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WO1993000292A1 - Procede de production d'oxyde de niobium - Google Patents

Procede de production d'oxyde de niobium Download PDF

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Publication number
WO1993000292A1
WO1993000292A1 PCT/US1992/005325 US9205325W WO9300292A1 WO 1993000292 A1 WO1993000292 A1 WO 1993000292A1 US 9205325 W US9205325 W US 9205325W WO 9300292 A1 WO9300292 A1 WO 9300292A1
Authority
WO
WIPO (PCT)
Prior art keywords
product
metal
temperature
alloy
ferroniobium
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/US1992/005325
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English (en)
Inventor
James A. Sommers
Verlin Q. Perkins
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
TDY Industries LLC
Original Assignee
Teledyne Industries Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Teledyne Industries Inc filed Critical Teledyne Industries Inc
Priority to JP50163493A priority Critical patent/JP3406597B2/ja
Priority to BR9206195A priority patent/BR9206195A/pt
Priority to EP92915641A priority patent/EP0591459A4/fr
Publication of WO1993000292A1 publication Critical patent/WO1993000292A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • 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
    • C01B13/00—Oxygen; Ozone; Oxides or hydroxides in general
    • C01B13/14—Methods for preparing oxides or hydroxides in general
    • C01B13/32—Methods for preparing oxides or hydroxides in general by oxidation or hydrolysis of elements or compounds in the liquid or solid state or in non-aqueous solution, e.g. sol-gel process
    • C01B13/322—Methods for preparing oxides or hydroxides in general by oxidation or hydrolysis of elements or compounds in the liquid or solid state or in non-aqueous solution, e.g. sol-gel process of elements or compounds in the solid state
    • 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
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B6/00—Hydrides of metals including fully or partially hydrided metals, alloys or intermetallic compounds ; Compounds containing at least one metal-hydrogen bond, e.g. (GeH3)2S, SiH GeH; Monoborane or diborane; Addition complexes thereof
    • C01B6/24—Hydrides containing at least two metals; Addition complexes thereof
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G31/00—Compounds of vanadium
    • C01G31/02—Oxides
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G33/00—Compounds of niobium
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G35/00—Compounds of tantalum
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/80—Compositional purity
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/80—Compositional purity
    • C01P2006/82—Compositional purity water content

