MXPA00011878A - Removal of oxygen from metal oxides and solid solutions by electrolysis in a fused salt - Google Patents

Abstract

A method for removing a substance (X) from a solid metal or semi-metal compound (M1X) by electrolysis in a melt of M2Y, comprises conducting the electrolysis under conditions such that reaction of X rather than M2 deposition occurs at an electrode surface, and that X dissolves in the electrolyte M2Y. The substance X is either removed from the surface (i.c. M1X) or by means of diffusion extracted fromthe care material. The temperature of the fused salt is chosen below the melting temperature of the metal M1. The potential is chosen below the decomposition potential of the electrolyte.

Description

e.

ELIMINATION OF OXYGEN OF METAL OXIDES AND SOLID SOLUTIONS BY ELECTROLYSIS IN A FUSED SALT DESCRIPTION OF THE INVENTION This invention relates to a method for reducing the level of dissolved oxygen or other elements of solid metals, metal compounds, semi-metallic compounds and alloys. In addition, the method refers to the direct production of metals from metal oxides or other compounds. Many metals and semi-metals form oxides, and some have a significant oxygen solubility. In many cases, oxygen is harmful and therefore needs to be reduced or eliminated before the metal can be fully exploited for its mechanical or electrical properties. For example, titanium, zirconium and hafnium are highly reactive elements and, when exposed to oxygen-containing environments, quickly form an oxide layer, even at room temperature. This passivation is the basis of its outstanding resistance to corrosion under oxidation conditions. However, this high reactivity has concomitant disadvantages which have dominated the extraction and processing of these metals. As convenient as oxidizing at high temperatures in the conventional way to form an oxide scale, titanium and other elements have a significant solubility for oxygen and other metalloids (for example, example, carbon and nitrogen) which results in a serious loss of ductility. This high reactivity of titanium and other elements of the IVA group extends to the reaction with refractory materials such as oxides, carbides, etc. at high temperatures, polluting and brittle again the base metal. This behavior is extremely harmful in the commercial extraction, fusion and processing of the metals concerned. Typically, extraction of a metal from the metal oxide is accomplished by heating the oxide in the presence of a reducing agent (the reductant). The selection of the reducer is determined by the comparative thermodynamics of the reducer oxide, specifically the free energy equilibrium in the reduction reactions. This balance must be negative to provide the driving force for the reduction to proceed. The kinetics of the reaction is mainly influenced by the reduction temperature and additionally by the chemical activities of the components involved. The latter is often an important feature to determine the efficiency of the process and the completion of the reaction. For example, it is frequently found that although this reduction must theoretically proceed to completion, the kinetics are considerably reduced by the progressive decrease in the activities of the components involved. In the case of an oxide source material, this it results in a residual content of oxygen (or other element that may be involved) which may be harmful to the properties of the reduced metal, for example, in lower ductility, etc. This frequently leads to the need for additional operations to refine the metal and remove the final residual impurities to achieve high quality metal. Because the reactivity of the elements of the group IVA is high, and the harmful effect of the residual impurities ^ 10 serious, the extraction of these elements is not carried out normally of the oxide, but after the preliminary chlorination, reducing the chloride . Magnesium or sodium are often used as the reducer. In this form, the effects of residual oxygen are avoided. This leads inevitably, however, at higher costs that make the final metal more expensive, which limits its application and value to a potential user. Faith Despite the use of this process, oxygen contamination still occurs. During processing at high For example, a hard layer of oxygen enriched material is formed below the more conventional oxide scale. In titanium alloys this frequently seals the "alpha box", from the stabilizing effect of oxygen on the alpha phase in alpha-beta alloys. Yes this layer does not eliminate the subsequent processing to the Room temperature can lead to the initiation of cracks in the hard and relatively brittle surface