Electrolyte permeable diaphragm including a polymeric metal oxide

A polymeric metal oxide such as polytitanic acid, polyzirconic acid or polysilicic acid is incorporated into a liquid permeable diaphragm formed of, e.g., asbestos, asbestos and a polymer resin, polytetrafluoroethylene, or a major amount polyfluorocarbon fibrils and a minor amount perfluorinated ion exchange material. Optionally, the diaphragm may also include inorganic materials such as zirconium oxide, titanium dioxide, aluminum oxide, talc, barium sulfate or potassium titanate, and hydrous inorganic gels such as magnesium oxide gel, zirconium oxide gel, titanium oxide gel or zirconyl phosphate gel.

FIELD OF THE INVENTION 
The present invention relates to diaphragms useful for the electrolysis of 
salt solutions, e.g., in the electrolysis of aqueous alkali metal halide 
solutions such as sodium chloride brine. 
BACKGROUND OF THE INVENTION 
Commonly, alkali metal halide brines, such as sodium chloride brines and 
potassium chloride brines, are electrolyzed in an electrolytic cell 
wherein a liquid permeable diaphragm divides the cell into an anolyte 
compartment with an anode therein and a catholyte compartment with a 
cathode therein to produce chlorine, hydrogen, and aqueous alkali metal 
hydroxide. Asbestos has been the most common diaphragm material, but has 
suffered from relatively short lifetimes and from environmental concerns. 
Numerous efforts have been made to improve the lifetimes and performances 
of asbestos diaphragms. For example, according to U.S. Pat. No. 3,991,251, 
asbestos diaphragms can be strengthened by the reaction between asbestos 
and sodium hydroxide at temperatures from about 110.degree. C. to 
280.degree. C. Other patents describe strengthening asbestos diaphragms by 
addition of polymeric resins, e.g., fluorine-containing polymers, to bind 
the asbestos diaphragms. See U.S. Pat. Nos. 4,065,534; 4,070,257; 
4,142,951; and 4,410,411. 
Asbestos-free microporous diaphragms have been produced by sintering 
materials such as polytetrafluoroethylene (PTFE) and a particulate pore 
forming additive followed by subsequent removal of the additive, as shown 
by for example U.S. Pat. Nos. 3,930,979, 4,098,672 and 4,250,002. U.S. 
Pat. No. 4,036,729 describes depositing discrete thermoplastic fibers of, 
e.g., a fluorinated hydrocarbon, from an aqueous medium containing acetone 
and preferably a fluorocarbon surfactant onto a cathode screen for use as 
a diaphragm in electrolytic cells. The deposited fibers form an 
entanglement or network which does not require bonding or cementing. 
Unfortunately, such polyfluorocarbon diaphragms generally are hydrophobic, 
i.e., difficult to wet with water. This hinders passage of an aqueous 
electrolyte through the diaphragm, and results in high cell voltages, 
particularly in comparison to asbestos-based diaphragms under similar cell 
conditions. 
U.S. Pat. No. 4,482,441 describes codeposition of fibrils of a hydrophobic 
organic polymer, e.g., a copolymer of tetrafluoroethylene and 
perfluoropropylene, and a hydrophilic group IIA metallic oxide, e.g., 
magnesium oxide particles, from an alkaline brine containing sodium 
hydroxide, sodium chloride and a polyethyleneimine-based retention agent 
onto the cathode of a cell. Such a deposited diaphragm may also include a 
surface active agent, e.g., a fluorinated surface active agent. 
Finally, U.S. Pat. No. 4,606,805 describes a diaphragm containing as its 
principal particulate ingredient an inorganic material such as talc, a 
metal silicate, an alkali metal titanate, an alkali metal zirconate or a 
magnesium aluminate, along with both polytetrafluoroethylene fibers and 
polytetrafluoroethylene particulates. 
