In situ cracking of silica beads in the SEM and TEM — Effect of particle size on structure–property correlations
In situ cracking of silica beads in the SEM and TEM — Effect of particle size on structure–property correlations
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DOI：
10.1016/j.powtec.2014.10.026
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发表时间：
2015
影响因子：
5.2
通讯作者：
Jonas Paul;Stefan Romeis;M. Mačković;V. Marthala;P. Herre;T. Przybilla;M. Hartmann;E. Spiecker;Jochen Schmidt;W. Peukert
中科院分区：
文献类型：
--
作者：
Jonas Paul;Stefan Romeis;M. Mačković;V. Marthala;P. Herre;T. Przybilla;M. Hartmann;E. Spiecker;Jochen Schmidt;W. Peukert
STöber Fink Bohn(SFB)二氧化硅是一种著名的胶体体系：单分散的球形颗粒很容易通过这种湿化学合成路线获得。尽管SFB二氧化硅的应用非常频繁，但人们对其力学性能的了解还不够全面。在此基础上，利用原位扫描电子显微镜和透射电子显微镜技术系统地研究了单颗粒超细颗粒的力学性能：颗粒特性的研究范围从1.5Tμm到200s nm。对未处理颗粒和1000℃下致密的热处理颗粒进行了研究。通过振动光谱学、固体核磁共振光谱学、扫描电子显微镜和聚焦离子束加工进行结构表征，可以将机械性能和内部颗粒结构联系起来。对于由弱交联性二氧化硅网络组成的未经处理的颗粒，发现了与低杨氏模数和硬度值相关的高度可塑性。在大应变下，只发生裂纹而不发生颗粒的完全断裂，因此裂纹路径明显与合成条件有关：对于通过多步生长过程获得的较大颗粒，裂纹沿着较弱的颗粒内界面扩展，并绕过核心结构。热处理后，SiO_2网络的交联性明显增强，杨氏模数与玻璃SiO_2相当，硬度增加。只有最小的颗粒才会出现破裂；超过500纳米的颗粒才会断裂成两个或更多个碎片。通过扫描电子显微镜成像发现，裂解成几个部分的相对发生率随着尺寸的增加而增加-这一行为与二氧化硅的脆性到韧性转变有关。通过对大量颗粒的测试，确保了统计意义。
Stöber Fink Bohn (SFB) silica is a well-known colloidal system: monodisperse spherical particles are readily obtained by this wet chemical synthesis route. Despite the frequent application of SFB silica, its mechanical properties are not comprehensively understood. Within this account, size dependent mechanical properties of single SFB particles are systematically investigated using in situ SEM and TEM techniques: particle properties are addressed in the size range of 1.5 μm down to 200 nm. Both, untreated particles and heat treated particles densified at 1000 °C are investigated. Structural characterization by vibrational spectroscopy, by solid state nuclear magnetic resonance spectroscopy, by scanning electron microscopy and by focused ion beam machining allows correlating mechanical properties and the internal particle structure. For untreated particles comprised of a weakly cross-linked silica network a high degree of plasticity associated with low Young's moduli and hardness values is found. At large strains only cracking without full fracture of the particles occurs, whereby the crack path is clearly linked to the synthesis conditions: for larger particles obtained from a multistep growth process cracks propagate along weak intraparticle interfaces and are deflected around an inner core structure. After the thermal treatment cross-linking of the silica network is significantly enhanced and Young's moduli comparable to vitreous silica accompanied by increased hardness values are found. Only the smallest particles exhibit cracking; fracture into two or more pieces is distinguished for particles above 500 nm. It is found by SEM imaging that the relative occurrence of cracking into several pieces is increasing with size — a behaviour associated with the brittle to ductile transition of silica. By testing a large quantity of particles, statistical significance is ensured.