Developments in Ceramic Materials Research

Optical Fluoride and Oxysulfide Ceramics: Preparation and Characterization 57
on the structure of oxide laser ceramics and shows that optically transparent ceramics is
formed at nanosized level.
Figure 1. (a) - Overview of the polished samples of the fluorite (CaF 2) with 10 mm thickness. On the
left is a artificial single crystal, on the right is the cryptocrystalline fluorite from Suran deposit, (b) – the
CaF2 artificial ceramics.
Experiments on hot pressing of fluoride optical ceramics are performed in K – 4772 high
temperature vacuum furnace with the graphite resistance heating element and MV – 4 MP
heatproof molybdenum alloy mould using a PSU – 50 hydraulic press capable of pressure at
the head of 50 t. The pressing parameters are as follows: temperature up to 1300 º С, pressure
up to 250 MPa.
This process allows to obtain ceramics with 100% density, but optical transparency is
varied in wide ranges. Results of the hot pressing of different precursors are presented in
Figure 3 and electron microphotographs of some powders used are in Figure 4. These
experiments confirm that the optical transparency of the ceramics depends on the quality of
precursors [7]. Unlike the glass melting and single crystals growth a hot pressing method of
preparation of optical ceramics does not include the purification of the initial materials.
Organic impurities and embedded foreign particles raise absorption and scattering of the light
in the sample. Even apparently highly purified raw material leads to the non – transparent
ceramics. An increase of evacuation value every so often leads to an improvement of the
optical transparency.
As a result of careful selection of the precursors the CaF2 ceramics with high
homogeneity and small optical losses is prepared. (Figure 1b). The electronic scanning
a
b