CA1094891A - Electrode coating method - Google Patents
Electrode coating methodInfo
- Publication number
- CA1094891A CA1094891A CA273,774A CA273774A CA1094891A CA 1094891 A CA1094891 A CA 1094891A CA 273774 A CA273774 A CA 273774A CA 1094891 A CA1094891 A CA 1094891A
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- CA
- Canada
- Prior art keywords
- tin
- coating
- electrode
- titanium
- compounds
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
- C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
- C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
- C25B11/073—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material
- C25B11/091—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of at least one catalytic element and at least one catalytic compound; consisting of two or more catalytic elements or catalytic compounds
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
- C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
- C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
- C25B11/073—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material
- C25B11/091—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of at least one catalytic element and at least one catalytic compound; consisting of two or more catalytic elements or catalytic compounds
- C25B11/093—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of at least one catalytic element and at least one catalytic compound; consisting of two or more catalytic elements or catalytic compounds at least one noble metal or noble metal oxide and at least one non-noble metal oxide
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Electrodes For Compound Or Non-Metal Manufacture (AREA)
- Electrolytic Production Of Metals (AREA)
- Inert Electrodes (AREA)
- Battery Electrode And Active Subsutance (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
Disclosed is a method for making an improved electrons for use in electrochemical processes wherein coating materials containing a tin sulfate compound are applied to a metal substrate by a method that signific-antly reduces the volatilization of the tin during the baking process to transform the compounds to their oxide forms.
Disclosed is a method for making an improved electrons for use in electrochemical processes wherein coating materials containing a tin sulfate compound are applied to a metal substrate by a method that signific-antly reduces the volatilization of the tin during the baking process to transform the compounds to their oxide forms.
Description
~194~9~l IMPROVED ELECT~ODE COATING METHOD
BACKGROUND OF THE INVENTION
This invention generally relates to a method for applying coating materials to an electrode substrate, generally of a valve metal, wherein the coating compositions have tin compounds which are later converted to thçlr oxide forms to produce an electrode having significantly increased reproduci-bility for method of manufacture, savings in manufacturing costs - -due to the more complete utilization of the tin metal, and reduced atmospheric pollution caused by the volatilization of tin compounds during the coating process. ~ore particularly the present disclosure~relates to a much improved method for manufacturing an electrode having a valve metal substrate such as titanium carrying an electrode coating composition having tin as a component thereof by using a sulfate form of the tin compound in the coating composition mixture.
Electrochemical methods of manufacture are becoming - ever increasingly important to the chemical industry due to their greater ecological acceptability9 potential for energy conservation, and the resultant cost reductions possible.
Therefore, a great deal of research and development efforts have been applied to electrochemical processes and the hardware for these processes. One major element of the hardware aspect is the electrode itself. The object has been to provide: an electrode which will withstand the corrosive environment within an electrolytic cell; an electrode having a minimum over-potential for the desired electrochemical reaction; and an electrode that can be manufactured with high quality control at a cost within the range of commercial feasibility. Only a few materials may effectively constitute an electrode especially ~as~s~
to be used as an anode because of the susceptibility of most other substances to the intense corrosive conditions present within the anode compartment of an electrolytic cell. Among these materials are: graphite, nickel, lead, lead alloy, platinum, or platinized titanium. Electrodes of this type have limited applications because of the various disadvantages such as: a lack of dimensional stability; high cost; high wear rate; contamination of the electrolyte; contamination of a cathode deposit; sensitivity to impurities; or high overpotentials for the desired reaction. Overpotential refers to the excess electrical potential over the theoretical potential at which the desired reaction occurs at a given current density.
The history of electrodes is replete with examples of attempts and proposals to overcome some of ~he problems assoc-iated with the electrode in an electrolytic cell, none of which have accomplished an optimi~ation of the desirable characteristics for an electrode to be used in an electrolytic cell. The problem is to find an electrode which will overcome many of the undesirable characteristics listed above and additionally have low overpotentials at higher current densities so as to conserve energy. It is known for instance that platinum is an excellent material for use in electrodes to be used as anodes in an electro-winning process and satlsfies many of the above-mentioned criteria.
- However, platinum is expensive and hence has not been found suitable for industrial use to date. Carbon and lead alloy electrodes have been used commercially, but the carbon anode wears fast which greatly pollutes the electrolyte, incraases electrical resistance, and increases the half cell potential.
This higher half cell potential causes the electrolytic cell to consume more electrical energy than is desirable. A dis-advantage of the lead alloy anode is that the lead dissolves ~(~9489~
in the electrolyte producing a lead deposit on the cathode which contaminates the desired deposit obtained. Also, PbO2 changes to a Pb304 which is a poor conductor. Oxygen may penetrate below this layer and flake off the film resulting in particles becoming trapped in the deposited copper on a cathode. This causes a degrading of the copper plating which is very undesir-able.
