聚丙烯腈基碳纤维中微孔洞的一维多取向小角X射线散射研究

应用一维多取向小角X射线散射(SAXS)方法研究了聚丙烯腈(PAN)基碳纤维中微孔洞的形态.结果表明,这些微孔洞沿纤维轴方向呈针状,并与纤维轴呈Φ=14°角的取向排列;微孔洞投影在碳纤维横截面上的平均半径R=1.14nm,投影在碳纤维轴向上的平均长度L=17.97nm.建立的一维多取向SAXS方法可以得到若干二维SAXS方法才能得到的微孔洞形态及分布信息等参数(如Φ和L),且在各种纤维的微孔洞或微纤维的表征方面具有一定的普适性.     

污泥热解过程中焦的表面孔隙结构分形生长

主要对污水污泥在高温热解和低温热解条件下热解焦炭的表面孔隙结构特性进行了研究。结果表明,污泥热解过程中随着挥发分的析出,污泥热解焦炭的孔隙结构逐渐发达。低温和高温热解过程中挥发分的析出,使得孔径为3.75 nm的孔得到了极大的发展。通过对污泥热解焦炭的N2吸附过程进行的分形分析发现,不同停留时间低温和高温热解焦炭的表面分形维数可以分为FD-1和FD-2。其中,FD-1主要表征了较大孔(0.86 nm)的表面分形维数,FD-2则主要表征了超微孔(0.86 nm)的表面分形维数。随着热解停留时间的延长,FD-1和FD-2逐渐增大并趋于稳定。与高温热解焦炭的超微孔表面分形维数相比低温热解焦炭出现了较大的增加,而较大孔的表面分形维数则相对低温热解焦炭未见有较大的改变。     

高性能聚丙烯腈碳纤维中纳米级微孔分析表征研究

高性能碳纤维由于其优异的性能,在各行各业中具有广泛应用。为深入研究碳纤维内结构与其性能之间的相关性,本文应用小角X射线散射研究了一系列典型的聚丙烯腈碳纤维样品,分析了样品内微孔的尺寸及取向,讨论了强度和模量与微孔的相关性,研究结果表明:高性能碳纤维的力学强度和模量与碳纤维内微孔缺陷的长度和长径比有关,控制碳纤维内微孔缺陷的长度有望实现高强碳纤维的制备,控制牵伸倍率从而控制碳纤维内微孔的长径比有望实现高模碳纤维的制备。     

焦化过程半焦孔隙结构时空变化规律的实验研究——孔结构的分形特征及其变化

应用分形理论的概念，结合压汞法测得的半焦孔隙结构数据，建立孔结构分形特征模型，考察了焦化过程中不同焦化温度、不同横向空间位置半焦孔隙结构分形特征及其变化规律。结果表明，孔径大于5μm 的孔不具有分形特征，孔径为20nm～5μm孔的孔隙结构具有分形特征，其分形维数为2.45～2.83，可以用分形维数定量表征孔隙结构；相同空间位置下，半焦孔结构分形维数低温时较高，随温度逐渐升高先减小，然后增大再减小；同一空间位置不同温度下分形维数的变化量较小(< 0.15)，表明温度对半焦孔隙结构复杂程度的影响不明显；相同焦化温度下，半焦中心和边缘处的孔结构分形维数大于中间部位，表明中心位置和边缘位置处的孔隙结构要比中间位置处的复杂。     

几种植物基活性炭材料的孔结构与吸附性能比较——(I)孔结构表征

测定了3种植物基活性炭材料:椰壳活性炭 (CAC4)、剑麻茎基活性炭 (SSAC) 和剑麻基活性碳纤维 (SACF) 的氮吸附等温线,并用不同的理论方法对其孔结构进行了分析和表征。结果表明:CAC4为微孔型,孔径分布集中且大部分是0.7nm以下的极微孔;在相同条件下制备的SSAC和SACF孔分布较为相似,都呈多分散性,结构中除微孔外,还含有丰富的中孔,中孔率均超过50%以上。两者相比,SACF的中孔量和平均孔径更大。3个样品的形态特征和孔结构虽然不同,但其吸附过程都可以用微孔多段填充机理来解析。     

