【作者】 陈鸯飞；

【导师】 刘洪波；

【作者基本信息】 湖南大学 ， 材料科学与工程， 2014， 博士

【摘要】 液相浸渍法制备C/C复合材料的性能与浸渍剂树脂的成炭率以及树脂炭的结构密切相关，因此，高成炭率树脂的制备以及树脂炭的催化石墨化研究就成为液相浸渍法制备C/C复合材料研究领域中最为重要的两个方面。本文以氨水为催化剂，利用甲醛和苯酚制备了C/C复合材料用高成炭率酚醛树脂。系统地考察了醛/酚摩尔比、合成温度、保温时间等反应条件对酚醛树脂的收率、固含量、游离甲醛含量、粘度、固化损失率以及成炭率等的影响，确立了制备高成炭率酚醛树脂的最佳工艺条件。采用了三种方法对已制备的酚醛树脂进行改性，进一步提高了其成炭率，为制备C/C复合材料打下了良好的基础。利用TG-MS，FTIR和固体C-NMR技术对比研究了常规酚醛树脂和硼酚醛树脂（BPF）的热解过程，确定了酚醛树脂热解成炭的温度区间。探讨了酚醛树脂的内在结构与其热稳定性和成炭率之间的关系。在酚醛树脂中加入硼、铬、锰、铁、钴和镍六种催化元素，并采用X射线衍射对树脂炭的催化石墨化效果及其催化机理进行了分析。在对比酚醛树脂炭催化石墨化效果的基础上，优化选择了硼、铬和铁三种元素催化的酚醛树脂炭制备的C/C复合材料作为研究对象，研究了C/C复合材料的弯曲强度、电阻率、摩擦系数和磨损量与基体炭材料石墨化度的关系。寻找一条低成本制备高性能C/C复合材料的方法。研究结果表明：甲醛/苯酚摩尔比、反应温度和保温时间是影响酚醛树脂结构和性能的主要因素，酚醛树脂的内在结构与其成炭性能密切相关。经优化得出在以氨水为催化剂的条件下最佳工艺为：甲醛/苯酚摩尔比为1.2:1，反应温度为90℃，保温时间为25min。在该工艺条件下制备的酚醛树脂固化物在700℃热处理后的成炭率可达73.8%。改性是提高C/C复合材料的树脂炭酚醛树脂基体的成炭率常用方法，本文采用了三种方法对合成的氨酚醛树脂进行了进一步改性处理。第一种方法是在氨酚醛树脂添加水杨醛和苯甲醛活性稀释剂，活性稀释剂分子链中的官能团与酚醛树脂形成共轭体系提高酚醛树脂的成炭率；第二种方法是在酚醛树脂中引入硼元素来改变其分子结构，生成键能较高的硼酯键以提高酚醛树脂的成炭率；第三种方法是对酚醛树脂进行复合改性，即在硼改性后的酚醛树脂中再添加活性稀释剂，从而进一步提高酚醛树脂的成炭率。初步实验结果表明，复合改性比单一改性的酚醛树脂具有更高的成炭率，经过700℃热处理后其成炭率大于80%。利用TG-MS、FTIR和固体C-NMR技术研究了醛酚比为1.2的酚醛树脂（PF1.2）的热解过程，探讨了酚醛树脂成炭率与其结构的关系，结果表明：酚醛树脂结构中不同取代位亚甲基的相对含量是影响酚醛树脂耐热性能和成炭率的主要因素。对对位（P-P’）位亚甲基的热稳定性高于邻邻位（O-O’）位亚甲基， O-O’位亚甲基在树脂热解前与两相邻酚羟基可环烷化成氧杂蒽环，从而提高树脂的成炭率。对比研究了硼酚醛树脂（BPF）和PF1.2的热解过程，探讨了硼元素的引入对酚醛树脂热稳定性和成炭率的影响，找出了影响硼酚醛树脂成炭率的主要结构因素及其热解成炭的温度区间。结果表明：引入的硼酸通过生成硼酯键改变了酚醛树脂的分子结构。正是由于硼酸改性酚醛树脂中生成的硼酯键使其具有比自制氨酚醛树脂更高的耐热性和成炭率。XRD分析结果表明：经过1600℃及以上高温热处理时，六种元素对酚醛树脂炭都有不同程度的催化石墨化效果。硼元素对酚醛树脂炭材料的催化石墨化过程如下：硼原子在高温下通过扩散作用与碳形成固溶体，硼原子进入炭材料六元环平面内的缺陷位置促使石墨结构的完善。因此通过硼催化的无定形炭材料可转化为均一的A组分。锰元素催化机理与硼元素类似，但其催化石墨化作用较硼差；铬元素与炭材料在高温下形成碳化物，通过碳化铬的分解转化为Ts组分；酚醛树脂炭先溶解于单质铁、单质钴和单质镍中，然后再析出石墨化G组分和Ts组分。对比研究了空白试样与分别添加硼、铁和铬的酚醛炭基C/C复合材料的电阻率、弯曲强度、摩擦系数和磨损量。实验结果表明，空白试样由于基体炭为难石墨化的，其电阻率高达39.44μ m，含催化剂的树脂炭石墨化程度较高；其中硼催化试样的电阻率为16.82μ m；铁催化试样的的电阻率为19.82μ m，铬催化试样的电阻率为30.72μ m，基体炭经催化石墨化后其电阻率降低幅度很大。催化石墨化后基体炭与碳纤维的界面结合强度减弱导致了C/C复合材料弯曲强度的降低。C/CBlank的弯曲强度高达176MPa， C/CB、C/CFe和C/CCr的弯曲强度分别为115MPa、66MPa和53Mpa，说明基体炭中含有催化剂的C/C复合材料的弯曲强度都有所降低。催化石墨化对酚醛炭基C/C复合材料的摩擦学性能有明显的影响。空白试样的摩擦系数为0.71，而硼催化试样和铁催化试样的摩擦系数较低，分别为0.27和0.28。磨损量与基体炭和炭纤维的界面接合情况相关，界面接合较弱C/CFe复合材料的磨损量最大，而界面接合较强的C/CBlank和C/CB复合材料磨损量较小。更多还原

【Abstract】 The performance of C/C composites prepared by liquid impregnation method isclosely related to the char yield of resin impregnation resin and the structure of resincarbon. Therefore, the research on the resin preparation with high char yield andresearch on catalytic graphitization of resin carbon become two most important partsin the research field of C/C composites prepared by liquid impregnation method.This study used ammonia as catalyst, used formaldehyde and phenol to prepareC/C composites with high char yield phenolic resin. And the study systematicallyexamined the impact of reaction conditions such as the ratio of formaldehyde/phenolmolar, synthetic temperature, holding time on the yield of phenolic resin, solidcontent, free formaldehyde content, viscosity, curing loss rate and char yield, theoptimum conditions to prepare the phenolic resin with high char yield wereestablished. Three methods had been used to modify the prepared phenolic resin inorder to further improve its char yield, which had laid a good foundation for thepreparation of C/C composites. TG-MS, FTIR and solid C-NMR techniques were usedto conduct comparative study on the pyrolysis process of conventional