EP0053565A1 - Apparatus and process for feeding TiCl4 to electrolysis cells used for the manufacture of titanium - Google Patents

Apparatus and process for feeding TiCl4 to electrolysis cells used for the manufacture of titanium Download PDF

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Publication number
EP0053565A1
EP0053565A1 EP81420173A EP81420173A EP0053565A1 EP 0053565 A1 EP0053565 A1 EP 0053565A1 EP 81420173 A EP81420173 A EP 81420173A EP 81420173 A EP81420173 A EP 81420173A EP 0053565 A1 EP0053565 A1 EP 0053565A1
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Prior art keywords
diaphragm
ticl
cathode
titanium
electrolyte
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German (de)
French (fr)
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EP0053565B1 (en
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Marcel Armand
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Pechiney SA
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Pechiney SA
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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C7/00—Constructional parts, or assemblies thereof, of cells; Servicing or operating of cells
    • C25C7/06—Operating or servicing
    • 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
    • C25C3/26—Electrolytic production, recovery or refining of metals by electrolysis of melts of titanium, zirconium, hafnium, tantalum or vanadium
    • C25C3/28—Electrolytic production, recovery or refining of metals by electrolysis of melts of titanium, zirconium, hafnium, tantalum or vanadium of titanium

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  • the device and the method which are the subject of the invention relate to the preparation of titanium by electrolysis in a bath of molten halides. They relate more particularly to the method of supplying the cell with TiCl 4 .
  • a feed device makes it possible to continuously introduce, as the electrolysis takes place, titanium tetrachloride into a bath of molten alkali or alkaline earth halides.
  • FIG. 1 represents such an electrolysis cell of the type described in FR 2,423,555 which comprises a metal casing (1) containing the molten electrolyte (2).
  • An anode (3) is placed inside an anode compartment (4).
  • a diaphragm (5) separates this compartment from the rest of the cell in which the deposition (6) and supply (7) cathodes are located.
  • the supply cathode (7) is tubular in shape. It is, for example, in wire mesh and connected to the negative pole of a current source.
  • This metallic fabric can be, for example, carbon steel or another metal such as nickel or stainless steel optionally coated with cobalt.
  • a supply of TiCl 4 is carried out inside the supply cathode (7) by means of the tube (8) placed in the vicinity of its axis. This tube is insulated from the cathode. Under these conditions, it can be seen that the TiCl 4 which leaves through the orifice (9) of the tube (8) is reduced at least partially to titanium subchloride which dissolves in the bath.
  • reaction (1) diffuses in the electrolyte and come to reduce at the supply cathode according to the reaction:
  • q is the mass of TiCl 4 introduced into the electrolyte in g / h and I 1 the intensity of the current in amperes.
  • the total current I which flows through the anode is such that:
  • the object of the invention is a device allowing the supply of TiCl 4 to an electrolysis cell for the preparation of titanium comprising at least one deposition cathode and a supply cathode; this device is a metallic diaphragm which surrounds the insulating cathode and which is insulated from it.
  • 'reference electrodes disposed on either side of the diaphgrame are connected to a means for measuring the voltage difference therebetween.
  • Another object of the invention is a method for supplying an electrolysis cell for the preparation of titanium, comprising at least one supply cathode for TiCl 4 surrounded by a diaphragm isolated from it, in which the intensity of current 1 which flows through the supply cathode is adjusted so as to maintain a drop in potential weak but not zero in the electrolyte which permeates the diaphragm.
  • this adjustment is carried out by controlling the intensity of the current flowing through the supply cathode to the drop in potential in the electrolyte impregnating the diaphragm or to a variable linked to this drop in potential.
  • the diaphragm (20) which constitutes one of the objects of the invention, is made of a metal having sufficient strength vis-à-vis the elec - trolyte in the temperature conditions in which one operates. It is possible, for example, to use unalloyed nickel, or nickel-based alloys or else steels, preferably stainless.
  • This diaphragm is connected to the upper part of the cover (19) of the electrolyser by means of a sealed metallic annular wall (21) which is fixed to the cover (19) by insulating and waterproof annular seals (22) and (23 ).
  • the annular wall (21) penetrates through its lower part into the electrolyte and thus obstructs the circulation of the gases present above the level of the electrolyte on either side of the diaphgram (20).
  • the essential role of this is to obstruct the diffusion of TiCl3 formed according to reaction (2) by the action of TiC1 4 on TiCl 2 , outside the space delimited by this diaphragm.
  • the electrolyte area located in the immediate vicinity of the rods (17) and (18), which constitute the supply cathode is enriched in TiCl 3 , which allows a very rapid redissolution of the titanium formed in contact with these rods by discharge of bivalent titanium ions.
  • the structure of the diaphragm (20) can be produced, for example, in the form of a metallic cloth such as a nickel cloth, or of a sheet obtained by sintering a metallic powder, for example based on steel. stainless, and having sufficient residual porosity.
  • the potential of this diaphragm (20) relative to the electrolyte in which it is immersed can be calculated by one of the following two equations, considering either the potential of the internal face of this diaphragm relative to the electrolyte (24) which is inside this diaphragm, that is to say the potential of the external face of the same diaphragm with respect to the electrolyte (25) located outside this diaphragm.
  • e o Ti 3+ / Ti 2+ represents the normal potential for reaction (6)
  • a Ti 3+ and a Ti 2+ represent the respective activities of the Ti 3+ and Ti2 + ions in the volume of electrolyte (24) contained in the space surrounded by the diaphragm (20).
  • n ° I which meets the best operating conditions of the cell, the solution, and this is the object of the invention, consists in regulating the current I 1 so that 'there is a drop in potential as small as possible, but not zero, in the bath permeating the diaphragm.
  • the porosity of it is not critical. It must be large enough not to overly brake the flow of electrolyte which passes through the diaphragm. It should be low enough to allow easy detection of a potential drop in the electrolyte permeating the diaphragm.
  • this drop in potential is relatively difficult to achieve. It is however possible to measure a value very close to this potential difference by having on either side of the diaphragm, but without contact with it, two reference electrodes, for example electrodes sensitive to chlorine ions (26 ) and (27) such as Ag / AgCl electrodes immersed in the electrolyte: the ends of these electrodes pass through the cell cover by insulating joints and are connected to a means of measuring the potential difference which will be used to control the current I 1 or what amounts to the same, the ratio I 2 / I 1 .
  • two reference electrodes for example electrodes sensitive to chlorine ions (26 ) and (27) such as Ag / AgCl electrodes immersed in the electrolyte: the ends of these electrodes pass through the cell cover by insulating joints and are connected to a means of measuring the potential difference which will be used to control the current I 1 or what amounts to the same, the ratio I 2 / I 1 .

