中间相沥青基炭泡沫体的制备、结构及性能

以合成中间相萘沥青为原料，采用加压发泡法制备孔径均匀的初生炭泡沫体，经700℃～1000℃和2300℃～2800℃热处理制备出炭化和石墨化炭泡沫体；以700℃炭化处理所得的炭泡沫体作为芯材制成夹芯复合材料。研究了原料性能、发泡以及热处理工艺参数对炭泡沫微观结构和力学性能的影响，考察了炭泡沫体夹芯复合材料的微波吸收性能。结果表明：发泡过程中保持均匀的温度场是制备孔径均匀的炭泡沫体的关键因素，压力是影响孔结构的主要因素。炭泡沫体的微晶结构、力学性能以及微波吸收性能沿xy和XZ面方向（分别表示垂直和平行于重力方向）具有各向异性。     

中间相沥青基泡沫炭的制备、结构及性能

以萘系中间相沥青为原料,考察了发泡条件、炭化和石墨化工艺对所制泡沫炭结构和性能的影响.结合粘温曲线、TG-DTG热重曲线以及不同发泡条件下泡沫炭的表面形貌分析,其最佳发泡条件为:发泡温度600℃,升温速率5℃/min,发泡压力5MPa.石墨化升温速率越低越有利于泡沫炭石墨微晶的生长及压缩强度的提高,其中以5℃/min升温至2800℃并恒温30min所制泡沫炭的压缩强度达1.38MPa.     

纳米碳管对泡沫炭的超临界发泡行为及其力学性能的影响机制

采用超声波?磁力搅拌的方法, 实现了纳米碳管(CNTs)在中间相沥青(MP)中的均匀分散, 并考察了CNTs对泡沫炭的超临界发泡行为及其压缩强度的影响. 研究结果表明: 在超临界发泡过程中, 处于过饱和状态的甲苯将优先在CNTs/MP固-液界面处成核, 进而不断扩散、聚集、膨胀和发泡, 导致泡沫炭孔结构的均一性得以提高; 当在中间相沥青中均匀分散3.5wt%的CNTs后, 所制泡沫炭的压缩强度由3.2MPa提高到4.7MPa, 升高了46.9%; CNTs良好的导热性能降低了基体碳在石墨化过程中的热应力差异, 使得微裂纹的数量减少, 并且其一维纳米结构使得石墨化泡沫炭的孔壁和韧带结构得以增强.     

超临界流体制备中间相沥青泡沫炭及其导热性能研究

以奈系中间相沥青为原料,在初始压力2.0～4.0MPa的范围内,利用甲苯作为超临界溶剂制备中间相沥青基泡沫,并经氧化炭化和石墨化获得了三维网状结构的泡沫炭,利用扫描电镜、x射线衍射、激光导热测定仪分析了泡沫碳的结构和导热性能,研究了泡沫炭结构与其导热性能的关系.结果表明,不同条件下所制备得到的泡沫炭泡孔结构和孔分布的不同对导热系数影响较大,在2350℃下石墨化后导热系数达到42(W/mK).     

沥青炭的微观结构对其压缩强度的影响

将高温煤沥青和浸渍剂沥青在不同压力下炭化,在2500℃下对所得沥青炭进行石墨化处理;测试了所得沥青炭的体积密度、开孔率;利用扫描电子显微镜（SEU）观察了所得沥青炭的显微结构;利用XRD检测了所得沥青炭石墨化处理后的石墨化度;测试了所得沥青炭的压缩强度。结果表明：随着炭化压力的增大,沥青炭的体积密度增大而开孔率减小,压缩强度也随之增大;随着炭化压力的增大沥青炭显微结构呈由流线型向镶嵌型和域型转变的趋势;流线型结构沥青炭石墨化度较高,但也导致沥青炭的压缩强度降低。     

预氧化对中间相沥青泡沫炭结构和性能的影响机制研究

研究了预氧化对萘系中间相沥青的表面化学性质、族组成分布以及对泡沫炭的发泡条件、泡孔形成、孔结构及微结构的影响机制.当中间相沥青经210℃预氧化2h后,其喹啉不溶物含量增加32.3%,族组成分布变窄.在600℃/3MPa发泡条件下,所制石墨化泡沫炭的平均孔径、压缩强度分别为200μm、2.8MPa.     

