块状无裂纹介孔炭的合成和表征

<正>以P123、F127作为模板剂,间苯二酚-甲醛为碳前驱体,利用水热合成技术制备了蠕虫状结构的块状无裂纹介孔炭。采用TG、FT-IR、TEM、N2吸附-脱附和元素分析等方法对介孔炭材料的结构进行了表征,分别研究了模板剂用量、模板剂种类对介孔炭结构的影响。结果表明:以F127和P123为模板剂制备的介孔炭均为蠕虫状结构。模板剂用量增加,介孔炭比表面积、孔径和孔容变大,但微孔的比表面积有所下降。模板剂种类不同,比表面积、微孔比表面积、孔容相差不     

复合模板剂对块状无裂纹介孔炭介孔结构的影响

用水热合成技术,以间苯二酚-甲醛为炭前驱体,F127或P123为模板剂,通过有机-有机自组装,制备了蠕虫状结构的块状无裂纹介孔炭。采用TEM、N2吸附-脱附和元素分析等方法对介孔炭材料的结构进行表征,主要研究了模板剂配比对介孔炭介孔结构的影响。结果表明:用复合模板剂P123/F127制备的介孔炭孔径分布较窄,且其孔径较SF-1增加100%以上;随着复合模板剂中P123含量的增加,介孔炭的微孔表面积和孔容均有所上升。     

不同焙烧温度对有序介孔炭孔结构参数的影响

以三嵌段共聚物F127为模板剂,线性酚醛树脂(PF)为炭前驱体,在F127与PF的质量比mF127∶mPF=1∶1时,利用溶剂挥发诱导自组装制备介孔炭材料,对在不同焙烧温度下制备的介孔材料进行表征,研究焙烧温度对所得介孔材料结构的影响。采用XRD、TEM、N2吸附/脱附等方法对介孔材料的结构进行了表征,研究了焙烧温度对上述介孔炭结构的影响。结果表明:介孔材料的晶面间距随着温度的升高而降低,当焙烧温度为600℃时,介孔材料的骨架从高分子材料转变为炭材料。其比表面积和C/H摩尔比均随着焙烧温度升高而增加,但其孔壁厚度和孔径却随着焙烧温度的升高而降低。孔径大小和孔壁厚度在600℃以后降低的幅度较小,基本上趋于稳定,碳骨架的收缩变得缓慢。随着焙烧温度的升高,其介观结构基本不发生改变。     

介孔炭制备参数对其介观结构的影响研究

采用软模板法制备介孔炭,探究碳源的碳链长度、碳源和模板剂的质量比以及模板剂的类型对介孔炭材料粒径大小和介孔结构的影响。结果表明,当酚醛树脂的热聚合时间为1.0 h时,介孔炭孔径较均匀,孔结构密实;当模板剂与酚醛树脂的质量比在1.0∶1.0时,所形成的介孔炭孔隙发达,比表面积和孔容较大;在碳源聚合时间为1.0 h,模板剂和酚醛树脂质量比为1.0∶1.0的条件下,模板剂P123和F127不影响介孔材料的孔结构,但会改变孔结构的形状,形成不同的空间结构。     

介孔炭制备参数对其介观结构的影响研究

采用软模板法制备介孔炭,探究碳源的碳链长度、碳源和模板剂的质量比以及模板剂的类型对介孔炭材料粒径大小和介孔结构的影响。结果表明,当酚醛树脂的热聚合时间为1.0 h时,介孔炭孔径较均匀,孔结构密实;当模板剂与酚醛树脂的质量比在1.0∶1.0时,所形成的介孔炭孔隙发达,比表面积和孔容较大;在碳源聚合时间为1.0 h,模板剂和酚醛树脂质量比为1.0∶1.0的条件下,模板剂P123和F127不影响介孔材料的孔结构,但会改变孔结构的形状,形成不同的空间结构。     

