Electrolysis: processes – compositions used therein – and methods – Electrolytic synthesis – Utilizing fused bath
Reexamination Certificate
2002-10-02
2004-11-02
King, Roy (Department: 1742)
Electrolysis: processes, compositions used therein, and methods
Electrolytic synthesis
Utilizing fused bath
C204S243100
Reexamination Certificate
active
06811678
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to electrochemical reduction of beryllium oxide in a solid state in an electrolytic cell.
The present invention relates particularly to electrochemical reduction of beryllium oxide in a solid state to produce high purity beryllium metal in an electrolytic cell.
2. Description of Related Art
Beryllium metal has a combination of physical and mechanical properties, such as low weight, stiffness, resistance to corrosion from acids, transparency to X-rays and other electromagnetic radiation, and electrical and thermal conductivity, that make it useful for various applications in metal, alloy and oxide forms.
Beryllium metal is used principally in aerospace and defence applications. Its high stiffness, light weight, and dimensional stability within a wide temperature range make it useful in satellite and space vehicle structures, inertial guidance systems for missiles, military aircraft brakes, structural components of military aircraft, and space optical system components.
Beryllium alloys include beryllium-copper, beryllium-nickel, and beryllium-aluminium alloys, of which beryllium-copper alloys are the most important commercially. Beryllium-copper alloys are used in a wide range of applications that require electrical and thermal conductivity, high strength and hardness, good corrosion and fatigue resistance, and non-magnetic properties. Beryllium-copper strip is manufactured into springs, connectors, and switches for use in applications in automobiles, aerospace, radar, and telecommunications, factory automation, computers, and instrumentation and control systems.
Beryllium metal is extracted from beryllium oxide-containing minerals beryl (3BeO—Al
2
O
3
—6SiO
2
) and bertrandite (4BeO—2SiO
2
—H
2
O) by chemical reduction. However, energy requirements and therefore production costs for producing beryllium by conventional chemical reduction technology currently being used are high.
An object of the present invention is to provide an alternative method of extracting beryllium metal from beryllium oxides.
SUMMARY OF THE INVENTION
The present invention was made during the course of an on-going research project on the electrochemical reduction of a range of metal oxides in a solid state in an electrolytic cell that is being carried out by the applicant.
During the course of the research project the applicant carried out experimental work on a range of different metal oxides in an electrolytic cell that included a graphite crucible that formed an anode of the cell, a pool of molten CaCl
2
-based electrolyte in the crucible, and a cathode that included solid metal oxides. One of the metal oxides tested by the applicant is beryllium oxide.
Accordingly, the present invention provides a method of reducing beryllium oxide in a solid state in an electrolytic cell, which electrolytic cell includes an anode, a cathode formed at least in part from beryllium oxide, and a molten electrolyte, the electrolyte including cations of a metal that is capable of chemically reducing beryllium oxide, and which method includes a step of operating the cell at a potential that is above a potential at which cations of the metal that is capable of chemically reducing beryllium oxide deposit as the metal on the cathode, whereby the metal chemically reduces beryllium oxide.
The applicant does not have a clear understanding of the electrolytic cell mechanism at this stage. Nevertheless, whilst not wishing to be bound by the comments in this paragraph, the applicant offers the following comments by way of an outline of a possible cell mechanism. The experimental work carried out by the applicant produced evidence of Ca metal in the electrolyte. The applicant believes that, at least during the early stages of operation of the cell, the Ca metal was the result of electrodeposition of Ca
++
cations as Ca metal on electrically conductive sections of the cathode. The experimental work was carried out using a CaCl
2
-based electrolyte at a cell potential below the decomposition potential of CaCl
2
. The applicant believes that the initial deposition of Ca metal on the cathode was due to the presence of Ca
++
cations and O
−−
anions derived from CaO in the electrolyte. The decomposition potential of CaO is less than the decomposition potential of CaCl
2
. In this cell mechanism the cell operation is dependent at least during the early stages of cell operation on decomposition of CaO, with Ca
++
cations migrating to the cathode and depositing as Ca metal and O
−−
anions migrating to the anode and forming CO and/or CO
2
(in a situation in which the anode is a graphite anode). The applicant believes that the Ca metal that deposited on electrically conductive sections of the cathode was deposited predominantly as a separate phase in the early stages of cell operation and thereafter dissolved in the electrolyte and migrated to the vicinity of the beryllium oxide in the cathode and participated in chemical reduction of beryllium oxide. The applicant also believes that at later stages of the cell operation part of the Ca metal that deposited on the cathode was deposited directly on partially deoxidised beryllium oxide and thereafter participated in chemical reduction of beryllium oxide. The applicant also believes that the O
−−
anions, once extracted from the beryllium oxide, migrated to the anode and reacted with anode carbon and produced CO and/or CO
2
and released electrons that facilitated electrolytic deposition of Ca metal on the cathode.
The beryllium oxide may be any suitable type.
The beryllium oxide may be any suitable form.
By way of example, the beryllium oxide may be in the form of pellets.
Preferably the metal deposited on the cathode is soluble in the electrolyte and can dissolve in the electrolyte and thereby migrate to the vicinity of the cathode metal oxide.
It is preferred that the electrolyte be a CaCl
2
-based electrolyte that includes CaO as one of the constituents of the electrolyte.
In such a situation it is preferred that the cell potential be above the potential at which Ca metal can deposit on the cathode, i.e. the decomposition potential of CaO.
The decomposition potential of CaO can vary over a considerable range depending on factors such as the composition of the anode, the electrolyte temperature and electrolyte composition.
In a cell containing CaO saturated CaCl
2
at 1373K (1100° C.) and a graphite anode this would require a minimum cell potential of 1.34V.
It is also preferred that the cell potential be below the potential at which Cl
−
anions can deposit on the anode and form chlorine gas, i.e. the decomposition potential of CaCl
2
.
In a cell containing CaO saturated CaCl
2
at 1373K (1100° C.) and a graphite anode this would require that the cell potential be less than 3.5V.
The decomposition potential of CaCl
2
can vary over a considerable range depending on factors such as the composition of the anode, the electrolyte temperature and electrolyte composition.
For example, a salt containing 80% CaCl
2
and 20% KCl at a temperature of 900K (657° C.), decomposes to Ca (metal) and Cl
2
(gas) above 3.4V and a salt containing 100% CaCl
2
at 1373K (1100° C.) decomposes at 3.0V.
In general terms, in a cell containing CaO—CaCl
2
salt (not saturated) at a temperature in the range of 600-1100° C. and a graphite anode it is preferred that the cell potential be between 1.3 and 3.5V.
The CaCl
2
-based electrolyte may be a commercially available source of CaCl
2
, such as calcium chloride dihydrate, that partially decomposes on heating and produces CaO or otherwise includes CaO.
Alternatively, or in addition, the CaCl
2
-based electrolyte may include CaCl
2
and CaO that are added separately or pre-mixed to form the electrolyte.
It is preferred that the anode be graphite or an inert anode.
The applicant found in the experimental work that there were relatively significant amounts of carbon transferred from the graphite anode to the electr
Osborn Steve
Ratchev Ivan
Strezov Lazar
BHP Billiton Innovation Pty Ltd.
King Roy
Kondracki Edward J.
Miles & Stockbridge P.C.
Wilkins, III Harry D.
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