新型轻质碳基泡沫材料研制

采用中间相沥青和原煤为碳源和发泡材料,硅粉为硅源,通过发泡、炭化和石墨化分别制备了高导热沥青基炭泡沫体、煤基炭泡沫体和碳化硅泡沫.采用扫描电子显微镜(SEM)和X射线衍射(XRD)分析了样品的微观结构,测定了样品的部分力学和热学性能.分析结果表明所制备样品性能达到了国外商业化产品的水平.     

高密度石墨泡沫及其石蜡复合材料的热物理性能(英文)

以中间相沥青和添加中间相炭微球的沥青为原料,调整发泡压力和发泡温度制备沥青泡沫,经1273K炭化和2973K石墨化,制备了高密度石墨泡沫。为了进一步提高石墨泡沫的密度,采用573 K的沥青反复浸渍炭化未添加中间相炭微球的沥青在1273K下所制的泡沫炭,再经2973K石墨化获得增密度后的石墨泡沫。而后制备了相应石墨泡沫/石蜡复合材料。研究了石墨泡沫热物理性能的影响因素和石墨泡沫/石蜡复合材料的热行为。研究表明:沥青组分、发泡温度和发泡压力决定了石墨泡沫的结构和热物理性能,而石墨泡沫的热导率决定了复合材料的热行为。与石蜡相比,石墨泡沫/石蜡复合材料的热扩散系数提高了768至1588倍。石墨泡沫/石蜡复合材料的潜热与石蜡的质量分数成正比。该复合材料是快速响应电子散热材料的良好选择。     

以芳基乙炔为前驱体制备高强度炭泡沫(英文)

以硫酸为催化剂,芳基乙炔为前驱体,经聚合、正戊烷发泡、炭化获得了高强度炭泡沫。通过选择合适的制备条件,如:发泡剂的用量,催化剂的浓度及用量,以及匀泡剂吐温80的添加量,可以制得孔结构良好、韧带和接点光滑的炭泡沫。芳基乙炔聚合物泡沫炭化后高的残炭率(86%)和良好的孔结构赋予炭泡沫较高的机械强度;所制炭泡沫的耐压强度达到25.8MPa,强度/密度比为43.0MPa/(g.cm-3).     

石墨化CVI泡沫炭的结构和性能

本文采用化学气相渗透技术(CVI)对泡沫炭进行复合处理,利用SEM、XRD等分析手段对石墨化样品进行了分析.研究结果表明,CVI热解炭在泡沫基体的沉积方式是:小颗粒积聚生长成为大颗粒·大颗粒不断接合,经石墨化处理后形成更加规则的结构.石墨化CVI泡沫炭相比原生石墨泡沫炭的电学和力学性能有很大提高,在350*C、2MPa压力条件下制备的石墨化CVI泡沫炭的电导率可以提高近0.9倍;在350"C、1MPa压力条件下制备的石墨化CVI泡沫炭的压缩强度增大近3.5倍.因此,CVI处理可以有效改善石墨泡沫炭的基体结构,提高石墨泡沫炭性能.     

羧基碳纳米管增强酚醛泡沫的压缩性能及热性能

研究了羧基碳纳米管(CNT-COOH)增强酚醛泡沫复合材料的制备工艺、微观结构、压缩性能和热性能,并结合红外光谱和泡沫在不同压缩应变下的变形破坏形貌,探讨了CNT-COOH对酚醛泡沫的增强机制。结果表明,CNT-COOH作为异相成核剂,使酚醛泡沫泡孔的平均尺寸减小,泡孔密度增大; 随着酚醛泡沫中CNT-COOH含量增加,CNT-COOH/酚醛泡沫复合材料的压缩模量和压缩强度提高。红外分析表明,CNT-COOH可能未与酚醛泡沫发生固化反应。CNT-COOH/酚醛泡沫复合材料在不同压缩应变下的SEM分析表明,CNT-COOH位于泡孔的孔壁上,并通过CNT-COOH/酚醛泡沫的界面传载作用承受了一定载荷,增强了泡沫的力学性能。热重分析和垂直燃烧试验表明,CNT-COOH作为稳定剂,降低了泡沫的热降解速率,使其热稳定性和阻燃性能均略有提高。     

