通用级沥青纤维预氧化过程中的增重规律及结构变化

本文通过对通用级沥青纤维预氧化过程中的增重分析，找出了增重变化的初步规律，强调了关系预氧化成败的关键温度范围。且利用元素分析、光声红外等手段，从结构上对预氧化反应作了解释。从中发现增重规律和结构变化是相符的。     

预氧化对涂层抗低温热腐蚀性能的影响

研究了预氧化处理对ＭＣｒＡｌＹ涂层抗低温热腐蚀性能的影响，结果表明，预氧化形成的氧化铬膜提高了涂层的抗腐蚀性。     

瓦楞纸板预氧化淀粉粘合剂的开发研究

介绍了预氧化淀粉及其粘合剂制备的原料、配方和方法。讨论了在制备过程中不同因素（温度、氧化剂及用量等）对预氧化淀粉及其对粘合剂粘合性能，丽楞纸板的剥离强度、边压强度、耐破强度的影响，阐述了预氧化淀粉氧化剂残留率的检测方法。     

超声蚀刻法研究聚丙烯腈预氧化纤维的皮芯结构

预氧化各温区纤维经超声蚀刻处理后,利用扫描电镜（SEM）观察其皮层和芯部的形貌差异,并借助Raman光谱证实了预氧化纤维皮层和芯部的化学结构差异。结果表明预氧化初期195～225℃预氧化纤维整体预氧化程度低,纤维皮层和芯部的结构几乎没有差异;预氧化中后期235～265℃预氧化纤维芯部的稳定化程度较皮层低,芯部被蚀刻溶解,皮、芯形貌差异明显;经275℃预氧化后,纤维芯部稳定化程度提高,无论皮层还是芯部都呈现不溶性;最终的预氧化纤维出现了宽化的石墨特征Raman散射峰,但皮层的衍射峰较芯部更为宽化,反映出皮、芯化学结构的差异。     

碳纤维体密度与预氧化当量时间的相关性研究

温度和时间是预氧化过程中的两个重要参数,预氧化当量时间是将温度和时间综合起来考量的一个参数。对经过不同预氧化当量时间处理的预氧纤维样品和碳纤维样品进行体密度分析,找出了预氧化当量时间与预氧纤维体密度和碳纤维体密度的相关性,并对其影响机理进行了研究。研究结果表明:预氧化当量时间越长,预氧纤维体密度越大,对应的碳纤维体密度越低,并在一定范围内呈现线性关系。     

预氧化温度对中空多孔炭纤维介电常数的影响

以中空多孔聚丙烯腈(PAN)原丝为原料,通过预氧化和炭化工艺制备了中空多孔炭纤维。研究了预氧化温度对其微观结构、元素组成和介电常数的影响。结果表明,预氧化温度对中空多孔炭纤维微观结构的影响不大;碳含量随预氧化温度的升高而减少,而氮、氧含量则相反。随预氧化温度的升高,所得中空多孔炭纤维的介电常数依次降低。在2GHz处,预氧化温度为250℃时ε′和ε″分别为23.12和73.51,而预氧化温度为310℃时ε′和ε″分别为19.32和9.87。因此,可通过预氧化温度来调节中空多孔炭纤维的介电常数。     

预氧化时间和温度对聚丙烯腈纤维预氧化的影响

通过在线监测聚丙烯腈(PAN)纤维在预氧化过程中热收缩行为,结合纤维预氧化前后性能变化,考察了时间和温度对预氧化的影响.实验结果表明:温度和时间作用不同,即温度作用不能用时间代替.温度在预氧化过程中起决定性作用,要得到较高的环化度,预氧化温度必须超过240℃.     

流态化预氧化PAN基纤维性能的研究

采用流态化预氧化技术对PAN基纤维进行预氧化实验,并对不同工艺方案下制得的预氧丝进行了氧含量、体密度、XRD、红外光谱等测试与分析。纤维经45min流态化预氧化后氧含量达到10.1%,体密度达到1.38g/cm3,XRD、红外光谱结果显示纤维发生了环化、脱氢的化学反应和组织结构变化,最终转变为耐热的梯形结构。实验结果说明,通过进一步优化工艺,流态化预氧化技术可以在保证预氧化质量的同时,大幅缩短预氧化时间,降低生产成本。     

预环化处理方式对腈纶预氧化纤维性能的影响

研究了预环化处理方式对预氧化纤维阻燃性能和力学性能的影响。实验结果表明,先用羟胺处理,再用水合肼处理,所得预氧化纤维的阻燃性能和力学性能相对较好,在预氧化温度260℃时,可得到极限氧指数36.5%的预氧化阻燃纤维。扫描电镜观察表明,表面处理后纤维外表面裂纹明显减少,预氧化处理后纤维裂纹有所恢复。红外光谱分析表明,表面处理后纤维有少量吡啶环状结构生成,而预氧化后纤维中有大量吡啶环化结构产生。X射线衍射分析显示,经表面处理和预氧化之后纤维的形态结构没有发生大的变化,仍为高有序区和非晶区组成的准晶有序结构。     

