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
  • C22B34/00—Obtaining refractory metals
  • C22B34/10—Obtaining titanium, zirconium or hafnium
  • C22B34/12—Obtaining titanium or titanium compounds from ores or scrap by metallurgical processing; preparation of titanium compounds from other titanium compounds see C01G23/00 - C01G23/08
  • C22B34/1263—Obtaining titanium or titanium compounds from ores or scrap by metallurgical processing; preparation of titanium compounds from other titanium compounds see C01G23/00 - C01G23/08 obtaining metallic titanium from titanium compounds, e.g. by reduction
  • C22B34/1277—Obtaining titanium or titanium compounds from ores or scrap by metallurgical processing; preparation of titanium compounds from other titanium compounds see C01G23/00 - C01G23/08 obtaining metallic titanium from titanium compounds, e.g. by reduction using other metals, e.g. Al, Si, Mn
• • 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
  • C22B34/12—Obtaining titanium or titanium compounds from ores or scrap by metallurgical processing; preparation of titanium compounds from other titanium compounds see C01G23/00 - C01G23/08
  • C22B34/1218—Obtaining titanium or titanium compounds from ores or scrap by metallurgical processing; preparation of titanium compounds from other titanium compounds see C01G23/00 - C01G23/08 obtaining titanium or titanium compounds from ores or scrap by dry processes
  • C22B34/1222—Obtaining titanium or titanium compounds from ores or scrap by metallurgical processing; preparation of titanium compounds from other titanium compounds see C01G23/00 - C01G23/08 obtaining titanium or titanium compounds from ores or scrap by dry processes using a halogen containing agent

Definitions

• the instant invention relates to a process for the preparation of titanium metal from an ore comprising titanium oxides which process comprises the steps of fluorinating the ore to convert the titanium oxides to titanium fluorides and then reducing the titanium fluorides to titanium metal. Such reduction may be carried out by contacting the titanium fluorides as a molten salt mixture with a molten alloy of zinc and aluminum at conditions whereby titanium is converted into a titanium-zinc alloy and the aluminum is converted into a fluoride of aluminum.
• the ore may be an ilmenite ore and the fluorination may be carried out by contacting said ilmenite ore with a fluosilicate salt as sodium fluosilicate.
• Titanium metal has been essential to the aerospace industry since the early fifties because it combines a high strength to weight ratio with the ability to perform at much higher temperatures than aluminum or magnesium. It also has growing usage in the chemical processing industries because of its excellent resistance to chloride corrosion. Recently the world demand for titanium has outstripped the limited production facilities causing it to be put on allocation in the United States. Most of the United States primary titanium is imported from
• titanium is made by the "Kroll Process” which involves magnesium reduction of titanium tetrachloride, which is in turn made from rutile (TiO 2 ). Titanium metal is also made by Na reduction and electrowinning.
• the product of the "Kroll Process” is a metallic sponge which is later consolidated by a high temperature arc melting process. The most important consideration for any process making titanium is to prevent contamination with either metallic or non-metallic impurities, because even small amounts of oxygen or nitrogen can make the product brittle and unworkable, although carefully controlled amounts of oxygen, nitrogen, and carbon may be added to strengthen titanium alloys.
• U.S. Patent 2,550,447 teaches a process for preparing titanium metal from titanium oxide ores such as rutile, anatase and ilmenite which comprises reduction of the ore by aluminum followed by iodination of the product obtained, from such reduction. The iodinated product is then reacted with potassium iodide. Finally, titanium tetraiodide is removed from the potassium iodide and converted to titanium metal by either heat decomposition or reduction. This process is a very expensive method for making titanium metal.
• U.S. Patent 2,781,261 discloses a process for converting titanium dioxide to titanium by fluorinating titanium oxide, neutralizing the fluotitanic acid obtained, and reducing the neutralized fluotitanic acid with aluminum.
• U.S. Patent 2,837,426 teaches a process for converting ilmenite to an alkali metal fluotitanate by reacting ilmenite with sulfuric acid to form the titanium sulfate, removing a portion of the iron included with said titanium sulfate by reduction and precipitation of a reduced iron compound, and finally converting the titanic sulfate filtrate to an insoluble fluotitanate by means of an ammonium and/or alkali metal fluoride solution.