Clearly, further developments are constantly sought whereby diaphragms may 
achieve improved performance in terms of cell voltages while exhibiting 
excellent wettability by aqueous electrolytes. 
SUMMARY OF THE INVENTION 
The invention herein contemplated provides a liquid permeable diaphragm for 
an electrolytic cell, the diaphragm including a polymeric metal oxide 
exemplified by polytitanic acid, polyaluminic acid, polysilicic acid, and 
polyzirconic acid. The polymeric metal oxide material is incorporated into 
the diaphragm by applying a solution including an alcohol, water, and a 
hydrolyzed metal alkoxide, the metal being selected from aluminum, 
titanium, zirconium or silicon, to a deposited or preformed diaphragm, and 
then heating the diaphragm including the applied solution at temperatures 
of from about 90.degree. C. to 150.degree. C. to cure the polymeric metal 
oxide material. In one embodiment, the diaphragm includes a major amount 
of fibrillated polyfluorocarbon, e.g., polytetrafluoroethylene, a minor 
amount of a perfluorinated ion exchange material and a polymeric metal 
oxide selected from the group of polyaluminic acid, polytitanic acid, 
polyzirconic acid, polysilicic acid or mixtures thereof. For example, the 
diaphragm may include from about 65 to 99 percent by weight fibrillated 
polyfluorocarbon and from about 1 to about 35 percent by weight 
perfluorinated ion exchange material, basis total weight of 
polyfluorocarbon and perfluorinated ion exchange material. Preferably, the 
polyfluorocarbon is polytetrafluoroethylene and the perfluorinated ion 
exchange material is a perfluorinated organic polymer containing ion 
exchange functional groups selected from the group consisting of 
carboxylic acid (--COOH), sulfonic acid (--SO.sub.3 H) or an alkali metal 
salt of carboxylic acid or sulfonic acid. Such perfluorinated ion exchange 
material can be present in the form of particulates usually dispersed 
throughout the diaphragm or as a film coating the fibrillated 
polyfluorocarbon. 
Such a diaphragm of fibrillated polyfluorocarbon and perfluorinated ion 
exchange material may also include a minor amount of inorganic 
particulates chemically resistant to the intended cell environment, such 
particulates exemplified by titanium dioxide, zirconium oxide, potassium 
titanate, silicon carbide, aluminum oxide, talc, barium sulfate, asbestos, 
and mixtures thereof. 
In another embodiment, the diaphragm consists essentially of fibrillated 
polyfluorocarbon, e.g., polytetrafluoroethylene, and the polymeric metal 
oxide as previously described. 
In still another embodiment the polymeric metal oxide is included within a 
liquid permeable diaphragm such as an asbestos diaphragm or an asbestos 
diaphragm including a polymeric resin. 
DETAILED DESCRIPTION OF THE INVENTION 
In the present invention, a polymeric metal oxide wherein the metal is 
selected from among titanium, zirconium, silicon, and aluminum or 
combinations thereof can be incorporated into a pre-formed diaphragm of, 
e.g., asbestos, asbestos in combination with a polymeric resin, 
fibrillated polyfluorocarbon such as polytetrafluoroethylene, or such 
fibrillated polyfluorocarbon with perfluorinated ion exchange material. 
Such polymeric metal oxides are exemplified by polytitanic acid, 
polyzirconic acid, polysilicic acid and polyaluminic acid. For example, 
the polymeric metal oxide can be added to a pre-formed diaphragm of 
fibrillated polyfluorocarbon and perfluorinated ion exchange material as a 
clear solution of a partially hydrolyzed metal alkoxide which prior to 
hydrolyzation is represented by the formula M(OR).sub.4 wherein M is 
titanium, zirconium, silicon, or aluminum, R is an alkyl with from 1 to 6 
carbon atoms and the solution solvent is an organic solvent for any 
metallic or metalloid alkoxide present in the solution. The organic 
solvent can be an alcohol such as propanol or ethanol. The clear solution 
also contains hydrolyzing water which is generally present in an amount 
from about 1 mole to about 4 moles per mole of metal alkoxide. In addition 
the solution may include a few drops of a mineral acid, such as nitric 
acid, as a catalyst. Such a clear solution may be allowed to age for up to 
several hours to provide time for completion of hydrolyzation whereupon 
polymerization and cross linking of the metal oxide can occur. The 
polymeric metal oxide is distributed throughout the diaphragm, e.g., by 
brushing or spraying the clear solution onto the diaphragm or by dipping 
the diaphragm into the clear solution to saturate the diaphragm. 
