AU2002218924A1 - Refractory hard metals in powder form for use in the manufacture of electrodes - Google Patents
Refractory hard metals in powder form for use in the manufacture of electrodesInfo
- Publication number
- AU2002218924A1 AU2002218924A1 AU2002218924A AU2002218924A AU2002218924A1 AU 2002218924 A1 AU2002218924 A1 AU 2002218924A1 AU 2002218924 A AU2002218924 A AU 2002218924A AU 2002218924 A AU2002218924 A AU 2002218924A AU 2002218924 A1 AU2002218924 A1 AU 2002218924A1
- Authority
- AU
- Australia
- Prior art keywords
- process according
- powder form
- refractory hard
- hard metal
- containing compounds
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Description
REFRACTORY HARD METALS LN POWDER FORM FOR USE IN THE MANUFACTURE OF ELECTRODES
Field of the Invention The present invention pertains to improvements in the field of electrodes for metal electrolysis. More particularly, the invention relates to refractory hard metals in powder form for use in the manufacture of such electrodes.
Background Art
Aluminum is produced conventionally in a Hall-Heroult reduction cell by the electrolysis of alumina dissolved in molten cryolite (Na3AlF6) at temperatures of up to about 950°C. A Hall-Heroult cell typically has a steel shell provided with an insulating lining of refractory material, which in turn has a lining made of prebaked carbon blocks contacting the molten constituents of the electrolyte. The carbon lining acts as the cathode substrate and the molten aluminum pool acts as the cathode. The anode is a consumable carbon electrode, usually prebaked carbon made by coke calcination.
During electrolysis in Hall-Heroult cells, the carbon anode is consumed leading to the evolution of greenhouse gases such as CO and CO2. The anode has to be periodically changed and the erosion of the material modifies the anode-cathode distance, which increases the voltage due to the electrolyte resistance. On the cathode side, the carbon blocks are subjected to erosion and electrolyte penetration. A sodium intercalation in the graphitic structure occurs, which causes swelling and deformation of the cathode carbon blocks. The increase of voltage between the electrodes adversely affects the energy efficiency of the process.
Extensive research has been carried out with refractory hard metals such as TiB2, as electrode materials. TiB2 and other refractory hard metals are practically insoluble in aluminum, have a low electrical resistance and are wetted by aluminum. However, the shaping of TiB2 and similar refractory hard metals is difficult because these materials have high melting temperatures and are highly covalent.
Disclosure of the Invention
It is therefore an object of the present invention to overcome the above drawbacks and to provide a refractory hard metal in powder form suitable for the manufacture of electrodes by thermal deposition or powder metallurgy.
According to one aspect of the invention, there is provided a refractory hard metal in powder form comprising particles having an average particle size of 0.1 to 30 μm and each formed of an agglomerate of grains with each grain comprising a nanocrystal of a refractory hard metal of the formula:
AxByXz (I) wherein A is a transition metal, B is a metal selected from the group consisting of zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, manganese, tungsten and cobalt, X is boron or carbon, x ranges from 0.1 to 3, y ranges from 0 to 3 and z ranges from 1 to 6.
The term "nanocrystal" as used herein refers to a crystal having a size of 100 nanometers or less.
The expression "thermal deposition" as used herein refers to a technique in which powder particles are injected in a torch and sprayed on a substrate. The particles acquire a high velocity and are partially or totally melted during the flight path. The coating is built by the solidification of the
droplets on the substrate surface. Examples of such techniques include plasma spray, arc spray and high velocity oxy-fuel.
The expression "powder metallurgy" as used herein refers to a technique in which the bulk powders are transformed into preforms of a desired shape by compaction or shaping followed by a sintering step. Compaction refers to techniques where pressure is applied to the powder, as, for example, cold uniaxial pressing, cold isostatic pressing or hot isostatic pressing. Shaping refers to techniques executed without the application of external pressure such as powder filling or slurry casting.
