WO2006136785A2 - Electrode - Google Patents

Electrode Download PDF

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Publication number
WO2006136785A2
WO2006136785A2 PCT/GB2006/002147 GB2006002147W WO2006136785A2 WO 2006136785 A2 WO2006136785 A2 WO 2006136785A2 GB 2006002147 W GB2006002147 W GB 2006002147W WO 2006136785 A2 WO2006136785 A2 WO 2006136785A2
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WO
WIPO (PCT)
Prior art keywords
electrode
based alloy
metallic element
alloy
group
Prior art date
Application number
PCT/GB2006/002147
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English (en)
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WO2006136785A3 (fr
Inventor
Animesh Jha
Xiaobing Yang
Original Assignee
University Of Leeds
Priority date (The priority date 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 date listed.)
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Publication date
Priority claimed from GB0512836A external-priority patent/GB0512836D0/en
Application filed by University Of Leeds filed Critical University Of Leeds
Priority to US11/922,806 priority Critical patent/US8147624B2/en
Priority to EA200702573A priority patent/EA013139B1/ru
Priority to CA002654272A priority patent/CA2654272A1/fr
Priority to AU2006260791A priority patent/AU2006260791B2/en
Priority to EP06744191A priority patent/EP1904668A2/fr
Publication of WO2006136785A2 publication Critical patent/WO2006136785A2/fr
Publication of WO2006136785A3 publication Critical patent/WO2006136785A3/fr
Priority to NO20080063A priority patent/NO20080063L/no
Priority to US13/418,025 priority patent/US8900438B2/en

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
    • C25C3/06—Electrolytic production, recovery or refining of metals by electrolysis of melts of aluminium
    • C25C3/08—Cell construction, e.g. bottoms, walls, cathodes
    • C25C3/12—Anodes

Definitions

  • the present invention relates to an electrode composed of an Al-M-Cu based alloy, to a process for preparing the Al-M-Cu based alloy, to an electrolytic cell comprising the electrode, to the use of an Al-M-Cu based alloy as an anode and to a method for extracting a reactive metal from a reactive metal-containing source using an Al-M-Cu based alloy as an anode.
  • Aluminium metal is produced via the electrochemical dissociation of alumina dissolved in a fluoride melt consisting of AIF3 and NaF known as cryolite (3NaF. AIF 3 ).
  • the cell reaction involves several steps (see F Habashi: A Handbook of Extraction Metallurgy, vol. 3, VCH, Berlin) and relies on the use of carbon anodes and cathodes. To illustrate the need for a consumable carbon anode, a simplified description of the cell reaction is.
  • the combustion of carbon is necessary to maintain the temperature of the molten aluminium and cryolite bath which moderates the electrical energy consumption of the cell.
  • the power consumption for making aluminium is of the order of 6.3 kWh/kg which is equivalent to 2.1 V and represents 50% of the total energy consumption of the cell.
  • the remaining 50% (or 2.1V) of the total energy consumption maintains the cell temperature in the face of heat losses (and is equivalent to 6.3 kWh/kg for making aluminium metal).
  • 333 kg of carbon is oxidised at the anode to carbon dioxide gas which escapes into the atmosphere.
  • the evolution of carbon dioxide is one of the main sources of greenhouse gas emission in the aluminium industry.
  • the carbon electrode Periodically (eg monthly) the carbon electrode is replaced with a new one. During this change over period, the electrolyte in the bath becomes under saturated and reacts with carbon to produce small concentrations of perfluorocarbon (PFC) gases.
  • PFC perfluorocarbon
  • the presence of fluoride salt melt in the Al-electrolytic cell and the large current surge during cell operation lead to decomposition of fluoride salts into reactive forms of fluorine gas which readily react with carbon present in the electrodes to generate PFCs.
  • PFCs also form during anode effect. When the PFCs escape into the atmosphere, they contribute to ozone depletion. PFCs also pose a major health risk to plant workers.
