Electrode elements for filter press membrane electrolytic cells

An electrode is provided which is formed by the metallurgical bonding technique of diffusion bonding the backplate, conductor elements and electrode surface together, then applying the catalytic coating to the electrode surface, and bonding the backplate to an electrical conducting plate.

BACKGROUND OF THE INVENTION 
The present invention relates generally to electrodes used in electrolytic 
cells. More specifically, the present invention relates to the improved 
electrode that may be employed in electrolytic cells produced by the 
metallurgical bonding technique of diffusion bonding. 
Chlorine and caustic, products of the electrolytic process, are basic 
chemicals which have become large volume commodities in the industrialized 
world today. The overwhelming amounts of these chemicals are produced 
electrolytically from aqueous solutions of alkali metal chlorides. Cells 
which have traditionally produced these chemicals have come to be known as 
chloralkali cells. The chloralkali cells today are generally of two 
principal types, the deposited asbestos diaphragm-type electrolytic cell 
or the flowing mercury cathode-type. 
Comparatively recent technological advances such as the development of 
dimensionally stable anodes and various coating compositions, have 
permitted the gap between electrodes to be substantially decreased or 
eliminated entirely. This has dramatically increased the energy efficiency 
during the operation of these energy-intensive units. 
The development of a hydraulically impermeable, ion selective membrane has 
promoted the advent of filter press membrane chloralkali cells which 
produce a relatively uncontaminated caustic product. This higher purity 
product obviates the need for caustic purification and decreases the need 
for concentration processing. The use of a hydraulically impermeable 
planar membrane has been most common in bipolar filter press membrane 
electrolytic cells. However, continual advances have been made in the 
development of monopolar filter press membrane cells. A hydraulically 
impermeable membrane also has found utility in electrolytic cells other 
than chloralkali electrolytic cells. 
The use of a hydraulically impermeable membrane, however, presents problems 
should the membrane become structurally damaged, such as ruptured by the 
passage of a sharp object therethrough. The puncturing of membranes by 
abrasion or puncturing with sharp electrode components is particularly 
troublesome since it permits the cross migration of ions between the anode 
and cathode compartments. This reduces the efficiency of the cell. 
Frequently the cause of these abrading electrode components are roughened 
weld surfaces or the unrestrained electrode component that results when a 
weld on the electrode fails. 
The number of welds on an electrode are numberous since each separately 
formed electrode element must be joined together. These elements include 
the individual electrode frame members, the electric current conducting 
elements and the electrode surfaces. The electrode surfaces, typically 
formed of a mesh, perforated or punched metal, especially have a large 
number of individually welded connections. Since the ion selective 
membranes are placed against these electrode surfaces, roughened weld 
surfaces or broken welds will easily puncture a membrane. 
Welding presents the additional problem of building up heat in the 
electrode components as they are joined together in assembly, frequently 
causing warpage or distortion that affects the ability of the electrode to 
function efficiently. Warpage creates a non-planar surface that results in 
poor or non-uniform current distribution during operation across the 
electrode surface. This warpage also causes the welds to either fail 
completely or to be subjected to extreme stress at the weld points when 
subjected to the assembly pressures necessary to compress and assemble the 
cell in a configuration that requires planar electrodes. 
These membranes are expensive. A commercial-size membrane cell, for example 
of the filter press type, will have up to thirteen or more membranes in 
each electrolytic cell unit comprising multiple cathode and anode units 
separated by a membrane. Damaged membranes therefore either require 
expensive replacements or are time consuming to locate and repair. 
Consequently, repair or replacement is a costly manual process. The exact 
position of structurally damaged membranes in the electrolytic cell unit 
must be identified before they can be replaced. 
Damaged membranes can also cause corrosion to occur in the metals used 
internally within the electrolytic cell by permitting the catholyte fluid 
with caustic or the anolyte fluid with brine to cross through the ruptured 
membrane and enter the adjacent electrode compartment. Caustic is 
extremely corrosive to the anode metals and the brine with chlorine in the 
anolyte will dissolve nickel in a cathode, forming a high oxidation state 
nickel compound that will build up in the membrane. Where titanium is used 
in the anode, caustic will dissolve it, forming a titanium oxide that will 
also buildup in the membrane. This metallic ion buildup in the membrane 
decreases the current efficiency of the cell and increases the cell 
voltage. 
Damaged membranes additionally will decrease the overall efficiency of the 
operating cell by decreasing the cathode and anode current efficiencies. 
The cathode current efficiency decreases are detectable in several ways, 
such as by measuring the weight of the caustic produced in a container 
vessel, calculating the actual production rate, and then comparing it to 
the expected production rate. Decreases in anode current efficiency are 
detectable because of the increase in the presence of oxygen in the cell 
gas and oxychlorides, such as hypochlorite, or chlorates in the spent 
anolyte stream or spent brine in a chloralkali cell. Changes in the pH of 
the spent anolyte stream are also indicative of such decreases. Obviously, 
damage to or ruptures of the membranes reduce the production capacity of 
the electrolytic unit, affect the quality of the cell product and 
adversely affect the economics of an operating commercial unit. 
