CA1151594A - Sintered titanium oxide electrode with manganese dioxide coating - Google Patents
Sintered titanium oxide electrode with manganese dioxide coatingInfo
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- CA1151594A CA1151594A CA000325986A CA325986A CA1151594A CA 1151594 A CA1151594 A CA 1151594A CA 000325986 A CA000325986 A CA 000325986A CA 325986 A CA325986 A CA 325986A CA 1151594 A CA1151594 A CA 1151594A
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- titanium
- sintered
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- titanium oxide
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Abstract
ABSTRACT
A sintered electrode especially for use in electrowinning is formed of a corrosion-resistant carrier consisting at least in part of sintered TiOx, wherein x = 0.25 to 1.5, having a coating of manganese dioxide covering at least part of the surface of the carrier.
A sintered electrode especially for use in electrowinning is formed of a corrosion-resistant carrier consisting at least in part of sintered TiOx, wherein x = 0.25 to 1.5, having a coating of manganese dioxide covering at least part of the surface of the carrier.
Description
~159~
This invention relates to a sintered electrode for electrochemical processes, especially ~or the electrochemical winning of metals, the electrode being corrosion-resistant under electrolysis conditions, as well as a method for manufacturing the electrode.
In the electrochemical winning of me-tals, because of the strong corrosive attack under the conditions of electrolysis, only few materials such as graphite, lead, nickel and platinum are suitable as electrodes, especially the anode. From the German Published Non-Prosecuted Applications 1 796 220, published July 15, 1971, applicant Imperial Metal Indusiries, and 26 36 447, published June 16, 1977, applicant Diamond Shamrock Technologies S.A., electrodes for this purpose are known which consist of a carrier or a base of titanium and a coating which covers the surface of the carrier and contains a substantial amount of manganese dioxide.
Since the surface of the carrier of such electrodes is passivated under electrolysis conditions, despite the activation coating and the cell voltage rises in the process with constant current density, the electrodes can generally be operated only with rather low current densities. It is known that one can delay the passivation of the electrode carrier by a special coating consisting of several layers.
According to German Published Non-Prosecuted Application 26 57 97 9, published July 7, 1977, applicant Diamond Shamrock Corp., the covering layer which is applied to the metal carrier that can be passivated, is composed of an intermediate layer which contains oxides of tin and antimony, and of a cover layer which consists substantially of m~nganese dioxide. An anode is known from French ;
~5i1594 Provisional Patent No. 2 236 027, published January 31, 1975, applicant Titanium Metals Corp. of America which has a first manganese dioxide layer formed by thermal decomposition of a manganese compound, and a second manganese dioxide layer which is deposited electrochemically on a sintered carrier of metallic titanium.
The preparation of coatings consisting of several individ-ual layers is relatively expensive and, in addition, passivation of the carrier can be prevented only if the diffusion of oxygen ions through the layers is completely inhibited or is, at least, very small.
The present inv~ntion is therefore directed to providing an electrode, and particularly, an anode with a coating of manganese dioxide, the voltage drop of which does not increase, or only insignificantly so, over extended periods of operation and which can be made simply.
According to the present invention, there is provided a sintered electrode for use in electrochemical processes which comprises a corrosion-resistant base covered at least in part by a first coating of sintered titanium oxide TioX, wherein x = 0.25 to 1.5, and at least in part by a second coating of manganese dioxide.
In another aspect of the present invention there is provided a corrosion resistant electrode for electrolysis of metal contained in aqueous solutions said electrode comprising a titanium base, a coating of titanium oxide TiOX on at least part of said base, wherein x = 0.25 to 1.5, the coated base having been sintered by heating in an inert gas atmosphere to a temperature of from 900 to ~5~L594 1400C, and at least a partial covering layer of manganese dioxide.