It has been proposed that platinum or other precious metals be applied to a titanium substrate to retain their attractive electrical characteristics and further reduce the manufacturing costs. However, even th~s limited use of precious metals such as platinum which can cost in the range of $30.00 per square foot ($323.00 per square meter) of electrode surface area is expensive and therefore not desirable for industrial use.
It has also been proposed ~hat the surfaces of titanium be plated electrically with platinum to which another electrical deposit either of lead dioxide or manganese dioxide~is applied.
The electrodes with the lead dioxide coating have the dis-advantage of co~paratively high oxygen overpotentials and both ~types of coatings have high internal stresses when electrolytical-ly deposited which are liable to be detached from the surface during commercial usage, contaminating the electrolyte and the produc- being deposited on the cathode surface. Thus, the current density of such anodes is limited and handling of such anodes must be done with extreme care. Another attempted improvement has been to put a layer of manganese dioxide on the surface of a titanium substrate which is relatively porous in nature and building up a number of layers of the manganese dioxide as to present an integral coating. This yields relative-ly low overpotentials as long as the current density remains .
~0~8~
below 0.5 ampere per square inch (77.5 milliamperes per squarecentimeter) but as the current density is increased to near 1 ampere per square inch (155 milliamperes per square centimeter) the overpotential required rises rather rapidly, resulting in a considerable disadvantage at higher current densities.
More recently a number of coatings have employed the use of titanium, ruthenium and tin dioxides, or tin and antimony oxides upon which a top coating of either manganese or lead oxide is pla~ed. These coatings have shown substantial promise in the area of lowering overpotential and yielding good life-times in the corrosive conditions within an electrolytic cell.
The ma;or drawback of these materials is that the methods of applying especially the tin oxide materials have resulted in volatilization of substantial amounts of the tin upon baking the coating to the tin oxides. This is because the tin compounds such as stannic chloride pentahydrate when baked converts to a stannic hydroxide species and then to the stannic oxides which are desired in the given electrode coating.
During this process much of the tin itself is volatilized into the atmsophere instead of remaining in the coating. This occurs at least partly because the stannic chlorides have boiling - points in the area of 114 centigrade and since the transform-ation of the tin compounds to their respective oxides occurs at much higher temperatures, most of these materials are lost into the atmosphere resulting in less than 50 percent utilization of the tin material in the actual coating. This causes a severe problem in the quality control of methods of manufacture for electrodes of large sizes and large quantities. The reproducability of a coating composition is nearly impossible with the volatilization of the tin caused by the current process for applying the coatings to the substrate materials.
, 39~
Therefore, only theoretical tin calculations can be made causing problems with regard to calculating possible lifetimes of a given electrode. To date, the use of tin in coating compositions has not met with the commercial success it should have because vola-tilization of the tin causes a reproducability problem, increases pollution which is under stringent standards currently, and in-creases the cost of production of a given electrode due to the loss of the tin.
SUMMARY OF TH~E INVENTION
It is therefore an object of the present invention to provide a method of preparation for electrode coating compositions having the desired quality control characteristics and a manufacturing cost within the range of commercial feasibility.
Another object of the present invention is to provide a method of preparation for electrode coating compositions which will significantly reduce the volatilization of tin into the atmosphere thus reducing atmospheric pollution problems associated with this manufacturing process.
These and other objects of the present invention, together with the advantages thereof over existing and prlor art forms which will become apparent to those skilled in the art from the detailed disclosure of the present invention as set forth herein-below, are accomplished by the improvements herein described and claimed.
Thus, in accordance with the present teachings, a method is provided for the manufacture of an electrode which comprises the steps of:
selecting a valve metal substrate from the group consisting of aluminum, molybdenum, niobum, tantalum, titanium, tungsten, zirconium, and alloys thereof;
~ .
~` ' ' ,; ':
948~1 applying to at least a portion of the surface of the sub-strate, a coating material consisting of an antimony compound and a tin sulfate compound;
drying the coating material;
baking the coating in an oxidizing atmosphere to convert the antimony and tin compounds to their respective oxide forms;
and applying to the surface of the coating metal, a topcoating of metal dioxide selected from the group consisting of manganese and lead.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The improved method for manufacture of electrode coating compositions of the present invention may be used in the pre-paration of any coating having as a substituent any tin compound for which the volatilization problem of the tin exists presently.
In the past, electrode coating compositions employing the use of tin have utilized thermally decomposable compounds of the chloride form which have a lower boiling point and therefore a volatiliza-tion problem. The present invention employs the use of a sulfate form of the tin or the use of the chloride compounds along with sulfuric acid to result in a sulfate form of the tin which has a simple decomposition mechanism for formation of the oxide form in the ultimate electrode coating composition and therefore drastic-ally reduces the volatilization of the tin upon baking. The sub-strate material for use in such an electrode coa~ing composition can be any electroconductive metal having sufficient mechanical strength to serve as a support for the coatings, typical metals including: aluminum, molybdenum, niobium, tantalum, titanium, tungsten, zirconium, nickel, steel, stainless steel and alloys thereof. A preferred valve metal based on cost, availability, electrical and chemical properties is titanium. There are a ~' ~J
~48¢~
number of forms the titanium substrate may take in the manufacture of an electrode, including for example: solid sheet material; expanded metal mesh material with a large percentage of open area; and porous titanium with a density of 30 to 70 percent pure titanium which can be produced by cold compacting titanium powder.