• U.S. Patent 3,857,264 teaches a process for preparing an alkali metal chlorotitanate by digesting ilmenite in a mixture of sulfuric and hydrochloric acid.
• iron present is precipitated out as ferrous sulfate and then further recovered by the addition of HC1 to precipitate a ferrous chloride.
• potassium chloride is added to salt out potassium chlorotitanate which may be reduced with a Group I metal to titanium.
• U.S. Patent 3,012,878 teaches a process for reducing titanium halides to titanium metal by use of sodium metal.
• U.S. Patent 3,825,415 teaches a process, similar to the process disclosed in U.S. Patent No. 3,012,878, except that the process is carried out in the vapor phase.
• U.S. Patent 4,127,409 and 4,073,056 are related to the recovery of zirconium and hafnium, respectively, by the reduction of the corresponding potassium chlorozirconates or hafniates by means of an alloy of aluminum and zinc.
• the instant invention relates to a process for the preparation of titanium metal from ores containing oxides of titanium by fluorinating said ore to convert the oxides of titanium to fluorides of titanium and then reducing said fluorides of titanium to titanium metal
• the ore is ilmenite which is a ferric titanate, i.e. ilmenite contains both iron and titanium in the oxide form.
• the fluorination is preferably carried out by contacting the ore with a fluosilicate salt such as an alkali metal fluosilicate, for example, K 2 SiF 6 , Na 2 SiF 6 , etc. at a temperature from about 600°C to 1000°C preferably 750°C to 950°C:
• the iron and titanium are converted to fluorides which may be leached from the fluorinated ore by an aqueous solution.
• the aqueous solution may contain a strong acid (a mineral acid) to enhance the recovery of soluble titanium.
• the leaching solution may be treated to oxidize the iron dissolved therein to the ferric state and precipitate out the hydrolysis product thereof as ferric hydroxide.
• the ferric hydroxide may be separated from the solution by filtration and filtrate utilized to recover soluble titanium. If an aqueous acid leaching solution is used, the iron may remain in the leaching solution after the fluorides of titanium are removed as shown below.
• the corresponding fluotitanate is the soluble titanium moiety.
• potassium fluosilicate utilized as the fluorinating agent
• a potassium fluotitanate salt will be dissolved in the leaching solution.
• the leaching solution will also contain, various other soluble fluorides such as for example potassium fluoride.
• the solution may be evaporated and cooled to precipitate out the fluotitanate, for example, the potassium fluotitanate.
• the fluotitanate precipitate may then be filtered and dried at a temperature of from about 110°C to 150°C and subsequently reduced to titanium metal.
• the most preferred method of reduction comprises contacting the fluotitanate as a molten salt with a molten zinc- aluminum alloy at a temperature of from 650°C to 1000°C in an inert atmosphere.
• the titanium present in the fluotitanate salt will be converted into a titanium-zinc alloy by contacting with the aluminum- zinc alloy under such conditions and the aluminum will be converted into corresponding aluminum halide, for example, aluminum fluoride.
• the aluminum halide will dissolve in the molten salt phase and may form a salt similar to cryolite, i.e. a pseudocryolite such as mixtures of Na 3 AlF 6 , Na 5 Al 3 F 4 and AIF 3 .
• the molten zinc-titanium alloy is separated from the molten salt mixture and passed through a distillation zone wherein the zinc is sublimed from the titanium under an inert atmosphere.
• the titanium may be recovered in the form of a sponge.
• the fluotitanate may alternatively be converted to titanium oxide by contacting the recrystalliz ⁇ d salt with an aqueous basic solution to hydrolyze the titanium to the titanium tetrahydroxide.
• the titanium tetrahydroxide may then be precipitated from the solution in the form of titanium oxide including two waters of crystallization.
