US3558465A - Electrolytic cell - Google Patents

Abstract

AN ELECTROLYTIC CELL FOR MAKING CHLORINE SOLUTIONS FROM AQUEOUS CHLORIDE SOLUTIONS FOR CHLORINATING SWIMMING POOLS AND DESIGNED FOR SELF-DESCALING OF THE CATHODE, IN WHICH THE CATHODE IS FORMED WITH ITS ACTIVE CATHODIC SURFACE CONTAINING A METAL BETWEEN ZINC AND MAGNESIUM INCLUSIVE IN THE ELECTROMOTIVE SERIES SUCH AS ZINC, ALUMINUM AND MAGNESIUM, AND THE ANODE CONTAINS A MEMBER OF THE PLATINUM FAMILY AT THE ACTIVE ANODIC SURFACE THEREOF, SAID CELL ALSO HAVING CIRCUIT MEANS FOR INTERMITTENTLY IMPRESSING A DIRECT ELECTRIC POTENTIAL BETWEEN SAID ANODE AND SAID CATHODE, WITH THE CIRCUIT ALSO BEING ADAPTED TO PROVIDE A CONTROLLED CIRCUIT BETWEEN THE ANODE AND CATHODE WHEN THE ELECTRIC POTENTIAL IS TURNED OFF.

Description

Jan. 26, 1971 o. COLVIN ETAL 3,558,465

ELECTROLYTIC CELL Filed April 15, 1968 r5 Sheets-Sheet 1 INVENTORS DONALD COL VIN VERNON A. 5 C HUL T ATTORNEYS Jan. 26, 1971 0 v ETAL ELECTROLYTIC CELL 3 Sheets-Sheet 5 Filed April 15, 1968 FIE-.5.

INVENTORS 00mm (Oil/IN vmvou A. 5cm 12 ATTORNEYS FIE-E- United States Patent U.S. Cl. 204228 Claims ABSTRACT OF THE DISCLOSURE An electrolytic cell for making chlorine solutions from aqueous chloride solutions for chlorinating swimming pools and designed for self-descaling of the cathode, in which the cathode is formed with its active cathodic surface containing a metal between zinc and magnesium inclusive in the electromotive series such as zinc, aluminum and magnesium, and the anode contains a member of the platinum family at the active anodic surface thereof, said cell also having circuit means for intermittently impressing a direct electric potential between said anode and said cathode, with the circuit also being adapted to provide a controlled circuit between the anode and cathode when the electric potential is turned off.

CROSS REFERENCES TO RELATED APPLICATIONS This application is a continuation-in-part of our copending application Ser. No. 378,411, now U.S. 3,378,479, filed June 26, 1964 and entitled Electrolytic Cell in Chlorinating System Using the Same, and is also a continuation-in-part of our co-pending application Ser. No. 536,439, now 3,476,675, filed Mar. 22, 1966 and entitled Electrolytic Cell.

BACKGROUND OF THE INVENTION The present invention relates to improvements in an electrolytic cell, and more particularly to an improved electrolytic cell for making chlorine from chloride solutions by electrolysis.

It is well known that chlorine is made by electrolytic processes, and it is also known to make chlorine electrolytically where it is needed for immediate use. In general, the electrolytic cell of the present invention is suitable for making chlorine electrolytically regardless of the use therefor. However, the cell has been found to be particularly valuable when utilized to provide chlorine for the chlorination of swimming pools. Two typical set-ups for the utilization of the cell constructed according to the invention in swimming pools will be illustrated herein, but it should be appreciated that this particular utility should in no way limit the invention.

One of the problems encountered in making electrolytic cells for the manufacture of chlorine is the deterioration of the anode where the chlorine is formed. Various systems have been developed and various types of anodes have been utilized, including graphite and other relatively inexpensive materials which are quite expendable, to extremely corrosion-resistant materials such as platinum. No matter what material is used, the cell has a limited life, and in certain applications this limited life should be as long as possible.