Definitions

  • This invention relates to the preparation of metal oxides of metals from Groups IV, V and VI, specifically including oxides of niobium and tantalum, and more particularly to a novel process for the direct production of substantially pure metal oxides from ferrometal alloys and nickel metal alloys.
  • Niobium oxide is exemplary of this need as it is an important intermediate for the production of pure niobium metal and high purity, i.e., vacuum grade, ferroniobium. It is, therefore, desirable to obtain substantially pure niobium oxide for the subsequent reduction reaction to niobium metal or by metallothermic reaction with iron to form vacuum grade ferroniobium.
  • niobium or tantalum is available in the form of metallurgical grade ferrometal alloys of these metals.
  • ferroniobium typically containing predominately iron and niobium and preferably more than 50% by weight niobium and most preferably between about 63% to 67% by weight niobium with the balance including iron and minor amounts of silicon and smaller amounts of tantalum, phosphorous and titanium is an attractive source of niobium which currently has not been commercially exploited.
  • Niobium chloride is then recovered by subsequently cooling the salt vapor to condense the (NbCl 5 ) .
  • NbCl 5 is then hydrolyzed by its addition to water which can then be neutralized, and the hydrolysis product dried, before calcining in a heated kiln in an oxygen containing atmosphere to produce relatively pure Nb 2 0 5 .
  • the drying and calcining is both energy intensive and expensive.
  • Nb 2 o 5 by the previously described chlorination route utilizes toxic chlorine gas reacted exothermically at elevated temperatures and pressures. These conditions can produce severe corrosion problems. Special equipment is necessary for handling the highly pressurized, corrosive liquid chlorine and it must be safely vaporized, metered and fed into the reactor. Likewise, the most suitable material for large scale reactor construction is graphite. This is a brittle material which can fracture and fail abruptly after a short time in use in this environment. Further, the chlorine is normally used in excess to ensure complete reaction with the FeNb and the excess must be neutralized creating an expensive, undesirable by-product.
  • the hydrolysis step involves contacting the condensed chloride product with a neutralizing agent such as ammonia, and then filtering the resulting hydrous oxide slurry or cake, optionally drying and then air firing it to the oxide in a kiln.
  • a neutralizing agent such as ammonia
  • Such slurries and cakes are gelatinous and therefore hard to handle.
  • a process for the preparation of substantially pure metal oxide derived from ferrometal alloys and nickel metal alloys where the Group IV, V and VI metal selected is provided by first reacting the metal alloy with hydrogen under conditions selected to produce a friable ferrometal alloy or nickel metal alloy hydride product containing at least some hydrogen. The friable material is then crushed and sized to preselected sizes and reacted with a nitrogen- containing gas to produce nitrides, for example, nitrides of iron and niobium.
  • the nitride-containing product produced by the foregoing reactions are then leached with dilute acid leach solution to substantially remove the acid soluble iron or nickel content of the nitride-containing product.
  • the acid insoluble metal nitride recovered can then be dried and contacted with a suitable oxidizing agent under conditions selected to convert substantially all of the insoluble recovered metal nitride product into its respective metal oxide.
  • leaching with an aqueous acid leach containing fluoride ions may be employed to remove unwanted impurities such as phosphorous and silicon.
  • Figure 1 is a schematic block diagram of the process of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
  • the present process is embodied in the following steps when applied to the preparation of niobium oxide from ferroniobium alloy. 1) Contacting ferroniobium with hydrogen- containing gas substantially free of oxygen;
  • step 2) Grinding the product of step 1) to preselected particle sizes
  • step 3 Reacting the product of step 2) with nitrogen-containing gas substantially free of oxygen at elevated temperatures;
  • ferroniobium Metallurgical grade ferroniobium is used as the starting material. Typically, the ferroniobium will contain from between about 60 to about 80% by weight niobium, about 20 and 40 weight percent iron and minor amounts, i.e., less than about 10% total weight percent of silicon, aluminum, tantalum, phosphorus and titanium.
  • the ferroniobium is contacted in a suitable reaction vessel with an exclusive atmosphere of hydrogen gas (i.e., in the absence of oxygen or other reactive gases) preferably maintained at a positive pressure of up to about 15 psig.
  • an exclusive atmosphere of hydrogen gas i.e., in the absence of oxygen or other reactive gases
  • the ferroniobium in less than about one inch chunks is charged into a vacuum-tight, sealable reactor.
