DE2323497B2

DE2323497B2 - Coated titanium anode for amalgam high-load cells

Info

Publication number: DE2323497B2
Application number: DE2323497A
Authority: DE
Inventors: Konrad Koziol; Karl-Heinz Sieberer; Baptist Zenk
Original assignee: C Conradty Nuernberg & Co Kg 8505 Roethenbach GmbH
Current assignee: C Conradty Nuernberg & Co Kg 8505 Roethenbach GmbH
Priority date: 1973-05-10
Filing date: 1973-05-10
Publication date: 1978-10-12
Also published as: BE814829A; CH571579A5; NL166728C; NO741667L; JPS5041800A; SU833176A3; NL166728B; NL7406364A; FI59269C; GB1454603A; NO140504C; IT1012275B; YU42135B; AT331821B; JPS5730910B2; FR2228542A1; IE39255L; ZA743002B; ES426103A1; FR2228542B1

Description

rundum beschichteten Titanstäben, 0 größer 5 mm, bestand, haben im Stromdichtebereich D_A von 10 bis 15kA/m² gezeigt, daß der Anodenprozeß fast ausschließlich auf der der Quecksilberkathode zugewandten Staboberfläche stattfindet und daß auch Vergrößerungen des Abstandes zwischen den Rundstäben die Stromstreuung nich wesentlich verbessern konnten.Titanium rods coated all around, 0 greater than 5 mm, have shown in the current density range D _A from 10 to 15 kA / m ² that the anode process takes place almost exclusively on the rod surface facing the mercury cathode and that even increases in the distance between the round rods do not significantly affect the current spread could improve.

Darüber hinaus sind Metallanoden bekannt, deren aktiver Teil aus beschichteten dünnen Titanstreifen besteht, die entweder senkrecht oder in einem beliebigen anderen Winkel zur Kathode angeordnet sind. In der belgischen Patentschrift 6 45 039 werden beispielsweise mit Platinmetall beschichtete Titananoden vorgeschlagen, deren aktiver Teil in Form von Rippen bzw. Platten vorliegt, die senkrecht zur Quecksilberkathode und parallel zur Hauptfließrichtung des elektrischen Stromes anordnet sind und in deren Nähe sich Gasabzugslöcher bzw. Spalten befinden. Die Platinmetallbeschichtung wird vorzugsweise oder ausschließlich an den senkrechten Flächen der Rippen bzw. Platten aufgebracht. Diese Maßnahme soll der Gefahr einer Beschädigung der empfindlichen Platinmetallbeschichtung durch das Amalgam im Falle einer Berührung mit der Kathode entgegenwirken. Sie soll auch den Betrieb der Anode in um ca. 1 mm größerer Entfernung von der Kathode bei gleicher Zellenspannung ermöglichen als eine aus Geflecht hergestellte Anode, wodurch ebenfalls die Kurzschlußgefahr herabgesetzt wird. Zu den entscheidenden Nachteilen der vorgeschlagenen Anoden zählen die geringe Höhe der aktiven Beschichtung von nur 2,54 mm und die kleine aktive Ist-Oberfläche im Nahbereich bezüglich der Gegenelektrode.In addition, metal anodes are known whose active part consists of coated thin titanium strips consists, which are either perpendicular or at any other angle to the cathode are. In Belgian patent 6 45 039, for example, titanium anodes coated with platinum metal proposed whose active part is in the form of ribs or plates perpendicular to the Mercury cathode and are arranged parallel to the main flow direction of the electric current and in their There are gas vent holes or gaps close by. The platinum metal coating is preferred or exclusive applied to the vertical surfaces of the ribs or plates. This measure is intended to reduce the risk damage to the sensitive platinum metal coating by the amalgam in the event of a Counteract contact with the cathode. You should also operate the anode in about 1 mm larger Allow removal from the cathode at the same cell voltage as one made from braid Anode, which also reduces the risk of short circuits. Among the major disadvantages of the proposed anodes include the low height of the active coating of only 2.54 mm and the small active actual surface in the vicinity of the counter electrode.