Thereafter, the diaphragm is heated at temperatures from about 100.degree. 
C. to 150.degree. C. for sufficient time, generally about 1 to 2 hours, to 
dry and cure the polymeric metal oxide. The diaphragm may then be operated 
in an electrolytic cell. 
In similar manner, the polymeric metal oxide may be combined with a 
diaphragm of fibrillated polyfluorocarbon, e.g., Polytetrafluoroethylene, 
in the absence of the perfluorinated ion exchange material. The polymeric 
metal oxide may provide such a diaphragm with the desired wettability 
usually provided by the perfluorinated ion exchange material. Generally, 
the polymeric metal oxide will be present in an amount of from about 1 to 
about 10 percent by weight, basis total weight of diaphragm. 
The polymeric metal oxide may also be added to a diaphragm formed of 
asbestos or asbestos in combination with a polymeric resin. Such asbestos 
and asbestos-polymeric resin diaphragms can be formed by deposition of the 
asbestos and optionally the polymeric resin from, e.g., an aqueous slurry 
including sodium hydroxide, followed by heat-treating the diaphragm to 
react the asbestos and sodium hydroxide. Such a heat treatment may be at 
temperatures whereat the polymeric resin does not undergo melting or 
sintering or optionally the resin may be melted or sintering. The 
polymeric resin can be chosen from those described in U.S. Pat. No. 
4,186,065 at columns 6 and 7 and such description is hereby incorporated 
by reference. Other methods of preparing asbestos or asbestos and 
polymeric resin diaphragms are well known to those skilled in the art. 
The diaphragm separators of this invention are liquid permeable, thus 
allowing an electrolyte subjected to a pressure gradient to pass through 
the diaphragm. Typically, the pressure gradient in a diaphragm cell is the 
result of a hydrostatic head on the anolyte side of the cell, that is, the 
liquid level in the anolyte compartment will be on the order of from about 
1 to about 25 inches higher than the liquid level of the catholyte, 
although higher or lower levels are permissible and restricted only by 
space or electrolytic cell hardware limitations. The specific flow rate of 
electrolyte through the diaphragm can vary with the type and use of the 
cell. In a chlor-alkali cell, the diaphragm should be able to pass about 
0.001 to about 0.5 cubic centimeters of anolyte per minute per square 
centimeter of diaphragm surface area. The flow rate is generally set at a 
rate that allows a predetermined, targeted product concentration, e.g., 
sodium hydroxide concentration, and the level differential between the 
anolyte and catholyte compartments is then related to the porosity of the 
diaphragm and the tortuosity of the pores. For use in a chlor-alkali cell 
the diaphragm will preferably have a permeability similar to that of 
asbestos-type diaphragms so that electrolytic cell equipment in operation 
with asbestos-type diaphragms can be utilized. 
A pre-formed diaphragm of the present invention can be prepared by 
depositing the diaphragm material from a slurry onto a liquid permeable 
substrate, e.g., a foraminous cathode. The foraminous cathode is 
electroconductive and may be a perforated sheet, a perforated plate, metal 
mesh, expanded metal mesh, metal rods, or the like. For example, the 
openings in foraminous cathodes commercially used today in chlor-alkali 
cells are usually about 0.05 to about 0.125 inches in diameter. Most 
commonly the cathode will be of iron or an iron alloy. By iron alloy is 
meant a carbon steel or other alloy of iron. Alternatively, the cathode 
can be nickel or other cell environment resistant electroconductive 
material. Cathodes suitably used in this invention include those having an 
activated surface coating, for example, those cathodes with a porous Raney 
nickel surface coating. Raney nickel coatings can provide a reduction of 
hydrogen overvoltage at the cathode and allow a savings in energy 
consumption and cost in the electrolysis of brine. Raney nickel coatings 
can be provided by various expedients well known to those skilled in the 
art. 