There is also provided in accordance with the invention a method for manufacturing a sintered electrode for electrochemical processes, which method comprises coating a base of titanium with titanium oxide TiOX, wherein x = 0.25 to 1.5, joining the layer of titanium oxide TiOX to the base of titanium by heating in an inert atmosphere to a temperature of 900 to 1400C, and covering at least in part the resultant sintered titanium oxide-titanium body with a coating of manganese dioxide.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as em-- 2a -~5~5~4 bodied in an electrode for electrochemical processes especially electrowinning, and method for manufacturing same, it is nevertheless not intended to be limitedto the details shown, since various mDdifications may be made therein without deFarting from the spirit of the invention and within the scope and range of equivalents of the claims.
m e invention is based on the surprising discovery that the oFer-ability, and in particular the magnitude of the critical current density and theconstancy in time of the electrode potential of anodes ccmprising coatings of m~ganese dioxide are to a substantial degree determmed by the material composi-tion of the carrier. Carriers consisting of metallic titanium ~orm under anodic load a thin surface layer of titanium dioxide, the thickness of which does not change as long as the critical current density is not exceeded. Under these con-ditions, the electric charges are transported exclusively by electrons. However,if the current density is increased beyond the critical limit, then oxygen ions diffuse from the manganese-dioxide-containing coating layer into the carrier metal.
x MnO2 Ti ~ x MnO2 ~ x + Tio2 (0 < x 1) me increasing thickness of the TiO2 - layer rapidly leads to oomplete inactivation of the anode.
Titanium oxides TioX, with x = 0.25 to 1.50, exhibit the same corro-sion resistance as metallic titanium. me passivation behavior, however, is sub-stantially different. If, for instan oe, an electrode of titanium is used as theanode, the current drops to zero within a few seconds even with higher voltages.Hcwever, the current decreases only slowly under the same conditions if an anodeis used which is provided with a TiO layer or consists completely of TiO , and the activity of the anode changes only after an extended time of operation to ~5~594 any appreciable degree. The effect can perhaps be explained by the greater mobility of the oxygen ions in the crystallographically disturbed lattice of the TiO -phases and the high electron conductivity of the suboxide, which inhibits the formation of a Tio2 barrier layer on the surface of the titanium carrier.
A titanium member made by powder metallurgy is particularly well suited as a carrier for an electrode according to the invention. The irregular surface shape of the titanium member makes a particularly advantageous adhesion base for a layer of titanium oxide TiOX which is applied to the surface of the carrier in known manner with a spatula, by brushing or pressing, or by flame or plasma spraying, and is then sintered-on at an elevated temperature. The thick-ness of the TioX layer is at least 0.1 mm and in particular 0.1 to 5 mm. Accord-ing to a further embodlment of the invention, the carrier consists entirely of a titanium oxide TiOX.
For preparing the compounds TioX, titanium metal and titanium dioxide powder are mixed in a ratio of 7:1 to 1:3, optionally after addition of a binder such as an aqueous solution of polyvinyl alcohol. The mixture is pressed into sheet or briquettes and the pressed blanks are sintered in an inert atmosphere in the temperature range of between 900 and 1500C. By the temperature treatment of the densified Ti-TiO2 powder mixture, substantially uniform TiOx-phases are formed which correspond to the respective stoichiometric composition, and with a considerably disturbed lattice. Thus, one has, for instance, in the range x =
0.6 to 1.25, a com~ound of the NaCl type with inccmpletely occupied lattice loca-tions. In the range x < 0.42, the ~-titanium lattice is expanded by embedded oxygen, and in the ranges x = 0.42 to 0.60 and x = 1.25 to 1.50, the reaction product consists of mLxtures of the disturbed ~-titanium and TiO-phases or the TiO and TiO2-phases. The blanks are comminuted and milled to make a fine po~der, the grain size of which is about 10 to 75 ~m. In this form, it is fed, for in-stan oe, to a plasma burner and applied in an argon atmosphere to the base part of the carrier which is made ~S~L594 of sintered titanium.
According to another preferred method, a binder such a polyvinyl alcohol or methyl cellulose is added to the powder, which is then applied to a sintered titanium member by painting, brushing or spraying and is sintered to the member ~y heating.
