Patent Number: 
Section: claims

1. A method of forming a joint between parts, wherein the parts comprise sapphire, the parts comprising respective surfaces configured for mutual contact, at least one of the parts further comprising a layer of aluminum nitride thereon whereby the aluminum nitride layer is juxtaposed between the surfaces when the parts are brought into contact, the method comprising bringing the parts into contact whereby the aluminum nitride layer is sandwiched between the surfaces of the respective parts, and providing localized heating of the aluminum nitride layer from a heat source that does not directly heat the parts, to at least the melting temperature of the juxtaposed surfaces of the parts, such that the aluminum nitride melts adjacent sapphire of the parts and reacts with the melted sapphire to form aluminum oxy-nitride compounds that, on cooling, join the parts. 2. The method of claim 1 wherein prior to making the joint, at least one of the sapphire parts is subjected to fine forming by thermal creep. 3. The method of claim 2 wherein said thermal creep fine forming comprises the steps of heating a rough sapphire part to about 1700-2000° C. following by passing the part through a die. 4. The method of claim 2 wherein said thermal creep fine forming comprises the steps of placing a rough sapphire part in a mold, wherein the mold has a lower thermal coefficient of expansion than sapphire, heating the part and mold to about 1700-2000° C. and removing the part from the mold. 5. The method of claim 1 wherein the step of providing a layer of aluminum nitride comprises coating a surface of at least one of the sapphire parts with aluminum nitride. 6. The method of claim 1 wherein the step of localized heating comprises directing a beam from the heat source, comprising infrared spectrum radiation, through at least one of the sapphire parts, wherein the sapphire parts are essentially transparent to the laser beam. 7. The method of claim 6 comprising the further step of detecting infrared radiation passing through the aluminum nitride layer and reducing the intensity of the infrared radiation when there is detected an increase in the infrared radiation passing through the aluminum nitride layer that exceeds a predetermined threshold. 8. The method of claim 6 wherein said beam comprises a laser beam. 9. The method of claim 1 wherein the parts comprise components of a nuclear reactor. 10. The method of claim 8 wherein said parts comprise components of a nuclear fuel element. 11. The method of claim 1 wherein the sapphire comprises single crystal sapphire. 12. The method of claim 1 wherein the layer of aluminum nitride comprises a wafer having a maximum thickness of about 0.1 millimeters. 13. The method of claim 1 further comprising the step of forming the layer of aluminum nitride by adhering aluminum nitride powder onto the surface of one or both of the parts. 14. The method of claim 1 further comprising the step of forming the layer of aluminum nitride by vapor deposition with aluminum nitride onto one or both of the parts. 15. A sapphire component fabricated by the method of claim 1. 16. The component of claim 13 comprising a component of a nuclear reactor. 17. The component of claim 14 wherein the component is a part of a nuclear fuel element. 18. A method of forming a joint between parts, wherein at least one of the parts comprises aluminum oxide, the parts comprising respective surfaces configured for mutual contact, at least one of the parts further comprising a layer thereon comprising aluminum nitride, the method comprising bringing the parts into contact whereby the aluminum nitride layer is sandwiched between the surfaces of the respective parts, and selectively heating the aluminum nitride layer to a temperature sufficient to react the aluminum nitride layer with the aluminum oxide of at least one of said parts to form a mixture of aluminum oxide and aluminum oxy-nitride compounds that, on cooling, joins the parts, wherein the selective heating comprises exposing the layer to a heat source that does not directly heat the parts. 19. The method of claim 18 wherein the parts are essentially transparent to a selected wavelength range of infrared radiation and the aluminum nitride layer absorbs the infrared radiation when unreacted, wherein the heating comprises exposing the aluminum nitride layer to infrared radiation from the heat source within the selected range whereby the infrared radiation passes through at least one of the parts. 20. The method of claim 19 comprising the further step of detecting infrared radiation passing through the aluminum nitride layer and reducing the intensity of the infrared radiation when there is detected an increase in the infrared radiation passing through the aluminum nitride layer that exceeds a predetermined threshold, indicative of said reaction occurring. 21. The method of claim 19 wherein the infrared radiation comprises a laser beam. 22. The method of claim 18 wherein the reaction forms a eutectic ratio mixture of aluminum nitride and aluminum oxide. 23. The method of claim 18 where the parts comprise sapphire. 24. The method of claim 18 wherein the layer of aluminum nitride comprises a solid wafer. 25. The method of claim 18 further comprising the step of forming the layer of aluminum nitride by adhering aluminum nitride powder onto the surface of one or both of the parts. 26. The method of claim 18 further comprising the step of forming the layer of aluminum nitride by vapor deposition with aluminum nitride onto one or both of the parts. 27. The method of claim 18 comprising the further step of applying a second layer between the parts, the second layer comprising a eutectic mixture of aluminum oxide and aluminum nitride, wherein the selective heating of the aluminum nitride layer indirectly heats the second layer and reacts the second layer with the aluminum oxide of at least one of the parts. 28. The method of claim 27 comprising the further step of providing a third layer between the parts, comprising a eutectic mixture of aluminum oxide and aluminum nitride, wherein the aluminum nitride layer is sandwiched between the second and third layers.