竹木电热复合材料的通电老化性能研究

以4种胶黏剂制备竹木电热复合材料,并在160 W/m^2功率下通电12周,测试通电过程材料的老化性能。结果表明:随通电时间延长,材料的电阻减小,明度、光泽度降低,色差增大,颜色变深;耐湿、热尺寸稳定性和翘曲度均达到相关标准的要求。除异氰酸酯胶制备的复合材料外,其他3种复合材料的浸渍剥离性能亦达到标准要求;酚醛胶竹木电热复合材料的电阻变化最小,温度-时间效应较好,性能最佳。

碳系木质电热复合材料制备及耐老化研究进展

碳系木质电热复合材料是以碳系材料为发热元件、木质材料作为基体经胶合形成具有电致发热的新型木质功能材料,可应用于制备电热木质地板、电热木质墙板、电热木质衣柜等木质电热制品,具有供暖与装饰一体化作用,在清洁供暖领域具有广阔应用前景。本文介绍了可应用于木质电热复合材料的碳纤维电热纸、碳纳米管电热复合材料、石墨烯电热复合材料、碳纤维电热线、碳黑电热材料和碳素晶体电热材料制备方法及应用。分析了工艺参数和材料结构对电热实木复合材料、电热纤维板复合材料、电热竹木复合材料的理化性能、导电性及电热性能的影响,并归纳了电热作用、湿热作用对耐老化的影响及电安全性的研究进展,最后展望了碳系木质电热复合材料未来的研究方向。

碳纤维纸木质电热复合材料面层电热效果的纵向尺寸效应

根据热力学能量守恒定律和傅里叶(Fourier)定律,利用一维传热理论推导基于碳纤维纸(CFP)的木质电热复合材料的结构特征与其表面空气温度效果之间的理论关系式,对其关系进行了定性分析,研究木质电热复合材料面层电热效果的纵向尺寸效应,分析表明面层板厚度与表面空气温度呈反比例关系。对面层板厚度分别为2 mm和4 mm的木质复合材料开展了温度测试试验,以验证理论计算结果正确性。结果显示,通过理论计算,得出基于CFP的木质电热复合材料面层厚度与表面空气温度之间呈反比关系;通过实验验证,对比两种不同面层材料厚度的电热复合材料表面空气温度,发现厚度为2 mm的电热复合材料表面空气温度高于厚度为4 mm的,与理论计算结果一致。在采暖领域,相对于面层板较厚的木质电热复合材料,面层板较薄的更能充分利用能源。

电热双敏型形状记忆石墨烯/聚氨酯/环氧树脂复合材料的制备及其性能

以自制聚氨酯预聚体与环氧树脂复合形成互穿聚合物网络结构,采用共混方法添加自制高导电性石墨烯,制备了电热双敏型形状记忆复合材料,研究了其性能.结果表明,以20%(?)聚氨酯/环氧树脂为基体所制1.0%(?)石墨烯/聚氨酯/环氧树脂复合材料的分散性良好,玻璃化转变温度稍低于纯环氧树脂,拉伸强度是纯环氧树脂的93%,导电性达3.58?10?4 S/m,固定率为95.5%,回复率为97.5%,循环5次后固定率不低于95%.

Microstructure and properties of Al/Si/SiC composites for electronic packaging

The Al/Si/SiC composites with medium volume fraction for electronic packaging were fabricated by gas pressure infiltration.On the premise of keeping the machinability of the composites,the silicon carbide particles,which have the similar size with silicon particles（average 13 μm）,were added to replace silicon particles of same volume fraction,and microstructure and properties of the composites were investigated.The results show that reinforcing particles are distributed uniformly and no apparent pores are observed in the composites.It is also observed that higher thermal conductivity（TC） and flexural strength will be obtained with the addition of SiC particles.Meanwhile,coefficient of thermal expansion（CTE） changes smaller than TC.Models for predicting thermal properties were also discussed.Equivalent effective conductivity（EEC） was proposed to make H-J model suitable for hybrid particles and multimodal particle size distribution.