  • the manufacture of carbon electrodes uses petroleum products which decompose and release hydrocarbon based greenhouse gases.
  • the processing and manufacturing route for electrodes is quite complex and time-consuming. In the lengthy process, the material is prebaked and fired for graphitization at 3000 0 C for 1 month.
  • a large volume of greenhouse gases eg methane, sulphur and sulphur dioxide
  • the costs of energy consumption for a carbon anode is as large as the production metal.
  • Coal tar pitch is used in making Soderberg anodes and during this process SO 2 forms and. contributes to environmental pollution. 11.5 mT of coke for making carbon anodes is consumed globally.
  • titanium diboride powders have been used for making ceramic electrodes for producing molten aluminium (see US-A-4929328).
  • the diborides exhibit high-temperature electrical resistivity of 14 ⁇ ohm cm and thermal conductivity of 59 W m "2 K '1 .
  • the sintered materials also exhibit high oxidation and corrosion resistance.
  • TiB 2 has a high melting point and so there is an inherent cost for processing and sintering ceramic powders. Adding alumina in the matrix for reducing the processing and sintering temperatures compromises the conductivity of TiB 2 and its composites.
  • the composite can also be fabricated by making a partially sintered material using the self-heating high-temperature synthesis (SHS) OfTiB 2 and alumina.
  • SHS self-heating high-temperature synthesis
  • the present invention is based on the recognition that certain Al-M-Cu based alloys exhibit high-temperature strength, corrosion resistance and electrical conductivity without major resistive heat loss and so can be exploited as an inert electrode, in particular as an inert electrode to replace carbon anodes in a Hall-Heraoult cell for extraction of reactive metals such as Al, Ti, Nb, Ta, Cr and rare-earth metals.
  • an electrode ⁇ eg an anode composed of an Al-M-Cu based alloy comprising an intermetallic phase of formula:
  • M denotes one or more metallic elements; x is an integer in the range 1 to 5; y is an integer being 1 or 2; and z is an integer being 1 or 2.
  • the electrical resistivity of embodiments of the electrode of the invention was found to decrease as a function of temperature and illustrates the usefulness of the ordered high-temperature alloy as an inert electrode.
  • the desirable electronic conductivity arises due to the presence of metallic copper which has the added advantage that it is much cheaper than alternatives such as silver and gold.
  • the electrode of the invention performs well as an anode an alumina-saturated cryolite bath at 85O 0 C.
  • the Al-M-Cu based alloy may be substantially monophasic or multiphasic.
  • the intermetallic phase is present in the Al-M-Cu based alloy in an amount of 50wt% or more ⁇ eg in the range 50 to 99wt%).
  • the Al-M-Cu based alloy further comprises an ordered high-temperature intermetallic phase of M with aluminium, particularly preferably Al 3 M. Other intermetallic phases may be present.
  • the Al-M-Cu based alloy is substantially free of CuAl 2 .
  • CuAl 2 has a tendency to melt at the elevated temperatures which are deployed typically in metal extraction ⁇ eg 75O 0 C for aluminium extraction).
  • CuAl 2 is complexed.
  • the Al-M-Cu based alloy falls other than on the M poor side of the tie line joining AI3M and MCu 4 ⁇ eg on the M rich side of the tie line joining AI3M and MCu 4 ).
  • the Al-M-Cu based alloy comprises an intermetallic phase falling on or near to the tie line joining AI 3 M and MCu 4 .
  • the Al-M-Cu based alloy falls other than on the M poor side of the tie line joining AI 3 M and AlMCu 2 ⁇ eg on the M rich side of the tie line joining AI3M and AlMCu 2 ).
  • the Al-M-Cu based alloy comprises an intermetallic phase falling on or near to the tie line joining Al 3 M and AlMCu 2 .
