METHOD FOR PREPARING A TITANIUM-ALUMINUM ALLOY

Abstract

The present invention belongs to the field of titanium metallurgy, and particularly relates to a method for preparing a titanium-aluminum alloy. The technical problem to be solved by the present invention is to provide a method for preparing a titanium-aluminum alloy, including the following steps: a. adding TiCl.sub.4 and AlCl.sub.3 to a molten electrolyte in a protective atmosphere, wherein the molten electrolyte is a mixture of at least one of alkali metal chloride or alkaline earth metal chloride and alkali metal fluoride; b. electrolyzing the mixture obtained in step a; and c. obtaining a titanium-aluminum alloy through vacuum distillation of a cathode product after electrolysis. The method of the present invention can shorten the preparation process of a titanium-aluminum alloy and reduce the manufacturing cost thereof, which is of great significance to the development of titanium alloy in practice.

Claims

1. A method for preparing a titanium-aluminum alloy, comprising the following steps: a. adding TiCl.sub.4 and AlCl.sub.3 to a molten electrolyte in a protective atmosphere, wherein the molten electrolyte is a mixture of at least one of an alkali metal chloride or an alkaline earth metal chloride and an alkali metal fluoride; b. electrolyzing the mixture obtained in step a; and c. obtaining a titanium-aluminum alloy through vacuum distillation of a cathode product after electrolysis.

2. The method for preparing a titanium-aluminum alloy according to claim 1, wherein the alkali metal chloride is at least one of LiCl, NaCl, KCl, RbCl or CsCl, and the alkaline earth metal chloride is at least one of BeCl.sub.2, MgCl.sub.2, CaCl.sub.2, BaCl.sub.2 or SrCl.sub.2 in step a.

3. The method for preparing a titanium-aluminum alloy according to claim 1, wherein at least one of the alkali metal chloride or the alkaline earth metal chloride is any one of NaCl—KCl, LiCl—KCl or CaCl.sub.2—NaCl in step a.

4. The method for preparing a titanium-aluminum alloy according to claim 1, wherein the alkali metal fluoride is at least one of LiF, NaF, KF, RbF or CsF in step a.

5. The method for preparing a titanium-aluminum alloy according to claim 1, wherein the alkali metal fluoride is NaF or KF in step a.

6. The method for preparing a titanium-aluminum alloy according to claim 1, wherein an amount of the alkali metal fluoride added is 10-90 wt % of the electrolyte in step a.

7. The method for preparing a titanium-aluminum alloy according to claim 1, wherein an amount of the alkali metal fluoride added is at least 6 times as much as a molar sum of Ti and Al in TiCl.sub.4 and AlCl.sub.3 in step a.

8. The method for preparing a titanium-aluminum alloy according to claim 1, wherein the protective atmosphere is any one of argon, helium or neon in step a.

9. The method for preparing a titanium-aluminum alloy according to claim 1, wherein the protective atmosphere is argon in step a.

10. The method for preparing a titanium-aluminum alloy according to claim 1, wherein an anode of the electrolyte is graphite, and a cathode thereof is a conductive metal in step b.

11. The method for preparing a titanium-aluminum alloy according to claim 10, wherein the conductive metal is a material that is not alloyed with titanium or aluminum and has a melting point higher than that of the electrolyte in step b.

12. The method for preparing a titanium-aluminum alloy according to claim 10, wherein the conductive metal is titanium-aluminum alloy or carbon steel in step b.

13. The method for preparing a titanium-aluminum alloy according to claim 1, wherein an electrolysis temperature is higher than a melting point of the electrolyte in step b.

14. The method for preparing a titanium-aluminum alloy according to claim 13, wherein the electrolysis temperature is 50-200° C. higher than the melting point of the electrolyte in step b.

15. The method for preparing a titanium-aluminum alloy according to claim 1, wherein an electrolysis voltage is 3.1-3.2 V in step b.

16. The method for preparing a titanium-aluminum alloy according to claim 1, wherein a temperature of the vacuum distillation is higher than a melting point of a substance with a highest melting point in the electrolyte, a vacuum degree of the vacuum distillation is less than 0.1 Pa, and an end point of the vacuum distillation is continuously stable in vacuum for more than 5 h in step c.

Description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] The present invention provides a method for preparing a titanium-aluminum alloy, comprising the following steps:

[0026] (1) A mixture of TiCl.sub.4 and AlCl.sub.3 is directly introduced into a molten electrolyte system of alkali metal chloride or alkaline earth metal chloride and alkali metal fluoride in a protective atmosphere (the temperature of the molten electrolyte is higher than the melting point thereof, and preferably is 50-200° C. higher than the melting point thereof), wherein TiCl.sub.4 and AlCl.sub.3 react with alkali metal fluoride in the molten electrolyte, as shown in formula (1).