Effects of thermal oxidation on microwave-absorbing and mechanical properties of SiC_f/SiC composites with PyC interphase

The SiCf/SiC composites containing PyC interphase were prepared by chemical vapor infiltration process. The influences of thermal oxidation on the complex permittivity and microwave absorption properties of Si Cf/Si C composites were investigated in the frequency range of 8.2-12.4 GHz. Both the real and imaginary parts of the complex permittivity decreased after thermal oxidation. The composites after 100 h thermal oxidation showed that reflection loss exceeded-10 d B in the frequency of 9.7-11.9 GHz and the minimum value was-11.4 d B at 11.0 GHz. The flexural strength of composites decreased but fracture behavior was improved obviously after thermal oxidation. These results indicate that the SiCf/SiC composites containing PyC interphase after thermal oxidation possess good microwave absorbing property and fracture behavior.

Synthesis and characterization of Na0.44MnO2 nanorods/graphene composite as cathode materials for sodium-ion batteries

Na0.44MnO2 nanorods have been prepared by a hydrothermal method.The experimental parameters have been systematically investigated and optimized.The results show that Na0.44MnO2 nanorods obtained via the hydrothermal treatment at 200℃for 16 h show the best electrochemical properties,which deliver the high initial discharge capacity of 110.7 mA·h/g at 50 mA/g in potential window 2.0-4.0 V.To further improve their electrochemical properties,a ball milling process with graphene has been carried out to obtain Na0.44MnO2/graphene composite.The initial discharge capacity of Na0.44MnO2/graphene composite is 106.9 mA·h/g at a current density of 50 mA/g.After 100 cycles,the residual discharge capacity is 91.8 mA·h/g and the capacity retention rate is 85.9%,which is much higher than that of pristine Na0.44MnO2 nanorods(74.7%)at the same condition.What is more,when the current density reaches 500 and 1000 mA/g,the corresponding discharge capacities of Na0.44MnO2/graphene composite are about 89 and 78 mA·h/g,respectively,indicating outstanding rate capability.

Electrocaloric behavior of Ba_(0.85)Ca_(0.15)Zr_(0.1)Ti_(0.88)Sn_(0.02)O_3 cement composites

A thrust for looking multifunctional materials for applications in civil engineering structures has attracted interest among researchers across the globe.Cement based Ba0.85Ca0.15Zr0.1Ti0.88Sn0.02O3(BCZT.Sn)composites were prepared for electrocaloric applications with varying BCZT.Sn to cement ratio.Hysteresis loops showed some signature of saturation in cement composites.However,loops of pure sample were saturated due to its ferroelectric nature.Furthermore,these composites were explored for the first time in solid state refrigeration technology namely electrocaloric effect(ECE).Peak electrocaloric performance shows an adiabatic temperature changes of 0.71,0.64 and 0.50 K and isothermal entropy changes of 0.86,0.80 and 0.65 J/(kg.K)for BCZT.Sn,10%and 15%cement composites,respectively,under application of 0-29 kV/cm electric field.The adiabatic temperature change in cement based composites is comparable with that of the BCZT-Sn ferroelectric ceramics.Furthermore,the dielectric constant(εr)of composites with different ceramic contents at room temperature reveals that dielectric constant increases with an increase in BCZT-Sn proportion in composites.These cement based BCZT.Sn composite materials may be used in solid state refrigeration as they are fairly competitive with the pristine sample.

Fracture toughness of multiphase TiAl-Nb alloy in situ consolidated by spark plasma sintering

A fine-grained TiAl alloy with a composition of Ti-45Al-5Nb-1.5Cr-0.2W （mole fraction, %） with multiphases was prepared by spark plasma sintering （SPS） and heat-treating at 1 100 ℃ for 48 h. The relationship among sintering temperature, microstructure and fracture toughness were investigated by X-ray diffractometry （XRD）, optical microscopy （OM）, scanning electron microscopy （SEM） and mechanical testing. The results show that microstructure of the bulk alloy depends on the sintering temperature strongly, and the main phase TiAl and few phases Ti3Al and niobium solid solution （Nbss） are observed in the SPS bulk samples. In the heat-treatment condition, the lamellar and Nbss phase can provide significant toughening by plastic strengthening, interface decohension, crack branch and crack bridge mechanisms. The fracture mode of the SPS TiAl composite samples is intergranular rupture and cleavage fracture.