  • the Al-M-Cu based alloy falls other than on the M poor side of the ⁇ , AIsM 2 Cu, MAlCu 2 and ⁇ -MCu 4 phase tie line (wherein ⁇ is a phase falling between Al 3 Ti and Al 2 Ti with 3 at% or less of Cu ⁇ eg 2-3 at% Cu)).
  • the Al-M-Cu based alloy comprises an intermetallic phase falling on or near to the ⁇ , AI5M2C11, MAlCu 2 and P-MCu 4 phase tie line.
  • the intermetallic phase is Al 5 M 2 Cu.
  • the Al-M-Cu based alloy further comprises Al 3 M.
  • the intermetallic phase is MAlCu 2 .
  • the Al-M-Cu based alloy further comprises ⁇ -MCu 4 .
  • the electrode may be composed of a homogenous, partially homogenous or non- homogeneous Al-M-Cu based alloy.
  • the electrode comprises a passivating layer.
  • the passivating layer withstands electrode oxidation in anodic conditions.
  • M is a single metallic element.
  • the single metallic element is preferably Ti.
  • M is a plurality (eg two, three, four, five, six or seven) of metallic elements.
  • a first metallic element is preferably Ti.
  • the first metallic element of the plurality of metallic elements is present in a substantially higher amount than the other metallic elements of the plurality of metallic elements.
  • Each of the other metallic elements may be present in a trace amount.
  • Each of the other metallic elements may be a dopant.
  • Each of the other metallic elements may substitute Al, Cu or the first metallic element. The presence of the other metallic elements may improve the high-temperature stability of the alloy (eg from 1200 0 C to 1400 0 C).
  • M is a pair of metallic elements.
  • a first metallic element is preferably Ti.
  • the first metallic element of the pair of metallic elements is present in a substantially higher amount than a second metallic element of the pair of metallic elements (eg in a weight ratio of about 9:1).
  • the second metallic element may be present in a trace amount.
  • the second metallic element may be a dopant.
  • the second metallic element may substitute Al, Cu or the first metallic element.
  • the presence of a second metallic element may improve the high-temperature stability of the alloy (eg- from 1200 0 C to 1400 0 C).
  • the pair of metallic elements have similar atomic radii.
  • the atomic radius of the second metallic element is similar to the atomic radius of Cu.
  • the atomic radius of the second metallic element is similar to the atomic radius of Al.
  • M is one or more of the group consisting of group B transition metal elements (eg first row group B transition metal elements) and lanthanide elements.
  • group B transition metal elements eg first row group B transition metal elements
  • M is one or more group IVB, VB, VIB, VIIB or VIIIB transition metal elements, particularly preferably one or more group IVB, VIIB or VIIIB transition metal elements.
  • M is one or more metallic elements of valency II, III, IV or V, preferably II, III or IV.
  • M is one or more metallic elements selected from the group consisting of Ti, Zr, Cr, Nb, V, Co, Ta, Fe, Ni, La and Mn. In a particularly preferred embodiment, M is one or more metallic elements selected from the group consisting of Ti, Fe, Cr and Ni.
  • M is or includes a metallic element capable of reducing the tendency of CuAl 2 towards grain boundary segregation at an elevated temperature.
  • the metallic element capable of reducing the tendency of CuAl 2 towards grain boundary segregation at an elevated temperature may be the second metallic element of a plurality (eg a pair) of metallic elements.
  • M is or includes a metallic element capable of forming a complex with CuAl 2 .
  • Preferred metallic elements for this purpose are selected from the group consisting of Fe, Ni and Cr, particularly preferably Ni and Fe, especially preferably Ni.
  • M is or includes a metallic element capable of reducing the tendency of the first metallic element or Cu to dissolve in molten extractant.
  • the metallic element may be the second metallic element of a plurality (eg a pair) of metallic elements.
  • Preferred metallic elements for this purpose are selected from the group consisting of Fe, Ni, Co, Mn and Cr, particularly preferably the group consisting of Fe and Ni (optionally together with Cr).
