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US3370923A - Method of making refractory metal nitride fibers, flakes and foil - Google Patents

Method of making refractory metal nitride fibers, flakes and foil Download PDF

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US3370923A
US3370923A US396780A US39678064A US3370923A US 3370923 A US3370923 A US 3370923A US 396780 A US396780 A US 396780A US 39678064 A US39678064 A US 39678064A US 3370923 A US3370923 A US 3370923A
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foil
refractory metal
furnace
metal
flakes
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Ralph L Hough
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B21/00—Nitrogen; Compounds thereof
    • C01B21/06—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron
    • C01B21/0615—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron with transition metals other than titanium, zirconium or hafnium
    • C01B21/0617—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron with transition metals other than titanium, zirconium or hafnium with vanadium, niobium or tantalum
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B21/00—Nitrogen; Compounds thereof
    • C01B21/06—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron
    • C01B21/076—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron with titanium or zirconium or hafnium
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/10—Particle morphology extending in one dimension, e.g. needle-like
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/20—Particle morphology extending in two dimensions, e.g. plate-like

Definitions

  • ABSTRACT OF THE DISCLOSURE Method for making thin section nitride fibers, flakes or foil of a clean refractory metal selected from Nb, Ta, Ti, Hf and Zr by rolling the metal to a thinness of from to 10 inch, positioning the metal on a conveyor belt chemically inert to the metal prior to the passage of the belt between an upper and a lower bathe of gas entering an oxygen-free nitriding chamber of a furnace with an atmosphere of nitrogen or ammonia wherein the bafiies direct the gas flow against both the top and the bottom of the metal on the conveyor belt, and maintaining the temperature of the metal within the range of the nitriding temperature of the meal on the conveyor belt.
  • a clean refractory metal selected from Nb, Ta, Ti, Hf and Zr
  • This invention concerns a new and improved process for the nitriding of fibers, flakes and filaments of the refractory metals Nb(Cb), Ta, Ti, Hf, and Zr and to a furnace suitable for practicing the process.
  • the material is used as missiles, nose cones, aircraft wing leading edges and the like.
  • metal nitrides has commonly been as coatings on substrates that are accomplished by reacting a volatile metal halide with hydrogen and with nitrogen or with ammonia, at a temperature of about between 2000 to 4000 F. by vapor deposition as a thin coating on the substrate.
  • the object of the present invention is to provide a new and improved method for making thin section nitride fibers, filaments, flake and foil, of a clean refractory metal.
  • the fibers etc. are impregnated with a plastic in making reinforcement for structural and ablative material that reiaiTlS its identity and its mechanical strength under great stresses and under high shear forces at high temperatures in the order of 5000 F. or 2760 C.
  • FIG. 1 is a side elevational view partly broken away and in section of a rectangular tubular furnace wherein the present invention may be practiced;
  • FIG. 2 is a diminished section taken along the line 22 of FIG. 1;
  • FIG. 3 is a fragmentary plan view of the metal foil undergoing thermal diffusion of oxygen and nitrogen by temperature gradients.
  • the furnace wall 10 is of rectangular cross section and has rectangular ends 11 and 11. Siits 12 in the ends 11 and 11 of the furnace 10 and dimensioned for a minimum clearance for the passage through the slits of a silica cloth conveyor belt 13 carrying strips of foil 14 the length of the furnace 10. Adjacent to the foil input end of the furnace 10 are a pair of baffles 15 and 15' that are positioned on opposite sides of the belt 13 and foil 14.
  • the bafiles 15 and 15 illustratively are cantilever supported from a pair of water conducting cooling pipes 16 and 16 that are coaxial with a nitrogen conducting pipe 17.
  • FIG. 3 of the accompanying drawing is indicated the fragment of the foil 14 at the input end of the furnace 10 and against a proximal edge of which nitrogen gas from the pipe 17 is discharged into the furnace 10.
  • T is the nitriding temperature within the furnace 10 and is higher than the temperature T of the continuously moving foil 14, as its edge passes through the nitrogen gas that is supplied from the pipe 17 to the furnace 10.
  • the nitrogen gas within the furnace 10 is held at a pressure that is sufficiently above ambient to maintain continuously pure nitrogen within the furnace 10.
  • the foil temperature T is sufliciently less than T such that the nitriding of the foil does not occur appreciably at T and such that in the zone A there exists a thermal gradient that causes oxygen occluded in the metal of the foil 14, to migrate by diffusion to the cooler edge 20 of the foil 14 where it appears as a dark discoloration in the end product.
  • the foil 14 may be replaced by short wires that extend across the belt 13.
  • the gas diffusion causes a dark discoloration adjacent the ends of the wire