Another related disadvantage of electrodes which must be welded together at 
the joints between various components is the amount of labor involved. 
Welding, whether TIG welding, resistance welding or spot welding, is 
labor-intensive and requires sizeable periods of time. It is difficult to 
adhere to the required tolerances where hand operations, such as welding, 
are performed. These tolerances are most critical in electrolytic cells 
that have no gap between the membranes and the adjacent cells. 
Additionally, the welds may not be consistently or uniformly made. The 
labor-intensive manual welding involved in the fabricating of an electrode 
significantly increases the cost of each cell. While it has been known for 
a number of years that certain metals, such as titanium and various 
alloys, may be metallurgically joined together by applying heat and 
pressure for a sufficient amount of time to cause intimate surface contact 
and interdiffusion of the atoms at the joint interface, such technology 
has not previously been successfully applied to electrolytic cell 
components. Similarly, while it has been known that certain metals, 
including titanium and various alloys, exhibit the characteristic of 
superplasticity or the ability of a material to develop unusually high 
tensile elongations under conditions of increased pressure and 
temperature, this process has not been previously successfully applied to 
the production of electrolytic cells. More recently, the combining of 
superplastic forming and diffusion bonding technology in making structural 
components has been accomplished, most notably in the aviation industry. 
The foregoing problems are solved by the product made by the process or 
method of the present invention wherein an electrode is formed by the 
metallurgical bonding technique of diffusion bonding and the adhesion of 
the corrosion-resistant electrode material to a conducting plate carrying 
electrical current to the electrode in a manner that reduces the 
electrical current flow resistance and the cost of the final electrode. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an electrode usable in 
an electrolytic cell that is fabricated employing the metallurgical 
bonding technique of diffusion bonding 
It is another object of the present invention to provide an electrode 
usable in an electrolytic cell that is fabricated by assembling a 
diffusion bonded subunit including at least a backplate, conducting 
elements and an electrode surface to a conducting plate by use of 
adhesives and a conductive coating that lowers the electrical resistance 
at the joint between the two electrode components. 
It is a feature of the present invention that the backplate, the conductor 
elements and the electrode surface form a subunit that are connected at 
joints by the metallurgical bonding process of diffusion bonding. 
It is another feature of the present invention that the diffusion bonded 
subunit of the backplate, conducting elements and electrode surface has 
its electrode surface separately catalytically coated to form the 
activated surface for use during electrolysis. 
It is still another feature of the present invention that the diffusion 
bonded subunit with its backplate, conductor elements and catalytically 
coated active electrode surface is mated to a conducting plate or surface 
by means of an adhesive and a conductive coating that lowers the 
electrical resistance at the joint or interface between the two electrode 
components. 
It is an advantage of the present invention that an electrode is obtained 
by the metallurgical bonding process of diffusion bonding which eliminates 
rough spots that could puncture the membrane. 
It is another advantage of the present invention that the amount of manual 
labor necessary to produce an electrode is dramatically reduced. 
It is still another advantage of the present invention that an electrode is 
obtained which is smooth at the joints between the individual components 
and is lower in weight and cost. 
It is yet another advantage of the present invention that heat distortion 
in the electrode produced by the process of diffusion bonding is more 
easily controlled than by conventional fabrication steps. 
It is a further advantage of the present invention that warpage of the 
electrodes is avoided and the required tolerances are maintained in an 
electrode produced by the subject process. 
These and other objects, features and advantages are obtained in the 
electrode produced by the process of diffusion bonding the joints of the 
separate components and the electrode together to form an electrode 
subunit of a backplate, conducting elements and an electrode surface that 
is mated to a conducting plate by an adhesive and a conductive coating 
that lowers the electrical resistance at the joint or interface between 
the backplate and the conducting plate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 shows a front perspective view of an electrode subunit indicated 
generally by the numeral 10 that is formed by the process of diffusion 
bonding. The electrode subunit 10 includes an electrode surface 11 that is 
shown as being a wire mesh. This electrode surface 11 may be formed from 
an expanded metal mesh which is flattened or unflattened, perforated or 
punctured sheets, flat sheets, or sheets having slits or louvered 
openings. The electrode surface 11 could also be formed from a series of 
rods that are metallurgically bonded to the conducting elements 14. An 
expanded metal mesh is a preferred form. The electrode surface 11 may be 
turned downwardly at its extremities 12 to prevent rough edges from coming 
into contact with a membrane in an assembled electrolytic cell. 