layer. These can then spread inside the metal body, below the alpha box. If the hard alpha box or cracked surface is not removed before further processing of the metal, or service of the product, there may be a serious reduction in performance, especially fatigue properties. Heat treatment in a reducing atmosphere is not available as a means to overcome this problem because the metals of the IVA group become brittle due to hydrogen and because the oxide or "dissolved oxygen" can not be reduced or decreased. The commercial costs to avoid this problem are significant. In practice, for example, the metal is frequently cleaned after heating by first removing the oxide flake by mechanical grinding, sandblasting, or using a molten salt, followed by acid deoxidation, often in mixtures of HNO3 / HF to remove the metal layer enriched with oxygen below the scale. These operations are expensive in terms of loss of metal production, consumables and not less in affluent treatment. To reduce the scale and the costs associated with the removal of the scale, heating is carried out at a temperature as low as practice. This, in itself, reduces the productivity of the plant, as well as increases the load on the plant due to the reduced viability of the material at lower temperatures. All these factors increase the processing costs. In addition, deoxidation with acid is not always easy to control, either in terms of hydrogen contamination of the metal, which leads to serious problems of fragility, or in the given surface and dimensional control. The latter is essentially important in the production of thin materials such as thin film, fine wire, etc. It is therefore evident that a process that can remove the oxide layer of a metal and additionally of the dissolved oxygen of the alpha sub-surface box, without the grinding and deoxidation described above, could have considerable technical and economic benefits over the processing metallic, including metal extraction. Such a process may also have advantages in subordinate stages of the purification treatment, or processing. For example, the turner waste material produced during the mechanical removal of the alpha box, or the machining to final size, are difficult to recycle due to their high content of oxygen and hardness, and the effect consequently on the chemical condition and increase in hardness of the metal within which they are recycled.

Even greater advantages could be added if the material that has been in service at elevated temperatures and has been oxidized or contaminated with oxygen could be rejuvenated by a sensitive treatment. For example, the life of an aerial machine compressor blade or disk made of titanium alloy is restricted to some degree, by the depth of the alpha box layer and the dangers of the initiation of surface cracks and propagation within the body of the disk, leading to premature failure. In this case, deoxidation with acid and mechanical grinding are not possible options since a loss of dimension could not be tolerated. A technique that decreases the dissolved oxygen content without accepting the total dimensions, especially in complex forms, such as sheets or compressor discs, would have obvious and very important economic benefits. Due to the greater effect of temperature on the thermodynamic efficiency these benefits would be compound and would allow the discs to operate not only for longer times at the same temperature, but also possibly at higher temperatures where greater fuel efficiency can be achieved. the aerial machine. In addition to titanium, an additional metal of commercial interest is germanium, which is a semi-conductor metalloid element found in the Group IVA of the Periodic Table. It is used in a highly purified state, in Infra-red and electronic optics. Oxygen, phosphorus, arsenic, antimony and other metalloids are typical of impurities that must be carefully controlled in germanium to ensure proper functioning. Silicon is a similar semi-conductor and its electrical properties critically depend on its purity content. The controlled purity of the relative silicon or germanium is fundamentally important as a safe and reproducible base, over which the required electrical properties can be built into computer chips, etc. U.S. Patent No. 5,211,775 describes the use of metallic calcium to deoxidize titanium. Okabe, Oishi and Ono (Met. Trans B. 23B (1992): 583) have used a calcium-aluminum alloy to deoxidize titanium aluminides, Okabe, Nakamura, Oishi and Ono (Met. Trans B. 24B (1993): 449) deoxidated titanium electrochemically by producing calcium from a calcium chloride fusion on the titanium surface Okabe, Devra, Oishi, Ono and Sadoway (Journal of Alloys