METHOD OF PRODUCING METAL

Abstract

A method of producing a non-metallic feedstock powder suitable for reduction to metal comprises the steps of combining a liquid with solid metal oxide particles to form a mixture, subjecting the mixture to high-shear mixing to form a liquid suspension of metal oxide and the liquid, and drying the liquid suspension using a fluidised-bed spray-granulation process to grow a plurality particles to form the non-metallic feedstock powder. The method allows feedstock powders to be grown to desired particle sizes. The method allows production of feedstock powders having controlled compositions.

Claims

1. A method of producing a non-metallic feedstock powder suitable for reduction to metal comprising the steps of; combining a liquid with solid metal oxide particles to form a mixture, subjecting the mixture to high-shear mixing to form a liquid suspension of metal oxide and the liquid, and drying the liquid suspension using a fluidised-bed spray-granulation process to grow a plurality particles to form the non-metallic feedstock powder.

2. The method according to claim 1, in which, the step of drying the liquid suspension comprises the further steps of, spraying a portion of the liquid suspension into a heated chamber of a fluidised-bed spray-granulation apparatus such that liquid is removed from individual droplets of the suspension to form a plurality of seed particles, maintaining the plurality of seed particles within the heated chamber by means of a fluidising gas stream, and spraying further portions of the liquid suspension into the heated chamber, droplets of the liquid suspension successively adsorbing to and drying on the plurality of seed particles, thereby growing particles to form the non-metallic feedstock powder.

3. The method according to claim 1, in which the liquid comprises water and an organic binder, for example in which the binder is an aqueous solution of polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), or hydroxyyethylcellulose (HEC).

4. The method according to claim 1, for producing a non-metallic feedstock powder suitable for reduction to a metallic alloy, in which a first set of metal oxide particles and a second set of metal oxide particles are combined with the liquid to form the mixture, the first set of metal oxide particles having a different composition to the second set of metal oxide particles.

5. The method according to claim 4, in which the first set of metal oxide particles and the second set of metal oxide particles have a different mean particle size, for example in which the first set of metal oxide particles and the second set of metal oxide particles have mean particle sizes that differ by greater than a factor of 2, or greater than a factor of 10, or by greater than a factor of 100.

6. The method according to claim 4, comprising three or more sets of metal oxide particles, each of the three or more sets having a different composition.

7. The method according to claim 1, in which the process of forming the feedstock powder is controlled such that the feedstock powder has a predetermined mean particle diameter.

8. The method according to claim 7, in which the predetermined mean particle diameter is between 10 micrometres and 10 millimetres, for example between 50 micrometres and 5 millimetres, for example between 50 micrometres and 200 micrometres.

9. The method according to claim 1, in which the process of forming the feedstock powder is controlled such that the feedstock powder has a particle size distribution of less than 100 micrometres between a D10 diameter and a D90 diameter, for example a particle size distribution of 50 micrometres or less.

10. The method according to claim 1, in which high-shear mixing is performed using a rotor rotating in excess of 5000 rpm, for example in excess of 6000 rpm, for example about 6500 rpm.

11. The method according to claim 1, in which the sum of all metal oxide particles combined with the liquid to form the mixture make up between 50 weight % and 70 weight % of the mixture.

12. The method according to claim 1, in which the process of forming in which forming the feedstock powder comprises the step of heat treating the plurality of feedstock particles to impart mechanical strength and/or chemical homogeneity to each particle, for example heat treating at a temperature of greater than 900 C., for example between about 1000 C. and 1400 C.

13. A method of producing metal comprising the steps of; forming a non-metallic feedstock using a method as defined in claim 1, and reducing the non-metallic feedstock powder to form the metal.

14. The method according to claim 13, in which the reduction of the non-metallic feedstock powder is effected by electrolytic reduction of the feedstock powder in contact with a molten salt, for example by the FFC process.