The electrical conducting elements 14 are connected to the electrode 
surface 11 at a plurality of individual locations or joints 15 by 
metallurgical bonding, such as diffusion bonding. The conducting elements 
14 may be in the form of hollow concave-shaped ribs, hollow tubes, or 
solid straight bars with or without holes. If holes are employed, they are 
intermittently spaced to permit fluid passage. The bottom surfaces of the 
conducting elements 14 are metallurgically bonded by the diffusion bonding 
process to the backplate 16. 
Where the subunit 10 is to be used as an anode in an electrolytic cell, the 
electrode surface 11, the electrical conducting elements 14, and the 
backplate 16 are fabricated from a conductive metal such as titanium or 
tantalum, columbium, niobium, but which is preferably titanium or titanium 
alloy. Although Grade 7 titanium is preferred, it is possible to use Grade 
1 or 2. Grade 12 is preferred when superplastic forming is employed to 
shape the subunit components. These grades of titanium are established by 
the ASTM Standard B 265-79. Titanium is especially useful where 
electrolysis of alkali metal chloride brines is involved. Other suitably 
fabricated conductive metals could include copper, nickel, silver, steel, 
magnesium or aluminum and alloys of these metals for electrodes as long as 
they are compatible in the type of electrolytic process in which they are 
employed. Copper sputtered onto titanium in a coating with a thickness of 
about 1000 Angstroms to about 20,000 Angstroms can also be employed to 
reduce the oxide formation that tends to occur on the metal over time. 
This oxide formation increases the electrical resistance at the joint or 
between the mated surfaces of metal. 
Where the subunit 10 is to be used as part of an electrode that serves as a 
cathode, the components are preferably fabricated from a nickel material, 
such as nickel 200. A nickel 301 that is precipitation hardened can also 
be satisfactorily used for the cathode conductive metals, as well as 
steel, nickel, copper or coated conductive materials such as nickel coated 
copper. 
FIG. 2 shows an electrode subunit 18 with the backplate 16 bonded to a 
generally planar mating conducting plate 19 formed of copper because of 
its conductive qualities and relative low cost. The electrode subunit 18 
has electrical conducting elements in the form of blades 20 which connect 
backplate 16 to the electrode surface 11. The electrical conducting 
elements or blades 20 have passages 21 therethrough to permit electrolyte 
to flow through the channels between the backplate 16 and the membrane 
(not shown) in an assembled cell. The blades 20 extend generally 
vertically from bottom to top in an assembled cell when the electrode is 
in an operating position. The blades 20 could equally well be horizontally 
or obliquely oriented in an assembled cell. 
FIG. 4 shows a sectional view of the assembled structure taken along the 
lines 4--4 of FIG. 2. The backplate 16 is bonded to the conducting plate 
19 in a manner that will be described hereafter. 
An adhesive is applied to the backplate 16 and/or the conducting plate 19 
after appropriate surface preparations. These surface preparations include 
a cleaning to remove the presence of any oxides, degreasing and the 
removal of any other surface contaminants. The oxides can include oxides 
of titanium, nickel, zirconium, tantalum, vanadium, or other base metals. 
Where the electrical conducting elements are in the form of blades 20, the 
blades are milled for proper sizing and drilled to provide the passages 
21. Cleaning must then be accomplished to remove any cutting fluids 
remaining from the milling and drilling operations. This cleaning consists 
of immersing or dipping in an alkaline solution or organic solvent, or 
immersing or dipping in a dilute acid. Alternately, the cleaning agent can 
be brushed on. The cleaning agent is then rinsed or removed from the 
applicable surfaces by either immersion or spot rinsing. 
Thus prepared and as illustrated in FIG. 3, a conductive coating 22 of a 
liquid metal mixture comprised of between about 20 and about 30% by weight 
indium and between about 70 and 80% by weight gallium, preferably between 
about 23 and about 26% by weight indium and between about 74 and 77% by 
weight gallium, is applied to the reverse side of backplate 16 in line 
with the conducting elements or blades 20 that have been previously 
metallurgically bonded to the backplate. This conductive coating is a 
eutectic having a melting point of approximately 15.7.degree. C. at the 
eutectic composition of 24.5% by weight indium, so it can be easily 
applied to the surfaces even at room temperature. The conductive coating 
22 does not immediately amalgamate or otherwise bond the backplate 16 to 
the conducting plate 19. The conductive coating 22 is applied preferably 
in a one inch wide strip by wiping on with a suitable applicator, such as 
a paint brush, swab or wiping cloth. As described in U.S. Pat. No. 
4,434,846 to Woodard et al., herein specifically incorporated by reference 
in pertinent part, the conductive coating 22 serves to reduce the 
electrical contact resistance between the conducting plate 19 and the 
backplate 16. 
The conductive coating 22 generally is not intended to function as a 
bonding agent and, in fact, subsequent data will show a lack of bonding 
between adjacent mating surfaces. However, it was found that the 
conductive coating by itself will bond the backplate 16 to a conducting 
plate 19, for example, when subjected to a temperature of about 90.degree. 