几种植物基活性炭材料的孔结构与吸附性能比较--(Ⅰ)孔结构表征

测定了3种植物基活性炭材料：椰壳活性炭(CAC4)、剑麻茎基活性炭(SSAC)和剑麻基活性碳纤维(SACF)的氮吸附等温线，并用不同的理论方法对其孔结构进行了分析和表征．结果表明：CAC4为微孔型，孔径分布集中且大部分是0．7nm以下的板微孔：在相同条件下制备的SSAC和SACF孔分布较为相似，都呈多分散性，结构中除微孔外，还含有丰富的中孔，中孔率均超过50％以上．两者相比，SACF的中孔量和平均孔径更大，3个样品的形态特征和孔结构虽然不同，但其吸附过程都可以用微孔多段填充机理来解析。     

纤维催化剂的孔结构特征Ⅱ．碳纤维载体的孔结构研究

测量了不同氧化深度的三类碳纤维(丙烯腈长丝、丙烯腈碳毡和粘胶碳毡)的低温氮吸附等温线。Pickett修正三参数BET方程能很好地关联这些等温线,三类碳纤维具有不同的n值。应用V—n作图法获得了它们的主要孔结构参数,利用Mp—Wp和D-R—Wp的组合方法获得了它们的孔分布数据。结果指出,总表面积、总孔体积、微孔表面积和微孔体积的大小与碳化温度和碳化原料有关,并且随氧化深度而增加;但非微孔表面积基本保持恒定,约为4—12m~2/g。微孔分布的最可几孔半径随氧化深度增加而减小,各类样品的非微孔分布几乎落在同一条孔分布曲线上。     

高取向度碳纤维原丝制备工艺研究进展

碳纤维原丝的性能好坏在很大程度上决定着碳纤维的最终性能。缺陷少、细旦化、高取向、高纯化等是高性能原丝的基本要求。其中原丝的取向度在很大程度上决定了碳纤维在预氧化、碳化过程中形成的类石墨片层的取向结构，这会影响碳纤维最终的强度和模量，所以制备出高取向的碳纤维原丝具有重大意义。本文聚焦于高取向碳纤维原丝制备工艺，首先分析了高取向原丝的重要性，然后在原丝制备工艺上将纺丝方法以及牵伸工艺对取向度的影响进行总结分析，同时介绍了微积分纳米层叠法和高取向复合纤维原丝的制备工艺，指出优质的初生纤维以及具有稳定化取向排列的原丝是制备高取向碳纤维原丝的关键，以期对提升原丝的取向度进而提升碳纤维性能的研究有所贡献。     

以离子液体为结构导向剂合成有序超微孔二氧化硅

在酸性条件下, 以1-十六烷基-3-甲基溴化咪唑为表面活性剂合成了具有有序超微孔结构的二氧化硅材料, 所合成的材料具有较高的比表面积和二维六方有序的孔结构, 样品的孔径尺寸为1.8 nm.     

酚醛树脂基球形微-介双阶多孔炭的软模板法制备

将苯酚和甲醛在碱性条件下聚合,然后在酸性条件下与软模板剂F127自组装形成中间相,经高温煅烧合成球形微-介双阶多孔炭。 通过扫描电子显微镜、透射电子显微镜、氮气吸附-脱附和热重分析技术对样品进行了形貌观察和性能测试。 结果表明,pH值、软模板剂用量和活化温度对样品形貌有调控作用。 当软模板剂F127的质量分数为20%、pH值为0.5和活化温度为700 ℃时,可制备出直径为100～200 nm的球形炭,球形粒子分散均匀,排列规整,呈明显蠕虫状排列的孔隙结构,比表面积为503 m2/g,孔容积0.416 cm3/g,介孔孔径集中分布在2.9 nm,微孔主要分布在1.3 nm。 随着活化温度升高,炭球的比表面积和孔容积增大,平均孔径减小。 F127的热解形成介孔结构,碳前驱体高温下的径向收缩形成微孔结构。     

预氧化过程中张力对聚丙烯腈预氧化纤维微缺陷结构的影响

本文报道用同步辐射二维小角X射线散射(2D\|SAXS)研究预氧化过程中张力对PAN纤维缺陷的影响.     