  • M is or includes a metallic element capable of promoting the passivation of the surface of the electrode (eg anode) in the presence of a molten electrolyte.
  • the metallic element may form or stabilise an oxide film.
  • the metallic element may be the second metallic element of a plurality (eg a pair) of metallic elements.
  • Preferred metallic elements for this purpose are selected from the group consisting of Fe, Ni and Cr.
  • M is Ti, Fe, Ni and Cr in which the formation of a combination of oxides such as iron oxides, chromium oxides, nickel oxides and alumina advantageously promotes passivation.
  • M is or includes a metallic element selected from the group consisting of Zr, Nb and V. Particularly preferred is V or Nb.
  • These second metallic elements are advantageously strong intermetallic formers.
  • the metallic element is the second metallic element of a plurality (eg a pair) of metallic elements.
  • M is or includes a metallic element capable of forming an ordered high- temperature intermetallic phase with aluminium metal.
  • M is or includes a metallic element capable of forming AI 3 M.
  • M is or includes Ti.
  • a titanium containing alloy typically has electrical resistivity in the range 3 to 15 ⁇ ohm cm at room temperature.
  • the intermetallic phase is AIsTi 2 Cu.
  • the Al-Ti-Cu based alloy further comprises AI 3 TL
  • the intermetallic phase is TiAlCu 2 .
  • the Al-Ti-Cu based alloy further comprises ⁇ -TiCu 4 .
  • M is or includes Ti and a second metallic element selected from the group consisting of Fe, Cr, Ni, V, La, Nb and Zr, preferably the group consisting of Fe, Cr and Ni.
  • the second metallic element advantageously serves to enhance high-temperature stability of the Al-Ti-Cu phases.
  • the electrode of the invention may be composed of an Al-M-Cu based alloy obtainable by processing a mixture of 35 atomic % Al or more (preferably 50 atomic % Al or more), 35 atomic % M or more (wherein M is a first metallic element as hereinbefore defined) and a balance of Cu and optionally M' (wherein M' is one or more additional metallic elements as hereinbefore defined).
  • the electrode of the invention is composed of an Al-M-Cu based alloy obtainable by processing a mixture of (65+x) atomic % Al, (20+y) atomic % M (wherein M is a first metallic element as hereinbefore defined) and (15-x-y) atomic % Cu, optionally together with z atomic % of M' (wherein M' is one or more additional metallic elements as hereinbefore defined) wherein M' substitutes Cu, Al or M.
  • the alloy may be obtainable by casting, preferably in an oxygen deficient atmosphere (eg an inert atmosphere).
  • an oxygen deficient atmosphere eg an inert atmosphere
  • a mixture may be melted in an argon-arc furnace under an atmosphere of argon gas and then solidified in an argon atmosphere.
  • the alloy may be obtainable by flux-assisted melting.
  • the electrode may be processed in near-net shape eg a finished square-shape rod.
  • the electrode of the invention is at least as conducting at elevated temperature (eg at 900 0 C) as a carbon electrode.
  • the electrode of the invention exhibits good thermal conductivity.
  • the electrode of the invention is electrochemically stable (eg is substantially non-soluble in the electrolyte).
  • the electrode of the invention is resistant to oxidation and corrosion at high temperatures.
  • the electrode of the invention exhibits good high- temperature strength, thermal shock and thermal and electrical fatigue resistance.
  • the electrode of the invention is wettable by a molten metal-containing source from which it is desired to extract metal (eg aluminium) whereby to reduce cathode resistance.
  • metal eg aluminium
  • the electrode will generally be non-toxic and non-carcinogenic (and not lead to the generation of toxic or carcinogenic materials).
  • the electrode may be recyclable.
  • the electrode may be safely disposable.
  • Al 3 Ti phase can be dispersed via the reactive melting of aluminium metal in the presence of K 2 TiF 6 .