In another method, a layer of titanium powder is overlaid with a layer of TiO powder and the layers are then pressed into a carrier of the desired dimensions and subsequently sintered. The development and stoichio-metric composition of the TiO -portion of the carrier are determined particu-larly b~ the sintering conditions. The sintering is accomplished in an inert atmosphere, for instance, in argon or in a vacuum. The sintering temperatures are preferably 900 to 1400C. In the temperature range up to about 1250C, the required sintering time is inversely proportional to the temperature.
Above about 1250C, the mobility of the oxygen increases considerably, so that a larger share of oxygen diffuses from the TiO -layer into the titanium layer of the carrier. This effect, which is advantageous for a firm anchor-ing of the two carrier layers, can be controlled by limiting the sintering time in such a manner that the overall formula TiO of the intermediate layer is ~ithin the limits x = 0.25 and x = 1.50. However, the actual composition 2Q varies, depending on the sintering conditions, over the thickness of this layer, the oxygen content declining from the surface toward the boundary layer. TiOx-layers with an oxygen content above 1.50 have an electric resis-tance which is not suitable for electrodes, and furthermore processing is made difficult because of the brittleness of the ma~erial. Layers with an oxygen content below 0.25 cannot sufficiently prevent, under unfavorable conditions, the formation of passivation layers. TiOx-layers with the com-position TiOX with x = 0.42 to 0.60 have particularly advantageous proper~
ties.
~L5~S94 All known coating methods are equally well suited for coating the electrode carrier with a coating of manganese dioxide. For instance, the carrier can be impregnated with an aqueous solution of a manganese salt such as manganese nitrate, and the salt can be decomposed by heating it to about 300C, whereby the oxide is obtained in the ~-form. According to another method, manganese dioxide is applied electrolytically from a manganese sulfate-containing solution to the surface of the carrier. The layer of manganese di-oxide forming part of the electrode according to the invention exhibits excel-lent stability, which is independent of the current load over a wide range.
Even after repeated tempering and subsequent quenching, no separation of the layer and decrease of the electrochemical activity can be observed.
The present invention will now be explained in more detail with the aid of the following examples.
Example 1 Titanium sheet sections with the dimensions 100 x 20 x 2 mm ~ere ~r vided with a coating of manganese dioxide.
Sample 1 - The sheet was immersed without special surface treatment in a 20-%
aqueous manganese nitrate solution, and was dried and heated to about 300C
for decomposing the manganese nitrate. After these steps were repeated five times, the coating contained about 1 mg/cm MnO2.
Sample 2 - The titanium sheet was sandblasted and coatad like Sample 1.
Sample 3 - A second MnO2-layer was applied electrolytically to a titanium sheet, which had first been provided with a coating of manganese dioxide as above, at a current density of 2 mA/cm and a temperature of 60C in an elec-trolytic bath containing lao g manganese ~ul~ate and 10 g concentrated sulfuric acid per liter. The coating contained a total of about 2 mg/cm MnO2.
Sample 4 - The titanium sheet was sandblasted and coated by brushing with an aqueous suspension containing 50% TiOo 56 powder with a grain size of less , .
i9~8 than 100 ~m and 0.3% methyl cellulose. The layer, the thickness of which was about 0.5 mm, was dehydrated at a temperature of ~0C and sintered in a vacuum with a pressure of 10 5 mbar by heating to a temperature of 1250C, whereby an insoluble bond with the sheet was formed. During the sintering, oxygen diffused from the oxide layer into the titanium sheet, so that the average composition of the layer was about TiOo 5. The sample was then provided, in the same manner as samples 1 and 2, with a coating of manganese dioxide, which contained, relative to the geometric surface, about 1 mg/cm MnO2.
The samples were tested at 25C as anodes in a cell which contained 10% sulfuric acid as the electrolyte. The electrode spacing was 3 mm and the current density 50 mA/cm .
