GB2111531A - Method for manufacturing titanium metal - Google Patents

Abstract

A method for manufacturing titanium metal comprises feeding a titanium chloride and powdered particles of a reducing metal into a reaction zone, and reacting the titanium chloride and powdered reducing metal at a temperature above the melting points of the reducing metal and the chloride salt of the reducing metal.

Description

SPECIFICATION Method for manufacturing titanium metal The present invention relates to a method for manufacturing titanium metal.

Two known methods are the so-called Hunter method and the Kroll method, though other methods have been conventionally used to manufacture titanium metal.

In the Kroll method, a retort-like reaction vessel is first charged with a reducing metal, e.g.

magnesium in the solid or molten state, prior to the initiation of the reaction. When solid magnesium is used, the magnesium is heated to a temperature sufficient to react with titanium tetrachloride. Then, liquid titanium chloride is added as droplets to the reaction vessel to initiate the reaction. The reaction zone is kept, by the heat of reaction and/or an outside heat source, at a temperature above the melting point of magnesium chloride (71 50C) which forms along with titanium metal so that the reaction may be conducted.

Magnesium metal has a melting point of 6500C, therefore, it is in the molten state at the above mentioned temperature. In order to allow titanium tetrachloride, which is added as droplets from the upper part of the reaction vessel to react smoothly and rapidly with magnesium, it is critical that the surface of the bath formed by the molten magnesium and magnesium chloride (hereinafter referred to as the "bath surface") must be occupied not by magnesium chloride, but by magnesium metal to permit magnesium to contact the titanium tetrachloride which drops into the bath. Fortunately, molten magnesium metal has a specific gravity less than molten magnesium chloride, which allows the molten magnesium chloride layer to be below the magnesium layer during at least the initial stage of the reaction.Thus, the bath surface is substantially occupied by magnesium, so that the reaction may proceed smoothly and rapidly. The titanium metal product of the reaction precipitates onto the bottom of the reaction vessel because it has a specific gravity greater than the molten magnesium and magnesium chloride, and it forms as a spongy titanium layer (hereinafter referred to as "sponge titanium layer").

The magnesium chloride and titanium increase in volume as the reaction progress. The sum of the volume increases of both materials is very large in comparison to the decrease in volume of magnesium as a result of its consumption.

Therefore, the total volume of material in the reaction vessel gradually increases as the reaction progresses. Moreover, in order to increase productivity, it is necessary to increase the production of titanium per unit volume of a reaction vessel, i.e., the volumetric efficiency of the reaction vessel. For this purpose, it is necessary to intermittently or continuously remove magnesium chloride as it forms in the reaction from the reaction vessel.

The precipitated layer of titanium metal in the form of a sponge gradually grows in the upward direction as the reaction progresses. In order to keep the reaction rate high, it is desired to position the magnesium layer above the sponge titanium layer to maintain good contact between magnesium and the titanium tetrachloride as it is dropwise added to the reaction vessel. If the surface of the magnesium layer is positioned far below the sponge titanium layer, the titanium tetrachloride must descend and penetrate through pores in the sponge titanium in order to achieve the desired contact and reaction with magnesium. However, this results in the reaction rate being very low.Accordingly, the timing for the removal of magnesium chloride from the reaction vessel and the quantity of magnesium chloride to be removed must be determined so as to allow the surface of the magnesium layer which floats on the magnesium chloride layer to always be at a position at a level substantially the same as or above the surface of the sponge titanium layer. However, even when the surface of the magnesium layer is controlled to such a level, it becomes necessary to force magnesium chloride which forms by the reaction of the magnesium with titanium tetrachloride at the surface of the magnesium layer to go down through the pores of the sponge titanium layer and to force magnesium to go up through the pores.

Thus, in the prior art processes, the positional replacement between the magnesium and the magnesium chloride must be accomplished through the pores of the sponge titanium layer.

The more the precipitated layer of sponge titanium grows, the less the rate of replacement.

This results in the magnesium layer which is required to be above or near the sponge titanium layer being retained in the sponge titanium layer and magnesium chloride, which must descend, to float above the sponge titanium layer. It is a matter of course that this phenomenon does not allow titanium tetrachloride to sufficiently contact the magnesium in order that the reaction may be smoothly conducted.