One type of coating the present invention may be utilized in is cne where a substrate material such as described above is coated with a semi-conductive intermediate coating of tin and antimony oxides. These compositions are generally mixtures of tin dioxide with minor amounts of antimony "dopent", the latter being present in an amount between 0.1 and 30 weight percent, calculated on the basis of total weight percent of SnO2 and Sb203. The preferred amount of antimony trioxide in most of these cases is between 3 and 15 weight percent. In the past these intermediate coatings have generally used a stannic chloride pentahydrate as one,of the materials of the mixture to be painted or somehow applied to the substrate material.
The present invention utilizes a tin sulfate material or the stannic chloride pentahydrate plus sulfuric acid to obtain the sulfate form of the tin. The sulfate form has a simple decomposi-tion mechanism at a temperature in the area of 320" centigrade such that the temperatures of baking to transform these materials into their respective oxides results in very little volatiliz-ation of the tin into the atmosphere. This allows the semi-conductive intermediate coating to be applied in a very few applications versus the past methods of using several làyered applications of the material to obtain a resultant tin weight in the desired range. Over the top of this semi-conductive intermediate coating may be applied a top coating of either manganese or lead dioxides in order to produce electrodes of good current ~fficiencies and good lifetimes.
There are many other examples of electrode coating composi~ions utilizing tin compounds in their makeup to produce a usa~le electrode coating compositions. Those skilled in the art may desire to precoat the substrate material with numerous other compositions before applying the tin sulfate containing coating composition.
A second example is a single layer coating composition having titanium, ruthenium and tin dioxides applied in a method similar to that described above. This type of coating composition is further described in the following patent - U.S. Patent ~o. 3,855,092.
A third type of coatlng composition employing the use of tin-containing compounds is a mixture of the oxides of tin, antimony, a platinum group metal, and a valve metal. These coating compositions are further described in the following patent, -- U.S. Patent ~o.
3,875,043, In order that those skilled in the art may more ~readily understand the present invention and certain preferred aspects by which it may be utilized, the following specific examples ar~ afforded.
q 4~
A series of electrodes were prepared by coating the substrate metal, in this case titanium, with a solution contain-ing antimony trichloride~ ruthenium trichloride and various compounds containing tin all in such amounts as to allow an initial tin/ruthenium ratio to be calculated and compared to an analysis of the final tin/ruthenium ratio. This shows the amount of volatilization of tin that occurred in each instance.
The initial tin/ruthenium ratio was determined from weights of the starting materials in the coating solution. Since the ruthenium compound does absorb water to some extent to form hydrates there is some inaccuracy to an amount of approximately 5 percent on thP calculation of the initial amount of ruthenium in the ratio. After these various materials were applied to the substrate material they were baked in an oxidizing atmosphere at temperatures of 475 to 625 centigrade for periods of 5 to 10 minutes to transform the compounds into their respective oxides. This process was repeated several times to achieve a layer of desired weight gain. The amount of coating material had no observed affect upon the resultant tin/ruthenium ratios.
Therefore any convenient welght of coating material could be used. Once this was accomplished the final tin/ruthenium ratio was determined by stripping the catalytic layer off of the titanium substrate by means of molten salts which are later dissolved in water to precipitate the metals and analyzing the resulting solution by atomic absorption to establish a final ratio of tin/ruthenium in the coating material. These ratios along with the tin compounds used are reported in Table I
below.
~0~48~
TABLE I
-Sn Compound Used Initial Sn/Ru Final Sn/Ru SnCl4 5H20 21.8 3.3 " 10.9 1.7 " 10.9 1.98 " 4.3 0.5 " 4.36 1.2 " 4.36 1.8 " 4.36 1.7 Sn(C4H9) 4 4.3 0.6 SnCl4 5H20/H2S04 5.7 6.4 " 7.6 6.7 " 7.6 7.5 " 7.6 7.7 : " 7.6 7.8 " 7.6 7.7 .
It can be seen that there is a tin volatilization loss in the order of 10 to 1 when the stannic chloride penta-hydrate was used versus a negligible loss of tin where the :~ tin compound used is stannic chloride pentahydrate reacted with sulfuric acid. In some cases the final ratio is e~en higher than the initial ratio where the sulfate form is used.
It is felt that this is due to experimental error caused by the ruthenium compound absorbing water and perhaps some material loss during ~he stripping process.
89~
A second experiment to show the substantial increase in the amount of tin retained in the coating was conducted. In this case a known amount of the solution mixture according to Example 1 using the various compounds containing tin was fired in a crucible and the residue analyzed by atomic absorption.