  • a corresponding diffusion of gaseous impurities discolors the ends of foil or Wire that is adjacent a metal support for the foil or wire.
  • the oxygen diffuses to the zone of lower temperature across the thermal gradient.
  • Thermal diffusion is the moving of atoms of impurities, here oxygen, within a metal under the influence of a temperature gradient, with the oxygen atoms moving toward lower temperatures.
  • the nitriding of ultra fine wires of pure zirconium meta-l in the order of 0.001 inch diameter at the temperature of from 1600 F. (871 C.) to 2600 (1427 C.) is most difficult to accomplish with pure nitrogen or with ammonia, because of the reaction kinetics that are involved.
  • the nitriding time of these ultra fine Zr wires of 0.001 inch diameter within the temperature range of from 1600 F. to 2600 F., is up to about one minute.
  • reaction kinetics of nitriding zirconium are such that it is the most time consuming of the group of refractory metals, that consists of niobium, tantalum, titanium, hafnium, and zirconium. These metals are rolled to very thin foil or drawn as wire in the order of 0.001 inch thickness.
  • the advantage of the fiat rolled wire is that its edge strains are minimized by having an elliptical section or an elliptically contoured edge.
  • the metal thin foil or fiat rolled wire is placed in a scavenged and evacuated chamber maintained in the temperature range of from 1800 to 2700 F. (982 to 1482 C.).
  • the chamber may be a mufile furnace for batch production, or a fused quartz tubular furnace with a conveyor belt passing axially through the tube for continuous production.
  • the furnace preferably is initially scavenged or baked out and then is evacuated.
  • the furnace is suppled with an atmosphere of ultra pure nitrogen or ammonia at slightly above atmospheric pressures.
  • the group of refractory metals may -be illustrated by Zirconium.
  • the nitrogen or the ammonia is procured as cylinder grade gas.
  • the nitrogen is passed through a dessicant, such as a desired succession of increasingly dehydrated containers of magnesium perchlorate, for the drated nitrogen is cleaned of oxygen, as by being passed through a desired plurality of beds of copper turnings that are maintained about in the range of from 1400 to 1800 F. (760 to 982 C.).
  • the resultant nitriding gas is supplied continuously as the ultra pure atmosphere in the chosen nitriding chamber.
  • the ultra pure nitriding gas in the chamber is passed over the zirconium or other foil, or flat rolled wire at 1800 to 2700" F., at a fiow rate that is maintained at the rate of the complete nitriding of the selected refractory metal end product.
  • the use of the long tube furnace with a conveyor system passing longitudinally through the tube requires gas baffiing to prevent back difiusion of ambient gases into the reaction zone, or requires the maintaining of a closed system for the entire operation.
  • the nitriding process is applied to foil or wire that is about in the range of from 0.001 to 0.0001 inch thick.
  • the ZrN so made had a melting point of 2980 C. or 5400" F. without sublimation or decomposition under a pressure of one atmosphere; an X-ray density of 7.349 g./cm. a vapor pressure below at 1730 C.; and a hardness of 8-9 mohs.
  • the nitrides of Nb, Ta, Ti, and Zr are substantially chemically inert at room temperature of 22 C., being attacked only by mixtures of strong acids and oxidizing agents.
  • the resultant ZrN in thickness in the order of 10 inch thick was then used by being combined with a polymerize d plastic such illustratively as an epoxy resin or the like, as a reinforced structural and ablative plastic composite for use at very high temperatures in the order of 2950 to 3310 C., with the exception of niobium nitride which melts at 2050 C., and of excellent thermal shock resistance.
  • a polymerize d plastic such illustratively as an epoxy resin or the like, as a reinforced structural and ablative plastic composite for use at very high temperatures in the order of 2950 to 3310 C., with the exception of niobium nitride which melts at 2050 C., and of excellent thermal shock resistance.
  • the fibrous material of zirconium nitride packed resin makes a tough and serviceable material from which are made ablative plastics to serve as the lead edges of aircraft wings and the like, by a molding operation.
  • refractory metal fibrous nitride flake by rolling a refractory metal selected from the group that consists of Nb, Ta; Ti, Hf and Zr to a thickness about in the range of from 10- to 10- inch; positioning the rolled refractory metal on top of a conveyor belt that is chemically inert to the metal, passing the metal on'the' belt between an upper and a lower bafile of gas entering an oxygen-free nitriding chamber of a furnace with an atmosphere selected from the group of gaseous nitrogen and ammonia at a pressure above ambient wherein the pair of bafiles direct the gas flow against both the top and the bottom of the refractory metal on the conveyor belt, maintaining the temperature of the refractory metal about within the range of the nitr'iding temperature of the metal on the conveyor belt, and removing the nitrided refractory metal from the nitriding chamber of the furnace.
  • a refractory metal selected from the group that consists of Nb, Ta; Ti,
  • baflles extend substantially parallel to the direction of flow of a stream of gas entering the chamber and on opposite sides of the metal on the conveyor belt.