Thus, even if the reaction is conducted under the conditions that the shape of the reaction vessel, the charge of magnesium, the timing for the removal of magnesium chloride and the amount of magnesium chloride to be removed are optimumly selected to maximize the operational efficiency inclusive of the volume efficiency of the reaction vessel, the reaction rate, the utilization of magnesium and the like; the problem of the positional replacement between magnesium and magnesium chloride begins to become a factor at the time when about 60% of the charged magnesium has reacted, this problem resulting in a substantially diminished reaction rate. Thus, the outstanding disadvantage of the conventional method is that the reaction rate decreases during the latter stages of the reaction because of the failure of magnesium to properly replace magnesium chloride in the system.This outstanding disadvantage of the prior art processes is also caused by the fact that the pores of the precipitated sponge titanium layer retain magnesium therein thereby preventing it from moving up to the surface of the bath. More particularly, the reaction between magnesium and titanium tetrachloride takes place in the vicinity of the surface of the magnesium layer, and the sponge titanium which forms at this position gradually moves down to the bottom of the reaction vessel, with some of the magnesium being retained in the pores of the precipitated sponge titanium thereby preventing the same from moving up to the surface of the bath. This effectively removes magnesium from the reaction such that it never reacts with titanium tetrachloride even when the replacernent between magnesium and magnesium chloride is fairly efficient.This is a major reason why the reaction ratio of initially charged magnesium or the utilization of magnesium is restrained up to 70% to 80% in the prior art. Thus, another disadvantage of the conventional method is that it does not efficiently utilize the magnesium reactant.

During the initial stages of the reaction in tne conventional method, the magnesium layer satisfactorily contacts the titanium tetrachloride.

Therefore, it is possible to indefinitely increase the reaction rate by increasing the rate of addition of the droplets of titanium tetrachloride. However, if the reaction rate becomes too great, a large amount of heat is produced by the reaction of magnesium with titanium tetrachloride, thereby resulting in a rapid rate of increase of the temperature in the reaction vessel. The reaction vessel is generally formed of iron or an iron based alloy to decrease the manufacturing cost.

Accordingly, when the reaction vessel is heated to a temperature higher than about 10500C, a portion of the reaction vessel eutectically melts with the titanium which forms in the reaction because the eutectic point between titanium and iron is about 1 0500C. Therefore, the conventional method cannot be practiced at a reaction rate which results in the production of heat in amounts which cause the temperature to exceed the above limit. Accordingly, a third disadvantage of the conventional method is that the reaction rate during the initial stages of the reaction must be below a predetermined level. A need, therefore, continues to exist for an improved technique of preparing titanium metal.

Accordingly, one object of the present invention is to provide a method for manufacturing titanium metal which is capable of effectively preventing the reaction rate from decreasing during the latter stages of the reaction thereby substantially shortening the reaction time and increasing the productivity of the reaction.

Another object of the present invention is to provide a method for manufacturing titanium metal which is capable of aliowing the reaction to rapidly proceed and which prevents the reducing metal used from being retained in the pores of the sponge titanium layer thereby minimizing the amount of reducing metal effectively removed from the reaction and increasing the utilization of the reducing metal.

Still another object of the present invention is to provide a method for manufacturing titanium metal which permits increases in the reaction rate without rapidly and locally increasing the reaction temperature which significantly increases the reacting weight per unit time or productivity, thereby allowing the total consumption of energy to be substantially decreased.

According to the invention, a method for manufacturing titanium metal comprises feeding titanium chloride and powdered particles of a reducing metal into a reaction zone, and reacting the titanium chloride and powdered reducing metal at a temperature above the melting points of the reducing metal and the chloride salt of the reducing metal.

Thus, the reaction may be carried out while feeding the titanium chloride and powdered particles of the reducing metal to the reaction zone.

In a second embodiment of the present invention, a titanium tetrachloride slurry containing powdered solid particles of the reducing metal and a partially reduced product is prepared by contacting titanium tetrachloride with droplets of a melt of the reducing metal to cool and solidify the droplets of the molten reducing metal and to partially reduce the titanium tetrachloride and the slurry is reacted with the reducing metal while feeding the slurry to the reaction zone, to form titanium metal.