and Compounds 237 (1996) 150) have deoxidized yttrium using a similar proposal. ard et al, Journal of the Institute of Metals (1961) 90: 6-12, describes an electrolytic treatment for the removal of various contaminants from molten copper during a refining process.Fused copper is treated in an electric battery with chloride of barium as the electrolyte. Experiments show that sulfur can be removed using this process. However, the elimination ^ Oxygen is less certain, and the authors state that spontaneous non-electrolyte oxygen loss occurs, which may mask the degree of oxygen removal by this process. Additionally, the process requires melting the metal, which adds to the total cost of the refining process. The process is therefore unsuitable for a metal such as titanium which melts at 1660 ° C, and which ^ 10 has a highly reactive fusion. According to the present invention, a method for removing a substance (X) from a solid metal or semi-metallic compound (M1X) by electrolysis in a melt of M2Y, comprises conducting low electrolysis conditions in such a way that the deposition reaction of X more than that of M2 occurs on an electrode surface, and that X dissolves in the electrolyte M2Y. ^ fc According to one embodiment of the invention, XX is a conductor and is used as the cathode. Alternatively, M1X can be an insulator in contact with a conductor. In a separate embodiment, the electrolysis product (M2X) is more stable than MXX. In a preferred embodiment, M2 can be any of Ca, Ba, Li, Cs or Sr and Y is Cl. Preferably, M1X is a coating superficial on a body of M1. In a preferred separate embodiment, X is dissolved within M1. In a further preferred embodiment, X is any of 0, S, C or N. In a further more preferred embodiment, M1 is any of Ti, Si, Ge, Zr, Hf, Sm, U, Al, Mg, Md, Mo , Cr, Nb, or any alloy thereof. In the method of the invention, electrolysis preferably occurs with a potential below the electrolyte potential. An additional metallic compound or a semi-metallic compound (MNX) may be present, and the electrolysis product may be an alloy of the metallic elements. The present invention is based on the realization that an electrochemical process can be used to ionize the oxygen contained in a solid metal so that oxygen dissolves in the electrolyte. When a suitable negative potential is applied in an electrochemical cell with the oxygen-containing metal as the cathode, the following reaction occurs: 0 + 2e ~ - O2 The ionized oxygen is then able to dissolve in the electrolyte. The invention can be used to extract oxygen dissolved from a metal, that is to say eliminating the alpha box, or it can be used to remove oxygen from a metal oxide. If a mixture of oxides is used, the cathodic reduction of the oxides will cause an alloy to form. The process for carrying out the invention is more direct and cheaper than the more usual reduction and refinement commonly used. In principle, other cathodic reactions involving the reduction and dissolution of other metalloids, carbon, nitrogen, phosphorus, arsenic, antimony, etc., could also take place. Various electrode potentials, relative to ENa = 0 V, at 700 ° C in fused chloride fusions containing calcium chloride, are as follows: Ba2 + 2e ~ = Ba -0.314 V Ca2 + 2e "= Ca -0.06 V Hf4 + + 4e "= Hf 1.092 V Zr4 + 4e" = Zr 1.516 V Ti4 + 4e ~ = Ti 2.039 V Cu + + e "= Cu 2.339 V Cu2 + 2e" = Cu 2.92 V 02 + 4e ~ = 202 ~ 2.77 V Metal , metallic compound or semi-metallic compound may be in the form of simple crystals or earthenware, sheets, wires, tubes, etc., commonly known as semi-finished or press products, during or after production; or alternatively in the form of an artifact made of a press product such as in forging, machining, welding, or a combination thereof during or after service. The element or its alloy can also be in the form of scrapes, chips, grinds to some other by-product of a manufacturing process. In addition, the metal oxide can also be applied to a metal substrate before the treatment, for example Ti02 can be applied to steel and subsequently reduced to the titanium metal. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic illustration of the apparatus used in the present invention. Figure 2 illustrates the hardness profiles of a surface sample of titanium before and after electrolysis at 3.0 V and 850 ° C; and Figure 3 illustrates the difference in streams for the electrolytic reduction of Ti02 pellets under different conditions. In the present invention, it is important that the potential of the cathode is maintained and controlled potentiostatically so that only the ionization of the oxygen occurs and not the more usual deposition of the cations in the fused salt.

