Ein glasklares Modell

Abstract

Amorphe Materialien strukturell aufzuklären — dieses Vorhaben scheiterte bisher an der Komplexität der Stoffklasse. Rastertunnelmikroskopie in Verbindung mit modernen Präparationsmethoden gelingt die Entschlüsselung des Alltagswerkstoffs Glas.

Physical boundaries within aggregates – differences between amorphous, para‐crystalline, and crystalline Structures

“…The samples: siliceous earth (8), bentonites (18)(19)(20) and calcium carbonate (22), which are of mineral origin, show dense and compact surfaces whereas all the other samples from different production technologies are formed by strongly agglomerated aggregates in a macroscopic arrangement and partly show open intergranular volume (figure 2, right). The limited resolution of the SEM micrographs suggests that the fine structure of the primary building blocks which form the granulated or beaded matter, in principle are similar and only differ in average size: the silica (1-7), the alumina (9,23) and the titania (11)(12)(13)(14)(15)(16)(17) samples show comparable shape in the surface regions of the agglomerated aggregates. To obtain insight into the material-specific outer and, especially, interior structure of the aggregates and the constituent particles themselves, they have to be separated by significant shear forces.…”

“…The SEM and TEM images (figure 3) reveal that the primary structures or constituents of an aggregate are strongly inter-grown and there is considerable interpenetration or overlap. In the TEM images of the amorphous silica samples (1-7) and the carbon black sample (21) no discrete primary particles are visible whereas in the case of the crystalline or semi-crystalline samples (8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(22)(23) the definition "aggregate means a particle comprising of strongly bound or fused particles" is applicable. A more detailed discussion of the TEM results follows in section 3.2.…”

“…r Crystalline structure in titania (11)(12)(13)(14)(15)(16)(17), iron oxide (10), fumed alumina (9), calcium carbonate (22) and alumina from the ammonium alum process (23). In Table 2 enhanced distances between sp 2 -type entities (0.35-0.37 nm) are also noted.…”

“…Most recently this model has been applied to, and confirmed by, analyzing the atomic force microscopy results of supported amorphous silica monolayers. The relative proportions of Si-O-Si rings of different size (4-9 membered rings) were evaluated [17] and the two-dimensional interface between amorphous and crystalline areas of a www.crt-journal.org Fig. 4 From top to bottom: TEM micrographs of an isolated (by ultra-sonication) entity of amorphous silica (precipitated silica, aerogel, gel, pyrogenic (fumed), samples 3, 5, 7, 1) and of crystalline titania (sample 11) recorded at different tilt angles relative to the incident primary electron beam.…”

Differences in the morphology and vibrational dynamics of crystalline, glassy and amorphous silica – commercial implications

“…High resolution transmission electron microscopy (HR-TEM) and, especially, electron tomography, 9 together with 3D-TEM, [9][10][11] have been shown to be well-suited to complement the information on amorphicity from X-ray diffraction data by direct imaging of the nano-structure. The short range geometry, down to the molecular scale of two-dimensional mono-/bi-layers, of amorphous and crystalline silica and a crystalline/vitreous interface were studied by means of atomic force microscopy (AFM) and evaluated in order of Si-O-Si ring sizes, [12][13][14][15] confirming the Zachariasen model. 5 The relative energies of hydroxylated double silica rings of different geometry were reported.…”