The titanium chloride which is used in the first embodiment of the present invention may be titanium tetrachloride or mixtures of titanium tetrachloride with titanium trichloride and/or titanium dichloride. Preferab!y, titanium tetrachloride is used as the titanium chloride because of its reactivity, reaction rate, ease of handling and the like. However, mixtures of titanium tetrachloride with other titanium chlorides can also be used, because the mixtures further facilitate the controi of the reaction temperature.

Suitable reducing metal which may be used in the present invention preferably include magnesium, sodium, lithium, potassium, calcium and the like. Magnesium is most preferred as the reducing metal.

The supply of the titanium chloride and reducing metal to the reaction zone may be achieved in various ways with the only requirement being that good contact between the reacting materials be maintained in order to smoothly perform the reaction. However, preferably these materials are fed directly onto the surface of a bath from the upper part of the reaction zone, because this allows the reaction to be smoothly and quickly carried out. More particularly, because of this procedure, it is not necessary to positionally replace magnesium with magnesium chloride in order that the magnesium metal move up to the surface of the bath so that the titanium chloride, for example, titanium tetrachloride, may react with the magnesium.

Prior to the supply of the titanium chloride and powdered particles of the reducing metal to the reaction zone to initiate the reaction, a portion of the reducing metal or a mixture of the reducing metal and a chloride thereof may be preferably charged into the reaction zone, because this allows the reaction to reach a predetermined reaction rate immediately after the start of the reaction.

The titanium chloride and the powdered particles of the reducing metal may be fed into the reaction zone in a continuous or intermittent manner depending upon the reaction conditions.

Alternatively, these materials may be separately fed directly to the reaction zone or fed together after mixing. When supplying the materials separately, the powdered particles of the reducing metal may be added during a portion of the total reaction period, the partial period being optionally selected depending upon the reaction conditions.

When feeding both materials together after mixing, the reaction may be conducted in such a manner that tlie mixture is added during a portion of the total reaction period, this portion of time being dependent upon the reaction conditions with only the titanium chloride being added during the remaining reaction period. When feeding the materials together after mixing, the use of titanium tetrachloride as the titanium chloride and magnesium as the reducing metal has the advantage that facilities such as the storage tank, the supply piping, the flow meter and the like can be commonly used for both materials and the materials can be homogeneously mixed without separation and uneven distribution; because both materials have substantially the same specific gravity at normal temperatures.

The particle size of the powdered particles of the reducing metal is not limited to a specific range, unless the particles are so large that the particles cannot be supplied to the reaction vessel or the temperature distribution in the reaction zone becomes locally, highly nonuniform because of the endothermic melting of the particles after they are fed to the reaction zone. The particle size should be selected depending upon the shape and size of the reaction vessel, the manner and rate of feeding the reducing metal and titanium chloride, and the like. However, preferably the particles are within the range of 10 ,um to 10 mm.A particle size which exceeds the upper limit of the range is not preferable because it renders the supply of the reducing metal to the reaction vessel difficult and the temperature distribution in the reaction zone nonuniform. A particle size below 10 ,am does not theoretically interfere with the reaction, however, it is not preferable from a practical point of view because a special apparatus is required to obtain such small particle sizes. In particular, when the reducing metal is fed to the reaction zone separately from the titanium chloride, such small particle sizes render the supply of metal to the reaction zone difficult.

In the second embodiment of the present invention, a reducing metal which is used preferably includes magnesium, sodium, lithium, potassium, calcium or the like, as in the first embodiment of the invention. Magnesium is most preferred as the reducing metal. In this embodiment, a partially reduced product is obtained by contacting titanium tetrachloride with droplets of a melt of the reducing metal. The partially reduced product containing titanium trichloride titanium dichloride and the chloride of the reducing metal. In this embodiment, as mentioned above, the droplets of the molten reducing metal are contacted with titanium tetrachloride to partially reduce the titanium salt and to solidfy the droplets themselves, so that a titanium tetrachloride slurry is formed which contains powdered particles of the reducing metal and the partially reduced product.The slurry is formed in such a manner that about 10% of the reducing metal reacts with a part of the titanium tetrachloride to produce titanium trichloride and dichloride, and the powdered particles of the reducing metal are uniformly dispersed in the slurry.

