Sitall

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Sitall aka Sitall CO-115M or Astrositall, is a crystalline glass-ceramic with ultra low coefficient of thermal expansion (CTE). It was originally manufactured in the former Soviet Union and was used in the making of primary mirrors for the Russian Maksutov telescopes, but since dissolution has diminished in quality. [1]

Sitall has a CTE of only 0±1.5 x 10−7/°C in the temperature range -60 to 60°C, placing it in a rather small group of transparent materials with low CTE such as Pyrex, Zerodur, Cervit and fused quartz. [2]

Materials of low coefficient of thermal expansion are critical in the manufacture of optical elements for telescopes. In segmented mirror telescopes, it is desirable to have this coefficient as near zero as possible, and to have a high degree of homogeneity in the material. The Southern African Large Telescope (SALT) selected Sitall for the manufacture of its 91 primary mirror segments by Lytkarino Optical Glass Factory (LZOS). Using this company was a direct result of increased scientific collaboration between Russia and South Africa since 1994. [3][4][5]

Sitall was used for the primary and secondary mirrors of the VLT Survey Telescope.

Sitall has been ballistically tested by The Pentagon for use as a complex composite armour system, intended to resist chemical and kinetic assault. [6]

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