US2939786A

US2939786A - Method of producing titanium and titanium alloys

Info

Publication number: US2939786A
Application number: US600704A
Authority: US
Inventors: Ginsberg Hans; Wilde Gunter
Original assignee: Vereinigte Aluminium Werke AG
Current assignee: Vereinigte Aluminium Werke AG
Priority date: 1955-07-29
Filing date: 1956-07-30
Publication date: 1960-06-07
Anticipated expiration: 1977-06-07
Also published as: DE1067601B; FR1150399A

Description

2 I ate METHOD OF PRODUCING TITANIUM AND TITANIUM ALLOYS Hans Ginsberg, Bad Godesburg, and Gunter Wilde, Lunen, Westphalia, Germany, assignors to Vereinigte AIuminium-Werke Aktiengesellschaft, Bonn (Rhine), Germany Thepresent invention relates to a method of producing titanium and titanium alloys, and more particularly it relates to a method of producing iron-free titanium alloysfromiromcontaining raw materials.

It is known to produce titanium-containing" aluminum alloys by electrolysis of a molten mass. As starting material for this process titanium dioxide is used, which together with aluminum oxide is introduced into the electrolyte- The composition of the electrolyte corresponds substantially to the composition of cryolite. Throughout this application the term cryolite is used to denote any material having substantially the same composition as cryolite; With the above described method it is possible to obtain aluminum-titanium alloys having a titaniumcontent of up to about 1%. However, it is not possible according to the method described above to produce aluminum-titanium alloys with a titanium content which is substantially higher than 1% It is therefore an object of the present invention to provide a method for the production of aluminum-tialloys of'any desired titanium content.

It is another object of the present invention to provide amethod for the production of iron-free aluminum-titanium alloys from iron-containing raw materials.

It is a further object of the present invention to prov'ide a. method" of producing aluminum-titanium alloys or also" titanium metal in asimple and economical manner.

it is yet another object of the present invention to provide amethod of separating in a raw material containing titaniumdioxide and also containing iron or iron compounds, the titanium dioxide from iron.

Other objects and advantages of the present invention will become apparent from a further reading of the deseription and the appended claims.

With the above and other objects in view, the present invention mainly comprisesin a method of separating titanium dioxide from iron in a raw material containing both, the steps of forming amolten mixture of cryolite and a raw materialcontaining iron and titanium dioxide whereby the titanium dioxide dissolves in the cryolite forming a molten solution while the iron does not dissolve in the solution, and separating the solution from the undissolved iron.

The present invention also includes in a' method of producing an alloy of aluminum and titanium the steps ofi forming a molten mixture including cryolite, titanium dioxide and aluminum, the amount of aluminum in' the molten mixture being greater than the amount necessary to reduce all of the titanium dioxide, so as to reduce substantially all of the titanium dioxide to titanium by reaction with only a portion of the aluminum, thereby forming an alloy of the unreacted aluminum and the ice and a raw material containing iron and titanium dioxide whereby the titanium dioxide dissolves in the cryolite forming a molten solution While the iron does not dissolve in. the solution, separatingthe molten solution from the undissolved iron, adding. aluminum to the molten solution, the amount of aluminum addedto the molten solution being greater than the amount necessary to-reduce all of the titanium dioxide therein, so as to reduce substantially all of the. titanium dioxide to titanium; by reaction with only a portion of the aluminum, thereby forming an alloy of the unreacted aluminum and the formed titanium, and recoveringthev thus-formed titanium-aluminumalloy.

According to the present invention it is possible to produce titanium-aluminum alloys of any desired aluminurn content as well as to produce titanium metal: and to produce such titanium metal or titanium-aluminum alloysfree'of iron.

Titanium dioxide-containing raw materials such as bauxite, rutile, or ilmenite are preferably used assuming, materials for the method of the present invention. While other. titanium dioxide-containing. raw materials may also-be used, the above mentioned areusually of greatest commercial importance and in order to further illustrate the method of. the present invention the usual composition of. these materials is given. in the following- Tablel;

TABLE I Bauxite:

Ignition loss 11-13%.

.Al Q g 44-55%.

Fe Oj 16-30%.

SiOg, l-5%.

TiO i 2-4% (sometimesup-to 10%)..

MnO ZnO' less than 1%. Rutil'ez TiO' -90%.

Fe O,

Nb O Sometimes. in varying amounts.

lltnenite:

TiQ 45-52%.

