The structural properties of finely divided inorganic materials such as metal and metalloid oxides, silicates or carbonates of both synthetic and natural origin are compared by means of electron microscopy and tomography. The structure of the outer surfaces of various compact or compacted agglomerates may suggest some striking similarities between various amorphous silica on the one hand and crystalline titania and alumina on the other however the details of the interior fine structure are completely different. Inside of the crystalline aggregates of, for example, alumina and titania distinct grain boundaries between the inter-grown primary crystallites exist. Also physical boundaries between different solid phases and crystalline/amorphous transitions in core/shell structures can occur. No physical grain or phase boundaries were found inside of synthetic amorphous silica or para-crystalline carbon black thus, the aggregate is the constituent particle. Synthetic amorphous silica from different production technologies (fumed/pyrogenic, precipitated, aerogel, gel) may exhibit different macro-morphology but distinct similarities of the amorphous silica networks. Computational studies on silica and titania underline the stability of constituent particles and aggregates as observed by means of TEM after dispersing the original materials by ultra-sonication.

SEM images of isolated aggregates of silica and titania show structural similarities at the several hundred nanometer scale (red). However, high resolution TEM reveals distinct differences of the interior structure down to the nanoscale. Pyrogenic titania entities are formed by intergrown crystallites (blue). Grain or solid phase boundaries are detected. Synthetic silicas of different production technology are completely amorphous (green) and, thus, the aggregate is the constituent particle. This conclusion is confirmed by 3D‐TEM investigations. (Picture: P. Albers et al., pp. 846–865, in this issue)

Reine Sande und Kiese werden immer knapper und daher immer mehr zu wertvollen, stark nachgefragten Gütern von strategischer Bedeutung für die verschiedenartigsten Industriezweige weltweit. Aus dem reinen, kristallinen Rohstoff Quarzsand werden Zwischenprodukte für die Herstellung hochreiner, synthetischer amorpher Siliciumdioxide (SAS) hergestellt. Die Umsetzung zu Natronwasserglas erlaubt die Herstellung gefällter SAS. Die Umsetzung von Silicium und Ferrosilicium mit HCl führt zu Chlorsilanen, die für die Herstellung pyrogener SAS eingesetzt werden. Die Untersuchung des Aufbaus dieser amorphen Produkte erfordert den Einsatz hochauflösender Transmissionselektronenmikroskopie. Pyrogene und gefällte SAS zeigen hierbei die gleiche Nanostruktur wie auch Silicagele und ‐aerogele. Unterschiede in der Amorphizität und nur kurzreichweitigen Nahordnung in feinteiligen, alkalifreien, amorphen SAS einerseits und in alkalihaltigen SiO2‐Netzwerken wie stückigem Wasserglas und technischen Gläsern andererseits sind noch nicht komplett aufgeklärt.