聚丙烯腈(PAN)基预氧丝的炭化工艺研究

利用正交实验,探索了PAN基预氧丝的炭化工艺条件,重点讨论了升温速率、炉内气压和张力大小对最终获得的聚丙烯腈基炭纤维(PAN-CF)性能的影响,结果表明,在1000℃采用适宜的炭化工艺条件炭化时,可制得拉伸强度(σ)为2.79 GPa,拉伸模量(E)为278.8 GPa的PAN-CF。     

炭纤维粉改性中间相沥青基泡沫炭的结构与性能

以添加聚丙烯腈基炭纤维粉的萘基中间相沥青为原料,采用高温自发泡法制备泡沫炭,研究炭纤维粉含量和不同石墨化温度对泡沫炭的微观结构、力学性能和导热性能的影响。结果表明,添加炭纤维粉可明显改善泡沫炭的压缩强度和热导率。纤维粉与沥青炭界面的应力石墨化作用可提高沥青炭的微区石墨化度,使其石墨微晶尺寸增大,从而泡沫炭的热导率得以提高。当炭纤维粉质量分数为6%时,泡沫炭的压缩强度达最高为18 MPa,石墨泡沫的压缩强度和热导率分别为8.1 MPa和83.0 W/(m·K),较未添加炭纤维粉的石墨泡沫的热导率(39.2 W/(m·K))提高一倍。     

热压工艺对碳纤维增强铜基复合材料力学性能的影响

研究了热压工艺对碳纤维增强铜基复合材料力学行为的影响。结果表明:随热压温度的提高,CF/Cu复合材料的拉伸强度增大,显微硬度提高;热压温度超过800℃后,材料的强度和显微硬度随热压温度的升高而降低。对复合材料显微组织的研究表明,随热压温度的提高,材料的显微组织更加均匀。SEM断口分析表明:CF/Cu复合材料的断裂以纤维拔出为主要方式。     

聚甲氧基有机硅/莫来石杂化材料的高温处理与热膨胀性能研究

制备了耐高温低膨胀聚甲氧基有机硅(PMOS)/莫来石杂化材料.FT-IR与XRD测试表明材料在热处理过程中PMOS基体逐渐降解,而莫来石晶体则随温度的升高而稍有生长;TG测试表明材料在800℃高温处理后仍有93.4%的质量残留;SEM显示莫来石均匀分散在PMOS基体中;材料的冲击强度随热处理温度的升高而先减小后增大,800℃热处理后材料的冲击强度为924 J/m2;材料的膨胀系数很低,且随莫来石含量的增加而减小;聚甲氧基有机硅/莫来石杂化材料具有良好的耐高温性能与低热膨胀性能.     

聚丙烯腈预氧丝的炭化结构和性能

通过负压力炭化实验,研究了2种PAN基预氧丝在不同温度下的炭化结构和性能,并将所得炭纤维的性能与相同条件下测试的,T300和TX-3相比较。研究表明:在相同炭化工艺条件下,国产PAN基预氧丝炭化后所得CF的失重率、微晶尺寸较大,层面间距较小,最佳性能超过了T300和TX-3;国外预氧丝获得的炭纤维性能在1300℃前炭化时比国产预氧丝稍差,但其最佳性能也超过T300和TX-3。     

高炉焦炭石墨化对其高温冶金性能的影响研究

针对焦炭在高炉内的石墨化过程,通过不同的加热温度,将恒温时间分别设定为0.5h和1.5h,对试验后焦炭样品进行微晶结构、粉化率及石墨化度等参数测定。实验结果显示,随着二次加热温度的上升,焦炭的La、Lc值均呈上升趋势,且恒温时间对La、Lc值的升高有促进作用;d002随二次加热温度的上升而降低;二次加热温度升高后焦炭的粉化率也随之增大,恒温时间的延长使焦炭结构劣化加剧,粉化现象更加明显,粉化率增大。由于焦炭的石墨化过程是一个放热过程,因此二次加热后的焦炭热值也会下降,且恒温时间越长热值下降越明显。     

放电等离子烧结下碳化硼对聚丙烯腈基碳纤维石墨化的影响

采用放电等离子烧结(spark plasma sintering,SPS)工艺制备碳纤维增强碳化硼(C_f/B₄C)复合材料,通过X射线衍射和激光拉曼光谱对聚丙烯腈(polyacrylonitrile,PAN)基碳纤维石墨化度进行表征,重点研究烧结温度、烧结压力和保温时间对碳纤维石墨化的影响。结果表明,温度、压力和保温时间均对碳纤维石墨化有影响,其中烧结温度的影响最明显。烧结温度为2 000℃时,碳纤维的(002)晶面间距d(002)和拉曼光谱中D峰强度I_D与G峰强度I_G的比值分别为0.336 nm和0.377,石墨化度达到92.21%。根据XRD所测的石墨化度和拉曼光谱中R^-1的对应关系,拟合得到拉曼光谱表征碳纤维石墨化度的公式。SPS下PAN基碳纤维的低温石墨化是由于SPS综合了温度、压力和电流的影响,以溶解-再析出为主要催化机理,其中界面活化程度或许是产生碳纤维石墨化度差异的根本原因。     