Sam~le Cell Volta~e ~t = 0 h~Service Life x) 1 3.1 V 50 h
This invention relates to a sintered electrode for electrochemical processes, especially ~or the electrochemical winning of metals, the electrode being corrosion-resistant under electrolysis conditions, as well as a method for manufacturing the electrode.
In the electrochemical winning of me-tals, because of the strong corrosive attack under the conditions of electrolysis, only few materials such as graphite, lead, nickel and platinum are suitable as electrodes, especially the anode. From the German Published Non-Prosecuted Applications 1 796 220, published July 15, 1971, applicant Imperial Metal Indusiries, and 26 36 447, published June 16, 1977, applicant Diamond Shamrock Technologies S.A., electrodes for this purpose are known which consist of a carrier or a base of titanium and a coating which covers the surface of the carrier and contains a substantial amount of manganese dioxide.
Since the surface of the carrier of such electrodes is passivated under electrolysis conditions, despite the activation coating and the cell voltage rises in the process with constant current density, the electrodes can generally be operated only with rather low current densities. It is known that one can delay the passivation of the electrode carrier by a special coating consisting of several layers.
According to German Published Non-Prosecuted Application 26 57 97 9, published July 7, 1977, applicant Diamond Shamrock Corp., the covering layer which is applied to the metal carrier that can be passivated, is composed of an intermediate layer which contains oxides of tin and antimony, and of a cover layer which consists substantially of m~nganese dioxide. An anode is known from French ;
~5i1594 Provisional Patent No. 2 236 027, published January 31, 1975, applicant Titanium Metals Corp. of America which has a first manganese dioxide layer formed by thermal decomposition of a manganese compound, and a second manganese dioxide layer which is deposited electrochemically on a sintered carrier of metallic titanium.
The preparation of coatings consisting of several individ-ual layers is relatively expensive and, in addition, passivation of the carrier can be prevented only if the diffusion of oxygen ions through the layers is completely inhibited or is, at least, very small.
The present inv~ntion is therefore directed to providing an electrode, and particularly, an anode with a coating of manganese dioxide, the voltage drop of which does not increase, or only insignificantly so, over extended periods of operation and which can be made simply.
According to the present invention, there is provided a sintered electrode for use in electrochemical processes which comprises a corrosion-resistant base covered at least in part by a first coating of sintered titanium oxide TioX, wherein x = 0.25 to 1.5, and at least in part by a second coating of manganese dioxide.
In another aspect of the present invention there is provided a corrosion resistant electrode for electrolysis of metal contained in aqueous solutions said electrode comprising a titanium base, a coating of titanium oxide TiOX on at least part of said base, wherein x = 0.25 to 1.5, the coated base having been sintered by heating in an inert gas atmosphere to a temperature of from 900 to ~5~L594 1400C, and at least a partial covering layer of manganese dioxide.
There is also provided in accordance with the invention a method for manufacturing a sintered electrode for electrochemical processes, which method comprises coating a base of titanium with titanium oxide TiOX, wherein x = 0.25 to 1.5, joining the layer of titanium oxide TiOX to the base of titanium by heating in an inert atmosphere to a temperature of 900 to 1400C, and covering at least in part the resultant sintered titanium oxide-titanium body with a coating of manganese dioxide.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as em-- 2a -~5~5~4 bodied in an electrode for electrochemical processes especially electrowinning, and method for manufacturing same, it is nevertheless not intended to be limitedto the details shown, since various mDdifications may be made therein without deFarting from the spirit of the invention and within the scope and range of equivalents of the claims.
m e invention is based on the surprising discovery that the oFer-ability, and in particular the magnitude of the critical current density and theconstancy in time of the electrode potential of anodes ccmprising coatings of m~ganese dioxide are to a substantial degree determmed by the material composi-tion of the carrier. Carriers consisting of metallic titanium ~orm under anodic load a thin surface layer of titanium dioxide, the thickness of which does not change as long as the critical current density is not exceeded. Under these con-ditions, the electric charges are transported exclusively by electrons. However,if the current density is increased beyond the critical limit, then oxygen ions diffuse from the manganese-dioxide-containing coating layer into the carrier metal.
x MnO2 Ti ~ x MnO2 ~ x + Tio2 (0 < x 1) me increasing thickness of the TiO2 - layer rapidly leads to oomplete inactivation of the anode.
