Metallic crucibles and methods of forming the same
View Patent ↗In various embodiments, a precursor powder is pressed into an intermediate volume and chemically reduced, via sintering, to form a metallic shaped article.
1. A crucible comprising:
an inner surface consisting essentially of (i) an alloy of molybdenum and tungsten or (ii) a mixture of molybdenum and tungsten;
extending from the inner surface through only a portion of a thickness of the crucible, an interior zone consisting essentially of (i) an alloy of molybdenum and tungsten or (ii) a mixture of molybdenum and tungsten; and
an outer surface, opposite the inner surface, consisting essentially of molybdenum.
2. The crucible of claim 1 , wherein a tungsten concentration within the interior zone is graded such that the tungsten concentration decreases toward the outer surface of the crucible.
3. The crucible of claim 2 , wherein the tungsten concentration within the interior zone is linearly graded.
4. The crucible of claim 2 , wherein the tungsten concentration within the interior zone decreases toward the outer surface of the crucible with an exponential dependence.
5. The crucible of claim 2 , wherein the tungsten concentration within the interior zone decreases toward the outer surface of the crucible in accordance with the complementary error function.
6. The crucible of claim 1 , wherein a total tungsten content within an entirety of the crucible is between approximately 5% and approximately 20% by weight.
7. A method of fabricating a crucible having a target set of final dimensions, the method comprising: pressing a precursor powder into a volume having intermediate dimensions larger than the final dimensions along at least one direction, the precursor powder comprising a compound comprising (i) molybdenum and (ii) a non-metallic chemical species; thereafter, sintering the pressed precursor powder to (i) chemically reduce the precursor powder, (ii) shrink the volume having intermediate dimensions into the crucible having the final dimensions, and (iii) release a non-metallic by-product; cooling the crucible; after cooling the crucible, disposing tungsten on at least one surface of the crucible; and annealing the crucible, thereby at least one of alloying or mixing the tungsten with the molybdenum to form the crucible comprising (i) an inner surface consisting essentially of (a)an alloy of molybdenum and tungsten or (b) a mixture of molybdenum and tungsten, (ii) an outer surface consisting essentially of molybdenum, and (iii) therebetween, an interior zone extending from the inner surface through only a portion of a thickness of the crucible and consisting essentially of (a) an alloy of molybdenum and tungsten or (b) a mixture of molybdenum and tungsten.
8. The method of claim 7 , wherein after cooling and before annealing, the crucible has a density less than approximately 95%.
9. The method of claim 7 , wherein annealing the crucible comprises: annealing the crucible at a first temperature to diffuse at least a portion of the tungsten into the crucible; and thereafter, annealing the crucible at a second temperature to alloy at least a portion of the tungsten with the molybdenum of the crucible.
10. The method of claim 9 , wherein (i) the first temperature is selected from the range of approximately 800° C. to approximately 1200° C., and (ii) the second temperature is selected from the range of approximately 20000 and approximately 2600° C.
11. The method of claim 9 , wherein (i) the first temperature is no greater than 1200° C. and (ii) the second temperature is no less than 2000° C.
12. The method of claim 7 , wherein disposing the tungsten on at least one surface of the crucible comprises at least one of applying a slurry or spray deposition.
13. The method of claim 7 , wherein the precursor powder comprises molybdenum dimolybdate.
14. The method of claim 13 , wherein sintering the pressed powder comprises:
sintering at a first temperature to chemically reduce ammonium dimolybdate to molybdenum trioxide; thereafter, sintering at a second temperature to chemically reduce molybdenum trioxide to molybdenum dioxide; thereafter, sintering at a third temperature to chemically reduce molybdenum dioxide to molybdenum; and thereafter, sintering at a fourth temperature to densify molybdenum, thereby forming the crucible.
15. The method of claim 14 , wherein (i) the fourth temperature is greater than the third temperature, (ii) the third temperature is greater than the second temperature, (iii) the second temperature is greater than the first temperature, and (iv) the first temperature is selected from the range of approximately 100° C. to approximately 650° C.
16. The method of claim 14 , wherein (i) the first temperature is selected from the range of approximately 450° C. to approximately 650° C., (ii) the second temperature is selected from the range of approximately 500° C. to approximately 700° C., (iii) the third temperature is selected from the range of approximately 800° C. to approximately 1000° C., and (iv) the fourth temperature is selected from the range of approximately 1450° C. to approximately 1800° C.
17. The method of claim 7 , wherein (i) the pressed precursor powder is sintered in an atmosphere consisting essentially of hydrogen, and (ii) the crucible is annealed in an atmosphere consisting essentially of hydrogen.
18. The method of claim 7 , wherein the non-metallic by-product comprises ammonia.
19. The method of claim 7 , wherein sintering the pressed precursor powder comprises: heating the pressed precursor powder at a first temperature to (i) chemically reduce the pressed precursor powder to an intermediate product comprising (a) molybdenum and (b) a second non-metallic chemical species, and (ii) release the non-metallic by-product; and thereafter, heating the intermediate product at a second temperature higher than the first temperature to (i) chemically reduce the intermediate product to molybdenum and (ii) release a second non-metallic by-product.
20. The method of claim 19 , wherein the second non-metallic by-product and the non-metallic by-product are different.
21. The method of claim 19 , wherein (i) the non-metallic by-product comprises ammonia and (ii) the second non-metallic by-product comprises water vapor.
22. The method of claim 7 , wherein a tungsten concentration within the interior zone is graded such that the tungsten concentration decreases toward the outer surface of the crucible.