In other words, where chlorine is made industrially, it is quite possible to utilize materials such as graphite effectively because the system is under the control of trained, qualified technicians and repair of the cell and maintenance thereof may be provided from time to time to keep the system operating. However, where the cell is 3,558,465 Patented Jan. 26, 1971 to be utilized by relatively untrained personnel, it is desirable to provide a cell having an especially long life of operation, with little or no maintenance problems. The cell of the present invention is developed to fit the latter category, where a long life of trouble-free maintenance is desirable.

In such cases, it is customary to utilize platinum or members of the platinum family as the anode since platinum is extremely corrosion resistant and will serve for rather long periods of time before it deteriorates beyond serviceable use. It will be appreciated, however, that platinum and members of the platinum family are rather expensive and therefore efiicient use of the platinum should be achieved by providing increased operating time with respect to the platinum used.

Another problem encountered in electrolytic cells is the formation of scale on the cathode which in turn interferes with the proper operation of the unit and increases the problem of anode deterioration. This scale problem is caused by calcium and related materials found in hard waters, and in waters of high pH. Such hard water is frequently used in swimming pools, because the pools are abundantly located in areas of water shortages or where good fresh water sources are limited. In addition, even where the pools are filled with soft water, the calcium concentration builds up to high levels because of contact between the water and pool plaster or the like.

Certain ways of attacking this scale problem have been suggested such as the use of water softener and conditioners, but such usage can be very expensive without being completely effective in solving the problem.

Accordingly, our two co-pending applications cited above describe two different electrolytic cells, each of which is constructed to automatically slough off scale and solve the scale problem by shorting out the anode and cathode during ofP periods and providing scale slough off due to the battery of galvanic effect occurring between the cathode and electrolytic solution. While these two prior applications are eminently satisfactory for most waters, it has been found that certain swimming pool Waters present particularly diflicult scale problems, and for these diflicult waters the present invention is suitable. It is found that particularly diflicult scale problems occur in water supply systems where the pH is allowed to become relatively high, and many of the areas of critical water supply coincide with areas where swimming pools are exceptionally desirable. Thus, the use of the present invention provides for a solution to the scale problem in the most ditficult water conditions likely to be encountered.

SUMMARY OF THE INVENTION It has now been found, quite unexpectedly, that when active metals are utilized at the active cathodic surfaces, excellent scale sloughing is achieved, yet the metals do not rapidly deteriorate as was heretofore believed. Thus an electrolytic cell constructed according to the invention suitable for making chlorine solutions for swimming pools by electrolysis of saline water, comprises a housing adapted for connection in a fluid conduit which will contain saline solution directed toward the swimming pool, a cathode carried within the housing and formed to pro vide an active cathodic surface in contact with said saline solution, an anode carried in said housing in contact with said saline solution for cooperating with a cathode and providing electrolysis thereof, said cathode being formed with the active cathodic surface metal being between zinc and magnesium inclusive in the electromotive series, said anode being formed with a metal of the platinum family at the active surface thereof, and circuit means for intermittently impressing an electric potential between said anode and said cathode, said circuit means also being adapted to provide a short circuit during the time period when the electric potential is turned oti.

As indicated in our prior co-pending applications, most metals above platinum on the electromotive series were considered to be operative, however, the preferred cathodic metals were believed to be nickel and chromium, and a stainless steel alloy containing any of the usual proportions of iron, nickel and chromium was believed to be exceptionally good. The reasons advanced for the value of stainless steel resided in its resistance to the corrosive electrolyte under the conditions of the metals and electrolyte acting as a cell during the off position as well as during the electrolytic process itself. However, it was believed that metals having too high an activity would probably be unsuitable as cathodes because of their inability to remain in such corrosive solutions. Of course, this concept is still correct because metals such as sodium, potassium, and calcium react readily with water let alone in the presence of the corrosive conditions involved in the cell.