The present invention also provides, in another aspect thereof, a process for producing a refractory hard metal in powder form as defined above. The process of the invention comprises the steps of:
a) providing a first reagent selected from the group consisting of transition metals and transition metal-containing compounds; b) providing a second reagent selected from the group consisting of boron, boron-containing compounds, carbon and carbon-containing compounds; c) providing an optional third reagent selected from the group consisting of zirconium, zirconium-containing compounds, hafnium, hafnium- containing compounds, vanadium, vanadium-containing compounds, niobium, niobium-containing compounds, tantalum, tantalum-containing compounds, chromium, chromium-containing compounds, molybdenum, molybdenum- containing compounds, manganese, manganese-containing compounds, tungsten, tungsten-containing compounds, cobalt and cobalt-containing compounds; and d) subjecting the first, second and third reagents to high-energy ball milling to cause solid state reaction therebetween and formation of particles
having an average particle size of 0.1 to 30 μm, each particle being formed of an agglomerate of grains with each grain comprising a nanocrystal of a refractory hard metal of formula (I) defined above.
The expression "high-energy ball milling" as used herein refers to a ball milling process capable of forming the aforesaid particles comprising nanocrystalline grains of the refractory hard metal of formula (I), within a period of time of about 40 hours.
Description of Drawing
In the accompanying drawing, the sole figure shows the X-ray diffraction of the refractory hard metal in powder form obtained in Example 1.
Modes for Carrying out the Invention Typical examples of refractory hard metals of the formula (I) include TiBL8, TiB2, TiB2.2, TiC, Tio.5Zro.5B2, Tio.9Zro.iB3, Tio.5Hfo.5B2 and Zr0.sNo.2B2. TiB2 is preferred.
Examples of suitable transition metals which may be used as the aforesaid first reagent include titanium, chromium, zirconium and vanadium. Titanium is preferred. It is also possible to use a titanium-containing compound such as TiH2, T1AI3, TiB and TiCl2.
Examples of suitable boron-containing compounds which may be used as the aforesaid second reagent include A1B2, A1B12, BH3, BΝ, NB, H2BO3 and Νa2B4O . It is also possible to use tetraboron carbide (B4C) as either a boron-containing compound or a carbon-containing compound.
Examples of suitable compounds which may be used as the aforesaid third reagent include HfB2, NB2, ΝbB2, TaB2, CrB2, MoB2, MnB2, Mo2B5, W2B5, CoB, ZrC, TaC, WC and HfC.
According to a preferred embodiment, step (d) of the process according to the invention is carried out in a vibratory ball mill operated at a frequency of 8 to 25 Hz, preferably about 17 Hz. It is also possible to conduct step (d) in a rotary ball mill operated at a speed of 150 to 1500 r.p.m., preferably about 1000 r.p.m.
According to another preferred embodiment, step (d) is carried out under an inert gas atmosphere such as a gas atmosphere comprising argon or helium, or under a reactive gas atmosphere such as a gas atmosphere comprising hydrogen, ammonia or a hydrocarbon, in order to saturate dangling bonds and thereby prevent oxidation of the refractory hard metal. An atmosphere of argon, helium or hydrogen is preferred. It is also possible to coat the particles with a protective film or to admix a sacrificial element such as Mg or Ca with the reagents. In addition, a sintering aid such as Y2O3 can be added during step (d).
In the particular case of TiB2 or TiC wherein titanium and boron or carbon are present in stoichiometric quantities, these two compounds can be used as starting material. Thus, they can be directly subjected to high-energy ball milling to cause formation of particles having an average particle size of 0.1 to 30 μm, each particle being formed of an agglomerate of grains with each grain comprising a nanocrystal of TiB2 or TiC.
The high-energy ball milling described above enables one to obtain refractory hard metals in powder form having either non-stoichiometric or stoichiometric compositions.
The refractory hard metals in powder form according to the invention are suitable for use in the manufacture of electrodes by thermal deposition or powder metallurgy. Due to the properties of refractory hard metals, the emission of toxic and greenhouse effect gases during metal electrolysis is lowered and the lifetime of the electrodes is increased, thus lowering maintenance costs. A lower and constant inter-electrode distance is also possible, thereby decreasing the electrolyte ohmic drop.