Such diaphragms are generally deposited upon the foraminous cathode in an 
amount of about 0.1 to about 0.5 pounds per square foot diaphragm material 
more preferably about 0.25 to 0.35 pounds per square foot diaphragm 
material, e.g., asbestos, polyfluorocarbon fibrils, perfluorinated ion 
exchange material, etc. The diaphragm will generally have a thickness of 
about 0.01 to 0.25 inches, preferably about 0.02 to 0.15 inches to achieve 
best results in terms of voltage and energy efficiency. 
The pre-formed diaphragm of this invention can include fibrillated 
polyfluorocarbon and optionally perfluorinated ion exchange material 
wherein such diaphragm is prepared by depositing any perfluorinated ion 
exchange material in the form of discrete particulates or as a solution, 
and polyfluorocarbon fibrils from a slurry onto a cathode, e.g., onto a 
cathode with a non-planar configuration. For example, polyfluorocarbon 
fibrils and discrete perfluorinated ion exchange material particulates can 
be dispersed within the liquid slurry without rapid settling with 
surfactants and viscosity modifiers added to aid in the dispersion. 
Following deposition, a fibrillated polyfluorocarbon mat having a highly 
branched structure, which branched structure provides support for the 
diaphragm through entanglement of the fibrils, is formed. The 
polyfluorocarbon fibrils can be drawn against the cathode under the 
pressure of a vacuum to provide packing of the diaphragm material. 
Inclusion of perfluorinated ion exchange material with the polyfluorocarbon 
fibrils can provide the diaphragm with wettability, i.e., an aqueous brine 
can pass through the diaphragm without the necessity of first passing a 
liquid such as an alcohol through the diaphragm. Also, such a diaphragm 
will not tend to accumulate gas bubbles and thus may maintain low steady 
voltages. Perfluorinated ion exchange material may serve additionally as a 
glue or binder for the fibrils. Generally, such a diaphragm will contain a 
major amount of the polyfluorocarbon fibrils, i.e., greater than 50 
percent by weight of the fibrils. As perfluorinated ion exchange material 
is generally more costly than polyfluorocarbon fibrils, the diaphragm more 
preferably includes from about 65 to about 99 percent by weight 
polyfluorocarbon fibrils and from about 1 to about 35 percent by weight 
perfluorinated ion exchange material. Within such percentage ranges, the 
larger percentages of polyfluorocarbon fibrils are most preferred to 
minimize diaphragm cost, i.e., the diaphragm includes from about 95 to 
about 99 percent by weight polyfluorocarbon fibrils and from about 1 to 
about 5 percent perfluorinated ion exchange material wherein the 
perfluorinated ion exchange material provides the diaphragm with 
wettability. 
Fibrillated polyfluorocarbon materials useful in this invention include, 
for example, polyvinylfluoride, polyvinylidene fluoride, 
polyperfluoro(ethylene-propylene), polytrifluoroethylene, 
poly(chlorotrifluoroethylene-ethylene), 
poly(tetrafluoroethylene-ethylene), polychlorotrifluoroethylene, and 
polytetrafluoroethylene. Preferably, the polyfluorocarbon is 
polytetrafluoroethylene (PTFE). 