• the hydrolysis of said fluotitanate salt may be effected in a solution having a pH of at least about 5.0, and preferably from at least about
• Ilmenite which is an ore comprising titanium and iron oxides in admixture, is available from various locations such as southern Georgia, northern Florida, and California. The ore will typically comprise from 25 to 50% by weight, titanium and from 8 to 36% by weight, iron.
• a suitable ilmenite ore may be ground to a finely divided physical state to make it more susceptible to fluorination. For example, the ore may be ground to a particle size of from 30 to 400 mesh and preferably from 100 to 400 mesh.
• the ore may be fluorinated by fluorination agents known in the art such as F 2 , HF, SiF 4 , NH 4 F,
• the fluorinating agent will be a fluosilicate salt. This material is especially suitable because the more active fluorinating agents tend to attack the various equipment suitable for carrying out the fluorinating process.
• the fluosilicate salt is a solid at the suitable fluorinating temperatures and therefore such fluorination may occur as a solid state reaction between the ore and the fluosilicate.
• Typical fluosilicates include potassium and sodium salts.
• Sodium fluosilicates for example, may be blended with the ore at a weight ratio of from
• titanium containing ores such as rutile and anatase, i.e. titanium oxides, may also be utilized in this process, however, ilmenite is preferred and therefore utilized herein for description of the invention.
• the fluorination will be carried out at conditions which are sufficient to convert both the titanium and the iron in the ore into the respective fluoride derivatives; that is, fluorides of titanium and iron, respectively.
• fluoride derivatives that is, fluorides of titanium and iron, respectively.
• sodium fluosilicate utilized as a fluorinating agent
• the mixture of the fluosilicate and the ore will be heated to a temperature of at least 600°C preferably from 750 to 950°C for a time sufficient to change the iron and titanium from oxides to the fluorides.
• the ilmenite ores having at least from 14 to 36% iron are very easily fluorinated by the above fluosilicates and may not require additional ferric oxide.
• the term “substantially iron free” shall mean less than about 14%, by weight, iron.
• the fluorination reaction is benefite by being carried out under an atmosphere of a gaseous fluorinating agent such as silicon tetrafluoride.
• a gaseous fluorinating agent such as silicon tetrafluoride.
• the silicon tetrafluoride may be the active fluorinating agent obtained from the fluosilicate and thus acts to initiate and enhance the fluorination reaction of the ilmenite ore.
• the fluorination reaction may be carried out under a partial pressure of from .1 to 5 psig, preferably at least about 1 to about 70 psig, e.g. 30 psig of silicon tetrafluoride.
• the upper pressure limit will be dictated by the economics of carrying out high pressure reactions.
• the fluorinated ore may be cooled and then ground prior to the recovery of the soluble titanium by leaching the ground mixture of the fluorinated ore and the residue of the fluorinating agent by contacting under agitation with the leaching solution.
• the iron which is present in the ore in the form of ferrous fluoride may be removed from the fluorinated ore by oxidation and hydrolysis of the oxidation product.
• the ground fluorinated ore may be heated in the presence of air to a temperature of from 50 to 95°C in order to oxidize the ferrous fluoride to the ferric state.
• oxidation may take place during leaching as noted or can be carried out prior to leaching.
• oxidation and leaching are carried out simultaneously so that the leaching solution assists by hydrolyzing the oxidized iron to an insoluble ferric hydroxide.
• Leaching of the fluorinated ore may be carried out in an aqueous solution which may beneficially contain a strong acid such as hydrochloric or sulfuric acid.
• the pH of said leaching solution is preferably at least about 0.1, preferably from about 2.0 to about 5.0.
• an aqueous acid leaching solution is utilized, the above described removal of iron may be eliminated and the iron can remain in solution after the separation of the fluorides of titanium as described below.
• the leaching may take place at a temperature of at least 25°C, preferably from 60°C to 95°C.
• the leaching is carried out for a time sufficient to recover as much of the soluble fluorides of titanium as economically possible.
• leaching is carried out for about 1 to 3 hours with the ratio of leaching solution to the fluorinated ore varying from 15:1 to 5:1, e.g., 10:1 on a volume to weight basis. It has been found that the recovery of the fluorides of titanium is enhanced by leaching with an aqueous hydrogen fluoride solution.
