ZERODUR
24Pages

ZERODUR® Zero Expansion Glass Ceramic

SCHOTT is an international technology group with more than 125 years of experience in the areas of specialty glasses and materials and ­ dvanced a technologies. With our high-quality products and intelligent solutions, we contribute to our customers’ success and make SCHOTT part of everyone’s life. SCHOTT Advanced Optics, with its deep technological expertise, is a valuable partner for its customers in developing products and cus­ tomized solutions for applications in optics, lithography, astronomy, opto-electronics, life sciences, and research. With a product portfolio of more than 100...

A Superlative High-Tech Material For more than 40 years, ZERODUR® glass ceramic has been the material of choice for a ­ stronomy, both on earth and in space. Here, a brief summary of some of the spectacular projects involving ZERODUR® glass ceramic substrates. The first 4 m-class mirror blank order from the Max Planck Institute for Astronomy (MPIA) telescope on Calar Alto in Southern Spain Eight ZERODUR® cylinders for the German X-ray telescope known as ROSAT (ROentgen SATellite), which was used in space from 1990 through 1999 43 disks for hexagonal s ­ egments made from ZERODUR® with a...

A 4.25 m base plate for the world’s largest ring laser gyroscope for measuring Earth’s rotation for the German Terrestrial Reference Station in Wettzell, Germany 4.1 m mirror substrate with a particularly strong curvature for the Visible and Infrared Survey Telescope for Astronomy (VISTA), the world’s largest wide field Survey Telescope located near the Cerro Paranal, Chile 1.5 m light weighted primary mirror for the GREGOR solar telescope. The mirror with a curved front plate incorporates 420 pockets on the back­ side for active cooling d ­ uring observation at the Teide Observatory on...

1. Introduction SCHOTT invented ZERODUR®, the zero e ­ xpansion glass ceramic, in 1968 and thus introduced a new era for various applications, of which the most challenging ones are telescope mirror substrates for astronomy. The most important properties of ZERODUR® are presented in this catalog. Information is also available on the SCHOTT website: http://www.schott.com/advanced_optics/ zerodur Detailed articles that contain technical information, or so-called TIEs, are available for some of the properties listed in this catalog. A stamp refers to the relevant TIEs, an overview of which can...

Extraordinary Properties ZERODUR® is a zero expansion glass ceramic with extraordinary properties for demanding applications in which geometrical shape and distance changes must be kept as small as possible during changes in temperature. The key properties of ZERODUR® are: • n A extremely low coefficient of thermal expansion (CTE) for a wide range of temperatures • Excellent CTE homogeneity throughout its entire volume • Very low level of imperfections • A wide range of precise geometrical shapes are possible using grinding processes • An extremely smooth surface is possible with residual...

2. Thermal Expansion of ZERODUR® Mean Coefficient of Linear Thermal Expansion ZERODUR® can be supplied with a mean coefficient of linear thermal expansion (CTE) in the temperature range 0°C to 50°C in three expansion classes as follows: CTE (0°C; 50°C) Specification tolerances Expansion Class 0 Expansion Class 1 CTE-Measurement Accuracy Expansion Class 2 Table 2.1 CTE tolerances Tighter tolerance available upon request. Standard Table 2.2 CTE-Measurement accuracy and repeatability Figure 2.1 below shows the typical relative expansion in length Δl/l and CTE of ZERODUR® as a function of...

Total Change of Length between -50°C to +100°C Homogeneity of the Coefficient of Thermal Expansion The homogeneity is evaluated by measuring CTE samples homogeneously distributed throughout the blank and calculating the difference in CTE between the highest and the lowest value measured. The homogeneity of linear expansion can be guaranteed in the following weight classes: CTE (0°C; 50°C) Homogeneity tolerances up to 18 tons up to 6 tons Table 2.3 CTE homogeneity tolerances -600 Figure 2.2 CTE distribution within a 1.5 m diameter blank with a measured CTE homogeneity of 0.004 · 10-6/K...

The structural relaxation behavior of glass ceramics can be described by a theoretical model. With this model, the relaxation behavior of a ZERODUR® cast can be predicted at any application temperature and temperature change rate upon special request. In applying the model, ZERODUR® batches that offer the best performance can be selected for extremely demanding applications. ZERODUR® K20 for High Application Temperatures ZERODUR® K20, a low thermal expansion version of ZERODUR®, has been optimized to withstand higher application temperatures. The material has a white color and offers good...

3. Internal Quality Inclusions Inclusions in ZERODUR® are mainly bubbles. For optical surfaces, a critical volume can be defined by setting tighter requirements. During inspection of ZERODUR® parts, all inclusions with a diameter > 0.3 mm are taken into consideration. If an inclusion has a shape other than spherical, the average diameter is reported as the mean of the length and width. Average number of inclusions per 100 cm3: Maximum diameter of individual inclusions in mm for different diameters or diagonals of the ZERODUR® part In the critical volume: < 500 mm Individual specifications...

Figure 3.1 ZERODUR® - the material of choice for segmented mirror telescopes Photo: Sagem Défense Sécurité Striae are locally confined transparent regions with compositions that differ from the basic material only very slightly. They are generally ribbon-shaped (or often called band-like) but are occasionally thread-shaped. The stress birefringence of striae is measured as a path difference in nm as listed in the table 3.3. In parts with thicknesses of more than 250 mm, the path difference is expressed in nm/ cm striae length and will be specified on an individual basis. Stress...