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  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
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Abstract

The apparatus and the process according to the invention concern the preparation of titanium by electrolysis in a bath of molten halides. The apparatus comprises a porous diaphragm which is disposed around a feed cathode permitting partial reduction of the TiCl4 introduced into the electrolyte. The intensity of the current which passes through the feed cathode is so regulated as to maintain a low but non-zero voltage drop, across the diaphragm which is insulated with respect to the feed cathode.

Description

Le dispositif et le procédé qui font l'objet de l'invention concernent la préparation du titane par électrolyse en bain d'halogénures fondus. Ils concernent plus particulièrement le mode d'alimentation de la cellule en TiCl4.The device and the method which are the subject of the invention relate to the preparation of titanium by electrolysis in a bath of molten halides. They relate more particularly to the method of supplying the cell with TiCl 4 .

Plusieurs publications ont décrit des cellules d'électrolyse permettant la préparation du titane et comportant des dispositifs d'alimentation en continu en TiCI4.Several publications have described electrolysis cells allowing the preparation of titanium and comprising devices for continuously supplying TiCI 4 .

Les figures ci-après permettront de mieux comprendre les caractéristiques des dispositifs connus et celles du dispositif et du procédé qui font l'objet de l'invention.

  • Figure 1 : cellule d'électrolyse du type connu pour la préparation du titane.
  • Figure 2 : dispositif d'alimentation en TiCl4 suivant l'invention, d'une cellule d'électrolyse pour la préparation du titane.
The figures below will make it possible to better understand the characteristics of the known devices and those of the device and of the method which are the subject of the invention.
  • Figure 1: electrolysis cell of the type known for the preparation of titanium.
  • Figure 2: TiCl 4 supply device according to the invention, an electrolysis cell for the preparation of titanium.

Dans le brevet FR 2.423.555, est décrite une cellule anéliorée pour la préparation par électrolyse de métaux polyvalents et plus particulièrement pour la préparation du titane.In patent FR 2,423,555, an improved cell is described for the preparation by electrolysis of polyvalent metals and more particularly for the preparation of titanium.

Dans cette cellule, un dispositif d'alimentation permet d'introduire de façon continue, au fur et à mesure de l'électrolyse, du tétrachlorure de titane dans un bain d'halogénures alcalins ou alcalinoterreux fondus.In this cell, a feed device makes it possible to continuously introduce, as the electrolysis takes place, titanium tetrachloride into a bath of molten alkali or alkaline earth halides.

La figure 1 représente une telle cellule d'électrolyse du type décrit dans le FR 2.423.555 qui comporte une enveloppe métallique (1) contenant l'électrolyte fondu (2). Une anode (3) est placée à l'intérieur d'un compartiment anodique (4). Un diaphragme (5) sépare ce compartiment du reste de la cellule dans lequel se trouvent les cathodes de dépôt (6) et d'alimentation (7). Comme on le voit, la cathode d'alimentation (7) est de forme tubulaire. Elle est, par exemple, en toile métallique et reliée au pôle négatif d'une source de courant. Cette toile métallique peut être, par exemple, en acier au carbone ou en un autre métal tel que du nickel ou de l'acier inoxydable éventuellement revêtu de cobalt. Une alimentation en TiCl4 est effectuée à l'intérieur de la cathode d'alimentation(7) au moyen du tube (8) placé au voisinage de son axe. Ce tube est isolé par rapport à la cathode. Dans ces conditions, on constate que le TiCl4 qui sort par l'orifice (9) du tube (8) est réduit au moins partiellement en sous-chlorure de titane qui se dissout dans le bain.FIG. 1 represents such an electrolysis cell of the type described in FR 2,423,555 which comprises a metal casing (1) containing the molten electrolyte (2). An anode (3) is placed inside an anode compartment (4). A diaphragm (5) separates this compartment from the rest of the cell in which the deposition (6) and supply (7) cathodes are located. As can be seen, the supply cathode (7) is tubular in shape. It is, for example, in wire mesh and connected to the negative pole of a current source. This metallic fabric can be, for example, carbon steel or another metal such as nickel or stainless steel optionally coated with cobalt. A supply of TiCl 4 is carried out inside the supply cathode (7) by means of the tube (8) placed in the vicinity of its axis. This tube is insulated from the cathode. Under these conditions, it can be seen that the TiCl 4 which leaves through the orifice (9) of the tube (8) is reduced at least partially to titanium subchloride which dissolves in the bath.

