羰基铁/聚苯乙烯复合材料的制备及微波吸收性能

采用热压法制备了羰基铁/聚苯乙烯复合材料。复合材料的结构、形貌和电磁性能分别采用X射线衍射仪(XRD)、扫描电镜(SEM)和HP8510网络分析仪进行了研究。结果表明,随着羰基铁粉含量的增加,羰基铁/聚苯乙烯复合材料的复介电常数的实部ε′和虚部ε″、复磁导率的实部μ′和虚部μ″都呈现逐渐增大的趋势。羰基铁粉含量为75%(质量分数)的羰基铁/聚苯乙烯复合材料具有最好的电磁波吸收性能,其最小反射率在14GHz为-15dB,-10dB带宽达4.1GHz。     

蒙脱土/聚苯乙烯复合材料的热分解成炭行为

将聚苯乙烯(PS)树脂与不同种类蒙脱土(MMT)进行熔融复合制备MMT/PS复合材料, 通过X射线衍射(XRD)和高分辨透射电镜(HRTEM)对复合材料的微观结构进行了研究。采用SEM、 EDX、 XRD、 氧指数法和锥形量热法研究了复合材料的热分解成炭行为和燃烧性能。结果表明: 用蒙脱土原土(NaMMT)制备的NaMMT/PS复合材料是一种简单物理混合物, 用有机蒙脱土(OMMT)制备的OMMT/PS复合材料是一种插层-部分剥离型纳米复合材料。MMT与PS质量比为6:100时, OMMT/PS复合材料的热释放速率峰值和平均值分别只有NaMMT/PS复合材料相应值的70.7%和67.4%, 火灾性能指数(FPI)是后者的1.2倍, 氧指数比后者增加1.0%, 热分解残余物表面碳元素含量是后者的2.5倍。OMMT/PS复合材料热分解后在材料表面生成一层厚厚的致密、 连续的含碳硅酸盐残余物层, 起到良好的阻燃作用, 而NaMMT/PS复合材料几乎没有成炭能力, 其热分解产物全部来自NaMMT本身的热分解, 阻燃性能很差。     

压电陶瓷粒度分布对锆钛酸铅/聚偏氟乙烯复合材料电性能的影响

将不同粒度的锆钛酸铅(PZT)陶瓷粉进行复配,制成不同粒度分布的PZT陶瓷颗粒,然后与聚偏氟乙烯(PVDF)复合制备不同PZT粒度分布的PZT/PVDF复合材料,研究了复合材料的介电性能和压电性能。结果表明,当陶瓷颗粒体积分数高达70%时,双峰分布复合材料的压电系数可达75 pC·N-1。这是由于双峰分布复合材料中大陶瓷颗粒保持了完整的钙钛矿结构,小陶瓷颗粒填充在大颗粒之间,陶瓷颗粒彼此联接,形成了更多的电-力耦合通道,有效地实现了压电效应的传递。大陶瓷颗粒完整的钙钛矿结构以及大、小颗粒的协同堆砌效应,提高了PZT/PVDF复合材料的电性能。     

炭黑改性对炭黑/高密度聚乙烯体系电性能稳定性的影响

采用熔体共混法制备了炭黑（CB）/高密度聚乙烯（HDPE）导电复合材料。研究了硝酸氧化对CB/HDPE导电复合材料正温度系数（PTC）、负温度系数（NTC）效应和电性能稳定性的影响。结果表明,填充氧化炭黑（CB-O）提高了CB-O/HDPE体系的电性能稳定性和PTC强度,部分消除或降低了复合材料的NTC效应。而CB-O/HDPE体系的室温电阻率比CB/HDPE体系只增加了0.3个数量级,但比经过交联处理的CB/HDPE（CB/crosslinked-HDPE）体系降低了1个数量级。CB-O/HDPE复合材料性能的改善主要是由于CB经氧化后,表面羧基、羟基等极性基团含量增加,抑制了CB粒子高温时的自团聚作用,减弱了体系的NTC效应;同时CB表面微晶晶界处导电性较差区域的减少,提高了CB的导电性,,并且CB-O表面大量孔洞和裂缝的形成,增强了CB-O与HDPE的物理吸附作用,提高了复合材料的电性能稳定性。      