The firing temperatures and cycles were similar to that employed in Example 1. The results of this experiment in terms of percentage of the given element remaining in the coating material after such firing is reported in Table II below.
TABLE II
Sn Compound % Sn % Ru % Sb Used Retained Retained Retained SnCl4 5H20/H2S04 81 90 43 SnS0~ 94 95 61 SnCl4 5H20 9 97 23 SnCl4 refluxed 19 94 15 in amyl alcohol From Table II, i~ can be seen that the use of a sulfate form of the tin yields significantly higher percentages of tin retention versus the usage of the chloride forms used heretofore.
~9 ~
A series of electrodes were prepared to evaluate half cell potentials and lifetimes of these electrodes in comparison with electrodes utilizing the chloride form compounds in such larger amounts as to yield a resultant amount of tin in the coating equal to that of the sulfate form compounds.
It was Eound that 25.1 grams of stannic chloride pentahydrate yielded approximately the same amount of tin as a mixture containing 5.48 grams stannic chloride pentahydrate reacted with sulfuric acid. It can be seen that in this case that approximately five times as much of the tin compound is necessary when the sulfate form is not used in the coatings. It was also found that when these two materials were applied in equal amounts in terms of grams per square foot of ruthenium on the titanium sample, the resultant electrodes gave approximately the same half cell potentials and had lifetimes as reported in Table III
below.
TARLE III
.
Grams per Lifetime of Lifetime of Square Foot Chloride form Sulfate form Ru in hours in hours .
~.1 17 14 0.2 5~ 68 0.3 79 108 Thus it can be seen that approximately five times as much of the chloride form of the tin versus the sulfate form of tin is required to yield equal lifetimes from the resultant electrodes. This means that a significant lesser amount of the sulfate form tin compounds can be used therefore resulting in a net manufacturing cost savings for a given electrode lifetime. As can be seen from Table I the reproducibility of the sulfate form tin compounds is significantly higher than that for the chloride form compounds thereby lending itself much more readily to a scale up of manufacturing process for ~ the electrode. Use of the sulfate form also will result in significantly less tin being volatilized into the atmosphere thus eliminating one pollution concern of the prior art process-ing methods.
Thus it should be apparent from the foregoing description of the preferred embodiment that the composition herein described accomplishes the objects of the invention and solves the problems attendant to the manufacture of electrode coating compositions and electrodes for use in electrolytic cells for electrochemical production.
BACKGROUND OF THE INVENTION
This invention generally relates to a method for applying coating materials to an electrode substrate, generally of a valve metal, wherein the coating compositions have tin compounds which are later converted to thçlr oxide forms to produce an electrode having significantly increased reproduci-bility for method of manufacture, savings in manufacturing costs - -due to the more complete utilization of the tin metal, and reduced atmospheric pollution caused by the volatilization of tin compounds during the coating process. ~ore particularly the present disclosure~relates to a much improved method for manufacturing an electrode having a valve metal substrate such as titanium carrying an electrode coating composition having tin as a component thereof by using a sulfate form of the tin compound in the coating composition mixture.
Electrochemical methods of manufacture are becoming - ever increasingly important to the chemical industry due to their greater ecological acceptability9 potential for energy conservation, and the resultant cost reductions possible.
Therefore, a great deal of research and development efforts have been applied to electrochemical processes and the hardware for these processes. One major element of the hardware aspect is the electrode itself. The object has been to provide: an electrode which will withstand the corrosive environment within an electrolytic cell; an electrode having a minimum over-potential for the desired electrochemical reaction; and an electrode that can be manufactured with high quality control at a cost within the range of commercial feasibility. Only a few materials may effectively constitute an electrode especially ~as~s~
to be used as an anode because of the susceptibility of most other substances to the intense corrosive conditions present within the anode compartment of an electrolytic cell. Among these materials are: graphite, nickel, lead, lead alloy, platinum, or platinized titanium. Electrodes of this type have limited applications because of the various disadvantages such as: a lack of dimensional stability; high cost; high wear rate; contamination of the electrolyte; contamination of a cathode deposit; sensitivity to impurities; or high overpotentials for the desired reaction. Overpotential refers to the excess electrical potential over the theoretical potential at which the desired reaction occurs at a given current density.
The history of electrodes is replete with examples of attempts and proposals to overcome some of ~he problems assoc-iated with the electrode in an electrolytic cell, none of which have accomplished an optimi~ation of the desirable characteristics for an electrode to be used in an electrolytic cell. The problem is to find an electrode which will overcome many of the undesirable characteristics listed above and additionally have low overpotentials at higher current densities so as to conserve energy. It is known for instance that platinum is an excellent material for use in electrodes to be used as anodes in an electro-winning process and satlsfies many of the above-mentioned criteria.
- However, platinum is expensive and hence has not been found suitable for industrial use to date. Carbon and lead alloy electrodes have been used commercially, but the carbon anode wears fast which greatly pollutes the electrolyte, incraases electrical resistance, and increases the half cell potential.
