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A process for producing a SiC ceramic microtube by oxidizing the surface of an organosilicon polymer to become infusible by exposure to an ionizing radiation, extracting the uncrosslinked central portion of the fiber with an organic solvent to make a hollow silicon polymer fiber, and firing it in an

A process for producing a SiC ceramic microtube by oxidizing the surface of an organosilicon polymer to become infusible by exposure to an ionizing radiation, extracting the uncrosslinked central portion of the fiber with an organic solvent to make a hollow silicon polymer fiber, and firing it in an inert gas so that it acquires a ceramic nature.

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1. A process for producing a SiC ceramic microtube, comprising:(a) oxidizing the surface of a fiber of polycarbosilane cross-linkable by oxygen by exposing the fiber to ionizing radiation in the presence of oxygen;(b) heat-treating the surface-oxidized fiber of step (a) in an argon atmosphere or in

1. A process for producing a SiC ceramic microtube, comprising:(a) oxidizing the surface of a fiber of polycarbosilane cross-linkable by oxygen by exposing the fiber to ionizing radiation in the presence of oxygen;(b) heat-treating the surface-oxidized fiber of step (a) in an argon atmosphere or in a vacuum the at a temperature in the range of 500° C.-700° C. to cross-link the oxidized polycarbosilane to form a fiber having a cross-linked surface portion and an uncross-linked polycarbosilane core portion;(c) removing the uncross-linked polycarbosilane of the fiber of step (b) by solubilizing it in a solvent for the uncross-linked polymer to form a cross-linked polycarbosilane tube; and(d) heating the cross-linked polycarbosilane tube of step (c) at a temperature and for a time sufficient to convert the cross-linked polycarbosilane tube to a ceramic SiC tube. 2. The process according to claim 1, wherein the ionizing radiation is electron beams. 3. The process according to claim 2, wherein the polycarbosilane selectively oxidized in the surface layer is heat treated so that the surface layer is crosslinked whereas only the interior of the fiber becomes extractable to form a cylindrical shape. 4. The process according to claim 3, wherein the polycarbosilane is exposed to an ionizing radiation in such a way that only the surface layer of the irradiated polymer becomes oxidized. 5. The process according to claim 4, wherein the wall thickness of the ceramic tube is controlled by adjusting the dose rate of the ionizing radiation being applied and the concentration of oxygen in the atmosphere for irradiation. 6. The process according to claim 3, wherein the wall thickness of the ceramic tube is controlled by adjusting the dose rate of the ionizing radiation being applied and the concentration of oxygen in the atmosphere for irradiation. 7. The process according to claim 2, wherein the polycarbosilane is exposed to an ionizing radiation in such a way that only the surface layer of the irradiated polymer becomes oxidized. 8. The process according to claim 7, wherein the wall thickness of the ceramic tube is controlled by adjusting the dose rate of the ionizing radiation being applied and the concentration of oxygen in the atmosphere for irradiation. 9. The process according to claim 2, wherein the wall thickness of the ceramic tube is controlled by adjusting the dose rate of the ionizing radiation being applied and the concentration of oxygen in the atmosphere for irradiation. 10. The process according to claim 1, wherein the polycarbosilane selectively oxidized in the surface layer is heat treated so that the surface layer is crosslinked whereas only the interior of the fiber becomes extractable to form a cylindrical shape. 11. The process according to claim 10, wherein the polycarbosilane is exposed to an ionizing radiation in such a way that only the surface layer of the irradiated polymer becomes oxidized. 12. The process according to claim 11, wherein the wall thickness of the ceramic tube is controlled by adjusting the dose rate of the ionizing radiation being applied and the concentration of oxygen in the atmosphere for irradiation. 13. The process according to claim 10, wherein the wall thickness of the ceramic tube is controlled by adjusting the dose rate of the ionizing radiation being applied and the concentration of oxygen in the atmosphere for irradiation. 14. The process according to claim 1, wherein the polycarbosilane is exposed to an ionizing radiation in such a way that only the surface layer of the irradiated polymer becomes oxidized. 15. The process according to claim 14, wherein the wall thickness of the ceramic tube is controlled by adjusting the dose rate of the ionizing radiation being applied and the concentration of oxygen in the atmosphere for irradiation. 16. The process according to claim 1, wherein the wall thickness of the ceramic tube is controlled by adjusting the dose rate of the ionizing rad iation being applied and the concentration of oxygen in the atmosphere for irradiation.