The degree to which the reaction occurs depends on the diffusion of oxygen on the surface of the metal cathode. If the diffusion rate is low, the reaction soon becomes polarized and, to keep the current flowing, the potential becomes more cathodic and the next cathodic competition reaction will occur, ie the deposition of the fused salt electrolyte cation. However, if the process is allowed to take place at elevated temperatures, the ionization diffusion of dissolved oxygen at the cathode will be sufficient to satisfy the applied currents, and the oxygen will be removed from the cathode. This will continue until the potential becomes more cathodic, due to the lower level of oxygen dissolved in the metal, until the potential equals the discharge potential for the electrolyte cation. This invention can also be used to remove dissolved oxygen or other dissolved elements, for example sulfur, nitrogen and carbon from other metals or semi-metals, for example germanium, silicon, hafnium and zirconium. The invention can also be used to electrolytically decompose oxides of elements such as titanium, uranium, magnesium, aluminum, zirconium, hafnium, niobium, molybdenum, neodymium, samarium and other rare earths. When the oxide mixtures are reduced, an alloy of the reduced metals will be formed.

The metal oxide compound must show at least some initial metallic conductivity or be in contact with a conductor. One embodiment of the invention will now be described with reference to the drawing, wherein Figure 1 shows a piece of titanium made in a cell which is made up of an inert anode submerged in a molten salt. The titanium may be in the form of a rod, sheet or other artifact. If the titanium is in the form of chip or particulate matter, it can be kept in a mesh basket. In the application of a voltage by means of a power source, the current flow will not start until the equilibrium reactions occur at the anode and cathode. At the cathode, there are two possible reactions, the discharge of the salt cation or the ionization and dissolution of the oxygen. The last reaction occurs at a more positive potential than the discharge of the metal cation and, therefore, will occur first. However, for the reaction to proceed, it is necessary for the oxygen to diffuse to the surface of the titanium and, depending on the temperature, this can be a slow process. For best results, therefore, it is important that the reaction is carried out at a suitably high temperature and, that it controls the cathodic potential, to prevent the potential from rising and that the metal cations in the electrolyte be discharged as a reaction of competition to ionization and dissolution of oxygen within the electrolyte. This can be ensured by measuring the potential of the titanium relative to a reference electrode, and prevented by potentiostatic control so that the potential never becomes sufficiently cathode to discharge the metal ions from the fused salt. The electrolyte should consist of salts that are preferably more stable than the equivalent salts of the metal being refined, and, ideally, the salt should be as stable as possible to remove oxygen at concentrations as low as possible. The selection includes the salts of barium chloride, calcium, cesium, lithium, strontium and yttrium. The melting and boiling points of these chlorides are given below: 15 Melting Point 0 (° C) Boiling Point (° C) BaCl 2 963 1560 CaCl 2 782 > 1600 CsCl 645 1280 LiCl 605 1360 20 SrCl2 875 1250 YC13 721 1507 When using salts with a low melting point, it is possible to use mixtures of these salts and a fused salt is required which melts at a lower temperature, for example when using a eutectic or almost eutectic mixture. It is also advantageous to have, as an electrolyte, a salt with a wide difference between the melting and boiling points, since this gives a wide operating temperature without excessive vaporization. In addition, the higher the operating temperature, the greater will be the diffusion of oxygen in the surface layer and therefore the time for deoxidation to take place will be correspondingly less. Any salt could be used with the proviso that the oxide of the cation in the salt is more stable than the oxide of the metal to be purified. The following examples illustrate the invention. In particular, examples 1 and 2 refer to the removal of oxygen from an oxide. Example 1 A pellet of white Ti02, 5mm in diameter and 1mm thick, was placed in a titanium crucible filled with molten calcium chloride at 950 ° C. A 3V potential was applied between a graphite anode and a titanium crucible. After 5 hours, the salt was allowed to solidify and then dissolved in water to reveal a black / metallic pellet. The