  • the reaction between molten aluminium and K 2 TiF 6 yields a mixture of Al 3 Ti and aluminium metal.
  • This technique has however been only used to make binary Al-Ti alloys with less than l-2wt% Ti for which the processing temperature is between 75O 0 C and 85O 0 C.
  • the present invention provides a process for preparing an Al-M-Cu based alloy as hereinbefore defined comprising:
  • the presence of fluorine advantageously reduces hydrogen solubility in the Al-M-Cu liquid to yield a porosity-free cast structure which would otherwise have a higher resistive loss due to a high volume of pores.
  • the alkali fluorometallate may be a potassium or sodium alkali fluorometallate (eg fluorotitanate) salt.
  • the source of Cu and source of Al may be a molten Al-Cu alloy.
  • step (a) is carried out in an oxygen deficient atmosphere (eg an inert atmosphere such as argon or nitrogen).
  • the process further comprises: (b) annealing the Al-M-Cu cast alloy from step (a).
  • Step (b) may be carried out in an oxygen deficient atmosphere (eg an inert atmosphere such as argon or nitrogen) at temperatures typically in the range 600-1000 0 C (eg about 800 0 C).
  • Step (b) serves to eliminate deleterious phases such as Al 2 Cu and other low melting point inhomogeneities.
  • Step (b) may be preceded or succeeded by (c) the formation (eg coating) of an oxide layer on the Al-M-Cu surface.
  • the oxide layer is preferably a mixed oxide layer containing alumina, iron oxide, nickel oxide and optionally chromium oxide.
  • Step (c) may be carried out at an elevated temperature.
  • the oxide layer may be formed from a slurry of mixed oxides which may be applied to the cast alloy before step (b) or be subjected to a separate heating step.
  • a preferred slurry is a 50:50 by volume water/ethyl alcohol comprising 35-45mol% Fe 2 Os, 30-45mol% NiO, 10- 20mol% alumina and 0-5mol% Cr 2 O 3 .
  • the present invention provides a method for extracting a reactive metal from a reactive metal-containing source comprising: electrolytically contacting an electrode composed of an Al-M-Cu based alloy with the reactive metal-containing source.
  • the electrode may be as hereinbefore defined for the first aspect of the invention.
  • the reactive metal may be selected from the group consisting of Al, Ti, Nb, Ta, Cr and rare-earth metals (eg lanthanides or actinides). Preferred is Al.
  • the reactive metal-containing source is a molten bath, particularly preferably a molten bath containing reactive metal oxide.
  • the molten bath is alumina-containing, particularly preferably alumina- saturated, especially preferably is an alumina-saturated cryolite flux.
  • the cryolite flux comprises sodium-containing potassium cryolite (eg sodium-containing 3KF-AlF 3 such as K 3 AlF 6 -Na 3 AlF 6 ).
  • the weight ratio of NaF to AlF 3 in the sodium- containing potassium cryolite may be in the range to 1:1.5 to 1:2.
  • KBF 4 is present in the cryolite flux. The presence Of KBF 4 dramatically improves the wettability of an electrode composed of an Al-M-Cu alloy.
  • alloy comprises a passivating layer which prevents oxidation under anodic conditions.
  • the present invention provides the use of an Al- M-Cu based alloy as an anode in an electrolytic cell.
  • the Al-M-Cu based alloy in this aspect of the invention is as hereinbefore defined.
  • the present invention provides an electrolytic cell comprising an electrode as hereinbefore defined.