真空预氧化对冷喷涂NiCoCrAlY涂层氧化行为的影响

利用冷喷涂技术制备了NiCoCrAlY涂层,并对涂层进行了真空预氧化处理。结合X射线衍射,扫描电镜和能谱分析等方法分析了NiCoCrAlY涂层真空预氧化前后的微观组织结构,并研究了真空预氧化处理对NiCoCrAlY涂层在1050℃下氧化行为的影响。结果表明:冷喷涂NiCoCrAlY涂层含氧量为0.25%(质量分数),孔隙率小于0.36%。真空预氧化处理使涂层由γ-Matrix Ni-Co-Cr单相结构转变为γ-Matrix Ni-Co-Cr固溶体和β-(Ni,Co)Al金属间化合物双相结构,并在涂层表面生成厚约0.47μm连续、致密的α-Al2O3氧化膜。喷涂态涂层和真空预氧化涂层在1050℃氧化200h后表面均生成致密、连续的以α-Al2O3为主的氧化膜。真空预氧化处理在100h内抑制了涂层表面尖晶石氧化物的形成,同时降低了氧化膜生长速率。     

沥青基活性碳纤维研究：1.沥青纤维的不熔化处理

利用热分析，红外光谱研究了通用型沥青纤维的不熔化机理，同时对影响不熔化反应的诸因素进行了实验研究。结果表明，不熔化处理使沥青纤维碳氧基团含量增大，形成碳氧网络，使纤维熔点提高，强度上升。不熔化温度，时间，氧化剂深度及升温速率是不熔化处理的主要影响因素，它们影响不熔化纤维的结构与性能，影响沥青繁华纤维的碳化和活化。     

A microscopic study on the oxidative stabilization of a coal-tar-based mesophase pitch and its blends with PVC pitch

Coal-tar-based mesophase pitch and its blends with PVC pitch at 5 or 10 wt% were oxidatively stabilized at 230, 270 and 300°C for variable periods to clarify the progress of stabilization and the effects of the blending with PVC pitch on the stabilization reactivity. PVC pitch which was prepared from PVC by heat-treatment at 420°C for 2h enhanced the stabilization reactivity of whole pitch fibres to shorten the stabilization time to a half of that for mesophase pitch alone. PVC pitch carrying considerable amounts of aliphatic components and large molecular weight may initiate, as a trigger, the stabilization reactions of mesophase constituent molecules. Carbonized fibres of 30μm diameter after stabilization at 270 and 300°C exhibited a skin-core structure, while fibres of 10μm diameter showed no skin-core structure, indicating a homogeneous progress of stabilization in the radial direction of the latter fibres. Lower stabilization temperatures provoked no skin-core structure even in the thick fibres. The rate of core diminishing became relatively slower in the later stage of the stabilization, even when the reactivity of the pitch fibres was enhanced by blending with PVC pitch and using a higher stabilization temperature. The diffusion of the oxidant and stabilization reactivity of the pitch fibres are discussed comparatively.     

碳纳米管对纳米炭复合纤维结构与性能的影响研究

采用不同方法将多壁碳纳米管(MWNTs)混合于中间相沥青中,利用氮压式单孔纺丝机进行纺丝,经预氧化、碳化后制得了纳米炭复合纤维,对比研究了混合方式对纳米炭复合纤维的结构和性能的影响.研究结果表明,MWNTs的加入最终改变了纤维的微观结构,尤其经浓酸处理后显著提高了纳米炭复合纤维的力学性能.     

Promoter action of sulphur on the stabilization of pitch spheres

Elemental sulphur was added into the starting pitch during the preparation of pitch-based spherical activated carbon in order to enhance the stabilization of pitch sphere. Pitch sphere (diameter 0.65–1.0 mm) without adding sulphur needs slow heating rate of 0.5 °C/min, high final temperature of 300 °C and long holding time of 20 h for the successful stabilization in air. While adding elemental sulphur with 2.5–10.0 wt % in total amount into starting pitch decreased the stabilization time significantly, pitch sphere containing 5.0 wt % of sulphur can be stabilized in air very easily at heating rate of 2.0 °C/min up to 270 °C without any holding time, and the successful stabilization time was only 3 h. Pitch molecules reacted with sulphur and some sulphur functional groups, such as C–SH, C–S–C, C=S, O=S=, O=S=O etc., were formed besides the oxygen functional groups under the stabilization condition. All of these sulphur functional groups acted as bridge bonds to make the pitch molecules polymerized so as to high up the softening point of pitch spheres, making the pitch spheres stabilized. Three kinds of sulfocompounds, i.e. H₂S, COS and CS₂ evolved in stabilization process.     