15. The method according to claim 13, in which the metal produced is a titanium-aluminium-vanadium alloy, particles of titanium oxide, aluminium oxide, and vanadium oxide being combined with the liquid to form the mixture, or in which the metal produced is a titanium-aluminium-niobium-chromium intermetallic, particles of titanium oxide, aluminium oxide, niobium oxide and chromium oxide being combined with the liquid to form the mixture, or in which the metal produced is a titanium-tantalum alloy, particles of titanium oxide and tantalum oxide being combined with the liquid to form the mixture, or in which the metal produced is a tantalum-tungsten alloy, particles of tantalum oxide and tungsten oxide being combined with the liquid to form the mixture, or in which the metal produced is a tantalum-aluminium alloy, particles of tantalum oxide and aluminium oxide being combined with the liquid to form the mixture.

16-19. (canceled)

20. A feedstock powder suitable for reduction to a metal, the feedstock powder being formed by a method as defined in claim 1, in which the feedstock powder consists of substantially spherical particles having a mean particle diameter of between 20 micrometres and 2000 micrometres, for example between 50 micrometres and 500 micrometres.

21. The feedstock powder according to claim 20, that is suitable for reduction to form a metallic alloy, for example a metallic alloy powder.

22. The feedstock powder according to claim 21, in which each non-metallic particle is a solid solution mixed oxide.

23. The feedstock powder according to claim 20, that is suitable for reduction to a TiAlV alloy, the feedstock powder comprising Titanium, Aluminium, Vanadium, and Oxygen.

24. The feedstock powder according to claim 20, that is suitable for reduction to a TiAlNbCr alloy, the feedstock powder comprising Titanium, Aluminium, Chromium, Niobium, and Oxygen, or a feedstock powder according to claim 20, that is suitable for reduction to a TiTa alloy, the feedstock powder comprising Titanium, Tantalum, and Oxygen, or a feedstock powder according to claim 20, that is suitable for reduction to a TaAl alloy, the feedstock powder comprising Tantalum, Aluminium, and Oxygen, or a feedstock powder according to claim 20, that is suitable for reduction to a TaW alloy, the feedstock powder comprising Tantalum, Tungsten, and Oxygen.

Description

SPECIFIC EMBODIMENTS OF THE INVENTION

[0060] Specific embodiments of one or more aspects of the invention will now be described with reference to figures in which;

[0061] FIG. 1 is a schematic diagram illustrating a high-shear mixing apparatus suitable for use in an embodiment of the invention,

[0062] FIG. 2 is a schematic diagram illustrating a fluidised-bed spray-granulation apparatus that may be used in embodiments of the invention,

[0063] FIG. 3 is a schematic diagram illustrating the formation of feedstock powder particles using a spray-granulation process,

[0064] FIG. 4 is a micrograph illustrating particles of a feedstock powder formed using an embodiment of the invention,

[0065] FIG. 5 is an electron micrograph of a portion of the powder of FIG. 4,

[0066] FIGS. 6, 7 and 8 are energy dispersive x-ray spectroscopy (EDS) element maps showing the distribution of aluminium (FIG. 6), vanadium (FIG. 7), and titanium (FIG. 8) over the area depicted in the micrograph of FIG. 5,

[0067] FIG. 9 is a schematic diagram illustrating an electrolysis apparatus arranged to reduce a feedstock powder according to an embodiment of the invention,

[0068] FIG. 10 is a schematic cross-sectional view illustrating additional detail of the cathode structure of the electrolysis apparatus of FIG. 9,

[0069] FIG. 11 is a plan view of the cathode illustrated in FIG. 10, and

[0070] FIG. 12 is a SEM micrograph of a TiAlV alloy powder particle produced by reducing the feedstock powder of FIG. 4.

[0071] The invention relates to a method of forming a feedstock powder suitable for reduction to metal. The invention also relates to a feedstock powder formed by the method and to a method of producing metal comprising the step of reducing a feedstock powder formed by the method. The method of forming the feedstock powder includes steps of combining a liquid and metal oxide particles to form a mixture, the mixture preferably having an oxide proportion of between 50% and 70% by weight, subjecting that mixture to high-shear mixing to form a liquid suspension, and drying the liquid suspension using a fluidised-bed spray-granulation process. The process is of high-shear mixing and fluidised-bed spray-granulation and will now be discussed in general terms.