Titanium oxides TioX, with x = 0.25 to 1.50, exhibit the same corro-sion resistance as metallic titanium. me passivation behavior, however, is sub-stantially different. If, for instan oe, an electrode of titanium is used as theanode, the current drops to zero within a few seconds even with higher voltages.Hcwever, the current decreases only slowly under the same conditions if an anodeis used which is provided with a TiO layer or consists completely of TiO , and the activity of the anode changes only after an extended time of operation to ~5~594 any appreciable degree. The effect can perhaps be explained by the greater mobility of the oxygen ions in the crystallographically disturbed lattice of the TiO -phases and the high electron conductivity of the suboxide, which inhibits the formation of a Tio2 barrier layer on the surface of the titanium carrier.
A titanium member made by powder metallurgy is particularly well suited as a carrier for an electrode according to the invention. The irregular surface shape of the titanium member makes a particularly advantageous adhesion base for a layer of titanium oxide TiOX which is applied to the surface of the carrier in known manner with a spatula, by brushing or pressing, or by flame or plasma spraying, and is then sintered-on at an elevated temperature. The thick-ness of the TioX layer is at least 0.1 mm and in particular 0.1 to 5 mm. Accord-ing to a further embodlment of the invention, the carrier consists entirely of a titanium oxide TiOX.
For preparing the compounds TioX, titanium metal and titanium dioxide powder are mixed in a ratio of 7:1 to 1:3, optionally after addition of a binder such as an aqueous solution of polyvinyl alcohol. The mixture is pressed into sheet or briquettes and the pressed blanks are sintered in an inert atmosphere in the temperature range of between 900 and 1500C. By the temperature treatment of the densified Ti-TiO2 powder mixture, substantially uniform TiOx-phases are formed which correspond to the respective stoichiometric composition, and with a considerably disturbed lattice. Thus, one has, for instance, in the range x =
0.6 to 1.25, a com~ound of the NaCl type with inccmpletely occupied lattice loca-tions. In the range x < 0.42, the ~-titanium lattice is expanded by embedded oxygen, and in the ranges x = 0.42 to 0.60 and x = 1.25 to 1.50, the reaction product consists of mLxtures of the disturbed ~-titanium and TiO-phases or the TiO and TiO2-phases. The blanks are comminuted and milled to make a fine po~der, the grain size of which is about 10 to 75 ~m. In this form, it is fed, for in-stan oe, to a plasma burner and applied in an argon atmosphere to the base part of the carrier which is made ~S~L594 of sintered titanium.
According to another preferred method, a binder such a polyvinyl alcohol or methyl cellulose is added to the powder, which is then applied to a sintered titanium member by painting, brushing or spraying and is sintered to the member ~y heating.
In another method, a layer of titanium powder is overlaid with a layer of TiO powder and the layers are then pressed into a carrier of the desired dimensions and subsequently sintered. The development and stoichio-metric composition of the TiO -portion of the carrier are determined particu-larly b~ the sintering conditions. The sintering is accomplished in an inert atmosphere, for instance, in argon or in a vacuum. The sintering temperatures are preferably 900 to 1400C. In the temperature range up to about 1250C, the required sintering time is inversely proportional to the temperature.