Le mécanisme de réduction de TiCl4 n'est pas connu avec certitude. Suivant une théorie généralement admise, il se produit une première réaction entre le TiCl4 gazeux et le TiCl2 dissous dans le bain.:

Figure imgb0001
The mechanism of reduction of TiCl 4 is not known with certainty. According to a generally accepted theory, a first reaction takes place between the TiCl 4 gas and the TiCl 2 dissolved in the bath:
Figure imgb0001

Puis, au cours d'une deuxième réaction, les ions Ti3+ formés par la réaction (1) diffusent dans l'électrolyte et viennent se réduire à la cathode d'alimentation suivant la réaction :

Figure imgb0002
Then, during a second reaction, the Ti 3+ ions formed by reaction (1) diffuse in the electrolyte and come to reduce at the supply cathode according to the reaction:
Figure imgb0002

On voit que, si l'on désire obtenir la transformation de tout le TiCl4 en TiCl2, il faut théoriquement, en admettant un rendement des ampères de 100 %, que le courant I1 qui traverse la cathode d'alimentation, soit égal à :

Figure imgb0003
We see that, if we wish to obtain the transformation of all the TiCl 4 into TiCl 2 , it is theoretically necessary, assuming an ampere efficiency of 100%, that the current I 1 which flows through the supply cathode, be equal at :
Figure imgb0003

Dans cette relation (3), q est la masse de TiCl4 introduite dans l'électrolyte en g/h et I1 l'intensité du courant en ampères.In this relation (3), q is the mass of TiCl 4 introduced into the electrolyte in g / h and I 1 the intensity of the current in amperes.

Dans le même temps, la cathode de dépôt (6) doit être traversée par un courant I2 = I1, afin de recueillir à chaque instant une quantité de titane correspondant à celle qui a été solubilisée. Le courant total I qui traverse l'anode est tel que :

Figure imgb0004
At the same time, the deposition cathode (6) must be traversed by a current I 2 = I 1 , in order to collect at each instant an amount of titanium corresponding to that which has been dissolved. The total current I which flows through the anode is such that:
Figure imgb0004

Dans ces conditions, on ne devrait observer aucun dépôt de titane sur la cathode d'alimentation. En fait, l'expérience montre que ce n'est pas le cas. En effet, du titane métallique se dépose sous forme de poudre très fine au voisinage de la cathode. Ce dépôt, qui forme avec l'électrolyte une sorte de boue, perturbe le fonctionnement de la cathode ; il est très difficile à extraire de la cellule et correspond à une perte de rendement qui peut être importante.Under these conditions, no titanium deposit should be observed on the supply cathode. In fact, experience shows that this is not the case. In fact, metallic titanium is deposited in the form of a very fine powder in the vicinity of the cathode. This deposit, which forms with the electrolyte a kind of mud, disturbs the operation of the cathode; it is very difficult to extract from the cell and corresponds to a loss which can be significant.

Deux hypothèses, pratiquement équivalentes, peuvent rendre compte de ce comportement anormal :

  • - lère hypothèse : dans les conditions opératoires, TiCl2 n'est stable qu'en présence d'une certaine quantité de TiCl3, sinon il se dismute par déplacement vers la droite de la réaction équilibrée :
    Figure imgb0005
  • - 2ème hypothèse : la réduction de Ti3+ en Ti2+ ne s'effectue pas directement à la cathode par la réaction (2), mais par l'intermédiaire des réactions suivantes :
    Figure imgb0006
    Ti métal + 2 TiCl3 dissous 3 TiCl2 dissous (5bis) c'est-à-dire par la réaction (4) déplacée vers la gauche.
Two hypotheses, practically equivalent, can account for this abnormal behavior:
  • - 1st hypothesis: under the operating conditions, TiCl 2 is only stable in the presence of a certain amount of TiCl 3 , otherwise it is disproportionated by displacement to the right of the balanced reaction:
    Figure imgb0005
  • - 2nd hypothesis: the reduction of Ti 3+ to Ti 2+ is not carried out directly at the cathode by reaction (2), but by means of the following reactions:
    Figure imgb0006
     Ti metal + 2 TiCl 3 dissolved 3 TiCl 2 dissolved (5bis), that is to say by reaction (4) shifted to the left.