phenolic resinand boron phenolic resin (BPF) and determine the temperature range of phenolic resinpyrolysis char. The relationship between the structure of phenolic resin and itsthermal stability and char yield was explored. Six catalytic elements of boron,chromium, manganese, iron, cobalt and nickel were added into phenolic resin, AndX-ray diffraction (XRD), scanning electron microscope (SEM) and metallographicmicroscope observation and Raman spectra were used to characterize the catalyticgraphitization effect of its catalytic resin carbon, and the catalytic mechanism of eachelement was analyzed. On the basis of contrasting phenolic resin carbon catalyticgraphitization effect, C/C composites prepared by phenolic resin carbon by threeelements of Boron, chromium, and iron catalysis were optimally selected to be theresearch object. The relationship of bending strength, resistivity, friction coefficientand wear volume of C/C composites and graphitization degree of matrix carbonmaterials was studied. A low cost method to prepare high performance C/Ccomposites was found.The results showed that the formaldehyde/phenol molar ratio, reactiontemperature and holding time were the main factors influencing the structure and performance of phenolic resin, the structure of phenolic resin was closely related toits char performance. It was obtained after optimization that the optimum processunder the condition of ammonium hydroxide as catalyst was as follows: the ratio offormaldehyde/phenol molar was1.2:1, the reaction temperature was90℃, theholding time was25min.The cured phenolic resin prepared by this process after heattreatment at700℃could reach73.8%.Modification is a common method to improve the char yield of C/C compositesresin carbon phenolic resin matrix; this study adopted three methods for synthesis ofammonia phenolic resin for further modification. The first method was to addsalicylaldehyde and benzaldehyde reactive diluents in ammonia phenolic resin, thefunctional groups in molecular chain reactive diluent and phenolic resin formedconjugate system, which improved char yield of phenolic resin; The second methodwas to introduce boron element in phenolic resin to change its molecular structure, thegenerated key could improve boron ester bond in order to improve the char yield ofphenolic resin; The third method was to conduct the compound modification ofphenolic resin, namely adding reactive diluent in boron modified phenolic resin, thusfurther improve char yield of phenolic resin. Preliminary experimental results showedthat the composites modification had higher char yield compared with the singlemodification phenolic resin, its char yield was larger than80%after700℃heattreatment.TG-MS, FTIR and solid C-NMR technology was used to study the pyrolysisprocess of PF1.2resin, the relationship between phenolic resin char yield and itsstructure was discussed. Results showed that the relative content of irreplaceablemethylene in the structure of phenolic resin was a main factor influencing phenolicresin heat resistance and the char yield. The thermal stability of (P-P ’) methylene washigher than that of O-O’ methylene, O-O ’ methylene could be naphthenic intoxanthene ring with two adjacent phenolic hydroxyl before pyrolysis of the resin,thereby increasing the resin char yield.The