  • the reactor is then evacuated and backfilled with hydrogen to a positive pressure up to from about 3 psig to about 15 psig.
  • the reaction begins immediately at room temperature and is exothermic. Higher temperatures may be employed as well as higher pressures up to 10 to 15 psig, however, that is not necessary for a successful reaction and acceptable reaction rate for the uptake of the hydrogen by the ferroniobium.
  • the hydrogen level of the product is raised to above about 200 ppm this level of hydrogen in the ferroniobium provides a product which is friable and easily comminuted into preselected particle sizes suitable for the subsequent reactions.
  • the product can contain much higher levels of hydrogen, i.e., substantially above 2000 ppm, however, 1200 ppm is normally observed in the reaction product.
  • the product of the hydrogen-contacting or hydriding step containing between about 200 to 3000 ppm hydrogen and typically about 1200 ppm hydrogen is removed from the reaction vessel and comminuted by grinding or rod milling or other equivalent operation to prepare a ferroniobium hydride product preferably having a particle size of less than 20 mesh and most preferably less than 140 mesh.
  • the comminuted product of ferroniobium described hereinbefore, at preselected particle sizes is charged into a suitable reactor where it is contacted with a nitrogen-containing gas containing substantially no oxygen at elevated temperatures.
  • the reactor is made of a non-reactive and non- contaminating material such as a nickel-containing metal alloy.
  • the reactor is evacuated and then backfilled with nitrogen, in the absence of oxygen, and nitrogen continuously supplied at a positive pressure. Subatmospheric pressure can, however, be employed with a suitable reactor.
  • the temperature of the reactor is raised to a temperature of from about 500"C to about 800°C.
  • the feed rate is controlled to maintain the exothermic reaction at an elevated temperature of from about 1100 ⁇ C to about 1400°C for a sufficient period of time for the reaction to continue to run to completion.
  • the vessel is maintained with a positive pressure of nitrogen until the reaction has run to completion and the vessel has cooled. Typically, 6 to 48 hours may be required.
  • the weight gain of the charge from the reaction with nitrogen will typically be on the order to 8 to 12 percent by weight of the charge.
  • Example 1 A charge of 8.4 lb of ferroniobium hydride product prepared as described herein by contacting ferroniobium with hydrogen gas was placed in a lidded, cylindrical stainless steel vessel. The vessel was evacuated, purged with argon and then fed with nitrogen gas while the temperature of the vessel was raised by heating. The temperature was monitored. At a vessel temperature of about 538 ⁇ C, the uptake of nitrogen was significant. Nitrogen was continuously fed into the vessel. The flow was increased when necessary to maintain a positive pressure during the course of the reaction. As the uptake of nitrogen proceeded, the temperature of the reaction vessel rose over about one hour to about 1250°C due to the exothermic nature of the reaction.
  • the temperature stayed over 1200°C for one hour and then cooled slowly over about 2 hours to about 1150 * C. It remained at 1150°C for 19 hours under constant nitrogen flow and then allowed to cool to ambient temperature.
  • the weight gain was 9.1% by weight of the original charge.
  • the nitride product recovered from the nitride reaction was then contacted with an aqueous acid preferably dilute hydrochloric acid at moderate temperatures (i.e., 40°C to 60°C) to dissolve and leach away any iron nitrides formed.
  • the soluble iron nitride is substantially leached away from the niobium nitrides formed.
  • ferroniobium alloys are completely unaffected even by prolonged contact with strong hydrochloric acid. In the process of the present invention, there are no requirements for excessively strong acid, excessively elevated temperatures or prolonged leaching times when separating the iron nitrides from the niobium nitrides formed as described herein.
  • Example 2 A total of 2270 grams of the nitrided ferroniobium product, produced as described hereinbefore in Example 1, was contacted with 22.7 liters of 2 normal HCl and held at 46 ⁇ C. The temperature varied from between about 46 ⁇ C to 55 P C over 4 hours of contact time with agitation. The product was then filtered away from the leach solution and further washed with 2 N HCl and then 30 liters of distilled water. The product was dried at 130°C for 12 hours and 1788 g of dried product recovered.
  • the described leached and dried product is contacted with an oxidizing agent to produce niobium oxide.
  • HLF1 a hydride run designated HLF1
  • 548 lb of ferroniobium feed was placed inside a vessel, which was evacuated overnight to 190 microns pressure.
  • the vessel was then pressurized with hydrogen gas to 6 psig.
  • the charge absorbed hydrogen rapidly, pulling a partial vacuum in the system. It was stored under static pressure overnight, and by morning registered a vacuum of 12 inches of mercury.