However, it has been found by experiment that active metals such as zinc, and even aluminum and magnesium are capable of withstanding these corrosive materials for relatively long periods of operation, and that they were especially suitable for scale removal under adverse conditions. In addition, it will be appreciated that zinc and aluminum are amphoteric and are therefore subject to attack by strong alkalis. Since sodium hydroxide is manufactured at the cathode during the electrolytic process, it would be expected that the electrolytic process would cause rapid solution of zinc or aluminum oxide. However, it has been found in practice that this is not the case. Perhaps the fact of simultaneous formation of hydrogen at the cathode tends to protect the zinc, but whatever the reason, we feel our discovery is unexpected and quite valuable.

Since it is relatively inexpensive to provide a cell constructed according to the invention, it is believed desirable to provide a cell which will operate under extreme conditions of scale problem, and at the same time, operate under water condtions which do not present serious problems and would ordinarily be usable with the cells of our prior applications. The advantage of this universal ability resides in the fact that a single cell provides a more universal purpose.

However, it will be appreciated, that where the scale problems are difficult, a low resistance short circuit should be provided during the off period, but when the scale problems are relatively easy, it is to advantage to provide a high resistance short circuit between the electrodes to insure protection thereof. Accordingly, another feature of this invention is to provide a circuit means having adjustable resistance in the short circuit portion thereof.

From the foregoing description, it is seen that a primary object of the present invention is the provision of an improved electrolytic cell which is specially constructed to automatically cause removal of scale that tends to form on the cathode thereof during the ordinary operating procedures, even with relatively serious scale forming waters.

Another object of the invention is to provide a swimming pool chlorinating system including the electrolytic cell of this invention so as to provide a simple and re liable system for chlorinating swimming pools that is suitable for the ordinary consumer.

A further object of the invention is the provision of an electrolytic cell of the character described which contains means for adjusting the scale sloughing ability so as to provide maximum life to the cell, yet maintain the cell under operating conditions in which removal of scale is positively assured.

Further objects and advantages of the invention will be apparent as the specification progresses, and the new and useful features of the electrolytic cell will be fully described in the claims attached hereto.

BRIEF DESCRIPTION OF THE DRAWINGS The preferred forms of the invention are illustrated in the accompanying drawings forming a part of this description, in which:

FIG. 1 is a perspective view of a typical cell constructed according to the invention, with parts broken away to illustrate internal structure, and including a typical circuit diagram utilized in the preferred form of the invention;

FIG. 2, a cross-sectional elevational view of the electrolytic cell of FIG. 1 with the cell being broken away to illustrate adjustment in the length thereof;

FIG. 3, a cross-sectional top view of the cell illustrated in FIG. 2;

FIG. 4, an enlarged sectional view taken substantially in the line 4--4 of FIG. 2;

FIG, 5, a schematic elevational view of a chlorinating system constructed in accordance with the present invention and containing another embodiment of a chlorinating cell constructed according to the invention therein;

FIG. 6, a cross-sectional elevational view in enlarged form of the chlorinating cell shown in the system illustrated in FIG. 5;

FIG. 7, a cross-sectional view of the cell illustrated in FIG. 6 taken substantially in the plane of line 77 thereof;

FIG. 8, an enlarged view of the cathode surface of the cell of FIGS. 5 and 6 illustrating the manner in which scale is removed therefrom; and

FIG. 9, a view of still another alternate form of cathode that may be utilized in the present invention.

While only the preferred forms of the invention are shown, it should be understood that various changes or modifications may be made within the scope of the claims attached hereto without departing from the spirit of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings in greater detail and more particularly to FIGS. 1 through 4, there is shown an electrolytic cell 11 comprising a metallic housing 12 formed to serve as the cathode and containing a section having two substantially flat walls 13 and 14 in substantially parallel relation for providing active cathodic surfaces, and a flat anode plate 16 (see FIG. 4) mounted in substantially evenly spaced relation between the flat walls 13 and 14 of the housing.

As here shown, the cathode is formed entirely of a single metal or alloy such as zinc, aluminum or magnesium. However, it will be appreciated that a stainless steel housing could be used which has a layer of zinc, aluminum or magnesium at the inner flat surfaces of Walls 14 and 16.

