JPS5941486A - Manufacture of raney nickel clad cathode and product - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of making an improved Raney nickel type low hydrogen overvoltage cathode for use in chlor-alkali electrolysis and to the cathode made thereby.

Raney nickel type cathodes are used, for example, in U.S. Pat. No. 4,116.
．． No. 804, No. 4,169, 0.25 and No. 4, 25
No. 1.344, known in the art.

However, although conventional Raney nickel coated cathodes exhibit good initial performance characteristics, they have certain drawbacks. Such Raney nickel coatings on cathode substrates have poor durability, ie they are easily damaged mechanically and removed even by jets of water, for example. For example, if such a cathode is used in a diaphragm-type chlor-alkali bath in which an asbestos diaphragm is placed over the cathode surface, such diaphragm will gradually become clogged, usually after about 9 to 15 months. It loses its transparency and must be removed and replaced. This removal is usually accomplished by spraying with a jet of water.

During such spraying, the jet of water causes some of the Raney nickel to dissipate in the form of flakes or debris. In addition, a replacement diaphragm was placed and the temperature was lowered to 355°C for 4 hours in normal air.
When baked for hours, oxidative passivation of the Raney nickel coating occurs. This gradual exfoliation and passivation of the Raney nickel after multiple washes and calcinations progressively eliminates the potential advantage imparted by the Raney nickel, i.e., progressively increases the cathode operating potential and increases the cathode substrate operating potential. bring it closer to

Accordingly, it is a principal object of the present invention to provide an improved Raney nickel-coated cathode and method for making the same having a more durable Raney nickel surface than those previously known.

Other purposes will become apparent from the description below.

Briefly, according to the present invention, a nickel/aluminum alloy composition containing 56-59% by weight of nickel is
A method of making a durable low hydrogen overvoltage cathode for chlor-alkali is provided, comprising applying it by plasma spray onto a suitable cathode substrate and then removing the aluminum by eluting with caustic.

More particularly, according to the invention: (a) nickel/containing 56-59% by weight of nickel;
plasma spraying a coating of an aluminum alloy composition onto a perforated substrate of iron, iron alloy, nickel or nickel alloy; and (b) removing the coating from the coating by contacting the material produced in step (α) with a caustic solution. A method of making a low hydrogen overpotential cathode for a chloralkali tank reservoir is provided, comprising: eluting aluminum.

The trowel of the present invention also provides a Raney nickel coated cathode produced by the method, a chloralkali bath containing the cathode, and a method for electrolysis of alkali metal chlorides in nuclides.

The nickel/aluminum alloy composition selected in this invention is applied to the conductive cathode substrate by plasma spraying. It is a requirement of the present invention that the nickel/aluminum alloy composition used to deposit onto the cathode substrate contains about 56-59% by weight nickel. Nickel/aluminum alloys within this composition range contain intermetallic compounds Ni and Al as main phases, with a small amount of N.
It also contains i A 1 and N i A l 3. These exact amounts will vary with the particular overall composition. Preferably the nickel/aluminum alloy composition contains 56 nickel
, 5 to 57.5% by weight, more preferably substantially 57% by weight.

The nickel/aluminum alloy preferably has dimensions of 36
~90 microns (165-400 meshes), more preferably 36-53 microns (270-400 meshes)
are suitably used in the form of particles or granules.

The conductive cathode substrate can have various forms, e.g. planar, tubular, finger, etc., but in all cases should be porous, e.g. woven wire screen, enlarged perforated sheet metal or perforated sheet metal.

Iron, iron alloys such as soft iron and stainless steel, nickel and nickel alloys are particularly suitable materials for this substrate.

Another requirement of the present invention is that the nickel/aluminum alloy composition be deposited onto the cathode substrate using plasma atomization, ie, plasma arc atomization. Plasma atomization is a well known technique for depositing metal particles onto a substrate. Briefly, streams of gas and metal particles are separately supplied to an atomizing nozzle (torch). There is an electrical input to the gas stream that ionizes the gas. Recombination of the cations and electrons in the gas stream after mixing with the metal particles releases energy that heats and partially melts the metal particles, and the partially molten metal adheres to the substrate with which it comes in contact. A variety of gases are suitable for this purpose, including nitrogen and argon.