  • the charge continued to consume hydrogen until afternoon, at which time the uptake began to slow markedly.
  • the vessel was hydriding, approximately 215 cubic feet of hydrogen gas was fed to the system, as measured by the rough gauge readings. This corresponded to a hydrogen content of about 2000 ppm.
  • the system was isolated and the time noted for its internal pressure to decrease by 30 mm, for example from 820 mm to 790 mm Hg. At 4_ hours after the maximum internal temperature, this time interval was 25 seconds and, at shutoff time, it had lengthened to 160 seconds.
  • the cooled charge weight 325.6 lb.
  • the reaction mass was substantially porous and could readily be reduced to fist- sized chunks.
  • 125 gallons of 11.6 N HCl was added to water (125 gallons) at 47"C in a 275 gallon fiber glass leach tank. Steam was sparged into the tank until the temperature of the solution was raised to 55"C. Hydrofluoric acid (48%, 50 lb) was added to the tank. Then, the less than 20 mesh nitrided ferroniobium from PP1 (220 lb) was gradually added over a period of about one hour, during which time the liquid temperature rose to 64°C. Stirring and air sparging were continued for 4 hours thereafter, during which time the temperature fell to 56°C. The slurring was filtered by vacuum filtration, washed with 22 gallons of 1 N HCl, then twice with 20 gallon portions of water. The damp solids recovered from the filter funnel weight 173 lbs and had a moisture content of 19%.
  • the product of PP1 and another run, PP2, of the same scale was converted to oxide in a single campaign in an indirect fired rotary kiln. Satisfactory conditions were found to be a feed rate of 5-10 lb/hr, 925°C, a rotation rate of 2-8 rpm and a residence time of about 30 minutes. Excessive feed rates were followed by emergence of a grey product signifying partial oxidation. Such material was recycled and emerged with the proper yellow- white color.
  • the overall blend of PP1 and PP2 had the following analysis: Fe, 5500 ppm, Si, 690 ppm; P, 69 ppm. The overall oxide yield was 503.4 lbs.
  • the above oxide was made part of a 1000 lb thermite shot. The reaction was observed to proceed smoothly and relative pure niobium metal was recovered.
  • the dried product or the wet filtered product may be charged directly into a kiln.
  • the kiln is fired in an atmosphere containing oxygen to a temperature of from about 300°C to about 1300 ⁇ C, the oxidation can be completed in a relatively short period of time depending on the size of the charge.
  • the temperature should be in the range of from about 300 ⁇ C to 1000 ⁇ C.
  • the foregoing oxidation product is suitable for the uses made normally of niobium oxide.
  • High purity niobium oxide which is suitable for the preparation of vacuum grade ferroniobium can be obtained with further leaching.
  • the cooled product can be leached with a solution of one percent ammonium bifluoride in 6 N HCl. This leached product is compared in Table 1 with the typical results of the standard leach before firing.
  • the niobium oxide product to be employed for use in the subsequent preparation of vacuum grade ferroniobium by aluminother ic reduction, as well as use as an intermediate for the preparation of other compounds of niobium and for the preparation of niobium metal itself. It is, therefore, preferred in the subsequent leaching step after firing, described herein, that the aqueous leach include the addition of some fluoride ion producing compound since it has been found that this best achieves the result of removing the unwanted silicon and phosphorus values.
  • hydrochloric acid is the preferred acid, although hydrofluoric acid and sulfuric acid could be used effectively for different results, if desired.
  • concentration of the acid should be in the range of from about 1 N to about 12 N.
  • About 2 N HCl is preferred.
  • a fluoride source could include hydrofluoric acid or alkali metal fluorides.
  • the temperature maintained during either leach should be between 25"C to about 100°C, preferably about
  • the time period for the leach solution to be in contact with the nitrided product can be from about 2 hours to about 12 hours, preferably about 4 hours. It is also preferred that stirring or other agitation be performed during contact with the leach solution.
  • the conditions useful during the calcining, oxidation step should include a length of time suitable for substantially complete oxidation at a temperature of from about 300"C to 1300°C, preferably between about 300"C to about 1000°C.
  • the atmosphere of the kiln can be any suitable oxygen-containing gas, including air.
  • niobium oxide Nb 2 0 5
  • a ferroniobium alloy the general teachings contained herein with variations in temperatures, times, reactants and leach compositions suitable for the materials employed, can be utilized for the preparation of tantalum oxide (Ta 2 0 5 ) from ferrotantalum, vanadium oxide (V 2 0 3 ; V 2 0 4 ; V 2 0 5 ) from ferrovanadium, silicon oxide (Si0 2 ) from ferrosilicon and other oxides from ferroalloys where the alloying element is selected from Groups IV, V and VI, as well as the corresponding nickel alloys.