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)

Description

Feb. 27, 1968 R. L HOUGH 3,370,923
METHOD OF MAKING REFRACTORY METAL NITRIDE mamas, FLAKES AND FOIL Filed Sept. 15, 1964 INVENTOR l ma /v A. #00619 United States Patent 3,370,923 METHOD OF MAKING REFRACTORY METAL NITRIDE FIBERS, FLAKES AND FOIL Ralph L. Hough, Springfield, Ohio, assignor to the United States of America as represented by the Secretary of the Air Force Filed Sept. 15, 1964, Ser. No. 396,780 Claims. (Cl. 23-191) ABSTRACT OF THE DISCLOSURE Method for making thin section nitride fibers, flakes or foil of a clean refractory metal selected from Nb, Ta, Ti, Hf and Zr by rolling the metal to a thinness of from to 10 inch, positioning the metal on a conveyor belt chemically inert to the metal prior to the passage of the belt between an upper and a lower bathe of gas entering an oxygen-free nitriding chamber of a furnace with an atmosphere of nitrogen or ammonia wherein the bafiies direct the gas flow against both the top and the bottom of the metal on the conveyor belt, and maintaining the temperature of the metal within the range of the nitriding temperature of the meal on the conveyor belt.
The invention that is described herein may be manufactured and used by or for the United States Government for governmental purposes without the payment to me of any royalty thereon.
' This invention concerns a new and improved process for the nitriding of fibers, flakes and filaments of the refractory metals Nb(Cb), Ta, Ti, Hf, and Zr and to a furnace suitable for practicing the process. The material is used as missiles, nose cones, aircraft wing leading edges and the like.
The previous synthesis of metal nitrides has commonly been as coatings on substrates that are accomplished by reacting a volatile metal halide with hydrogen and with nitrogen or with ammonia, at a temperature of about between 2000 to 4000 F. by vapor deposition as a thin coating on the substrate.
The object of the present invention is to provide a new and improved method for making thin section nitride fibers, filaments, flake and foil, of a clean refractory metal. The fibers etc. are impregnated with a plastic in making reinforcement for structural and ablative material that reiaiTlS its identity and its mechanical strength under great stresses and under high shear forces at high temperatures in the order of 5000 F. or 2760 C.
An illustrative embodiment of a suitable furnace arrangement in which the present invention is practiced is represented in the accompanying drawing wherein:
FIG. 1 is a side elevational view partly broken away and in section of a rectangular tubular furnace wherein the present invention may be practiced;
FIG. 2 is a diminished section taken along the line 22 of FIG. 1; and
FIG. 3 is a fragmentary plan view of the metal foil undergoing thermal diffusion of oxygen and nitrogen by temperature gradients.
In FIG. 1 the furnace wall 10 is of rectangular cross section and has rectangular ends 11 and 11. Siits 12 in the ends 11 and 11 of the furnace 10 and dimensioned for a minimum clearance for the passage through the slits of a silica cloth conveyor belt 13 carrying strips of foil 14 the length of the furnace 10. Adjacent to the foil input end of the furnace 10 are a pair of baffles 15 and 15' that are positioned on opposite sides of the belt 13 and foil 14. The bafiles 15 and 15 illustratively are cantilever supported from a pair of water conducting cooling pipes 16 and 16 that are coaxial with a nitrogen conducting pipe 17.
The thermal diffusion of oxygen and nitrogen in zirconium is discussed by G. D. Ruick and H. A. C. M. Bruning in volume 190, Nature, p. 1181, published in 1961.
In FIG. 3 of the accompanying drawing is indicated the fragment of the foil 14 at the input end of the furnace 10 and against a proximal edge of which nitrogen gas from the pipe 17 is discharged into the furnace 10.
In FIG. 3, T is the nitriding temperature within the furnace 10 and is higher than the temperature T of the continuously moving foil 14, as its edge passes through the nitrogen gas that is supplied from the pipe 17 to the furnace 10. The nitrogen gas within the furnace 10 is held at a pressure that is sufficiently above ambient to maintain continuously pure nitrogen within the furnace 10.
The foil temperature T is sufliciently less than T such that the nitriding of the foil does not occur appreciably at T and such that in the zone A there exists a thermal gradient that causes oxygen occluded in the metal of the foil 14, to migrate by diffusion to the cooler edge 20 of the foil 14 where it appears as a dark discoloration in the end product.
The foil 14 may be replaced by short wires that extend across the belt 13. The gas diffusion causes a dark discoloration adjacent the ends of the wire A corresponding diffusion of gaseous impurities discolors the ends of foil or Wire that is adjacent a metal support for the foil or wire.
In the described manner traces of oxygen can be eliminated from the foil or wire by thermal diffusion of the Ludwig-Soret type. This phenomenon is established in this process by the thermal gradient within the reaction zone.
The oxygen diffuses to the zone of lower temperature across the thermal gradient.
Thermal diffusion is the moving of atoms of impurities, here oxygen, within a metal under the influence of a temperature gradient, with the oxygen atoms moving toward lower temperatures.
The nitriding of ultra fine wires of pure zirconium meta-l in the order of 0.001 inch diameter at the temperature of from 1600 F. (871 C.) to 2600 (1427 C.) is most difficult to accomplish with pure nitrogen or with ammonia, because of the reaction kinetics that are involved. The nitriding time of these ultra fine Zr wires of 0.001 inch diameter within the temperature range of from 1600 F. to 2600 F., is up to about one minute.
