击断面显示是韧性断裂。X射线衍射显示Mo_IFR加入PP中,对PP的结晶性能没有显著的影响,IFR与PP的相容性良好。     

Thermal, Mechanical and Dielectric Properties of Nanostructured Epoxy-polyhedral Oligomeric Silsesquioxane Composites

This paper presents the results of the thermal, mechanical and dielectric measurements conducted on polymer nanocomposites consisting of epoxy and polyhedral oligomeric silsesquioxane (POSS). The material composites were analyzed with a scanning electron microscope (SEM), an atomic force microscope (AFM) and a transmission electron microscope (TEM). Glass transition temperatures of the composites were measured with differential scanning calorimeter (DSC). Stress, strain, modulus and impact strength of epoxy nanocomposites were tested. Ac and lightning impulse (LI) breakdown strength of the composites were measured. Relative permittivity, loss factor and volume resistivity measurements were also conducted on the material samples. Two types of POSS, glycidyl and octaglycidyldimethylsilyl, were used in different quantities. Statistical analysis was applied to the measurement results to determine the effects of the additive type and amount on the properties of epoxy. The paper discusses the possibilities and restrictions in order to achieve advantages in high voltage applications using polyhedral oligomeric silsesquioxanes.     

MgO/LDPE纳米复合材料制备及其空间电荷特性

为了降低低密度聚乙烯中的空间电荷积累,在自制纳米MgO粉体的基础上,采用熔融共混法,制备了氧化镁/低密度聚乙烯(MgO/LDPE)纳米复合材料,并通过扫描电镜(SEM)观察了MgO/LDPE纳米复合材料中的MgO粒径大小和分散情况,采用差热扫描量热法(DSC)确定了不同MgO质量分数纳米复合材料的结晶度,采用电声脉冲法(PEA)测量了不同MgO质量分数纳米复合材料的空间电荷分布,测量了不同MgO质量分数纳米复合材料的拉伸性能。试验结果表明,MgO/LDPE纳米复合材料体系中,MgO粒径约为50nm,且分散均匀;不同MgO质量分数纳米复合材料的弹性模量和抗张强度均高于纯LDPE的,且MgO质量分数为2%时达到最大值;不同MgO质量分数纳米复合材料的结晶度均高于纯LDPE的;纳米MgO能抑制空间电荷的注入和其在材料体内的迁移,质量分数为3%时,MgO/LDPE纳米复合材料中的空间电荷得到了良好的抑制。     

Magnetoresistance effect in PP + Fe based nanocomposite system

The article investigates the acqusition, structure, magnetic properties and magnetoresistance effect of nanocomposites on the basis of polypropylene matrix and iron nanoparticles, structure, magnetic properties and magnetoresistance. AFM results illustrate that the increase in the volume content of Fe nanoparticles in the polymer matrix causes changes on its supramolecular structure. As a result of the MFM studies, it has been defined that, nanoparticles dispersed in the polymer matrix form domains in the local areas and the sizes of domains vary from 150 to 400?nm. The study of magnetic properties of PP?+?Fe based nanocomposites showed that intrinsic magnetization increases with increasing magnetic field intensity and saturation occurs at certain value of intensity. If the field is reduced, remanent magnetization and hysterezis loop is observed. The dependence of PP?+?Fe based nanocomposites on the magnetic field was investigated and magnetoresistive effect was observed and it was found to be related with the presence of tunneling magnetoresistance effect in these nanocomposites.     