  • Figure Ia is a phase diagram of the Al-Ti-Cu alloy system (isothermal section at
  • Figure Ib is a phase diagram of the Al-Ti-Cu alloy system (isothermal section at
  • Figure Ic is a phase diagram of the Al-Ti-Cu alloy system showing various equilibrium points (not an isothermal section);
  • Figure 2a illustrates the results of microstructure and energy dispersive X-ray analysis of the as-cast Alloy- 1;
  • Figure 2b illustrates the results of microstructure and energy dispersive X-ray analysis of heat treated Alloy- 1 ;
  • Figure 3a illustrates the results of microstructure and EDX analysis of as-cast Alloy-2
  • Figure 3 b illustrates the results of microstructure and EDX analysis of heat treated
  • Figure 4 illustrates the effect of thermal cycling on the resistivities of Alloy- 1 and
  • Figure 5b illustrates the results of DTA of Alloy 2 in the as-cast and after a 1 st thermal cycle
  • Figure 6a is an illustration of a cell with a power supply
  • Figure 6b is a detailed illustration of the cell of Figure 6a;
  • Figure 7 is a plot of time verses cell voltage for the electrolysis of a S-NiFeCr alloy anode at 85O 0 C for 4 hours;
  • Figure 8 illustrates the microstructure of the S-NiFeCr alloy anode after an electrolysis experiment in an alloy anode/carbon cathode test cell
  • Figure 9 is a phase diagram of the Al-Ti-(Cu 5 Fe 5 Ni 5 Cr) pseudo ternary section at
  • Figures 10a and b illustrate the microstructure of a S-NiFeCr alloy after a corrosion experiment in cryolite at 950 0 C for 4 hours (The micrometer bar represents 200 ⁇ m in
  • Figures l la-d are a comparison of two alloys after a corrosion test in cryolite at
  • the micrometer bar represents 200 ⁇ m in (a-b) and 100 ⁇ m in (c- d));
  • Figure 12 is a comparison of two alloys after a corrosion test in a CaCl 2 bath at 950°C for 4 hours (The micrometer bar represents 100 ⁇ m).
  • Metallic copper is capable of forming an ordered CuAl 2 phase.
  • the phase relationship between Al 3 Ti, Al x Ti y Cu z and CuAl 2 at 54O 0 C is shown by way of example in Figure Ia and at 800 0 C is shown by way of example in Figure Ib (see A Handbook of Ternary Aluminium Alloys - eds G. Petzow, G. Effenberg, Weiheim VCH, vol.8, Berlin (1988), pp. 51-67).
  • the amount of titanium metal required for making the ternary intermetallic phase (AIsTi 2 Cu) was calculated and the proportionate amount of potassium fluorotitanate (K 2 TiF 6 ) salt was obtained.
  • the salt was reduced in the presence of liquid Al-Cu alloy to effect dissolution of Ti metal.
  • the reduction of the salt with molten aluminium alloy is an exothermic reaction. Consequently the alloy temperature rises to maintain the homogeneity of the alloy phase.
  • the interaietallic phases AIsTi and AIsTi 2 Cu are virtually insoluble in molten aluminium and in the fluoride flux and so offer a unique property for casting alloy almost as a single phase by following the tie line in the Al- Ti-Cu phase diagram. It is evident from the ternary sections shown in Figures Ia and Ib that it is along the ⁇ , Al 5 Ti 2 Cu, TiAlCu 2 and ⁇ -TiCu 4 phase tie line that the structurally stable compositions fall.
  • Liquid (L) ⁇ + CuTi 2 Al 5 2b
  • compositions were investigated in which the structural and environmental stabilities of the alloy phase were optimised against the electronic conductivity.
  • the reduction in the electronic resistivity as a function of temperature was established to demonstrate the usefulness of the ordered high- temperature alloys as inert electrodes.
  • Three different types of alloy composition were prepared.
  • a first example of a composition (Alloy- 1) according to the formula (65+x) atomic % Al, (20+y) atomic % Ti, and (15-x-y) atomic % Cu was fixed along the isoplethal lines of Al:Ti ratio of 2-3 (preferably 2.7) with substitution of aluminium by copper.
  • a second example of a composition falls along the tie line joining AI 3 T1 with the AlTiCu 2 phase field. This is a high copper phase field for which the electronic conductivity is much higher than Alloy- 1.