The following non-limiting examples illustrate the invention.
EXAMPLE 1.
A TiB2 powder was produced by ball milling 3.45g of titanium and 1.55g of boron in a hardened steel crucible with a ball-to-powder mass ratio of 4.5:1 using a SPEX 8000 (trademark) vibratory ball mill operated at a frequency of about 17 Hz. The operation was performed under a controlled argon atmosphere to prevent oxidization. The crucible was closed and sealed with a rubber O-ring. After 5 hours of high-energy ball milling, a TiB2 structure was formed, as shown on the X-ray diffraction pattern in the accompanying drawing. The structure of TiB2 is hexagonal with the space group P6/mmm (191). The particle size varied between 1 and 5 μm and the crystallite size, measured by X-ray diffraction, was about 30 nm.
EXAMPLE 2. A TiB2 powder was produced according to the same procedure as described in Example 1 and under the same operating conditions, with the exception that the ball milling was carried out for 20 hours instead of 5 hours.
The resulting powder was similar to that obtained in Example 1. The crystallite size, however, was lower (about 16 nm).
EXAMPLE 3.
A TiC powder was produced according to the same procedure as described in Example 1 and under the same operating conditions, with the exception that titanium and graphite were milled.
EXAMPLE 4.
A TiB2 powder was produced by ball milling titanium diboride under the same operating conditions as in Example 1, with the exception that the ball milling was carried out for 20 hours instead of 5 hours. The starting structure was maintained, but the crystallite size decreased to 15 nm.
EXAMPLE 5.
A TiBi.s powder was according to the same procedure as described in Example 1 and under the same operating conditions, with the exception that 3.6 g of titanium and 1.4 g of boron were milled.
EXAMPLE 6.
A TiB2.2 powder was according to the same procedure as described in Example 1 and under the same operating conditions, with the exception that 3.4 g of titanium and 1.7 g of boron were milled.
EXAMPLE 7.
A Tio.5Zro.5B2 powder was according to the same procedure as described in Example 1 and under the same operating conditions, with the exception that 1.9 g of titanium, 3.1 g of zirconium diboride and 0.8 g of boron were milled.
EXAMPLE 8.
A Ti0.9Zr0.iB2 powder was according to the same procedure as despribed in Example 1 and under the same operating conditions, with the
exception that 2.9 g of titanium, 0.6 g of zirconium and 1.5 g of boron were milled.
EXAMPLE 9. A Ti0.5Hf0.5B2 powder was according to the same procedure as described in Example 1 and under the same operating conditions, with the exception that 0.9 g of titanium, 3.3 g of hafnium and 0.8 g of boron were milled.
EXAMPLE 10.
A Zro.sNo.2B2 powder was according to the same procedure as described in Example 1 and under the same operating conditions, with the exception that 3.5 g of zirconium, 0.5 g of vanadium and 1.0 g of boron were milled.
Claims (45)
1. A refractory hard metal in powder form comprising particles having an average particle size of 0.1 to 30 μm and each formed of an agglomerate of grains with each grain comprising a nanocrystal of a refractory hard metal of the formula:
AxByXz (I) wherein A is a transition metal, B is a metal selected from the group consisting of zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, manganese, tungsten and cobalt, X is boron or carbon, x ranges from 0.1 to 3, y ranges from 0 to 3 and z ranges from 1 to 6.
2. A refractory hard metal in powder form according to claim 1, wherein A is a transition metal selected from the group consisting of titanium, chromium, zirconium and vanadium.
3. A refractory hard metal in powder form according to claim 2, wherein A is titanium, X is boron and y is 0.
4. A refractory hard metal in powder form according to claim 3, wherein x is 1 and z is 1.8.
5. A refractory hard metal in powder form according to claim 3, wherein x is 1 and z is 2.
6. A refractory hard metal in powder form according to claim 3, wherein x is 1 and z is 2.2.
7. A refractory hard metal in powder form according to claim 2, wherein A is titanium, X is carbon and y is 0.
8. A refractory hard metal in powder form according to claim 7, wherein x is 1 and z is 1.
9. A refractory hard metal in powder form according to claim 2, wherein A is titanium, B is zirconium or hafnium, X is boron and is other than 0.