This higher half cell potential causes the electrolytic cell to consume more electrical energy than is desirable. A dis-advantage of the lead alloy anode is that the lead dissolves ~(~9489~
in the electrolyte producing a lead deposit on the cathode which contaminates the desired deposit obtained. Also, PbO2 changes to a Pb304 which is a poor conductor. Oxygen may penetrate below this layer and flake off the film resulting in particles becoming trapped in the deposited copper on a cathode. This causes a degrading of the copper plating which is very undesir-able.
It has been proposed that platinum or other precious metals be applied to a titanium substrate to retain their attractive electrical characteristics and further reduce the manufacturing costs. However, even th~s limited use of precious metals such as platinum which can cost in the range of $30.00 per square foot ($323.00 per square meter) of electrode surface area is expensive and therefore not desirable for industrial use.
It has also been proposed ~hat the surfaces of titanium be plated electrically with platinum to which another electrical deposit either of lead dioxide or manganese dioxide~is applied.
The electrodes with the lead dioxide coating have the dis-advantage of co~paratively high oxygen overpotentials and both ~types of coatings have high internal stresses when electrolytical-ly deposited which are liable to be detached from the surface during commercial usage, contaminating the electrolyte and the produc- being deposited on the cathode surface. Thus, the current density of such anodes is limited and handling of such anodes must be done with extreme care. Another attempted improvement has been to put a layer of manganese dioxide on the surface of a titanium substrate which is relatively porous in nature and building up a number of layers of the manganese dioxide as to present an integral coating. This yields relative-ly low overpotentials as long as the current density remains .
~0~8~
below 0.5 ampere per square inch (77.5 milliamperes per squarecentimeter) but as the current density is increased to near 1 ampere per square inch (155 milliamperes per square centimeter) the overpotential required rises rather rapidly, resulting in a considerable disadvantage at higher current densities.
More recently a number of coatings have employed the use of titanium, ruthenium and tin dioxides, or tin and antimony oxides upon which a top coating of either manganese or lead oxide is pla~ed. These coatings have shown substantial promise in the area of lowering overpotential and yielding good life-times in the corrosive conditions within an electrolytic cell.
The ma;or drawback of these materials is that the methods of applying especially the tin oxide materials have resulted in volatilization of substantial amounts of the tin upon baking the coating to the tin oxides. This is because the tin compounds such as stannic chloride pentahydrate when baked converts to a stannic hydroxide species and then to the stannic oxides which are desired in the given electrode coating.
During this process much of the tin itself is volatilized into the atmsophere instead of remaining in the coating. This occurs at least partly because the stannic chlorides have boiling - points in the area of 114 centigrade and since the transform-ation of the tin compounds to their respective oxides occurs at much higher temperatures, most of these materials are lost into the atmosphere resulting in less than 50 percent utilization of the tin material in the actual coating. This causes a severe problem in the quality control of methods of manufacture for electrodes of large sizes and large quantities. The reproducability of a coating composition is nearly impossible with the volatilization of the tin caused by the current process for applying the coatings to the substrate materials.
, 39~
Therefore, only theoretical tin calculations can be made causing problems with regard to calculating possible lifetimes of a given electrode. To date, the use of tin in coating compositions has not met with the commercial success it should have because vola-tilization of the tin causes a reproducability problem, increases pollution which is under stringent standards currently, and in-creases the cost of production of a given electrode due to the loss of the tin.
SUMMARY OF TH~E INVENTION
It is therefore an object of the present invention to provide a method of preparation for electrode coating compositions having the desired quality control characteristics and a manufacturing cost within the range of commercial feasibility.
Another object of the present invention is to provide a method of preparation for electrode coating compositions which will significantly reduce the volatilization of tin into the atmosphere thus reducing atmospheric pollution problems associated with this manufacturing process.
These and other objects of the present invention, together with the advantages thereof over existing and prlor art forms which will become apparent to those skilled in the art from the detailed disclosure of the present invention as set forth herein-below, are accomplished by the improvements herein described and claimed.
Thus, in accordance with the present teachings, a method is provided for the manufacture of an electrode which comprises the steps of:
selecting a valve metal substrate from the group consisting of aluminum, molybdenum, niobum, tantalum, titanium, tungsten, zirconium, and alloys thereof;
~ .
~` ' ' ,; ':
948~1 applying to at least a portion of the surface of the sub-strate, a coating material consisting of an antimony compound and a tin sulfate compound;
drying the coating material;
baking the coating in an oxidizing atmosphere to convert the antimony and tin compounds to their respective oxide forms;
and applying to the surface of the coating metal, a topcoating of metal dioxide selected from the group consisting of manganese and lead.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The improved method for manufacture of electrode coating compositions of the present invention may be used in the pre-paration of any coating having as a substituent any tin compound for which the volatilization problem of the tin exists presently.
