PAN纤维预氧化过程的结构变化及热行为

采用X射线衍射(XRD)、透射电子显微镜(TEM)和差示扫描量热分析(DSC)研究了PAN纤维在预氧化过程的结构和热性能变化。结果表明:随着预氧化温度的升高,纤维的微晶尺寸增大,到220~230℃时达到最大,此后逐渐减小,原准晶结构逐渐被破坏。纤维的芳构化指数随预氧化温度的升高不断增大,PAN链状分子在逐渐演变成梯形环状分子结构,230℃和275℃是PAN原丝热稳定化的转折点。随着预氧化温度的升高,洋葱球非晶组织发生了结构演变。非晶化转变是从晶区边界开始,由外部向芯部逐步进行。纤维的环化度随着预氧化温度的升高表现为增大。在较低温度增加较快,随后增加变缓。230℃后,环化反应加剧,环化度迅速提高。     

硅系油剂对PAN纤维预氧化的影响

改变聚丙烯腈(PAN)纤维纺丝工艺,制得无油纤维和含油纤维,在空气气氛下对两种纤维进行预氧化处理。借助体密度、差示扫描量热仪(DSC)、傅里叶变换红外光谱仪(FT-IR)和X射线衍射仪(XRD)等测试手段,通过表征PAN纤维的预氧化程度,揭示硅系油剂的作用。结果表明,硅系油剂在190℃～250℃温度区间,即本论文讨论的预氧化反应全程,不发生化学反应,依然均匀涂覆在PAN纤维的表面;在预氧化反应的前期(190℃～220℃),纤维表面的油剂阻碍热的传递和氧的扩散,使得含油纤维的体密度、环化度、相对环化率和芳构化指数均低于无油纤维;在预氧化后期(220℃～250℃),由于前期油剂对预氧化反应的抑制,使得前期形成的结构有利于氧的扩散,表象上硅系油剂在预氧化后期起着促进的作用。     

晶态结构对聚丙烯腈(PAN)原丝预氧化反应的影响EI北大核心CSCD

对不同晶态结构特点的聚丙烯腈(PAN)原丝进行预氧化处理,采用X射线衍射(XRD)、红外光谱法表征PAN纤维的晶态结构(物理)和化学结构变化。结果表明,PAN原丝的晶态结构影响预氧化反应及反应程度,结晶度小的PAN原丝由于其有序性差,易于向预氧纤维芳构化结构转化,而结构疏松,有利于氧的扩散,促进环化反应和初期氧化反应,PAN纤维芳构化指数和相对环化率都较高,预氧化反应程度较高;原丝结晶度的差异对纤维晶粒尺寸的变化起决定性作用,结晶度大的PAN原丝到预氧化后期仍保持较大的晶粒尺寸。     

晶态结构对聚丙烯腈(PAN)原丝预氧化反应的影响

对不同晶态结构特点的聚丙烯腈(PAN)原丝进行预氧化处理,采用X射线衍射(XRD)、红外光谱法表征PAN纤维的晶态结构(物理)和化学结构变化。结果表明,PAN原丝的晶态结构影响预氧化反应及反应程度,结晶度小的PAN原丝由于其有序性差,易于向预氧纤维芳构化结构转化,而结构疏松,有利于氧的扩散,促进环化反应和初期氧化反应,PAN纤维芳构化指数和相对环化率都较高,预氧化反应程度较高;原丝结晶度的差异对纤维晶粒尺寸的变化起决定性作用,结晶度大的PAN原丝到预氧化后期仍保持较大的晶粒尺寸。     

氧对聚丙烯腈预氧化环化的促进机理EI北大核心CSCD

通过比较聚丙烯腈(PAN)纤维在空气条件下的热重分析(TG)及不同含氧量气氛中的差示扫描量热分析(DSC)结果,发现氧对PAN纤维有增重及对预氧化环化有促进作用。氧化增重是气氛中的氧对PAN分子链氧化的结果,氧化对PAN分子链螺旋结构的解旋有利于PAN预氧化环化。借助于纤维电子强力仪、显微镜等技术,测定了样品PAN的初始模量、断裂强度及断裂模量。统计结果表明,氧通过参加PAN分子链上的反应,促使PAN分子链的螺旋结构解旋,形成了非螺旋结构,有利于分子内的环化反应,提高了预氧化环化的速度及质量。     

氧对聚丙烯腈预氧化环化的促进机理

通过比较聚丙烯腈(PAN)纤维在空气条件下的热重分析(TG)及不同含氧量气氛中的差示扫描量热分析(DSC)结果,发现氧对PAN纤维有增重及对预氧化环化有促进作用。氧化增重是气氛中的氧对PAN分子链氧化的结果,氧化对PAN分子链螺旋结构的解旋有利于PAN预氧化环化。借助于纤维电子强力仪、显微镜等技术,测定了样品PAN的初始模量、断裂强度及断裂模量。统计结果表明,氧通过参加PAN分子链上的反应,促使PAN分子链的螺旋结构解旋,形成了非螺旋结构,有利于分子内的环化反应,提高了预氧化环化的速度及质量。     

PAN纤维热稳定化过程中环化反应对氧化反应的影响

在惰性气氛中制备了不同环化程度的聚丙烯腈(PAN)热稳定化纤维,并将其在含氧气氛中进一步氧化处理,通过差示扫描量热仪(DSC)、傅立叶变换红外(FT-IR)和元素分析(EA)等方法研究了PAN纤维热稳定化过程中环化反应对氧化反应的影响。结果表明,与环化反应相比,氧化反应可在更低的温度下进行;对于环化程度越高的PAN热稳定化纤维,在含氧气氛中经相同条件热处理后氧含量越高,即氧化反应程度越高,故环化反应对氧化反应具有促进作用。     

