Process for the production of crystalline titanium powder

Abstract

The invention provides a process for the production of crystalline titanium powder containing single crystals or agglomerates of single crystals having an average crystal size (by volume) greater than 1 m, said process including reacting a titanium chloride species, preferably titanium dichloride, and reducing metal in a continuous back-mix reactor to produce a free flowing suspension of titanium powder in molten chloride salt wherein: i. both the titanium chloride species and the reducing metal are dissolved in a molten chloride salt and fed to the reactor containing a chloride salt of the reducing metal; ii. the average feed ratio of the titanium chloride species and reducing metal to the continuous back-mix reactor is within 1%, preferably within 0.1%, of the stoichiometric ratio required to fully reduce the titanium chloride salt to titanium metal; iii. the concentration of titanium powder in the fluid suspension of titanium powder in molten salt in the continuous back-mix reactor is between 2 and 23 mass %; and iv. The reducing metal is lithium, sodium, magnesium, or calcium.

Claims

1. A process for the production of crystalline titanium powder containing single crystals or agglomerates of single crystals having an average crystal size (by volume) greater than 1 m, said process including reacting a titanium chloride species, and reducing metal in a continuous back-mix reactor to produce a free flowing suspension of titanium powder in molten chloride salt wherein: i. both the titanium chloride species and the reducing metal are dissolved in a molten chloride salt including suspended titanium powder and fed to the reactor containing a chloride salt of the reducing metal; ii. the average feed ratio of the titanium chloride species and reducing metal to the continuous back-mix reactor is within 1% of the stoichiometric ratio required to fully reduce the titanium chloride salt to titanium metal; iii. the concentration of titanium powder in the fluid suspension of titanium powder in molten salt in the continuous back-mix reactor is between 2 and 23 mass %; and iv. the reducing metal is lithium, sodium, magnesium, or calcium.

2. A process as claimed in claim 1, wherein some molten salt and titanium powder product is withdrawn together from the continuous back-mix reactor and they are separated from each other outside the reactor.

3. A process as claimed in claim 1, wherein the feed of the dissolved titanium chloride species is produced in a separate vessel external to the continuous back-mix reactor.

4. A process as claimed in claim 3, wherein the feed of the dissolved titanium chloride species is produced in a separate vessel external to the continuous back-mix reactor by reacting TiCl.sub.4 with metallic titanium dispersed in molten chloride salt recycled from the continuous back-mix reactor.

5. A process as claimed in claim 1, wherein the reducing metal is pre-dissolved in molten chloride salt prior to feeding to the continuous back-mix reactor.

6. A process as claimed in claim 5, wherein the reducing metal is pre-dissolved in molten chloride salt prior to feeding to the continuous back-mix reactor by recycling molten salt from the continuous back-mix reactor to a vessel where the reducing metal is dissolved in the chloride salt.

7. A process as claimed in claim 1, wherein vessels to produce the dissolved titanium chloride salt and the dissolved reducing metal are electrically isolated from each other and also from the continuous back-mix reactor.

8. A process as claimed in claim 1, wherein the molar concentration of dissolved titanium cations of the titanium chloride salt is less than 25% of the molar concentration of chloride anions in the molten salt feed solution.

9. A process as claimed in claim 8, wherein the molar concentration of dissolved titanium cations of the titanium chloride salt is less than 5% of the molar concentration of chloride anions in the molten salt feed solution.

10. A process as claimed in claim 1, wherein the molar concentration of dissolved reducing metal atoms in the molten chloride salt feed is less than 3.5% of the chloride anions of the molten salt solution.

11. A process as claimed in claim 10, wherein, the molar concentration of dissolved reducing metal atoms in the molten chloride salt feed is less than 0.5% of the chloride anions of the molten salt solution.

12. A process as claimed in claim 1, wherein the feed of dissolved reducing metal to the continuous back-mix reactor is in excess of the stoichiometric requirement to reduce all the titanium sub-chloride in the feed to the continuous back-mix reactor.

13. A process as claimed in claim 1, wherein the temperature of the continuous back-mix reactor is less than 800 C.

14. A process as claimed in claim 13, wherein the temperature of the continuous back-mix reactor is less than 650 C.

15. A process as claimed in claim 1, wherein the residence time in said reactor is expressed as a ratio of the volume of titanium powder inside the continuous back-mix reactor to the volumetric rate of titanium powder produced in the continuous back-mix reactor, and is more than five minutes.

16. A process as claimed in claim 15, wherein the residence time in the reactor is expressed as a ratio of the volume of titanium powder inside the continuous back-mix reactor to the volumetric rate of titanium powder produced in the continuous back-mix reactor, and is more than twenty minutes.

17. A process as claimed in claim 1, wherein there is an excess of dispersed titanium recycled to the vessel producing the dissolved titanium halide species relative to the stoichiometric requirement to fully reduce TiCl.sub.4 feed to titanium dichloride.

18. A process as claimed in claim 1, wherein the titanium chloride species is titanium dichloride.

19. A process as claimed in claim 1, wherein the average feed ratio of the titanium chloride species and reducing metal to the continuous back-mix reactor is within 0.1% of the stoichiometric ratio required to fully reduce the titanium chloride salt to titanium metal.

Description

DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

(1) The invention will now be discussed with reference to the illustrative diagrammatic block diagram which is not intended to limit the scope of the invention.

(2) In the block flow diagram illustrating the titanium synthesis part of the CSIR-Ti process is shown in the figure above. In essence TiCl.sub.4 is continuously reduced in two stages, firstly in a pre-reduction stage TiCl.sub.4 is reacted with Ti to form titanium subchlorides dissolved in molten salt and a final reduction stage where the dissolved titanium subchloride is reacted with dissolved reducing metal to form titanium. The final reactor is operated as a CSTR. The final reactor can also be classified as a reactive crystallizer since the two dissolved reactants react rapidly in the reactor to form insoluble titanium particles.

(3) Three streams exit the reactor. The first stream is passed to a reducing metal dissolution vessel where the reducing metal to be used is dissolved in the stream before recycling it to the final subchloride reduction reactor. Another stream containing part of the suspended titanium particles are passed to first stage TiCl.sub.4 reduction reactor to partially reduce the TiCl.sub.4 feed to the process. The final stream is quenched as it is removed from the reactor and then passed to downstream processes to separate the titanium product from the salt and to recover the salt (not shown).

(4) The process is believed to overcome or reduce some or all of the following problems: Blocking of TiCl.sub.4 feed lines Formation of titanium lumps on the reactor internals. Growth of primary titanium particles that are on average larger than 5 micron. Smaller particles are not ideally suitable for powder metallurgy and the relative size of the passivating oxygen layer equates to high levels of oxygen contamination. Sintering of titanium particles. Chloride levels are of significant importance in downstream processing; sintering may encapsulate salt and make the powder non-viable in many applications. Corrosion of reactor internals. Salt evaporation. Evaporation of reducing metal.