Dans les deux cas, le résultat final est le même : le passage d'une intensité I1 = 1/2

Figure imgb0007
ampères aboutit à un dépôt de titane, soit par dismutation d'une partie de TiCl2 fomé, soit par réduction incomplète du TiCl3 par le titane métal déposé sur la cathode par la réaction (5) conformément à l'équilibre (4).In both cases, the end result is the same: the passage of an intensity I 1 = 1/2
Figure imgb0007
 amperes leads to a deposition of titanium, either by disproportionation of a part of TiCl2 formed, or by incomplete reduction of TiCl 3 by the titanium metal deposited on the cathode by reaction (5) in accordance with equilibrium (4).

L'objet de l'invention est un dispositif permettant l'alimentation en TiCl4 d'une cellule d'électrolyse pour la préparation du titane comportant au moins une cathode de dépôt et une cathode d'alimentation ; ce dispositif est un diaphragme métallique qui entoure la cathode d'alimentation et qui est isolé.par rapport à celle-ci. De façon avantageuse, 'des électrodes de référence disposées de part et d'autre du diaphgrame, sont reliées à un moyen de mesure de leur différence de potentiel.The object of the invention is a device allowing the supply of TiCl 4 to an electrolysis cell for the preparation of titanium comprising at least one deposition cathode and a supply cathode; this device is a metallic diaphragm which surrounds the insulating cathode and which is insulated from it. Advantageously, 'reference electrodes disposed on either side of the diaphgrame, are connected to a means for measuring the voltage difference therebetween.

Un autre objet de l'invention est un procédé d'alimentation d'une cellule d'électrolyse pour la préparation du titane, comportant au moins une cathode d'alimentation en TiCl4 entourée d'un diaphragme isolé par rapport à elle, dans lequel on règle l'intensité du courant 1 qui traverse la cathode d'alimentation de manière a maintenir une chute de potentiel faible mais non nulle dans l'électrolyte qui imprègne le diaphragme. De façon avantageuse, ce réglage est effectue en asservissant l'intensité du courant qui traverse la cathode d'alimentation à la chute de potentiel dans l'électrolyte imprégnant le diaphragme ou à une variable liée à cette chute de potentiel.Another object of the invention is a method for supplying an electrolysis cell for the preparation of titanium, comprising at least one supply cathode for TiCl 4 surrounded by a diaphragm isolated from it, in which the intensity of current 1 which flows through the supply cathode is adjusted so as to maintain a drop in potential weak but not zero in the electrolyte which permeates the diaphragm. Advantageously, this adjustment is carried out by controlling the intensity of the current flowing through the supply cathode to the drop in potential in the electrolyte impregnating the diaphragm or to a variable linked to this drop in potential.

Grâce à ce dispositif et ce procédé, on réalise une régulation des teneurs en TiCl3 et en TiCl2 dissous à la cathode d'alimentation dans des proportions conformes à l'équilibre (4).Thanks to this device and this method, the contents of TiCl 3 and of TiCl2 dissolved at the feed cathode are regulated in proportions in accordance with equilibrium (4).

La figure 2 représente, à titre d'exemple non limitatif, un dispositif de cathode d'alimentation suivant l'invention.FIG. 2 represents, by way of nonlimiting example, a feed cathode device according to the invention.

Ce dispositif est placé à l'intérieur d'une cellule (10) pour la préparation par électrolyse de titane à partir d'un électrolyte fondu (11). Cette cellule comporte, comme celle de la figure 1, une anode (12) entourée d'un diaphragme (13) et, au moins, une cathode de dépôt (14). Seul le dispositif d'alimentation suivant l'invention est décrit de façon détaillée. Il comporte un tube (15) qui permet d'introduire le TiCl4 qui sort dans l'électrolyte par l'orifice (16). La cathode d'alimentation est constituée de deux tiges en acier (17) et (18) disposées de part et d'autre du tube (15). Elles traversent le couvercle (19) de la cellule à travers des joints isolants et sont reliées au pôle négatif d'une source de courant non représentée.This device is placed inside a cell (10) for the preparation by electrolysis of titanium from a molten electrolyte (11). This cell comprises, like that of FIG. 1, an anode (12) surrounded by a diaphragm (13) and, at least, a deposition cathode (14). Only the supply device according to the invention is described in detail. It comprises a tube (15) which makes it possible to introduce the TiCl 4 which leaves the electrolyte through the orifice (16). The feed cathode consists of two steel rods (17) and (18) arranged on either side of the tube (15). They pass through the cover (19) of the cell through insulating joints and are connected to the negative pole of a current source not shown.