Fe 0, up to 8%.

FeO depending on the percentage;

of. TiO; in the stoichiometric amount. corresponding to the formula FeOTiOg.

MgO up to 1%.

As can be seen from Table I, all of the customarily used raw materials containiron oxides. contains water of hydration, as indicated by. the ignition loss. I

Raw materials containing water of hydration, suchas bauxite, have first to be calcined in order toremove the. Water. The ignition loss of calcined material should be. less than 0.5%. 1

It is also sometimes desirable, and especially in the case of ilmenite as raw materialit'is important to reduce at least aporti'on of the iron oxides in theraw material. Whenfor instance bauxite is calcined in the presence of carbon-containing material; about 50% ofthe iron oxides are reduced to metallic iron and about 50% of the zinc oxides are reduced and volatilized Rutile as raw material requires neither calcination nor reduction. In the case of ilmenite calcination isnot' necessary, however inorder' to separatetheFeO of the ilmenite, the same is preferably molten in: the presence-of: carbon-containing materials so asto: reduce the: iron'oxid'es, whereby avery pure' tree- Bauxite also ball containing about 96% iron and about 4% carbon is obtained.

The raw material after preliminary calcination or reducing treatment, if required, is then molten together with cryolite at a temperature of about 1,000 C.

In the molten mixture of cryoliteand the raw material, practically all of the oxides present except Fe O are dissolved. Since Fe O is soluble in cryolite only to a very small extent, the iron oxide is separated from the molten mixture. In this manner a nearly complete separation between titanium dioxide which is dissolved in the molten cryolite, and iron which is present in the form of Fe,0, is achieved. Thus, according to the present invention, it is possible in a simple and economical manner to completely separate titanium dioxide from iron contained in the raw material, by first reducing iron present in a form other than Fe O to metallic iron which is separated from the molten raw material, and by then dis-' solving the Fe o -containing raw material in molten cryolite whereby titanium dioxide and oxides of other metals except iron are/dissolved in the molten cryolite,

while Fe O is not'soluble therein to any substantial 7 extent.

The titanium dioxide-containing cryolite is preferably then transferred from the furnace in which the same has been produced into another furnace in which an alumino thermic reaction takes place at a temperature of about 1,000" C. by introduction of metallic aluminum in the form'of shavings, scrap or the-like. The aluminum which is thus introduced into the molten-cryolite containing dissolved titanium dioxide reduces titanium dioxide to metallic titanium which forms a metal sump at the bottom of the reaction vessel, while simultaneously an equivalent amount of aluminum is oxidized and dissolved in the molten cryolite in the form of aluminum oxide. In this manner it is possible to remove substantially all of the titanium from the molten cryolite; while for instance silicon dioxide originating from the raw material and also dissolved in the molten cryolite remains in the same.

By using an induction 'furnace for alumino thermic reduction of. the titanium dioxide in the molten cryolite, it is also possible to agitate the metal sump which forms at the bottom of the furnace and which consists of titanium and usually also aluminum, by utilizing the electromagnetic pinch effect. The length of time during which the metal sump is to be electromagnetically agitated and the length of time for which the metals are to remain in the metal sump on the bottom of the induction furnace before being removed therefrom depends on the size of the furnace, respectively on the quantity of the molten material therein. It is important to avoid overheating of the bath which might cause excessive convection. It is also important to prevent the temperature from rising above about 1,000 C. 4

The maximum solubility of titanium dioxide in molten cryolite having a temperature of about 1,000 C. amounts to about 5% titanium dioxides, Consequently, depending on the titanium dioxide content of the raw materials, ap-

proximately 100 parts by weight of bauxite may be used' to form a molten mixture with 100 parts by weight of cryolite, while in the case of rutile approximately 5 parts by weight, and in the case of ilmenite approximately 10 parts by weight of raw materials may beused to form a molten mixture with 100 parts by weight of cryolite.

When a raw material is used which, for instance like bauxite, contains a considerable quantity of impurities, all other metals which are present and which are more electro-positive than aluminum are also separated in the metal sump during the alumino thermic reaction. Surprisingly it has been found that contrary to theoretical expectations, due to the free reaction enthalpies of the oxides, also silicon dioxide is separated from titanium dioxide. While the titanium dioxide is nearly quantitatively reduced and thus removed from themolten solu- 7 tion, only a small portion of the silicon dioxide is thereby reduced. 1

relation to the amount of titanium dioxide contained in the molten cryolite, the metal sump on the bottom of the furnace is formed either of metallic titanium alone or-of an alloy-forming mixture of titanium and aluminum. If metallic aluminum is introduced in an amount suificient to reduce the titanium dioxide, substantially only metallic titanium 'is obtained, when the amount of aluminum which is introduced into the titanium dioxide-containing molten cryolite is increased to an amount greater, than the amount necessary to reduce all ofthe dissolved titanium dioxide, then the aluminum which is not reacted with titanium dioxide also becomes part of the metal sump.

