条缝式纤维空气分布系统速度压力性能实验

以干冰作为发烟物质可视化研究了条缝式纤维空气分布系统表面空气的流动情况,研究了条缝式纤维空气分布系统表面空气流速和内部空气压力(总压、静压和动压)沿径向和轴向方向的分布特性。实验结果表明:采用条缝式纤维空气分布系统送风时,部分空气以较低的流速从纤维孔隙中向外渗透,其余空气则以较高的流速从孔口处射出,方向垂直于纤维壁面,各股射流流态相似,到达一定射程后开始掺混,形成类似条缝式的气流;表面空气流速(渗透流速和射流流速)沿管长方向(轴向方向)近似均匀分布;空腔内部空气径向总压、静压近似均匀分布,动压呈辐射状向壁面处递减;轴向总压和和动压逐渐减小,静压逐渐增加,且入口处压力梯度较大。     

凝固条件对PBO初生纤维孔结构及拉伸强度的影响

研究了凝固浴条件对PBO初生纤维孔结构及拉伸强度的影响。结果表明：在考察范围内,随凝固浴温度的降低、凝固浴浓度的增大,初生纤维的孔体积总量减小,孔径分布范围变窄,优势孔的孔径分布峰数量减少,初生纤维的强度增大。随着凝固牵伸倍率（2～10）的增加,孔体积减小、优势孔的孔径分布峰数量减少;但当牵伸倍率大于10倍时,总孔体积和优势孔的孔径分布峰数量开始增加;初生纤维的强度则随牵伸倍率的增大而增长。     

聚丙烯腈基炭纤维中微孔的演变规律

利用二维小角X射线散射技术(SAXS),结合纤维孔结构解析理论及分形原理得到了炭纤维形成过程中纺丝、预氧化、低温和高温炭化等四个阶段样品的微孔结构信息。结果表明:原丝中孔隙沿纤维轴向择优取向,呈长梭状,其长轴与短轴的平均尺寸分别为24.3nm和19.2nm,长径比为1.27。遗留到预氧化阶段的原丝孔洞使得预氧化纤维出现高达1.85的长径比极大值,这可能与原丝线性结构向预氧丝耐热梯形结构转化有关。炭化阶段微孔尺寸迅速减小,长轴、短轴分别达到3.56nm和2.85nm左右,长径比也减小至1.24。分形状态研究表明:表面分形维数DS值介于2.42～2.88之间,且随工艺的进行逐渐增大,低温炭化阶段变化幅度较大,说明各级产品在微观结构上越来越复杂,亦证明低温炭化是促进炭纤维微观结构转变的重要的工艺段。     

静电纺丝法制备聚苯乙烯微纳米纤维膜及其过滤性能

采用静电纺丝法制备聚苯乙烯(PS)微纳米纤维膜,研究了静电纺丝工艺对PS纤维膜微观形貌、纤维直径以及孔隙尺寸分布的影响,并表征了其对固体颗粒物的过滤性能。结果表明:随着纺丝电压和接收距离的增加,PS纤维膜的直径和孔隙尺寸均减小且分布集中,随着推进速率增加,PS纤维膜的直径和孔隙尺寸逐渐增加且分布范围变宽;当纺丝电压为24kv,收集距离为24cm,推进速率为0.318mL/h时所得PS纤维膜的直径和孔隙中位径分别为940.1nm和1979.4nm,过滤尺寸范围为0.1~35μm的固体颗粒后,剩余颗粒的平均粒径仅为2.19μm。     

乙醇火焰燃烧制备螺旋碳纳米纤维及结构分析

采用乙醇火焰燃烧, 借助于基板材料上涂敷锡盐作为催化剂前驱体, 制备了螺旋结构碳纳米纤维; 借助于扫描电子显微镜、透射电子显微镜、XRD和拉曼光谱等分析了螺旋碳纤维的形貌和结构. 螺旋碳纳米纤维螺旋直径约为100nm, 纤维直径约为50nm, 螺距约80nm. 螺旋碳纤维的石墨层方向基本垂直于轴向, 近似鱼骨型结构, 相邻碳层间距为0.34nm. 借助于高分辨电子显微镜分析了螺旋碳纳米纤维的形成机理, 认为碳原子沿催化剂SnO₂各晶面析出速度不同是形成螺旋碳纳米纤维的主要原因.     

