New Technology Silicon Carbide (NTSIC®) is a reaction sintered silicon carbide with very high bending strength. Two times higher bending strength than other SiC materials is important characteristics in an optical mirror for space application. The space optics is to endure the launch environment such as mechanical vibration and shock as well as lightweight and good thermal stability of their figure. NTSIC has no open pore. It provides good surface roughness for infrared and visible application, when its surface is polished without additional coatings. Additional advantages are in the fabrication process. The sintering temperature is significantly lower than that of a sintered silicon carbide ceramics and its sintering shrinkage is less than one percent. These advantages will provide rapid progress to fabricate large structures and will enable that one meter mirror will put practical use. The fabrication capability has developed from 250mm to about one meter in these two years, after previous report of NTSIC. It is concluded that NTSIC has potential to provide large lightweight optical mirror.
Newly developed high-strength reaction-sintered silicon carbide is an attractive material for lightweight optical mirror with two times higher bending strength than other SiC materials. The polished surface has no pore and is suited to visible region as well as infrared without CVD SiC coating. The fabrication process, with low temperature and small shrinkage, is also suited to develop large scale objects.
Silicon carbide (SiC) is the most advantageous as the material of various telescope mirrors, because of high stiffness,
low thermal expansion, high thermal conductivity, low density and excellent environmental stability. Newly developed
high-strength reaction-sintered SiC, which has two to three times higher strength than a conventional sintered SiC, is one
of the most promising candidates in applications such as lightweight substrates of optical mirrors, due to being fully
dense and having small sintering shrinkage (±1 %), and low sintering temperature.
In this study, in order to improve nano-scale homogeneity of the high-strength reaction-sintered SiC, the microstructure
of high-strength reaction-sintered SiC was investigated using scanning electron microscopy (SEM) and microscope type
interferometer in comparison with the conventional sintered SiC. And also, the microstructure was investigated by
focusing on the crystal structures and the interface of each crystal through transmission electron microscopy and X-ray
diffraction analysis. As a result, it was the confirmed that the high-strength reaction-sintered SiC was fully dense in
comparison with the conventional sintered SiC, and the finer-scale microstructure consisted of large particles (~1 μm in
diameter) of α-SiC starting powder and small particles (<1 μm in diameter) of β-SiC synthesized during the
reaction-sintering (Si+C→SiC) with residual silicon (Si) filling the remaining pores. In addition, the β-SiC synthesized
during the reaction-sintering was identified as the cubic type (3C), and the α-SiC of the starting powder was identified as
the hexagonal type (6H).
New-Technology Silicon Carbide (NTSIC(R)) is a reaction sintered silicon carbide with very high bending strength. Two
times higher bending strength than other SiC materials is important characteristics in an optical mirror for space
application. The space optics is to endure the launch environment such as mechanical vibration and shock as well as
lightweight and good thermal stability of their figure. NTSIC has no open pore. It provides good surface roughness for
infrared and visible application, when its surface is polished without additional coatings. Additional advantages are in the
fabrication process. The sintering temperature is significantly lower than that of a sintered silicon carbide ceramics and
its sintering shrinkage is less than one percent. These advantages will provide rapid progress to fabricate large structures.
Both reaction bonding method and brazing are studied in order to larger application for larger telescope. It is concluded
that NTSIC has potential to provide large lightweight optical mirror.
Silicon carbide (SiC) is the most advantageous as the material of various telescope mirrors, because of high stiffness, low density, low coefficient of thermal expansion, high thermal conductivity and thermal stability. Newly developed high-strength reaction-sintered silicon carbide (NTSIC), which has two times higher strength than sintered SiC, is one of the most promising candidates for lightweight optical mirror substrate, because of fully dense, lightweight, small sintering shrinkage (±1 %), good shape capability and low processing temperature. In this study, 650mm in diameter mirror substrate of NTSIC was developed for space telescope applications. Three developed points describe below. The first point was to realize the lightweight to thin the thickness of green bodies. Ribs down to 3mm thickness can be obtained by strengthen the green body. The second point was to enlarge the mirror size. 650mm in diameter of mirror substrate can be fabricated with enlarging the diameter in order. The final point was to realize the homogeneity of mirror substrate. Some properties, such as density, bending strength, coefficient of thermal expansion, Young's modulus, Poisson's ratio, fracture toughness, were measured by the test pieces cutting from the fabricated mirror substrates.
New-Technology Silicon Carbide (NT-SiC) is a reaction sintered silicon carbide with very high bending strength. Two times higher bending strength than other SiC materials is important characteristics in an optical mirror for space application. The space optics is to endure the launch environment such as mechanical vibration and shock as well as lightweight and good thermal stability of their figure. NT-SiC has no open pore. It provides good surface roughness for infrared and visible application, when its surface is polished without additional coatings. Additional advantages are in the fabrication process. The sintering temperature is significantly lower than that of pure silicon carbide ceramics and its sintering shrinkage is smaller than one percent. These advantages will provide rapid progress to fabricate large structures and will enable that one meter mirror will put practical use. It is concluded that NT-SiC has potential to provide large lightweight optical mirror.
Newly developed high-strength reaction-sintered silicon carbide, called New-Technology Silicon Carbide (NT-SiC) is an attractive material for lightweight optical mirror with two times higher bending strength than other SiC materials. The material has advantages in its fabrication process. The sintering temperature is significantly lower than that of pure silicon carbide ceramics and its sintering shrinkage is smaller than one percent. These advantages will provide rapid progress to fabricate large structures. The characteristics of the material are also investigated. The polish of the test piece demonstrated that the polished surface has no pore and is suited to visible region as well as infrared without CVD SiC coating. It is concluded that NT-SiC has potential to provide large lightweight optical mirror.
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