高模量PAN基炭纤维结构的表征与性能分析

利用扫描电镜(SEM)、广角X射线衍射(WARD)、小角X射线散射(SAXS)、拉曼(Raman)光谱、X射线光电子能谱(XPS)等测试技术对热处理温度2400℃～3000℃的PAN基炭纤维的微观结构、表面形貌及化学组成进行了表征,分析了材料的微观组织结构与宏观性能的关系.结果表明:随热处理温度的升高,炭纤维的强度下降,模量升高,表面化学活性降低.表现在乱层石墨间距d002逐渐减小,平均微晶尺寸La、Lc逐渐增大,石墨化程度不断提高,微孔缺陷尺寸增大,大孔洞所占总微孔缺陷比例增加,PAN基炭纤维表面的O/C值降低.     

PAN基碳纤维制备过程中微孔结构的形成与转变

利用扫描电镜(SEM)、小角X射线散射(SAXS)对PAN基碳纤维制备过程中不同阶段纤维的表面形貌、微孔结构进行了测试,计算了PAN基碳纤维制备过程中不同阶段微孔的大小、各微孔占总微孔的体积分数、微孔的平均尺寸及表面的分形维数,分析了碳纤维的微孔结构在制备过程中的形成与转变。结果表明,原丝内部微孔的平均尺寸较大,预氧化过程中、后期,纤维内部微孔的平均尺寸及各相微孔的体积分数都发生了较大变化。低温碳化后,纤维中微孔的平均尺寸减小,且大孔洞的体积分数增大。高温碳化后,微孔的平均尺寸进一步减小,大孔的体积分数增大。原丝的微孔表面比较粗糙,在预氧化过程中微孔表面的分形维数减小。低温碳化后,微孔表面的分形维数增加。高温碳化后,微孔的形状由曲面转变为曲线。     

PAN基碳纤维微观结构与其性能相关性研究

借助扫描电子显微镜(SEM)、透射电子显微镜(TEM)和小角x射线衍射(SAXS)等微观结构表征手段,对国内不同厂家生产的3种聚丙烯腈(PAN)基碳纤维内部存在的大孔和微孔等微观结构进行了系统测试、分析。研究结果发现,3种PAN基碳纤维内部都存在着大孔和微孔结构,且这些孔隙结构对碳纤维的机械性能有很大影响,若碳纤维的大尺寸孔洞少,而微孔分布均匀、沿纤维轴取向度高,则碳纤维的综合性能较高。     

PAN纤维微观结构与其性能相关性的研究

利用碘吸附法、扫描电子显微镜(SEM)、透射电子显微镜(TEM)和小角x射线(SAXS)等测试方法对国内外企业生产的几种聚丙烯腈(PAN)基碳纤维原丝的形貌结构、组织结构和孔分布等微观结构进行了系统的测试与研究。结果表明,各种PAN纤维的表面均有沟槽、裂纹等缺陷;内部都存在着尺寸分布不均的孔结构,包括大孔和微孔。对各种纤维原丝碘吸附的数值进行对比分析发现,日本三菱和东丽公司生产的PAN纤维碘吸附数值小,纤维的致密性较高。对各种PAN纤维的SAXS测试结果分析发现,PAN纤维内都存在尺寸分布一定且具有一定取向性的微孔结构。这些微观结构对PAN纤维的性能有着不同的影响作用,并决定着由其生产的PAN基碳纤维的结构与性能。     

聚丙烯腈纤维预氧化过程中微观结构的演变

利用扫描电镜(SEM)、广角X射线衍射(WAXD)和小角X射线散射(SAXS)对200～275℃范围内逐步预氧化的聚丙烯腈纤维的断面形貌与微观结构进行了测试.根据各样品的WAXD,SAXS数据,分别计算了预氧化纤维的微晶尺寸、纤维内微孔大小、小孔洞所占的体积分数及微孔的分形维数,分析了材料的微观组织结构在预氧化过程中的变化.结果表明:随着预氧化温度的升高,纤维的微晶尺寸先增大后减小,纤维内微孔的尺寸先减小后增大,小孔洞所占的体积分数不断增大,微孔的分形维数先减小后增大.     

