图1 单层石墨烯及其衍生物示意图[1]

Fig. 1 Schematic diagrams of graphene and its derivatives[1]

图2 球磨后的粉体FESEM照片

Fig. 2 FESEM micrographs of high energy ball milled graphite powder (a) As-milled graphite powder; (b) Graphite layers with a thickness of 20-50 nm that were highly distorted due to heavy impact of milling balls; (c) and (d) Carbon tubes with a diameter of 80-300 nm and a length of several microns produced during the milling[15]

图3 TiC/C复合材料断面的FESEM照片, 展示了纳米尺寸的石墨烯片和碳管, 约15%的孔隙率, 且平均孔径为3 μm[15]

Fig. 3 FESEM micrographs showing nanosized graphene sheets and carbon tubes on fractured surface of TiC/C composite and pores of an average size of about 3 μm with a porosity of about 15%[15]

图4 FESEM照片: (a)未经处理的作为起始原料的多壁碳纳米管; (b)和(c)摩擦抛光后的多壁碳纳米管表面((b)一个由高密度聚集的碳纳米管构成的有光泽表面, (c)从密集到疏松过渡的碳纳米管); (d)摩擦抛光后的块体材料表面, 在表面的多壁碳纳米管结构已经发生改变, 外凸的石墨烯壁从碳管上脱落[16]

Fig. 4 FESEM micrographs showing: (a) the raw MWCNTs used as the starting material; (b-c) polished surface with a scratch of MWCNTs ((b) a shiny surface comprised of high- density aggregation CNTs; (c) transition from the dense to the loose CNTs); (d) polished surface with a scratch on it, MWCNTs in the surface have changed their structure and the outer graphene walls have come off the tubes[16]

图5 SiOC/GNS 断面SEM照片, 石墨烯在陶瓷中形成片层状结构, 呈一定取向分布[20]

Fig.5 SEM image of the fracture surface of SiOC/GNS composite, with graphene forming a lamellar structure of a certain aligned distribution in the ceramic matrix[20]

图6 Al2O3/石墨烯块体复合材料的制备过程示意图

Fig. 6 Schematic diagram of the preparation process of Al2O3/GNS bulk composites

图 7 纯氧化铝陶瓷(a)及GNSs含量为 1vol%的GNS/ Al2O3复合材料(b~d)的断面SEM照片[22]

Fig. 7 SEM images of fractured surfaces of a pure Al2O3 ceramic (a) and a GNS/Al2O3 composite containing 1vol% GNSs (b-d) (c) and (d) are magnified parts of (b)[22]

图 8 GNSs含量为 5vol%的GNS/Al2O3 复合材料的TEM和HRTEM照片

Fig. 8 TEM and HRTEM images of a GNS/Al2O3composite containing 5vol% GNSs (a) GNSs surrounding Al2O3 nanoparticles; (b) A magnified image of GNSs with a thickness of about 10 nm in (a); (c) GNSs with a thickness of 2.5 nm; (d) Overlap of GNSs between Al2O3 nano-particles[22]

图9 Si3N4/石墨烯块体复合材料的制备示意图

Fig. 9 A proposed scheme of the fabbrication of Si3N4/graphene bulk composites

图 10 复合材料的增韧机制

Fig. 10 Toughening mechanisms of composites (a) Crack deflection on a plane with larger size and crack plane orientation almost parallel (fracture line)[29]; (b) Crack branching during crack propagation in the nanographene platelet-reinforced composite (fracture line)[34]; (c) Sheet put-out with a GPL on the fracture surface, with the plane of the sheet perpendicular to the plane of the fracture surface[28]; (d) Crack bridging by GPLs on the fracture line with the plane orientated of sheet nearly perpendicular to the plane of the polished surface[34]

图11 沿着2个方向测量直流和交流电导率的实验装置示意图

Fig. 11 Diagram of experimental setup of dc and ac electrical conductivity (σdc ,σac) measurements along different directions[35] (a) perpendicular (defined by superscript┴) and (b) parallel (superscript″) to the SPS pressing axis; (c) sample and graphite die in the SPS furnace

图12 Si3N4/GNP块体复合材料的断面FESEM照片(a)和高倍率图像显示纳米片沿着基体晶界Z字形弯曲(b)[36]

Fig. 12 FESEM micrographs of the fracture surface of the Si3N4/GNP composite where nanoplatelets protrude from the surface (a) and high magnification image showing the zigzag bending of nanoplatelets along the matrix grain boundaries (b)[36]

图13 对于复合材料的两个取向: 平行(a和b)和垂直(c和d)于SPS压轴线, 由G(a和c)和D(b和d)峰强度建立的拉曼图像; (e)为两个扫描区域的平均光谱图; (f)为具有2D峰强度的多层石墨烯单一频谱图, 该单一频谱是从集合的(c)图中提取的; (g)为断面(平行取向)SEM照片, 显示了GNPs的(箭头所指)择优取向; (h和i)为平行(左)和垂直(右)于SPS压轴的两个样品取向的扫描区域(轮廓)的光学图像[38]

Fig. 13 Raman images built from G (a and c) and D peak intensities (b and d) for both composite orientations: parallel (a and b) and perpendicular (c and d) to the SPS pressing axis. Average spectra of both scanned regions (e). Example of a single spectrum extracted from the collection of image (c) with the intense 2D peak of few layer graphene (f). SEM micrograph of the fracture surface (parallel orientation) (g), showing the preferential orientation of projected GNPs (pointed by arrows). (h and i) Optical images of the scanned zones (outlined) for both specimen orientations parallel (left) and perpendicular (right) to the SPS axis[38]

图14 几何形状测量电流的简化原理图(在样品表面边缘的对电极), (a)垂直于SPS加压轴线的导电路径; (b)平行于SPS加压轴线的导电路径[36]

Fig. 14 Simplified schematics of the measuring geometry (counter-electrode at the sample surface edge) to illustrate the conducting paths for the orientations perpendicular (a) and parallel (b) respect to the SPS pressing axis[36]

图15 α-SiC复合材料样品的TEM照片, 显示了不同石墨烯层数的几个区域。1区: (a)研究区域的低倍率TEM照片, (b)是富含SP2杂化区的P1区域(突出显示的矩形区域)的高倍率图像, 显示了少层石墨烯片(2L、3L和5L)的不同截面; 暗线条线之间的间距与石墨烯之间一致。(e)是分别在P1和P2位置碳K边界的电子能量损失谱(去除多重散射背景后)。2区: (c)具有形成石墨岛屿晶界的低倍率TEM照片, (d,g)是同一区域的高分辨率TEM照片, 插图是右侧SiC颗粒的电子衍射图。3区:(f)几十纳米的石墨形成区。4区: (h和i)代表双层石墨烯的两个不同晶界[40]

Fig. 15 TEM images of the α-SiC composite sample, showing several regions with different number of graphene layers. Region 1: (a) low magnification TEM image of the region of interest. (b) is a higher magnification image of the P1 region (inside the highlighted rectangular region) which is rich in sp2 carbon, showing different cross-section views of few-layers graphene flakes (2L, 3L and 5L); the spacing between dark contrast lines is consistent with the spacing between graphene sheets. (e) are electron energy loss spectroscopy spectra (after multiple-scattering background removal) of the carbon K edge at positions P1 and P2, respectively. Region 2: (c) low magnification TEM image of a grain boundary with formation of a graphite island, (d, g) high-resolution TEM images of the same region, the inset is SEAD of the right side SiC grain. Region 3: (f) graphitic formation of several tens of nanometers. Region 4: (h and i) two different grain boundaries presenting bi-layer graphene[40]