Le diaphragme (20), qui constitue l'un des objets de l'invention, est réalisé en un métal présentant une tenue suffisante vis-à-vis de l'élec- trolyte dans les conditions de température où l'on opère. On peut faire appel, par exemple, à du nickel non allié, ou à des alliages à base de nickel ou encore à des aciers, de préférence inoxydables. Ce diaphragme est raccordé à la partie supérieure au couvercle (19) de l'électrolyseur au moyen d'une paroi annulaire métallique étanche (21) qui est fixée au couvercle (19) par des joints annulaires isolants et étanches (22) et (23). La paroi annulaire (21) pénètre par sa partie inférieure dans l'électrolyte et fait ainsi obstacle à la circulation des gaz présents au-dessus du niveau de l'électrolyte de part et d'autre du diaphgrame (20). Le rôle essentiel de celui-ci est de faire obstacle à la diffusion du TiCl3 formé suivant la réaction (2) par action de TiC14 sur TiCl2, en dehors de l'espace délimité par ce diaphragme. De cette façon, la zone de l'électrolyte située au voisinage immédiat des tiges (17) et (18), qui constituent la cathode d'alimentation, s'enrichit en TiCl3, ce qui permet une redissolution très rapide du titane formé au contact de ces tiges par décharge des ions titane bivalents.The diaphragm (20), which constitutes one of the objects of the invention, is made of a metal having sufficient strength vis-à-vis the elec - trolyte in the temperature conditions in which one operates. It is possible, for example, to use unalloyed nickel, or nickel-based alloys or else steels, preferably stainless. This diaphragm is connected to the upper part of the cover (19) of the electrolyser by means of a sealed metallic annular wall (21) which is fixed to the cover (19) by insulating and waterproof annular seals (22) and (23 ). The annular wall (21) penetrates through its lower part into the electrolyte and thus obstructs the circulation of the gases present above the level of the electrolyte on either side of the diaphgram (20). The essential role of this is to obstruct the diffusion of TiCl3 formed according to reaction (2) by the action of TiC1 4 on TiCl 2 , outside the space delimited by this diaphragm. In this way, the electrolyte area located in the immediate vicinity of the rods (17) and (18), which constitute the supply cathode, is enriched in TiCl 3 , which allows a very rapid redissolution of the titanium formed in contact with these rods by discharge of bivalent titanium ions.

La structure du diaphragme (20) peut être réalisée, par exemple, sous forme d'une toile métallique telle qu'une toile de nickel, ou d'une feuille obtenue par frittage d'une poudre métallique, par exemple à base d'acier inoxydable, et présentant une porosité résiduelle suffisante.The structure of the diaphragm (20) can be produced, for example, in the form of a metallic cloth such as a nickel cloth, or of a sheet obtained by sintering a metallic powder, for example based on steel. stainless, and having sufficient residual porosity.

L'expérience a montré qu'un tel diaphragme, réalisé par exemple en toile de nickel et isolé par rapport à la cathode d'alimentation, se comporte comme une électrode indicatrice de la réaction d'oxydo réduction :

Figure imgb0008
Experience has shown that such a diaphragm, made for example of nickel cloth and insulated with respect to the supply cathode, behaves like an electrode indicative of the redox reaction:
Figure imgb0008

Le potentiel de ce diaphragme (20) par rapport à l'électrolyte dans lequel il est plongé, peut se calculer par l'une des deux équations suivantes, en considérant soit le potentiel de la face interne de ce diaphragme par rapport à l'électrolyte (24) qui se trouve à l'intérieur de ce diaphragme, soit le potentiel de la face externe du même diaphragme par rapport à l'électrolyte (25) situé à l'extérieur de ce diaphragme.The potential of this diaphragm (20) relative to the electrolyte in which it is immersed, can be calculated by one of the following two equations, considering either the potential of the internal face of this diaphragm relative to the electrolyte (24) which is inside this diaphragm, that is to say the potential of the external face of the same diaphragm with respect to the electrolyte (25) located outside this diaphragm.

Le potentiel de la face interne du diaphragme se calcule par la formule bien connue des électrochimistes :

Figure imgb0009
The potential of the internal face of the diaphragm is calculated by the formula well known to electrochemists:
Figure imgb0009

Dans cette formule, eo Ti3+/Ti2+ représente le potentiel normal pour la réaction (6), et a Ti3+ et a Ti2+ représentent les activités respectives des ions Ti3+ et Ti2+ dans le volume d'électrolyte (24) contenu dans l'espace entouré par le diaphragme (20).In this formula, e o Ti 3+ / Ti 2+ represents the normal potential for reaction (6) , and a Ti 3+ and a Ti 2+ represent the respective activities of the Ti 3+ and Ti2 + ions in the volume of electrolyte (24) contained in the space surrounded by the diaphragm (20).

Le potentiel de la face externe du diaphragme (20) se calcule de façon identique par la réaction :

Figure imgb0010
Dans cette formule, a2 Ti3+ et a2 Ti2+ représentent les activités respec- tives des ions Ti et Ti dans l'électrolyte (25) avec lequel se trouve en contact la face externe du diaphragme (20).The potential of the external face of the diaphragm (20) is calculated identically by the reaction:
Figure imgb0010
 In this formula, a 2 Ti 3+ and a 2 Ti 2+ represent the respective activities of the Ti and Ti ions in the electrolyte (25) with which the external face of the diaphragm (20) is in contact.

Du fait de la présence de Ti métal sur la cathode de dépôt (14), l'électrolyte (25) est en équilibre avec le titane métal conformément à l'équilibre (4) et l'on peut également écrire :

Figure imgb0011
où e Ti2+/Tio représente le potentiel normal de la réduction des ions Ti2+ à l'état métallique, les autres paramètres de l'équation étant déjà définis plus haut. Cette relation montre que, pour une teneur donnée en titane dissous dans l'électrolyte (25) ce potentiel est déterminé.Due to the presence of Ti metal on the deposition cathode (14), the electrolyte (25) is in equilibrium with the titanium metal in accordance with equilibrium (4) and one can also write:
Figure imgb0011
 where e Ti 2+ / Ti o represents the normal potential for the reduction of Ti2 + ions in the metallic state, the other parameters of the equation being already defined above. This relationship shows that, for a given content of titanium dissolved in the electrolyte (25), this potential is determined.