The Effect of Ionizing Radiation and Magnetic Field on Deformation Properties of High Density PolyethylenelAcrylonitrile-Butadiene Composites

The effect of magnetic field and ionizing radiation on the mechanical properties of polymer blends consisting of high density polyethylene （HDPE） and acrylonitrile-butadiene rubber （NBR） has been investigated. The purpose of the work was to create HDPE/NBR blend composites of significantly different compositions （with an excess of HDPE, intermediate ones, and with an excess of NBR） and to investigate the role of composition on mechanical deformation properties under the influence of magnetic field. The investigation has importance from the engineering viewpoint, since thermoplastic composite materials have been used as structural elements in thermonuclear and engineering fields, like wires, insulation materials and others, which are frequently subjected to mechanical loadings under the effect of magnetic field greater than 1 T. One part of the blends has been irradiated with 5 MeV accelerated electrons up to absorbed dose D equal to 150 kGy. Unirradiated and the radiation modified blends have been exposed to a constant magnetic field with induction B equal to 1.0 T, 1.5 T and 1.7 T. It is found that the action of magnetic field decreases the elastic modulus of unirradiated materials. Decrement of elastic modulus is reduced with increase of the content of NBR in composites. It is also found that preliminary irradiation noticeably decreases the effect of magnetic field. Data of the influence of the magnetic field, radiation cross-linking, and the ratio of the components on the creep are also obtained.

Processing of advanced thermoelectric materials

Last two decades have witnessed significant progress in thermoelectric research, to which materials processing has crucial contributions. Compared with traditional zone-melting method used for fabricating bismuth telluride alloys, new powder-based processes have more freedom for manipulating nanostructnres and nanocomposites. Thermoelectric performance enhancement is realized in most thermoelectric materials by introducing fine-grained and nano-composite structures with accurately controlled compositions. This review gives a comprehensive summary on the processing aspects of thermoelectric materials with three focuses on the powder synthesis, advanced sintering process and the formation of nanostructures in bulk materials.

All-organic composites with strong photoelectric response over a wide spectral range

2-hydroxynaphthylidene-1′-naphthylamine(HNAN) and –NO_(2) modified HNAN(HNAN-NO_(2)) Schiff base compounds were synthesized and exhibited strong visible light absorption(<650 nm). These compounds were added to poly(vinylidene fluoride-trifluoroethylene)(P(VDF-Tr FE))ferroelectric polymer, obtaining composites with high photoelectric response under visible and infrared light. It was found that the modification of HNAN by the nitro group and the poling of the composites under a high electric field can greatly enhance the photoelectric response of the composites. The composites can generate high photovoltages of 1386 and352.7 mV under irradiation with near-infrared light(915 nm)and green light(532 nm). The mechanism of the photoelectric response of the composites under green light was explored and it was found that the response originates mainly from the coupling effect of the photothermal effect of the Schiff base and the pyroelectric effect of the ferroelectric polymer. The composites, which can be utilized as photodetector materials,are promising for next-generation artificial retina applications and the sensing capability of retina can be extended in a wide wavelength range from visible to infrared light.

Hot deformation behaviour and processing maps of AA6061-10 vol. % SiC composite prepared by spark plasma sintering

AA6061-10 vol.% SiC composite was successfully prepared by spark plasma sintering. The deformation behaviour of this composite was studied using the uniaxial compression test, which was conducted at temperatures between 300 and 500℃ and strain rates between 0.001 and 1 s^-1. Results indicate that the stress-strain curves of the AA6061-10 vol.% SiC composite typically feature dynamic recrystallization. The steady stress can be described by a hyperbolic sine constitutive equation, and the activation energy of the composite is 230.88 kJ/mol. The processing map was established according to the dynamic materials model. The optimum hot deformation temperature is 450-500℃ and the strain rate is 1-0.1 s^-1. The instability zones of flow behaviour can also be identified using the processing map.