TiCl.sub.4/AlCl.sub.3+MF.fwdarw.M.sub.2TiF.sub.6/M.sub.3AlF.sub.6+MCl  (1)

[0027] (2) An electrolysis step is carried out by taking graphite as the anode and conductive metal as the cathode, wherein alkali metal fluorotitanate and alkali metal fluoroaluminate produced by the reaction of formula (1) react in the electrolysis process, as shown in formula (2).

M.sub.2TiCl.sub.4 M.sub.2AlCl.sub.3+MCl.fwdarw.Ti−Al+Cl.sub.2(g)+MF  (2)

[0028] (3) After the electrolysis, the cathode product is transferred to a vacuum furnace where the electrolyte is removed by distillation at high temperature and the vacuum degree is controlled to be less than 0.1 Pa.

[0029] Further, the ratio of TiCl.sub.4 to AlCl.sub.3 depends on a molar ratio according to the requirements for the titanium-aluminum alloy.

[0030] Further, the amount of alkali metal fluoride added should be sufficient to form fluorotitanate/fluoroaluminate. Preferably, the amount of alkali metal fluoride added is at least 6 times as much as the molar sum of Ti and Al in TiCl.sub.4 and AlCl.sub.3.

[0031] Further, the electrolysis temperature mainly depends on the melting point of the electrolyte, and varies with electrolytes. In most cases, the electrolysis temperature should be 50-200° C. higher than the melting point of molten salt. If the electrolysis temperature is too high, the electrolyte will become more volatile, resulting in a high loss. The electrolysis step proceeds at constant voltage to ensure that titanium and aluminum can be precipitated at the same time. Only metallic titanium is precipitated at low voltage, and alkali metal or alkaline earth metal may be precipitated at high voltage. So, the electrode voltage is preferably 3.1-3.2 V.

[0032] Further, after electrolysis, the cathode product of titanium-aluminum alloy entrains a large amount of electrolytes, including electrolyte components as well as newly generated alkali metal fluorotitanate and alkali metal fluoroaluminate with low solubility in an aqueous solution. Thus, the required titanium-aluminum alloy can be obtained by distillation. Due to high melting points of alkali metal fluorotitanate and alkali metal fluoroaluminate, the distillation temperature should be higher than their melting points.

[0033] According to the method of the present invention, the cathode product is a titanium-aluminum alloy, the anode product is chlorine, and the by-product is alkali metal fluoride after electrolysis. Therefore, the essence of the preparation method lies in directly preparing a titanium-aluminum alloy from TiCl.sub.4 and AlCl.sub.3.

Embodiment 1

[0034] Adding a certain amount of NaCl and KCl in an equal molar ratio to a reaction vessel, adding NaF (accounting for 20 wt % of the total electrolyte), dehydrating in vacuum at 300° C. for 5 h, then heating to 750° C. in an argon atmosphere to melt the electrolyte. Slowly adding TiCl.sub.4 and AlCl.sub.3 with a mass ratio of 4:1 to the molten salt via a charging pipe, wherein the amount of TiCl.sub.4 and AlCl.sub.3 added was stoichiometrically calculated as per formula (1). Proceeding to the electrolysis step at a controlled voltage of 3.2 V by taking a graphite rod as the anode and a carbon steel rod as the cathode. After electrolysis, transferring the cathode product to a vacuum furnace, distilling for 6 h at the vacuum degree controlled to be less than 0.1 Pa and temperature of 1100° C., cooling and taking out the product. The ICP analysis revealed that the content of Ti and Al in the product was 82.4 wt % and 16.6% respectively, close to 83.3 wt % and 16.7% when added. The product contained about 1% of impurities, mainly partial oxidation of the product and trace metal impurity elements. So, a titanium-aluminum alloy with this ratio was obtained.

Embodiment 2

[0035] Adding a certain amount of NaCl and CaCl.sub.2 in an equal molar ratio to a reaction vessel, adding KF (accounting for 30 wt % of the total electrolyte), dehydrating in vacuum at 300° C. for 5 h, then heating to 850° C. in a helium atmosphere to melt the electrolyte. Slowly adding TiCl.sub.4 and AlCl.sub.3 with a mass ratio of 1:1 to the molten salt via a charging pipe, wherein the amount of TiCl.sub.4 and AlCl.sub.3 added was stoichiometrically calculated as per formula (1). Proceeding to the electrolysis step at a controlled voltage of 3.1 V by taking a graphite rod as the anode and a carbon steel rod as the cathode, wherein the initial current density of cathode and anode was 0.2 A/cm.sup.2 and 0.25 A/cm.sup.2, respectively. After electrolysis, transferring the cathode product to a vacuum furnace, distilling for 6 h at the vacuum degree controlled to be less than 0.1 Pa and temperature of 1300° C., cooling and taking out the product. The ICP analysis revealed that the content of Ti and Al in the product was 52.7 wt % and 47.0%, respectively, close to 56.0 wt % and 44.0% when added. The product contained about 0.3% of impurities, mainly partial oxidation of the product and trace metal impurity elements. So, a titanium-aluminum alloy with this ratio was obtained.