US 2823991 A
Description (OCR text may contain errors)
PROCESS FOR THE MANUFACTURE OF TIT METAL Jonas Kamlet, New York, N. Y., assignor to National Distillers and Chemical Corporation, New York, N. Y., a corporation of Virginia No Drawing. Application June 23, 1954 Serial No. 438,873
12 Claims. (Cl. 75-844) This invention relates to a process for the manufacture of titanium metal. More particularly, it relates to a process for the manufacture of titanium metal by the reaction of certain readily preparable inorganic titanium compounds with metallic sodium. Its objective is to provide a relatively simple process for the manufacture of metallic titanium from cheap and readily available raw materials and reagents.
Numerous processes have been proposed for the manufacture of titanium metal. The most practical among these is the so-called Kroll process involving the reaction of titanium tetrachloride with magnesium metal. Other processes which have attracted attention involve the reaction of titanium tetrachloride with sodium metal or sodium amalgam, the reaction of titanium dioxide with calcium metal or with calcium hydride, the thermal dissociation of titanium tetraiodide or tetrabromide, and the electrolysis of titanium compounds in fused salt baths under specified conditions.
The reduction of alkali metal fluotitanates with sodium metal has heretofore been proposed as a method for the preparation of titanium metal. Thus, in the past, a preformed mixture of potassium fluotitanate with sodium metal has been fused. In this manner, there was obtained an exceedingly impure product which was amorphous in character, colloidally dispersed, and very diflicult to recover. On drying, this product proved to be pyrophoric. In a modification of this process, large quantities of K TiF and Na TiF were carefully purified, and premixed with a limited amount of sodium metal. This mixture was tightly packed in an iron tube which was then heated to the fusion temperature. There was obtained an impure, amorphous titanium product which was subsequently used as the starting material for conversion to pure titanium metal by the thermal dissociation of titanium tetraiodide as described above. Thus, it has heretofore been impossible to prepare directly a commercially satisfactory grade of titanium metal by the reduction of an alkali metal fluotitanate With sodium metal. Because of the basically unsatisfactory product obtained by the above described method, this process has never attained any importance as a commercial method for the production of titanium metal.
One of the purposes of this invention is to provide a process whereby titanium metal, in a high degree of purity, and in a physical form suitable for easy recovery and for further processing, is manufactured by the reduction of alkali metal fluotitanates with sodium metal. The preparation of titanium tetrachloride includes the steps of a high temperature chlorination of a titaniferous concentrate followed by a distillation and purification, with the attendant problems including equipment corrosion. However, the preparation of the alkali metal fiuotitanates can be effected at comparatively loW cost, using comparatively simple equipment and starting directly with the inexpensive ilmenite or titaniferous iron ores. The alkali metal fluotitanate may be regenerated from the salts obtained as a slag or by-product of the process.
2,823,991 Patented Feb. 18', 1%58 The reducing agent, sodium metal, is cheap and readily available industrially in large tonnages. The titanium metal obtained as the end product of this process is in the form of large pellets or buttons. The titanium is thus readily separated and recovered from the reaction mixture by filtration, leaching with water, physical grinding or maceration or by any of the well known processes of the prior art. This end-product titanium is a highly pure product, meeting and surpassing present specifications for pure titanium metal. It can be further processed or fabricated as, for instance, by forging, grinding, machining, welding, brazing, bending, forming, riveting, annealing, etc.
Thus, it has been found that a pure titanium metal, in globular or massive physical form (i. e. rather than in colloidal dispersion) may be obtained by adding an anhydrous alkali metal fluotitanate chosen from the group consisting of sodium fluotitanate and potassium fluotitanate to sodium metal maintained at a temperature between 500 C. and 1300 C., under an atmosphere which is inert to titanium under the reaction conditions. The sodium metal is used in an amount at least equal to the amount theoretically required by the equations:
Four equivalents of sodium per mole of alkali metal fluotitanate, and preferably a 10% to 20% excess, i. e. 4.4 to 4.8 equivalents of sodium per mole of alkali metal fluotitanate are required. The reaction must be effected in an atmosphere which is inert to titanium under the reaction conditions in the absence of substances, such as oxygen, nitrogen, carbon dioxide, etc. While N and CO are usually considered as inert gases, they are not inert toward titanium metal at the temperatures at which this reaction is effected. Under these conditions, titanium will readily form oxides, nitrides and carbides with these gases at 500 C. to 1300 C., and these contaminants must be scrupulously avoided to obtain a titanium metal of satisfactory purity. The inert gases suitable for use in the process of this invention are the rare gaseshelium, neon, argon and krypton and mixtures of these gases. For practical purposes, helium and argon are preferred. It is also possible to evacuate all the gases from the freeboard area of the reactor and effect the reaction in an atmosphere of sodium metal vapor. The reaction of this invention can be effected at atmospheric, sub-atmospheric or super-atmospheric pressures.