The droplets of the molten reducing metal may be formed in a variety of ways with the objective being that powdered particles of the reducing metal are obtained which have a particle size within a desired range. However, the droplets are preferably formed by such suitable techniques as dropping, centrifugal spraying or the like.

The supply of the titanium tetrachloride slurry containing the powdered particles of the reducing metal and the partially reduced product to the reaction zone may be carried out in a variety of ways with the objective being that satisfactory contact between both materials should be achieved and that the reaction be rapidly advanced. However, the slurry is preferably supplied from the upper part of the reaction zone onto the surface of the bath because this allows the reaction to be smoothly and quickly carried out.

Also, as in the first embodiment, the reaction zone is preferably charged with a part of the reducing metal or a mixture of the reducing metal and a chloride thereof prior to the supply of titanium tetrachloride to the reaction zone to initiate the reaction, because this allows the reaction to be more smoothly and quickly carried out.

In addition, the titanium tetrachloride slurry may be continuously or intermittently fed to the reaction zone. Alternatively, the supply maybe carried out in such a manner that the slurry is added to the reaction zone during a part of the total reaction period optionally selected depending upon the reaction conditions with only the titanium tetrachloride being fed during the remaining portion of the reaction period.

From the above description, it can be understood that the present process significantly restrains increases in temperature in the reaction vessel from the heat of reaction, because the reducing metal in the solid state which is fed directly to the reaction zone has a heat content lower than the molten reducing metal used in the conventional method. More particularly, the heat content of solid magnesium at the reaction temperature of 1 0000C is low in an amount of about 8.7 kcal/mol, in comparison to that of molten magnesium at that temperature.This is equivalent to about 28% of 31.4 kcal/mol which is the quantity of heat produced from 1 mol of magnesium in the reaction between titanium tetrachloride and magnesium at a temperature of 10000 Thus, it should be evident that the first embodiment of the present process significantly reduces the third disadvantage of the prior art mentioned above. The first embodiment of the present process is capable of reducing the limitation on the reaction rate, which limitation is necessary to avoid a rise in temperature resulting from the heat of reaction in the prior art, by the differences between the heat contents of solid magnesium and molten magnesium. Supposing that the rate of heat radiation from two reaction vessel is the same, the first embodiment of the present invention can result in an increase in the reaction rate of about 28%.

In addition, the second embodiment of the present process may effectively eliminate the third disadvantage of the prior art. More particularly, supposing that, in the formation of the titanium tetrachloride slurry, 10% of the magnesium reacts with a part of the titanium tetrachloride to reduce it to titanium trichloride the heat produced by the reduction of the slurry by magnesium at a temperature of 1 0000C may be lower by about 11.4 kcal/mol than the heat produced by the reduction of only titanium tetrachloride by magnesium at the same temperature.

This is equivalent to about 36% of the heat produced by the reduction of titanium tetrachloride by magnesium. Thus, the second embodiment of the present process is capable of substantially reducing the need for control of the reaction rate, which has been necessary in the prtor art to prevent increase in temperature, this being allowed by the differences in the heat content of magnesium and by the reduction in heat of reaction because of the formation' of the partially reduced product in the titanium tetrachloride slurry. The second embodiment allows the reaction rate to be increased by about 64%, with the assumption that the radiant heat from the reaction vessels is the same.

The invention may be carried into practice in various ways and some specific examples will now be described for the purposes of illustration.

Example 1 In this example, sponge titanium was prepared as follows: A reduction apparatus was used which comprised a reaction vessel constructed of an outer cylindrical vessel of stainless steel and an inner cylindrical vessel of iron fitted in the outer vessel, and an electrical heater provided on the outside of the outer cylindrical vessel to heat the reaction vessel. The reaction vessel was equipped with a titanium tetrachloride supply pipe inserted thereinto through the central portion of an upper lid thereof and with a magnesium particle supply pipe in proximity to the titanium tetrachloride supply pipe.