Neben einer großen Höhe des aktiven Anodenteiles sollte die verbesserte Titananode sich auszeichnen durchIn addition to a large height of the active anode part, the improved titanium anode should stand out by

1. eine überaus große aktive Oberfläche und das sowohl im Nah- wie auch im Fernbereich bezüglich der Gegenelektrode,1. an extremely large active surface, both at close range and at a distance the counter electrode,

2. kurze Stromwege, geringen inneren Widerstand,2.short current paths, low internal resistance,

3. Langlebigkeit der Konstruktion und Beschichtung, auch bei hoher Stromüberlastung,3. Longevity of the construction and coating, even with high current overload,

4. gute Notlaufeigenschaften auch nach eventuellen Kurzschlüssen,4. good emergency running properties even after possible short circuits,

5. problemlose Be- und Widerbeschichtung sowie5. Problem-free coating and recoating as well

6. Unkompliziertheit und Preiswürdigkeit.6. Simplicity and value for money.

Diese Aufgabe wird in besonders vorteilhafter Weise gelöst durch die erfindungsgemäße Anode, deren aktiver beschichteter Teil, gemessen von der Anodenunterseite, höher als 5 mm und nicht höher als 20 mm und so beschaffen ist, daß seine Ist-Oberfläche bis zu den Höhen, 5, 7'/2, 10 und 15 mm mindestens um das 2V2-, 3V3-, 4- und 4³Afache die projizierte Anodenfläche übersteigt und wobei mindestens die Hälfte der Ist-Oberfläche senkrecht zur Basisfläche der Anode angeordnet ist.This object is achieved in a particularly advantageous manner by the anode according to the invention, the active coated part of which, measured from the underside of the anode, is higher than 5 mm and not higher than 20 mm and is such that its actual surface is up to the heights, 5, 7 '/ 2, 10 and 15 mm at least 2V2-, 3V3-, 4- and 4 ³ A times the projected anode area and with at least half of the actual surface is arranged perpendicular to the base area of the anode.

Nachfolgend werden anhand der Zeichnungen einige Ausführungsformen der erfindungsgemäßen Anode beispielsweise beschrieben.Some embodiments of the anode according to the invention are described below with reference to the drawings for example described.

F i g. 1 zeigt eine Anode, deren aktiver Teil 1 aus beschichteten, vertikal angeordneten, 1 mm starken und 20 mm hohen Titanbändern besteht. Der Abstand zwischen den beschichteten Titanbändern beträgt 2 mm. Die Bänder sind an ihrer Oberseite durch einige querverlaufende Schweißnähte 2 miteinander verbunden. Die Stromverteilung besorgt ein aufgeschweißter Querbalken 3 aus unbeschichtetem Titan, der mit dem Titanschutzrohr 4 der Stromzuleitung versehen ist.F i g. 1 shows an anode whose active part 1 consists of coated, vertically arranged, 1 mm thick and 20 mm high titanium bands. The distance between the coated titanium strips is 2 mm. The bands are connected to one another on their upper side by a few transverse weld seams 2. The power distribution is provided by a welded-on crossbar 3 made of uncoated titanium, which is connected to the Titanium protective tube 4 of the power supply line is provided.

Aus dieser Konstruktion resultieren folgende Verhältnisse der Ist-Oberfiäche zur projizierenden Anodenfläche: This construction results in the following relationships between the actual surface and the projecting anode surface:

Höhe 5 mm 3,67:1, Höhe IUi mm 5,33:1, Höhe 10 mm 7:1, Höhe 15 mm 10,33:1, Höhe 20 mm 14:1. Über 95% der aktiven Ist-Oberfläche sind hier senkrecht zur Basisfläche der Anode angeordnet.Height 5 mm 3.67: 1, height IUi mm 5.33: 1, height 10 mm 7: 1, height 15 mm 10.33: 1, height 20 mm 14: 1. Over 95% of the active actual surface is arranged here perpendicular to the base surface of the anode.

ίο F i g. 2 stellt eine Anode mit der projizierten Fläche 400 χ 400 mm dar, deren aktiver Teil 1 aus geschlitztem und beschichtetem, 12 mm starkem Titanblech besteht. Die Schlitz- und Stegbreite beträgt 2,5 mm. Der nicht eingeschnittene mittlere Bereich des aktiven Teiles, der gleichzeitig als Stromverteilung dient, ist 60 mm breit und an seiner Unterseite mit 2,5 mm breiten und 2.5 mm tiefen Rillen versehen. In dessen Mitte liegt der Schraubkontakt für den Kupfer-Stromzuleiter, von dem nur die Titanschutzhülse 4 sichtbar ist.ίο F i g. 2 represents an anode with the projected area 400 χ 400 mm, the active part 1 of which consists of slotted and coated, 12 mm thick titanium sheet. The slot and web width is 2.5 mm. The non-incised central area of the active part, the serves as power distribution at the same time, is 60 mm wide and on its underside with 2.5 mm wide and 2.5 mm deep grooves. In the middle of this is the screw contact for the copper current feeder from which only the titanium protective sleeve 4 is visible.

Das Verhältnis der Ist-Oberfläche zur projizierten Anodenfläche beträgt hier 5,13 :1 und ca. 80% der aktiven Ist-Oberfläche sind senkrecht zur Basisfläche der Anode angeordnet.The ratio of the actual surface to the projected anode surface is here 5.13: 1 and approx. 80% of the active actual surface are arranged perpendicular to the base surface of the anode.