The metal sump is removed from time to time from the reaction vessel in which the alumino thermic reaction takes place. After tapping the metal sump, the relative amount of titanium in the aluminum-titanium alloy can be further increased by heating the metal'to a tempera-. ture of at least 1,000 C. or even higher and by sub sequent cooling whereby by liquation the alloy compound Al Ti having a titanium content of 37.2% or more is obtained. Those skilled in the art may easily understand from the known diagram of the binary alloy AlTi that the compound Al Ti precipitates in solid form under the given working conditions, and this the more the. cooling of the molten metal proceeds.

. If care is taken that the temperature of the, molten metal does not essentially fall below 900, C. the V precipitated crystals of the compound Al Ti may be separated'from the liquid melt by filtering, centrifuging or similarknown methods.

The utilization of this knowledge for the present process is new. 7 1

By performing the liquation process and the heating of the metals to a temperature of higher than 1,000 C.

' after-the metals have been removed fromthe reaction vessel in which the alumino thermic reaction takes place, evaporation losses of cryolite due to heating of the same above 1,000 C. are avoided.

The molten cryolite into which the titanium dioxidecontaining raw material is introduced, as well as the molten cryolite having titanium dioxide dissolved therein to which aluminum is added for execution of the alumino thermic reaction with the dissolved titanium dioxide is preferably kept at a temperature of between 1,000 and l,050 C. and it is generally advisable that the temperature of the molten cryolite should not be below 950 C.

and not above 1,100 C. By reducing the temperature of.- the molten mass below the above indicated minimumfigures, the molten cryolite may eventually solidify. In

' any event, even prior to solidification of the molten cryolite, the reduction of FeO contained in the raw material which may be etfected'by adding carbon-containing materials 'to the raw material and-the-molten. cryolite, will be incomplete'if the temperature fallsbei low 950 C. By exceeding a temperature of 1,100 C.,

an uneconomically great loss of cryolite due to evaporation of the same is experienced.

It is also within the scope of the present invention to use the cryolite from which titanium dioxide has been removed by an alumino thermic reaction and which contains aluminum oxide, i.e. the cryolite which has been employed in the production of metallic titanium or titanium,

. I electrolytic cell.

The following examples are given as illustrative of the method of the present invention'only, the present int me 5 vention however not being limited to thespecific details of the examples. 7

Example 1- Bauxite of Greek orig in containing. 18% of l e- 56% of alumina and 3.2% of titanium dioxide is first calcined under addition of cokei'n a rotary furnace. The thusprepared bauxite which has lost its water of hydration and part of the iron oxide of which has been reduced, is then introduced into a bath of molten cryolite which is kept at 1,000 C, Equal amounts of cryolite and bauxite are thus mixed under stirring. The molten mixture remains for 20minutes at a temperature of 1,000 C. Thereafter, the molten titanium dioxide-containing cryolite is tapped and removed to a second react-ion vessel, preferably an induction furnace. After removal of the titanium dioxide-containing molten cryolite, there remains on the bottom of the vessel a body containing about 95% of the originally presentFe O mainly in the form of Fe, as Well as 16% of theori'ginally present silicon dioxide. The material is free of titanium and titanium dioxide. Consequently all of the titanium dioxide contained in the raw material has beendissolved in the molten cryolite.

The molten cryolite which now contains about 5% titanium dioxide is then treated in a reduction furnace with a quantity of metallic aluminum, suflicient to reduce all of the titanium dioxide to metallic titanium, and to form with the metallic titanium an aluminum-titanium alloy of desired proportions of aluminum and titanium. During the alumino th'ermic reaction a temperature of between 950? and 1,000 C., preferably of 1,000 C. is maintained.

Example 2 The process of thepresent invention is executed with rutile as raw material substantially as described in Example 1. However calcination. and carbon reduction of the raw material are omitted. In view of the higher percentage amount of titanium dioxide contained in rutile and in view of the maximum solubility of titanium dioxide in molten cryolite at 1,000 C. of about 5%, approximately 5 parts by weight of rutile are introduced into 100 parts by weight of molten cryolite.