A 600 kg amount of molten magnesium was charged into the outer cylindrical vessel and heated to a temperature of 8000 C. Thereafter, titanium tetrachloride and magnesium particles (particle size of 2 to 4 mm) were fed into the reaction vessel through the titanium tetra chloride and magnesium particle supply pipes at rates of2100 cc/min and 926 g/min, respectively.

The feed rates were kept constant until the supply was complete. This took 31.5 hours and 1726 kg of sponge titanium was obtained. The reaction temperature was 10000C and the excess magnesium ratio was 1.35. The rate at which sponge titanium was manufactured was 54.8 kg/hr.

Comparison Example 1 A conventional method was practiced to manufacture sponge titanium utilizing a reaction vessel constructed in substantially the same manner as in Example 1. The reaction vessel was charged with 2200 kg of magnesium which corresponds to the total amount of magnesium to be necessary for the reaction and the magnesium was heated to a temperature of 800"C.

Thereafter, titanium tetrachloride was fed to the reaction vessel at a feed rate of 2100 to 1000 cc/min and reacted with the magnesium at a temperature of 1000 C. The supply of titanium tetrachloride was conducted over 42 hours. The reaction yielded 1 500 kg of sponge titanium. The excess magnesium ratio was 1.47 and the rate of manufacturing sponge titanium was 35.7 kg/hr.

Example 2 Sponge titanium was manufactured in a reduction apparatus comprising a reaction vessel constructed of an outer cylindrical vessel of stainless steel and an inner cylindrical vessel of iron fitted within the outer vessel, and an electrical heater provided on the outside of the outer vessel to heat the reaction vessel. The reaction vessel was equipped with a supply pipe, which was inserted into the reaction vessel through an upper lid thereof and which acted to feed a mixture of titanium tetrachloride and magnesium particles to the reaction zone.

A particle mixture was prepared by charging titanium tetrachloride and magnesium particles in a molar ratio of 1:2 in a mixing tank and mixing the materials in the tank by means of an agitator thereby forming a homogeneous mixture.

A 600 kg amount of molten magnesium was charged in the outer cylindrical vessel and heated to a temperature of 8000 C. Thereafter, the mixture of titanium tetrachloride and magnesium particles was fed through the supply pipe into the reaction vessel so that the titanium tetrachloride and magnesium particles were respectively fed at rates of 2100 cc/min and 926 g/min. The mixture was fed keeping the composition of the mixture in the mixing tank without sedimentation of the magnesium particles, because the difference in specific gravity between titanium tetrachloride and magnesium particles was only 0.014 at normal temperatures.

The supply of the mixture was complete in 31.5 hours after the initiation of the reaction and 1733 kg of sponge titanium was obtained.

The reaction temperature was 10000C and the excess magnesium ratio was 1.34. The rate of manufacturing sponge titanium was 54.8 kg/hr.

Example 3 A titanium tetrachloride slurry was prepared as follows: A liquid film of titanium tetrachloride having a thickness of 4 mm and running down at a rate of 1 m/sec. along the wall of a spray tank having an innner diameter of 1000 mm and a height of 1300 mm was formed. Molten magnesium heated to 8000C was fed onto a disc 200 mm in diameter disposed in the spray tank and rotatiny at a rate of 400 rpm. The magnesium was divided into droplets of 2 mm or less in diameter and sprayed onto the peripheral wall of the spray tank, so that it was cooled and solidified by the liquid film of the titanium tetrachloride running down along the peripheral wall. Simultaneously, a portion of the titanium tetrachloride was reduced by the molten magnesium.As a result, lower valence state titanium chloride and magnesium chloride were produced, the amount of which was about 10% of the supplied magnesium. Thus, a titanium tetrachloride slurry containing magnesium particles, lower valence state titanium chloride and magnesium chloride was formed in the spray tank. The slurry was supplied to a cooler by a pump to be cooled and then allowed to flow down along the wall of the spray tank, so that a slurry which is equiva!ent to a molar ratio of 1:2 in terms of titanium tetrachloride and magnesium was prepared.