Effects of ultra-high temperature treatment on the microstructure of carbon fibers

The microcrystalline structure and microvoid structure in carbon fibers during graphitization process(2300-2700 °C) were characterized employing laser micro-Raman scattering(Raman), X-ray diffraction(XRD), small angle X-ray scattering(SAXS), and high-resolution transmission electron microscopy(HR-TEM). The crystalline sizes(L_a, L_c) increased and interlayer spacing(d_(002)) decreased with increasing heat treatment temperature(HTT). The microvoids in the fibers grew up and contacted to the neighbors with the development of microcrystalline. In addition, the preferred orientation of graphite crystallite along fiber axis decreased and microvoids increased. The results are crucial for analyzing the evolution of microstructure of carbon fibers in the process of heat treatment and important for the preparation of high strength and high modulus carbon fibers.     

2D SAXS/WAXD analysis of pan carbon fiber microstructure in organic/inorganic transformation

Structure of PAN fibers during pre-oxidation and carbonization was studied using two dimensional small angle X-ray scattering/wide angle X-ray diffraction(2D SAXS/WAXD).The SAXS results show that during pre-oxidation between 180 ℃ and 275 ℃,the volume content of microvoids increases with the temperature increasing,which may be one of reasons for the decrease of tensile strength of pre-oxidized fibers.253 ℃ was the critical transition temperature,the length,diameter,aspect ratio and orientation distribution of microvoids increased with temperature before this temperature and decreased after this temperature.After the high temperature carbonization,lots of spindly microvoids formed.WAXD patterns demonstrate that the crystallite size of PAN fibers first increased before 230 ℃ and then decreased with the increase of temperature during the pre-oxidation.The diffraction peak of PAN fibers at 2θ≈ 17° almost disappeared at the end of preoxidation while the diffraction peak of aromatic structure at 2θ≈ 25° appeared at 253 ℃.During carbonization,the peak intensity at 2θ≈ 25° increased apparently due to the formation of graphite structure.The results obtained give a deep understanding of the microstructure development in the PAN fibers during pre-oxidation and carbonization,which is important for the preparation of high performance carbon fibers.     

Study of Microstructure of High-Surface-Area Polyacrylonitrile Activated Carbon Fibers

High-surface-area polyacrylonitrile (PAN) activated carbon fibers having different pore size distribution activated by KOH were investigated. Nitrogen adsorption, XRD, SEM, and TEM were used to characterize the microstructure of PAN-ACFs. The specific surface area of samples was calculated from the standard BET method, and micropore surface area and volume were obtained from the Horvath-Kawazoe equations. The average pore size and characteristic energy were calculated by the Dubinin-Radushkevich equation according to the multistage adsorption mechanism. The whole pore size distribution was calculated by employing the regularization method according to the density functional theory, which is based on a molecular model for the adsorption of nitrogen in porous solids. It was shown that the isotherms were type I, the pore size was around 0.4-0.8 nm, and the mesorpore size was around 2-4 nm. The XRD pattern showed that PAN-ACFs activated by KOH are of amorphous material composed of very small crystallites. The SEM and TEM results showed that the monograph differs with differing activation degree, and the network is uniform or disordered. That all of these methods are in good agreement with one another. Copyright 2001 Academic Press.     

PREPARATION OF ACTIVATED CARBON FIBER AND THEIR XENON ADSORPTION PROPERTIES（Ⅱ）-XENON ADSORPTION PROPERTIES

The adsorption of xenon from air has an interest in the monitoring of nuclear explosion oraccident, or in the treatment of nuclear waste gas. In this paper, the pore structure of several series ofactivated carbon fibers has been characterized. The adsorption properties of xenon on theseactivated carbon fibers under different temperatures have been studied in details. The results showthat the xenon adsorption amount on activated carbon fibers do not increase with specific surfacearea of adsorbents, but are closely related to their pore size distribution. Pores whose radius equal toor narrow than 0.4nm would be more advantageous to the adsorption of xenon.     