[0072] FIG. 1 is a schematic illustration of a high-shear mixing apparatus 10 that may be suitable for forming the liquid suspension in embodiments of the invention. The high-shear mixing apparatus 10 comprises a tank 11 containing a mixture of liquid and metal oxide particles 12. A high-shear mixer 20 is arranged in contact with the liquid mixture 12. The high-shear mixer includes a motor 21, a connecting shaft 22, a rotor 23 and a stator 24. The rotor 23 is separated from the stator 24 by a narrow gap 25. In use, the motor 21 causes the rotor 23 to rotate at speeds of typically between 5000 rpm and 10000 rpm. As the rotor rotates the stator remains static and the differences in velocity of the liquid in the region of the rotor and the stator result in high-shear within the liquid.

[0073] Typically the liquid mixture 12 consists of an aqueous solution of a binder, such as polyvinyl alcohol (PVA), and a proportion of metal oxide particles. The high-shear forces set up in the liquid mixture 12 cause milling of the metal oxide particles. Various parameters may be altered to influence the final particle size of the milled oxide. For example, parameters such as rotational speed of the rotor 23, distance of the gap 25 between the rotor and the stator, and proportion of metal oxide to liquid in the liquid mixture 12, as well as mixing time, may all be varied to influence the particle size of the metal oxide resulting from the high-shear mixing process. The high-shear mixing forms a suspension of finely milled metal oxide particles in a liquid, for example, an aqueous solution of PVA.

[0074] A range of suitable high-shear mixers or batch mixers are known and commercially available. For example, IKA manufacture a wide range of batch mixers for forming suspensions of pharmaceutical products. These high-shear mixers may be suitable for use in embodiments of the present invention.

[0075] FIG. 2 is a schematic illustration of a fluidised-bed spray-granulation apparatus 30. The apparatus includes a heated chamber through which an upwardly directed stream of hot air 32 is passed. A nozzle 33 allows droplets of a liquid suspension 34 to be injected into the heated chamber 31. The droplets of the liquid suspension 34 may be supplied directly from a high-shear mixing apparatus 10 or may be transferred to a separate holding tank prior to injection. Once in the heated chamber 31 the droplets of liquid suspension 34 are dried and form solid particles 35. These solid particles 35 are maintained within the heated chamber 31 by the fluidising action of the heated airstream 32. As further droplets of liquid suspension 34 are injected into the heated chamber 31 they adsorb to existing particles 35 and dry, thereby increasing the diameter of the particles 35. As the particles grow, they eventually reach a mass that is too great for them to remain in a fluidised state within the chamber. Once the particles reach this diameter they drop towards the bottom of the chamber and are collected.

[0076] The size, shape, and mass of the collected particles 36 and the size distribution of the collected particles 36 can be influenced by controlling parameters such as oxide loading of the liquid suspension, injection pressure and initial droplet size, and flow rate of the fluidising airflow.

[0077] The use of spray-granulation technology enables a large degree of flexibility in controlling particle sizes and particle size distributions. Through control and optimisation of the process parameters, particle sizes within a range of 10 micrometres to 10 millimetres may be achieved. The system has the advantage that any undersize particles that have passed through the spray-granulator may be returned to the heated chamber 31 for further growth. Furthermore, any oversize particles may be returned to the high-shear mixer. Thus, process yields should comfortably exceed 90%, and preferably exceed 95%, or exceed 98%.

[0078] FIG. 3 is an illustration depicting the growth of particles within a fluidised-bed spray-granulation apparatus. Droplets of the liquid suspension 34, once injected into the heated chamber of the spray-granulation apparatus, swiftly dry to form small seed particles 35. As discussed in relation to FIG. 2, these seed particles 35 are fluidised by a stream of heated air. Subsequent droplets of the liquid suspension 37 adsorb to the surface of the seed particles 35. These additional liquid droplets swiftly coat the surface of the seed particle and dry to add a layer of thickness to the seed particle. Over a period of time, more and more droplets adsorb to the surface of the fluidised particles and form a layered, onion-like, particle 36. FIG. 3 illustrates a cutaway of a fully formed particle 36 showing the layered structure.

