We report the results of testing samples made of glass ceramics with a zero thermal expansion coefficient. The samples consist of two parts, joined by a new technology of solid-phase sintering polished parts with vacuum-deposited aluminum coating of nanosized thickness. Also reported are data on the stability of these samples after exposure to extreme factors such as cryogenic temperature (temperature of liquid nitrogen), high temperatures of 400 and 1000°C, laser radiation, etc. The test results show that the suggested technology can be used for producing light-weight astronomical telescope mirrors of Zerodur glass ceramics. In our opinion, the suggested design of a light-weight astronomical telescope mirror with two parts joined by the new technology [the bottom part is silicon carbide (SiC) and the upper is an optical layer of glass ceramics with a thermal expansion close to that of SiC in value] is promising.
The results of ellipsometric investigations of surfaces of glassceramic samples with ultra low coefficient of thermal expansion are presented. These glassceramic samples are used in manufacturing of precision parts of optical instruments, for instance for telescope mirrors manufacturing. The aim of these investigations was to study the influence of the surface damaged layer and elastic deformations on the residual ellipticity of polished surfaces of glassceramic
samples with ultra low temperature expansion coefficient. It was shown that with increasing of the surface layer polished depth damaged by grinding, the residual ellipticity decreases up to the value that remains a constant. Its value is determined by the material structure and stresses in the surface layer.
From the analysis of the known data and the results of investigations carried out, advantages and limitations of different methods of unglue bonding of glass-ceramic parts like Zerodur with ultra low coefficient of thermal expansion (CTE), are presented. It seems that by (quality-cost) criterion the solid-phase bonding of polished parts (SBPP) with the use of thin layer aluminum or its alloys to bond the ceramic optical parts is favorable. In optimal case the metal coatings
for glass-ceramics bonding should be multilayer. The examples of SBPP bonding of glass-ceramic parts are presented which are close to strength characteristics of a monolith. It is shown that for bonding quality control the optical methods, including thermo-vision, can be applied.