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.     

The Research of Anti-Wear Properties of Organomolybdenum Compounds in the Engine Oils

A four-ball tester was used to evaluate the anti-wear performance of three kinds of organomolybdemun compounds in the engine oils, i. e., molybdenum dialkyldithiophosphate (MoDDP), molybdenum dialkyldithiocarbamate ( MoDTC), and sulphur and phosphorus freeorganomolybdeum (Molybdate). The results indicate that a low concentration of MoDDP doesn' t improve the anti-wear properties of the commercial engine oils, but a high concentration of MoDDP can obviously improve the anti-wear properties and the load-carrying capacity of the engine oils. MoDTC doesn' t improve the antiwear properties of the engine oils, but worsens the anti-wear properties of the oils. Signifi can timprove ment of frictional and wear characteristics is obtained with Molybdate added in the commercial engine oils and the formulated oils.     

Effect of Permeable Crystalline Material on Steel Reinforcement Corrosion of Concrete

Permeable crystalline materialcan permeate into pores and cracks of concrete and catalyze the reaction between Ca(OH) 2and unhydrated cement to generate a great quantity needle non-soluble crystals, which can stop up the pores and cracks of concrete, and increase the impermeability of concrete. This paper reported the results of a study conducted to evaluate steel reinforcement corrosion of concrete specimens uncoated and coated with permeable crystalline material as well as mixed with the permeable crystalline material. The properties evaluated for corrosion test were water impermeability, water absorption, compressive strength and potential. The results of water impermeability, water absorption, compressive strength clearly showed that the permeable crystalline material could prohibit water, any soluble salts and moisture from penetrating the concrete to cause corrosion, leaking, and other problems, and it did increase the compressive strength, which was favorable for protection of corrosion of reinforcing steel. Moreover, it was concluded from the potential-time curve that the steel reinforcement of uncoated specimen was in the state of activation whereas that of other specimens coated and mixed with the permeable crystalline material was in the state of inactivation. Above all, it was indicated that the permeable crystalline materialis very effective to protect the steel reinforcement of concrete from corrosion.     

The Research and Application About "Dry Peeling Off" Technology for Airplane Surface Paint Layer

In this paper, the principle of spurting take off lacquer were introduced; and with orthogonal method the unsaturate polyester was prepared ;it was easy to peel airplane paint layer off with this material and equipment.     

Quality Study of Honeycomb Core Shaping Without Wax Stabilization

Sandwich panels utilizing honeycomb cores result in lightweight, high-strength units that are very rigid. Indeed, they give honeycomb panels the best strength-to-weight ratio of any construction type available. Conventionally, the wax is poured into the cell of the core to strengthen the structure and prevent the core from being crushed during milling. Much time and labor is required to wax, mill, and clean the cores. In this study, the process of pouring wax into the core was skipped. In other words, the cutter directly milled the core. Experiments showed that the compressive strength of the core produced without wax stabilization was only 3% lower than that of cores produced using the traditional method. In addition, the drum peel strengths of cores produced without wax stabilization were 38.4% higher than cores produced using the traditional method, in which residual wax seriously polluted the adhesive. It was also found that eliminating the wax process can reduce costs.     

Certification Becomes Important for the I Quality; and Safety Supervision of the Chinese Liquor Sector

The end of 2007, over 200 unit products of more than 80 Chinese firms have passed the quality grade certification for liquor products. These products involve distilled spirits, beer, wine, yellow wine, fruit syrup wine and others, and cover over 80% of the national top-branded liquor products.……     

Deposition and Coating Properties on CVD Tungsten

Surface characterization and microstructure studies are performed on chemical vapor deposited (CVD) tungsten coating. There is about 2 μm thickness diffusion layer of tungsten in the molybdenum substrate. The thermal shock test shows tungsten coating has good adhesion with molybdenum substrate, but the elements of oxygen and carbon in the tungsten coating have the bad affection to the adhesion. The result of high-temperature diffusion experiment is the diffusion rate from molybdenum substrate to tungsten coating is faster.     

Analysis of marine hydrobiont lipid extracts as possible cryoprotective agents

We studied a combined effect of the cryoprotectants both of lipid and carbohydrate origin at the presence of DMSO or without it on cell viability and the RNA synthesis in the embryonic mollusc and echinoderm cell cultures obtained at different developmental stages. Cryoprotective properties of exogenous lipids correlated with their thermotropic behavior. Lipid extracts from marine hydrobiontes, which thermal transitions are characterized by relatively small part of calorimetric thermogram area lying at temperatures above 0 °C (6–18%), were found to possess a considerable cryoprotective activity. The results are discussed in relation to the prediction of the cryoprotective activity of lipid extracts for marine animal cells. In addition, it was found that marine invertebrate cells can be cryopreserved without DMSO at the presence of trehalose and lipid extracts of some marine hydrobiontes.     

Low-Temperature Properties of Silver

Pure silver is used extensively in the preparation of high-temperature superconductor wires, tapes, films, and other configurations in which the silver not only shields the superconducting material from the surrounding materials, but also provides a degree of flexibility and strain relief, as well as stabilization and low-resistance electrical contact. Silver is relatively expensive, but at this stage of superconductor development, its unique combination of properties seems to offer the only reasonable means of achieving usable lengths of conductor. In this role, the low-temperature physical (electrical, thermal, magnetic, optical) and mechanical properties of the silver all become important. Here we present a collection of properties data extracted from the cryogenic literature and, to the extent possible, selected for reliability.     

Early ironwork in Biscay: Survey,excavation, experimentation and materials characterization. An integral study of the mountainside ironworks (ferrerías de monte or “haizeolak”)

ABSTRACT

The production of iron in Biscay (Basque Country, Spain) has been a hallmark of this territory of the North of the Iberian Peninsula throughout its history. The Archaeology team of the Basque Country Mining Museum has spent 13 years, so far, studying the origins of this activity through the evidences left at the old pre-hydraulic iron production workshops known as mountainside ironworks (ferrerías de monte) or haizeolak. It has catalogued 170 archaeometallurgical sites of this type in Biscay, and the archeological excavation of some of them has led to the knowledge of the different stages of the production process that took place in these workshops. The team has also experimentally reproduced the work carried out in a mountainside ironworks from the High Middle Ages, and it has currently started the characterization process of this type of activity through the study of the collected materials.     

In-process thermal treatment of polylactic acid in fused deposition modelling

Polylactic acid (PLA) is one of the most widely used open source fused filament fabrication materials due to its ease of extrusion, biodegradability, and mechanical strength. The mechanical strength of PLA largely depends on the proper growth of its semi-crystalline structure, which can be severely impaired by a low rate of crystallization, particularly in open source printers. This can be further aggravated by the non-uniform thermal distribution of heat that causes improper curing among the extruded beads of the printing material. As a result, PLA printed on open source printers does not achieve the best mechanical properties. This research, for the first time, proposes an additive-free solution implemented through a detailed set of experimentation to improve the curing rate through in-process temperature variations to cure the joints among the beads. Scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy is used to confirm the improvements in the bead joints. This work is conducted in two phases of experiments. In the first phase, a full factorial ANOVA is used to investigate various process parameters and the important variables are used in the second phase to print test specimens in four different sets.