Free-standing silicon carbide articles formed by chemical vapor deposition and methods for their manufacture
Improved methods for manufacturing silicon carbide rings using chemical vapor deposition. Cylindrical tubes are used as deposition substrates and the resulting material deposited on the inside surface of cylindrical tubes or on the outside surface of cylindrical mandrels, or both, is sliced or cut into the desired ring size and shape. The resulting rings have a crystal growth that is oriented substantially planar to the finished article. The invention also relates to nitrogen doped silicon carbide material, as well as to silicon carbide structures having axes of grain growth substantially parallel to the plane of the structure and to each other, and having rotational orientation that is substantially random with respect to the axes of grain growth of the grains.
1. A structure formed by chemical vapor deposition having a planar direction and a normal direction, wherein the structure has a dimension in the planar direction that is larger than the dimension in the normal dimension, the chemical vapor deposition structure being a material having grains, wherein a majority of the grains are generally oriented more parallel to the planar direction than to the normal direction.
2. A structure, as claimed in claim 1 , wherein the structure is a flat ring having a circumference and wherein the grains are oriented in a substantially radial direction around the circumference of the ring.
3. A structure, as claimed in claim 1 , wherein the structure comprises silicon carbide.
4. A structure, as claimed in claim 1 , wherein the structure is a ring that comprises an inner diameter and an outer diameter and wherein the distance between the inner diameter and outer diameter is approximately 25 mm (one inch).
5. A structure, as claimed in claim 4 , wherein the inner diameter is between about 100 mm to 600 mm in diameter.
6. A structure, as claimed in claim 1 , having an axial thickness of between about 5 mm (0.2 inches) to 356 mm (fourteen inches).
7. A structure, as claimed in claim 1 , wherein the structure is a flat ring that has a curved outer surface.
8. A structure, as claimed in claim 1 , wherein the structure is a flat ring having a circumference that has substantially symmetrical stresses around the circumference of the ring.
9. A structure, as claimed in claim 1 , in which the structure comprises CVD deposited silicon carbide comprising an opacifying dopant dispersed in the silicon carbide in an amount sufficient to provide an opacity greater than 10,000 times that of CVD-deposited silicon carbide.
10. A structure, as claimed in claim 9 , in which the dopant is nitrogen in an amount 100 ppm to about 5000 ppm.
11. A structure, as claimed in claim 1 , in which the structure comprises CVD deposited silicon carbide material comprising FCC Moissanite-3C silicon carbide having a peak ratio of 220 planes to 111 planes ranging between about 0.30 and about 1.25, as measured by x-ray diffraction.
12. A structure, as claimed in claim 1 , wherein x-ray diffraction measurements of the structure result in peak ratio ranges between about 0.33 and about 0.60.
13. A structure, as claimed in claim 1 , in which the structure comprises CVD deposited silicon carbide material comprising grains having their axes of growth substantially parallel to each other, and having rotational orientation that is substantially random with respect to the axes of grain growth of the grains.
14. A structure, as claimed in claim 1 , in which the structure comprises silicon carbide and further comprises a layer of silicon deposited on at least one surface thereof.