Example 3 When ilmenite is used as raw material for the process of the present invention, calcination for removal of water of hydration is not required, however the ilmenite has first to be reduced with a carbon containing material in order to remove the FeO. Ilmenite is molten with a sufficient quantity of carbon containing material so as to eiiect this reduction, whereby an iron ball containing about 96% iron and about 4% carbon is formed. The raw material which is thus freed from FeO is then introduced into molten cryolite, the titanium dioxide of the raw material dissolved in the molten cryolite and the process of the present invention is further executed as described in Example 1.

Example 4 After the reducing melting of bauxite and cryolite the melt contained 0.56% TiO 50 kilograms of an aluminum alloy were added to 500 kilograms of the liquid melt. This melt was then stirred for ten minutes and let stand for sixty minutes at a temperature between 950 and 1000 C. After this time the melt contained only 0.01% of TiO Thus the titanium was reduced and alloyed with the aluminum down to this content.

In another case 15 kilograms of pure aluminum were added to 750 kilograms of melt. Thereby the content of TiO;, in the melt was lowered beneath 0.006%.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this in- 8 vention and; therefore", such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. In a method of separating titanium dioxide from iron in a raw materialcontaining titanium dioxide and at least one substance selected from the group consisting of metallic ironand iron compounds the steps of forming a mixture of' a predetermined quantity of cryolite and said raw material at a predetermined temperature above the melting point of said cryolite so as to melt the same, said predetermined quantityof cryolite in' relation to the quantity of titanium dioxide in said raw material, and

said predetermined temperature of said molten mixture being chosen in such a manner asto substantially completely dissolve all of said titanium dioxide of said raw material in said molten cryolite; while said substance does not dissolve" in the thus-formed solution; and separating said iron-free, titanium dioxide containing solution from the remainder of said mixture.

2. In amethod of separating titanium dioxide from iron in araw material containing" titanium dioxide and at least one substance selected from the group consisting of metallic iron and ironcompounds and also containing water of hydration, the steps of calcining said raw material thereby removing said water of hydration; forming a mixture of a predetermined quantity ofcryolite and of said calcinedraw material, the quantity of cryolite being at least equal to about 20" times the quantity of titanium dioxide present in said raw material, and the temperature of up w; 1000 .61 ane'being higher than the melting point of cryolite andsufliciently' high so that substantially all of the titanium dioxide will be. dissolved in said molten cryolite forming .a' molten solution,,whilel said substance does not dissolve in said solution; and separating said iron-free, titanium-dioxide containing s'olu-' tion from the remainder of said mixture.

3. In a method of separating titanium dioxide from iron in a raw material containing titanium dioxide and an iron-containing compound, the steps of melting said raw material in the presence of a carbon-containing material thereby reducing at least a portion of said ironcontaining compound to iron; forming a mixture having a temperature of up to 1000 C. of a predetermined quantity of molten cryolite and of said raw material containing iron and titanium dioxide, said predetermined quantity of cryolite being so chosen in relation to the quantity of titanium dioxide in said raw material as to cause substantially complete dissolution of all of said titanium dioxide in said molten cryolite and to form a molten solution of said titanium dioxide in said cryolite, while said iron-containing compound and iron do not dissolve in said solution; and separating said iron-free, titanium-dioxide containing solution from the remainder of said mixture.

4. A method of producing an alloy of aluminum and titanium from a raw material containing titanium dioxide and at least one substance selected from the group consisting of metallic iron and iron compounds, comprising the steps of forming a mixture of a predetermined quantity of cryolite and of said raw material at a predetermined temperature above the melting point of said cryolite so as to melt the same, said predetermined quantity of cryolite in relation to the quantity of titanium dioxide in said raw material, and said predetermined temperature of said molten mixture being chosen in such a manner as to substantially completely dissolve all of said titanium dioxide of said raw material in said molten cryolite, While said substance does not dissolve in the thus-formed solution; separating said molten iron-free, titanium dioxide-containing solution from the remainder of said mixture; adding aluminum to said molten iron-free solution, the amount of aluminum added to said molten solution being greater than the amount necessary to reduce all of the 7 titanium dioxide therein, so as to reduce substantially all of said'titanium dioxide to titanium by reaction with only a portion of said aluminumflhereby forming an alloy of the unreactcd'aluminum and the formed "titanium; and recovering thethus-formed titanium-aluminum alloy.