Study on the electrical behavior of MWCNTs in GF/Epoxy composites

The multi-wall nanotubes (MWCNTs) were divisionalized equably by the fabric of glass in composites. Then the electrical properties such as permittivity, conductance and electromagnetic interference (EMI) shielding effectiveness (SE) of MWCNTs in GF/EP composite were studied. The effect of the content and dispersion of MWCNTs were researched in this work. Firstly the permittivity of MWCNTs/GF/EP composites were studied respectively by keeping layers of glass fabric and increasing content of MWCNTs or keeping content of MWCNTs and changing layers of glass fabric in electromagnetic wave band (5.85-18 GHz). Then the conductance of MWCNTs/GF/EP composites with different MWCNTs contents was tested. Furthermore, the EMI SE of composites with different MWCNTs contents in electromagnetic wave band (5.85-18 GHz) were studied. In addition, the morphologies of MWCNTs/GF/EP composites with the different MWCNTs weight percent were observed. The results show that the real part of permittivity of composites can be improved highest up to 75 and the imaginary part increase maximum up to 80. However there is no disciplinarian about effect of layers of glass fabric on dielectric property. The MWCNTs/GF/EP composite can be changed from the insulator to the semiconductor along with increasing the weight percent of MWCNTs. In electromagnetic wave band 5.85-18 GHz, the values of SE are increasing with increasing content of the MWCNTs.     

Effect of modification and ceramic particles on solidification behavior of aluminum-matrix composites

Thermal analysis is used to establish the relationship between solidification history and the microstructure of SiC particulate reinforced Al-Si alloy-matrix composites. The results show that cooling curves are influenced by the presence of SiC particles and by strontium modification. The eutectic growth temperature of SiC_P/359 composites modified with Sr lies in the range of 840 to 843 K, i.e., about 5 to 7 K higher than that of Sr-modified unreinforced 359. For the same composite, the eutectic undercooling is higher with Sr modification than without. The eutectic solidification time of the composites is shorter than that of the unreinforced base alloy because of the presence of the ceramic particles. Strontium modification has the tendency to extend the eutectic solidification time. Microstructure analysis reveals that Sr modification has a refining effect on eutectic silicon for the composites, and SiC particles in the composite melt serve as the substrates for eutectic Si phase nucleation.     

橡胶相尺度对亚微米或纳米橡胶颗粒填充环氧复合材料性能的影响

对比研究了由液体橡胶在环氧树脂中原位形成的亚微米橡胶/环氧复合材料和在环氧树脂中直接添加纳米橡胶颗粒形成的纳米橡胶/环氧复合材料的性能。研究表明：未固化混合物的黏度随着纳米橡胶相的加入逐渐增加,但随着亚微米橡胶相含量的增加而降低;橡胶/环氧复合材料的玻璃化转变温度随着纳米橡胶颗粒的加入逐渐增加,但随着亚微米橡胶相含量的增加而降低;两种橡胶相的添加均使复合材料的弹性模量降低,断裂延伸率增加;在较低含量时,纳米橡胶颗粒可以提高环氧的拉伸强度;两种橡胶填充的橡胶/环氧复合材料均显示出明显的增韧效果。微观形貌分析表明,两种橡胶均可以在应力作用下脱粘并促进裂纹尖端的塑性变形。     

Rheological behavior of short sisal fiber-reinforced polystyrene composites

The rheological behavior of short sisal fiber-reinforced polystyrene composites containing short sisal-fiber has been studied using an Instron capillary rheometer. The effect of fiber length, fiber loading, shear rate, shear stress and temperature on the rheological behavior of the composites was studied. Unlike other short fiber-reinforced thermoplastics at lower temperature the melt viscosity of polystyrene(PS)-sisal composites are lower than that at higher temperatures. At 180°C the viscosity of the composite is governed by wall-slip, which decreases the viscosity and at 190°C the viscosity is governed by fiber melt interaction that increases the viscosity. The morphology of the extrudate was studied using optical and electron microscopy.     

Effects of particle size on the thermal expansion behavior of SiCp/Al composites

The coefficients of thermal expansion (CTEs) of 20 vol% SiCp/Al composites fabricated by powder metallurgy process were measured and examined from room temperature to 450 °C. The SiC particles are in three nominal sizes 5, 20 and 56μm. The CTEs of the SiCp/Al composites were shown to be apparently dependent on the particle size. That the larger particle size, the higher CTEs of the composites, is thought to be due to the difference in original thermal residual stresses and matrix plasticity during thermal loading. At low temperature, the experimental CTEs show substantial deviation from the prediction of the elastic analysis derived by Kerner and rule of mixture (ROM), while the Kerner’s model agrees relatively well at high temperatures for the composite with the larger particle size.     