[0079] Once the particles have reached the predetermined particle size they are collected from the spray-granulation apparatus. It is then preferable that the particles are heat treated in order to drive off any remaining binder from the particles and to provide some mechanical stability. A heat treatment may also have the result that the composition of the particles is homogenised. Thus, the collected particles 36 may be subjected to a heat treatment regime. The heat treatment may be a two-step regime comprising, for example, heating to 500 C. and holding for a period of time followed by heating to 1000 C. and holding for a further period of time.

[0080] After the particles have been collected and, if required, heat treated, the feedstock powder may be reduced to form metal. Preferably the feedstock powder is directly reduced in powder form to produce a metallic powder. It may be desirable, however, to form the feedstock powder into a preform shape or pellet prior to reduction to metal.

[0081] FIG. 9 illustrates an electrolysis apparatus 110 configured for use in performing a reduction of a feedstock powder. The apparatus comprises a stainless steel cathode 120 and a carbon anode 130 situated within a housing 140 of an electrolysis cell. The anode 130 is disposed above, and spatially separated from, the cathode 120. In certain embodiments the housing 140 may contain 500 kg of a calcium chloride based molten salt electrolyte 150, the electrolyte comprising CaCl.sub.2 and 0.4 wt % CaO. Both the anode 130 and the cathode 120 are arranged in contact with the molten salt 150. Both the anode 130 and the cathode 120 are coupled to a power supply 160 so that a potential can be applied between the cathode and the anode.

[0082] The cathode 120 and the anode 130 are both substantially horizontally oriented, with an upper surface of the cathode 120 facing towards a lower surface of the anode 130.

[0083] The cathode 120 incorporates a rim 170 that extends upwards from a perimeter of the cathode and acts as a retaining barrier for a feedstock powder 190 supported on an upper surface of the cathode. The rim 170 is integral with, and formed from the same material as, the cathode. In other embodiments, the rim may be formed from a different material to the cathode, for example from an electrically insulating material.

[0084] The structure of the cathode may be seen in more detail in FIG. 10 and FIG. 11. The rim 170 is in the form of a hoop having a diameter of 30 cm. A first supporting cross-member 175 extends across a diameter of the rim. The cathode also comprises a mesh-supporting member 171, which is in the form of a hoop having the same diameter as the rim 170. The mesh-supporting member has a second supporting cross-member 176 of the same dimensions as the supporting cross-member 175 on the rim 170. A mesh 180 is supported by being sandwiched between the rim 170 and the mesh-supporting member 171 (the mesh 180 is shown as the dotted line in FIG. 10). The mesh 180 comprises a stainless steel cloth of mesh-size 100 that is held in tension by the rim 170 and the mesh-supporting member. The cross-member 175 is disposed against a lower surface of the mesh 180 and acts to support the mesh. An upper surface of the mesh 180 acts as the upper surface of the cathode.

[0085] The stainless steel cloth forming the mesh 180 is fabricated from 30 micrometre thick wires of 304 grade stainless steel that have been woven to form a cloth having square holes with a 150 micrometre aperture. The mesh size may be varied and should, in general, be of smaller diameter than the mean particle diameter of the feedstock powder that is being reduced. The mesh 180, cross-member 175 and rim 170 that form the cathode are all electrically conductive. In other embodiments, the mesh may be the only electrically conductive component of the cathode.

[0086] In use, the feedstock powder may be reduced by applying a potential between the cathode 120 and the anode 130 sufficient to remove oxygen from the feedstock powder 190. The metallic powder products remaining after reduction can be removed and washed to separate the metallic powder from any remaining salt.