热处理对PAN基碳纤维结构的影响

本文用X-射缦衍射技术,通过计算机进行背底扣除、劳伦滋-偏光因子校正,分峰,然后计算在不同温度热处理的PAN基碳纤维及沥青碳纤维的晶粒尺寸(L_a、L_ē),L_ē表示乱层结构中C轴方向层面堆砌的平均厚度,L_a表示乱层中网平面的平均直径,二者均随热处理温度的增加而增加。同时,还求取了PAN基纤维的芳构化指数随温度的变化,可用该指数表征PAN纤维热处理过程中环化的程度。     

PAN基稳定化纤维的微观结构

引言目前,PAN纤维被认为是制造碳纤维最重要,最有前途的原丝。PAN经220～330℃的热处理,改性成为具有不燃性的稳定化纤维,并且在高温炭化处理中也不会受到重大破坏,继而转变为有良好力学性能的碳纤维。碳纤维的稳定化过程包括相邻分子间的氧化交联反应和腈基环化反应。通常认为稳定化的速度随含氧气氛的稳定化温度和时间而增大。大多数化学家和纺织科学家已把兴趣集中在稳定化期间化学反应是怎样发生的及PAN纤维物理性能的变化情况。本文主要讨论有关稳定化纤维的形态及微观结构。     

PAN基碳纤维原丝致密性及其孔结构研究

利用碘吸附法、扫描电子显微镜（SEM）、透射电子显微镜（TEM）和小角x射线衍射（SAXS）等测试方法对国内外企业生产的几种聚丙烯腈（PAN）基碳纤维原丝的致密性及孔结构进行了较系统的测试与研究。结果表明,各种PAN原丝内部都存在着疏松的孔结构,致使其致密性较差,且孔结构的尺寸分布不均。PAN基碳纤维原丝的结构缺陷对其性能有着重要的影响作用。     

碳纤维微观结构表征:小角X射线散射

小角X射线散射技术(SAXS)是研究碳材料内部微孔结构的重要方法之一.当X射线照射到样品上时,如试样内部存在任何纳米尺度的密度不均匀区,在入射X射线束周围小角度范围内均会出现不同程度的X射线散射现象.基于此,利用SAXS不仅可以获得碳材料的孔结构信息,更微观的微电子密度起伏和较大尺度的微原纤结构信息都可以通过适当的方法解析出来.近年来,针对碳纤维等碳结构的SAXS解析理论逐渐深入,包括Debye相关距离理论等经典理论纷纷出现新的应用尝试,而Unified fit模型、"Ruland streak"法等的出现也使研究者对碳结构有了更新和更全面的理解.首先,准两相体系下碳纤维微观结构的SAXS分析取得突破.以De-bye相关距离理论为突破口对碳纤维散射体系类型进行分析时发现,碳纤维与其石墨化纤维在微观和介观尺度上存在显著差异性,其差异性的根源在于碳的无定型结构状态,且此类结构的散射信息可以被SAXS所捕捉,进而成为总散射强度的分量.此时,利用Unified fit模型或"双Debye"模型可以很好地分析准两相体系中无定形结构和微孔的结构特征.其次,基于"Ruland streak"法的散射体取向分析方法被成功应用于碳纤维孔结构分析.该方法假设了择优取向的散射体具有较大的长径比,而散射强度主要集中于散射体主轴的法向,单个散射体将产生一个沿法向的散射条纹,因此散射体的取向可以通过分析接收器平面内散射体法向散射信号的分布而得到.此外,将Porod理论应用于碳结构内部微电子密度起伏分析和将麦克斯韦函数应用于碳纤维孔结构分布分析也是近年来涌现的新理论、新技术.据此本文综述了近年来应用SAXS对碳纤维进行微观结构表征的进展,对SAXS应用于碳材料微电子密度起伏、分形结构、孔隙结构、择优取向、无定形结构的测试及数据解析进行了详细阐述.     

XRD研究沸水热处理对PAN原丝结构与性能的影响

采用X射线衍射分析(XRD)研究了沸水热处理前后3种不同PAN原丝的凝聚态结构,并比较了它们体密度、强度、断裂伸长率等性能的变化.发现经过沸水热处理后,3种原丝的非晶散射峰所占比例均增加,结晶度降低.由于沸水热处理所采用的温度(100℃)略高于PAN原丝的玻璃化转变温度(95.78℃),在此温度下只有非晶区的分子链段可以运动,所以X射线衍射曲线的变化是由非晶区取向结构的变化引起的.该结果表明,原丝内部由微晶区、取向非晶区和无规非晶区组成;除了晶区结构外,非晶区中的有序结构对X射线衍射峰同样有一定贡献.经过沸水热处理后,由于微晶边缘有序程度下降,导致微晶的平均尺寸也略有减小.沸水热处理使PAN原丝中伸直的分子链段变为蜷曲构象,增加了链段所占据的自由体积,因此处理后原丝的体密度减小;热处理后原丝非晶区有序程度降低,导致其取向度降低,强度降低,断裂伸长率增加.     