analysis of the pellet showed that they were 99.8% titanium. Example 2 A thin sheet strip of titanium metal was oxidized strongly in air to give a thick oxide coating (c.50mm). The thin sheet of metal was placed in calcium chloride melted at 950 ° C and a potential of 1.75V was applied for 1.5 hours. By removing the thin sheet of titanium metal from the melt, the oxide layer had been completely reduced to metal. Examples 3-5 refer to the removal of dissolved oxygen contained within a metal. EXAMPLE 3 Sheets of titanium (oxygen 1350-1450 hardness number of Vickers 180) of commercial purity (CP) were made the cathode in a melt of molten calcium chloride, with a carbon anode. The following potentials were applied for 3 hours at -950 ° C followed by 1.5 hours at 800 ° C. The results were as follows: V (volt) Vickers hardness content number of oxygen 3 V 133.5 < 200 ppm 3.3 V 103 < 200 ppm 2.8 V 111 < 200 ppm 3.1 101 < 200 ppm The 200 ppm was the lowest detection limit of the analytical equipment. The hardness of titanium is directly related to the oxygen content, and thus measuring the hardness provides a good indication of the oxygen content. The decomposition potential of pure calcium chloride at this temperature is 3.2 V. When considered Polarization losses and resistive losses require a cell potential of around 3.5V to deposit calcium. Since it is not possible for calcium to be deposited below this potential, these results prove that the cathodic reaction is: 0 + 2e "= O2" This further demonstrates that oxygen can be removed from titanium by this technique. Example 4 A titanium sheet of commercial purity was heated for 15 hours in air at 700 ° C to form an alpha box on the surface of the titanium. After sampling the cathode in a CaCl2 fusion with a carbon anode at 850 ° C, apply a power of 3V for 4 hours at 850 ° C, the alpha box was removed as shown by the hardness curve (Figure 2), where VHN represents the hardness number of Vicker. Example 5 A 6 Al 4V titanium alloy sheet containing 1800 ppm oxygen was made the cathode in a CaCl 2 melt at 950 ° C and a 3V cathode potential was applied.

After 3 hours, the oxygen content decreased from 1800 ppm to 1250 ppm. Examples 6 and 7 show the removal of the alpha box from a thin sheet of alloy metal.

Example 6 A thin sheet metal sample of Ti-6A1-4V alloy with an alpha box (thickness of approximately 40 μm) under the surface was electrically connected at one end to a cathode current collector (a Kanthal wire) and then was inserted into a CaCl2 fusion. The fusion was contained in a titanium crucible which was placed in a sealed Inconel reactor which was continuously washed with argon gas at 950 ° C. The sample size was 1.2 mm thick, 8.0 mm wide and ~ 50 mm long. The electrolysis was carried out in a controlled voltage form, 3.0V. It was repeated with two different experimental times and final temperatures. In the first case, the electrolysis lasted for one hour and the sample was immediately removed from the reactor. In the second case, after 3 hours of electrolysis, the oven temperature was allowed to cool naturally while electrolysis was maintained. When the oven temperature dropped slightly less than 800 ° C, the electrolysis was finished and the electrode was removed. Washing with water revealed that the 1-hour sample had a metallic surface but no brown parts, while the three-hour sample was completely metallic. Both samples were then sectioned and mounted on a bakelite tip and a normal grinding and polishing procedure was carried out. The cross section of the Samples were investigated by microhardness test, electron scanning microscopy (SEM) and energy dispersive X-ray analysis (EDX). The hardness test showed that the alpha box of both samples disappeared, although the three-hour sample showed a hardness near the surface much lower than that in the center of the sample. In addition, SEM and EDX detected insignificant changes in structure and elemental composition (except for oxygen) in the deoxygenated samples. Example 7 In a separate experiment, thin sheet metal samples TÍ-6A1-4V as described above (1.2 mm thick 8 mm wide and 25 mm long) were placed on the bottom of the titanium crucible which functioned as the cathode current collector. The electrolysis was then carried out under the same conditions as mentioned in Example 6 for the 3 hour sample except that the electrolysis lasted for 4 hours at 950 ° C. Again the use of the microhardness, SEM and EDX test revealed the successful elimination of the alpha box in all three samples without altering the structure and elemental composition except for oxygen. Example 8 shows a sliding melting technique for the fabrication of the oxide electrode.