Perfluorinated ion exchange material may be incorporated in a diaphragm of 
this invention in the form of, e.g., a solid, a gel or a solution. As a 
solid, for example, the perfluorinated ion exchange material can be added 
to the slurry as discrete particulates or fibers. As a solution, 
perfluorinated ion exchange material can be added to the slurry dissolved 
in any suitable solvent such as ethanol although rather than being 
dissolved the perfluorinated ion exchange method may be highly solvated 
particles. The solid perfluorinated ion exchange material may be, e.g., in 
the acid form of the perfluorinated ion exchange material and may be 
swollen with an organic liquid such as ethanol or isopropanol. 
Such perfluorinated ion exchange material is generally an organic copolymer 
formed from polymerization of a fluorovinylether monomer containing a 
functional group, i.e., an ion exchange group or a functional group easily 
converted into an exchange group, and a monomer chosen from the group of 
fluorovinyl compounds, e.g., vinyl fluoride, vinylidene fluoride, 
trifluoroethylene, tetrafluoroethylene, hexafluoropropylene, 
chlorotrifluoroethylene, and perfluoro(alkylvinylether) with the alkyl 
being a C.sub.1 -C.sub.10 alkyl group. The functional groups are --COOM or 
--SO.sub.3 M or may be --PO(OM).sub.2 or --OPO(OM).sub.2 where M is 
hydrogen or an alkali metal ion. Further, the functional groups may be 
precursors of the --COOM or --SO.sub.3 M groups which can be converted to 
the carboxylic acid or sulfonic acid and salts thereof by hydrolysis. 
The content of the fluorovinylether having the functional groups in the 
copolymer is important as it determines the ion exchange potential of the 
perfluorinated ion exchange material and thus, controls its hydrophilicity 
or wettability. The fluorovinyl ether content is generally in the range of 
about 1 to about 50 mole percent, preferably about 2 to about 40 mole 
percent. Generally, the equivalent weight of the perfluorinated ion 
exchange material will be from about 600 to 2000. Equivalent weight is the 
weight of material in grams which contains one equivalent of potential ion 
exchange capacity. 
The perfluorinated ion exchange material can generally be from those 
materials presently supplied for use as electrolyte impermeable membranes 
in various electrolytic cells, in particular, the membrane materials known 
as Nafion.RTM., available from E. I. DuPont de Nemours and Company and 
those known as Flemion.RTM., available from Asahi Glass Company, Ltd. 
In a preformed diaphragm of fibrillated polyfluorocarbon and perfluorinated 
ion exchange material, the diaphragm may further include a minor amount of 
chemically resistant inorganic particulates e.g., particulates selected 
from the group of zirconium oxide, titanium dioxide, potassium titanate, 
aluminum oxide, silicon carbide, talc, asbestos, barium sulfate and 
mixtures thereof. Such diaphragms may contain from about 70 to about 95 
percent by weight fibrillated polyfluorocarbon, e.g., 
polytetrafluoroethylene, from about 1 to about 5 percent by weight of the 
perfluorinated ion exchange material, i.e., an amount sufficient to 
provide wettability, and a minor amount of the inorganic particulates, 
i.e., from about 1 to 25 percent by weight, more preferably from about 5 
to 15 percent by weight inorganic particulates, basis total weight of 
diaphragm. 
It may be desirable and even preferable that the pre-formed diaphragm be 
asbestos-free. Thus, the polymer metal oxide would be incorporated into an 
asbestos-free diaphragm, e.g., a diaphragm of fibrillated 
polyfluorocarbon. Also in those diaphragms including fibrillated 
polyfluorocarbon, e.g., polytetrafluoroethylene, it may be preferable to 
use unsintered polytetrafluoroethylene to form the diaphragm. Such 
unsintered, fibrillated polytetrafluoroethylene may be preferred over 
fibrillated polytetrafluoroethylene that has been sintered at some stage 
prior to fibrillation. 