The anode plate is fabricated of a single sheet of material of the platinum family, such as platinum or platinumiridium alloy. As best seen in FIG. 4, the anode p ate 16 has each side facing one of the cathode plates 13 or 14 so that a single sheet is operative to provide two cell areas 17 and 18. Preferably, the anode plate 16 is corrugated to provide added strength thereto and also to provide an increased active surface.

The anode plate is securely held in position by holding means 19 comprising a corrosion-resistant frame 21 mounted in the housing through suitable mounting means 22.

In general, this corrosion-resistant frame can be any suitable member capable of supporting the anode plate securely in its proper position and carrying an electrical connection thereto. Accordingly, the frame could be made of plastic with any type of wire sealingly encased therein or a corrosion-resistant electrical conductor such as tantalum or titanium which is capable of supporting the anode plate and also bringing an electric current thereto. The preferred structure is shown in the drawings in which a tantalum frame is shown which is substantially rectangular with parallel sides 23 and 24 disposed in a centrally aligned position between plates 13 and 14, The sides 23 are disposed substantially axially on the housing 12 and have the anode plate wrapped therearound as shown at 26 in FIG. 4. In this way, the connection is axial to the flow of liquid through the housing and provides a secure fastening, in which the corrugations also have their long axis corresponding with the flow of the current of water through the electrolytic cell.

The sides 24 have V-shaped support members 27 attached thereto, with the support members preferably being centrally aligned, as shown, and passing through the inclined surface of the housing between the flattened section and tubular portion, as best seen in FIG. 2.

The frame 21 is preferably sized just slightly smaller than the diameter of the tube from which housing 12 is made so that it may be fit therethrough and into position as best seen in FIG. 3. The support members 27 can be temporarily bent out of shape and seated through the mounting means 22, or one of the support members welded in place by spot welding or the like at the bend thereof. The preferred form of mounting means is shown in FIG. 2 where there is provided a threaded fitting 28 in the form of a threaded sleeve passing through the housing to provide an opening therethrough and a Teflon plug 29 having a shoulder portion 31 adapted to fit within nut 32. With the frame properly positioned, nut 32 is tightened to provide a sealing grip on support member 27 so that the member may act as an electrical conductor insulated from the housing by the Teflon plug 29 and remain sealingly in place. The angular offset of the support members assists in providing a secure anchoring through the Teflon plug.

In order to protect the anode plate 16 from physical damage when strong currents of liquid are pumped through the cell structure, a pair of cover plates 33 are disposed on each side of the anode plate. These cover plates may be formed of any corrosion-resistant material which is capable of providing added strength, such as tantalum mesh or a suitable plastic such as any of the polyolefin plastics, including but not limited to polyethylene, polypropylene, polytetrafluoroethylene, and polystyrene.

As shown in the drawings, the cover plates are made of a polyethylene plastic and are constructed to be held securely in place by the tantalum frame in sufficient spaced relation to fit against the corrugations of the anode plate on each side. The cover plates are also equipped with holes 34 to allow better movement of gases such as hydrogen and chlorine therethrough, if and when necessary. With this construction, the platinum anode is thoroughly protected and will continue operation until substantially all of the platinum has been eaten away by use. When this happens, it is seen that the cell may be easily reconstructed to include another anode plate.

As indicated above, the housing 12 serves as a cathode and therefore should be of metallic or electrically conducting construction. It is also important to provide a cathode of a material which will slough off scale through the mechanism of reversed polarity between the on period and the off period, as hereinafter explained. Thus, it is important to utilize a metal cathode having an especially smooth surface whereby metal oxide formed on the cathode may be sloughed off from the cathode surface along with the scale to effect removal therefrom.

In accordance with the present invention, the metal providing the active cathode surface has an activity such that it includes zinc and magnesium and metals of intermediate activity in the electromotive series. Any metal higher than platinum will form an oxide coating through the galvanic effect when the cell is turned off" so that even materials such as copper, which is below hydrogen, will form such an oxide coating. However, it is important that the oxide coating be relatively easily formed and removable from the base metal. Accordingly, the active metals indicated are required for severe operating conditions, as well as being suitable under ordinary operating conditions.