Example 8 A powder of Ti02 (anatase, Aldrich, 99.9 +% purity, the powder possibly contains a surfactant) was mixed with water to produce a solution (Ti02: H20 = 5: 2 by weight) which was then melted by sliding and a variety of shapes (round pellets, rectangular blocks, cylinders, etc.) and sizes (from millimeters to centimeters), dried in room / ambient atmosphere at night and sintered in air, typically for two hours at 950 ° C in air. The resulting Ti02 solid has a working strength and a porosity of 40 ~ 50%. There was negligible but noticeable shrinkage between the sintered and non-sintered Ti02 pellets. 0.3g ~ 10g of the pellets was placed on the bottom of a titanium crucible containing a fresh CaCl2 fusion (typically 140g). The electrolysis was carried out at 3.0V (between the titanium crucible and a graphite rod anode) and 950 ° C under an argon environment for 5 ~ 15 hours. It was observed that the current flow at the beginning of the electrolysis increased almost proportionally with the amount of the pellets and followed approximately a pattern of 1 g Ti02 corresponding to IA of initial current flow. It was observed that the degree of reduction of the pellets can be estimated by the color in the center of the pellet. A smaller or metallized pellet is gray completely, but a less reduced pellet is dark gray or black in the center. The degree of reaction of the pellets can also be judged in distilled water for a few hours during the night. The partially reduced pellets are automatically broken into fine black powders while the metallized pellets remain in the original form. It was also noted that even for metallized pellets, the oxygen content can be estimated by the resistance to pressure applied at room temperature. The pellets became a gray powder under the pressure if there was a high level of oxygen, but a metallic sheet if the oxygen levels were low. The SEM and EDX investigation of the pellets revealed considerable difference in the composition and structure between the metallized and partially reduced pellets. In the metallic case, the typical structure of the dendritic particles was always seen, and little or no oxygen was detected by EDX. However, the partially reduced pellets were characterized by crystallites having a composition of CaxTiyOz as revealed by EDX. Example 9 It is highly desirable that the electrolytic extraction be carried out on a large scale and the product be conveniently removed from the molten salt at the end of the electrolysis. This can be done, for example, by placing Ti0 pellets in a basket-type electrode. The basket was made by drilling many holes (~ 3.5 mm in diameter) into a thin sheet of titanium metal (~ 1.0 mm thick) which was then bent at the edge to form a hollow cuboid basket with an internal volume of 15x45x45 mm3 . The basket was connected to a power source by a Kanthal wire. A large graphite crucible (140 mm deep, 70 mm diameter and 10 mm wall thickness) was used to contain the CaCl2 fusion. It also connected to the power source and functioned as the anode. Approximately 10 g of pellets / ampoules of Ti02 melted by sliding (each was approximately 10 mm in diameter and 3 mm in maximum thickness) were placed in the titanium basket and lowered into the melt. The electrolysis was conducted at 3.0V, 950 ° C, for about 10 hours before the furnace temperature was dropped naturally. When the temperature reached approximately 800 ° C, electrolysis was completed. The basket was then raised from the melt and held in a water cooled upper part of the Inconel reactor tube until the furnace temperature dropped below 200 ° C before being removed for analysis. After acid leaching (HCl, pH < 2) and washing with water, the electrolyzed pellets showed the same SEM and EDX characteristics as previously observed.