不同损伤源对玄武岩纤维增强混凝土孔隙结构变化特征的影响

为了研究玄武岩纤维增强混凝土在高温和力学两种损伤源下的孔隙结构变化特征，采用核磁共振(NMR)和扫描电镜(SEM)技术，观察试件T₂谱分布、孔径分布、孔洞和裂隙发育情况。结果表明，高温作用后基准混凝土、短玄武岩纤维增强混凝土、长玄武岩纤维增强混凝土均呈微孔数量不断减小、介孔数量不断增加的趋势。通过对比发现，长玄武岩纤维增强混凝土T₂谱主峰孔隙数量最多，孔径分布最大。以长玄武岩纤维增强混凝土为例，研究在高温和力学两种损伤源下玄武岩纤维增强混凝土的孔隙结构变化特征。发现弛豫时间在0.1~10 ms内高温损伤下玄武岩纤维增强混凝土的孔隙数量大于力学损伤下的孔隙数量，且随着温度升高，T₂谱主峰向右偏移，随着荷载增加，T₂谱主峰几乎不发生变化，表明温度升高更能加剧损伤，每级温度作用下新生孔径不断增大。T₂谱主峰幅值和孔径分布随温度升高不断增大，随荷载增加出现先减小后增大的现象，表明高温作用对混凝土直接构成损伤，而力学作用使混凝土先密实再产生损伤，SEM观察得到了相同的结论。      

聚丙烯腈基炭纤维制备过程中的表面形态和结构研究

为了制备高性能的聚丙烯腈基炭纤维，用SEM和TEM等分析方法跟踪炭纤维生产全过程中纤维微观结构所发生的变化。在湿法纺丝中，控制预牵伸倍数为7倍，调整凝固浴的温度为16℃时，可纺出截面近似圆形的高质量原丝，纤维的截面和表面的微纤比较紧凑，表面缺陷和裂纹较少；原丝经过预氧化后仍保持原来的微原纤结构，纤维外部表层的石墨微晶较大，所含孔隙较少，内部的微晶较小且含有大量孔隙。用高锰酸钾改性原丝能够得到质量优异的预氧化纤维，改性预氧丝的纤维基面增加比未改性的多，基面沿纤维轴排列的程度更高。所制备的炭纤维具有由原丝演变来的微观结构，微纤沿纤维轴高度取向，微纤之间有细长的孔隙，并堆砌在一起形成枝化微纤的伸展网络，炭纤维截面形状也近似为圆形。合理调整制备工艺，得到了强度为3．6GPa-4．2GPa，断裂延伸率为1．6％-1．8％，模量为235GPa-240GPa的聚丙烯腈基炭纤维。结果表明：炭纤维的微观组织结构与原丝的微观组织结构密切相关，高强度、高取向度和结构均匀的原丝是获得高强度和高模量炭纤维的前提。     

基于孔结构分析的多尺度聚丙烯纤维混凝土耐久性

为研究不同尺度纤维对混凝土耐久性的影响,借助压汞法技术测定多尺度聚丙烯纤维混凝土内部孔隙的孔径大小及分布情况,通过孔径分布、最可几孔径、平均孔径等孔隙特征参数的变化情况,探究多尺度聚丙烯纤维在抗渗试验、抗硫酸盐侵蚀循环试验、抗冻融试验中对混凝土耐久性的影响.研究结果表明:不同尺度聚丙烯纤维的掺入,均使得混凝土内部多害孔...     

CA SELECTS Carbon Graphite Fibers

高强碳纤维丙烯腈原丝的制备Makishima,Toshihiro,Kawakami,Michiro JP04 91,230 湿法纺丙烯腈含量≥93%的聚合物,得到孔体积(Vg)<1.2cm~3/g、最大孔径(Rg)<300A的纤维,首先在水膨胀状态下牵伸1—6倍,最终的牵伸倍数≥8,使Vg与牵伸后纤维孔体积之比>1,Rg与牵伸后纤维最大孔径之比≥1。如98—2的丙烯腈—甲基丙烯酸共聚物湿纺,水膨胀状态下     

硝苯地平在球状活性炭中的吸附及缓释行为

采用球状活性炭作为硝苯地平药物载体,借助N2吸附仪表征了球状活性炭的比表面积和孔结构,利用SEM表征了球状活性炭的表面形貌,通过考察球状活性炭比表面积、孔隙结构与吸附性能和体外释放性能的关系,研究了球状活性炭对硝苯地平的吸附及缓释行为。结果表明:比表面积大、孔隙结构发达、孔径分布集中在2nm~5nm之间的中孔型活性炭,对硝苯地平的吸附能力较强,吸附量可达19.5mg/g;所制缓释微丸缓释效果良好,在接近人体胃液介质中累计释放率达到19.2%;球状活性炭对硝苯地平的释放动力学符合Higuchi模型,药物基本以恒定速率主动释放。     

静电纺丝制备多孔醋酸纤维素超细纤维

采用静电纺丝法制备了大量尺寸为60 nm～750 nm椭圆形多孔醋酸纤维素(CA)纤维.利用扫描电镜(SEM)表征了纤维及孔的形态和大小,液氮吸附法(BET)测定了纤维的比表面积.探讨了溶刑种类、溶剂配比和溶液浓度对多孔CA纤维的影响.通过调节纺丝溶液性质和纺丝参数,CA纤维表面多孔大小和分布密度是可调控的.成孔机理是...     