非水体系下介孔炭的快速合成与表征

结合溶胶-凝胶技术和非水体系快速挥发法,以嵌段聚醚F127与酚醛树脂的共混聚合物为无机物成核的模板导向剂和碳源前驱体直接制备介孔炭材料.利用N2物理吸附-脱附,X射线衍射,热失重(TGA),扫描电镜(SEM)及透射电镜(TEM)对所得介孔炭产品的结构形貌性能进行了表征.结果表明,随着酚醛树脂/F127的质量比在0-1.5内增加,介孔炭颗粒的孔隙结构经历了由三维体心立方向二维六方再到蠕虫状无序结构的转变过程.同时其最佳几率孔径随酚醛树脂/F127比值的增加呈现先减小后增大的趋势.     

非水体系下介孔炭的快速合成与表征

结合溶胶-凝胶技术和非水体系快速挥发法,以嵌段聚醚F127与酚醛树脂的共混聚合物为无机物成核的模板导向剂和碳源前驱体直接制备介孔炭材料。利用N2物理吸附-脱附,X射线衍射,热失重(TGA),扫描电镜(SEM)及透射电镜(TEM)对所得介孔炭产品的结构形貌性能进行了表征。结果表明,随着酚醛树脂/F127的质量比在0-1.5内增加,介孔炭颗粒的孔隙结构经历了由三维体心立方向二维六方再到蠕虫状无序结构的转变过程。同时其最佳几率孔径随酚醛树脂/F127比值的增加呈现先减小后增大的趋势。     

酚醛树脂基高度有序介孔炭材料的合成及其电容性

以碱性条件下制备出的A阶酚醛树脂为炭前驱体,三元嵌段共聚物P123及F127为介孔模板剂,采用乙醇溶剂蒸发诱导自组装与程序升温策略,制备出高度有序、比表面积达550.12 m2/g、孔容为0.385 4 cm3/g、平均孔径为3.97 nm的酚醛树脂基有序介孔炭材料。利用小角X射线衍射、扫描电镜、透射电镜、物理吸附及电化学性能测试等技术,研究了不同合成条件下得到的有序介孔炭材料的结构和电化学性能。结果表明,在6 mol/L KOH电解质溶液的三电极体系中,该优化有序介孔炭材料在1 A/g的电流密度下比电容可达146.5 F/g。     

简易模板法制备有序介孔碳及其表征

目前制备有序介孔碳的方法工艺复杂、繁琐耗时,为了简化其制备工艺,缩短实验流程,本文提出一种不需要添加额外溶剂直接制备有序介孔碳的方法。以三嵌段共聚物F127为模板剂,自制低分子量酚醛树脂为碳前体,制备了具有二维六方结构的介孔碳。采用红外光谱对酚醛树脂和F127进行表征,研究了两者之间的作用力;采用X射线衍射、透射电镜和N2吸附/脱附等手段对介孔碳结构进行表征,研究了酚醛树脂的合成温度和模板剂用量对介孔碳结构的影响。结果表明酚醛树脂合成温度为70℃,F127：PF=1时,得到的介孔碳比表面积、孔容和孔径分别为490m2/g、0.41cm3/g和4.15nm。     

制备工艺对酚醛树脂基炭分子筛性能影响

以工业酚醛树脂㈣为碳源,三嵌段聚合物F127作为模板剂制备炭分子筛材料。采用TG、SEM、FTIR和N_2-BET等表征手段对制备的炭分子筛进行了表征,研究了前驱体制备工艺对炭分子筛孔径分布的影响。结果表明,F127用量、搅拌时间、反应温度对炭分子筛孔径分布影响很大。在酚醛树脂与F127质量比1:1,反应温度45℃,搅拌时间6 h,800℃炭化条件下制备的炭分子筛孔径分布最为集中,BET比表面积和单点总孔容分别为716.59 m~3·g~(-1)和0.55775 cm~3·g~(-1)。     