• the solutions of from 1 to 10%, by weight, HF extract the soluble fluorides of titanium, at a faster rate than the other leaching solutions including hydrochloric and sulfuric acid solutions.
• the hydrogen fluoride solutions may extract up to 100% of the titanium originally present in the ore while corresponding solutions of HCl and sulfuric acid may obtain only 70% of such titanium over the same time period.
• Higher concentrations of HF are operable, but are more corrosive and require difficult handling procedures.
• the leaching solution may be filtered to remove oxidized iron as the ferric hydroxide.
• the filtrate will comprise soluble fluorides of titanium, for example in the preferred embodiment K 2 TiF 6 or
• various other soluble fluorides may be present in the filtrate such as the fluoride salt of the corresponding alkaline fluosilicate, such as sodium fluoride or potassium fluoride. It has been surprisingly found that it is easy to separate the fluorides of titanium from certain other soluble fluorides since solubility characteristics are such that the fluorides of titanium precipitate as the temperature of the solution is lowered while other fluorides such as sodium fluoride are more soluble in lower temperature solutions. Thus, the solution may be evaporated to concentrate soluble fluorides and then the temperature decreased until the fluorides of titanium crystallize. The crystals of the fluorides of titanium may be separated and dried at a temperature of from 50°C to 150°C to remove excess water.
• the fluorides of titanium may be crystallized from an acidic iron containing solution substantially without contamination thereof.
• the dried crystals of the fluorides of titanium may be reduced in a reducing zone wherein they are preferably contacted, in a molten state, with a molten zinc-aluminum alloy,
• the alloy may comprise from 1:99 to 20:80 parts of Al to Zn.
• the molten salt and the alloy are mutually immiscible, and therefore agitation must be provided in such reducing zone to assure intimate contact.
• the reduction will take place at a temperature of at least 650°C to 1000°C preferably from 700°C to 900°C.
• the time of contacting of said molten alloy and molten salt will be varied to assure that the titanium present in the salt is converted into a titanium-zinc alloy.
• the aluminum present in the aluminum-zinc alloy during the course of the reduction is converted into the corresponding fluoride and may be isolated, when sodium fluosilicate is used as the fluorinating agent, as the pseudo cryolite described above.
• the reduced mixture separates with the molten salt rising to the top wherein it may be decanted from such mixture.
• the molten titanium zinc alloy may be separated from the bottom of the vessel and passed to the reducing zone. Reduction must take place under inert conditions because of titanium metal's propensity to pick up oxygen and nitrogen.
• an argon atmosphere is present during the reduction step.
• a suitable vessel for carrying out the aforementioned reduction, as well as any of the various high temperature operations described herein may be graphite.
• titanium-zinc alloy boils at approximately 915°C. At that temperature, only 15% titanium can be dissolved into the zinc before solids begin forming. However, if the reactor is placed under elevated pressure (about 1.5 atmospheres), then the molten zinc-alloy boils at 950°C and approximately 25% titanium can be dissolved in zinc before the onset of solids formation.
• the reactor may be operated at 2 atmospheres which will allow a temperature of slightly over 1000°C before the mixture boils and 25% by weight of titanium can be dissolved in the solution without solids formation. This results in a significant reduction in the amount of zinc to be distilled from the titanium in the subsequent step. It should be noted that if the pressure is increased still more in the hope of further increasing the titanium solubility two problems occur.
• the first problem is the solubility does not increase rapidly with temperatures beyond 950°C and secondly, there is a substantial increase in contamination by carbon from the reactor wall.
• the degree of carbon contamination is severe above 1100°C.
• the argon, atmosphere or other inert atmosphere may be also utilized during the subsequent separation of the titanium from the titanium-zinc alloy.
• the molten titanium-zinc alloy will be passed to a distillation zone wherein the zinc may be distilled off at a temperature of from about 800°C to 1000°C to leave behind a titanium sponge.
• the zinc may be distilled from the zinc-titanium alloy under a vacuum and at somewhat lower temperatures.