C., a minimal pressure of about 10 psi, and aged for 3 days. These are 
conditions that occur during normal operation of a filter press membrane 
type of a cell. It is thus possible for an electrolytic cell to be 
assembled without the use of a specially selected adhesive and have some 
bonding occur after normal use. 
An adhesive 24 is applied to the backplate 16 between the electrical 
conducting elements or blades 20 in any pattern or uniformly. As seen in 
FIG. 3, it is applied in an illustrative Z-type pattern. The adhesive 24 
is also applied to the backplate 16 outside of the blades 20. This 
application pattern permits the adhesive 24, when compressed by having the 
backplate 16 mated to the conducting plate 19, to be dispersed and spread 
out to cover substantially most of the contact surface area between the 
backplate 16 and the conducting plate 19. 
The adhesive 24 may be one of several types of conductive or non-conductive 
adhesives. It may be a silver-filled epoxy, a copper-filled epoxy, a 
silver coated copper-filled epoxy, a tin-lead solder mix in paste form or 
preformed strips, a tin-silver solder mix in paste form or preformed 
strips, or a non-conductive epoxy, as will be explained hereafter. Whether 
the adhesive 24 is conductive or non-conductive, its use obviates the need 
for time-consuming, labor-intensive welding which can cause heat 
distortion in the backplate 16 or the conducting plate 19 due to heat 
buildup. 
The adhesive 24, when non-conductive, can be a clear, low viscosity 
two-component expoxy adhesive system that contains no solvent and cures 
quickly at room temperature. Commercially available two-component epoxy 
adhesives of this type serve as excellent thermal and electrical 
insulators with chemical resistance to aqueous solutions and other 
chemicals. Such non-conductive adhesives, when mixed in a one to one ratio 
by weight or volume, cure at ambient temperatures within 24 hours, but 
bonding can be accelerated to about 4 hours when cured at about 160 to 
about 170.degree. F. 
Silver-filled two-component conductive epoxy coatings may also be employed 
which exhibit high electrical conductivity and heat resistance after 
curing. Such adhesives can be employed by brushing, spraying or screen 
printing in coatings of two mils or less. Such adhesives are heat cured 
generally at temperatures from about 80.degree. C. to about 150.degree. C. 
for about two hours to about 3 minutes, dependent upon the particular 
formulation employed. 
Copper-filled adhesives may be employed that are paste like in consistency 
and which will cure in about 30 minutes to about 120 minutes at 
temperatures at about 150.degree. C. or about 125.degree. C., 
respectively. 
The solder mix may be a commercial paste formulation that contains about 
95% tin and about 5% silver by weight, or alternately about 60% tin and 
about 40% lead by weight mixed with a flux. These type of solder pastes 
are especially useful in wetting copper and nickel. 
The metallurgical bonding process of diffusion bonding is employed on the 
electrode subunits 10 and 18. The backplates 16, electrode surfaces 11, 
and the electrical conducting elements 14 and 20 are milled and cut to the 
proper size. Then they are cleaned to remove the oxides or other 
contaminants previously described from the contact surface areas. This 
cleaning is accomplished by the aforedescribed techniques. After drying, 
any areas not to be bonded, such as the areas to be subjected to 
superplastic forming, are coated with an appropriate stop-off compound, 
such as boron nitride, yttria, alumina or other stable oxides. The subunit 
10 or 18 is placed in an appropriate mold or workpiece in a vacuum chamber 
which is heated and maintained at a temperature that is optimum for the 
metals being formed and bonded together. Diffusion bonding temperatures 
can vary from about 787.degree. C. to about 1010.degree. C. For an 
electrode formed of titanium, the temperature can be preferably between 
about 815.degree. C. to about 898.degree. C., while an electrode formed of 
a nickel will preferably range from about 871.degree. C. to about 
954.degree. C. The heat is provided within the press or workpiece, for 
example, by resistance-heated nichrome wire that may be embedded in 
ceramic platens. Other portions of the tooling may be formed of stainless 
steel. 
The tooling serves as a press to maintain the structure being bonded under 
pressure that can vary from about 100 pounds per square inch (psi) to 
about 2000 psi or more, preferably from about 150 psi to about 650 psi 
over a time period of 30 minutes to about 15 hours. The pressure may be 
applied hydraulically or by a gas that may also protect against surface 
enrichment of the metals being bonded. For example, argon gas or helium 
may be employed. The tooling or platens may be held together in counter 
resistance to the internal forces by hydraulics. This process will permit 
the electrode subunits 10 or 18 to be bonded together in all areas except 
where the stop-off compound has been applied. Once subjected to sufficient 
pressure and for a sufficient length of time, the subunits 10 or 18 are 
allowed to cool and are removed from the press and tooling. 