Thereafter the slurry was transported to a storage tank equipped with an agitator by a pump.

About 1.5 ton of sponge titanium was manufactured utilizing a reduction apparatus which comprises a reaction vessel constructed of an outer cylindrical vessel of iron and an inner cylindrical vessel of iron, a slurry supply pipe inserted into the reaction vessel through the central portion of a lid thereon, and an electrical heater disposed on the outside of the outer cylindrical vessel, as follows: A 500 kg amount of molten magnesium was charged into the outer cylindrical vessel and heated to a temperature of 8000 C. Thereafter, the titanium tetrachloride slurry was fed through the supply pipe into the reaction vessel at a rate of 8693 g/min (titanium tetrachloride being at 4000 cc/min and magnesium being at 1 773 g/min). The supply of the slurry was complete in about 1 5 hours after the start of the reaction.

The reaction temperature was 10000C and the excess magnesium ratio was 1.35. The rate of manufacturing sponge titanium was 104.7 kg/hr.

Comparative Example 2 By the conventional method, 2200 kg of magnesium, which corresponds to the total amount of magnesium to be necessary for the reaction, was charged into a reaction vessel prior to the reaction and heated to 8000C. Titanium tetrachloride was fed into the reaction vessel at a rate of 2000 to 1000 cc/min for 42 hours and reacted with the magnesium at 10000C to obtain 1 500 kg of sponge titanium. The excess magnesium ratio was 1.47 and the rate of manufacturing sponge titanium was 35.7 kg/hr.

Claims (14)

Claims

1. A method for manufacturing titanium metal which comprises feeding titanium chloride and powdered particles of a reducing metal into a reaction zone, and reacting the titanium chloride and povvdered reducing metal at a temperature above the melting points of the reducing metal and the chloride salt of the reducing metal.

2. A method as claimed in Claim 1, in which the titanium chloride is titanium tetrachloride.

3. A method as claimed in Claim 1, in which the titanium chloride is a mixture of titanium tetrachloride, with titanium trichloride and/or titanium dichloride.

4. A method as claimed in any preceding claim in which the reducing metal is magnesium.

6. A method as claimed in any preceding claim in which the particles of reducing metal have a particle size of 10 Mm to 10 mm.

6. A method as claimed in any preceding claim in which the titanium chloride and the reducing metal are fed into the reaction zone from the upper part of the reaction zone.

7. A method as claimed in any preceding claim in which a portion of the reducing metal is fed into the reaction zone prior to the supply of the titanium chloride and the powdered particles of reducing metal.

8. The method as claimed in any preceding claim in which the titanium chloride and the powdered reducing metal are fed into the reaction zone during a portion of the total reaction period.

9. A method as claimed in any preceding claim in which the titanium chloride and the powdered reducing metal are separately fed into the reaction zone.

1 0. A method as claimed in any oF Claims 1 to 8 in which the titanium chloride and the powdered reducing metal are fed together to the reaction zone after having been mixed.

11. A method as claimed in Claim 10, in which the mixture of titanium chloride the said powdered particles of the reducing metal are fed into the reaction zone during a portion of the total reaction period, with only titanium chloride being fed during the remaining reaction period.

12. A method as claimed in Claim 10 in which the titanium tetrachloride is first contacted with droplets of molten reducing metal to cool and solidify the droplets and to partially reduce the titanium tetrachloride, thereby forming a titanium tetrachloride slurry containing the powdered particles of the reducing metal and a partially reduced titanium product, and subsequently feeding the slurry to the reaction zone.

13. A method as claimed in Claim 12 in which the titanium tetrachloride slurry is fed into the reaction zone from the upper part of the reaction zone.

14. A method as claimed in Claim 12 or Claim 13, in which a portion of the reducing metal is fed into the reaction zone prior to the supply of the titanium tetrachloride slurry.

1 5. A method as claimed in any of Claims 12 to 14 in which the titanium tetrachloride slurry is fed into the reaction zone during a portion of the total reaction period, with only titanium tetrachloride being fed into the zone during the remaining reaction period.

1 6. A method for manufacturing titanium metal substantially as herein specifically described in any one of Examples 1,2 and 3.