Aufgrund ihrer Merkmale bietet die erfindungsgemäße Anode erstmals die Möglichkeit einer sehr weitgehenden Nutzung der Stromstreuung und Minderung der anodischen Stromdichte, woraus eine entsprechende Erniedrigung der Zellenspannung resultiert.
Fig.3 zeigt die Zellenspannungen in AbhängigkeitDue to its features, the anode according to the invention offers for the first time the possibility of a very extensive use of the current spread and reduction of the anodic current density, which results in a corresponding reduction in the cell voltage.
3 shows the cell voltages as a function

3ü von der anodischen Stromdichte Da für drei mit den gleichen Substanzen des Typs Me(I)_ca. ojPt304 aktivierte Titananodentypen, wobei die mit I gekennzeichnete Kurve mit Titananoden aus 1 mm starken und 10 mm hohen Bändern mit 3 mm breitem Spalt zwischen den Bändern und einer Beschichtungshöhe von 2 mm und die mit II und III gekennzeichneten Kurven mit Titananoden aus lmm starken und 15 mm hohen Bändern mit gleichem Spalt und einer Beschichtungshöhe von 5 bzw. 10 mm erhalten wurden. Der Abstand zwischen Anode und Quecksilberkathode betrug dabei 3 mm.3ü from the anodic current density Since for three with the same substances of the type Me (I) _approx . ojPt304 activated titanium anode types, the curve marked with I with titanium anodes made of 1 mm thick and 10 mm high strips with a 3 mm wide gap between the strips and a coating height of 2 mm and the curves marked with II and III with titanium anodes made of 1 mm thick and 15 mm high ribbons with the same gap and a coating height of 5 or 10 mm were obtained. The distance between the anode and the mercury cathode was 3 mm.

F i g. 4 zeigt, daß die Abhängigkeit der Zellenspannung von der anodischen Stromdichte durch Vergrößerung der aktiven Ist-Oberfläche im kathodennahen und -fernen Bereich wesentlich verbessert werden kann. Kurve II entspricht hier Anoden, deren aktiver Teil aus 2 mm starken und 12 mm hohen vollends beschichteten Titanbändern mit 2 mm breitem Spalt zwischen den Bändern besteht, während es sich bei Kurve I um dieF i g. 4 shows that the dependence of the cell voltage on the anodic current density by magnification the active actual surface in the area near and far from the cathode can be significantly improved. Curve II here corresponds to anodes, the active part of which is completely coated from 2 mm thick and 12 mm high Titanium bands with a 2 mm gap between the bands, while curve I is the

so gleiche Anodentype von Fig.3 mit 10mm hoher Beschichtung handelt.so same anode type of Fig. 3 with 10mm higher Coating is about.

Die Stromdichteminderung bewirkt außerdem eine entsprechende Erhöhung der Lebensdauer der aktiven Anodenbeschichtung. Die große Höhe des elektrochemisch aktiven Teils der Anode bei verhältnismäßig kleiner Anodenbasisfläche und die überwiegend vertikale Anordnung der aktiven Ist-Oberfläche gewährleisten gute Notlaufeigenschaften, auch bei eventuellen Kurzschlüssen, und eine rasche Ableitung der Chlorgas-The reduction in current density also causes a corresponding increase in the service life of the active ones Anode coating. The great height of the electrochemically active part of the anode at relatively small anode base area and the predominantly vertical arrangement of the active actual surface good emergency running properties, even in the event of a short circuit, and rapid discharge of the chlorine gas

bo blasen. Die große Höhe erlaubt schließlich die Unterbringung der Stromverteilung innerhalb des aktiven Anodenteiles, wodurch die Anode auf sehr einfache Weise beidseitig Verwendung finden kann. Die erfindungsgemäße Anode wird damit allen Erfordernissen eines sicheren und wirtschaftlichen Hochlastbetriebes voll gerecht.blow bo. The great height finally allows that Accommodation of the current distribution within the active anode part, whereby the anode on very can easily be used on both sides. The anode according to the invention thus meets all requirements a safe and economical high-load operation fully fair.

Hierzu 2 Blatt ZeichnungenFor this purpose 2 sheets of drawings

Claims

Claim:

Coated titanium anode for amalgam high-load cells, for use with anodic current densities D _A greater than 10kA / m ² , characterized in that the active coated part, measured from the underside of the anode, is higher than 5 mm and not higher than 20 mm and is such that its Actual surface up to heights of 5.7 '/ 2.10 and 15 mm at least 2V2-, 3'Λ-, 4 and 4 ³ A times the projected anode area and with at least half of the actual surface perpendicular to the Base surface of the anode is arranged.