Argon is a suitable gas. The electrical input need only be sufficient to partially melt the metal particles, for example 2'0 to 30 kilowatts in a conventional sized device.

In many cases, to fabricate the cathode, it is preferred to coat the woven cathode component using a perforated sheet material.

This is because melt bonding and other bonding techniques can be easily performed on this substrate in its uncoated state.

It is also best to clean the surface of the substrate before coating, such as by sand blasting or other abrasive materials such as alumina blasting.

The cathode of the present invention may be coated on one or both sides. However, if only the negative side is coated, it is preferred to coat the membrane or the side facing the diaphragm in order to reduce the sliding potential to the maximum.

The cathode substrate is coated with a nickel/aluminum alloy coating, suitably about 13-508 microns (0.5-2.
0 mils), preferably about 127-254 microns (5-254 microns)
applied at a thickness of 1o mil).

Following deposition of the nickel/aluminum alloy composition onto the substrate, the Raney nickel surface is revealed by treating the coated object with any strong base, such as a caustic solution, to elute the aluminum Ramura coating. The concentration of this caustic is not critical, but for this purpose 5-15% by weight
An aqueous caustic solution containing NaOH of 5 hours to 1 day is suitable for elution. A typical example is 16 hours with a 10% by weight aqueous caustic solution. Similarly, the temperature of elution is not critical. Temperatures from room temperature to the boiling point of the caustic solution are suitable. For coatings of the above thicknesses, typically 70-90% of the aluminum is removed during such elution. Although it appears that some aluminum remains even after very long elution times, this does not appear to be critical to the performance of the resulting cathode. This elution step can also be referred to as activation and can be performed before or after assembly of the vessel. When dried, the Raney nickel cathode produced in this manner generates heat on contact with air due to the pyrophoric nature of Raney nickel.

The Raney nickel coated cathode prepared as described above exhibits low hydrogen overpotentials and the coating is resistant to delamination by flakes and debris as described below in Example 9 and Comparative Examples B, C and D. Shows improved resistance. The nickel/aluminum alloy compositions applied as coatings in the method of the present invention exhibit unexpectedly higher performance than alloys containing 55% by weight or less nickel, which flake off at commercially unacceptable rates. provides an activated Raney nickel cathode surface that is resistant to flaking and flaking.

Also, as shown in the examples above, all compositions tested initially give a good reduction in hydrogen overpotential, but when the coating according to the method of the invention is applied as a composition of nickel/aluminum alloy, Less (55% by weight and less) and more (6% by weight)
The improvement in hydrogen overpotential remains unexpectedly high even after the wash/bake cycle than in the case containing nickel in an amount of 2% by weight).

The cathode produced by this method is a conventional cathode comprising a cathode chamber, a cathode disposed within the cathode chamber, an anode chamber, an anode disposed within the anode chamber, and a separator disposed between the anode and cathode chambers. It can be used as a cathode in types of electrochemical baths. This is particularly useful in such types of chloralkali baths.

The separator can be, for example, a liquid-permeable diaphragm, and such a diaphragm can be made, for example, from asbestos fibers or fluorinated polymer fibers. The separator may also be a membrane of highly fluorinated or perfluorinated ion exchange polymers, for example. Such membranes of polymers containing sulfonate and/or carboxylate groups are currently well known in chlor-alkali technology (e.g. U.S. Pat. No. 4,194,725, U.S. Pat. No. 4.065,366 and U.S. Pat. Section 4.178.2
No. 18). As is currently known in the art, such membrane cells can be operated in narrow gap (anode to cathode spacing of 1 to 3 mm) and zero gap configurations (both electrodes in contact with the membrane).

In the chlor-alkali process for the electrolysis of alkali metal chlorides, e.g. sodium chloride, in such electrolytic cells, an aqueous alkali metal chloride solution is introduced into the anode chamber, a current is passed through the cell, and an aqueous alkali metal hydroxide solution is introduced into the anode chamber. is taken out from the cathode chamber, and chlorine is taken out from the anode chamber. In a membrane bath, water (or dilute alkali metal hydroxide at the beginning) is generally introduced into the cathode compartment and the spent alkali metal chloride solution is removed from the anode compartment. In the diaphragm, all unreacted alkali metal chloride solution is passed through the diaphragm to the cathode chamber and removed along with the caustic product.