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Inorganic Compounds Of Heavy Metals (AREA)
  • Silicon Compounds (AREA)
  • Oxygen, Ozone, And Oxides In General (AREA)

Abstract

L'invention concerne un procédé de préparation et de récupération d'oxydes métalliques à partir de leurs alliages ferrométalliques et métalliques de nickel. Des exemples d'étapes du procédé comprennent la réaction de l'alliage avec de l'hydrogène suivi de la subdivision du produit hydruré et la nitruration du matériau subdivisé pour former des nitrures métalliques mélangés. Les nitrures métalliques mélangés sont ensuite mis en contact avec une fraction de lixiviation acide aqueuse pour dissoudre tout nitrure de fer ou de nickel présent. On fait ensuite réagir les nitrures métalliques insolubles pour former le produit d'oxyde métallique.
PCT/US1992/005325 1991-06-27 1992-06-26 Procede de production d'oxyde de niobium Ceased WO1993000292A1 (fr)

Priority Applications (3)

Application Number Priority Date Filing Date Title
JP50163493A JP3406597B2 (ja) 1991-06-27 1992-06-26 酸化ニオビウムの製造方法
BR9206195A BR9206195A (pt) 1991-06-27 1992-06-26 Processo para a produção de óxido de nióbio
EP92915641A EP0591459A4 (fr) 1991-06-27 1992-06-26 Procede de production d'oxyde de niobium.

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US72188691A 1991-06-27 1991-06-27
US721,886 1991-06-27

Publications (1)

Publication Number Publication Date
WO1993000292A1 true WO1993000292A1 (fr) 1993-01-07

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ID=24899719

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/US1992/005325 Ceased WO1993000292A1 (fr) 1991-06-27 1992-06-26 Procede de production d'oxyde de niobium

Country Status (5)

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EP (1) EP0591459A4 (fr)
JP (1) JP3406597B2 (fr)
AU (1) AU2316792A (fr)
BR (1) BR9206195A (fr)
WO (1) WO1993000292A1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
RU2228291C1 (ru) * 2002-10-21 2004-05-10 Томский научный центр СО РАН Способ получения нитрида ниобия

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4318987A (en) * 1979-11-16 1982-03-09 Murillo Araujo Francisco J β-Carotene producing strains of the fungus phycomyces blakesleenus
US4425318A (en) * 1981-11-12 1984-01-10 Allied Corporation Hydriding body-centered cubic phase alloys at room temperature
US4440737A (en) * 1982-09-20 1984-04-03 Allied Corporation Room temperature reaction of vanadium-based alloys with hydrogen
US4741894A (en) * 1986-06-03 1988-05-03 Morton Thiokol, Inc. Method of producing halide-free metal and hydroxides
US4812301A (en) * 1986-04-24 1989-03-14 The United States Of America As Represented By The Secretary Of The Interior Production of titanium nitride, carbide, and carbonitride powders

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR1335556A (fr) * 1962-07-04 1963-08-23 Commissariat Energie Atomique Perfectionnements apportés aux procédés et appareils pour la préparation de nitrures métalliques susceptibles d'être frittés ultérieurement, notamment ceux de l'uanium
JPH0339426A (ja) * 1989-07-05 1991-02-20 Nkk Corp 金属ニオブの製造方法
JPH03249144A (ja) * 1990-02-27 1991-11-07 Nkk Corp ハロゲン化ニオブ、酸化ニオブ、窒化ニオブ、炭化ニオブ及び金属ニオブの製造方法

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4318987A (en) * 1979-11-16 1982-03-09 Murillo Araujo Francisco J β-Carotene producing strains of the fungus phycomyces blakesleenus
US4425318A (en) * 1981-11-12 1984-01-10 Allied Corporation Hydriding body-centered cubic phase alloys at room temperature
US4440737A (en) * 1982-09-20 1984-04-03 Allied Corporation Room temperature reaction of vanadium-based alloys with hydrogen
US4812301A (en) * 1986-04-24 1989-03-14 The United States Of America As Represented By The Secretary Of The Interior Production of titanium nitride, carbide, and carbonitride powders
US4741894A (en) * 1986-06-03 1988-05-03 Morton Thiokol, Inc. Method of producing halide-free metal and hydroxides

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See also references of EP0591459A4 *

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
RU2228291C1 (ru) * 2002-10-21 2004-05-10 Томский научный центр СО РАН Способ получения нитрида ниобия

Also Published As

Publication number Publication date
EP0591459A4 (fr) 1995-04-12
EP0591459A1 (fr) 1994-04-13
AU2316792A (en) 1993-01-25
JP3406597B2 (ja) 2003-05-12
JPH07500078A (ja) 1995-01-05
BR9206195A (pt) 1994-12-13

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