If it is desired to superplastically form some of the components of the 
electrode subunit, such as the electrical conducting elements 14 of 
subunit 10, the subunit 10 is left in the press after the diffusion 
bonding temperature and time cycle has been completed. The bonding occurs 
to the unstopped-off areas. Gas pressure is increased by introduction of 
an appropriate inert gas into the tooling area at a controlled rate until 
a breakthrough in the stopped-off area occurs so the gas creates a flow 
path to the stopped-off areas. This causes the areas to be 
superplastically and uniformly formed, while avoiding strain rates in 
excess of the superplastic range of the material being formed. It is 
desirable to have a low breakthrough pressure-time product, such as less 
than 100 psi-minutes. The combined superplastic forming and diffusion 
bonding operation is described in detail in U.S. Pat. No. 3,927,817. 
In the case of the electrode shown in FIGURE 5, diffusion bonding and 
superplastic forming can be employed to fabricate the desired electrode 
frame, indicated generally by the numeral 28. The electrode surface 11, 
the electrical conducting element 14 and the frame channels 25 are 
diffusion bonded to the backplate 16, except where the stop-off compound 
has been applied to permit breakthrough to occur. The A-shaped 
configuration of the electrical conducting elements 14 and the generally 
rectangular shape of frame elements 25 are obtained by superplastic 
forming of the components. It may be necessary to first diffusion bond the 
backplate 16 to the unstopped-off areas 26 of the sheet of metal from 
which the frame elements 25 and the electrical conducting elements 14 are 
formed prior to superplastic forming these elements. It may then be 
necessary to diffusion bond the electrode surface 11 to the 
superplastically formed conducting elements 14. The conducting plate 19, 
which is made of copper, may then be appropriately bonded to the backplate 
16. 
Alternately, the electrode frame 28 could be fabricated without the 
backplate 16 by directly bonding the unstopped-off areas 26 of the sheet 
of metal from which the frame elements 25 and the electrical conducting 
elements 14 are formed to the conducting plate 19. The electrode surface 
11 could also be flush against the frame elements 25 and either at a 
height that is below, even with, or above the height of the frame elements 
25. 
The electrode surfaces are then ready to be coated with a high surface area 
coating or an activated coating, such as any of the commercially available 
catalytic coatings, for example those prepared by thermal decomposition, 
electrodeposition, sputtering, vapor phased deposition, and ion 
implantation. The application of the high surface area or activated or 
catalytic coatings to the electrode surfaces 11 at this point in the 
process has the additional advantage of employing a coating application 
temperature cycle that is lower than that employed in the diffusion 
bonding operation. Minimum warpage occurs in the electrodes and tolerances 
in the electrodes thus can be maintained. The catalytically active 
coatings may be selected from the group consisting of lanthanum, 
pentanickel, Raney-nickel, precious metals, precious metal oxides, 
electroplated alloys of nickel and leachable metals of zinc, cadmium or 
aluminum. 
In order to exemplify the results achieved, the following Examples are 
provided without any intent to limit the scope of the instant invention to 
the discussion therein. 
EXAMPLE I 
A 1".times.2" coupon of copper alloy C-110 approximately 0.045 inches 
thick, a 1".times.2" coupon of nickel 200 commercial grade approximately 
0.055 inches thick, and a 1".times.2" coupon of Grade 1 titanium 
approximately 0.0385 inches thick with copper sputtered on one side were 
deburred along the edges and cleaned as described hereafter. The coupons 
were vapor degreased. The copper and copper sputtered titanium coupons 
were cleaned in a 12% H.sub.2 SO.sub.4 solution for about 10 seconds at 
room temperature and then rinsed in distilled water and dried. The nickel 
200 coupon was cleaned in a solution of about 37.8 milliliters of water, 
56 milliliters of H.sub.2 SO.sub.4 and 85.2 milliliters of HNO.sub.3 at a 
temperature of about 20.degree. C. to about 35.degree. C. for 10 seconds, 
rinsed with distilled water and dried. 
A thin layer of 95% tin--5% silver by weight solder paste was applied to 
the coupons and the coupons were mated, loaded in a press to a pressure of 
approximately 100 psi and heated to about 270.degree. C. for about 10 
minutes. The coupons were then cooled to below about 200.degree. C. while 
under pressure. Kelvin clips were attached to the free end of the couples 
for measurement of the electrical resistance with a Biddle digital 
resistance meter. The readings thus recorded measured the serial 
resistance comprising the resistance from the two mating components in the 
couple and the junction between the two components. The joint resistance 
is measured in milliohms. The shear stress of the bond between the couples 
was also noted. These data are recorded in Table 1. No bonding was 
achieved with the copper and copper sputtered titanium coupons. 
EXAMPLE II 
A copper-filled, single-component, high strength adhesive designed for use 
in microelectronic applications was evaluated by application to coupons of 
the same composition and dimension as recited in Example I above. The 
coupons were cleaned according to the procedure described in Example I. 
