Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B9/00—General processes of refining or remelting of metals; Apparatus for electroslag or arc remelting of metals
  • C22B9/16—Remelting metals
  • C22B9/22—Remelting metals with heating by wave energy or particle radiation
  • C22B9/228—Remelting metals with heating by wave energy or particle radiation by particle radiation, e.g. electron beams
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B34/00—Obtaining refractory metals
  • C22B34/10—Obtaining titanium, zirconium or hafnium
  • C22B34/14—Obtaining zirconium or hafnium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B9/00—General processes of refining or remelting of metals; Apparatus for electroslag or arc remelting of metals
  • C22B9/04—Refining by applying a vacuum

Definitions

• This invention relates to the production of purified zirconium.
• the conventional process for making zirconium metal utilizes a fluidized bed process in which the ore is subjected to a chlorination step which produces a relative­ly impure, hafnium-containing zirconium tetrachloride and by-product silicon tetrachloride (which by-product is relatively easily separated).
• the hafnium and zirconium containing material is then subjected to a number of purifying operations and also a complex hafnium separation operation. These operations result in purified oxides of zirconium and hafnium, which, of course, are maintained separate.
• the purified oxides are separately chlorinated.
• Zirconium and hafnium are commonly reduced from the chlo­ride by means of a reducing metal, typically magnesium.
• a reducing metal typically magnesium.
• the commercial processes are batched-type processes.
• U.S. Patent Specification No. 3,966,460 describes a process of introducing zirconium tetrachloride vapor onto molten magnesium, with the zirco­nium being reduced and traveling down through the magnesium layer to the bottom of the reactor and forming a metallic sponge.
• the metallic sponge (containing remaining chloride and some remaining excess reducing metal) is then placed in a distillation vessel for removal of the remaining salt and reducing metal by high temperature vacuum distillation.
• the sponge material is generally crushed, screened and pressed into electrodes for vacuum arc melting. Particu­larly, the material is multiple (typical double or triple) vacuum arc melted to provide ingots which are then further fabricated into various shapes.
• Most of the zirconium currently is used to produce Zircaloy.
• Zircaloy tubes as cladding material to contain the uranium dioxide fuel.
• a Zircaloy ingot is processed into a so-called "trex" and pilgering operations are used to reduce the trex inside diameter and wall thickness to size.
• Ultra-pure zirconium has been proposed for a liner for the inside surface of Zircaloy tubing which is used as a cladding for nuclear fuel and is described in, for example, U.S. Patent Specification No. 4,372,817 (Armijo et al.).
• a similar use of moderate purity material is proposed in U.S. Patent Specification No. 4,200,492 (Armijo et al.).
• EB (electron beam) melting of materials has been discussed in a number of U.S. patent specifications.
• EB melting has been used to consolidate crushed particles or chips in so called hearth furnaces and to separate impurities by either overflowing floating inclusions (U.S. Patent Specification No. 4,190,404 (Drs et al.) or to produce an electrode for arc melting (U.S. Patent Specification No. 4,108,644 (Walberg et al.).
• a number of U.S. patent specifications have used EB melting of powders or granules, often producing an ingot in a chilled mold. These powder melting EB patent specifica­tions include U.S. Patent Specification Nos.
• 3,091,525 to (D. A. Hunt) describes adding a small amount of zirconium, for example, to hafnium, for example and melting in an EB furnace to deoxidize the hafnium.
• Japanese application 1979-144789 Kawakita, published as patent publication 1981-67788 describes the use of a very small ingot with a high power density and ultra slow melting to produce a deep molten pool to produce a high purity ingot directly usable for lining of Zircaloy tubing for nuclear reactor applica­tions.
• Such laboratory sized apparatus with its high powered consumption and very low throughput is, of course, not practical for commercial production.
• a process for producing zirconium in purified form comprises reducing zirconium tetrachloride to produce a sponge of metallic zirconium which is distilled to generally remove residual magnesium and residual magne­sium chloride, and melting the distilled sponge to produce an ingot, characterized by vacuum baking the distilled sponge for at least one-half hour at 120-400°C; and elec­tron beam melting said vacuum baked sponge.
• this process provides material much purer than the so-called sponge material and almost as good as the crystal bar material, at a fraction of the cost of crystal bar material.
• Generally purified zirconium produced according to the present invention has oxygen in the 250-350 ppm range and iron in the 50-300 ppm range.
• Total impurities are generally in the 500-1000 ppm range (total impurities for these purposes generally comprise the elements listed in the afore-mentioned U.S. Patent Specification No. 4,200,492).
• Vacuum baking in the temperature range of 120-400°C gener necessarilyally removes moisture absorbed on the surface of the sponge (it is felt that the moisture generally is in the form of absorbed moisture on small amounts of residual magnesium chloride salt which still may remain after distillation).
• the EB melting generally removes iron from the zirconium. The combined baked and EB melted material provides high purity material approaching the quality of crystal bar.
• the vacuum baked material is general­ly maintained in an inert atmosphere between the vacuum baking and EB melting to avoid moisture pick up.
• the vacuum baking can be performed within the EB furnace prior to the start of melting and the vacuum maintained until melting is begun, thus generally avoiding the regaining of moisture.
• the distilled sponge is tested and only sponge having less than about 600 ppm of oxygen is selected for use in the instant process.
• the baking at 120-400°C for at least one-half hour is most desirably done within the EB furnace such that the material can be maintained under vacuum until melting
• the material can be baked in any vacuum chamber, including the EB welding chambers which are sometimes used to weld end stubs on electrodes which have been fabricated by pressing sponge material.
• the crushed sponge can be baked prior to pressing (again preferably generally keeping the materi­al in a dry, inert atmosphere) and then pressed and possi­bly subjected to a second baking cycle.
• the product of this process has low total impurities, and especially a low oxygen and low iron (the iron level generally being controlled by the number of passes through the EB furnace).
• the process is relatively inexpensive and, being compatible with existing production processes, requires little additional capital investment.

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Citations (6)

• 1987
  • 1987-06-02 DE DE8787107946T patent/DE3781206T2/de not_active Expired - Fee Related
  • 1987-06-02 EP EP87107946A patent/EP0248397B1/fr not_active Expired - Lifetime
  • 1987-06-02 ES ES198787107946T patent/ES2033736T3/es not_active Expired - Lifetime
  • 1987-06-05 KR KR870005721A patent/KR880000612A/ko not_active Application Discontinuation

Patent Citations (6)

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