In the past, electrode coating compositions employing the use of tin have utilized thermally decomposable compounds of the chloride form which have a lower boiling point and therefore a volatiliza-tion problem. The present invention employs the use of a sulfate form of the tin or the use of the chloride compounds along with sulfuric acid to result in a sulfate form of the tin which has a simple decomposition mechanism for formation of the oxide form in the ultimate electrode coating composition and therefore drastic-ally reduces the volatilization of the tin upon baking. The sub-strate material for use in such an electrode coa~ing composition can be any electroconductive metal having sufficient mechanical strength to serve as a support for the coatings, typical metals including: aluminum, molybdenum, niobium, tantalum, titanium, tungsten, zirconium, nickel, steel, stainless steel and alloys thereof. A preferred valve metal based on cost, availability, electrical and chemical properties is titanium. There are a ~' ~J
~48¢~
number of forms the titanium substrate may take in the manufacture of an electrode, including for example: solid sheet material; expanded metal mesh material with a large percentage of open area; and porous titanium with a density of 30 to 70 percent pure titanium which can be produced by cold compacting titanium powder.
One type of coating the present invention may be utilized in is cne where a substrate material such as described above is coated with a semi-conductive intermediate coating of tin and antimony oxides. These compositions are generally mixtures of tin dioxide with minor amounts of antimony "dopent", the latter being present in an amount between 0.1 and 30 weight percent, calculated on the basis of total weight percent of SnO2 and Sb203. The preferred amount of antimony trioxide in most of these cases is between 3 and 15 weight percent. In the past these intermediate coatings have generally used a stannic chloride pentahydrate as one,of the materials of the mixture to be painted or somehow applied to the substrate material.
The present invention utilizes a tin sulfate material or the stannic chloride pentahydrate plus sulfuric acid to obtain the sulfate form of the tin. The sulfate form has a simple decomposi-tion mechanism at a temperature in the area of 320" centigrade such that the temperatures of baking to transform these materials into their respective oxides results in very little volatiliz-ation of the tin into the atmosphere. This allows the semi-conductive intermediate coating to be applied in a very few applications versus the past methods of using several làyered applications of the material to obtain a resultant tin weight in the desired range. Over the top of this semi-conductive intermediate coating may be applied a top coating of either manganese or lead dioxides in order to produce electrodes of good current ~fficiencies and good lifetimes.
There are many other examples of electrode coating composi~ions utilizing tin compounds in their makeup to produce a usa~le electrode coating compositions. Those skilled in the art may desire to precoat the substrate material with numerous other compositions before applying the tin sulfate containing coating composition.
A second example is a single layer coating composition having titanium, ruthenium and tin dioxides applied in a method similar to that described above. This type of coating composition is further described in the following patent - U.S. Patent ~o. 3,855,092.
A third type of coatlng composition employing the use of tin-containing compounds is a mixture of the oxides of tin, antimony, a platinum group metal, and a valve metal. These coating compositions are further described in the following patent, -- U.S. Patent ~o.
3,875,043, In order that those skilled in the art may more ~readily understand the present invention and certain preferred aspects by which it may be utilized, the following specific examples ar~ afforded.
q 4~
A series of electrodes were prepared by coating the substrate metal, in this case titanium, with a solution contain-ing antimony trichloride~ ruthenium trichloride and various compounds containing tin all in such amounts as to allow an initial tin/ruthenium ratio to be calculated and compared to an analysis of the final tin/ruthenium ratio. This shows the amount of volatilization of tin that occurred in each instance.
The initial tin/ruthenium ratio was determined from weights of the starting materials in the coating solution. Since the ruthenium compound does absorb water to some extent to form hydrates there is some inaccuracy to an amount of approximately 5 percent on thP calculation of the initial amount of ruthenium in the ratio. After these various materials were applied to the substrate material they were baked in an oxidizing atmosphere at temperatures of 475 to 625 centigrade for periods of 5 to 10 minutes to transform the compounds into their respective oxides. This process was repeated several times to achieve a layer of desired weight gain. The amount of coating material had no observed affect upon the resultant tin/ruthenium ratios.
Therefore any convenient welght of coating material could be used. Once this was accomplished the final tin/ruthenium ratio was determined by stripping the catalytic layer off of the titanium substrate by means of molten salts which are later dissolved in water to precipitate the metals and analyzing the resulting solution by atomic absorption to establish a final ratio of tin/ruthenium in the coating material. These ratios along with the tin compounds used are reported in Table I
below.
~0~48~
TABLE I
-Sn Compound Used Initial Sn/Ru Final Sn/Ru SnCl4 5H20 21.8 3.3 " 10.9 1.7 " 10.9 1.98 " 4.3 0.5 " 4.36 1.2 " 4.36 1.8 " 4.36 1.7 Sn(C4H9) 4 4.3 0.6 SnCl4 5H20/H2S04 5.7 6.4 " 7.6 6.7 " 7.6 7.5 " 7.6 7.7 : " 7.6 7.8 " 7.6 7.7 .