Once cleaned, a thin layer of the copper-filled adhesive was spread on the 
clean surfaces and the surfaces were mated. The mated surfaces were then 
loaded in a press to approximately 100 psi and were cured at a temperature 
of about 170.degree. C. to 180.degree. C. for about 30 minutes. This 
adhesive resulted in a joint with a somewhat elevated electrical 
resistance for the copper and copper sputtered titanium couples, but with 
excellent shear strength. The results are also shown in Table 1. 
EXAMPLE III 
Coupons of the identical size and material were selected and cleaned as 
described in Example I above. A conductive coating of between about 20 and 
30% by weight indium and between about 70 and 80% by weight gallium was 
applied to one of the coupons and the pairs identified in Table 1 were 
mated together. The conductive coating reduces the electrical resistance 
at the joint or interface between the couples. The couples were loaded in 
a press to approximately 100 psi and cured for about 16 hours from about 
195.degree. C. to about 200.degree. C. Reduced electrical resistances were 
recorded as shown in Table 1, using the same measuring techniques as 
described with respect to Example I, but no bonding between the couples 
took place. 
TABLE 1 
__________________________________________________________________________ 
CONTACT SURFACE PROPERTY SUMMARY 
Electrical 
Bonding Resistance 
Shear Stress Load (pounds) 
Adhesive (Milliohms) 
(1" .times. 1" Lap Joints) 
__________________________________________________________________________ 
Ni/Cu Couples Copper-filled Single- 
0.19 1310 
component Adhesive 
95% Sn - 5% Ag 
0.09 1590 
Solder Paste 
Low Electrical 
0.19 No Bond 
Resistance 
Conductive Coating 
Cu Sputtered Ti/Cu Couples 
Copper-filled Single- 
0.95 1320 
component Adhesive 
95% Sn - 5% Ag 
Did not wet Cu 
No Bond 
Solder Paste 
sputtered Ti 
Low Electrical 
0.66 No Bond 
Resistance 
Conductive Coating 
__________________________________________________________________________ 
EXAMPLE IV 
Coupons of the identical size, grade and thickness were selected and 
cleaned as described in Example I. An additional 1".times.1" titanium 
coupon of Grade 1 with a thickness of about 0.039 inches was also 
selected, cleaned and mated with a matching copper coupon. The coupons 
were not bonded together by a specific adhesive. Table 2 shows the effect 
of aging on the electrical joint resistance of couples of different 
composition. The resistance is measured in milliohms. The couples were 
aged at about 90.degree. C. temperature and 10 psi loading. Table 2 
compares the electrical resistance of the unbonded couples not employing a 
conductive coating with couples employing a conductive coating of the type 
described in Example III that lowers the electrical resistance at the 
joint or interface between the coupons. Those couples employing the 
conductive coating show significantly lower electrical resistance. The 
conductive coating appears to prevent or significantly hamper the 
oxidation of the mating contact surfaces that can significantly increase 
joint resistance with aging. The copper-copper sputtered titanium coupons 
employing the conductive coating showed decreases in electrical resistance 
with aging. Those coupons mated without the electrical resistance lowering 
conductive coating on the copper-copper sputtered titanium coupons have 
ranges for the resistances recorded at 11 and 17 days because of the 
multiple coupons tested and the large difference in readings. The copper 
coupons mated without the conductive coating showed some reduction in the 
measured resistance with aging because of what is thought to be attributed 
to the formation over time of copper oxides which exhibit semiconductor 
qualities. 
TABLE 2 
______________________________________ 
CONTACT SURFACE STUDY 
Resistance (milliohms) 
Aging Time 
(Days) Cu/Cu Cu/Ni Cu/Cu Sputtered Ti 
Cu/Ti 
______________________________________ 
Couple With Electrical Resistance Lowering Conductive Coating 
1 0.051 0.21 0.98 -- 
3 0.057 0.19 1.02 2.60 
(4 days) 
8 0.045 0.21 0.63 0.95 
10 0.055 0.07 0.64 -- 
15 0.055 0.19 0.65 -- 
25 0.060 0.14 0.85 -- 
38 0.048 0.186 0.736 1.1 
(28 days) 
Couples Without Electrical Resistance 
Lowering Conductive Coating 
0 0.15 0.55 4.4 -- 
4 9.58 2.80 50.5 170 
6 7.33 63.50 60.5 190 
(8 days) 
11 8.05 142.5 35-100 -- 
17 10.50 135.6 60-70 -- 
27 6.95 7.0 65 130 
(28 days) 
______________________________________ 
EXAMPLE V 
One inch square couples of titanium and copper and nickel and copper of the 
thickness and grade described in Example I were mated together using a 
silver-filled epoxy that is solvent-based and heat cured. The adhesive is 
a two-component adhesive that is electrically conductive. The couples were 
cured at about 100.degree. C. for one hour under an applied load of about 
100 psi. Two samples of each couple were initially employed and electrical 
resistance was measured using the procedure explained in Example I. 
