On the sliding wear of nanoparticle filled polyamide 66 composites

The tribological properties of polyamide 66 (PA66) composites, filled with TiO₂ nanoparticles, short carbon fibres, and graphite flakes, were investigated. Sliding tests were performed on a pin-on-disk apparatus under different contact pressures, p, and sliding velocities, v. It was found that nano-TiO₂ could effectively reduce the frictional coefficient and wear rate, especially under higher pv (the product of p and v) conditions. In order to further understand the wear mechanisms, the worn surfaces were examined by scanning electron microscopy and atomic force microscopy. A positive rolling effect of the nanoparticles between the material pairs was proposed which contributes to the remarkable improvement of the load carrying capacity of polymer nanocomposites.  

铁钴镍合金粒子/石墨薄片复合材料的制备与吸波性能研究

利用超声和酸处理工艺将膨胀石墨剥离成纳米厚度的薄片,并利用简单的共沉积和退火还原工艺在石墨薄片上均匀沉积了铁钴镍磁性合金粒子.样品静磁性能与吸波性能的测试结果表明,此类材料具备优异的软磁性能和电磁波吸收性能.以600℃退火的Fe₃Co₆Ni/石墨薄片作为吸波剂的复合材料在12.6GHz处最大吸收可达-24dB,有效吸收带宽(<-5dB)达8GHz.通过调节合金的元素比例和退火工艺,可以控制样品的吸波性能.  

石墨/石蜡复合相变储热材料的热性能研究

膨胀石墨(EG)在超声作用下解离成微米级石墨片层(MSGF),并加入到石蜡基体中制备得到石墨/石蜡复合相变储热材料,并对复合相变材料的结构和热性能进行表征。实验结果表明,该石墨/石蜡复合相变储热材料储热速率加快,化学性质稳定。随MSGF质量分数的增加,固态及液态复合材料的导热系数均呈非线性显著增长,相变温度及相变潜热略有降低。  

Computation and application of local solidification times of grey cast iron cast in metallic moulds

Heat conduction equations applicable to the solidification of grey cast iron cast in moulds of the same material were solved for the cases of plate and cylindrical shaped castings made by pouring the metal at different temperatures into moulds of different wall thicknesses preheated to different temperatures, when the heat transfer coefficient at the casting-mould interface was assumed to have different values. An explicit finite difference method was used to solve the equations with the aid of a digital computer. Local solidification times at different nodal points were determined from the solutions and a relationship between the local solidification time and the location in a ‘casting’ was established. The application of local solidification times for predicting the microstructure and estimating the ultimate tensile strength of these “castings” cast in metallic moulds has been demonstrated.  

Preparation and Surface Characterization of Highly Ordered Polymer/Graphite Nanosheet Composites

Graphite nanosheets obtained from sonicating expanded graphite were coated chemically with magnetite nanoparticles. The modified graphite nanosheets were dispersed in epoxy or unsaturated polyester prepolymer, and subjected to a magnetic field before the suspension solidified. Composites with graphite nanosheets of highly ordered alignment have been prepared via the described approach. Several techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), and optical microscopy were used to characterize the modified graphite nanosheets and the polymer/graphite nanosheet composites.  

Numerical investigation of elastic mechanical properties of graphene structures

The computation of the elastic mechanical properties of graphene sheets, nanoribbons and graphite flakes using spring based finite element models is the aim of this paper. Interatomic bonded interactions as well as van der Waals forces between carbon atoms are simulated via the use of appropriate spring elements expressing corresponding potential energies provided by molecular theory. Each layer is idealized as a spring-like structure with carbon atoms represented by nodes while interatomic forces are simulated by translational and torsional springs with linear behavior. The non-bonded van der Waals interactions among atoms which are responsible for keeping the graphene layers together are simulated with the Lennard-Jones potential using appropriate spring elements. Numerical results concerning the Young’s modulus, shear modulus and Poisson’s ratio for graphene structures are derived in terms of their chilarity, width, length and number of layers. The numerical results from finite element simulations show good agreement with existing numerical values in the open literature.  