短纤维增强C/C-SiC复合材料的制备工艺

为缩短制备周期和降低成本, 采用水悬浮法制得含硅短炭纤维料饼, 经树脂模压成形和炭化后成为预制体, 再经浸渍/炭化增密和高温反应生成SiC, 制备了C/C SiC复合材料, 并对材料的显微组织、物相组成、石墨化度、力学性能和摩擦磨损性能进行了研究。结果表明制备的预制体密度为1.1 g·cm-3左右, 短炭纤维优先在摩擦面上交错排布, 部分在厚度方向上排布, 预制体中硅颗粒分布均匀; 最终石墨化处理后, 复合材料密度为1.75 g·cm-3左右, 组成相为炭和βSiC, 其中炭的石墨化度为54%左右; 复合材料的破坏形式为脆性断裂, 材料基本具有功能材料应具备的结构力学性能; 随炭纤维体积含量的增加, 材料的摩擦因素和磨损率均呈下降趋势,纤维体积含量为25%时具有适中的摩擦磨损性能, 摩擦因素为0.28, 磨损率为2.75 mm3·kJ-1。     

含炭纤维湿式铜基摩擦材料的性能

采用粉末冶金方法制备含短炭纤维的湿式铜基摩擦材料,研究炭纤维含量对湿式摩擦材料的摩擦磨损性能和力学性能的影响,以及制动条件对动摩擦因数的影响。结果表明:随着炭纤维含量及材料的孔隙率增加、硬度及密度均降低,摩擦因数呈先增加后减小的变化趋势,磨损量呈先减小后增大的趋势。炭纤维含量为(质量分数)1%时材料的摩擦磨损性能最好,摩擦因数最大且最稳定,磨损量最小。材料摩擦因数随着载荷增大而增大,随炭纤维含量增加磨损率呈先减小后增大的趋势。炭纤维的加入提高了材料的能量许用值。     

高炉焦炭石墨化过程中的微观组织和冶金性能演变

当前低碳高炉冶炼条件下使得炉内焦炭层变薄,恶化了料柱的透气透液性,焦炭在炉缸高温区石墨化过程中产生的焦粉是导致该现象出现的主要原因之一.为了研究焦炭在高炉下部的石墨化过程对其在炉缸内的冶金性能影响,研究了1100~1500℃不同温度下焦炭的石墨化度改变;同种焦炭石墨化程度与焦炭反应性及反应后强度之间的关系;不同石墨化度焦炭与碱金属侵蚀之间的关系;观察并分析了试验后不同焦炭试样的微观形貌.结果表明,随着温度的升高,焦炭石墨化程度加深,且温度每升高100℃,焦炭石墨化度约提高1.8倍,层间距d₀₀₂值约降低2%,微晶结构层片直径L_a值约提高3%,层片堆积高度L_c值约提高15%;焦炭的表面气孔减少,特别是大气孔减少,焦炭表面镶嵌组织减少,各向同性组织增多,焦炭的结构有序化程度增强.随着焦炭石墨化程度的加深,焦炭的反应性逐渐减小、反应后强度逐渐提高,焦炭表面的劣化情况减弱,生成的大气孔减少,气孔壁破坏趋势减弱.碱金属对焦炭的反应性有促进作用,使焦炭的反应性提高,反应后强度降低.而焦炭的石墨化对焦炭的碱侵害具有一定的抵抗作用,降低了焦炭表面的劣化程度.      

Effect of Rare Earths on Tribological Properties of Carbon Fibers Reinforced PTFE Composites

Carbon fibers （CF） were surface treated with air-oxidation and rare earths （RE）, respectively. The effect of RE surface treatment on tensile strength and tribological properties of CF reinforced polytetrafluoroethylene （PTFE） composites was invest/gated. Experimental results revealed that RE was superior to air ox/dation in improving the tensile strength, elongation, and the tensile modulus of CF reinforced PTFE （CF/PTFE） composite. Compared to the untreated and air-oxidated CF/PTFE composite, the RE treated composite had the lowest friction coefficient and specific wear rate under a given applied load and reciprocating sliding frequency. The RE treatment effectively improved the interfacial adhesion between CF and PTFE. With strong interfacial coupling, the carbon fibers carried most of the load, and direct contact and adhesion between PTFE and the counterpart were reduced, accordingly the friction and wear properties of the composite were improved.     