Characterization of close-celled cellular aluminum alloys

The deformation behaviour of two different types of aluminium alloy foam are studied under tension, compression, shear and hydrostatic pressure. Foams having closed cells are processed via batch casting, whereas foams with semi-open cells are processed by negative pressure infiltration. The influence of relative foam density, cell structure and cell orientation on the stiffness and strength of foams is studied; the deformation mechanisms are analysed by using video imaging and SEM (scanning electronic microscope). The measured dependence of stiffness and strength upon relative foam density are compared with analytical predictions. The measured stress versus strain curves along different loading paths are compared with predictions from a phenomenological constitutive model. It is found that the deformations of both types of foams are dominated by cell wall bending, attributed to various process induced imperfections in the cellualr structure. The closed cell foam is found to be isotropic, whereas the semi-open cell foam shows strong anisotropy.     

Open cell lead foams: processing, microstructure, and mechanical properties

Open cell lead foams with the porosities between 48 and 74 % were prepared by means of powder metallurgical and casting routes, using ammonium bicarbonate particles, silica beads, and sodium chloride salt particles as space holder. The resulting foam samples structure closely resembled open cell foam structure: each cell had few interconnections with neighboring cells. Small-sized lead (II) fluoride precipitates were microscopically observed in the interior of cells in the foam samples prepared using silica beads as space holder, resulting from the reaction between silica and hydrofluoric acid in the space holder dissolution step. The compression stress–strain curve of foam samples prepared by powder metallurgical route showed brittle deformation behavior following the initial elastic deformation region, while the foam samples prepared by casting route showed characteristic foam deformation behavior: cell edge crushing on the bent cell walls, and cell wall tearing. The collapse stresses, densification strains, and elastic moduli of the prepared foams were further fitted with scaling relations.     

Compressive and tensile behaviour of aluminum foams

The uniaxial compressive and tensile modulus and strength of several aluminum foams are compared with models for cellular solids. The open cell foam is well described by the model. The closed cell foams have moduli and strengths that fall well below the expected values. The reduced values are the result of defects in the cellular microstructure which cause bending rather than stretching of the cell walls. Measurement and modelling of the curvature and corrugations in the cell walls suggests that these two features account for most of the reduction in properties in closed cell foams.     

Foam formation mechanisms in particle suspensions applied to metal foams

At first glance, metal foams appear to be peculiar. On the one hand, they show a high stability with life times of minutes up to hours. On the other hand, metal foams should be highly unstable due to capillary forces. Generally, the cell structures show odd cell configurations. In addition, the cell walls are thick, about 100 m, and exhibit pronounced local swellings and indents.In this paper, we show that this apparent discrepancy is a direct consequence of an underlying foam stabilization mechanism for metals which is based on a barrier effect induced by particles confined in cell walls. Numerical simulation based on a lattice Boltzmann model shows how particles get confined within cell walls and induce a repulsive disjoining pressure there. This disjoining pressure is responsible for the high foam stability generally observed. The identified stabilization mechanism also explains the presence of irregular cell structures generally observed for metal foams and represents the basis for further developments.     

用超临界二氧化碳技术制备硅橡胶/碳纳米管/炭黑复合导电泡沫材料

以超临界二氧化碳为物理发泡剂,制备出一种具有良好导电性能的硅橡胶/碳纳米管/炭黑多相复合泡沫材料。系统研究了不同碳纳米管含量及不同加工参数对硅橡胶发泡行为和最终硅橡胶泡沫材料导电性能的影响。实验结果表明,碳纳米管和炭黑在硅橡胶基体中分散良好,无明显团聚体出现。均匀分散的碳纳米管能够提高发泡时的成核密度,从而得到具有较小泡孔尺寸和较高泡孔密度的泡沫材料。研究发现随着饱和温度升高,泡孔尺寸变大,泡孔合并现象明显;随饱和压力增加,泡孔尺寸变小,泡孔密度增加,泡孔合并现象减少。不同泡孔形态对应其导电性能也有所不同,当泡孔尺寸较小,泡孔分布均匀的泡沫材料导电性能较好。     