碳纳米管/聚乙烯/聚苯乙烯多相复合材料的制备及导电性能研究

用熔融共混的方法分别制备了两相复合材料MWNT(多壁碳纳米管)/LDPE、MWNT/PS和多相复合材料MWNT/LDPE/PS,以上3种复合材料的导电渗滤阈值分别为8%(wt,下同)、6%和4%.SEM观察发现,MWNT选择性的分布于MWNT/LDPE/PS复合材料的LDPE相中.当LDPE/PS的质量比为50/50时,聚合物基体形成双连续结构,由于双重渗滤的作用,复合材料的渗滤阈值降低到4%.     

Effect of grain size and second phase particles on the hydrogen occlusivity of iron and steels

The trapping of hydrogen by various interfaces in iron and steels has been studied. The hydrogen content of pure iron specimens was found to depend more on hydrogen than those of low angle, and thus specimens with low angle grain boundaries were less susceptible to hydrogen damage. Inclusions and thermo-mechanical treatments were also significant in determining the hydrogen pick-up in iron. A critical volume fraction of inclusions was detected, below which no hydrogen- induced cracking occurred. Ferrite/pearlite and pearlite/pearlite colony interfaces in steel were found to trap hydrogen, whereas the ferrite/comentite interface within the pearlitic colonies had little effect on the hydrogen occlusivity. Received: 26 May 1999 / Reviewed and accepted: 28 October 1999     

Effect of AlN particles on the corrosion behavior of Al/AlN<Subscript>P</Subscript> composites

The corrosion behavior of Al/AlN_P composites has been examined by using potentiodynamic polarization technique in 3.5wt% NaCl solution with the pH value of 5, 8.6, and 11.6 respectively. Electrochemical impedance spectra (EIS) measurements have also been carried out to assess the long-term effects of AlN particles. It has been found that Al/AlN_p composites show the increased susceptibility to pitting attack compared with the unreinforced Al, which is attributed to the micro-galvanic action between AlN particles and the matrix Al. The micro-galvanic action mainly arises as a result of hydrolysis of AlN particles. In addition, EIS measurements reveal that the corrosion mechanism of Al/AlN_p composites changes a lot with increasing immersion time, which is controlled by diffusion process at last.     

The role of disorder on the AC and DC electrical conductivity of vapour grown carbon nanofibre/epoxy composites

Four dispersion methods were used for the preparation of vapour grown carbon nanofibre (VGCNF)/epoxy composites. It is shown that each method induces certain levels of VGCNF dispersion and distribution within the matrix, and that these have a strong influence on the composite electrical properties. A homogenous VGCNF dispersion does not necessarily imply higher electrical conductivity. In fact, it is concluded that the presence of well distributed clusters, rather than a fine dispersion, is more important for achieving larger conductivities for a given VGCNF concentration. It is also found that the conductivity can be described by a weak disorder regime.     

Effect of size and shape of metal particles to improve hardness and electrical properties of carbon nanotube reinforced copper and copper alloy composites

Utilizing the extra-ordinary properties of carbon nanotube (CNT) in metal matrix composite (MMC) for macroscopic applications is still a big challenge for science and technology. Very few successful attempts have been made for commercial applications due to the difficulties incorporating CNTs in metals with up-scalable processes. CNT reinforced copper and copper alloy (bronze) composites have been fabricated by well-established hot-press sintering method of powder metallurgy. The parameters of CNT–metal powder mixing and hot-press sintering have been optimized and the matrix materials of the mixed powders and composites have been evaluated. However, the effect of shape and size of metal particles as well as selection of carbon nanotubes has significant influence on the mechanical and electrical properties of the composites. The hardness of copper matrix composite has improved up to 47% compared to that of pure copper, while the electrical conductivity of bronze composite has improved up to 20% compared to that of the pure alloy. Thus carbon nanotube can improve the mechanical properties of highly-conductive low-strength copper metals, whereas in low-conductivity high-strength copper alloys the electrical conductivity can be improved.     