Resistance was also recorded after the couples had been aged at about 
90.degree. C. for one day. Initial shear strengths were in excess of 500 
psi. These couples show a range of resistance values in milliohms which 
did not tend to increase significantly over a short period of time. These 
results are shown in Table 3. 
TABLE 3 
______________________________________ 
Electrical Resistance 
(milliohms) 
Couple Initial 1 Day 
______________________________________ 
Cu--Ni 0.1, 0.1 0.2, 0.2 
Ti--Cu 2.1, 2.4 2.1, 2.4 
______________________________________ 
EXAMPLE VI 
One inch square coupons of nickel and copper of the thickness and grade 
described in Example I were selected, cleaned as described in Example I 
and mated or coupled together. Prior to mating a uniform film of a 
conductive coating of the type described in Example II was applied to the 
mating surface of both coupons, except for a 1/8 inch wide strip along 
three sides. In this 1/8 inch strip on both coupons a copper-filled, 
single component epoxy adhesive was applied in a uniform thin film. Three 
couples of nickel-copper coupons were thus formed and were cured for about 
30 minutes at about 150.degree. C. The couples were subjected to less than 
50 pounds per square inch pressure during curing. Aging was conducted at 
about 90.degree. C. to simulate conditions in an operating filter press 
membrane electrolytic cell of the chlor-alkali type. The following table 
shows the electrical resistance in milliohms measured in the manner 
described in Example I. The shear stress load of the bonds between the 
couples was measured for couple #1 as 60 pounds on Day 1 and for couple #3 
as 72 pounds on Day 70. No measurement was made for couple #2. 
TABLE 4 
______________________________________ 
Aging Time Resistance (Milliohms) 
(Days) Cu/Ni #1 Cu/Ni #2 Cu/Ni #3 
______________________________________ 
1 .122 .124 .117 
5 -- .121 .133 
30 -- .118 .128 
70 -- .110 .110 
______________________________________ 
EXAMPLE VII 
One inch square coupons of copper, nickel and titanium of the thickness and 
grade described in Example I were selected, cleaned as described in 
Example I and mated or coupled together to form three sets each of 
copper-nickel and copper-titanium couples. Prior to mating, a uniform film 
of a conductive coating of the type described in Example III was applied 
to the mating surface of the copper coupon of each couple. A uniform film 
of a copper-filled, single component epoxy adhesive was applied to the 
entire surface of the nickel and titanium coupons. The couples were cured 
under 50 pounds per square inch pressure for 30 minutes at 145.degree. C. 
The couples were aged at about 90.degree. C. The following table shows the 
electrical resistance in milliohms measured in the manner described in 
Example I. 
The shear stress load of the bonds between the couples were measured at 
various times. Copper-nickel couple #1 had 415 pounds on Day 1, 
copper-nickel couple #2 had 620 pounds on Day 70, and copper-nickel couple 
#3 was not measured. Copper-titanium couple #1 had a shear stress load of 
670 pounds on Day 1, copper-titanium couple #3 had 510 pounds on Day 70, 
and copper-titanium couple #2 was not measured. 
The data suggests that the copper-filled single component epoxy adhesive 
did not protect the surface of the nickel and titanium coupons from 
oxidation. 
TABLE 5 
______________________________________ 
Resistance (Milliohms) at Various 
Aging Times (Days) 
Shear Stress Load 
Couple Day 1 Day 30 Day 70 (Pounds) 
______________________________________ 
Cu/Ni #1 
.280 -- -- 415 (Day 1) 
Cu/Ni #2 
.185 .165 .175 620 (Day 70) 
Cu/Ni #3 
.500 .650 1.120 -- 
Cu/Ti #1 
6.1 670 (Day 1) 
Cu/Ti #2 
18.6 34.2 52.5 -- 
Cu/Ti #3 
2.9 3.9 4.5 510 (Day 70) 
______________________________________ 
EXAMPLE VIII 
A 0.15 square meter filter press membrane chlor-alkali electrolytic cell 
employing a half anode and half cathode was fabricated. The electrodes 
were formed by utilizing diffusion bonding of a mesh electrode surface to 
generally vertical electrical conducting elements or blades and the blades 
to the backplates. The electrode subunits were mounted to copper 
conducting plates with adhesives. The anode was titanium and was bonded to 
its conducting plate using a copper-filled, single-component epoxy after 
the mating surfaces were cleaned as described in Example I. A conductive 
coating of the type described in Example III that lowers the electrical 
resistance at the joint or interface was applied to the backplate in line 
with the conducting blades prior to mating the conducting plate to the 
backplate. The cathode assembly was formed from a nickel electrode subunit 
soldered to the copper conducting plate with a 95% tin, 5% silver solder 
compound. A nickel sheet was soldered with the same solder material to the 
opposing side of the copper conducting plate to control the bimetallic 
expansion that results from heating. 
