Open-cell silicon foam for ultralightweight mirrors

Arthur J. Fortini

doi:10.1117/12.363824

28 September 1999 Open-cell silicon foam for ultralightweight mirrors

Arthur J. Fortini

Proceedings Volume 3786, Optomechanical Engineering and Vibration Control; (1999) https://doi.org/10.1117/12.363824
Event: SPIE's International Symposium on Optical Science, Engineering, and Instrumentation, 1999, Denver, CO, United States

Abstract

Elemental silicon is a lightweight material that shows great promise for optical applications. Specifically, open-cell silicon foam can be used as a core material for ultralightweight mirrors by bonding single-crystal silicon faceplates to the foam. Not only does silicon have a low density, but it also has a low thermal expansion coefficient and a high thermal conductivity. Further, because of its widespread use in the semiconductor industry, it is an extremely well-characterized material. The fabrication of silicon foam begins with open-cell polyurethane foam, which is available in a wide variety of cell sizes ranging from 3 to 100 pores per linear inch. After chemical conversion to a glassy carbon foam, the individual ligaments are coated with silicon by chemical vapor deposition/infiltration (CVD/CVI), and the carbon cores are removed by oxidation. The end result is an open-cell foam composed exclusively of silicon. CVD/CVI is a very versatile process because it allows the amount of silicon in the foam to be varied. As the relative density of the foam increase, so does its strength and stiffness. Consequently, the mechanical properties of the foam can be tailored to meet the needs of a given application. For example, for space-based applications where light weight is critical, lower density foams can be used. For terrestrial applications requiring high stiffness, higher density foams can be used. In all cases, the relative density of the foam is a parameter that can be optimized to meet the needs of a particular application.

Citation Download Citation

Arthur J. Fortini "Open-cell silicon foam for ultralightweight mirrors", Proc. SPIE 3786, Optomechanical Engineering and Vibration Control, (28 September 1999); https://doi.org/10.1117/12.363824

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