  • compositions (Alloys-4 to -8) were multi-component derivatives of a third composition (Alloy-3) resulting from partial substitution by phase stabilising elements (Fe, Cr, Ni, V, La, Nb, Zr) to enhance high-temperature stability of the phases. These elements tend to form ordered phases with Al, Ti, and Cu along the tie lines shown in Figure Ib.
  • phase stabilising elements Fe, Cr, Ni, V, La, Nb, Zr
  • the alloy compositions were melted by the following techniques.
  • the reaction between the potassium fluorotitanate salt and molten aluminium is exothermic and the heat generated is sufficient to keep a large volume of alloy above the liquidus temperature when the mass of the alloy exceeds a few kilograms. Excess thermal energy improves alloy homogeneity.
  • the addition of copper at an early stage of melting proves advantageous for enhancing the solubility of titanium in the alloy phase.
  • the arc-melted and the flux-melted alloy compositions were homogenised at 135O 0 C and then allowed to cool inside the copper crucible in the arc melter and alumina crucible in the radio-frequency coil respectively.
  • the alloy produced after reactive melting with the fluoride salt in air was cast into a small mould.
  • the as-cast material was analysed to determine its properties.
  • Alloys-1 and 2 were thermally cycled using a differential thermal analysis instrument to study the effect of temperature on the likely phase transformation reactions which may potentially cause dimensional changes in the electrode structure.
  • Table 2 presents the hardness of Alloys-1 and 2 in the as-cast and thermally-cycled conditions (E ⁇ v , load 10 kg) and their as-cast resistivity.
  • the density of Alloy-2 is 4.2gcm "3 .
  • the microstructure of the as-cast and heat treated Alloys are shown in Figures 2a, 2b, 3 a and 3b.
  • the corresponding energy dispersive X-ray analysis of the alloy microstructures is summarised in Tables 2a and 2b in terms of an elemental analysis of the matrix phase rich in Al and M elements and the conducting Cu-containing phases.
  • the as-cast resistivity of alloy 1 was 5 ⁇ ohm cm which dropped to 4 ⁇ ohm cm after the 1 st thermal cycling.
  • the effect of thermal cycling on the resistivities of Alloy- 1 and 2 are shown in Figure 4 and the corresponding DTA curves are shown in Figures 5a and 5b.
  • the alloy surface was slightly tarnished by developing a yellowish metal-like tinge which was also observed on the surface of Ti metals and its alloys. No weight change was observed.
  • iii) The presence of a small concentration OfKBF 4 (less than 5wt%) improved dramatically the wettability of alloy with KsAlFe-Na 3 AlFo flux. It was observed that when the alloy was withdrawn from the B -containing flux, the alloy surface was clean and shiny compared with when no boron was present in the flux.
  • cryolite (21) saturated with alumina
  • cell tests for extracting aluminium metal (41) were carried out (see Figures 6a and 6b).
  • the cell was an alumina crucible (22) comprising a cathode (24) with an alumina sheath (27), reference electrode (26) and anode (23) separated by an alumina partition (25).
  • the alumina crucible (22) was situated in a carbon crucible (29) inside a stainless steel container (30).
  • the cell further comprises a thermocouple (33) and an argon gas supply (2).
  • Electrolysis experiments included the use of alloy anode and carbon cathode, carbon anode and carbon cathode, carbon anode and alloy cathode and alloy anode and TiB 2 cathode to study reactions with cryolite.
  • the electrolyte (21) consisted of 36 wt% NaF and 64 wt% AlF 3 .
  • the bath was saturated with alumina using alumina spheres.
  • the alumina and salt were charged through a port (35).
  • the electrolysis experiment was carried out for 4-6 hours at different temperatures.
  • a constant DC current of 4-6 A from a DC power supply (1) was passed through the cell and the cell voltage and temperature were measured using a data logger (3).