It will be appreciated that the housing or active layer of cathode will also be slowly deteriorated away by the formation of oxide coating through the galvanic eflect, but the housing or active layer carried thereon can be made sufficiently thick that this slow process is unimportant as compared to the anode damage mentioned above. In addition, it will be appreciated that housings made according to the invention may be fabricated quite easily and inexpensively.

The operation achieved by the galvanic effect is believed to take place substantially as follows: During the oif period of the cell, oxide coatings form on the smooth cathode surface through the galvanic effect and build up to an amount sufficient that they will assist in the removal of scale as they themselves are dislodged from the surface of the base metal. This dislodgement tends to occur during the on operation due to the physical action provided by the turbulence of moving water and, more important, by the production of hydrogen gas on the surface of the cathode. In this way, the scale is removed as it is formed during the on period.

In order to assist and control this galvanic action, it is preferred to utilize the circuit illustrated in FIG. 1. As there shown, an alternating current is provided by any suitable source 36 through lines 37 and 38, with one of the lines containing a switch 39 and a fuse 41. This line then passes through a clock timer 42 or other control device that will provide the desired line output at 43. When control device 42 and switch 39 are on, relay 44 is actuated to the position shown in phantom in FIG. 1, and current is supplied to the primary coil 46 of transformer 47. Secondary coils 48 and 49 are then each operative to pick up a half wave of the alternating current which will pass through silicon diodes 51 contained in lines 52 and 53 and thence to the cathode. Anode lead 54 provides the other tap for direct current to the anode and may be equipped with an ammeter 56 as shown.

When the cell is switched to the off" position, either through the switch 39 or the control device 42, relay 44 moves to the position shown in solid lines and provides a short circuit between the anode and cathode through lines 57 and 58, as shown. With this load, the cell functions in a manner similar to a battery during this off period and builds up the oxide coating through the galvanic effect mentioned above. The short circuiting system is particularly valuable in increasing this galvanic action which occurs during the off period, and therefore a circuit of this nature is preferred. In the absence of the short circuit provided, it is seen that the galvanic effect is operative through the high resistance circuit including the rectifiers 51 and transformer secondary coils. Thus, the short circuit provides an increase in galvanic or battery operation. However, a complete short is not always satisfactory, when utilizing the active cathodes of this invention, and the desired control is provided by a variable resistor in the short circuit. Thus, as here shown variable resistor 55 is provided in line 57.

It will also be appreciated that the cell will only operate when electrolyte is present between the anode and the cathode and this will be provided in accordance with the use designed for the particular cell. In FIG. 1, there is a diagrammatic illustration of the use of the cell in a system for chlorinating a swimming pool 59. Briefly speaking, the operation includes the use of a conduit or pipe 61 which will draw liquid from the swimming pool and recycle it thereto. Typically, this conduit could be the conduit utilized in the filter system of the swimming pool. As shown in FIG. 1, the conduit contains a filter 62 upstream of a pump 63 which in turn is upstream of the electrolytic cell 11 so that the effluent from the cell 11 is returned directly to the swimming pool.

Suitable amounts of chloride ion are added to the swimming pool water in the form of sodium chloride, and preferably sutficient salt is added to retain the salt content above about 0.4% in order to achieve good descaling in the system here shown. Control for the system is provided by the clock timer 42 or by other suitable means. A more complete description of a system suitable for chlorinating swimming pools is shown in FIG. 5, and discussed in detail hereinafter.

Since the preferred conduit includes a pair of silicon diodes suitable for rectifying the alternating current, the electrolytic cell 11 preferably includes these diodes in mounted position thereon. As shown in FIG. 2, a terminal block 64 is securely welded, brazed or otherwise secured to the housing 12 and contains a pair of wells 66 in which the silicon diodes fit, with the diodes being connected on one side to the main body of the terminal block and on the other side to lead wires 52 and S3. The entire assembly is fit into the well with suitable insulating materials such as a ceramic insulating material. As here shown, the terminal block is made of copper, and line 58 is simply attached thereto to allow reverse flow in the short circuit system mentioned above.