La cellule étant alimentée avec un courant i = I1 + I2, la cathode d'alimentation avec un courant I1 et un débit de TiCl4, q = 1,772 I, la cathode de dépôt avec un courant I2, on observe que, suivant l'intensité du courant I1, trois situations peuvent se présenter :

  • a) l'intensité I1 est choisie de manière a ce que
    Figure imgb0012
     reste constant et conforme à la valeur d'équilibre de la réaction (4) c'est-à-dire égal à
    Figure imgb0013
     on observe alors une simple réduction des ions Ti3+ à l'état Ti2+ à la cathode d'alimentation à l'exclusion de tout dépôt métallique, les potentiels de part et d'autre du diaphragme restent inchangés et égaux, et un courant électronique égal à I1 s'établit dans les portions métalliques du diaphragme entraînant la réduction des ions Ti2+ à l'état métallique sur la face externe du diaphragme et l'oxydation en quantité équivalente des ions Ti2+ à l'état Ti3+ sur la face interne ; cependant, simultanément, l'alimentation en TiCl4 entraîne l'apparition d'un flux d'électrolyte (24) à travers le diaphragme qui entraîne le TiCl3 ainsi formé vers la face externe du diaphragme, où il réagit sur le Ti déposé en redonnant du TiCl2.
  • b) l'intensité I1 est choisie à une valeur supérieure à la précédente ; un excès de TiCl2 est produit à la cathode d'alimentation, une partie de cet excès est réduitedirectement à l'état métallique sur cette cathode, et le reste se dismute dans l'électrolyte (24) conformément à l'équilibre (4) en donnant naissance à des particules de Ti très fines qui forment avec l'électrolyte une sorte de boue ; le rapport
    Figure imgb0014
     reste ainsi inchangé, ainsi que les potentiels de part et d'autre du diaphragme. Le courant I1 passe toujours par voie électronique avec, comme conséquence, le dépôt de titane métallique sur la face externe et formation en quantité équivalente d'ions Ti3+ sur la face interne ; cependant, le TiCl3 en excès ainsi formé est à son tour immédiatement réduit à l'état de TiCl2 par les boues de titane métallique en suspension dans l'électrolyte (24), le flux d'électrolyte (24) traversant le diaphragme ne contient plus alors assez de TiCl3 pour redissoudre le titane métallique sur la surface externe du diaphragme qui se colmate progressivement.
  • c) l'intensité I1 est choisie à une valeur inférieure à celle qui a été choisie en a) : un excès de TiCl3 non réduit à la cathode reste dis-Ti3+ sous dans l'électrolyte, et le terme
    Figure imgb0015
     diminue en valeur absolue, une chute de potentiel
    Figure imgb0016
     appa-raît dans l'électrolyte, imprégnant le diaphragme qui est alors parcouru par un courant ionique, ce qui entraîne une diminution du courant électronique dans les parties métalliques du diaphragme ; le dépôt de titane métallique sur la surface externe du diaphragme, qui résulte du passage de ce courant, diminue et ce dépôt est complètement redissous par le flux d''électrolyte (24) traversant le diaphragme par suite de l'alimentation en TiCl4 ; du TiCl3 en excès diffuse dans le bain (25). Cependant, étant donné l'importance du volume du bain (25) par rapport à celui du bain (24), la présence de ce TiCl3 en excès ne modifie pas sensiblement le potentiel de la face externe du diaphragme, mais il vient se réduire au contact de la cathode de dépôt, ce qui diminue le rendement de la cellule.
The cell being supplied with a current i = I 1 + I 2 , the supply cathode with a current I 1 and a flow of TiCl 4 , q = 1.772 I, the deposition cathode with a current I 2 , it is observed that , depending on the intensity of the current I 1 , three situations can arise:
  • a) the intensity I 1 is chosen so that
    Figure imgb0012
     remains constant and conforms to the equilibrium value of reaction (4), i.e. equal to
    Figure imgb0013
     a simple reduction of the Ti 3+ ions in the Ti2 + state is then observed at the supply cathode to the exclusion of any metallic deposit, the potentials on either side of the diaphragm remain unchanged and equal, and an electronic current equal to I 1 is established in the metal portions of the diaphragm causing the reduction of Ti 2+ ions in the metallic state on the external face of the diaphragm and the oxidation in equivalent quantity of Ti 2+ ions in the Ti 3 state + on the internal face; however, simultaneously, the supply of TiCl 4 causes the appearance of an electrolyte flow (24) through the diaphragm which drives the TiCl 3 thus formed towards the external face of the diaphragm, where it reacts on the Ti deposited in restoring TiCl 2 .
  • b) the intensity I 1 is chosen at a value greater than the previous one; an excess of TiCl 2 is produced at the supply cathode, part of this excess is reduced directly to the metallic state on this cathode, and the rest is disproportionated in the electrolyte (24) in accordance with the equilibrium (4) by giving rise to very fine Ti particles which form with the electrolyte a kind of mud; The report
    Figure imgb0014
     thus remains unchanged, as well as the potentials on either side of the diaphragm. The current I 1 always passes electronically with, as a consequence, the deposition of metallic titanium on the external face and formation in equivalent quantity of Ti 3+ ions on the internal face; however, the excess TiCl 3 thus formed is in turn immediately reduced to the state of TiCl 2 by the slurries of metallic titanium suspended in the electrolyte (24), the flow of electrolyte (24) passing through the diaphragm more then contains enough TiCl 3 to redissolve the metallic titanium on the external surface of the diaphragm which gradually becomes clogged.
  • c) the intensity I 1 is chosen at a value lower than that which was chosen in a): an excess of TiCl 3 not reduced at the cathode remains dis-Ti 3+ under in the electrolyte, and the term
    Figure imgb0015
     decreases in absolute value, a drop in potential
    Figure imgb0016
     appears in the electrolyte, permeating the diaphragm which is then traversed by an ion current, which causes a decrease in the electronic current in the metal parts of the diaphragm; the deposit of metallic titanium on the external surface of the diaphragm, which results from the passage of this current, decreases and this deposit is completely redissolved by the flow of electrolyte (24) passing through the diaphragm as a result of the supply of TiCl 4 ; TiCl 3 in diffuse excess in the bath (25). However, given the importance of the volume of the bath (25) relative to that of the bath (24), the presence of this TiCl 3 in excess does not substantially modify the potential of the external face of the diaphragm, but it is reduced in contact with the cathode of deposit, which decreases the efficiency of the cell.