• the titanium sponge may be sintered to reduce its surface area. After sintering and cooling the sponge is passified by exposure to dilute O 2 to give a thin (monomolecular) protective coating of titanium oxide thereon before the sponge is exposed to a non-inert atmosphere.
• the zinc will be recovered and recycled for use in subsequent reducing steps.
• ilmenite having a composition of 31.6% titanium and 35% iron is ground to a particle size of 100 mesh in grinding zone 10.
• the ground ilmenite is then blended with 70,735 lbs. of sodium fluosilicate in blending zone 11.
• the blended mixture is passed into calcining zone 12 wherein it is heated to a temperature of from 750 to 850°C, in the presence of one atmosphere of SiF 4 , for a time of about 6 hours whereby the titanium oxides present in the ilmenite are converted to fluorides of titanium and the silicon fluorides present in the fluosilicate are converted to silicon dioxide.
• the titanium is converted to a product having the general formula Na 2 TiF 6 in accordance with the following reaction.
• This reaction also shows that the iron present in the ilmenite is converted to ferrous fluoride.
• the fluorinated mixture is then ground in grinding zone 13 and leached with an aqueous hydrofluoric acid solution containing 2.5% by weight hydrofluoric acid at a ratio of 10 lbs. of solution/lb. reactant.
• the leaching is carried out under oxidizing conditions, for example, air may be contacted with the mixture during leaching to assist in oxidizing the ferrous ions present in the leaching solution to ferric ions which precipitate from the leaching solution at a pH of about 7.
• the solution may be adjusted to that pH if necessary by addition of a suitable base, e.g. NaOH etc.
• a suitable base e.g. NaOH etc.
• the silicon dioxide reaction product of the fluorination will also be precipitated. The separation of the iron and silicon dioxide are evident from the following equations which describe the leaching step.
• the ferric oxide and insoluble SiO 2 are removed from said grinding and leaching zone and may be dried and recovered as a mixture of silicon dioxide and ferric oxide in zone 14.
• the solution after filtration of the ferric oxide is passed to a crystallizing and drying zone 15 wherein about 740,000 lbs. of water is removed by heat and/or vacuum and the dewatered solution is cooled to a temperature of about 4°C to crystallize sodium fluotitanate.
• the crystallized fluotitanate is filtered and may then be passed into a reducing zone 16 wherein 46,906 lbs. of fluotitanate is contacted under an inert atmosphere at a temperature of about 805°C with 45,688 lbs.
• the fluotitanate is added, with agitation to the molten alloy over a 2 hour time period, whereby the molten salt and molten alloy solution are intimately contacted, i.e. by forming a dispersion of the molten salt and the molten alloy.
• the reaction is instantaneous, therefore, after such 2 hour period of addition the titanium has been converted to a zinc titanium alloy and the aluminum has been converted to an aluminum fluoride.
• the titanium-zinc alloy is removed from the bottom of reducing zone 16 and passed into distillation zone 17 wherein zinc is distilled off at a temperature of at least 800°C and at a vacuum of about 10-5 torr.
• the distilled zinc is recycled back to reduction zone 16 for subsequent reuse.
• Titanium metal is recovered from distillation zone 17 as a sponge 18.
• the molten salt mixture which is a mixture of sodium and aluminum fluoride, i.e. a pseudo cryolite, is recovered from the top of reduction zone 16 and sent to recovery zone (19).
• the recrystallized sodium fluotitanate from zone 15 may be passed into a precipitation-filtration zone 20 wherein the solution is contacted with an aqueous sodium hydroxide solution to convert the soluble titanium to the titanium oxide form.
• the titanium oxide precipitates from the solution and is recovered in zone 21.
• Approximately 334 lbs. of NaOH per pound of soluble titanium is required to precipitate the titanium dioxide.
• the filtrate from zone 20 containing soluble fluorides is contacted with calcium oxide in precipitation-filtration zone 22 to precipitate calcium fluoride which may be recovered at zone 23.