Nanocomposites-a review of electrical treeing and breakdown

Polymer nanocomposites are composite materials having several wt% of inorganic particles of nanometer dimensions homogeneously dispersed into their polymer matrix. This new type of polymer composite has recently drawn considerable attention because nanocomposites or nanostructured polymers have the potential of improving the electrical, mechanical, and thermal properties as compared to the neat polymers [1]. Polymer nanocomposites are, among other applications, increasingly desirable as coatings, structural, and packaging materials in a wide range of automobile, civil, aerospace, and electrical engineering applications. Also, nanocomposites find applications in medical services, healthcare, and decorative coloring [2], [3]. These new materials show excellent mechanical properties such as high tensile strength, increased hardness and toughness, improved flexural strength modulus, and greater heat and chemical resistance. Polymer nanocomposites are characterized by an enormously large interfacial surface area between the inorganic particles and the polymer matrix into which they are embedded. This ratio is typically more than two orders of magnitude greater than that in traditional microcomposite materials. The percentage by weight of the nanoparticles is usually quite low because of the low nanoparticle percolation threshold, particularly for the commonly used platelet and nanotube particles [4]. However, when the nanoparticle content increases beyond the percolation threshold, the nanocomposite may loose its beneficial properties [5]. Various polymers such as polyamide (PA), polyethylene (PE), polypropylene (PP), ethylene vinyl acetate (EVA), epoxy resin (EP), and silicone rubber (SiR) can be combined with inorganic particles such as layered silicate (LS), silica (SiO2), titania (TiO2), alumina (Al2O3), and magnesia (MgO) [1], and there are a number of papers that describe the tests and the properties of the aforementioned combinations of materials [6]?[10].     

Study of structural and electrical properties of Ag-starch nanocomposites

ABSTRACT

In the present work, Ag nanoparticles prepared by chemical reduction were used to synthesize Ag-starch nanocomposites. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used to ascertain the formation of Ag-starch nanocomposites. Current-voltage (I-V) measurements reveal that the conductivity of starch increases with increasing concentration of Ag nanoparticles. I-V data was further analysed to ascertain the actual conduction mechanism responsible for charge transport in starch and Ag-starch nanocomposites. Poole-Frenkel (PF) emission was found to be dominant conduction mechanism responsible for increased conductivity of Ag-starch nanocomposites.     

增容剂对纳米碳酸钙/聚丙烯/聚苯乙烯复合材料的等温结晶行为的影响

采用Avrami方程研究了纳米碳酸钙/聚丙烯/聚苯乙烯(nano CaCO3/PP/PS)复合材料的等温结晶动力学。研究结果表明,nanoCaCO3填充PP/PS增容共混物复合材料的结晶速率明显高于nano CaCO3/PP/PS共混物复合材料的,而且结晶速率对结晶温度的依赖性显著降低,大分子相容剂对PP等温结晶行为的影响大于nano CaCO3。     

Design and property study of a new type centrifugal crusher wear block

Abstract

A new type wear block made of medium carbon low alloy steel was designed to improve the service of a centrifugal crusher. A reasonable casting technology was chosen and ViewCast software was used to simulate the solidification process, then the location of the defeats was predicted, the scheme was optimized and the production verification was carried out. Annealing, quenching and tempering of wear resistant block was carried for performance testing. The observed metallographic microstructure indicates that it was organized as a strip martensite and a small amount of needle martensite after heat treatment. The analysis of mechanical properties indicates the hardness was 54.8HRC, the tensile strength was 1325MPa, the impact energy of V-notch and no notch was 15.7J and 142.7J respectively. Analysis of tensile and impact fracture scanning electron microscopy indicates that the fracture mechanism is subject to eutectic fracture. The performance test results show that the new type centrifugal crusher wear block can meet the requirements of the actual condition.     

用基于全通滤波器的ⅡR陷波器抑制工频通信中的谐波干扰

针对双向工频通信的信号特征，为了解决IIR陷波滤波器系数在低频段敏感度高的问题，提出采用基于全通滤波器的IIR陷波滤波器来消除电网谐波干扰的新方法。该陷波器可以由格型运算结构来实现，并因为全通滤波器的分子与分母之间的镜像对称关系，使滤波器在低频段具有非常低的系数敏感度。该文详细论述了该陷波滤波器的基本原理和设计方法，并通过一个设计实例说明了该方式由于量化效应引起的频率偏移量要远远小于级联方式。现场实验与仿真都证明了该滤波器能够非常有效地抑制电网中的基波和3、5次谐波，大大提高了对双向工频通信信号的检测能力。