Effect of core–shell composite particles on the sintering behavior and properties of nano-Al2O3/polystyrene composite prepared by SLS

Nano-Al₂O₃ particles coated with polystyrene (PS) by emulsion polymerization were used as fillers to reinforce PS based composites prepared by selective laser sintering (SLS). The influences of the treated and untreated nanoparticles on the sintering behavior and mechanical properties of the laser sintered specimens were investigated. It was found that there were many uneven holes in the untreated composites. However, for the treated composites, due to the nanoparticle surfaces treated by emulsion polymerization, the absorbance of laser was improved and the nanoparticles dispersed well in the polymer matrix; a full dense structure was obtained and the properties were enhanced, such as the notched impact strength increased 50%, the maximum value was 12.1 kJ/m²; the tensile strength increased up to 300%, the maximum value was 31.2 MPa, comparing to the unfilled PS. FE-SEM studied the tensile fractured surfaces of the sintered specimens. It was noted that the fractured surfaces of composites with treated nanoparticles were rougher than those of unfilled PS and those of the untreated composite. Drawing from the results, it can be confirmed that a full dense structure can be obtained and the polystyrene matrix was strengthened and toughened when the nanoparticles were coated with PS by emulsion polymerization. This work forms a theoretical and technique basis for the production of selective laser sintered nano-Al₂O₃/PS functional products.     

热处理对炭/炭-铜复合材料载流磨损行为的影响

为探明炭/炭(C/C)多孔体热处理对炭/炭-铜(C/C-Cu)复合材料载流磨损行为的影响,采用化学气相渗透法(CVI)增密的C/C多孔体,再通过压力熔渗法制备C/C-Cu复合材料.采用载流动态磨损试验机测试C/C-Cu复合材料载流磨损行为,利用数字式三维视频显微镜和扫描电子显微镜观察复合材料磨损前后的表面形貌,研究了C/C多孔体经过2 000℃热处理对C/C-Cu复合材料载流磨损行为的影响.结果表明:C/C-Cu复合材料的质量磨损率和线磨损率比C/C多孔体未经热处理的复合材料分别降低了34.42%和17.84%;C/C多孔体经过2 000℃热处理,石墨化度提高,片层劈裂阻力减小,在载荷的作用下石墨片层易于劈裂形成细小的石墨微晶碎片,迅速填充修复表面缺陷,形成具有一定润滑作用、平整的摩擦膜,有效抑制了局部非均匀磨损的扩大,减弱了磨粒磨损和电弧放电引起的烧蚀、粘着、氧化磨损之间的循环交替磨损,载流磨损性能提高.     

Thermoelectric power and AC electrical properties of PAN-based carbon fiber composites

The thermoelectric power and AC electrical properties of conductive polymer composites made of polycarbonate filled with randomly distributed PAN-based carbon fibers of different concentration: 0, 5, 10, 18, and 30 wt% were studied. The thermoelectric power was measured as a function of temperature in the frequency range from 200 kHz to 12 MHz. It was found that the observed Seebeck coefficient and thermoelectric activation energy depend on temperature, frequency and fiber concentration. The Seebeck coefficient calculated using the electrical transport theory of semiconductors decreases with both increasing temperature and carbon fiber content. The thermoelectric power results revealed that the composites function electrically as semiconductors. Dielectric constants and AC conductivity were calculated from impedance and phase angle measurements. It was found that both increase with increasing temperature. The activation energy and relaxation time decrease with increasing temperature measured and applied frequency. The thermoelectric power results indicated that electrical conduction in bulk composites is produced from a combination of transport processes involving: electrons, holes, ions and charged impurity motion in addition to protonic migration.     

C/ C坯体对 C/ C2Cu复合材料摩擦磨损行为的影响

采用无压熔渗方法制备炭纤维整体织物/炭2铜 (C/ C2Cu) 复合材料 , 在 MM22000型环2块摩擦磨损试验机上考察复合材料的摩擦磨损性能 , 利用扫描电子显微镜观察分析磨损表面形貌 , 研究 C/ C坯体对材料的摩擦磨损行为的影响及机制。结果表明 : 随着 C/ C坯体密度的增加 , 摩擦系数及 C/ C2Cu材料自身和对偶的磨损量均降低 ; 采用浸渍/炭化 ( I/ C) 坯体的 C/ C2Cu材料摩擦系数及自身和对偶件的磨损量均高于采用化学气相渗透(CVI) 坯体的试样; 摩擦面平行于纤维取向的试样摩擦系数低于垂直于纤维取向的试样 , 但磨损率较高。