The liquid permeability of the diaphragms can be adjusted by utilization of 
a pore forming material, inorganic gels or combinations thereof. For 
example, a pore forming material can be included, e.g., codeposited with 
polyfluorocarbon fibrils and perfluorinated ion exchange material. Such 
pore forming material is subsequently removable, e.g., by chemical 
leaching after formation of the diaphragm, by heating to decomposition 
temperatures of the pore forming material following formation of the 
diaphragm, or by removal in situ during subsequent operation of the cell 
via the chemical action of an electrolyte within the cell. Among suitable 
pore formers in the preparation of the diaphragms are cellulose, rayon, 
polypropylene, calcium carbonate, starch, polyethylene and nylon. 
Cellulose, rayon, polypropylene, polyethylene or nylon can be present in 
any suitable particulate form, e.g., granular or fibrous form. Preferably, 
the pore forming material is polyethylene or polypropylene and present in 
fibrous form. Generally, the pore forming material can be added in an 
amount from about 1 to about 30 percent by weight, more preferably from 
about 1 to about 20 percent by weight, basis total weight of diaphragm 
materials. 
The diaphragm can also incorporate an inorganic gel. The inorganic gel may 
be a hydrous metal oxide gel such as magnesium oxide gel, zirconium oxide 
gel, or titanium oxide gel, a zirconyl phosphate gel, or combinations 
thereof. Such inorganic gels can serve to reduce the liquid permeability 
of a diaphragm to a desired level and may also provide ion exchange 
properties to the diaphragm. The inorganic gel is added to the diaphragm 
after formation of the diaphragm and preferably after the polymeric metal 
oxide is incorporated into the diaphragm. For example, after a diaphragm 
of fibrillated polytetrafluoroethylene and perfluorinated ion exchange 
material is formed upon a non-planar cathode and the polymeric metallic 
oxide is incorporated into the diaphragm in accordance with the present 
invention, an inorganic gel can be added to the diaphragm matrix by 
filling the matrix with an inorganic gel precursor, i.e., a solution of an 
inorganic salt, e.g., zirconium oxychloride, titanium oxychloride, or 
magnesium chloride and thereafter, hydrolyzing the inorganic salt thereby 
providing a hydrous oxide of the zirconium, titanium or magnesium as the 
inorganic gel. Magnesium and zirconium inorganic gels can be prepared, 
e.g., in the manners described in U.S. Pat. Nos. 4,170,537, 4,170,538 and 
4,170,539. A zirconyl phosphate gel can be formed by filling the diaphragm 
matrix with a solution of zirconium oxychloride and then contacting the 
matrix with a solution of dibasic sodium phosphate to precipitate zirconyl 
phosphate gel. 
Precursors of such hydrous inorganic gels can be deposited in various ways. 
For example, a solution of the precursor can be brushed or sprayed onto 
the diaphragm matrix if the solution will penetrate or soak into the 
porous matrix. Otherwise, the diaphragm matrix can be immersed in the 
solution, a vacuum drawn to remove the air from the matrix and the vacuum 
released to draw the solution into the matrix. 
Inorganic gels can also be incorporated in the diaphragm in situ during 
cell operation. For example, an inorganic salt such as magnesium chloride 
hexachloride or zirconium oxychloride can be added to anolyte, i.e., the 
brine feed, while the diaphragm is operated in a chlor-alkali cell whereby 
an inorganic gel can be formed within the diaphragm pores in situ. 
Mixtures of inorganic salts may be added. Preferably, the inorganic salts 
may be added to the anolyte immediately after cell startup, i.e., within 
the first few hours, more preferably, first few minutes, in the period 
before the hydroxide ions formed at the cathode have begun to migrate 
substantially through the diaphragm towards the anode. 
In operation of chlor-alkali cells containing the diaphragms of this 
invention, sodium chloride brine feed generally containing from about 290 
to 330 grams per liter of sodium chloride will be fed to the anolyte 
compartment. Such a brine feed can have a quality similar to that 
typically used in asbestos-type diaphragm cells, i.e., the brine generally 
can contain about 2 to 3 parts per million alkaline earth metal ion 
impurities such as calcium and magnesium. In some instances, it may be 
desirable to use higher quality brine, i.e., brine containing less than 
about 20 parts per billion alkaline earth metal impurities. Brine 
treatment methods capable of obtaining the desired quality levels are well 
known to the skilled in the art.