By the procedure of adding the anhydrous alkali metal fluotitanate to the molten sodium metal, it is assured that at all times an excess of the reducing agent is available for the immediate reduction of the alkali metal fluotitanate. The coalescing or the agglomeration of the titanium metal particles into a globular or massive form is effected during the reaction. The use of a slight stoichiometric excess of sodium metal insures that no unreduced alkali metal fluotitanate remains behind in the reaction mixture at the conclusion of the reaction.
The sodium fluotitanate or the potassium fluotitanate may be added to the molten sodium as anhydrous solids, or as anhydrous molten salts. Na TiF melts at 700 C., and K TiF melts at 780 C. .Since these compounds are quite hygroscopic, it is highly important that they be scrupulously freed of all traces of moisture prior to their addition to the molten salt bath. Potassium fluotitanate forms a monohydrate when crystallized from aqueous solution, but loses its Water of crystallization at 35 C. It is nevertheless highly desirable to effect a scrupulous dehydration of the alkali metal fluotitanate prior to its addition to the molten sodium metal in the reactor. One preferred method for efiecting this dehydration involves melting the salt, and maintaining the molten salt at 800 -900 0, under vacuum, until it is freed of the last traces of moisture. Any other methods known to the art may be used to remove moisture. The anhydrous, molten salt is then added in a slow stream to the molten sodium in the reactor, the entire reactiommixture being maintained under an inert atmosphere such as helium, neon, argon, krypton, or sodium vapor.
The process of this invention can various types of reactors and it it to any particular type of apparatus or equipment. Molybdenum-lined direct-fired steel crucibles have been found to be highly useful and are resistant to attack by the reagents employed. The process may be carried out on a batchwise basis or as a semi-continuous process or as a continuous process.
The reactor is charged with the total sodium required per batch, that is, at least 4.0 and preferably 4.4 to 4.8 equivalents per mole of alkali metal fluotitanate. The sodium can be distilled to free it of traces of impurities. The sodium is charged to the reactor under an atmosphere of inert gas and heated to within the reaction temperature range i. e. 500 C. to 1300 C., and preferably 700 C. to 900 C. It is also entirely feasible to add the sodium metal to the reactor in a pre-heated form. The reactor is equipped with suitable means for agitation. The alkali metal fluotitanate, scrupulously dried, is then added in small porcns or as a slow stream to the well-agitated mass of sodium metal. Reduction takes place immediately upon the mixing of the reagents, and the temperature of the reaction mixture may rise to a terminal temperature of ll-l300 C.
At the conclusion of the reaction, the molten reaction mixture is rapidly drained from the reactor, and the end-proclucts of the reaction, i. e. titanium metal, excess sodium metal, Na? or a mixture of NaF and KP are separated by any one of a series of methods, such as, for example: a
(l) The molten reaction mixture is filtered, using for instance, a filter made of platinum mesh or titanium metal mesh. Since the globules or pellets of titanium metal, M. P., 1800 C., are dispersed as solids in the molten slag of fluoride salts and molten sodium, these can be separated by filtering, cooling and Washing with Water to remove traces of adhering salts. A final washing with 10% H 80 solution containing 1% of HP will free the titanium pellets from any adhering surface coating of oxide.
(2) The contents of the crucible can be cooled and solidified, preferably under an inert gas, then broken into lumps and further comminuted, for instance, with roll crushers. The coarse powder obtained may then be slurried with water and the titanium pellets separated from the slurry-solution of fluoride salts and NaOH which is formed by the reaction of the excess sodium with the water. above described.
1 Any other convenient method can be used for working' up the titanium metal product.
The process of this invention can also be effected on a continuous or a semi-continuous basis'by the simultaneous continual addition of molten sodium metal and alkali metal fluotitanate to a heated reaction zone maintained within the indicated temperature range, under an inert atmosphere. It is necessary to maintain a stoichiometric excess of sodium metal in the reaction zone at all times. The reaction mixture efiiuent from the heated reaction zone can then be treated as above described for the recovery of the titanium metal and the by-product alkali metal fluorides.
It is preferred to use he carried out in potassium fluotitanate in the process of this invention. The by-product of the reduction consists of a mixture of one mole of KP to two moles of NaF. The required K TiF can be regenerated from this lay-product mixture of lKFzZNaF.
The titanium metal pellets are further treated as.
is not intended to limit then rapidly drained The yields of titanium metal obtained in this process are very good, often as high as 95% of the theoretical, based on the alkali metal fiuotitanate consumed. The metal thus obtained contains less than 0.05% oxygen, less than 0.03% nitrogen and less than 0.08% carbon, and is over 99.5% pure titanium. it has a Brinnell hardness of to 200, and meets the most stringent present specifications for pure titanium metal.
The by-product slag, consisting of Na? (if Na TiF is employed) melting at 980 C., or a mixture of 2 moles of Net? to 1 mole of KP (if K TiF is employed) melting at 880 C., is usually molten at the conclusion of the reaction, and can thus be readily separated from the solid regulus of titanium metal, which melts at 1800 C.
The following example is given to define and to illustrate the invention but in no way is it intended to limit it to reagents, proportions, equipment, or conditions described therein. Obvious modifications will occur to any person skilled in the art. All proportions given are in parts by weight.