  • the cell results are shown in Table 4.
  • a typical plot of time against cell voltage and temperature is presented in Figure 7.
  • Table 5 shows a typical example of a new composition of an AlTiCu alloy with the transition metals Ni, Fe and Cr (new S-NiFeCr) compared with composition S-NiFeCr of Example 2 (alloy code 5).
  • the new composition falls in the left hand part of the ternary phase diagram illustrated in Figure 9 with an arrow.
  • an equi-atomic ratio of Al: Ti eg 35:35
  • a minor metal M Cu, Fe, Cr or Ni which may vary between 3 at% to 30 at%.
  • the alloy was melted in an argon atmosphere above 1500 0 C and was cast as before for the composition S-NiFeCr of Example 2.
  • the development of the new composition arises from the analysis of the passivation layer in the S-FeNiCr alloy system of Example 2.
  • Figures 10-12 compare the corrosion behaviour of two alloys in a different salt bath under identical temperature and atmospheric conditions.
  • Figures 11a and c illustrate corrosion behaviour of the new S-NiFeCr composition compared with that of the S-NiFeCr composition of Example 2 (alloy code 5) in Figures l ib and d.
  • the new composition is shown to be more resistant to corrosion than the compositions discussed in Example 2 which had 60-70a% Al, 20-25 at% Ti, 3-5 at% Cu and the balance Fe 5 Cr, and Ni.
  • the improved corrosion performance in the CaCl 2 bath also used in the molten salt electro-winning of metals has been compared and verified.
  • the small crevices in the microstructure are due to the presence of HCl induced corrosion which is always prevalent when calcium chloride is heated above its melting point. This can be removed by proper vacuum drying technique.

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  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
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  • Materials Engineering (AREA)
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  • Electrolytic Production Of Metals (AREA)

Abstract

L'invention concerne une électrode composée d'un alliage à base d'Al-M-Cu, un procédé de préparation de cet alliage, une cellule d'électrolyse comprenant l'électrode, l'utilisation d'un alliage à base d'Al-M-Cu comme anode et un procédé permettant d'extraire un métal réactif d'une source renfermant un métal réactif au moyen de l'alliage à base d'Al-M-Cu utilisé comme anode.
PCT/GB2006/002147 2005-06-21 2006-06-13 Electrode WO2006136785A2 (fr)

Priority Applications (7)

Application Number Priority Date Filing Date Title
US11/922,806 US8147624B2 (en) 2005-06-21 2006-06-13 Electrode
EA200702573A EA013139B1 (ru) 2005-06-21 2006-06-13 Электрод
CA002654272A CA2654272A1 (fr) 2005-06-21 2006-06-13 Electrode
AU2006260791A AU2006260791B2 (en) 2005-06-21 2006-06-13 Electrode
EP06744191A EP1904668A2 (fr) 2005-06-21 2006-06-13 Electrode
NO20080063A NO20080063L (no) 2005-06-21 2008-01-04 Electrode
US13/418,025 US8900438B2 (en) 2005-06-21 2012-03-12 Electrolytic cell and electrochemical process using an electrode

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
GB0512836.8 2005-06-21
GB0512836A GB0512836D0 (en) 2005-06-21 2005-06-21 Inert alloy anodes for aluminium electrolysis cell using molten salt bath confidential
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FR650982A (fr) * 1927-03-22 1929-02-13 Alais & Froges & Camarque Cie Alliages d'aluminium et leur procédé de fabrication
DE19812444A1 (de) * 1998-03-21 1999-09-30 Max Planck Inst Eisenforschung TiAl-Basislegierung
US6083362A (en) * 1998-08-06 2000-07-04 University Of Chicago Dimensionally stable anode for electrolysis, method for maintaining dimensions of anode during electrolysis

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US8900438B2 (en) 2005-06-21 2014-12-02 University Of Leeds Electrolytic cell and electrochemical process using an electrode

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