Effect of graphite flake on the mechanical properties of hot pressed ZrB2-SiC ceramics

A ZrB₂ ceramic containing 20 vol.% SiC and 10 vol.% graphite flake (ZrB₂-SiC-G) was fabricated by hot pressing. It was shown that the fracture toughness was improved due to the introduction of graphite flake, whereas the flexure strength and hardness decreased slightly. The fracture toughness of ZrB₂-SiC-G composite was 6.1 ± 0.3 MPa·m^1/2, which was much higher than that of monolithic ZrB₂, ZrB₂-SiC composite and similar ZrB₂-SiC-C composite. The toughening mechanisms are crack deflection and branching as well as stress relaxation near the crack tip. The results here pointed to a potential method for improving fracture toughness of ZrB₂-based ceramics.  

基于石墨烯特征制备新型柔性石墨膜的研究进展

石墨材料具有密度低、热膨胀系数低和热导率较高等优点，是近年来最具有发展前景的导热材料。主要综述了聚酰亚胺薄膜制备高导热新型柔性石墨膜的研究进展，并结合笔者的研究对形成石墨膜过程中存在的问题进行了简要分析。在此基础上着重综述了碳化和石墨化过程中化学结构的变化，薄膜由无序堆积结构转变成类石墨结构，其导电和导热性显著提高。综述了温度变化导致结构变化，从而对薄膜导电导热型产生影响的研究进展。这种新型薄膜在电子封装和国防工业等诸多领域都有极大的应用前景，薄膜对于该领域的前景和发展都具有重要的科学意义和应用价值。  

膨胀石墨的形貌、成分与结构变化研究

膨胀石墨是重要的工业应用材料,但其微观形貌、成分与晶体结构随膨胀倍率的变化规律认识仍不足。选择H₂SO₄₊HNO₃₊KMnO₄₊FeCl₃作为插层氧化体系,通过对鳞片原料石墨化学氧化制备出可膨胀石墨,分别在400 ℃、600 ℃、800 ℃、1000 ℃下膨化处理获得不同的膨胀石墨。针对上述几种石墨,采用OM、SEM、EDS、XRD等技术对比研究了其形貌、成分与结构的变化。结果表明,原料石墨、可膨胀石墨与膨胀石墨分别呈现层片状、褶皱状和蠕虫状的微观形貌,插层物主要由S与O组成,膨胀石墨的S与O含量显著低于可膨胀石墨,且其含量随着膨化温度提高逐渐降低。这些石墨具有相同的密排六方结构,其中可膨胀石墨的晶格常数显著大于原料石墨,反映出插层后石墨结晶度的严重劣化。膨胀石墨的结晶度稍差于原料石墨,但压片处理后得到改善,更高温度膨化的石墨改善更加明显,且优于原料石墨,这预示着高温膨化石墨的应用可塑性更强,具有更好的应用前景。  

Managing the degree of exfoliation and number of graphene layers using probe sonication approach

We have demonstrated a fast, versatile, and scalable approach to synthesize high-quality few layer graphene sheets with low defect ratio and high crystallinity produced from exfoliation of graphite flakes in DMF by using probe sonication. The effect of sonication time on degree of exfoliation and number of graphene layers has been fully investigated. The degree of exfoliation of graphene sheets as a function of sonication time has been successfully analyzed by XRD, UV-Vis spectroscopy, TEM, and BET studies. The morphological changes at different sonication times have also been observed by SEM. A structural and defect characterization of graphene sheets has been discussed in detail by Raman spectroscopic technique. The shift in position of 2D Raman band and its de-convolution provided information about formation of multi to few layer graphene sheets with sonication. Moreover, Raman results are highly consistent with TEM studies as per number of graphene layers is concerned.