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CVD SILICON CARBIDE®
for Reflective Optics Applications
CVD
SILICON CARBIDE® is an excellent reflective optics material
exhibiting superior polishability with low scatter, exceptional thermal and
cryogenic stability and high resistance to atomic oxygen and electron beam
degradation. CVD SILICON CARBIDE® is used as substrates for
fabricating mirrors for surveillance, high energy lasers, laser radar systems,
synchronotron x-ray and VUV telescopes, large astronomical telescopes and
weather satellites. CVD SILICON CARBIDE® lightweight mirrors
can be produced either by conventional fabrication, Near-Net-Shape fabrication
or precision machining
Ultraviolet and Infrared Reflectivity of
CVD SILICON CARBIDE®
| Ultraviolet Reflectivity of CVD SILICON CARBIDE® (1) | |
| Wavelength | % Reflected |
| 58.4 nm | 26 |
| 72.5 nm | 33 |
| 103.2 nm | 38 |
| 104.8 nm | 39 |
| 112.5 nm | 41 |
| 120 - 190.0 nm | >41 |
Infrared Reflectivity of CVD SILICON CARBIDE®(1) |
|
| Wavelength | % Reflected |
| 2.5 - 6.0 mm | >16 |
| 8.0 mm | 12 |
| 10.0 mm | 3 |
| 10.5 mm | 70 |
| 11.0 mm | 92 |
| 12.0 mm | 99 |
| 13.0 mm | 63 |
| 16.0 mm | 34 |
| 16.0 - 50.0 mm | >26 |
| (1) | (Test samples were polished and un-coated. The normal angle of incidence was used.) |
CVD SILICON CARBIDE® Comparison
to Other Materials and Processes
Until recently, most silicon carbide was made by the sintering and/or hot pressing of powders. These forms of silicon carbide are usually two phase materials which contain additives or are not theoretically dense, therefore, they cannot be optically polished to a high degree of surface finish and they do not possess the high temperature oxidation resistance or strength of silicon carbide made by the CVD process. In the chart below, CVD SILICON CARBIDE® is compared to other competing optical materials (beryllium and ULE (Corning)), semiconductor materials (quartz and polysilicon) and other forms of silicon carbide.
Typical Material Properties
(at room temperature unless otherwise noted)
| Typical Material Properties | ||||||
Other Materials  |
Density (gcm-3) |
Thermal- Conductivity (Wm-1K-1) |
Specific Heat (Jkg-1K-1) |
Elastic Modulus (GPa) |
CTE RT to 10000C (K-1x10-6) |
Polishability (Angstroms RMS) |
| Be(0-50) | 1.85 | 216 | 1880 | 303 | 11.4(2) | <10 |
| ULE(1) (7971) | 2.20 | 1.3 | 708 | 67 | 0.03(2) | < 3 |
| Polysilicon | 2.3 | 150 | 920 | 110 | 3.8 | < 5 |
| Quartz | 2.2 | 1.4 | 1210 | 70 | 0.5 | < 3 |
| CVD SILICON CARBIDE | 3.21 | 300 | 640 | 466 | 4.0 2.2(2) |
< 3 |
| React.Bonded SiC | 3.1 | 120-170 | - | 391 | 4.3 | > 20 |
| Hot Pressed SiC |
3.2 | 50-120 | - | 451 | 4.6 | > 50 |
| Sintered SiC | 3.1 | 15-120 | - | 408 | 4.5 | >100 |
Other  Processes |
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| 1 Corning Inc., Corning
NY 2 Room Temperature |
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