Nanographite-reinforced carbon/carbon composites

Carbon/carbon composites (C/Cs) with nanographite platelets (NGP) filler in a matrix derived from phenolic resin were produced. Different weight concentration (0.5, 1.5, 3, 5 wt.%) NGP were introduced by spraying the NGP during the prepreg formation. The NGP-reinforced C/Cs were characterized for effect of NGP concentration on microstructure, porosity, interlaminar shear strength (ILSS), flexural, ultrasonic and vibration damping behavior. At 1.5 wt.% NGP C/C, the highest values of ILSS observed was 10.5 MPa (increased by 22%), flexure strength of 142.4 MPa (increased by 27%), flexural modulus of 59.2 GPa (increased by 68%) and porosity of 18.8% (reduced by 17.5%) in comparison to neat (without NGP) densified C/C. Ultrasonic testing revealed an average increase of 15% through the thickness Young’s modulus of NGP-C/C; (3.12 GPa at 1.5 wt.% NGP). A 20% average decrease in the damping ratio of the first four modes of vibration was observed in 1.5 wt.% NGP densified C/C. At low concentration (⩽1.5 wt.%) the NGP filled in the pores, cracks and debonded interface but at concentration higher than 1.5 wt.% NGP lost their effectiveness due to agglomeration. The required cycles for desired density/properties are projected to be less compared to neat C/C due to less porosity observed in ⩽1.5 wt.% NGP concentration C/C.     

Pulsed electrodeposition of carbon nanotubes-hydroxyapatite nanocomposites for carbon/carbon composites

Carbon nanotubes-hydroxyapatite (CNTs-HA) composite coatings, which behaved like single composites, were synthesized by a combined method composed of electrophoretic deposition and pulsed electrodeposition. The phase compositions and the microstructure of the composite coatings were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared spectrometry (FTIR). Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) studies showed that the CNTs-HA composite coatings protected the bare carbon/carbon composites from corrosion in simulated body fluid (SBF) solution. The adhesion strength of CNTs-HA composite coating prepared by the combined method is 14.57±1.06 MPa achieved at the CNTs EPD time of 10 min. Compared to the other CNTs-HA composite coatings with different content of CNTs, the CNT-HA composite coating with the electrophoretic deposition of 10 min showed the best corrosion resistance. The morphology of CNTs-HA composite coatings immersed in SBF solution rendered the formation of HA crystallites. In addition, in vitro cellular responses to the CNTs-HA composite coatings were assessed to investigate the proliferation and morphology of mouse cells 3T3 cell line.     

Single-walled carbon nanotube buckypaper and mesophase pitch carbon/carbon composites

Carbon/carbon composites consisting of single-walled carbon nanotube (SWCNT) buckypaper (BP) and mesophase pitch resin have been produced through impregnation of BP with pitch using toluene as a solvent. Drying, stabilization and carbonization processes were performed sequentially, and repeated to increase the pitch content. Voids in the carbon/carbon composite samples decreased with increasing impregnation process cycles. Electrical conductivity and density of the composites increased with carbonization by two to three times that of pristine BP. These results indicate that discontinuity and intertube contact barriers of SWCNTs in the BP are partially overcome by the carbonization process of pitch. The temperature dependence of the Raman shift shows that mechanical strain is increased since carbonized pitch matrix surrounds the nanotubes.     

Kinetics of pyrolytic carbon infiltration for the preparation of ceramic/carbon and carbon/carbon composites

Carbon/carbon and zeolite/carbon composites have been prepared by pyrolytic carbon infiltration of organic and inorganic substrates with different porous structures. The chemical vapour infiltration kinetics of these substrates has been studied in a thermogravimetric system at atmospheric pressure, using benzene as pyrolytic carbon precursor. The rate of pyrolytic carbon infiltration seems to depend on the porosity of the substrate available to the pyrolytic carbon precursor, irrespective of the nature of the substrate studied. Activation energy values of about 180 kJ/mol were found for the different substrates used in the temperature range of 700-800 °C, where the cracking reaction of benzene takes place, predominantly, in a heterogeneous form. At higher temperatures homogeneous reactions compete with heterogeneous ones and higher values of activation energies (280-380 kJ/mol) were obtained. The oxidation of the pyrolytic carbon deposited on the different substrates studied takes place in the same range of temperature, which suggests the presence of a similar pyrolytic carbon structure on substrates of different nature or a similar accessibility to the deposited layer.     