EXAMPLE 1

[0087] As a specific example, a TiAlV alloy was formed using various aspects of the invention disclosed herein. The initial starting oxide powders used to form the feedstock powder for reduction were TiO.sub.2, Al.sub.2O.sub.3 and V.sub.2O.sub.5. The TiO.sub.2 oxide powder had a mean particle size of 1.2 microns. The Al.sub.2O.sub.3 oxide powder had a mean particle size of 8.2 micrometres. The V.sub.2O.sub.5 powder had a mean particle size of 97.7 micrometres. It would be extremely difficult to combine these three oxide powders in a suitable ratio to form an alloy containing low proportions of Al and V, for example a Ti-6Al-4V alloy powder, due to the large disparity between the initial particle sizes of the starting oxides. While large pellets having a desirable ratio of the oxides may be formed, it is clear that the short range composition is unlikely to proximate that required to form a Ti-6Al-4V alloy.

[0088] A total of 4800 grams of mixed oxide powder was used. Of this 4800 grams, 4195 grams was TiO.sub.2, 402 grams was Al.sub.2O.sub.3, and 203 grams V.sub.2O.sub.5. This corresponds to a proportion of metallic elements of 88.5% Ti, 7.5% Al, and 4% V. This feedstock was produced as an initial proof of concept. An oxide feedstock powder of this composition was expected to produce, upon reduction by the FFC process, an alloy of composition approximating Ti-6Al-4V. It is noted that the proportion of aluminium in the feedstock powder was deliberately increased above 6% in order to account for losses of aluminium during the reduction process.

[0089] The oxide powder was mixed with a liquid to form a slurry having 59.5% solid oxide. The liquid consisted of an aqueous solution of demineralised water and PVA. The proportion of PVA was dependent on the total oxide loading. Thus, the proportion of PVA was 2.5 wt % with respect to the total oxide loading. The liquid mixture was then subjected to high-shear mixing for 15 minutes at a rotation speed of 6500 rpm. Shear-mixing was achieved using an IKA dispersion mixer model no. G45M.

[0090] After shear-mixing the liquid and oxide mixture had formed a suspension of milled oxide particles in the liquid/binder. The particle size of the oxides had been substantially homogenised, with the oxide particles in the suspension having diameters in the region of 2 micrometres or less. This liquid suspension was then subjected to a fluidised-bed spray-granulation process to produce solid oxide particles. A Glatt Procell Labsystem spray-granulator was used to form the metal oxide particles. Process parameters were set such that the fluidising airflow through the apparatus was 150 m.sup.3 per hour, the air temperature was 120 C. The liquid suspension was sprayed into the chamber at a spraying pressure of 3 bar and a spray rate of 57 grams per minute. These parameters were selected to provide a mean product particle size within the range of 100 and 200 micrometres.

[0091] After spray-granulation the collected oxide particles were heat treated. Heat treatment was carried out in order to remove organic components of the PVA binder and to impart mechanical strength to each individual powder particle.

[0092] The heat treatment schedule also homogenised the composition of each particle forming a solid solution of the metal oxide mixture.

[0093] In order to heat treat the oxide particles produced by spray granulation they were heated to a temperature of 550 C. at a rate of 3 C. per minute in an electrically heated furnace. The particles were maintained at this temperature for a period of 1 hour to remove traces of the organic binder. The particles were then heated to 1000 C. at 3 C. per minute and held at that temperature for a further 2 hours before cooling to room temperature. The resulting feedstock powder is illustrated in FIG. 4.

[0094] FIG. 4 illustrates a feedstock powder for reduction to form a TiAlV powder. The feedstock powder was analysed using a Malvern Mastersizer 2000 and found to comprise a plurality of feedstock particles having a mean particle diameter of about 160 micrometres. The D10 particle size is 119 micrometres and the D90 particle size is 225 micrometres. The feedstock powder is substantially spherical and has a mixed oxide composition comprising titanium, aluminium and vanadium.

[0095] A portion of the feedstock powder was mounted and polished. FIG. 5 illustrates an SEM micrograph of the powder. The powder particles can be seen to be substantially the same size and relatively porous. The porosity of the powder may enhance the reduction of the powder using molten salt reduction processes.