As indicated above, the more active metals are better at handling scale problems than the less active metals for the cathode surface. However. it will be appreciated that highly active metals, and particularly those having soluable oxides, will not be operative because of the reaction thereof with water. In fact, all of the metals above hydrogen are theoretically capable of reacting with water, but

do not do so because of protective oxide coatings. Ac-

cordingly, metals such as aluminum form protective oxide coatings in aqueous solution and the aluminum does not displace hydrogen from water. Nevertheless, the aluminum is amphoteric and in the presence of strong alkali the oxide forms soluable aluminates. Accordingly, it is well known that aluminum will react to displace hydrogen in strong alkaline aqueous solutions such as sodium hydroxide.

Since the cathode of the present invention produces sodium hydroxide as well as hydrogen during the on time and since the metals utilized in this invention have extremely high activity constants, it did not appear very likely that these materials would stand up very long under the operating conditions of the electrolytic cell. However, it has been found, quite unexpectedly, by experimentation that the metals incorporated in this application stand up quite well. It is not understood exactly why these metals are capable of relatively long lives under proper operating conditions as electrolytic cells in saline solutions, but the following examples will illustrate test results indicating that they do.

EXAMPLE 1 An electrolytic cell was constructed according to the embodiment shown in FIGS. 1 through 4 except that the housing was entirely stainless steel and was coated on its internal surface with a layer of zinc of 0.0005 inch. The cell was utilized in a normal pool installation and found to be operative for a period of two months. This actual operative test shows a natural rate of zinc loss as the cathode of about one mil per four months. Accordingly, excellent periods of operation may be obtained by utilizing larger thicknesses.

EXAMPLE 2 The procedure of Example 1 was repeated except that the amount of zinc placed in the cathode area was 0.007 inch. After six months of actual operation, the cell was still operating satisfactorily.

EXAMPLE 3 (a) A cell is made according to the embodiment of H68. 1 through 4, except that the housing 12 is constructed entirely of zinc. In view of the data given in Examples 1 and 2 above, excellent operational results are expected.

(b) The electrolytic cell of the embodiments of P165. 1 through 4 is cast with a ,3 inch layer of zinc over a stainless steel housing on the inner fiat walls 13 and 14 thereof. In view of the data given above for Examples 1 and 2, excellent life in actual operation is expected for this cell.

EXAMPLE 4 A test cell was made utilizing a magnesium strip as a cathode and a platinum anode in a brine solution similar to the brine solution utilized in chlorinating swimming pools. The magnesium and platinum electrodes were shorted out and the cathode examined after four months. On this test, magnesium was still in excellent condition with the uniform surface and no pitting or visible loss. Accordingly, it is believed that magnesium plates are also suitable for electrodes constructed according to the invcntion.

EXAMPLE 5 The procedure of Example 4 is repeated except that aluminum is utilized in place of magnesium. Similarly good results are obtained.

From the above examples, it is seen that the metals of the class consisting of zinc, magnesium and aluminum exhibit unexpectedly good resistance to corrosion under the operating conditions of electrolytic cells to be utilized in the chlorination of swimming pools by electrolysis of sodium chloride solution. Since these metals are all similarly related, and fit rather closely together in the electromotive series, it is believed that the invention is equally applicable to all of the metals. In addition, it is believed that aluminum and magnesium would make excellent housings and serve as the cathode by replacing housing 12 with such metal. In order to maintain excellent strength, it is believed that metals such as stainless steel should be utilized with the housing and coated with at least, say, 0.01 inch of line for excellent results utilizing zinc as the cathode. However, it will be appreciated from the data given in Examples 1 and 2 that lesser thicknesses of zinc will also be valuable.

It will be noted that the range of the electromotive series between zinc and magnesium also includes manganese, and it is believed that manganese will also give good results by reason of its position and the nature of its oxides. However, manganese provides dark unsightly oxides, and for this reason it is preferred not to utilize manganese as the cathode material.

