Carbon fiber reinforced carbon aerogel composites for thermal insulation prepared by soft reinforcement

To overcome the brittleness and the pyrolysis shrinkage of carbon aerogels, carbon fiber reinforced composites were prepared by copyrolysis of polyacrylonitrile fiber reinforced resorcinol-formaldehyde aerogel composites (PAN/RFs). The PAN/RFs were obtained by impregnating the PAN fiber felt with RF sol and then supercritical drying. Upon carbonization the PAN fiber shrinks with the RF aerogel, thus reducing the shrinkage differences between the fiber and the aerogel, and results in crack-free carbon fiber reinforced carbon aerogel composites, with a thermal conductivity of 0.073 W/m K at 25 °C in air. Our new method may greatly expand the usage of carbon aerogels in general applications.     

耐高温氧化铝气凝胶隔热复合材料研究进展

氧化铝气凝胶是一种高孔隙率、低密度、高比表面积、耐高温和低热导的纳米多孔材料,在高温隔热领域(如航天飞行器热防护系统、工业窑炉保温材料等)具有广阔的应用前景.但是,纯氧化铝气凝胶因耐温性(1000℃以上)、力学性能和高温隔热性能相对较差难以直接应用,需要引入增强相和遮光组分制备成气凝胶复合材料以进行改善.本文对耐高温氧...     

Aramid fibers reinforced silica aerogel composites with low thermal conductivity and improved mechanical performance

Aramid fibers reinforced silica aerogel composites (AF/aerogels) for thermal insulation were prepared successfully under ambient pressure drying. The microstructure showed that the aramid fibers were inlaid in the aerogel matrix, acting as the supporting skeletons, to strengthen the aerogel matrix. FTIR revealed AF/aerogels was physical combination between aramid fibers and aerogel matrix without chemical bonds. The as prepared AF/aerogels possessed extremely low thermal conductivity of 0.0227 ± 0.0007 W m⁻¹ K⁻¹ with the fiber content ranging from 1.5% to 6.6%. Due to the softness, low density and remarkable mechanical strength of aramid fibers and the layered structure of the fiber distribution, the AF/aerogels presented nice elasticity and flexibility. TG–DSC indicated the thermal stability reaching approximately 290 °C, can meet the general usage conditions, which was mainly depended on the pure silica aerogels. From mentioned above, AF/aerogels present huge application prospects in heat preservation field, especially in piping insulation.     

SiOC气凝胶/柔性陶瓷纤维复合材料的制备和性能

选用正硅酸乙酯(TEOS)和甲基三甲氧基硅烷(MTMS)为前驱体,用溶胶-凝胶法制备不同C/Si(原子比,下同)比的SiOC气凝胶,再用大气喷涂法将其喷涂在柔性陶瓷纤维隔热毡中制备出SiOC气凝胶/柔性陶瓷纤维复合材料。C/Si比,是影响SiOC气凝胶/柔性陶瓷纤维复合材料性能的主要因素。随着C/Si比的提高SiOC溶液的凝胶时间延长且更易浸入隔热毡,材料的密度和热导率先降低后提高。C/Si比为0.67的材料热导率最低,其室温热导率为0.026 W/m·K,1000℃时的热导率为0.174 W/m·K。与未改性的隔热毡相比,其热导率显著降低,尤其是在高温下热导率降低47%;同时,这种材料还具有优异的耐高温和抗氧化性能,在1200℃空气中静烧1 h后试样的质量损失只约为1%,静烧3 h后约为5%,随着C/Si比的提高其质量损失随之提高;同时,SiOC气凝胶复合材料还具有良好的疏水性能、柔性和回弹性。     

预测纤维增强气凝胶复合材料热导率的研究进展

SiO2气凝胶复合材料具有纳米尺度结构和极低热导率,作为隔热保温材料在航天航空、建筑和其他工业领域具有重要的科学和应用价值。根据纤维在气凝胶基体中的不同分布方式,概述了预测 SiO2气凝胶复合材料的气固耦合热导率的研究进展;基于纤维和气凝胶的消光系数的不同计算方法,概述了预测 SiO2气凝胶复合材料的辐射热导率的研究进展。并提出了纤维增强气凝胶复合材料体系存在的跨尺度、多物相、分级及相互耦合等仍需进一步解决的难题,结合最新发展的格子 Boltzmann 方法(LBM),指出了预测 SiO2气凝胶复合材料等效热导率的可能发展方向。     