Some of the pellets were ground into a powder and analyzed by thermogravimetry and elemental vacuum fusion analysis. The results showed that the powder contained approximately 20,000 ppm of oxygen. The SEM and EDX analysis showed that, apart from the typical dendritic structure, some crystallites of CaTiOx (x < 3) were observed in the powder which may be responsible for a significant fraction of the oxygen contained in the product. If this is the case, it is expected that by melting the powder, purer titanium metal ingot can be produced. An alternative to the basket-type electrode is the use of a "sweet" Ti02 electrode. This is composed of a central current collector and on the upper part of the collector a reasonably thick layer of porous Ti02. In addition to a reduced surface area of the current collector, other advantages of using a sweet type Ti02 electrode include: first, that it can be removed from the reactor immediately after electrolysis, saving processing time and CaCl2; second, and more important than the potential and current distribution and therefore the efficiency of the current can be greatly improved. EXAMPLE 10 A slurry of Ti02 Anatase Aldrich powder was melted by sliding into a capped cylindrical candy slightly (~ 20 mm in length and ~ mm in diameter) comprising a thin sheet of titanium metal (0.6 mm thick, 3 mm wide and ~ 40 mm long) in the center. After sintering at 950 ° C, the candy was electrically connected at the end of the thin sheet of titanium metal to a power source by a Kanthal wire. The electrolysis was carried out at 3.0V and 950 ° C for about 10 hours. The electrode was removed from the melt at about 800 ° C, washed and leached with HCl acid (pH 1-2). The product was then analyzed by SEM and EDX. Again a typical dendritic structure was observed and oxygen, chlorine and calcium could not be detected by EDX. The sliding melt method can be used to make large or cylindrical rectangular blocks of Ti02 which can then be machined into an electrode with a desired shape and size suitable for industrial process. In addition, large crosslinked Ti02 blocks, foams of Ti02 with a coarse skeleton can also be made by sliding fusion, and this will aid in the draining of the salt. The fact that there is little oxygen in a freshly dried CaCl2 fusion suggests that the discharge of chloride anions should be the dominant anodic reaction in the initial stage of electrolysis. This anodic reaction will continue until the oxygen anions of the cathode are transported to the anode. The reactions can be summarized as follow: anode: Cl "- Cl2 1 + e cathode: Ti02 + 4e - Ti + 202 ~ total: Ti02 + 4C1" - Ti + 2C12 | + 202 ~ When enough O2- ions are present in the anodic reaction it becomes: O2"- 4 02 + 2e" and the total reaction: Ti02 - Ti + 02 | Apparently the exhaustion of the chloride anions is irreversible and consequently the cathodically formed oxygen anions will remain in the melt to balance the charge, leading to an increase in the concentration of oxygen in the melt. Since the oxygen level in the titanium cathode is in a chemical equilibrium or quasi-equilibrium with the oxygen level in the melt for example by means of the following reaction: Ti + CaO-TiO + Ca K (950 ° C) = 3.28xl0 ~ 4 It is expected that the final oxygen level in the electrolytically extracted titanium can not be very low if the electrolysis proceeds in the same fusion controlling the voltage only. This problem can be solved by (1) controlling the initial rate of cathodic oxygen discharge and (2) reducing the concentration of oxygen in the melt. The last it can be achieved by controlling the current flow in the initial stage of electrolysis for example by gradually increasing the applied cell voltage to the desired value so that the current flow will not go beyond a limit. This method can be called "doubly controlled electrolysis". The last solution to the problem can be achieved by performing electrolysis in a first fusion with high oxygen level, which reduces the Ti02 to the metal with a high oxygen content, and then transferring the metal electrode to a low oxygen fusion for additional electrolysis . The electrolysis in the fusion of low oxygen can be considered as an electrolytic refining process and can be called "double fusion electrolysis". Example 11 illustrates the use of the principle of "double fusion electrolysis". Example 11 A sweet Ti02 electrode was prepared as described in Example 10. A first electrolysis step was carried out at 3.0V, 950 ° C overnight (-12 hours) in refined CaCl2 contained within a crucible of alumina. A graphite rod was used as the anode. The sweet electrode was then transferred immediately to a fresh fusion of CaCl2 contained within a titanium crucible. A second electrolysis was then carried out for about 8 hours at the same voltage and temperature as the first electrolysis, again with a graphite rod as the anode. The sweet electrode was removed from the reactor at approximately 800 ° C, it was washed, leached with acid and washed again in distilled water with the help of an ultrasonic bath. Again SEM and EDX confirmed the success in the extraction. The thermo-weight analysis was applied to determine the purity of the titanium extracted based on the principle of re-oxidation. Approximately 50 mg of the sample from the sweet electrode was placed in a small alumina crucible with a lid and heated in air at 950 ° C for about 1 hour. The crucible containing the sample was weighed before and after heating and the increase in weight was observed. The increase in weight was then compared with the theoretical increase when pure titanium is oxidized to titanium dioxide. The result showed that the sample contains 99.7 +% titanium, implying less than 3000 ppm of oxygen. Example 12 The principle of this invention can be applied not only to titanium but also to other metals and their alloys. A mixture of powders of Ti02 and A1203 (5: 1 by weight) was slightly moistened and pressed into pellets (20 mm in diameter and 2 mm thick) which were then sintered in air at 950 ° C for 2 hours. The pellets sintered were white and slightly smaller than before sintering. Two of the pellets were electrolyzed in the same manner as described in Example 1 and Example 3. The SEM and EDX analysis revealed that after electrolysis the pellets changed to the Ti-Al metal alloy although the elemental distribution in the pellet it was not uniform: the concentration of Al was higher in the central part of the pellet than near the surface, varying from 12% by weight to 1% by weight. The microstructure of the Ti-Al alloy pellet was similar to that of the pure Ti pellet. Figure 3 shows the comparison of currents for the electrolytic reduction of the Ti02 pellets under different conditions. It can be shown that the amount of current flow is directly proportional to the amount of oxide in the reactor. More importantly, it also shows that the current decreases with time and therefore probably the oxygen in the ionizing dioxide and not the calcium deposition. If calcium were deposited, the current would remain constant over time.