The invention has many advantages over conventional methods.

These include (1) high resistance to flaking, splintering and mechanical damage of the #i hardened coating, (2) resistance to heating in oxidizing atmospheres, e.g. air in firing of diaphragms, (3) mild steel cathode and (4) Good tolerance to moderate amounts of contamination due to iron top plating; (5) Usability of various substrates including mild steel, stainless steel and nickel ft. , (6
) low cost and convenient application to preformed cathode components, and (7) heating the substrate rarely above 200°C so that the deflection i = min/J's. .

The following examples are presented to further illustrate the novel aspects of the invention.

The following abbreviations are used in the examples: pTFE stands for polytetrafluoroethylene; TFE/EVE stands for tetrafluoroethylene and methyl perfluoro(4,7-thioxal-5-methyl-8-nonenoate). Expression: TFE/PSEPVE represents a copolymer of tetrafluoroethylene and perfluoro(3,6-thioxer-4-methyl-7-octensulfonyl fluoride); EW represents equivalent weight.

EXAMPLES Example 1 A commercially available cathode screen made of 0.23 cm (0.092 inch) diameter steel wire and 0.42 m (6 mesh) center spacing was sand-blasted and then blown to a nominal composition using a Glazma arc. The thickness of the nickel aluminide alloy is 15% N, 43% AI and the grain size range is 100% less than 90 microns (i.e. passing through 165 mesh) and 30% less than 45 microns (i.e. passing through 325 mesh). One side was coated with a 178-203 micron (7-8 mil) coating. The spray conditions were as follows: Netco Type 7 MC (T Jf B) - Qi 707 nozzle MeLco 3J4p Dual power Feeder Torch gas - Nitrogen '2-1 Fufu ? /hour Bordeaux 60 Ampia - 425 Kilowatts - 27,3 Number of passages - 5 The screen surface was cooled with compressed air jets.

A part of the screen was cut out as a sample, and a circular part with a diameter of 7.62 cr++ was cut out from this sample.

This circular part is welded to a stainless steel cathode holder,
Place the coated side facing the anode in the assembled cypress, and
% caustic and a PTFE fiber-asbestos diaphragm (TAB Diamond Jamrock (Di
Amond Shamrock composition) was deposited with Raney nickel on the surface of the coated screen and fired. The performance of this cathode was as shown below, along with that of a typical steel cathode for comparison.

Example 1 Steel current density, ampere/dm' 18.3
18.3 Actual Current, Amps 8.3
8.3 Potential of tank, volts
2.85 3.10 Advantages over steel, mV
250 Example 2 A cathode finger from a Diamond Jamrock kfDC-s 5 cathode assembly was sprayed on one side with nickel aluminide of the same composition as in Example 1.

This was degreased and sandblasted before spraying the fingers. The spray conditions were as follows: Metco Type 7 M'C (TMB) Torch - 707 Nozzle Torch Gas - Nitrogen 2.1 y++'/hour Bordeaux 62 Amps - 450 Kilowatts - 27,9 Number of Passages - 4 Screen The surface was cooled with a compressed air jet.

Samples were cut from the screen, eluted in 10% caustic, covered directly with a TAB diaphragm over the Raney nickel coated surface, and tested in a 7.62 cm diameter Diafuzim bath. At this time, the surface coated with Raney nickel faced the anode.

The performance of the coated samples at two different current densities was as follows: Example 2 Current Density, Amps/dm” 18.3 11
Actual Current, Amps 8.3 5.0 Bath Potential, Volts 2.83 154 The advantage of the cathode of Example 2 over the steel cathode shown for comparison in Example 1 was 270 mU.

Example 3 Nickel aluminide of the same composition as Example 1 was applied to the fingers of three Diamond Jamrock MDC-55 cathode assemblies (cathode cans) under the conditions outlined in Example 2, followed by diaphragm Only the side of the finger covered with the coating and facing the anode was plasma sprayed. Each was then eluted with cold 10% caustic solution for approximately 16 hours. The cans were then cleaned and each was fitted with a Diamond Jamlock TAB diaphragm and fired. Assemble each in a chloralkali tank,
It was operated in the tank line. All cans performed similarly. The performance against steel was as follows.