遮光剂掺杂Al2O3-SiO2气凝胶/莫来石纤维毡复合材料的高温隔热性能研究

分别以TiCl₄和ZrOCl₂·8H₂O作为钛源和锆源, 经过溶胶-凝胶和超临界CO₂干燥过程, 将遮光剂粒子TiO₂和ZrO₂掺入到Al₂O₃-SiO₂气凝胶, 并进一步以莫来石纤维毡为增强相制备出具有一定力学性能的耐高温气凝胶复合材料, 分别探究了两种遮光剂粒子对复合材料的微观结构、力学性能和热导率的影响。结果显示: 遮光剂粒子的引入可以有效阻止气凝胶在高温下的塌陷和团聚, 保持气凝胶高孔隙率的特性; 复合材料呈现典型的气凝胶填充纤维结构, 并且具有轻质(0.21~0.24 g·cm^-1)和高强度(弯曲强度为0.98~1.26 MPa)的优异性能, 拓展了材料的实用性; 在 1050℃的高温下, 由于 TiO₂ 和 ZrO₂ 粒子对红外电磁波具有吸收和散射作用, 可以将复合材料的热导率由0.098 W·m^-1·K^-1分别降低至0.085 W·m^-1·K^-1和0.076 W·m^-1·K^-1, 从而有效提高材料的高温隔热性能。     

High strain recovery with improved mechanical properties of gelatin–silica aerogel composites post-binding treatment

Silica aerogels are very light and highly porous materials that are intriguingly and complexly networked with large internal surface area, high hydrophobicity with extremely low density and thermal conductivity. These features make them ideal choice for applications as thermal and acoustics insulators or as optical, electrical, and energy storing devices. However, their exploitation for structural applications is primarily inhibited by their brittleness. The brittleness of the silica aerogels makes their processing and handling difficult. Volumetric shrinkage occurs, which becomes more apparent at elevated temperatures. While there are hybrid silica aerogels doped with materials such as polymer, ceramics, metals in the market, the improvements in the mechanical properties are compromised with tremendous increase in density and reduction in the insulation performance. Post-synthesis binding treatment of silica aerogels composites are not extensively explored due to the chemically inert trimethylsilyl (TMS) terminal groups on the surface of the hydrophobic silica aerogels. This paper discusses a unique fabrication method of developing a ductile silica aerogel composite solid via post-synthesis binding treatment. Gelatin–silica aerogel (GSA) and GSA–sodium dodecyl sulfate (SDS) composite blocks were produced by mixing hydrophobic aerogel granulates in a gelatin–SDS foamed solution by frothing method. The entire fabrication process and grounds for using a controlled % of gelatin as the main binder and SDS as an additive are explained. The compression testing of the blocks is presented. The associated strain recovery—an unusual phenomenon with brittle silica aerogels, observed upon unloading is highlighted and studied. The microstructure and surface characterization of these composites was examined via FESEM/EDX and XPS/ESCA, respectively. The dependency of process variables involved were analyzed through analysis of variance (ANOVA) model. Empirical models that relate the composition of gelatin, aerogel, and SDS to achieve the optimal strain recovery with the associated compressive modulus and strength and density are established. The transition from brittleness to ductility is measured in terms of compressive stress versus strain behavior for various mass fractions of gelatin and SDS. The test data presented indicate analogous behavior of these to creep-like behavior of a material typically identified as the primary, secondary, and tertiary stages. The rationale and mechanisms behind such creep-like three stages are explained using schematic diagrams.     