10. A refractory hard metal in powder form according to claim 9, wherein B is zirconium, x is 0.5, y is 0.5 and z is 2.
11. A refractory hard metal in powder form according to claim 9, wherein B is zirconium, x is 0.9, y is 0.1 and z is 2.
12. A refractory hard metal in powder form according to claim 2, wherein B is hafnium, x is 0.5, is 0.5 and z is 2.
13. A refractory hard metal in powder form according to claim 2, wherein A is zirconium, B is vanadium, X is boron and y is other than 0.
14. A refractory hard metal in powder form according to claim 13, wherein x is 0.8, y is 0.2 and z is 2.
15. A refractory hard metal in powder form according to claim 1, wherein said average particle size ranges from 1 to 5 μm.
16. A process for producing a refractory hard metal in powder form as defined in claim 1, comprising the steps of: a) providing a first reagent selected from the group consisting of transition metals and transition metal-containing compounds; b) providing a second reagent selected from the group consisting of boron, boron-containing compounds, carbon and carbon-containing compounds; c) providing an optional third reagent selected from the group consisting of zirconium, zirconium-containing compounds, hafnium, hafnium- containing compounds, vanadium, vanadium-containing compounds, niobium, niobium-containing compounds, tantalum, tantalum-containing compounds, chromium, chromium-containing compounds, molybdenum, molybdenum- containing compounds, manganese, manganese-containing compounds, tungsten, tungsten-containing compounds, cobalt and cobalt-containing compounds; and d) subjecting said first, second and third reagents to high-energy ball milling to cause solid state reaction therebetween and formation of particles having an average particle size of 0.1 to 30 μm, each particle being formed of an agglomerate of grains with each grain comprising a nanocrystal of a refractory hard metal of the formula (I) as defined in claim 1.
17. A process according to claim 16, wherein said first reagent comprises a transition metal selected from the group consisting of titanium, chromium, zirconium and vanadium.
18. A process according to claim 17, wherein said transition metal is titanium.
19. A process according to claim 16, wherein said first reagent comprises a titanium-containing compound selected from the group TiH2, TiAl3, TiB and TiCl2.
20. A process according to claim 16, wherein said second reagent comprises boron.
21. A process according to claim 16, wherein said second reagent comprises a boron-containing compound selected from the group consisting of A1B2, A1B12, BH3, BN, NB2, H2BO3 and Νa2B4O7.
22. A process according to claim 16, wherein said second reagent comprises carbon.
23. A process according to claim 16, wherein said second reagent comprises tetraboron carbide.
24. A process according to claim 16, wherein said third reagent is a compound selected from the group consisting of HfB2, NB2, ΝbB2, TaB2, CrB2, MoB2, MnB2, Mo2B5, W2B5, CoB, ZrC, TaC, WC and HfC.
25. A process according to claim 16, wherein step (d) is carried out in a vibratory ball mill operated at a frequency of 8 to 25 Hz.
26. A process according to claim 25, wherein said vibratory ball mill is operated at a frequency of about 17 Hz.
27. A process according to claim 16, wherein step (d) is carried out in a rotary ball mill operated at a speed of 150 to 1500 r.p.m.
28. A process according to claim 27, wherein said rotary ball mill is operated at a speed of about 1000 r.p.m.
29. A process according to claim 16, wherein step (d) is carried out under an inert gas atmosphere.
30. A process according to claim 29, wherein said inert gas atmosphere comprises argon or helium.
31. A process according to claim 16, wherein step (d) is carried out under a reactive gas atmosphere.
32. A process according to claim 31, wherein said reactive gas atmosphere comprises hydrogen, ammonia or a hydrocarbon.
33. A process according to claim 16, wherein step (d) is carried out for a period of time of about 5 hours.
34. A process according to claim 16, wherein a sintering aid is added during step (d).
35. A process for producing a refractory hard metal in powder form as defined in claim 5 or 8, comprising subjecting TiB2 or TiC to high-energy ball milling to cause formation of particles having an average particle size of 0.1 to 30 μm, each particle being formed of an agglomerate of grains with each grain comprising a nanocrystal of TiB2 or TiC.