En définitive, c'est le cas n°I qui répond aux meilleures conditions de fonctionnement de la cellule, la solution, et c'est là l'objet de l'invention, consiste à régler le courant I1 de façon a ce qu'il existe une chute de potentiel aussi faible que possible, mais non nulle, dans le bain imprégnant le diaphragme. La porosité de celui-ci n'est pas critique. Elle doit être suffisamment grande pour ne pas freiner exagérément le flux d'électrolyte qui traverse le diaphragme. Elle doit être suffisamment faible pour permettre la détection facile d'une chute de potentiel dans l'électrolyte imprégnant le diaphragme.Ultimately, this is the case n ° I which meets the best operating conditions of the cell, the solution, and this is the object of the invention, consists in regulating the current I 1 so that 'there is a drop in potential as small as possible, but not zero, in the bath permeating the diaphragm. The porosity of it is not critical. It must be large enough not to overly brake the flow of electrolyte which passes through the diaphragm. It should be low enough to allow easy detection of a potential drop in the electrolyte permeating the diaphragm.

La mesure exacte de cette chute de potentiel est relativement difficile à réaliser. Il est par contre possible de mesurer une valeur très proche de cette différence de potentiel en disposant de part et d'autre du diaphragme, mais sans contact avec celui-ci, deux électrodes de références, par exemple des électrodes sensibles aux ions chlores (26) et (27) telles que des électrodes Ag/AgCl plongées dans l'électrolyte : les extrémités de ces électrodes traversent le couvercle de la cellule par des joints isolants et sont reliées à un moyen de mesure de la différence de potentiel qui servira à piloter le courant I1 ou ce qui revient au même, le rapport I2/I1.The exact measurement of this drop in potential is relatively difficult to achieve. It is however possible to measure a value very close to this potential difference by having on either side of the diaphragm, but without contact with it, two reference electrodes, for example electrodes sensitive to chlorine ions (26 ) and (27) such as Ag / AgCl electrodes immersed in the electrolyte: the ends of these electrodes pass through the cell cover by insulating joints and are connected to a means of measuring the potential difference which will be used to control the current I 1 or what amounts to the same, the ratio I 2 / I 1 .

D'autres méthodes de mesure de cette différence de potentiel peuvent être utilisées pour la réalisation du dispositif ou du procédé suivant l'invention, qui ne sortent pas du domaine de l'invention.Other methods of measuring this potential difference can be used for the realization of the device or the method according to the invention, which do not depart from the field of the invention.

Claims (5)