Above about 1250C, the mobility of the oxygen increases considerably, so that a larger share of oxygen diffuses from the TiO -layer into the titanium layer of the carrier. This effect, which is advantageous for a firm anchor-ing of the two carrier layers, can be controlled by limiting the sintering time in such a manner that the overall formula TiO of the intermediate layer is ~ithin the limits x = 0.25 and x = 1.50. However, the actual composition 2Q varies, depending on the sintering conditions, over the thickness of this layer, the oxygen content declining from the surface toward the boundary layer. TiOx-layers with an oxygen content above 1.50 have an electric resis-tance which is not suitable for electrodes, and furthermore processing is made difficult because of the brittleness of the ma~erial. Layers with an oxygen content below 0.25 cannot sufficiently prevent, under unfavorable conditions, the formation of passivation layers. TiOx-layers with the com-position TiOX with x = 0.42 to 0.60 have particularly advantageous proper~
ties.
~L5~S94 All known coating methods are equally well suited for coating the electrode carrier with a coating of manganese dioxide. For instance, the carrier can be impregnated with an aqueous solution of a manganese salt such as manganese nitrate, and the salt can be decomposed by heating it to about 300C, whereby the oxide is obtained in the ~-form. According to another method, manganese dioxide is applied electrolytically from a manganese sulfate-containing solution to the surface of the carrier. The layer of manganese di-oxide forming part of the electrode according to the invention exhibits excel-lent stability, which is independent of the current load over a wide range.
Even after repeated tempering and subsequent quenching, no separation of the layer and decrease of the electrochemical activity can be observed.
The present invention will now be explained in more detail with the aid of the following examples.
Example 1 Titanium sheet sections with the dimensions 100 x 20 x 2 mm ~ere ~r vided with a coating of manganese dioxide.
Sample 1 - The sheet was immersed without special surface treatment in a 20-%
aqueous manganese nitrate solution, and was dried and heated to about 300C
for decomposing the manganese nitrate. After these steps were repeated five times, the coating contained about 1 mg/cm MnO2.
Sample 2 - The titanium sheet was sandblasted and coatad like Sample 1.
Sample 3 - A second MnO2-layer was applied electrolytically to a titanium sheet, which had first been provided with a coating of manganese dioxide as above, at a current density of 2 mA/cm and a temperature of 60C in an elec-trolytic bath containing lao g manganese ~ul~ate and 10 g concentrated sulfuric acid per liter. The coating contained a total of about 2 mg/cm MnO2.
Sample 4 - The titanium sheet was sandblasted and coated by brushing with an aqueous suspension containing 50% TiOo 56 powder with a grain size of less , .
i9~8 than 100 ~m and 0.3% methyl cellulose. The layer, the thickness of which was about 0.5 mm, was dehydrated at a temperature of ~0C and sintered in a vacuum with a pressure of 10 5 mbar by heating to a temperature of 1250C, whereby an insoluble bond with the sheet was formed. During the sintering, oxygen diffused from the oxide layer into the titanium sheet, so that the average composition of the layer was about TiOo 5. The sample was then provided, in the same manner as samples 1 and 2, with a coating of manganese dioxide, which contained, relative to the geometric surface, about 1 mg/cm MnO2.
The samples were tested at 25C as anodes in a cell which contained 10% sulfuric acid as the electrolyte. The electrode spacing was 3 mm and the current density 50 mA/cm .
Sam~le Cell Volta~e ~t = 0 h~Service Life x) 1 3.1 V 50 h
2 3.0 175
3 2.9 400
4 2.5 > 3000 x) Service life is the time at which the cell voltage is less than 5 V.
The initial voltage and the service life of the anodes are improved by mechanical pretreatment of the surface of the titanium carrier ~Sample 2) and by coating layers containing several individual layers ~Sample 3). The anode 4 prepared in accordance with the invention e~hibited a cell voltage of about 15% lower, which did not change during the test time of 3000 hours.
~xample 2 20 g titanium sponge with a grain size of 0.5 to 2.0 mm were filled into a press dia and the powder bed was overlaid with 6 g TiOo 5-powder. The layers arranged on top of each other were pressed with a pressure of 30 kN/cm to form an anode with the dimensions 20 x 50 x 6 mm. The thickness of the ~5~9~
oxide layer was about 1 mm. The pressed blank was sintered at a pressure of 10 5 mbar at a temperature of 1250C.