PAN基预氧化纤维不织布增强酚醛树脂制作炭/炭复合材料

以预氧化纤维不织布经不同热处理后,采用液态含浸法浸酚醛树脂后经热压成型,制成炭／炭复合材料前驱体,随之将这些前驱体经２３０℃稳定化,６００℃及１０００℃炭化处理,讨论了不同纤维不织布的结构变异,以及各种炭／炭复合材料其微细结构及物性之变化,在物性分析方面,主要是以挠曲强度的测试为骨架,并以扫瞄式电子显微镜（ＳＥＭ）观察破断表面,探讨各种复合材料经不同温度处理后之破坏行为,研究结果显示,以预氧化纤维及经６００℃处理后之纤维所制复合材料经三个不同温度（２３０℃,６００℃,１０００℃）处理后,其破坏行为均呈现剧烈的脆性破坏,且具有平滑之破断表面,而以经１０００℃处理后之纤维所制复合材料经６００℃及１０００℃炭化后则呈现拟塑性破坏模式,并伴随显著的纤维拖出现象。     

溶胶配比对碳纤维增强炭气凝胶隔热复合材料力学性能的影响

以异丙醇(I)为溶剂、 六次甲基四胺(H)为催化剂, 配制间苯二酚(R)-糠醛(F)的醇溶胶, 经浸渍纤维预制件、凝胶老化、超临界干燥和炭化制得碳纤维增强炭气凝胶隔热复合材料。研究了溶胶配比对碳纤维增强炭气凝胶隔热复合材料密度、微观结构和力学性能的影响规律。结果表明:随着异丙醇与间苯二酚物质的量之比增大, 碳纤维增强炭气凝胶隔热复合材料的密度逐渐降低, 基体炭气凝胶内及与碳纤维形成的界面内孔径增大, 大孔数量增多, 碳纤维增强炭气凝胶隔热复合材料的强度降低。当异丙醇与间苯二酚物质的量之比由18增加到28时, 压缩强度由2.498 MPa(应变10%)降至0.716 MPa(应变10%), 拉伸强度由2.019 MPa降至1.001 MPa, 弯曲强度由3.984 MPa降至1.818 MPa。随着六次甲基四胺与间苯二酚物质的量之比增大, 碳纤维增强炭气凝胶隔热复合材料的密度先增大后减小, 基体炭气凝胶内及与碳纤维形成的界面内孔径先减小后增大, 大孔数量先减少后增加, 碳纤维增强炭气凝胶隔热复合材料的强度先增大后减小。当六次甲基四胺与间苯二酚物质的量之比为0.008 5时, 碳纤维增强炭气凝胶隔热复合材料的密度最大, 强度最大, 其压缩强度为1.066 MPa(应变10%), 拉伸强度为1.256 MPa, 弯曲强度为3.556 MPa。      

(C-SiC)f/C复合材料的烧蚀性能

将SiC纤维毡与C纤维毡交替层叠, 通过针刺工艺制备(C-SiC)_f/C预制体, 采用化学气相渗透与前驱体浸渍裂解复合工艺(CVI+PIP)制备(C-SiC)_f/C复合材料, 研究(C-SiC)_f/C复合材料H₂-O₂焰烧蚀性能。利用SEM、EDS和XRD对烧蚀前后材料的微观结构和物相组成进行分析, 探讨材料抗烧蚀机理。结果表明: (C-SiC)_f/C复合材料表现出更优异的耐烧蚀性能。烧蚀750 s后, (C-SiC)_f/C复合材料的线烧蚀率为1.88 μm/s, 质量烧蚀率为2.16 mg/s。与C/C复合材料相比, 其线烧蚀率降低了64.5%, 质量烧蚀率降低了73.5%; SiC纤维毡在烧蚀中心区表面形成的网络状保护膜可以有效抵御高温热流对材料的破坏; 在烧蚀过渡区和烧蚀边缘区形成的熔融SiO₂能够弥合材料的裂纹、孔洞等缺陷, 阻挡氧化性气氛进入材料内部, 使材料表现出优异的抗烧蚀性能。     

SiO2/C/M气凝胶纳米复合材料的结构及吸波性能

本文在SiO2/M(M=Fe,Co,i)复合气凝胶骨架上采用气相催化裂解乙炔的方法合成出SiO2/C/M气凝胶纳米复合材料,用扫描电镜、比表面分析仪、激光导热仪等对材料的结构和物理性能进行了表征,并初步测试了其电磁吸波性能.结果表明,在SiO2/C/M气凝胶纳米复合材料中,碳元素一般以纤维形式均匀分布于气凝胶骨架中,该材料具有低密度,低热导率().05～0.2W/mk),在2mm厚度,8-18GHz的范围内有一定的吸波性能,且吸波性能随频率升高而增加.     