The invention relates to a coated titanium anode for amalgam high-load cells, in particular for use with anodic current densities D _A greater than 10 kA / m ² .

The ones in the high-current loaded chlor-alkali electrolysis cells For energy reasons, large quantities of chlorine gas developed at the anode must be carried out as quickly as possible can be removed from the electrode area. Lingering of the chlorine gas bubbles in the electrode area is known to cause a sensitive increase in cell voltage and a decrease in current yield. This phenomenon, known under the collective term "gas bubble effect", led to the last Years to design changes to the graphite anodes. For example, the horizontal arranged anode plates are provided with numerous slits and gas vent holes, which can go as far as Stromdich- J5 th

Da = 10 kA / m ²

actually brought the desired success. The ceramic-like graphite anode of classic design gradually stands in the way of a further increase in the current density. In the case of very high current densities, since greater than 10 kA / m ² , it becomes difficult to remove the chlorine gas that has evolved from the underside of the horizontal anode plate, which is itself amply slotted and provided with a large number of gas outlet holes, quickly enough. The result is higher overvoltage on the graphite and greater voltage losses in the electrolyte enriched with chlorine gas bubbles. In addition, the internal resistance, the graphite loss and the transport sensitivity of the anodes increase with the number of slots and gas vent holes. Attempts are made to circumvent this restriction by using the graphite anode described in DT-AS 20 29 640. It is an anode, which consists of a row of thin, vertical graphite plates and in which the graphite plates are positioned transversely ζμΓ flow direction of the mercury cathode at intervals adapted to the respective current density, their length corresponds to the cathode width, and their underside is slotted like a comb Wear their top sunk contact sockets made of anodically resistant material and with the interposition of trough-shaped bellows made of corrosion-resistant elastomer are connected to power distribution bars that with the exception of the socket-equipped graphite plates, all current-carrying parts remain excluded from the inside of the cell. Hg cells equipped with this anode construction, which were operated with current densities Da of 10 to 13 kA / m ² , actually allowed the saving coefficient (k value) to drop below 0.11 - rJ ~ - , which was previously the case for amalgam cells equipped with electrographite anodes seemed impossible. The anode described in DT-AS 20 29 640 has thus met the goal of enabling intensified chlor-alkali electrolysis in modern amalgam cells with low voltage. However, a precise analysis of the processing image of the anode in question leads to the conclusion that stress coefficients k less than 0.10 will remain unattainable despite further improvements to the graphite anode. The 12.5 mm wide webs (teeth) obtained by slitting the 40 mm thick graphite plates have become ^{so sharply pointed as a result of the NaCl electrolysis operated with current densities between 10 and 13 kA / m 2} that the anode part facing the Hg cathode soon only had prismatic teeth with a width of the sharply worked out profile of approx. 10 mm and a profile height of approx. 15 mm. The anode areas further away from the cathode also showed unusually strong traces of electrochemical attack. This processing image with a simultaneously favorable Jt value is extraordinarily surprising, as it is practically the same as the processing image, often briefly described with the expression »shark teeth«, of horizontal graphite anode plates in NaCl electrolytes contaminated by alkali entrainment, which always causes high cell voltages despite strong pressure on these anodes. From this it had to be concluded that the high-load anode according to DT-AS 20 29 640, due to its better chlorine gas bubble discharge, scatters the electric current far better than the classic, stamp-shaped, horizontally arranged anode plate provided with slots and gas drainage holes. In electrolysis operated with high current densities, it is still very effective up to great heights, ie up to surface areas that are 15 and more millimeters away from the web tips.

This important finding should be fully taken into account in the development of an improved coated titanium anode for amalgam high-load cells, in particular for use with anodic current densities Da greater than 10 kA / m ^2.

There are known metal anodes for amalgam cells, the active part of which is made of coated titanium in the form of Perforated sheet metal or expanded metal is made. These anodes lack the height and height necessary for current scattering large surface.

Furthermore, metal anodes are known whose active coating on a horizontally arranged parallel Series of titanium rods is applied, which are held together by uncoated transverse ribs. Such anodes made of thin titanium rods also lack the height necessary for current scattering. Anodes, which are made of thick round rods, have the necessary height, but the upper half of the activated rod surface in an unfavorable position compared to the mercury cathode; it lies in the shadow of the lower half of the rod. The current scatter to the activated surface of the upper Bar half is also made more difficult or completely prevented by the strong accumulation of the Electrolytes with chlorine gas bubbles in the narrow area of the gap between the round bars. Technical electrolysis experiments with metal anodes whose active part is made up