5. A method of producingan alloy of aluminum and titanium from a raw material containing titanium dioxide and at least one substance selected from the group consisting of metallic iron and iron compounds, comprising the steps of calcining a raw material containing said substance, titanium dioxide and also containing Water of hydration thereby removing said water of hydration; forming a mixture having atemperature of up to 1000 C. of a predetermined quantity of cryolite and said calcined raw material at a predetermined temperature above the melting point of said cryolite so as to meltthe same, said predetermined quantity of cryolite in relation to the quantity of titanium dioxide in said raw material, and said predetermined temperature of said molten mixture being chosen in such a manner as to substantially completely dissolve all of said-titanium dioxide of said raw material in said molten cryolite while said substance does not dissolve in the thus-formed solution; separating said molten iron-free, titanium dioxide-containing solution from said undissolved substance; adding in an induction furnace aluminum to said iron-free solutidn,-the amount of aluminum added to said molten solution being greater than the amount necessary to reduce all of the titanium V dioxide thereimso as to reduce substantially all of said titanium dioxide to titanium vby reaction with only a portion of said aluminum, therebyforming below the molten mixture in said induction furnace a metal sump comprising the unreacted aluminum and the formed titanium, while simultaneously electromagnetically agitating said metal sump; recovering said metal sump from said induction furnace; adjusting the temperature of said recovered metal sump to about 1000 C.; slowly cooling said metal sump, thereby formingiby liquation an aluminum-titanium alloy of high titanium content; and re covering the thus-formed titanium-aluminum alloy.

6. A method of producing titanium. from a raw material containing titanium dioxide and; at least one substance selected from the group consisting of metallic iron and iron compounds, comprising the steps of form-' ing a mixture of a predetermined quantity of cryolite and said raw material at a predetermined temperature above the melting point of said cryolite so as to melt'the same, said predetermined quantity of cryolite in relation to the quantity of, titanium dioxide in said raw material, and said predetermined temperature of said molten mixture being chosen in such a manner as to substantiallyv completely dissolve all of said titanium dioxide of said raw material in said molten cryolite while said substance remains substantially: undissolved in the thus-formed solution; separating said molten, iron-free, titanium dioxidecontaining solution from said undissolved substance; adding aluminum to said iron-free, molten solution, the amount of aluminum added being substantially equal to the amount necessary to reduce all of said dissolved titanium dioxide to'titanium, so as to transform substantially all of said titanium dioxide into titanium; and separating the thus-formed titanium from the remainder of the molten solution.

References Cited in the file of this patent UNITED STATES PATENTS 451,405 Langley Apr.v 28, 1891 778,345 Weber Dec. 27, 1904 1,533,505 Lowbowsky Apr. 14, 1925 2,439,216 McLellan Apr. 6, 1948 2,451,490 Johnson Oct. 19, 1948 2,451,492 Johnson Oct. 19, 1948

Claims

1. IN A METHOD OF SEPARATING TITANIUM DIOXIDE FROM IRON IN A RAW MATERIAL CONTAINING TITANIUM DIOXIDE AND AT LEAST ONE SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF METALLIC IRON AND IRON COMPOUNDS THE STEPS OF FORMING A MIXTURE OF A PREDETERMINED QUANTITY OF CRYOLITE AND SAID RAW MATERIAL AT A PREDETERMINED TEMPERATURE ABOVE THE MELTING POINT OF SAID CRYOLITE SO AS TO MELT THE SAME, SAID PREDETERMINED QUANTITY OF CRYOLITE IN RELATION TO THE QUANTITY OF TITANIUM DIOXIDE IN SAID RAW MATERIAL, AND SAID PREDETERMINED TEMPERATURE OF SAID MOLTEN MIXTURE BEING CHOSEN IN SUCH A MANNER AS TO SUBSTANTIALLY COMPLETELY DISSOLVE ALL OF SAID TITANIUM DIOXIDE OF SAID RAW MATERIAL IN SAID MOLTEN CRYOLITE, WHILE SAID SUBSTANCE DOES NOT DISSOLVE IN THE THUS-FORMED SOLUTION, AND SEPARATING SAID IRON-FREE, TITANIUM-DIOXIDE CONTAINING SOLUTION FROM THE REMAINDER OF SAID MIXTURE.