Metallic crucibles and methods of forming the same

Abstract

In various embodiments, a precursor powder is pressed into an intermediate volume and chemically reduced, via sintering, to form a metallic shaped article. In a further embodiment the invention concerns a method of fabricating a shaped article having a target set of final dimensions and consisting essentially of molybdenum, the method comprising the pressing of an ammonium-based molybdenum-precursor powder, in particular ammonium dimolybdate, and a stepwise sintering process, defining four different temperature levels. In a further aspect, embodiments of the invention feature a method of treating a shaped article. An additive is disposed on at least one surface of a shaped article including or consisting essentially of one or more metals. In yet a further aspect, embodiments of the invention feature a crucible that includes or consists essentially of an inner layer consisting essentially of an alloy of molybdenum and tungsten, an outer layer consisting essentially of molybdenum, and therebetween, a zone consisting essentially of a graded concentration of molybdenum and tungsten.

Description

[0001] related application [0002] This application claims the benefit and priority of U.S. Provisional Patent Application No. 61 / 652,393, filed May 29, 2012, and U.S. Patent Application No. 13 / 799,796, filed March 13, 2013, the entire contents of each of which are incorporated herein by reference. technical field [0003] In various embodiments, the invention relates to the formation of crucibles and other shaped articles, particularly using powder metallurgy techniques. Background technique [0004] Molybdenum (Mo) crucibles are widely used in the production of sapphire single crystals due to their beneficial refractory properties including high melting point. Most Mo crucibles are fabricated either by deep-drawing Mo plates or by powder metallurgy techniques using high-purity Mo powder. However, such techniques are often difficult and expensive to implement. For example, powder metallurgy of Mo generally requires expensive high-purity Mo powder. In addition, the pow...

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Problems solved by technology

In addition, the powder metallurgy process of Mo powder usually results in less than 100% compaction of Mo crucibles, which affects the mechanical properties (such as toughness) of such crucibles

[0005] In addition, although Mo crucibles are suitable for many sapphire manufacturing processes, pure Mo often has a relatively high vapor pressure, which may lead to contamination when growing sapphire from liquid melts.

Although crucibles made of tungsten (W) or even homogeneous Mo-W alloys (for example, formed by powder metallurgy of mixed Mo powder and W powder) can reduce some of the problems caused by using pure Mo crucibles, such crucibles are often Bulky (and thus difficult to work with), rather expensive and generally less tough (especially in pure W)

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