Specialized metallurgical processes – compositions for use therei – Processes – Producing or purifying free metal powder or producing or...
Patent
1993-10-22
1995-03-14
Rosenberg, Peter D.
Specialized metallurgical processes, compositions for use therei
Processes
Producing or purifying free metal powder or producing or...
75617, 75619, C22B 500
Patent
active
053973755
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a process for the production of metallic titanium and intermediates useful in the processing of ilmenite and related minerals.
Australia is the major world producer of ilmenite which is exported for about A $75 per tonne. The cost of metallic titanium in ingot form is about A$20,000 per tonne. In a more refined form, for example, as the titaniumbased alloy from which jet engine fan blades are fabricated, the value of metallic titanium is very much greater. Metallic titanium is, by comparison with most other metals and alloys, very resistant to chemical corrosion and is in great demand in the manufacture of chemical plants and for heat-exchangers and other units in power plants. Another important application is the use of metallic titanium in surgical and dental implants and supports. an a strength-for-weight basis, metallic titanium is stronger than steel and is widely used in the construction of supersonic military aircraft. A cheaper manufacturing route to the production of titanium would make feasible its use in civil aircraft to replace aluminium alloys which have proved to be subject to fatigue failure. This is one of the many applications in which the light, strong and non-corrosive metallic titanium would find wide commercial usage, if available more cheaply than from current processes.
Currently, metallic titanium is produced commercially by two closely related processes. Titanium tetrachloride (TiCl.sub.14) is reduced by either metallic sodium (Na) or magnesium (Mg). Each process yields an initial material called "titanium sponge" which may contain 10 to 20% of sodium chloride (NaCl) or magnesium chloride (MgCl.sub.2) as products of the initial reaction. To avoid inclusion in the sponge of chlorides of titanium in lower oxidation states (e.g. TiCl.sub.2 or TiCl.sub.3), excess reducing metal (Na or Mg) is also in the sponge. Both methods of production are batch processes and the sponge, on solidification after reaction, must be removed from the reactor manually. It is reported that jack-hammers and even explosives are used. The sponge is then purified at least three times by vacuum arc-melting. The processes are both labour and energy intensive.
We have now found that a flee-flowing powder of metallic titanium can be produced by employing a process which is similar to conventional aluminium smelting.
According to the present invention there is provided a process for the production of metallic titanium, characterized in that the process comprises reducing a titanium-fluorine compound selected from titanium tetrafluoride and any hexafluorotitanate soluble in a molten fluoroaluminate, with metallic aluminium in a molten fluoroaluminate.
The preferred titanium-fluorine compound is an alkali hexafluorotitanate, more preferably, sodium hexafluorotitanate (Na.sub.2 TiF.sub.6) or potassium hexafluorotitanate (K.sub.2 TiF.sub.6).
Preferably the molten fluoroaluminate is a hexafluoroaluminate, more preferably, cryolite (Na.sub.3 AlF.sub.6).
In one particular embodiment of the invention, sodium hexafluorotitanate (Na.sub.2 TiF.sub.6) or potassium hexafluorotitanate (K.sub.2 TiF.sub.6) is dissolved in cryolite (Na.sub.3 AlF.sub.6) at about 1000.degree. to 1100.degree. C. and metallic aluminium (Al) is added. Aluminium is chosen as the reductant because it is compatible with the melt, being oxidized in the first instance to aluminium fluoride (AlF.sub.3) and then interacting with sodium fluoride (NaF) to form cryolite (Na.sub.3 AlF.sub.6). In addition, aluminium is much less energy-intensive and cheaper to produce than sodium or magnesium reductants used in the current processes.
Recovery of metallic titanium is achieved as a consequence of the relative densities of the reactants and the molten medium. Aluminium is less dense than cryolite which, in turn, is less dense than metallic titanium. Therefore, metallic titanium has a tendency to collect at the bottom of the reaction bath and may be tapped from that position with molten cryolite.
The overall reaction for the reduction of Na.su
REFERENCES:
patent: 2647826 (1953-08-01), Jordan
patent: 2986462 (1961-05-01), Wright
patent: 3825415 (1974-07-01), Johnston
patent: 3847596 (1974-11-01), Holland
Besida John
O'Donnell Thomas A.
Pong Tersesa K. H.
Wood David G.
Rosenberg Peter D.
The University of Melbourne
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