  Aims. In this paper we study the Spitzer and TIMMI2 infrared spectra of
post-AGB disc sources, both in the Galaxy and the LMC. Using the observed
infrared spectra we determine the mineralogy and dust parameters of the discs,
and look for possible differences between the Galactic and extragalactic
sources. Methods. Modelling the full spectral range observed allows us to
determine the dust species present in the disc and different physical
parameters such as grain sizes, dust abundance ratios, and the dust and
continuum temperatures. Results. We find that all the discs are dominated by
emission features of crystalline and amorphous silicate dust. Only a few sample
sources show features due to CO2 gas or carbonaceous molecules such as PAHs and
C60 fullerenes. Our analysis shows that dust grain processing in these discs is
strong, resulting in large average grain sizes and a very high crystallinity
fraction. However, we do not find any correlations between the derived dust
parameters and properties of the central source. There also does not seem to be
a noticeable difference between the mineralogy of the Galactic and LMC sources.
Even though the observed spectra are very similar to those of protoplanetary
discs around young stars, showing similar mineralogy and strong grain
processing, we do find evidence for differences in the physical and chemical
processes of the dust processing.

Solar and Stellar Astrophysics