Research on nano-ceramics

Ceramics are dielectric materials with a heterogeneous microstructure. An important type of ceramics are glass-ceramics, i.e. crystalline grains in a glassy matrix. Grains and matrix may have the same or very different chemical compositions. Apart from the size of the inclusions or precipitates, their shape and orientation are important factors that govern the macroscopic properties of the material.

Fig.: Schematic of different types of particle in a matrix Fig.: Types of ceramic interface

Nano-ceramics, i.e. ceramics with nanometre-sized particles embedded in a matrix, are particularly interesting because, as a consequence of the small particle size, the volume fraction of material located in or near the interface between the two components is very large. The interface can have a structural (and chemical) gradient, it can be amorphous, or a crystal interface with dislocations and other faults due to local strain can develop.
One way to prepare nano-ceramics is ball-milling crystalline raw materials. In particular, we have investigated the effect of particle shape on the interface fraction and the reversible and irreversible effects ball-milling has on the nanostructure of quartz.
Nanoparticles can also be prepared chemically from liquid precursors (sol-gel technique). This leads to very fine particles which are often amorphous due to the fast reactions leading to the nucleation of the material.

One way to make dense glass-ceramics is to sinter a powder mixture of nanoparticles and crushed glass. Depending on the sintering conditions, loosely embedded particles or chemically bonded particles will make up the granular phase of the resulting ceramic. The chemical and structural features of the interface between particle and matrix govern the resistance of the material to attack by corrosives. We are studying such ceramic systems and their corrosion --in-situ where possible-- by NMR, diffraction, and small-angle scattering.
Related publications:
SAXS at the Zr-K edge of Al2O3-ZrO2-silicate nanoceramic; see also here
Annealing of Al2O3-ZrO2-silicate nanoceramic / NMR and SAXS
Pressure-amorphisation in ball-milled nano-SiO2 / NMR and XRD
Grain size and shape of nano-LixTiS2 / NMR and XRD 1)
1)experiments done at Universität Hannover

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