The present invention is more particularly described by the following 
example which is intended as illustrative only, since numerous 
modifications and variations will be apparent to those skilled in the art. 
Example 1 
Polytetrafluoroethylene powder (TEFLON.RTM.60, available from E. I. DuPont 
deNemours and Co.) was blended with granular sodium chloride in a 
Brabender mixer at a PTFE:salt weight ratio of 1:10. The resultant clump 
was removed from the mixer and chopped in a blender to break up the clump. 
The salt was dissolved in water and polytetrafluoroethylene fibrils of 
about 20 to 250 microns in diameter and about 1 to 4 millimeters in length 
were washed, dried and recovered. A mixture including 8.6g of the PTFE 
fibrils, 0.96g of polypropylene fibers (POLYWEB.RTM. available from James 
Rivers Corporation), 1.25g of an ethanol solution of a perfluorinated ion 
exchange material having sulfonic acid functional groups, 8.3 weight 
percent of the ion exchange material (Nafion 601.RTM., available from E. 
I. DuPont de Nemours and Co.), 4.0 g of RHEOTHIK.RTM. 80-11 viscosity 
modifier and 4.0 g of a non-ionic surfactant (a polyethoxylated aliphatic 
chloride, i.e., C.sub.10-15 (OCH.sub.2 CH.sub.2).sub.9 Cl) was blended in 
about 225 ml of water. 
The slurry was poured over a 3 inch by 3 inch perforated steel plate 
cathode covered with cellulose filter paper and a 25 inch mercury vacuum 
was applied to draw the slurry liquids through the cathode. The solids 
were filtered out as a mat atop the filter paper. The cathode and 
diaphragm mat were placed in an oven and dried at temperatures between 
120.degree. C. to 130.degree. C. for 30 minutes with continued application 
of the vacuum. 
After the diaphragm mat cooled, the diaphragm was impregnated with a clear 
solution of both partially hydrolyzed silicon alkoxide and zirconium 
alkoxide. The clear solution was formed by adding 10 g tetraethoxysilane 
(Si(OC.sub.2 H.sub.5).sub.4) to 100 g of 2-propanol. To this mixture was 
added 0.87g water and four drops concentrated nitric acid, followed by 
stirring for 30 minutes at 60.degree. C. Then 15g Zr(OC.sub.3 
H.sub.7).sub.4 was added and the mixture stirred for 5 minutes. Another 
50g of 2-propanol was added, followed by the addition of 2.6g water in 16g 
2-propanol. Finally, another 25g 2-propanol was added. The diaphragm was 
impregnated with the solution by dipping in the solution. A vacuum was 
drawn on the impregnated diaphragm to maintain an air flow through the 
diaphragm thereby maintaining permeability and the diaphragm was heated 
for two hours at 120.degree. C. A second coat of the solution was applied 
via dipping. 
The cathode-diaphragm assembly was then placed into a laboratory 
chlor-alkali cell having a ruthenium oxide/titanium oxide coated titanium 
mesh anode. The cell was operated with the anode against the surface of 
the diaphragm. The cell was fed a purified sodium chloride brine (25 
weight percent NaCl) containing less than 20 parts per billion total of 
calcium and magnesium. The cell was operated at about 90.degree. C. with a 
current density of 133 amperes per square foot (ASF) produced 10.4 weight 
percent sodium hydroxide (125 gpl) at 2.82 volts and with a cathode 
current efficiency of 92.6 percent. 
Although the present invention has been described with reference to 
specific details, it is not intended that such details should be regarded 
as limitations upon the scope of the invention, except as and to the 
extent they are included in the accompanying claims.