Current density, ampere/d tn” 11.3
11.3 Actual Current, Amps 62
Potential of 62 tanks, built 2.7
0 2.88 Advantages over steel, mV
180 Example 4 Type 304 stainless steel screen (6 mesh) with 0.18 cm diameter wires placed with center spacing of 0.42 on
A sample of 1 was bath coated on a stainless steel cathode ring and nickel Aldo of the same composition as in Example 1 was subsequently coated with a diaphragm coating and only on the side facing the anode to a thickness of 0.015t-rn(
6 mil) coating.

This coating was eluted with 10% caustic. The TAB diaphragm was placed on the screen and fired, and the cathode assembly was operated in a 7.62 crn bath. After the first run, the diaphragm was removed, a new diaphragm was installed, and a second experiment was performed.

The data were as follows: Navy Blue ＼ ＼ TO TODO 0 ( TO 1 When EXAMPLE 5 Cathode Manufacturing for Evaluation in Narrow Gap Membrane Baths The cathode for the membrane bath in the laboratory was long
way diamond ) 2.54 an X S
F I) (5hort way clearmond)
) 0.635 tm X Strand width 0.16 c
It was prepared by cutting a 7.62 crn diameter disc from a 200 type nickel flattened metal with dimensions of 0.12 on TnX thickness.

A long piece of 0.635 crn nickel tubing was welded to the center of the disk to serve as a conductor.

Plasma spray was applied to both sides of this cathode with Ni570.
A coating of 5% by weight and 0.5% by weight of A143 alloy was applied. The alloy is 42-110 microns (i.e. 1
It was in the form of a fine powder with a particle size of 40 to 325 mesh. The application conditions were as follows: Input -40V and 5BOA (23,2kw) Arc gas -2,637723/hour (93CFII).

Argon, 3.448X10'Pα (50 psi) TTWD (torch to working distance) -10, '16 m Coating thickness was 203 microns (8 mils) on both sides of the spread metal. The coating was activated by soaking the cathode in 99AOE for 16 hours at room temperature. The cathode was then rinsed with water and kept moist until installed in the bath.

Example 6 Performance of the double-sided coated cathode in a finite gap membrane cell evaluation The cathode of Example 5 was placed in a small cell with an effective area of 45 cnl, along with a reinforced fluorinated ion exchange membrane and a dimensionally stable anode. Placed. This membrane consists of TF with an equivalent weight of 108.0,
38 micron (1.5 mil) layer of E/EVE, equivalent weight 1
a 100 micron (4 mil) layer of TFE/pSEPrE with 100, a woven layer with both pTFE filaments and polyethylene terephthalate and an equivalent weight of 110.
It consists of a 25 micron (1 mil) layer of TFE/PSEPVE with 0% KOH and 30% KOH.
% dimethyl sulfoxide to hydrolyze the functional groups to carboxylate and sulfonate groups. The membrane was placed with the carboxylate side to the cathode. The electrodes were arranged so that there were three cages of gaps between them. The tank was constructed such that water pressure equivalent to about 25.4 on of water on the cathode side pressed the membrane against the anode. The tank was operated at 90° C. and a current density of 31 A/dm.
It was supplied to the anode chamber at such a rate as to maintain a concentration of Na/It. Water was added to the cathode chamber to maintain the concentration of the resulting caustic at 32±1%.

After 7 days, the cell was operating at 96% current efficiency and 3.17 volts. This performance remained unchanged after 110 days of operation.

Comparative Example A Example 6 was repeated except that the cathode was made from uncoated mild steel mesh. After 7 days, the cell was operating at 96.4% current efficiency and 3.51 volts. This was also 340 mV higher than that of the activated cathode of Example 6.

Example 7 Performance of a Single Side Coated Cathode in a Finite Gap Membrane Cell Example 5 was repeated except that the coating was applied to only one side of the cathode facing the membrane in the cell. This cathode was then placed in a test tank and operated under the same conditions as in Example 6.