Example A molybdenum-lined, direct gas-fired steel crucible equipped with means for agitation is evacuate and then charged with 106 parts of distilled sodium metal (4.6 moles) under an argon atmosphere. The sodium metal is then heated to a temperature of 850880 C. and the agitator is set into motion.
Potassium fluotitanate is melted and heated under vacuum (Ml-l5 mm. Hg) at 800900 C. until it is scrupulously free of moisture. The molten K TiP is now added in a slow stream, over the course of two hours, tothe agitated sodium metal until a total of 7.41 parts of K TiF (1 mole) has been added. After all of the K TiF has been added, and the temperature has risen to a terminal temperature of ll00-l300 C., the reaction mixture is agitated for a further 15 minutes, and is from the reactor under an argon atmosphere, and is allowed to cool and crystallize. The cooled (35 C.) reaction mixture is then broken into lumps with a pneumatic hammer, and is then reduced to a coarse powder by passage through a jaw crusher and a roll crusher.
The coarse powder is then slurried with 1000 parts of hot water, and the slurry of salts separated by decantation from the insoluble sediment of titanium metal globules. The titanium globules are thoroughly washed first with water, then with a solution of 10% H 80 and 1% HP in water, and are then dried. The yield of pure titanium (over 99.5% Ti) thus obtained is 45.5 parts, or of theory based on the K TiF consumed. i
The by-product slurry-solution of 168.0 parts of NaF (4 moles), 116.2 parts of RF (2 moles) and 24.0 parts of NaOH in 1000 parts of water may be further processed for the regeneration of the potassium fluotitanate.
What is claimed is:
l. A process for the manufacture of titanium metal which comprises adding anhydrous alkali metal fluotitanate chosen from the group consisting of sodium fluotitanate, potassium fluotitanate, and mixtures thereof, to a body of molten sodium, with agitation of the reaction mixture, maintained under an atmosphere inert to titanium, at a temperature between 500 C. and 1300 C., there being at least four equivalents of sodium metal present for each mole of alkali metal fiuotitanate, and thereafter separating the titanium metal formed from the lay-product slag.
2. The process described in claim 1 in which the temperature' is between 700 C. and 1200 C.
3. The process described in claim 1 wherein there are present from 4.4 to 4.8 equivalents'of sodium metal for each mole of alkali metal tluotitanate.
4. The process described in claim 1 wherein the alkali metal fluotitanate is sodium fluotitanate.
5. The process described in claim 1 wherein the alkali metal fluotitanate is potassium fiuotitanate.
. 6. The process described in claim 1 wherein the process is carried out under an atmosphere of an inert gas.
7. The process described in claim 1 wherein the process is carried out in an argon atmosphere.
8. The process described in claim 1 wherein the process is carried out in an atmosphere of sodium vapor.
9. The process described in claim 1 wherein the process is carried out in a helium atmosphere.
10. A process for the manufatcure of titanium metal which comprises adding anhydrous potassium fluotitanate to a body of molten sodium with agitation of the reaction mixture, at a temperature between 700 C. and 1300 C. in the presence of an atmosphere inert to titanium, While continuously maintaining a stoichiometric excess of sodium in the reaction zone, and thereafter separating the titanium metal formed from the by-product slag of alkali metal fluorides and excess sodium metal.
11. A process for the manufacture of titanium metal which comprises reacting anhydrous alkali metal fluotitanate chosen from the group consisting of sodium fluotitanate, potassium fluotitanate, and mixtures thereof with molten sodium by simultaneous continual addition of molten sodium and said alkali metal fluotitanate to a reaction zone, with agitation of the resulting reaction mixture, maintaining said reaction mixture under an atmosphere inert to titanium, at a temperature between 500 C. and 1300 C., there being at least four equivalents of sodium metal present for each mole of alkali 6 metal fluotitanate, and thereafter separating the titanium metal formed from the by-product slag.
12. A process for the manufacture of titanium metal which comprises reacting anhydrous potassium fluotitanate with molten sodium by simultaneous continual addition of molten sodium and potassium fluotitanate to a reaction zone, with agitation of the resulting reaction mixture, maintaining said reaction mixture under an atmosphere inert to titanium, at a temperature between 700 C. and 1300 C., while continuously maintaining a stoichiometric excess of sodium in the reaction zone, and thereafter separating the titanium metal formed from the by-product slag of alkali metal fluorides and excess sodium metal.
References Cited in the file of this patent UNITED STATES PATENTS 2,148,345 Freudenberg Feb. 21, 1939 2,546,320 Rostron Mar. 27, 1951 2,607,674 Winter Aug. 19, 1952 FOREIGN PATENTS 1814/31 Australia Oct. 9, 1931 480,787 Great Britain Feb. 28, 1938 1,042,104 France June 3, 1953 OTHER REFERENCES Comprehensive Treatise on Inorganic and Theoretical Chemistry, by Mellor, vol. 7, pages 8, 9 and 10. Published 1927 by Longmans, Green & Co., New York.