• the sodium fluoride-containing solution from zone 22 may be passed into zone 24 wherein it may be contacted with a 23% solution of H 2 SiF 6 to precipitate sodium fluosilicate which after drying in zone 25, may be recycled to zone 11 for further fluorination use.
• Ilmenite ore concentrates of about 100 mesh particle size are blended with sodium fluosilicate salt (and in certain examples powdered iron oxide and/or carbon) to form a homogenous mixture.
• the proportions of the ingredients consist of 102 parts of ore,
• EXAMPLE 6 One hundred parts of ilmenite ore containing 26.4 wt. % titanium and 36.4 wt. % iron were admixed with 244.5 parts of sodium fluosilicate salt and 12 parts of carbon powder and formed into briquets. The briquets were calcined in a furnace at 750°C for six hours. After cooling the briquets were cooled, pulverized, and leached with a ten fold volume of 5 volume percent mineral acid at 96°C for two hours.
• the crucible and contents are placed in an appropriate furnace and the furnace sealed.
• a purge of argon gas is used to remove air from furnace and provide an inert gas at atmosphere.
• the mixture is heated to about 500°C then a graphite stirrer is inserted into the molten mixture. Heating is continued along with stirring of the mixture until the temperature reaches about 620°C. The temperature is maintained at 620°C for about one hour to ensure complete reaction of the sodium fluotitanate and aluminum metal.
• the furnace power is turned off and allowed to cool to room temperature and the fused reaction mass removed.
• the salt portion at the top and the bottom melt portion containing elemental titanium are separated.
• the titanium metal containing alloy is then placed in a zinc distillation unit and the zinc distilled off at 910°C, in the presence of Argon, to leave a residue of titanium metal.
• Table 3 shows the conversion of titanium from the salt, Na 2 TiF 6 , to the zinc-titanium metal.
• a 78 lb. charge of zinc, 16.5 lbs. aluminum, and 100 lbs. of sodium fluotitanate are placed in a graphite reactor maintained under 2 atmospheres of argon pressure. The reactor is then heated to 960°C and all ingredients are allowed to melt. A graphite agitator is then lowered into the melt rotated sufficiently rapidly to disperse the salt phase into the molten alloy phase for 30 minutes. After stirring the metal, the agitator is raised and salt and alloy are poured separately into the cast iron molds still under 2 atmospheres argon pressure. The yield is a metal casting of 78 lbs. of zinc, 21 lbs. titanium and 0.005 lb. aluminum. The salt phase contains 2 lbs. titanium, 16.5 lbs. aluminum, 22 lbs. sodium and 55 lbs. fluorine. The salt product from the reaction can be further processed with additional aluminum zinc alloy to remove the residual titanium and yield a salt suitable as an ingredient in aluminum electro- winning cells.
• the alloy is processed by either vacuum distillation or distilled with a carrier gas to remove zinc and to sinter the titanium into a titanium sponge product.
• the starting materials must be correspondingly free of impurities, particularly phosphorus, iron and silicon.
• impurities particularly phosphorus, iron and silicon.
• the most difficult one to control when separating the preferred sodium fluotitanate is the silicon.
• SiO 2 which can redissolve in acid solution containing fluoride ion as follows:
• ilmenite ore approximately 100 mesh particle size containing 26.4 percent titanium and 36 percent iron were mixed with 244.5 parts of sodium fluosilicate salts and formed into compacts of briquets or pellets.
• the briquets were heated in a closed, evacuated furnace to a temperature of 750°C. Silicon tetrafluoride gas was then admitted to the furnace until a pressure of 90 min. of Hg (approximately 30 psig) was attained.
• the briquets were maintained at 750°C and under 30 psig SiF, pressure for six hours. After cooling and removal of the residual silicon tetra- fluoride gas the briquets were crushed and ground to pass a 60 mesh sieve.
• the ground material was leached three successive times with 10 fold weights of water at 95°C for two hour periods each.
• the amount of titanium extracted by the water leaches represented 61.2 percent of the titanium present in the ore.
• the increase in silicon tetrafluoride gas pressure was responsible for a nine percent increase in titanium recovery.

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