Investigation on the influence of cell shape anisotropy on the mechanical performance of closed cell aluminium foams using micro-computed tomography

The mechanical behaviour of closed-cell aluminium foams made by both powder metallurgy (LKR) and liquid state (Hydro) processes is investigated. Hydro foams exhibit a significant anisotropy in their mechanical behaviour. The transverse direction stands out as the most favourable one in terms of strength. In contrast, LKR foams show an almost isotropic compressive behaviour. Both foams perform at a level far below the theoretical predictions. The reduced values are a result of imperfections and defects in the cellular microstructure. X-ray microfocus computed tomography (μCT) is therefore used for internal investigation of the foam cell structure. 2D and 3D quantitative image analyses have been performed on μCT images to characterise the morphometric parameters of the foams. The main parameters of interest are cell size, cell size distribution and cell features information. A preferred cell orientation in Hydro foams is observed along the normal and the transverse directions of the specimen. This cell shape anisotropy is quantified using the dimensions of the three axes of the equivalent ellipsoids. The orientation of the cells is well characterised by pole figures of the three axes of equivalent ellipsoids. The influence of this geometrical anisotropy on the mechanical behaviour of the foam is discussed.     

Elastic behavior of multi-scale,open-cell foams

The mechanical properties of cellular materials are still subject to numerous theoretical and experimental investigations. In particular, the impact of cell size on the foam’s elastic response has not been studied systematically mainly due to the lack of experimental techniques with which the cell size and relative density of materials can be varied independently. This paper presents the results of a study of the elastic behavior of open-cell foams as a function of relative density and the size of the interconnected, spherical pores. First, the chemical procedure allowed us to produce polystyrene open-cell foams in which the relative density and the average cell diameters were varied independently. The results of compression tests performed on these foams showed an unexpected influence of the cell diameter (at constant relative density) on the elastic response. The analysis of the microstructure of the foam revealed the presence of a complex nanostructure in the edge of the cells that appeared during the synthesis procedure. An analytical model (an extension of the Gibson–Ashby model) is presented, which takes into account the complex multi-scale structure of the foam and accurately describes the observed dependence of the measured Young’s moduli on cell size. This approach was confirmed further by a finite element numerical simulation. We concluded that the observed dependence of elastic modulus on cell size was due to the heterogeneous nature of the material that constitutes the walls of the cells.     

Nonlinear material behaviour and failure of closed-cell polymer foams

Classical strength criteria, like the von Mises criterion, are used to postulate the failure of ductile materials like steel or brass. It is known that for the application of foams in modern lightweight structures extended criteria are required, since foams are sensitive to hydrostatic stress. This observation on the macroscale can be explained by the deformation mechanisms of one single foam cell. Under hydrostatic stress, the deformation of the cell causes a non-uniform stress state of the cell walls. To understand the mechanism on the microlevel, a finite element model on the basis of a tetrakaidecahedron as unit cell was implemented. Utilising a strain energy-based homogenisation concept, the effective properties of the foam can be obtained. To adapt the geometric properties of the model to the real microstructure of the foam, results of a computer tomography image analysis were used by considering several imperfections in the cell geometry. For the analysis of the stress state on the microlevel, different load cases were applied to the unit cell. By means of these simulations, the geometrically nonlinear stress–strain curves on the macrolevel were deduced. Furthermore, the analysis of the finite element model provides an insight into the deformation mechanism on the microscale and allows the prediction of failure as well. Finally, the predicted failure points are represented in the Burzyński plane and compared with experimental results. The current paper focuses on the hard foam ROHACELL\({^{\circledR}}\) IG-series (industrial grade), which is a closed-cell PMI foam produced by Evonik Industries AG, Germany.     

开孔泡沫金属压缩实化特性研究

对开孔泡沫金属微结构实化过程进行分析,理论分析表明开孔泡沫金属的实化应变不但与其相对密度成幂律关系,而且还与泡沫金属的单元结构特征密切相关.由此提出了一种用于描述相对密度较低的开孔泡沫金属压缩实化特性的数学模型,在该模型中泡沫结构和筋条材料对泡沫金属实化特性的影响以材料常数的形式体现,理论分析结果与试验结果完全一致.