Referring again to the drawing, there is shown in FIGS. 5 through 9 a system for chlorinating a swimming pool utilizing different forms of electrodes, but which are constructed according to the invention. Thus ElG. 5 shows a swimming pool 59a comprising a fluid line 61a in fluid connection with the pool 59a at 67 and 68 and containing an electrolytic cell 11a therein for the electrolytic production of chlorine. The system also includes a pump 63a, and filter 62a in advance of the pump and accumulator trap 69 downstream of the electrolytic cell for removing scale formed in the cell from the line 61a.

The preferred order of components for line 61a is illustrated in FIG. 5, where the filter 62a is nearest the inlet portion 67 to protect the pump from entry of any foreign materials, and the cell 11a is downstream of the pump so that the highly chlorinated stream will not pass through the pump. The accumulator trap 69 is positioned downstream of cell 1111 in order to collect the calcium scale formed in the cell and moved downstream therefrom by the moving current of Water in the supply line 61a. The filter and pump may be any conventional filter and pump system suitable for use in swimming pools.

As here shown, the pump may be an electric pump supplied from conventional current sources through supply lines 71. This supply line 71 goes through a control board 72 which provides suitable switching and rectifying units as shown in FIG. 1 whereby conventional line current from any suitable power source such as source 36a may be rectified into direct current for the operation of the electrolytic cell and also supply current through suitable switches to operate the pump and a heating element in the cell when such heating element is provided. Control unit 72 is also provided with a suitable clock timer 42a for automatic operation that can be set to continue operation in the absence of adjusted manual operation.

The electrolytic cell 11a is constructed to contain the novel cathode of this invention, which is capable of discarding calcium scale from the surface thereof to solve the problems heretofore occurring when the build-up of calcium scale prevented proper operation of the cell. In addition, the cell is formed for simple internal visual inspection.

Thus, as shown in FIG. 6, cell 11a comprises a transparent tubular housing 73, a pair of end fittings 74 and 76 which have recesses 77 therein adapted to receive the ends of the housing 73, and assembly bolts 78 for drawmg the two fittings together and sandwiching the housing therebetween. Suitable sealing gaskets 79 are provided in recesses 77 to seal the unit. With this construction, the unit may be easily disassembled for service or replacement of parts. The transparent housing is preferably made of glass in order to provide the desired physical properties and give a surface which is easily cleaned. However, it will be appreciated that other transparent materials such as certain plastics may be used, if desired.

The plastic fittings 74 and 76 also provide an insulating barrier so that any potential in the electrolytic cell that might otherwise be present at the ends of the cell do not cause a shock hazard or other problems; Accordingly, these fittings are built long enough that they may be attached to metal pipes with minimal potential in the electrolyte at their distal ends from the cell. In this connection, it is preferred to utilize rather low voltage such as say 12 to 18 volts in the cell.

In addition to the basic structure of this cell, there is provided a cathode 81 which is preferably cylindrical or rod shaped and centrally disposed within the transparent housing 73. An anode 82 is also provided in juxtaposed position to the housing 73 and is preferably disposed in opposed position to the cathode so that uniform current densities are provided throughout the interior of the cell.

An important feature of this invention is to provide the anode 82 in close proximity to the transparent glass housing 73 so that the hydrochloric acid and any other acid formed in the vicinity of this anode will keep the glass clean at all times and positively assure the ability of the operator to visually inspect the interior of the cell. In this connection, it is not only important that the housing be transparent, but it is also important to provide an anode which may be seen through. Accordingly, we prefer to utilize a mesh-like anode having openings therein with the entire anode sleeve-shaped to fit within the housing as indicated above. In this way, substantially all of the water flowing through line 12 passes through the annular space between the cathode and anode.

A typical anode having openings for viewing is constructed of expanded wire. In order to render the anode capable of making chlorine over a suitable period of time, it is preferred to construct the anode from platinum rolled onto tantalum. Such a product is manufactured by the Texas Instrument Company and is readily available. Thus the anode also has a platinum surface which is resistant to acids and chlorine and capable of long continued operation. Suitable platinum substitutes may also be used, if desired, such as iridium and platinum-iridium alloy.