A study of ultrafine porosity in hydrated cements using small angle neutron scattering

Small angle neutron scattering makes use of the neutron contrast due to differences in the scattering power between small, particulate regions and the general background medium, and has only very recently been applied to study the porosity in hydrated cement systems. The technique is applied to pore sizes below approximately 30 nm and produces data on pore size distribution, pore volume and pore shape without recourse to drying techniques and the potential structural degradation which may occur. Results indicate a bi-modal pore size distribution at approximately 5 and 10 nm diameter, with a total volume accounting for some several percent of the total cement block. The best estimate of the 5 nm pore shape is considered to be curved-faced tetrahedra. The pores appear to be relatively unaffected by changes in the water-to-cement ratio or accelerating admixture investigated, but macro defect free cement does show significant pore structure alteration.     

Ultrafine porous fibers electrospun from cellulose triacetate

Ultrafine porous cellulose triacetate (CTA) fibers were prepared by electrospinning with methylene chloride (MC) and a mixed solvent of MC/ethanol (EtOH) and their intra- and inter-fiber pore structures was investigated. Ultrafine porous CTA fibers electrospun with MC had isolated circular shape pores with a narrow size distribution in the range of 50–100 nm. In the case of ultrafine CTA fibers electrospun with MC/EtOH (90 / 10 v/v), they had interconnected larger pores in the range of 200–500 nm. These porous structures were induced by phase separation resulting from the rapid evaporation of solvent during the electrospinning process. However, non-porous corrugated fibers were obtained from MC/EtOH (85 / 15 v/v) and MC/EtOH (80 / 20 v/v) due to their lower vapor pressure. The pore sizes in ultrafine CTA fibers electrospun with MC showed a bimodal distribution centered at ∼17 and ∼64 nm. CTA fibers electrospun with MC/EtOH (90 / 10 v/v) showed the greatest porosity due to their larger intra-fiber pores and fiber diameter.     

Synthesis and characterization of magnetically active carbon nanofiber/iron oxide composites with hierarchical pore structures

Polyacrylonitrile (PAN) solution containing the iron oxide precursor iron (III) acetylacetonate (AAI) was electrospun and thermally treated to produce electrically conducting, magnetic carbon nanofiber mats with hierarchical pore structures. The morphology and material properties of the resulting multifunctional nanofiber mats including the surface area and the electric and magnetic properties were examined using various characterization techniques. Scanning electron microscopy images show that uniform fibers were produced with a fiber diameter of ～600?nm, and this uniform fiber morphology is maintained after graphitization with a fiber diameter of ～330?nm. X-ray diffraction (XRD) and Raman studies reveal that both graphite and Fe(3)O(4) crystals are formed after thermal treatment, and graphitization can be enhanced by the presence of iron. A combination of XRD and transmission electron microscopy experiments reveals the formation of pores with graphitic nanoparticles in the walls as well as the formation of magnetite nanoparticles distributed throughout the fibers. Physisorption experiments show that the multifunctional fiber mats exhibit a high surface area (200-400?m(2)?g(-1)) and their pore size is dependent on the amount of iron added and graphitization conditions. Finally, we have demonstrated that the fibers are electrically conducting as well as magnetically active.     

Effect of the pore shape on the thermal conductivity of porous media

The effect of the pore shape on the thermal conductivity of porous media is studied in this work, considering random and aligned distributions of spheroidal pores within the matrix. This is done by using the Bruggeman differential effective medium theory which is suitable for pores with different sizes, as is usually the case of practical interest. The obtained results can be applied for porous media with low as well as high porosities, and they show that: (1) the effect of the pore shape becomes stronger as the porosity increases. (2) The thermal conductivity for randomly oriented pores takes its maximum value for spherical pores and this value is the geometric average of the thermal conductivities along the three principal axes of the pores, when they are aligned. (3) In the case of aligned pores, the thermal conductivity along a principal axis increases with its length, in such a way that it is larger along the principal axis with longer dimensions. The predictions of the proposed approach are in good agreement with reported data and are expected to be useful to provide insights on the thermal behavior of porous media.     

Stretching DNA using the electric field in a synthetic nanopore

The mechanical properties of DNA over segments comparable to the size of a protein-binding site (3-10 nm) are examined using an electric-field-induced translocation of single molecules through a nanometer diameter pore. DNA, immersed in an electrolyte, is forced through synthetic pores ranging from 0.5 to 1.5 nm in radius in a 10 nm thick Si(3)N(4) membrane using an electric field. To account for the stretching and bending, we use molecular dynamics to simulate the translocation. We have found a threshold for translocation that depends on both the dimensions of the pore and the applied transmembrane bias. The voltage threshold coincides with the stretching transition that occurs in double-stranded DNA near 60 pN.     