1. Nouveau dispositif permettant l'alimentation en TiCl4 d'une cellule d'électrolyse pour la préparation du titare, caractérisé en ce qu'il comporte au moins une cathode d'alimentation entourée d'un diaphragme métallique isolé par rapport à celle-ci.1. New device for supplying TiCl 4 to an electrolysis cell for the preparation of titanium, characterized in that it comprises at least one supply cathode surrounded by a metal diaphragm isolated from it. this. 2. Nouveau dispositif suivant revendication I, caractérisé en ce qu'il comporte des électrodes de référence disposées de part et d'autre du diaphragme et reliées à un moyen de mesure de leur différence de potentiel.2. New device according to claim I, characterized in that it comprises reference electrodes arranged on either side of the diaphragm and connected to a means for measuring their potential difference. 3. Procédé d'alimentation d'une cellule d'électrolyse pour la préparation du titane dans lequel au moins une cathode d'alimentation en TiCl4 est entourée d'un diaphragme isolé par rapport à celle-ci, caractérisé en ce que l'on règle l'intensité du courant qui traverse la cathode d'alimentation, de manière à maintenir une chute de potentiel faible mais non nulle dans l'électrôlyte qui imprègne le diaphragme.3. Method for supplying an electrolysis cell for the preparation of titanium in which at least one TiCl 4 supply cathode is surrounded by a diaphragm isolated from it, characterized in that the the intensity of the current flowing through the feed cathode is adjusted so as to maintain a small but not zero potential drop in the electrolyte which permeates the diaphragm. 4. Procédé suivant revendication 3, caractérisé en ce que l'intensité du courant qui traverse la cathode d'alimentation en TiCl4 est asservie à la chute de potentiel dans l'électrolyte imprégnant le diaphragme ou à une variable liée à cette chute de potentiel.4. Method according to claim 3, characterized in that the intensity of the current flowing through the TiCl 4 supply cathode is subject to the drop in potential in the electrolyte impregnating the diaphragm or to a variable linked to this drop in potential . 5. Procédé suivant revendication 3 ou 4, caractérisé en ce que l'intensité du courant qui traverse la cathode d'alimentation est asservie à la différence de potentiel mesurée entre des électrodes de référence, placées de part et d'autre du diaphragme.5. Method according to claim 3 or 4, characterized in that the intensity of the current flowing through the supply cathode is controlled by the potential difference measured between reference electrodes, placed on either side of the diaphragm.
EP81420173A 1980-11-27 1981-11-25 Apparatus and process for feeding ticl4 to electrolysis cells used for the manufacture of titanium Expired EP0053565B1 (en)

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AT81420173T ATE15080T1 (en) 1980-11-27 1981-11-25 DEVICE AND METHOD FOR DELIVERY OF TICL4 INTO ELECTROLYTIC CELLS FOR TITANIUM PRODUCTION.

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FR8025505A FR2494725A1 (en) 1980-11-27 1980-11-27 NEW DEVICE AND METHOD FOR THE TICL4 POWERING OF ELECTROLYTIC CELLS FOR THE PREPARATION OF TITANIUM
FR8025505 1980-11-27

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Cited By (1)

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FR2579629A1 (en) * 1985-03-28 1986-10-03 Pechiney PROCESS FOR CONTINUOUSLY CONTROLLING THE DISSOLVED METAL CONTENT IN A FILLED SALT BATH AND ITS APPLICATION TO THE CONTINUOUS SUPPLY OF AN ELECTROLYSIS CELL IN SALTS OF THIS METAL

Families Citing this family (6)

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US4521281A (en) * 1983-10-03 1985-06-04 Olin Corporation Process and apparatus for continuously producing multivalent metals
US7504017B2 (en) * 2001-11-22 2009-03-17 Qit-Fer Et Titane Inc. Method for electrowinning of titanium metal or alloy from titanium oxide containing compound in the liquid state
WO2006084318A1 (en) * 2005-02-08 2006-08-17 Bhp Billiton Innovation Pty Ltd Supplying solid electrolyte to an electrolytic cell
EP2794943B8 (en) 2011-12-22 2019-07-10 Universal Achemetal Titanium, LLC A method for extraction and refining of titanium
RU2750608C2 (en) 2016-09-14 2021-06-29 ЮНИВЕРСАЛ АКЕМЕТАЛ ТИТАНИУМ, ЭлЭлСи Method of production of a titanium-aluminium-vanadium alloy
AU2018249909B2 (en) 2017-01-13 2023-04-06 Universal Achemetal Titanium, Llc Titanium master alloy for titanium-aluminum based alloys

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US2760930A (en) * 1952-01-31 1956-08-28 Nat Lead Co Electrolytic cell of the diaphragm type
US4219401A (en) * 1978-08-07 1980-08-26 The D-H Titanium Company Metal electrowinning feed cathode

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US2712523A (en) * 1951-06-12 1955-07-05 Nat Lead Co Purification of titanium tetrachloride
US4113584A (en) * 1974-10-24 1978-09-12 The Dow Chemical Company Method to produce multivalent metals from fused bath and metal electrowinning feed cathode apparatus

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US2760930A (en) * 1952-01-31 1956-08-28 Nat Lead Co Electrolytic cell of the diaphragm type
US4219401A (en) * 1978-08-07 1980-08-26 The D-H Titanium Company Metal electrowinning feed cathode

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2579629A1 (en) * 1985-03-28 1986-10-03 Pechiney PROCESS FOR CONTINUOUSLY CONTROLLING THE DISSOLVED METAL CONTENT IN A FILLED SALT BATH AND ITS APPLICATION TO THE CONTINUOUS SUPPLY OF AN ELECTROLYSIS CELL IN SALTS OF THIS METAL
EP0198775A1 (en) * 1985-03-28 1986-10-22 Pechiney Process for the continuous monitoring of the dissolved metal concentration in a molten salts bath and its use in the continuous feeding of these metal salts to an electrolysis cell

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EP0053565B1 (en) 1985-08-21
NO156171C (en) 1987-08-12
DE3171944D1 (en) 1985-09-26
FR2494725A1 (en) 1982-05-28
JPS5833314B2 (en) 1983-07-19
NO814029L (en) 1982-05-28
ATE15080T1 (en) 1985-09-15
US4396472A (en) 1983-08-02
JPS57116790A (en) 1982-07-20
FR2494725B1 (en) 1982-12-10

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