<p>Carbon-fiber-reinforced plastic (CFRP) has a higher strength-to-weight ratio and forming flexibility than metals, making it suitable for fabricating lightweight x-ray mirrors. However, CFRP has the disadvantages of print-through and deformation due to moisture absorption, which have prevented its use in optical mirrors. To expand the application of CFRP, we studied the formation of a moisture barrier layer on CFRP substrates. We formed a flattening layer a few micrometers thick on a CFRP substrate, following which we coated the substrate with SiO<sub>x</sub> as a moisture barrier. The effect of moisture absorption was then evaluated using accelerated aging tests. We found that the diffusivity of the CFRP substrate at 60°C and a relative humidity of 100% was ∼2 × 10<sup> − 6</sup> mm<sup>2</sup> h<sup> − 1</sup>, which is 1/500th that of the barrier-less substrate. In the tests, the moisture absorption rate increased after ∼800 h. As we observed cracks on the flattening layer after 600 h, the rate increase could be associated with these cracks. Considering the damage to the barrier layer, we propose a modified model for the time profile, which is congruent with the observed time profile of the moisture content.</p>
We fabricated X-ray mirrors from carbon-fiber-reinforced-plastic (CFRP) with a tightly nested design for X-ray satellites. The mirror shape is Wolter type-I quadrant shell geometry with a diameter of 200 mm and a focal length of 12 m. The mirror substrates were successfully formed with a rms error of about 1 μm. Through a replication process, a smooth surface was obtained on the CFRP substrate. We are developing a positioning method of thin mirrors in a telescope housing. It is found that a piezo-linear motor is very useful to adjust the mirror position with accuracy of sub μm. The CFRP mirrors were evaluated by using 20 keV X-ray pencil beam at BL20B2 in SPring-8 synchrotron radiation facility. The HPD of the mirrors was estimated to be about 2.3 arc-minutes. The spread of X-ray image would be caused by small waviness on the mirror surface after replication.