The reaction kinetics of nitriding zirconium are such that it is the most time consuming of the group of refractory metals, that consists of niobium, tantalum, titanium, hafnium, and zirconium. These metals are rolled to very thin foil or drawn as wire in the order of 0.001 inch thickness. The advantage of the fiat rolled wire is that its edge strains are minimized by having an elliptical section or an elliptically contoured edge.
The metal thin foil or fiat rolled wire is placed in a scavenged and evacuated chamber maintained in the temperature range of from 1800 to 2700 F. (982 to 1482 C.). The chamber may be a mufile furnace for batch production, or a fused quartz tubular furnace with a conveyor belt passing axially through the tube for continuous production. The furnace preferably is initially scavenged or baked out and then is evacuated. During the production of the nitrided metal, the furnace is suppled with an atmosphere of ultra pure nitrogen or ammonia at slightly above atmospheric pressures. The group of refractory metals may -be illustrated by Zirconium.
The nitrogen or the ammonia is procured as cylinder grade gas. Illustratively, the nitrogen is passed through a dessicant, such as a desired succession of increasingly dehydrated containers of magnesium perchlorate, for the drated nitrogen is cleaned of oxygen, as by being passed through a desired plurality of beds of copper turnings that are maintained about in the range of from 1400 to 1800 F. (760 to 982 C.). The resultant nitriding gas is supplied continuously as the ultra pure atmosphere in the chosen nitriding chamber.
The ultra pure nitriding gas in the chamber is passed over the zirconium or other foil, or flat rolled wire at 1800 to 2700" F., at a fiow rate that is maintained at the rate of the complete nitriding of the selected refractory metal end product. The use of the long tube furnace with a conveyor system passing longitudinally through the tube requires gas baffiing to prevent back difiusion of ambient gases into the reaction zone, or requires the maintaining of a closed system for the entire operation.
The nitriding process is applied to foil or wire that is about in the range of from 0.001 to 0.0001 inch thick. With the refractory metal 0.00014 inch Zr foil at 1920 F., the Zr is completely nitrided in one minute, by experimental determination. The ZrN so made had a melting point of 2980 C. or 5400" F. without sublimation or decomposition under a pressure of one atmosphere; an X-ray density of 7.349 g./cm. a vapor pressure below at 1730 C.; and a hardness of 8-9 mohs. The nitrides of Nb, Ta, Ti, and Zr are substantially chemically inert at room temperature of 22 C., being attacked only by mixtures of strong acids and oxidizing agents.
The resultant ZrN in thickness in the order of 10 inch thick was then used by being combined with a polymerize d plastic such illustratively as an epoxy resin or the like, as a reinforced structural and ablative plastic composite for use at very high temperatures in the order of 2950 to 3310 C., with the exception of niobium nitride which melts at 2050 C., and of excellent thermal shock resistance. The fibrous material of zirconium nitride packed resin makes a tough and serviceable material from which are made ablative plastics to serve as the lead edges of aircraft wings and the like, by a molding operation.
It is to be understood that the details of the process that are disclosed herein may be modified somewhat without departing from the spirit and the scope of the present invention- H I claim:
1. The method of making refractory metal fibrous nitride flake by rolling a refractory metal selected from the group that consists of Nb, Ta; Ti, Hf and Zr to a thickness about in the range of from 10- to 10- inch; positioning the rolled refractory metal on top of a conveyor belt that is chemically inert to the metal, passing the metal on'the' belt between an upper and a lower bafile of gas entering an oxygen-free nitriding chamber of a furnace with an atmosphere selected from the group of gaseous nitrogen and ammonia at a pressure above ambient wherein the pair of bafiles direct the gas flow against both the top and the bottom of the refractory metal on the conveyor belt, maintaining the temperature of the refractory metal about within the range of the nitr'iding temperature of the metal on the conveyor belt, and removing the nitrided refractory metal from the nitriding chamber of the furnace.
2. The method described in claim 1 wherein the conveyor belt is made of silica cloth.
3. The method defined by claim 1 wherein the refractory metal is a foil.
4. The method defined by claim 1 wherein the refractory metal is a wire.
5. The method defined by claim 1 wherein the baflles extend substantially parallel to the direction of flow of a stream of gas entering the chamber and on opposite sides of the metal on the conveyor belt.
References Cited UNITED STATES PATENTS 2,461,019 2/1949 Alexander 2319l 2,750,268 6/1956 Erasmus et al 23-191 2,784,639 3/1957 Keenan et a1 148-166 OSCAR R. VERTIZ, Primary Examiner.
H. S. MILLER, Assistant Examiner.
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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3630766A (en) * 1969-11-25 1971-12-28 Carborundum Co Refractory fibers and method of producing same
WO1991008322A1 (en) * 1989-11-30 1991-06-13 President And Fellows Of Harvard College Process for chemical vapor deposition of transition metal nitrides
DE4330955A1 (en) * 1993-09-09 1995-03-16 Reetz Teja Prof Dr Rer Nat Hab Refractory material for the thermal insulation of high-temperature furnaces having a non-oxidising heat-treatment atmosphere
US5665326A (en) * 1995-11-13 1997-09-09 Advanced Refractory Technologies, Inc. Method for synthesizing titanium nitride whiskers