纤维素纳米纤丝-还原氧化石墨烯/聚苯胺气凝胶柔性电极复合材料的制备与性能

利用高长径比的纤维素纳米纤丝（CNF）与片层结构的氧化石墨烯（GO）形成的CNF-GO复合水凝胶经抗坏血酸还原制备出CNF-还原氧化石墨烯（rGO）复合水凝胶材料。通过冷冻干燥法得到CNF-rGO复合气凝胶,并进一步通过苯胺单体在CNF-rGO复合气凝胶的孔道内原位聚合制备出CNF-rGO/聚苯胺（PANI）气凝胶柔性电极复合材料。研究了不同苯胺、CNF和GO的质量比对CNF-rGO/PANI气凝胶柔性电极复合材料的结构形貌和电化学性能的影响。结果表明,苯胺原位聚合后所得CNF-rGO/PANI复合气凝胶仍具有紧密的三维多孔网络结构。与rGO/PANI气凝胶电极复合材料相比,CNF-rGO/PANI气凝胶电极复合材料具有更理想的电容行为。当CNF与GO质量比为60∶40,PANI添加量为0.1 mol时,CNF-rGO/PANI气凝胶电极复合材料比电容可达85.9 Fg-1,且其电化学性能几乎不受弯曲程度的影响,展现出了良好的柔韧性和电化学性能。      

莫来石纤维增强SiO2气凝胶复合材料的制备及性能研究

以正硅酸乙酯为硅源,采用溶胶-凝胶及超临界干燥技术制备了掺杂莫来石纤维的SiO2气凝胶复合材料,并对材料的热学性能和力学性能进行了测试,结果表明:SiO2气凝胶复合材料的热导率与其密度、温度和纤维添加量有关;添加莫来石纤维可以明显提高SiO2气凝胶的弹性模量和机械强度,改善材料的力学性能;莫来石纤维添加量控制在3%左右可以使SiO2气凝胶材料保持较低的热导率和较高的机械强度.     

石墨烯/炭气凝胶的制备及其结构与性能研究

以间苯二酚(R)和甲醛(F)为炭前驱体原料, 通过溶胶-凝胶法制备石墨烯/炭气凝胶复合材料。采用XRD、Raman、SEM和N₂吸附/脱附等对样品进行结构表征。结果表明: 石墨烯为R和F的聚合提供形核场所, R和F首先在氧化石墨烯(GO)表面聚合, 随着RF含量的增加, 复合炭气凝胶(RF)结构从石墨烯薄片层为骨架的三维网络, 经RF基炭球包裹于石墨烯的网络结构, 最终转变为球形团簇交联的三维网络。石墨烯/炭气凝胶复合材料的比表面积随着RF的增加先增大后减小。当GO与RF质量比为1︰100时, GO/RF-100用作超级电容器电极材料, 在6 mol/L KOH电解液中的比电容达169 F/g, 具有较好的电容特性。     

SiO_2溶胶配比对气凝胶隔热复合材料力学性能的影响

以无机陶瓷纤维为增强体,与SiO2溶胶混合,经超临界干燥制备了SiO2气凝胶隔热复合材料,研究了SiO2溶胶配比对气凝胶及其复合材料微观结构和力学性能的影响。结果表明,随着SiO2溶胶中乙醇含量的增大,SiO2气凝胶的密度逐渐降低,平均孔径增大,气凝胶中含有的大孔、连孔数量增加,网络骨架结构强度降低。纤维与SiO2气凝胶复合后,气凝胶充满了纤维间的孔隙,形成较好的界面结合。当乙醇/正硅酸乙酯(EtOH/TEOS)摩尔比由2∶1增加到20∶1时,SiO2气凝胶基体传递载荷能力逐渐减弱,材料的力学性能逐渐降低,其拉伸强度、弯曲强度和压缩强度分别由1.9 MPa、2.7 MPa、1.73 MPa(10%应变)降低到0.17 MPa、0.12 MPa、0.04 MPa(10%应变)。     

