Modeling of the thermal expansion behavior of ZERODUR® for the site conditions of the upcoming Extremely Large Telescope's (ELT's) allows an optimized material selection to yield the best performing ZERODUR® for the mirror substrates. The thermal expansion of glass ceramics is a function of temperature and a function of time, due to the structural relaxation behavior of the materials. The application temperature range of the upcoming ELT projects varies depending on the possible construction site between -13°C and +27°C. Typical temperature change rates during the night are in the range between 0.1°C/h and 0.3°C/h. Such temperature change rates are much smaller than the typical economic laboratory measurement rate, therefore the material behavior under these conditions can not be measured directly. SCHOTT developed a model approach to describe the structural relaxation behavior of ZERODUR®. With this model it is possible to precisely predict the thermal expansion behavior of the individual ZERODUR® material batches at any application temperature profile T(t). This paper presents results of the modeling and shows ZERODUR® material behavior at typical temperature profiles of different applications.
[1]
J. Seguel,et al.
Thirty Meter Telescope Site Testing I: Overview
,
2009,
0904.1183.
[2]
Peter Hartmann,et al.
CTE characterization of ZERODUR® for the ELT century
,
2009,
Optical Engineering + Applications.
[3]
W. Pannhorst,et al.
Thermal expansion and length stability of Zerodur in dependence on temperature and time.
,
1985,
Applied optics.
[4]
Peter Hartmann,et al.
Homogeneity of the linear thermal expansion coefficient of ZERODUR measured with improved accuracy
,
2006,
SPIE Astronomical Telescopes + Instrumentation.
[5]
Armin Bunde,et al.
Ionic glasses: History and challenges
,
1998
.
[6]
D B Hall.
Dimensional stability tests over time and temperature for several low-expansion glass ceramics.
,
1996,
Applied optics.