After 7 days, the oak was operating at a current efficiency of 97.6% and 3.20 volts. After 30 days, the paddle potential was 3.18 volts and remained unchanged after 110 days of operation. This was also 330 mV lower than that of the mild steel cathode of Comparative Example A.

Example 8 Performance of a double-sided coated cathode in a zero-gap membrane bath A cathode prepared as in Example 5 was installed in a small cypress with an effective area of 45i. The membrane has an equivalent weight of 1080 TFE/
38 micron (1,5 mil) layer of EVE and equivalent weight 11
00 TP'E/PSEPVE with a 100 micron (4 mil) layer of 950 equivalent weight TFE/P on both sides.
Z grafted with ethanol solution of SEPVE copolymer
rO, consisting of particles. Coated with an inorganic non-conductive layer, it was dried and treated with KO,H as in Example 6 to hydrolyze the functional groups to carboxylate and sulfonate groups. A dimensionally stable anode was used and the electrodes were placed close together with the membrane between them so that there was no gap between the membrane and either old electrode.

The membrane was placed with the carboxylate side toward the cathode.

The cell was operated at 90° C. and a current density of 31 A/dm”.

A saturated solution of purified sodium chloride was added to a concentration of 200%/
It was supplied to the anode chamber at a rate to maintain IINαC1. The concentration of caustic produced by supplying water to the cathode chamber is 32±1
% was maintained.

After 7 days, the cell was operating at 97.8% current efficiency and 3.09 volts.

Example 9 and Comparative Examples B, C, D Made from 0.23 cm diameter clasp, center spacing 0, 4
20 In (6 mesh) and 700 micron (
5.5 x 1011P of alumina abrasive (24 mesh)
Mild steel cathode screen samples cleaned by α spraying were plasma sprayed under the following conditions: Volts - 40 Amps - 620 Power - 24.8 kt.

TTII'D (distance between torch and working part -6, 3~7,
6 am arc gas -2,637)? / hour, argon.

3.45X10', Pα Nickel/aluminum weight ratio is 52/48 (Comparative example B
), 55/45 (Comparative Example C), 5r/43 (Example 9) and 62/38 (Comparative Example D) were used. All had particle sizes of 42-110 microns (140-325 mesh). The thickness of the applied coating was 152-
It was 178 microns (6-7 mils).

The plasma spray coated cathode was activated by sequential elution in 2% aqueous caustic at 25°C, 5% aqueous caustic at 25°C, 10% aqueous caustic at 25°C and 10% aqueous caustic at 80°C. did.

However, each step was continued until hydrogen generation was completed and the next step was proceeded.

Each cathode (circular, diameter 8.25 crn or 3.25α) was performance tested in a small chloralkali bath as follows. The vessel had an anode and cathode chamber separated by a membrane of A-fluorinated ion exchange polymer having sulfonate groups. The area used for the membrane was 3.5 cm in diameter. The anode was a platinum screen. The reference standard Amagi electrode and the cathode to be tested were placed in the cathode chamber such that the Amagi electrode was as close as possible to, or in contact with, the cathode under test. Fill the anode chamber with a sodium chloride solution (NaC125Of/l of solution) and fill the cathode chamber with a sodium chloride/sodium hydroxide solution containing about 13% sodium hydroxide (NaCl solution 3 above).
1. 1.51 liters of water and 5851 ml of NaOH).

Electrolysis was carried out for 15.5 min until a stable electrode potential was achieved.
A/dm! The test was carried out at a current density of about 90°C. The potential difference between the test cathode and the reference Amagi electrode was measured with a high impedance digital electrometer at intervals throughout the electrolysis period. Performance was compared to an uncoated mild steel cathode. The advantages of coated cathodes over mild steel are reported below as Millipold.

Each test cathode was then applied to each side of the cathode in a 1.03 x 10
It was subjected to water jetting at 7 Pa for 3 minutes to simulate the removal of used asbestos diaphragms and to 355° C. for 4 hours to simulate the firing of newly applied asbestos diaphragms. However, in these cases, tests were conducted without actually removing or installing asbestos. The amount of Raney nickel coating that flakes off during water injection was collected by filtration and weighed. The cleaned and fired cathode was re-evaluated for performance in the bath. This was repeated 10 times for each test cathode. The results are summarized in Tables 1 and 2.