Claims (25)

1. CLAIMS 1. A method for removing a substance (X) from a solid metal, a metal compound or a semimetallic compound (MXX) by electrolysis in a fused salt of M2Y or a mixture of salts, characterized in that it comprises conducting electrolysis under such conditions that the deposition reaction of X more than M2 occurs on an electrode surface, and that X dissolves in the electrolyte M2Y.
2. 2. The method according to claim 1, characterized in that M1X is a conductor and is used as the cathode.
3. 3. The method according to claim 1, characterized in that M X is an insulator and is used in contact with a conductor.
4. 4. The method according to any preceding claim, characterized in that electrolysis is carried out at a temperature of 700 ° C-1000 ° C.
5. 5. The method according to any preceding claim, characterized in that the electrolysis product (M2X) is more stable than M1X.
6. 6. The method according to any preceding claim, characterized in that M2 is Ca, Ba, Li, Cs, or Sr and Y is Cl.
7. 7. The method according to any preceding claim, characterized in that M1X is a surface coating on a body of M1.
8. 8. The method according to any of claims 1 to 6, characterized in that X is dissolved from within M1.
9. The method according to any preceding claim, characterized in that X is O, S, C or N.
10. 10. The method according to any preceding claim, characterized in that M1 is Ti or an alloy thereof.
11. 11. The method according to any of claims 1 to 9, characterized in that M1 is Si or an alloy thereof.
12. The method according to any of claims 1 to 9, characterized in that M1 is Ge or an alloy thereof.
13. The method according to any of claims 1 to 9, characterized in that M1 is Zr or an alloy thereof.
14. The method according to any of claims 1 to 9, characterized in that M1 is Hf or an alloy thereof.
15. 15. The method according to any of claims 1 to 9, characterized in that M1 is Sm or an alloy thereof.
16. 16. The method according to any of claims 1 to 9, characterized in that M1 is U or an alloy thereof.
17. 17. The method according to any of claims 1 to 9, characterized in that M1 is Al or an alloy thereof.
18. 18. The method according to any of claims 1 to 9, characterized in that M1 is Mg or an alloy thereof.
19. 19. The method according to any of claims 1 to 9, characterized in that M1 is Nd or an alloy thereof.
20. 20. The method according to any of claims 1 to 9, characterized in that M1 is Mo or an alloy thereof.
21. 21. The method according to any of claims 1 to 9, characterized in that M1 is Cr or an alloy thereof.
22. 22. The method according to any of claims 1 to 9, characterized in that M1 is Nb or an alloy thereof.
23. 23. The method according to any preceding claim, characterized in that MXX is in the form of a porous pellet or powder.
24. 24. The method of compliance with any Claim 1, characterized in that electrolysis occurs with a potential below the potential decomposition of the electrolyte. The method according to any preceding claim, characterized in that an additional metallic compound or semi-metallic compound (MNX) is present, and the electrolysis product is an alloy of the metallic elements.