The cell was initially operated at a current density of about 2.4 
kiloamperes per square meter. The cell performance averaged 3.04 volts and 
94.9% current efficiency with a DC power consumption of 2148 kilowatt 
hours per metric ton of caustic produced. The cell employed a FLEMION.RTM. 
757 membrane, 229 grams per liter of NaCl, and operating at a temperature 
of 88.degree. C., producing a 34.92% concentrated caustic. 
Voltage losses normalized to a current density of 3 kiloamperes per square 
meter were 5 millivolts through the anode and 1 millivolt through the 
cathode. 
EXAMPLE IX 
A 0.15 square meter filter press membrane electrolytic cell employing a 
half anode and a half cathode was fabricated. The electrodes were formed 
by utilizing diffusion bonding of a mesh electrode surface to generally 
vertical electrical conducting elements or blades and the blades to the 
backplates. The electrode subunits were mounted to copper conducting 
plates with adhesives. The titanium anode subunit was bonded to its 
conducting plate using the copper-filled, single-component epoxy of 
Example VI, after the mating surfaces were cleaned as described in Example 
I. A conductive coating of the type identified in Example III that lowers 
the electrical resistance was applied to the reverse side of the backplate 
in line with the conducting blades prior to mating the conducting plate to 
the backplate. The cathode was formed from an electrode subunit of nickel 
adhesively bonded to the copper conducting plate with a two-component, low 
viscosity, non-conductive epoxy adhesive system combined with a conducting 
coating that lowers the electrical resistance between the subunit 
backplate and the copper conducting plate. The conductive coating was 
applied as with the anode. The mating of the surfaces of the backplates 
and the copper conducting plates also employed a pressure contact joint 
that is a silver plated berylium copper sold commercially under the 
ELECTROMATE tradename. 
The cell was operated with pumped electrolyte circulation and a 
FLEMION.RTM. 775 membrane. For the first 16 days of operation cell 
performance averaged 3.31 volts and 94.9% current efficiency at 3.6 
kiloamperes per square meter current density. Cell performance for the 
next 14 days of operation ranged from about 93.5% to about 95% current 
efficiency at current densities between about 4.5 and about 5.0 
kiloamperes per square meter. After 74 days of operation hardware voltage 
losses at 6.0 kiloamperes per square meter were 8.5 millivolts for the 
anode and 8.5 millivolts for the cathode. Voltage losses normalized to 3.0 
kiloamperes per square meter were 4.5 millivolts for the anode and 4.5 
millivolts for the cathode. 
While the preferred structure made by the diffusion bonding process in 
which the principles of the present invention have been incorporated is 
shown and described above, it is to be understood that the invention is 
not to be limited to the particular details thus presented, but in fact, 
widely different means may be employed in the practice of the broader 
aspects of this invention. For example, it is possible to metallurgically 
bond the electrode surface 11 to the electrical conducting element 14 or 
20 by the diffusion bonding technique and then bond the combined electrode 
surface-electrical conducting elements to the backplate 16 by means of one 
of the adhesives disclosed and discussed herein in combination with the 
conductive coating also discussed. The conductive coating would then be 
applied along the center line of the conducting elements with the adhesive 
applied along the outer sides of the conducting element surface to be 
mated to the backplate. 
It is possible to assemble the electrode subunits without the use of any 
adhesives by assembling the electrodes in a horizontally oriented, 
vertically rising stack and then compressing the assembled electrode 
stack. The stack could then be rotated 90.degree. to a vertical 
orientation and operated. 
It is to be understood also that although only a half electrode is shown in 
FIGS. 2"5, the electrode can equally well be a full electrode with two 
active surfaces on opposing sides. The full electrode may be either 
monopolor or bipolar. The full electrode would then merely have the 
electrode subunits 10 or 18 on both sides of the electrical conducting 
plate 19 with the desired adhesive and conductive coating application 
applied to both backplates in the manner described with reference to FIG. 
3 prior to applying the backplates 16 to both sides of the conducting 
plate 19. It is also possible in a bipolar configuration to adhesively 
bond the cathode subunit, for example made of nickel, directly to the 
anode subunit, for example made of titanium, utilizing the conductive 
coating and omitting the conducting plate. 
Further, it should be understood that the electrode subunits and the 
electrodes produced by the processes described in this disclosure may be 
used in any type of electrolytic process and are not to be limited to just 
utilization in chlor-alkali cells. For example they could be employed in 
water electrolytic cells, whether employing alkaline or acid electrolytes, 
HCl electrolyzers, fuel cells, whether employing molten carbonate or 
phosphoric acid electrolytes, electrowinning cells for lead, copper, zinc, 
nickel or manganese, and electroplating cells for nickel, chromium and 
copper. 
The scope of the appended claims is intended to encompass all obvious 
changes in the details, materials, arrangement of parts and processes 
which will occur to one of skill in the art upon a reading of the 
disclosure.