Table 1 1 163 173 160
1502 153 162 153 1463
153 150 146 1414
143 146 146 1365
137 143 143 1
366 133 137 138
1327 133 118
132 1288 117 1
20 126 1039 10
8 105 123 9810
99 98 116
80 Y Table 1 6.7 6.1 4.4
0.72 12y9 13.1 1
1.9 8v33 13.6 1
4.7 16.8 21.44 45
22.2 25.5 25.8s
45.8 27.3 25.5
26.56 45.8 63.7 32.
6 28.27 48.2 63.7
32.6 28.28 54.2 6
9.2 32.7 29.29 7? ,0
91.2 36.3 29.910
84.0 91.6 37.3 34
．． 7 The present invention is useful where Raney nickel coated electrodes are desired. It has been found to be particularly useful in the chlor-alkali field where low hydrogen overpotential cathodes are required. The present cathode is more durable than those of conventional methods and has other advantages as mentioned above.

Patent Applicant: E.I. Dupont de Nimoas
and company

Claims (1)

Claims: 1. (α) Plasma spraying a coating of a nickel/aluminum alloy composition containing 56-59% by weight of nickel onto a porous substrate of iron, iron alloy, nickel or nickel alloy; A method for producing a low hydrogen overpotential cathode for a chlor-alkali bath, characterized in that: b) the aluminum is leached from the coating by contacting the material produced in step (a) with a caustic solution. 2. The method of claim 1, wherein the nickel/aluminum alloy composition used in step (a) is in the form of particles of 36 to 90 microns. & Step (The coating formed in (Z) has a thickness of 13
3. The method of claim 2, wherein the particle diameter is 508 microns. 4. The method of claim 3, wherein the nickel/aluminum alloy composition used in step (α) is in the form of particles of 36 to 53 microns. 5. The coating formed in step (a) has a thickness of 127
5. The method of claim 4, wherein the particle size is ˜254 microns. 6. The method according to claim 5, wherein the plasma atomization is performed using ah-gon or elemental gas plasma generated at a power of 20 to 30 kilowatts. 7. The method of claim 5, wherein step (b) is carried out for a period of time sufficient to remove about 70-90% by weight of the aluminum from the coating. 8. The caustic solution of step (b) contains 5-15% by weight of aqueous N
6. The method of claim 5, wherein the contact is for a period of 5 hours to 1 day. 9. Claim 1, wherein the nickel/aluminum alloy composition contains 56.5 to 57.5% by weight of nickel.
, 3 or 5. 10. The method of claim 9, wherein said nickel/aluminum alloy composition is substantially 57% by weight nickel. 11. A cathode manufactured by the method according to claim 1, 3 or 5. 12. Nine poles manufactured by the method described in claim 2.4, 6.7 or 8. 13. A cathode manufactured by the method according to claim 9. 14. Range of Permissible Percentages A cathode produced by the method described in item 10. 15 a cathode chamber, a cathode disposed within the cathode chamber, an anode chamber,
A chlor-alkali bath comprising an anode disposed within the anode chamber and a separator disposed between the anode and cathode chambers, wherein the cathode is the cathode according to claim 11. Chlor-alkali bath. 16. The method of claim 15, wherein the separator is a liquid permeable diaphragm. 17. The method according to claim 16, wherein the diaphragm contains asbestos fibers. 18. The chloralkali tank of claim 15, wherein said separator is a highly fluorinated ion exchange polymer membrane. 19. A method for electrolyzing alkali metal chloride in an electrochemical tank divided into an anode chamber and a cathode chamber by a separator, in which an aqueous solution of alkali metal chloride is introduced into the anode chamber of the nuclide, and an electric current is applied to the nuclide. and removing an aqueous alkali metal hydroxide solution from the cathode chamber and removing chlorine from the anode chamber, and using the chloralkali bath according to claim 15 as the electrochemical bath. An electrolytic method for alkali metal chlorides characterized by the following.