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2461019A (en) * 1945-03-02 1949-02-08 Metal Hydrides Inc Production of zirconium nitride
US2750268A (en) * 1952-05-01 1956-06-12 Union Carbide & Carbon Corp Silicon nitride
US2784639A (en) * 1953-05-04 1957-03-12 Eastman Kodak Co Titanium nitride coated optical element

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2461019A (en) * 1945-03-02 1949-02-08 Metal Hydrides Inc Production of zirconium nitride
US2750268A (en) * 1952-05-01 1956-06-12 Union Carbide & Carbon Corp Silicon nitride
US2784639A (en) * 1953-05-04 1957-03-12 Eastman Kodak Co Titanium nitride coated optical element

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3630766A (en) * 1969-11-25 1971-12-28 Carborundum Co Refractory fibers and method of producing same
WO1991008322A1 (en) * 1989-11-30 1991-06-13 President And Fellows Of Harvard College Process for chemical vapor deposition of transition metal nitrides
US5139825A (en) * 1989-11-30 1992-08-18 President And Fellows Of Harvard College Process for chemical vapor deposition of transition metal nitrides
DE4330955A1 (en) * 1993-09-09 1995-03-16 Reetz Teja Prof Dr Rer Nat Hab Refractory material for the thermal insulation of high-temperature furnaces having a non-oxidising heat-treatment atmosphere
US5665326A (en) * 1995-11-13 1997-09-09 Advanced Refractory Technologies, Inc. Method for synthesizing titanium nitride whiskers

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