36. A process according to claim 35, wherein said high-energy ball milling is carried out in a vibratory ball mill operated at a frequency of 8 to 25 Hz.
37. A process according to claim 36, wherein said vibratory ball mill is operated at a frequency of about 17 Hz.
38. A process according to claim 35, wherein said high-energy ball milling is carried out in a rotary ball mill operated at a speed of 150 to 1500 r.p.m.
39. A process according to claim 38, wherein said rotary ball mill is operated at a speed of about 1000 r.p.m.
40. A process according to claim 35, wherein said high-energy ball milling is carried out under an inert gas atmosphere.
41. A process according to claim 40, wherein said inert gas atmosphere comprises argon or helium.
42. A process according to claim 35, wherein said high-energy ball milling is carried out under a reactive gas atmosphere.
43. A process according to claim 42, wherein said reactive gas atmosphere comprises hydrogen, ammonia or a hydrocarbon.
44. A process according to claim 35, wherein said high-energy ball milling is carried out for a period of time of about 20 hours.
45. A process according to claim 35, wherein a sintering aid is added during said high-energy ball milling.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA2,330,352 | 2001-01-05 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| AU2002218924A1 true AU2002218924A1 (en) | 2002-07-16 |
Family
ID=
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| KR101370007B1 (en) | Thermal and electrochemical process for metal production | |
| US20040052713A1 (en) | Refractory hard metals in powder form for use in the manufacture of electrodes | |
| CN113880580B (en) | High-entropy carbide ultra-high temperature ceramic powder and preparation method thereof | |
| CN1479810B (en) | Method for producing intermetallic compounds | |
| HUT68650A (en) | Composite electrode for electrochemical processing having improved high temperature properties and method for preparation thereof | |
| JP2004508461A (en) | Ultra-coarse single crystal tungsten carbide, method for producing the same and hard alloy produced therefrom | |
| EP1144147B1 (en) | METHOD FOR PRODUCING METAL POWDERS BY REDUCTION OF THE OXIDES, Nb AND Nb-Ta POWDERS AND CAPACITOR ANODE OBTAINED THEREWITH | |
| US20040045402A1 (en) | Inert electrode material in nanocrystalline powder form | |
| Song et al. | Preparation of niobium carbide powder by electrochemical reduction in molten salt | |
| CN112359395B (en) | Preparation method of metal boride coating | |
| US20100006448A1 (en) | Method, apparatus and means for production of metals in a molten salt electrolyte | |
| AU2002218924A1 (en) | Refractory hard metals in powder form for use in the manufacture of electrodes | |
| Liu et al. | In situ nano-sized ZrC/ZrSi composite powder fabricated by a one-pot electrochemical process in molten salts | |
| Song et al. | Electrochemical fabrication of multicore-shell Ni-TaC composite particles in molten salt | |
| Zhang et al. | Fabrication of TiB2 coatings by electrophoretic deposition of synthesized TiB2 nanoparticles in molten salts | |
| JP2007045670A (en) | Manufacturing method of metal carbide | |
| KR100714978B1 (en) | The method for fabricatiing ultrafine crystalline TiN/TiB2 composite cermet | |
| JPH0553755B2 (en) | ||
| Shah | Molten salt synthesis of TiB2 nanopowder by reduction of TiO2 with MgB2 | |
| Malyshev et al. | Galvanic powders of borides, carbides, and silicides of metals of the iv–vi groups | |
| RU2639797C1 (en) | Method of producing carbide powder | |
| Van Vuuren et al. | Opportunities in the electrowinning of molten titanium from titanium dioxide | |
| IL139061A (en) | Metal powders produced by the reduction of the oxides with gaseous magnesium | |
| CA2441578A1 (en) | Inert electrode material in nanocrystalline powder form | |
| RU2718022C1 (en) | Method of electrochemical production of nano-sized powder of metal silicide |