Structural features of polyacrylonitrile-based carbon fibers

The structural changes as functions of spinning conditions and heat treatments were investigated with respect to the structural feature of PAN-based carbon fibers by scanning tunneling microscopy (STM). The distinct granule structure on the cross section of both high tensile strength and high modulus carbon fibers was observed by SEM, while slender granule-shape domain on the longitudinal surface was revealed by STM. A structure model was proposed, which depicted that the PAN-based carbon fiber was a heterogeneous structure composed of aggregated mesostructural domains. These domains were closely arranged into spiral form along fiber axis, allowing the fibers have high strength and good elongation. The initial shape and size of domains was determined by the precursor composition and spinning conditions and also strongly depended on the heat-treated temperature and stretching conditions. The smaller or slender domain, the higher tensile strength obtained for fibers. We expect that the PAN-based carbon fiber with better performance should be produced by optimizing the size and shape of these domains.     

Templated pores in hydrogels for improved size selectivity in gel permeation chromatography

The pore structures of cross-linked polyacrylamide gels can be altered by polymerizing in the presence of high concentrations of unreactive, micellar surfactant cosolutes which act as "templates". Removal of surfactant after polymerization is expected to leave pores with the approximate shape and dimensions of the surfactant micelles. A simple model was developed to simulate gel permeation chromatography (GPC) separations of globular proteins on templated gels. The model assumes that the partition coefficient for sieving of a protein is equal to the fraction of gel volume accessible to a sphere with a radius equal to the protein Stokes radius. The total gel volume is considered to include a fraction that is a conventional, random gel matrix and a remaining fraction contributed by templated pores. The pore size distribution of the conventional gel was estimated using the Ogston equation, which approximates the matrix as a random collection of long, thin, rigid fibers. Templated pores were assumed to have a Gaussian distribution of radii centered about some mean determined by the micelle radius. In comparison to conventional media, gels with templated pores are predicted to exhibit more sharply defined exclusion limits and improved resolution over a narrow size range centered on the mean templated pore size. Selectivity and resolution are expected to increase as the volume fraction of templated pores is increased and as the dispersion of templated pore radius is decreased. Small changes in template radius lead to large changes in the molecular weight range of optimal separation of globular proteins. It should be possible to create a series of GPC media that collectively offer high resolution over the molecular weight range of most globular proteins of interest.     

Mechanism of Pt loading on multi-walled carbon nanotubes

Microwave treatment of multi-walled carbon nanotubes (MWCNTs) with nitric acid (HNO3) and 0.2 M sodium chlorate (NaClO3) can generate and enhance defects on the surfaces of MWCNTs. These defects are the important sites to load Pt nanoparticles (NPs). We investigated the defect induced Raman spectra and observed a decrease in the R-values (D-band/G-band peak ratio) and a slight up-shift of the both peaks as the amount of loaded Pt NPs increased. Using the Brunauer-Emmett-Teller (BET) method, we observed that the pore size distribution and the pore volume changed according to the amount of Pt NPs loaded. Fewer micropores and mesopores were observed on MWCNTs loaded with Pt NPs. Based on the pore size distribution calculated from the BET results, Pt NPs loaded mainly on pores/defects with a size of 2-8 nm. Transmission electron microscopy and Raman spectroscopy results confirmed that most well-crystallized Pt NPs loaded on the surface defect sites and pores spontaneously through the exchange of electrons between Pt and C atoms.     

基于图像技术的喷墨打印纸表面孔隙分析

目的利用图像技术量化纸张表面孔隙结构,并分析孔隙与纸张表面性能的关系。方法使用拉普拉斯算子和中值滤波,处理喷墨打印纸表面扫描电镜图片(SEM),提取出喷墨打印纸表面孔隙结构,对不同粒径分布的Si O2形成的涂层孔隙进行量化和对比,得到孔的个数、面积、面积方差及面积分布情况,探讨了孔面积和分布对纸张表面性能如光泽度、粗糙度、平滑度的影响。结果 Si O2粒径分布影响纸张表面孔隙的个数、面积和均匀程度,进一步影响纸张的表面性能。Si O2粒径分布越宽,形成的孔隙个数越多,面积越大,孔隙越不均匀,所得到的表面越粗糙,平滑度和光泽度也越低。结论利用图像技术可以量化涂层表面的孔隙情况,为喷墨打印纸表面孔隙及表面性能的研究提供了可以借鉴的方法。