Unspecified Takato Honjo Profile

Takato Honjo

at Kyocera Corp

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Proceedings Article | 13 December 2020 Poster + Paper

F-molding: a new production method for largely aspherical mirrors of Cordierite

Hidehito Himeno, Yuji Ikeda, Shinji Mukai, Hidenori Yamanokuchi, Takato Honjo, Yuuki Nishi, Shinichi Yamaguchi, Kenichi Hamamura, Junpei Yamaguchi, Masatsugu Kamiura, Shinobu Nagata

Proceedings Volume 11451, 114512X (2020) https://doi.org/10.1117/12.2562006

KEYWORDS: Mirrors, Astronomy, Glasses, Raw materials, Polishing, Surface finishing, Surface roughness, Light scattering, Liquids, Segmented mirrors

Read Abstract +

Cordierite is a ceramic with low thermal expansion properties similar to Zerodure and ULE glasses in large-mirror telescopes used in Astronomy. Coefficient of thermal expansion of Cordierite is not only comparable to low thermal expansion glasses, but also has additional advantages with minimal dimensional deformation with time (~3.8nm/m/year), high Young's modulus (~145GPa), and high thermal conductivity (~4W/mK). However, Cordierite mirror is susceptible to voids generated by crushed grains leading to tetrahedral gaps from sphere packing of raw powder material during CIP (Cold Isostatic Pressing) process. These voids often appear with mirror polishing of Cordierite and may become a source of light scattering. To solve this problem, we propose Flexible Molding (Fmolding) as our new fabrication method for Cordierite. With F-molding, raw material powder is converted to liquid slurry which is then poured into a resin mold and solidified directly into near net shape of a mirror. Liquid slurry of Fmolding are thus cured in forming without pressurized sphere packing which generates void defects. In addition, the mold prepared from F-molding is an effective tool for processing multiple volumes of identical structures and is an ideal process for segmented mirror designs. To confirm the feasibility of F-molding for large mirrors used in Astronomy, we prepared a light-weighted flat mirror (270 mm in diameter) using the method with our Cordierite. In this paper, we introduce details of our F-molding mirror fabrication method, and report on measurement results of its optical performances.

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