Activated graphitization of carbon fibers in a composite material with a nickel matrix

Conclusions Activated graphitization of nickel-plated carbon fibers commences at the instant when diffusional penetration of the nickel into the fibers begins. As nickel-activated graphitization advances, the amount of nickel in the fibers rises, reaching some hundredths of one weight percent in fully graphitized fibers. A dominant role in the initiation and propagation of nickel-activated graphitization of carbon fibers is played by the high dispersion of their internal structure, which ensures effective penetration of nickel into the fibers at anomalously low temperatures. A hypothesis is advanced according to which the graphite phase appearing in carbon fibers during their nickel-activated graphitization forms through the packing of structural complexes — defect-free portions of the (002) basal planes of the graphite structure.Translated from Poroshkovaya Metallurgiya, No. 4(208), pp. 57–62, April, 1980.     

石墨化钢石墨化过程的金相分析及其动力学方程

在650、680和710 ℃不同温度条件下对碳质量分数为0.66%的淬火高碳钢进行了石墨化处理,并利用场发射扫描电子显微镜、电子探针、X-射线衍射仪和透射电子显微镜对其石墨化过程的组织进行金相分析,以及利用组织转变动力学理论,绘制了其石墨化过程的动力学曲线,并建立了相应的动力学方程。研究结果显示:在石墨化过程中,淬火马氏体首先向析出碳化物的稳定状态转变,且在碳化物为渗碳体Fe₃C时,石墨粒子析出速度开始明显增加;基体组织中针叶状α-Fe发生再结晶,由等轴状铁素体逐步代替针叶状的α-Fe;铁素体中的碳含量随着石墨化时间的延长而逐步降低,即由过饱和状态转变为稳定态,碳含量在石墨粒子中突变增为峰值,而铁含量则突变降为谷值,由此表明,渗碳体分解的碳向石墨核心扩散,铁自石墨核心处扩散出来,而形成石墨粒子;石墨粒子面积分数随时间变化的曲线呈S形状,即该动力学过程符合动力学模型JMAK（Johnson-Mehl-Avrami-Kolmogorov）方程,且该方程中的n值为1.5～1.7。      

Mechanical properties and strength retention of carbon fibre-reinforced liquid crystalline polymer (LCP/CF) composite: an experimental study on rabbits

A novel composite material with ultra-high flexural strength and cortical-bone-matched elastic modulus made of liquid crystalline polymer reinforced with carbon fibres (LCP/CF) is described. Cylindrical rods of 3.2 mm diameter and 50 mm length were fabricated by a preimpregnation/pultrusion method. The initial mechanical properties of the LCP/CF rods were as follows: flexural strength 448 MPa, flexural modulus 43 GPa, shear strength 164 MPa, and interlaminar shear strength 15.3 MPa. In the in vitro study the LCP/CF rods were immersed in phosphate-buffered saline of 37 degrees C for 12, 24, and 52 weeks. In the in vivo study the LCP/CF rods were implanted into the medullary cavity of both femora and subcutaneous tissue of the New Zealand White rabbits for 12, 24, and 52 weeks. The flexural strength of the LCP/CF rods at 52 weeks was 463 MPa in saline, 467 MPa in the subcutaneous tissue and 466 MPa in the medullary cavity of the femur. The flexural modulus was 44.6, 48.9 and 46.2 GPa, respectively. The corresponding shear strength values were 160, 178 and 181 MPa. We conclude that the LCP/CF is a promising material for high-load applications and the LCP/CF rods retain their initial mechanical properties in one-year follow-up in vivo and in vitro.     

Cementites decomposition of a pearlitic ductile cast iron during graphitization annealing heat treatment

Cementites decomposition of a pearlitic ductile cast iron during graphitization annealing heat treatment was investigated.Fractographies and microstructures of heat treated samples were observed using a scanning electron microscope and mechanical properties were measured by a universal tensile test machine.The results indicated that during isothermal annealing at 750°C,the tensile strength of pearlitic ductile cast iron was increased to a peak value at 0.5h,and decreased gradually thereafter but the elongation was enhanced with the increase of annealing time.Moreover,the diffusion coefficient of carbon atoms could be approximately calculated as 0.56μm2/s that could be regarded as the shortrange diffusion.As the holding time was short(0.5h),diffusion of carbon atoms was incomplete and mainly occurred around the graphites where the morphology of cementites changed from fragmentized shape to granular shape.In addition,the ductile cast iron with tensile strength of 740MPa and elongation of 7% could be achieved after graphitization annealing heat treatment for 0.5h.Two principal factors should be taken into account.First,the decomposition of a small amount of cementites was beneficial for increasing the ductility up to elongation of 7%.Second,the diffusion of carbon atoms from cementites to graphites could improve the binding force between graphites and matrix,enhancing the tensile strength to 740 MPa.     