Insertion of triangulated surfaces into a meccano tetrahedral discretization by means of mesh refinement and optimization procedures

In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method.     

Certification Institutions Expected to Update and Transfer Information on Present Standards

Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.……     

From Industry 4.0 to Research 4.0. Development of High Performance Fibers in the Light of Digitization

We associate a variety of innovations with the term ＂Industry 4.0＂. The pioneer of many 4.0 modifications forms the basisfor the trend towards the integrated di...     

Flow calorimeter for enthalpy increment measurements on condensed gases

A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa.     

Refrigerators Enter a New Era of Health Preservation Frestech initiates the establishment of China's first standard for household sterilization refrigerators

On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.……     

Roman iron and steel: A review

ABSTRACT

The production of ferrous metal increased during the Roman Late Republican period, Principate and Empire. The direct bloomery process was used to extract the metal from its ores using slag-tapping and slag-pit furnaces. The fuel was charcoal and an air blast was introduced by bellows-operated tuyères. Iron formed as a bloom, often as a spongy mass of metal, which contained impurities from the smelting process, including unreacted ore, fuel, slag and fragments from the furnace walls, while the metal was often inhomogeneous with varied carbon contents. Blooms were either smithed directly into bars or ingots or they were broken up, which also allowed the removal of gross impurities and a selection of pieces with similar properties to be made. These could then be forge-welded together and formed into characteristically shaped ingots. Making steel in the furnace seems to have been achieved: it depended on the ore and the furnace and conditions within it. Surface carburization was also carried out. Iron and steel were used extensively in construction and for tools and weapons. Fire welding was often used to add pieces of steel to make the edges of tools and weapons, which could be heat-treated by quenching to harden them.     

Optimum-Simulation von Ernteprozessen

Zusammenfassung Bei der Gestaltung von Ernteprozessen — beispielsweise des Prozesses Mähdrusch, Körnertransport und -abnahme — als transportverbundene Fließarbeitsverfahren mit mindestens zwei verschiedenen Arbeitsmitteln gibt es einen großen Optimierungsspielraum. Solche Prozesse sind mehrstufige Bedienungsprozesse mit gemischter Anordnung der Bedienungseinrichtungen. Außerdem besitzen sie stark ausgeprägte räumliche Aspekte. Es wird vor allem gezeigt, welche Merkmale solcher Prozesse in Simulationsmodellen abgebildet sein müssen, welche Zielgrößen in Abhängigkeit von welchen Einflußgrößen unter Berücksichtigung welcher Prozeßbedingungen ermittelt werden sollten und wie der Bewertungsprozeß zur Ermittlung der gewünschten Informationen gestaltet werden muß.     

A study of centrifugal cast high boron high speed steel

In the present study a high‐boron high speed steel (HSS) roll material was designed. Many expensive alloy elements have been substituted by cheap boron alloy, and high‐boron high speed steel roll has been manufactured by centrifugal casting method. The microstructures, mechanical properties and wear resistance of centrifugal casting high‐boron high speed steel roll have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), and X‐ray diffraction (XRD) analysis, hardness test, impact test and wear test. The results indicated that the solidification microstructures of high‐boron high speed steel roll consisted of M₂(B,C), (W,Mo)₂(B,C), M₃(B,C), M₂₃(B,C)₆ type borocarbides and martensite, a small amount of retained austenite. Borocarbides were continuously distributed over the grain boundary. After quenching from 1050 °C, local broken network appeared in partial borocarbides, and fine secondary borocarbide precipitated from the matrix. After tempering from 525 °C, the amount of precipitated borocarbide increased significantly. After heat treatment, the hardness of high‐boron high speed steel roll excelled 60 HRC, and its impact toughness excelled 8.0 J/cm². The single groove steel rolling amount of high‐boron high speed steel rolls increases by 500% than that of bainite cast iron roll, when the rolls are used in K₁ mill housing of bar mill.     

Thixotropy of Systems with Shear Thinning and Plastic Flow Behavior

The definition of the thixotropy is a decrease in viscosity with time in shear and a subsequent recovery of viscosity after the shear deformation is removed.We ...