To a first carrier slab (Sample 1), a coating of manganese dioxide was applied by thermal decomposition of manganese nitrate, as described in Example 1. A second carrier slab (Sample 2) was provided with a manganese dioxide layer by means of electrodeposition.
The samples were tested as anodes in an electrolyte which contained 100 g sulfuric acid, 50 g copper ions and 10 g nickel ions per liter. The current density was 100 mA/cm .
10Runnin~ Time Sample 1 Sample 2 0 h 1.8 V 1.7 V
500 2.2 2.2 1000 2.3 2.0 1500 2.1 2.1 2000 2.1 2.1 2500 2.1 2.1 The cell voltage is independent of the kind of methcd used for making the coating of manganese dioxide and, after a slight rise during the initial phase, is practically constant.
20Example 3 ~ fter the addi~ion of 5 parts by weight of a 2% aqueous polyvinyl alcohol solution, 61.4 parts by weight titanium powder ~grain size less than 0.06 mm) and 38.6 parts by weight rutile powder (grain size less than 0.01 mm) were mixed in a high-speed mixer for 10 min. and were subsequently pressed in a die press into cylindrical bodies with a diameter of 5n mm at a pressure of 30 kN/cm . The blanks dried at a temperature of 105C were then heated to 1250C for 4 hours in an argon atmosphere, and subsequently comminuted in a ~aw crusher and milled in a vibratory mill down to a grain size of less than 0.06 mm. The brittle powder with a color like cast iron had a composition of 0.56 To lO0 parts by weight of powder, 5 parts by weight of a 10% solu-tion of hard paraffin in toluol were added and then mixed in a vortex mixer for 5 minutes and pressed in a die press under a pressure of 25 kN/cm2 into slab-shaped electrode carriers which were heated, after a drying treatment, in a gravity-discharge furnace to 1300 C in an argon atmosphere. The electric s 2 w~s resistivity-t~ about 1.8 ohm mm /m, the accessible pore volume ~ about 15%.
The carriers were provided with a coating of manganese dioxide as described in Example 1 and tested under the same conditions as anodes. The mean cell voltage was 2.1 V.
_ g _
The initial voltage and the service life of the anodes are improved by mechanical pretreatment of the surface of the titanium carrier ~Sample 2) and by coating layers containing several individual layers ~Sample 3). The anode 4 prepared in accordance with the invention e~hibited a cell voltage of about 15% lower, which did not change during the test time of 3000 hours.
~xample 2 20 g titanium sponge with a grain size of 0.5 to 2.0 mm were filled into a press dia and the powder bed was overlaid with 6 g TiOo 5-powder. The layers arranged on top of each other were pressed with a pressure of 30 kN/cm to form an anode with the dimensions 20 x 50 x 6 mm. The thickness of the ~5~9~
oxide layer was about 1 mm. The pressed blank was sintered at a pressure of 10 5 mbar at a temperature of 1250C.
To a first carrier slab (Sample 1), a coating of manganese dioxide was applied by thermal decomposition of manganese nitrate, as described in Example 1. A second carrier slab (Sample 2) was provided with a manganese dioxide layer by means of electrodeposition.
The samples were tested as anodes in an electrolyte which contained 100 g sulfuric acid, 50 g copper ions and 10 g nickel ions per liter. The current density was 100 mA/cm .
10Runnin~ Time Sample 1 Sample 2 0 h 1.8 V 1.7 V
500 2.2 2.2 1000 2.3 2.0 1500 2.1 2.1 2000 2.1 2.1 2500 2.1 2.1 The cell voltage is independent of the kind of methcd used for making the coating of manganese dioxide and, after a slight rise during the initial phase, is practically constant.