[0096] An analysis of the distribution of aluminium, vanadium and titanium was carried out using elemental X-ray mapping in the scanning electron microscope (SEM). FIG. 6 illustrates the distribution of aluminium within the sample of FIG. 5, FIG. 7 illustrates the distribution of vanadium in the same sample, and FIG. 8 illustrates the distribution of titanium in the same sample. While the distribution of aluminium in FIG. 6 is not clear, possibly due to the lower atomic weight of aluminium, it can be seen that the distribution of vanadium and titanium appears to be homogenous within the particles. That is, there are no vanadium rich or vanadium deficient regions in the particles illustrated in FIG. 5. Given that the initial vanadium particle size was approximately 100 micrometers it can be seen that the steps of high-shear mixing followed by spray-granulation have produced homogenous feedstock powder particles of mean particle size in the region of 160 micrometres, having the desired elemental distribution.

[0097] The feedstock powder was reduced to a metallic alloy powder using apparatus of the type discussed above in relation to FIG. 9. Approximately 20 grams of the feedstock powder was arranged on the upper surface of the cathode 20 and in contact with the molten salt 150. The feedstock powder 190 was supported by the mesh 180 of the cathode. The depth of the feedstock powder 190 was approximately 1 centimetre.

[0098] The molten salt 50 (CaCl.sub.2 and 0.4 wt % CaO) was maintained at a temperature of 950 C. and a potential was applied between the anode and the cathode. Thermal currents and gas lift deflects generated by buoyancy of gases generated at the anode (predominantly CO and CO.sub.2) cause the molten salt to circulate within the cell and generate a flow of molten salt through the bed of feedstock powder. The cell was operated in constant current mode, at a current of 5 amps for a period of 16 hours. After this time the cell was cooled and the cathode was removed and washed to free salt from the reduced feedstock powder.

[0099] The reduced feedstock powder was removed from the cathode as a friable lump of metallic alloy powder particles. The lumps were crushed in an agate pestle and mortar and the material separated out into individual powder particles. These particles were then dried and analysed. Analysis revealed the powder particles to be a homogenous titanium alloy having a composition of approximately Ti-6Al-6V. FIG. 12 is a SEM micrograph showing one of the metallic powder particles. This initial trial shows that, by varying the oxide ratios or species used to form the feedstock, common commercial alloys such as Ti-6Al-4V or Ti-6Al-6V-2Sn can be produced using embodiments of this invention.

EXAMPLE 2

[0100] As a further specific example, a titanium-aluminide intermetallic (TiAlNbCr intermetallic) was formed using various aspects of the invention disclosed herein. The initial starting oxide powders used to form the feedstock powder for reduction were TiO.sub.2, Al.sub.2O.sub.3, Nb.sub.2O.sub.5 and Cr.sub.2O.sub.3. The TiO.sub.2 oxide powder had a mean particle size of 1.2 microns. The Al.sub.2O.sub.3 oxide powder had a mean particle size of 8.2 micrometres. The Nb.sub.2O.sub.5 powder had a mean particle size of 0.5-2 micrometres, and the Cr.sub.2O.sub.3 powder had a mean particle size of 1-5 micrometres.

[0101] A total of 5000 grams of mixed oxide powder was used. Of this total, 2861.4 grams was TiO.sub.2, 1826.7 grams was Al.sub.2O.sub.3, 198.4 grams was Nb.sub.2O.sub.5, and 113.5 grams was Cr.sub.2O.sub.3.

[0102] The oxide powder was mixed with an aqueous solution of demineralised water and PVA to form a slurry having 59.5% solid oxide. The slurry was then subjected to high-shear mixing and spray granulation as described in relation to Example 1. The spray granulation parameters were selected to provide a particle size distribution within the range of 100 and 250 micrometres. The product of spray granulation was a free-flowing powder of grey-greenish granules.

[0103] After spray-granulation the collected oxide particles were heat treated to form a feedstock powder as described above in relation to Example 1. The feedstock powder was then reduced using the reduction process described in relation to Example 1. The reduced powder was then collected and washed. SEM-EDX analysis of a number of powder particles revealed a metallic alloy powder a mean composition of 45.46 atomic % Al, 50.23 atomic % Ti, 2.09 atomic % Cr, and 2.22 atomic percent Nb.