It can be seen that there is a tin volatilization loss in the order of 10 to 1 when the stannic chloride penta-hydrate was used versus a negligible loss of tin where the :~ tin compound used is stannic chloride pentahydrate reacted with sulfuric acid. In some cases the final ratio is e~en higher than the initial ratio where the sulfate form is used.
It is felt that this is due to experimental error caused by the ruthenium compound absorbing water and perhaps some material loss during ~he stripping process.
89~
A second experiment to show the substantial increase in the amount of tin retained in the coating was conducted. In this case a known amount of the solution mixture according to Example 1 using the various compounds containing tin was fired in a crucible and the residue analyzed by atomic absorption.
The firing temperatures and cycles were similar to that employed in Example 1. The results of this experiment in terms of percentage of the given element remaining in the coating material after such firing is reported in Table II below.
TABLE II
Sn Compound % Sn % Ru % Sb Used Retained Retained Retained SnCl4 5H20/H2S04 81 90 43 SnS0~ 94 95 61 SnCl4 5H20 9 97 23 SnCl4 refluxed 19 94 15 in amyl alcohol From Table II, i~ can be seen that the use of a sulfate form of the tin yields significantly higher percentages of tin retention versus the usage of the chloride forms used heretofore.
~9 ~
A series of electrodes were prepared to evaluate half cell potentials and lifetimes of these electrodes in comparison with electrodes utilizing the chloride form compounds in such larger amounts as to yield a resultant amount of tin in the coating equal to that of the sulfate form compounds.
It was Eound that 25.1 grams of stannic chloride pentahydrate yielded approximately the same amount of tin as a mixture containing 5.48 grams stannic chloride pentahydrate reacted with sulfuric acid. It can be seen that in this case that approximately five times as much of the tin compound is necessary when the sulfate form is not used in the coatings. It was also found that when these two materials were applied in equal amounts in terms of grams per square foot of ruthenium on the titanium sample, the resultant electrodes gave approximately the same half cell potentials and had lifetimes as reported in Table III
below.
TARLE III
.
Grams per Lifetime of Lifetime of Square Foot Chloride form Sulfate form Ru in hours in hours .
~.1 17 14 0.2 5~ 68 0.3 79 108 Thus it can be seen that approximately five times as much of the chloride form of the tin versus the sulfate form of tin is required to yield equal lifetimes from the resultant electrodes. This means that a significant lesser amount of the sulfate form tin compounds can be used therefore resulting in a net manufacturing cost savings for a given electrode lifetime. As can be seen from Table I the reproducibility of the sulfate form tin compounds is significantly higher than that for the chloride form compounds thereby lending itself much more readily to a scale up of manufacturing process for ~ the electrode. Use of the sulfate form also will result in significantly less tin being volatilized into the atmosphere thus eliminating one pollution concern of the prior art process-ing methods.
Thus it should be apparent from the foregoing description of the preferred embodiment that the composition herein described accomplishes the objects of the invention and solves the problems attendant to the manufacture of electrode coating compositions and electrodes for use in electrolytic cells for electrochemical production.
Claims
1. A method for the manufacture of an electrode comprising the steps of:
selecting a valve metal substrate from the group consisting of aluminum, molybdenum, niobum, tantalum, titanium, tungsten, zirconium, and alloys thereof;
applying to at least a portion of the surface of said substrate, a coating material consisting of an antimony compound and a tin sulfate compound;
drying said coating material;
baking said coating material in an oxidizing atmosphere to convert the anitmony and tin compounds to their respective oxide forms; and applying to the surface of said coating material, a topcoating of metal dioxide selected from the group consisting of manganese and lead.