预氧结构对PAN纤维热裂解行为的影响

通过采用固体~(13)C核磁谱图(~(13)C-NMR)、元素分析(EA)、热失重-红外联用(TG-IR)和拉曼光谱分析仪(Raman)等研究了热处理聚丙烯腈(PAN)纤维的结构演变及其热裂解行为。结果表明,随着预氧化温度的升高,环化结构与含氧结构相对含量的比值先升高后降低。过多的含氧结构在后续热裂解过程中携带碳原子脱除,降低了预氧纤维的热稳定性和最终碳纤维的有序度。在充分环化的基础上,环化结构与含氧结构比值为10.39时,PAN预氧纤维热稳定性最佳。     

硼酸改性对预氧化过程中PAN纤维结构变化的影响

预氧化前对聚丙烯腈(PAN)纤维进行硼酸溶液浸渍改性,通过红外吸收光谱和固体核磁研究硼酸改性对PAN纤维预氧化结构变化的影响。结果表明:硼酸对PAN纤维预氧化环化反应有一定的抑制作用,随着硼酸溶液浓度增加,硼酸对PAN纤维环化反应的抑制程度增加。硼酸对环化反应的抑制可防止纤维外层致密层的形成,有利于均质化程度的提高,并可防止PAN纤维表面被过度氧化。     

共聚单体改性PAN原丝热性能研究

采用溴化1-烯丙基3-乙基咪唑(VIM-Br)与丙烯腈(AN)自由基溶液共聚,以偶氮二异丁腈为引发剂在二甲基亚砜中合成了聚丙烯腈(PAN)纺丝溶液,并用湿法纺丝纺制得了PAN原丝。运用差示扫描量热分析(DSC)、红外光谱(FT-IR),13 C固体核磁(13 C-NMR)研究了VIM-Br对PAN原丝预氧化热性能的影响。结果表明,在预氧化反应过程中,含有强极性Br原子的共聚单体VIM-Br能够催化环化反应,降低预氧化起始反应温度,缓和预氧化反应放热;和传统共聚单体衣康酸(IA)相比,VIM-Br的空间效应为氧气向PAN纤维内部扩散提供了分子级的通道,增加了进入纤维内部的氧气量,提高了预氧化反应程度。     

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.     

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.     

Mechanism Study on the Wear of CrAlTiN Coated High-Speed Steel Twist Drills Under Dry Cutting Conditions

As demands about environment protection are growing up, dry cutting technology is getting more and more concerns from all over the world. Main works performed here are study on dry cutting performances and wear mechanisms of M2high-speed steel (HSS) twist drills with CrAlTiN multicomponent coatings, which was deposited using magnetron sputter ion plating system, in drilling 45 and 30CrMnSiA steel, and their comparisons to those in drilling the same steel but using monolayer CrN and commercial TiN coated drills. Drilling performances of drills are evaluated mainly through the measurements of width on outer corner flank land and the cutting forces. Results show that performances of CrAlTiN coated drills are better than those of monolayer CrN and TiN coated drills. In drilling 45 and 30CrMnSiA steel, the average tool life of the CrAlTiN coated drills are 17.2 and 11.8 times higher than those of the uncoated drills. Observing wear of the drill with scanning electronic microscope, results show that there is no crack or spallation of the CrAlTiN coatings in wear zones. Main mechanism of the wear here is adhesion.     

Study on Bond Ability of Arc-Spraying Coatings with Different Surface Pretreatment on Cast-Iron

Arc spraying coatings are widely used in various applications, but uncommon in cast iron substrate. Different surface pretreatment technology is tested on substrates of gray cast iron. Surface roughness and residual stress were measured by TR200 and X-ray diffraction analyzer. Influence of different surface pretreatment methods ( dry blasting and fusebond) on roughness and residual stress was analyzed. The arc-sprayed coatings of wire 3Cr13 (φ2mm) on gray cast iron substrate is studied. The microstructure and interface of bonding layer were observed by SEM. The bond strength was taken by tensile test. Results show that bond strength with grit blasting is higher than fuse-bond; it is feasible to make wire 3Cr13 coating with arc spraying on cast iron substrate roughened by grit blasting.     

Structural Characteristics of TiO2 Ceramic Coating by Micro-Plasma Oxidation

TiO2 ceramic coatings with thickness of 20 μm were formed on the surface of pure titanium by micro-plasma oxidation. Their micro-structures were investigated by by using X-ray diffraction and their surface images were detected by using scan electronic microscope. There were three kinds of TiO2 coatings, pure anatase type TiO2 phase, mixed phases consisted of rutile type TiO2 phase and anatase type TiO2 phase, pure rutile type TiO2 phase. The coating surface with the pure anatase type TiO2 phase is rough, while the coating surface with the pure rutile type TiO2phase is smooth. The upper coating surface with the mixed type TiO2 phases is anatase type TiO2 structure and the subsurface of the TiO2 coating is rutile type TiO2structure.     

Evaluation of fatigue life of steel using steel grain size

The insightful discussion of the relationship between the construction of metallographic and fatigue life and proposition of mathematical relationships describing this relationship was conducted in the paper. This paper presents a method for estimating the fatigue life, based on the construction of the microstructural material taking into account the grain size and the participation of ferrite and pearlite phase.