EXAMPLE 3

[0104] As a further specific example, a titanium-tantalum alloy (TiTa alloy) was formed using various aspects of the invention disclosed herein. The initial starting oxide powders used to form the feedstock powder for reduction were TiO.sub.2 and Ta.sub.2O.sub.5. The TiO.sub.2 oxide powder had a mean particle size of 1.2 microns. The Ta.sub.2O.sub.5 oxide powder agglomerate had a mean particle size of 300 micrometres.

[0105] A total of 5000 grams of mixed oxide powder was used. Of this total, 3806.3 grams was TiO.sub.2 and 1193.7 grams was Ta.sub.2O.sub.5.

[0106] The oxide powder was mixed with an aqueous solution of demineralised water and PVA to form a slurry having 53.2% solid oxide. The slurry was then subjected to high-shear mixing and spray granulation as described in relation to Example 1. The spray granulation parameters were selected to provide a particle size distribution within the range of 100 and 250 micrometres. The product of spray granulation was a free-flowing powder of grey-greenish granules.

[0107] After spray-granulation the collected oxide particles were heat treated to form a feedstock powder as described above in relation to Example 1. The feedstock powder was then reduced using the reduction process described in relation to Example 1. The reduced powder was then collected and washed. SEM-EDX analysis of a number of powder particles revealed a metallic alloy powder a mean composition of 70.19 weight % Ti and 29.81 weight % Ta.

EXAMPLE 4

[0108] As a further specific example, a tantalum-tungsten alloy (TaW alloy) was formed using various aspects of the invention disclosed herein. The initial starting oxide powders used to form the feedstock powder for reduction were Ta.sub.2O.sub.5 and W.sub.2O.sub.3. The Ta.sub.2O.sub.5 oxide powder agglomerate had a mean particle size of 300 micrometres. The WO.sub.3 oxide powder had a particle size distribution of 0.5-5 micrometres.

[0109] A total of 5000 grams of mixed oxide powder was used. Of this total, 4871 grams was Ta.sub.2O.sub.6 and 129 grams was WO.sub.3.

[0110] The oxide powder was mixed with an aqueous solution of demineralised water and PVA to form a slurry having 59.5% solid oxide. The slurry was then subjected to high-shear mixing and spray granulation as described in relation to Example 1. The spray granulation parameters were selected to provide a particle size distribution within the range of 100 and 250 micrometres. The product of spray granulation was a free-flowing powder of grey-greenish granules.

[0111] After spray-granulation the collected oxide particles were heat treated to form a feedstock powder as described above in relation to Example 1. The feedstock powder was then reduced using the reduction process described in relation to Example 1. The reduced powder was then collected and washed. SEM-EDX analysis of a number of powder particles revealed a metallic alloy powder a mean composition of 93.61 weight % Ta and 6.39 weight % W.

EXAMPLE 5

[0112] As a further specific example, a tantalum-aluminium alloy (TaAl alloy) was formed using various aspects of the invention disclosed herein. The initial starting oxide powders used to form the feedstock powder for reduction were Ta.sub.2O.sub.5 and Al.sub.2O.sub.3. The Ta.sub.2O.sub.5 oxide powder agglomerate had a mean particle size of 300 micrometres. The Al.sub.2O.sub.3 oxide powder agglomerate had a mean particle size of 120 micrometres.

[0113] A total of 5000 grams of mixed oxide powder was used. Of this total, 4847 grams was Ta.sub.2O.sub.5 and 153 grams was Al.sub.2O.sub.3.

[0114] The oxide powder was mixed with an aqueous solution of demineralised water and PVA to form a slurry having 59.5% solid oxide. The slurry was then subjected to high-shear mixing and spray granulation as described in relation to Example 1. The spray granulation parameters were selected to provide a particle size distribution within the range of 100 and 250 micrometres. The product of spray granulation was a free-flowing powder of grey-greenish granules.

[0115] After spray-granulation the collected oxide particles were heat treated to form a feedstock powder as described above in relation to Example 1. The feedstock powder was then reduced using the reduction process described in relation to Example 1. The reduced powder was then collected and washed. SEM-EDX analysis of a number of powder particles revealed a metallic alloy powder a mean composition of 97.84 weight % Ta and 2.16 weight % Al.