selecting a valve metal substrate from the group consisting of aluminum, molybdenum, niobum, tantalum, titanium, tungsten, zirconium, and alloys thereof;
applying to at least a portion of the surface of said substrate, a coating material consisting of an antimony compound and a tin sulfate compound;
drying said coating material;
baking said coating material in an oxidizing atmosphere to convert the anitmony and tin compounds to their respective oxide forms; and applying to the surface of said coating material, a topcoating of metal dioxide selected from the group consisting of manganese and lead.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA350,504A CA1110932A (en) | 1976-03-15 | 1980-04-23 | Electrode coating method |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US66720276A | 1976-03-15 | 1976-03-15 | |
| US667,202 | 1976-03-15 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1094891A true CA1094891A (en) | 1981-02-03 |
Family
ID=24677240
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA273,774A Expired CA1094891A (en) | 1976-03-15 | 1977-03-11 | Electrode coating method |
Country Status (20)
| Country | Link |
|---|---|
| JP (5) | JPS586786B2 (en) |
| AU (1) | AU516392B2 (en) |
| BE (1) | BE852419A (en) |
| BR (1) | BR7701546A (en) |
| CA (1) | CA1094891A (en) |
| CH (1) | CH619492A5 (en) |
| DD (1) | DD131043A5 (en) |
| DE (1) | DE2710802C3 (en) |
| DK (1) | DK110877A (en) |
| FI (1) | FI65284C (en) |
| FR (1) | FR2344644A1 (en) |
| GB (2) | GB1573297A (en) |
| IT (1) | IT1086682B (en) |
| MX (1) | MX145434A (en) |
| NL (1) | NL7702742A (en) |
| NO (1) | NO148751C (en) |
| PL (1) | PL110048B1 (en) |
| SE (1) | SE427192B (en) |
| TR (1) | TR20097A (en) |
| ZA (1) | ZA771521B (en) |
Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS586786B2 (en) * | 1976-03-15 | 1983-02-07 | ダイヤモンド・シヤムロツク・コ−ポレ−シヨン | Improved electrode manufacturing method |
| JPS60162787A (en) * | 1984-01-31 | 1985-08-24 | Tdk Corp | Electrode for electrolysis |
| JPS6254017U (en) * | 1985-09-25 | 1987-04-03 | ||
| JPH0315190Y2 (en) * | 1985-10-15 | 1991-04-03 | ||
| JPS62274087A (en) * | 1986-05-22 | 1987-11-28 | Permelec Electrode Ltd | Durable electrode for electrolysis and its production |
| JPH0218722U (en) * | 1988-07-25 | 1990-02-07 | ||
| GB2301413B (en) * | 1995-05-31 | 1999-03-10 | Titus Int Plc | Joint forming devices |
| JP5309813B2 (en) * | 2008-09-05 | 2013-10-09 | アタカ大機株式会社 | Oxygen generating electrode |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1244650A (en) * | 1968-10-18 | 1971-09-02 | Ici Ltd | Electrodes for electrochemical processes |
| DE2113676C2 (en) * | 1971-03-20 | 1985-09-12 | Conradty GmbH & Co Metallelektroden KG, 8505 Röthenbach | Electrode for electrochemical processes |
| US3793164A (en) * | 1973-04-19 | 1974-02-19 | Diamond Shamrock Corp | High current density brine electrolysis |
| US3875043A (en) * | 1973-04-19 | 1975-04-01 | Electronor Corp | Electrodes with multicomponent coatings |
| US3882002A (en) * | 1974-08-02 | 1975-05-06 | Hooker Chemicals Plastics Corp | Anode for electrolytic processes |
| US4028215A (en) * | 1975-12-29 | 1977-06-07 | Diamond Shamrock Corporation | Manganese dioxide electrode |
| US4040939A (en) * | 1975-12-29 | 1977-08-09 | Diamond Shamrock Corporation | Lead dioxide electrode |
| JPS586786B2 (en) * | 1976-03-15 | 1983-02-07 | ダイヤモンド・シヤムロツク・コ−ポレ−シヨン | Improved electrode manufacturing method |
-
1977
- 1977-03-11 JP JP52026870A patent/JPS586786B2/en not_active Expired
- 1977-03-11 DE DE2710802A patent/DE2710802C3/en not_active Expired
- 1977-03-11 CA CA273,774A patent/CA1094891A/en not_active Expired
- 1977-03-14 DD DD7700197839A patent/DD131043A5/en unknown
- 1977-03-14 PL PL1977196653A patent/PL110048B1/en unknown
- 1977-03-14 FI FI770806A patent/FI65284C/en not_active IP Right Cessation
- 1977-03-14 NO NO770908A patent/NO148751C/en unknown
- 1977-03-14 GB GB23725/79A patent/GB1573297A/en not_active Expired
- 1977-03-14 FR FR7707474A patent/FR2344644A1/en active Granted
- 1977-03-14 BE BE175750A patent/BE852419A/en not_active IP Right Cessation
- 1977-03-14 SE SE7702837A patent/SE427192B/en unknown
- 1977-03-14 DK DK110877A patent/DK110877A/en not_active Application Discontinuation
- 1977-03-14 IT IT48463/77A patent/IT1086682B/en active
- 1977-03-14 ZA ZA00771521A patent/ZA771521B/en unknown
- 1977-03-14 BR BR7701546A patent/BR7701546A/en unknown
- 1977-03-14 CH CH316177A patent/CH619492A5/en not_active IP Right Cessation
- 1977-03-14 MX MX168351A patent/MX145434A/en unknown
- 1977-03-14 GB GB10704/77A patent/GB1573173A/en not_active Expired
- 1977-03-14 NL NL7702742A patent/NL7702742A/en active Search and Examination
- 1977-03-15 AU AU23212/77A patent/AU516392B2/en not_active Expired
- 1977-03-15 TR TR20097A patent/TR20097A/en unknown
-
1979
- 1979-12-27 JP JP54173857A patent/JPS5822551B2/en not_active Expired
-
1981
- 1981-09-19 JP JP56148662A patent/JPS5833313B2/en not_active Expired
- 1981-09-19 JP JP56148663A patent/JPS5782477A/en active Pending
-
1982
- 1982-09-16 JP JP57161537A patent/JPS5930791B2/en not_active Expired
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