Mechanical behavior of two-dimensional carbon/carbon composites with interfacial carbon layers

Effect of interfacial carbon layers on the mechanical properties and fracture behavior of two-dimensional carbon fiber fabrics reinforced carbon matrix composites were investigated. Phenolic resin reinforced with two-dimensional plain woven carbon fiber fabrics was used as starting materials for carbon/carbon composites and was prepared using vacuum bag hot pressing technique. In order to study the effect of interfacial bonding, a carbon layer was applied to the carbon fabrics in advance. The carbon layers were prepared using petroleum pitch with different concentrations as precursors. The experimental results indicate that the carbon/carbon composites with interfacial carbon layers possess higher fracture energy than that without carbon layers after carbonization at 1000°C. For a pitch concentration of 0.15 g/ml, the carbon/carbon composites have both higher flexural strength and fracture energy than composites without carbon layers. Both flexural strength and fracture energy increased for composites with and without carbon layers after graphitization. The amount of increase in fracture energy was more significant for composites with interfacial carbon layers. Results indicate that a suitable pitch concentration should be used in order to tailor the mechanical behavior of carbon/carbon composites with interfacial carbon layers.     

Microstructure of carbon/carbon composites reinforced with pitch-based ribbon-shape carbon fibers

Carbon/carbon composites were prepared with ribbon-shape pitch-based carbon fibers serving as reinforcement and thermosetting PFA resin and thermoplastic pitch as matrix precursors. The composites were heat treated to 1000, 1600 and 2700 °C. Microstructural transformations taking place in the reinforcement, carbon matrix, and the interface were studied using polarized optical and scanning electron microscopy. The fiber/matrix bond and ordering of the carbon matrix in heat-treated composites was found to vary depending on the heat treatment temperature of the fibers. Stabilized fiber cleaved during carbonization of resin-derived composites. In contrast, fibers retain their shape during carbonization of pitch matrix composites. Optical activity was observed in composites made with carbonized fibers; the extent decreases with increased heat treatment of the fibers. Studies at various heat treatment temperatures indicate that ribbon-shape fibers developed ordered structure at 1600 °C when co-carbonized with thermosetting resin or thermoplastic pitches.     

Porous carbon/carbon composites produced from carbon black and petroleum pitch

Granular porous carbon/carbon composites were prepared by mixing carbon black, petroleum pitch and a solvent, followed by granulating the mixture and carbonization of the resulting pellets in an inert atmosphere. The pore structure of this material is studied by mercury porosimetry and scanning electron microscopy. Based on the obtained results, a model for it is proposed. The effects of carbon black type used, filler/binder ratio, heat treatment temperature and mixing time on surface area, total pore volume and strength of the finished pellets were investigated. Comparison with activated carbons indicates that the investigated material can find industrial applications as a catalyst support and as an adsorbent for adsorption of large molecules due to the meso- and macroporous structure and low ash content.     

Friction behaviors of carbon/carbon composites with different pyrolytic carbon textures

Friction and wear properties of carbon/carbon (C/C) composites with a smooth laminar (SL), a medium textured rough laminar (RL) and a high textured RL pyrolytic carbon texture were investigated with a home-made laboratory scale dynamometer to simulate airplane normal landing (NL), over landing (OL) and rejected take-off (RTO) conditions. The morphology of worn surfaces at different braking levels was observed with scanning electron microscopy. The results show that C/C composites with RL have nearly constant friction coefficients, stable friction curves and proper wear loss at different braking levels, while friction coefficients of C/C composites with SL pyrolytic carbon decrease intensely and their oxidation losses increase greatly under OL and RTO conditions. Therefore, C/C composites with a high and medium textured RL pyrolytic carbon may satisfy the requirements of aircraft brakes. The good friction and wear properties of C/C composites with RL are due to the properties of RL, which leads to a uniform friction film forming on the friction surface.