| 30 | 30 | || '''30.01.2015''' || '''Peter Hartmann (Schott AG)''' ||'''ZERODUR®: Glass ceramic with ultra-low thermal expansion '''[[BR]][[BR]]Requirements on shape and dimensional stability of high tech components are continuously growing. Mirror shape profile must be kept constant within 10 nm, in microlithography silicon wafers must be positioned to 0.3 nm precision. Active temperature stabilization must be complemented by using materials which change their extension lowest possible with temperature variations.[[BR]][[BR]]Here the glass ceramic ZERODUR® takes a prominent position with more than 45 years of successful application. Even though being unchanged in its composition it was subject of significant progress nonetheless in the last ten years. The production process enables mirrors of 4 and 8 m size with extreme homogeneity of the coefficient of thermal expansion in the 10^-9^/K range. Tempering processes basing on a physical model allow keeping CTE within limit of +/- 7×10^-9^/K. Even matching relative expansion Delta l/l to given temperature profiles for example for observatories is possible down to 10×10^-9^. CTE minimization is also possible for the temperature range 70 to 250 K. Bubbles, inclusions and striae content is very low as well as residual bulk stress. New processing methods enable lightweight structures with almost 90% weight reduction. Better modelling and an increased data base for bending strength support application at higher mechanical loads.[[BR]][[BR]]A large number of earth-bound and space-based projects prove the high material quality and its reproducibility, which is a decisive precondition for extremely large telescopes.[[BR]][[BR]]Talk: German[[BR]]Slides: English[[BR]]Questions: German, English || |