熔盐电化学石墨化研究进展及展望

近年来,提出了一种高效、环境友好的熔盐电化学转化方法,可将碳污染物直接转化为高附加值的石墨化产物。本文综述了熔盐电化学石墨化的工艺流程、产物的结构特征与转化机理。详细介绍了碳纳米材料在锂离子电池和铝离子电池等二次电池中的应用前景,突出了转化和利用丰富的二次碳资源实现高附加值应用的高效策略。最后,对开发熔盐电化学石墨化与规模化低能耗电解技术、构建先进高温熔盐电化学原位表征技术与定量化分析方法、深入研究电化学石墨化微观转化机理、推动石墨化产品的工程化应用进行了分析与展望。      

Residual Tensile Properties of GFRP Reinforcing Bars after Loading in Severe Environments

The long-term behavior of glass fiber-reinforced polymer (GFRP) reinforcing bars is one of the most critical issues for the acceptance of these materials as reinforcement for concrete structures. There is a high demand for experimental studies to investigate the stability of the tensile strength, ultimate elongation, and elasticity modulus. GFRP reinforcing bars inherently have a low elasticity modulus, which must not significantly decrease over time under loading or the serviceability behavior of the concrete element containing them will be jeopardized. This paper evaluates the residual tensile properties of three sizes of sand-coated GFRP reinforcing bars in alkaline and water environments combined with sustained loading and elevated temperature. Bar diameters of 15.9 (No. 5), 12.7 (No. 4), and 9.5?mm (No. 3) were loaded for different durations, then tested in axial tension for residual tensile properties. The test periods varied from 1?to?4?months under elevated temperature to hasten degradation and simulate extended service periods. The reduction in tensile strength was found to be 7–13% of the guaranteed strength for the three bar sizes under elevated temperature, which is at least 26% higher than the specified design strength as recommended by ACI 440.1R-03. More importantly, no significant change in the elastic modulus was observed.     

炭化工艺参数对铁焦冶金性能的影响

摘要：复合铁焦被认为是实现低碳高炉炼铁的革新技术之一。为了获得高质量的铁焦,需要采用适宜的炭化工艺条件。研究了炭化工艺参数对铁焦机械强度、反应性和反应后强度等冶金性能的影响,并对炭化后铁焦的金属化率、微观结构和碳微晶结构进行了解析。结果表明,炭化温度的升高可以提高铁焦的抗压强度和反应性。当温度为900～1000℃时,铁焦的抗压强度和反应性较优。炭化时间的延长可以使铁焦的抗压强度提高,反应性降低。当炭化时间为3～4h时,铁焦抗压强度和反应性较优。升温速度越快,铁焦的机械强度越低。适宜的升温速度为:Ⅰ段（室温至550℃）小于7℃/ min,Ⅱ段（550℃至1000℃）小于5℃/min。为防止铁焦冶金性能因碳气化溶损反应而劣化,在CO和CO2混合炭化气氛中,CO2与CO体积比(V(CO2)/V(CO))应控制在0.11以下。在优化的炭化工艺条件下,制备的铁焦抗压强度大于3500N,反应性大于60%,反应后强度在16%左右。     

The effect of thermal exposure on the mechanical properties of aluminum-graphite composites

The mechanical properties of aluminum-graphite composites were measured at room temperature in the as-received condition, after elevated temperature exposure and after thermal cycling. The composites were fabricated by solid-state diffusion bonding of liquid-phase Al-infiltrated Thornel 50 fibers. The results showed that the maximum longitudinal tensile strength of the as-received material was 80,000 psi (552 MN/m²), which corresponds well with the rule of mixture value. The composite strength was observed to vary widely, depending on the extent of wetting of the fibers by the aluminum. The strength of the composites in the transverse direction was generally very low, due to poor interfacial bonding. Aluminum carbide (A1₄C₃) formed at the surface of the fibers at temperatures greater than 500‡C (773 K). Development of the carbide was shown to be diffusion-controlled and was dependent on the time and temperature used. It was shown that the tensile strength was virtually unaffected by heat-treatment up to 500‡C (773 K); beyond that temperature a drastic degradation of tensile strength occurred. The degradation could be correlated with the extent of carbide development at the interface. Thermal cycling of the composites below 500‡C (773 K) resulted in an observable degradation of the composite strength. Scanning electron microscopy of fractured surfaces indicated that the relatively weak interface governs the mode of failure in tension.