pyrolysis processes of boron phenolic resin (BPF) and PF1.2werecomparatively studied, the impact of introducing boron element on the phenolic resinthermal stability and char yield was explored, and the major structural factorsinfluencing boron phenolic resin char yield and the temperature range of its pyrolysischar were identified. The results showed that the introduced boronic acid changedmolecular structure of the phenol resin by generating boron ester bond. It was becausethe generated keys in Boronic acid-modified phenolic resin that made it had a higher heat resistance and char yield than the homemade ammonia phenolic resin.The analysis results of XRD, Raman spectroscopy and metallographicobservation showed that after the heat treatment of high temperature above1600℃,six elements had different degrees of catalytic graphitization effect on phenolic resincarbon. The catalytic graphitization process of boron on phenolic resin carbonmaterials was as follows: Boron atoms formed a solid solution with carbon bydiffusion at high temperature; the defect position of boron atoms into thesix-membered ring carbon material plane promoted the improvement of the graphitestructure. Therefore, amorphous carbon material catalyzed by boron could beconverted into a homogeneous Component A. Catalytic mechanism of manganese wassimilar to that of boron, but its catalytic graphitization was worse than boron;Chromium and carbon materials form the carbide at high temperatures, chromiumcarbide was decomposed and transformed into Ts component; Phenolic resin carbonwas dissolved first in elemental iron, elemental cobalt and elemental nickel and thengraphite Component G and Component Ts were precipitated.The resistance, bending strength, friction coefficient and wear of blank sampleadded respectively to boron, iron and chromium, phenolic carbon-based C/Ccomposites were comparatively studied. Experimental results showed that theresistivity of blank sample was up to39.44μ m because the carbon matrix wasdifficult to graphitize, the resin carbon containing catalyst had a higher degree ofgraphitization; among them, the resistivity of boron catalytic was16.82μ m, theresistivity of the iron catalyzed sample was19.82μ m, the resistivity of chromiumcatalyzed sample was30.72μ m, the resistivity matrix carbon after catalyticgraphitization reduced significantly. The interface bonding strength of matrix carbonafter catalytic graphitization and carbon fiber weakened, leading to the decrease ofC/C composites bending strength. The bending strength of C/CBlankwas up to176MPa, the bending strength of C/CB、C/CFeand C/CCrwere115MPa、66MPa and53Mpa, respectively, indicating the bending strength of C/C composites in the matrixcarbon containing catalyst reduced. The catalytic graphitization had a distinct effecton the tribological properties on phenolic carbon matrix C/C composites. The frictioncoefficient of blank sample was0.71, and the friction coefficients of boron catalyticsamples and iron catalytic sample were low, they were0.27and0.28respectively.Wear extent was related to the interface bonding situation of matrix carbon and carbonfiber, weak interfacial bonding C/CFecomposites materials had the biggest wearextent, and strong interfacial bonding C/CBlankand C/CBcomposites had the smallest wear extent.更多还原