PREPARATION OF ACTIVATED CARBON FIBER AND THEIR XENON ADSORPTION PROPERTIES (II)-XENON ADSORPTION PROPERTIES

1. INTRODUCTION The adsorption and concentration of xenon has practical application interest in the purification of radioactive waste gas released from nuclear plant operation. Moreover, the monitor of xenon isotopic, derived from nuclear explosion or nu…     

Ordered mesoporous silica with large cage-like pores: structural identification and pore connectivity design by controlling the synthesis temperature and time

FDU-1 silicas with large cage-like pores (diameter about 10 nm) were synthesized under acidic conditions from tetraethyl orthosilicate in the presence of a poly(ethylene oxide)-poly(butylene oxide)-poly(ethylene oxide) triblock copolymer template B50-6600 (EO(39)BO(47)EO(39)). High-resolution transmission electron microscopy and small-angle X-ray scattering provided strong evidence that FDU-1 silica synthesized under typical conditions is a face-centered cubic Fm3m structure with 3-dimensional hexagonal intergrowth and is not a body-centered cubic Im3m structure, as originally reported. Samples synthesized in a wide range of conditions (initial temperatures from 298 to 353 K; hydrothermal treatment at 333-393 K) exhibited similar XRD patterns and their nitrogen adsorption isotherms indicated a good-quality cage-like pore structure. The examination of low-pressure nitrogen adsorption isotherms for FDU-1 samples, whose pore entrance diameters were evaluated using an independent method, allowed us to conclude that low-pressure adsorption was appreciably stronger for samples with smaller pore entrance sizes. This prompted us to examine low-pressure adsorption isotherms for a wide range of samples and led us to a conclusion that the FDU-1 pore entrance size can be systematically enlarged from about 1.3 nm (perhaps even lower) to at least 2.4 nm without an appreciable loss of uniformity by increasing the temperature of the hydrothermal treatment or the initial synthesis. Further enlargement of pore entrance size was achieved for sufficiently long hydrothermal treatment times at temperatures of 373 K or higher, as seen from the shape of nitrogen desorption isotherms. This allowed us to obtain samples with uniform pore sizes, high adsorption capacity, and with pore entrances enlarged so much that their size was similar to the size of the pore itself, resulting in a highly open porous structure. However, in the latter case, there was evidence that the pore entrance size distribution was quite broad.     

Using collagen fiber as a template to synthesize hierarchical mesoporous alumina fiber

Hierarchical mesoporous alumina fiber was synthesized by using collagen fiber as the template, and characterized by means of scanning electron microscopy, transmission electron microscopy, N2 adsorption techniques, X-ray photoelectron spectroscopy, and X-ray diffraction. The alumina fiber obtained is approximately 1-4 microm in outer diameter and 0.5-1 mm in length. The pore size distribution of the alumina fiber is narrow (2-20 nm), and its pore size is controllable by varying preparation methods. This study indicates that collagen fiber, which has hierarchical supermolecular structure, could be used as an ideal template to prepare well-defined porous metal oxide fibers.     

Synthesis and characterization of transparent silica-based aerogels using methyltrimethoxysilane precursor

Silica-based aerogels with high transparency and high bending strength were prepared using methyltrimethoxysilane and non-ionic surfactant under supercritical drying condition of CO₂. Non-ionic surfactant, ethylene oxide/propylene oxide block copolymer, was appropriate to form the three dimensional-connected thinner fibers of silica skeletons, which was extruded by soaking the wet gel in hot water at 50 °C, resulting in the formation of porous materials having small pores with narrow size distribution. The transparency of aerogels increased with decreasing the pore size, reaching to higher than 65 and 88% at 400 and 600 nm wavelength, respectively, for 10 mm thickness of sample. The formation of fiber skeletons were discussed using small angle X-ray scattering experiments.