20Example 3 ~ fter the addi~ion of 5 parts by weight of a 2% aqueous polyvinyl alcohol solution, 61.4 parts by weight titanium powder ~grain size less than 0.06 mm) and 38.6 parts by weight rutile powder (grain size less than 0.01 mm) were mixed in a high-speed mixer for 10 min. and were subsequently pressed in a die press into cylindrical bodies with a diameter of 5n mm at a pressure of 30 kN/cm . The blanks dried at a temperature of 105C were then heated to 1250C for 4 hours in an argon atmosphere, and subsequently comminuted in a ~aw crusher and milled in a vibratory mill down to a grain size of less than 0.06 mm. The brittle powder with a color like cast iron had a composition of 0.56 To lO0 parts by weight of powder, 5 parts by weight of a 10% solu-tion of hard paraffin in toluol were added and then mixed in a vortex mixer for 5 minutes and pressed in a die press under a pressure of 25 kN/cm2 into slab-shaped electrode carriers which were heated, after a drying treatment, in a gravity-discharge furnace to 1300 C in an argon atmosphere. The electric s 2 w~s resistivity-t~ about 1.8 ohm mm /m, the accessible pore volume ~ about 15%.
The carriers were provided with a coating of manganese dioxide as described in Example 1 and tested under the same conditions as anodes. The mean cell voltage was 2.1 V.
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Claims (10)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1 A sintered electrode for use in electrochemical processes which comprises a corrosion-resistant base covered at least in part by a first coating of sintered titanium oxide TiOx, wherein x = 0.25 to 1.5, and at least in part by a second coating of manganese dioxide.
2. An electrode according to claim l, wherein x = 0.42 to 0.60.
3. An electrode according to claim 1 or claim 2, wherein the base consists entirely of titanium oxide TiOx.
4. An electrode according to claim 1, wherein the base consists of sintered titanium and a sintered-on layer of titanium oxide TiOx.
5. An electrode according to claim 4, wherein the thickness of the sintered-on layer is 0.1 to 5 mm.
6. A corrosion resistant electrode for electrolysis of metal contained in aqueous solutions said electrode comprising a titanium base, a coating of titanium oxide TiOx on at least part of said base, wherein x = 0.25 to 1.5, the coated base having been sintered by heating in an inert gas atmosphere to a temperature of from 900 to 1400°C, and at least a partial covering layer of manganese dioxide.
7. Method for manufacturing a sintered electrode for electro-chemical processes, which method comprises coating a base of titanium with titanium oxide TiOx, wherein x = 0.25 to 1.5, joining the layer of titanium oxide TiOx to the base of titanium by heating in an inert atmosphere to a temperature of 900 to 1400°C, and covering at least in part the resultant sintered titanium oxide-titanium body with a coating of manganese dioxide.
8. Method according to claim 7, wherein the temperature of heating in an inert atmosphere is about 1250°C.
9. Method according to claim 7 wherein the base of titanium is formed by moulding titanium powder.
10. Method according to claim 9 wherein the base of titanium is sintered prior to said coating with titanium oxide TiOx.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000325986A CA1151594A (en) | 1979-04-20 | 1979-04-20 | Sintered titanium oxide electrode with manganese dioxide coating |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000325986A CA1151594A (en) | 1979-04-20 | 1979-04-20 | Sintered titanium oxide electrode with manganese dioxide coating |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1151594A true CA1151594A (en) | 1983-08-09 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000325986A Expired CA1151594A (en) | 1979-04-20 | 1979-04-20 | Sintered titanium oxide electrode with manganese dioxide coating |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1151594A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN106283099A (en) * | 2016-08-25 | 2017-01-04 | 岭南师范学院 | A kind of surfactant assist in electrodeposition synthesizing anatase type titanium dioxide and the method for manganese dioxide nano-composite material and application thereof |
-
1979
- 1979-04-20 CA CA000325986A patent/CA1151594A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN106283099A (en) * | 2016-08-25 | 2017-01-04 | 岭南师范学院 | A kind of surfactant assist in electrodeposition synthesizing anatase type titanium dioxide and the method for manganese dioxide nano-composite material and application thereof |
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