A structural study on the stabilization and enhancement of mesophase pitch fibre

The components of coal tar-derived mesophase pitch fibre and its blend with polyvinyl chloride (PVC) pitch were studied for chemical changes after the stabilization. Microanalyses, solubility and solid ¹³C NMR measurements were performed. The temperature was found to be very influential on the progress of the stabilization. At a temperature of 230° C, PVC pitch enchanced the oxygen uptake of both fusible pyridine soluble (PS) and non-fusible pyridine insoluble (PI) fractions in the pure mesophase pitch, so shortening the time required for complete stabilization and raising more rapidly the softening point of the PS fraction. More oxygen-containing functional groups, such as phenolic, ether, carboxylic and carbonyl groups, were formed in both fractions. It is noted that any increase in the aromatic ring size of the PI fraction is rather limited at this temperature. In contrast, stabilization of PVC pitch at a higher temperature of 300° C, accelerated the increase in PI without accelerating oxygen uptake of both fractions. Hence, the softening point of the remaining PS was unchanged or even lowered. An increase of aromatic ring size of the PI component by stabilization was marked at the higher temperature. Suggested stabilization schemes and the role of added PVC pitch in accelerating stabilization are discussed for each of these temperatures taking account of the above results.     

溶剂处理对沥青球氧化稳定化的影响研究

研究了溶剂处理时间、温度等条件对石油沥青球和煤沥青球的收率、氧化破损率及氧化稳定化效果的影响,结果表明：在室温下用烷烃类浸泡沥青球,可以有效地除去沥青球中的萘和轻组份,打通氧气向内扩散的通道,缩小沥青球表面和呐部氧化反应程度差别,促进沥青球的快速均匀不熔化;提高溶剂处理温度,容易刻蚀球表面,影响球的外观和强度;较低软化点的石油沥青球比煤沥青球比煤沥青球表面更易于刻蚀更难于氧化稳定化。     

煤沥青微球和石油沥青微球的制备及其氧化稳定化研究

采用浮化法由芳香添加剂与高软化点沥青混合物制备了沥青球。通过热重差热分析研究了不同沥青种类、不同添加剂／高软化点沥青比例和不同结构的沥青球在空气中的氧化稳定化行为。结果表明：芳香添加剂可以大大降低成球沥青的软化点，促进氧化稳定化；与煤沥青球相比，石油沥青球更易氧化，但氧化的沥青球表面成为双扩散的障碍，从而抑制沥青球的氧化稳定化；增加芳香添加剂含量，使沥青球氧化反应易于进行。     

Blending mesophase pitch to improve its properties as a precursor for carbon fibre Part 1 Blending of PVC pitch into coal tar and petroleum-derived mesophase pitches

The blending of mesophase pitch with isotropic PVC pitch was studied to improve their properties as a precursor for carbon fibre. PVC pitch prepared at 420° C which remained almost isotropic was found to be miscible with coal tar-derived mesophase pitch without reducing the anisotropic content and spinnability. The tensile strength of pitch fibres remained unchanged by the blending; however, the reactivity for stabilization was enhanced. The resultant carbon fibres from the blend exhibited slightly higher tensile strength. In contrast, petroleum-derived mesophase pitch failed to dissolve the PVC pitch, leaving a number of isotropic droplets. The structural factors of mesophase pitches with regard to their compatibility with PVC pitches are briefly discussed.     

Oxidation properties of mesophase pitch prepared by a heterogeneous nucleation method

Mesophase pitches prepared by a heterogeneous nucleation method from various mixtures of coal tar-derived isotropic pitch and petroleum-derived mesophase pitch (MP-P) were oxidatively stabilized, and the dependence of chemical reactivity and stabilization rate on their chemical structure was investigated. The rate and amount of oxygen uptake of the mesophase pitch fibres, revealed by thermogravimetry, increased under given conditions of oxidation with the amount of added MP-P, but the rate of stabilization showed a reverse trend. The lower chemical reactivity of coal tar-derived mesophase pitch (MP-C) appears to induce a slower rate of oxygen uptake, while the higher content of pyridine-insoluble fraction and higher aromaticity of MP-C may result in a lesser content of oxygen being required for stabilization, as compared with MP-P.     

Structure and properties of mesophase pitch carbon fibre with a skin-core structure carbonized under strain

Coal tar mesophase pitch fibres stabilized at 270° C to different extents were carbonized under strain by the constant load or constant length, using different heating rates, and further graphitized at 2500° C. Shallow and moderate stabilization provided a skin-core structure in the resultant fibres which exhibited higher orientation, tensile modulus, and better graphitizability after calcination at 1300° C and graphitization at 2500° C than deep stabilization. The tensile strength and modulus of the graphitized fibre was significantly improved through the strained carbonization when the stabilization was performed to a moderate extent. The strain tended to give an onion-like alignment in the fibre to improve the preferred orientation of carbon planes. Larger load and more rapid heating during carbonization modified the structure and properties of resultant fibres through a significant longitudinal elongation. The stabilization extent of pitch fibres governs the mobility or fusibility of mesogen molecules at the carbonization which allows their better alignment by the strain.