Studies of the moisture absorption of thin carbon fiber reinforced plastic substrates for x-ray mirrors

Abstract

Abstract. We study a lightweight x-ray mirror with a carbon fiber reinforced plastic (CFRP) substrate for nextgeneration x-ray satellites. For tightly nested x-ray mirrors, such as those on the Suzaku and ASTRO-H telescopes, CFRP is the suitable substrate material because it has a higher strength-to-weight ratio and forming flexibility than those of metals. In flat CFRP substrate fabrication, the surface waviness has a root mean square (RMS) of ∼1 μm in the best products. The RMS approximately reaches a value consistent with the RMS of the mold used for the forming. We study the effect of moisture absorption using accelerated aging tests in three environments. The diffusivity of the CFRP substrate at 60°C and at relative humidity of 100% is ∼9:7 × 10 −4 mm 2 · h −1 , and the acceleration rate to the laboratory environment was 180 times higher. We also develop co-curing functional sheets with low water-vapor transmissivity on the CFRP substrate. Co-curing the sheets successfully reduced the moisture absorption rate by 440 times compared to the un-co-cured substrate. Details of the CFRP substrate fabrication and moisture absorption tests are also reported. © The Authors.Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

Effect of barrier layer on moisture absorption of thin carbon-fiber-reinforced plastic mirror substrates

“…We previously performed a precursor experiment for a moisture barrier in 2015. 31 In that experiment, both sides of a CFRP substrate were covered with a moisture barrier film, and it was noted that a moisture barrier film with low water-vapor transmissibility of <0.1 g • m −2 • day −1 showed high-barrier properties. In particular, a barrier film coated with SiO x worked well.…”

“…The swelling phenomenon is caused by moisture absorption, which originates from the resin. Sugita et al 31 measured the deformation of a CFRP substrate after drying and moisture absorption and found that the history of drying and moisture absorption influence the deformation. Thus, it is crucial to make the change of the moisture content in CFRP small, in order to suppress the deformation.…”

“…We previously coated a thin CFRP substrate with functional sheets having a low watervapor transmissivity and found that such coating is effective for reducing moisture absorption. 31 Although it is easy to laminate a flat CFRP substrate with functional sheets, it might not be easy to laminate a CFRP substrate with a complex geometry, such as Wolter-I optics. Thus, in the present study, we coated a moisture barrier layer on the CFRP substrate, instead of using functional sheets, and evaluated its moisture absorption effect by using accelerated aging tests.…”

“…We previously found that the time profile of moisture absorption in a CFRP substrate with a barrier layer cannot be reproduced by a simple diffusion model. 31 To evaluate the effect of the moisture barrier, in the present study, a model characterizing the time profile of the moisture absorption is proposed to represent the time profile considering damage to the moisture barrier. In the fabrication of flat CFRP substrates for studying the moisture barrier, we utilized a prepreg sheet as the substrate material.…”

“…We adopted quasi-isotropic 8-ply lamination with the laminated constitution of [0/45/−45/90] s. Further details are described in our previous report. 31 After laminating the prepreg sheets on the mold, we employed a vacuum-bagging method for applying pressure on the laminated prepreg. In this method, both the prepregs and the mold are bagged with seal film and pressed at atmospheric pressure.…”