腈纶废丝/硬脂酸相变纤维的制备及性能研究

以硬脂酸(SA)为相变储能物质,腈纶废丝(PAN)为聚合物基体,采用湿法纺丝法制备了PAN/SA相变纤维。研究表明,相变纤维中PAN与SA大分子依靠分子间作用力结合在一起;SA在纤维基体中分布均匀,无相分离现象;PAN/SA相变纤维的相变焓达到48.84J/g,且DSC热循环显示纤维具有较好的热稳定性;PAN/SA相变纤维相对于PAN纤维具有良好的保温性;PAN/SA相变纤维在110℃热空气中迅速干燥的力学性能优于常温处理的力学性能。     

Paraffin/carbon aerogel phase change materials with high enthalpy and thermal conductivity

Two kinds of carbon aerogels, graphene aerogels (GA) and carbon nanotubes-graphene aerogels (CGA), were prepared by modified hydrothermal method. The form-stable phase change materials (PCMs) were fabricated by adsorbing paraffin into carbon aerogels. Morphology, structure, form stability and thermal property were characterized by scanning electron microscope (SEM), in situ X-ray diffraction (in situ XRD) and differential scanning calorimeter (DSC). The results showed that GA presented wrinkled surface textures with curling edges, and carbon nanotubes (CNTs) were interspersed or attached to GA sheets. The phase transition temperature and the phase change enthalpy of the GA/paraffin PCM composite were 48.7 °C and 223.2 J/g, respectively. Thermal and mechanical properties of PCM composites achieved a qualitative leap with the adding of carbon aerogels. The PCM composites had a thermal conductivity of about 2.182 W/m K at the carbon aerogels loading fraction of 2 wt%. The form-stable PCM composites with high thermal conductivity and high enthalpy could be promising for thermal energy storage applications in construction field.     

Strong, low density, hexylene- and phenylene-bridged polysilsesquioxane aerogel–polycyanoacrylate composites

Nanocomposite aerogels were prepared by chemical vapor deposition and polymerization of cyanoacrylate on the surface of bridged polysilsesquioxane aerogels. Phenylene- and hexylene-bridged aerogels were prepared by sol–gel polymerizations and supercritical carbon dioxide drying. Hydrophobic organic bridging groups in the polysilsesquioxane aerogels reduced the amount of adsorbed water available for initiating polymerizations and led to higher molecular weight polycyanoacrylate than was observed with silica aerogels. Densities increased as much as 65% due to the addition of the organic polymer, but the nanocomposite aerogels remained highly porous with surface areas between 440 and 750 m²/g. Polycyanoacrylate–phenylene-bridged aerogel composites were the strongest with flexural strengths up to 780 kPa or 16-fold stronger than the untreated phenylene-bridged aerogels and fivefold stronger than a silica aerogel of the same density. The strongest polycyanoacrylate–hexylene-bridged aerogel composites had flexural strength of 285 kPa or ninefold stronger than the untreated hexylene-bridged aerogels and twice as strong as a silica aerogel of comparable density. The greater strength of the new composites is, in part, due to the greater strength of the bridged aerogels. However, higher molecular weight polycyanoacrylate, due to less surface water on the hydrophobic bridged aerogels, also contributes to the greater nanocomposite strengths.     

碳纤维上原位生长碳纳米管对C/C复合材料弯曲性能的影响

以碳毡为基底原位生长了碳纳米管（CNTs）,借助化学气相渗透制备了CNTs-C/C复合材料。研究了催化剂含量对碳纳米管生长的影响以及不同含量碳纳米管对C/C复合材料弯曲性能的影响。结果表明：催化剂对CNTs产量影响较大,且含量越多,生成的CNTs量越大;原位生长CNTs引入的催化剂会导致CNTs-C/C复合材料弯曲性能变差;CNTs的加入改变了热解碳的沉积行为,诱导了球状和锥状小尺寸热解碳的形成,减少了微裂纹的出现。适量CNTs能提高C/C复合材料的弯曲强度和模量,并改善材料的断裂行为。     

反应物结构对酚醛凝胶及其气凝胶的影响

为研究反应物酚与醛的结构对酚醛凝胶过程及其气凝胶结构的影响,采用不同的酚与醛制备出了多种气凝胶。研究了反应物结构对凝胶过程的影响,并通过扫描电镜和孔径分析仪等仪器详细研究了气凝胶的结构。结果表明,酚醛反应的凝胶时间受反应物的活性及位阻效应共同影响,反应体系选择不当可能导致无法凝胶。采用不同的酚-醛体系,所得气凝胶结构也...