As indicated above, it is preferred to locate the cathode 81 along the central axis of the electrolytic cell so as to provide a substantially uniform distance between the cathode and the anode and maintain a substantilally uniform current density within. Thus, the cathode may be tubular shaped as shown in FIGS. 5 and 6, or it may be in the shape of a helix shown in FIG. 9, or it may be in the shape of a relatively narrow flat strip adapted to fit in the central portion of this cell. Alternatively, it will be appreciated that the cathode could be broken up into a number of smaller cathodes and in such a case these would form a substantially elongated cathode position along the axis of the tube when all of the cathodes are considered together.

The first requirement for the cathode in a cell of this nature is the utilization of a metal cathode having an active surface containing a metal of activity between zinc and magnesium inclusive in the electromotive series. It is also valuable to provide an especially smooth surface 83 whereby metal oxides formed on the cathodes may be sloughed off from the cathode surface along with the scale to effect removal therefrom.

The operation achieved by the galvanic effect takes place as described above, with bits of scale such as the scale 84 peeling off the surface 83 of cathode 81 as shown in FIG. 8.

While scale may be removed through the galvanic action which provides easily removable oxide coatings, it is also sometimes desirable to provide heat at the electrode so as to condition the scale as it is laid down thereon and render it easier to remove. A certain amount of heat is inherent in the operation of the unit and whatever heat is provided by the electrical energy dissipated in the cathode will be to advantage. However, when the scale problem is especially severe, it is sometimes desirable to provide an auxiliary heater. This heater causes the scale adjacent to the electrode surface to dry and form a hard scale. This hard scale will flake off easily and provide scale flakes which will be removed from the system and also render the water softer as explained above. When the heat is minimal, the scale tends to lay down in a comparatively wet form, and this wet scale is harder to flake off. In addition, the wet scale tends to redissolve easily and reharden the pool water.

Whether it is necessary to provide heat in addition to the galvanic effect described above will depend somewhat on the nature of the water used in the swimming pool and the extent of the galvanic action as explained above as well as the mechanical factors involved in the removal of scale flakes. These mechanical factors not only include the turbulance of the water and the formation of hydrogen, both of which will vary with different systems, but also depends upon the expansion characteristics of the cathode which are considered to be important.

In other words, the alternate expansion and contraction of the smooth cathode surface which is obtained during the alternate heating and cooling that the cathode undergoes between operation and non-operation, and particularly where a heater is used, increases the ability of the cathode to shed calcium. This expansion may be substantially linear as in the embodiment of FIGS. 5 through 8, or it may provide a rather large change in curvature such as is encountered in the embodiment of FIG. 9. It should also be appreciated, that some change in curvature will also occur in the embodiments of FIGS. 5 through 8 through the alternate expanding and shrinking of the circumferential cylindric surface. However, the use of. the helical electrode of FIG. 9 or other highly changing surfaces such as a bimetallic strip, will give excellent changes in curvature with respect to changes in temperature that will greatly assist in the removal of the scale.

Referring again to FIGS. 5 and 6, it is seen that the cathode 81 contains a smooth surface 83 on the outer surface of a tubular member with a heater 86 held within the tube in conventional manner. The sleeve then serves as a cathode and has a L-shaped holding piece 87 with lead wire 88 wired thereto in much the same fashion that lead wire 89 is wired to the anode 82. Lead wires 88 and 89 are connected to a suitable direct current source contained in control unit 72 as explained above. Heat for the heater is provided through supply line 91 which may be connected to the conventional power source 36a through suitable switching means on the board 72.

The embodiment of FIG. 9 is similar to that of FIGS. and 6 except that a different form of cathode 11b is shown. In this embodiment, the cathode 11b consists of a helical strip of metal 92 of the class herein defined and having a smooth surface 93. This strip 92 is suitably attached by welding or soldering or other means to a holding tube or piece 94 that extends through the housing in a similar fashion to the tube 87 and has the lead wire 88 connected thereto. In the embodiment of FIG. 9, no heater is shown, but it will be appreciated that a heater could be provided with this embodiment also, if desired. It should also be appreciated that other means of changing the curvature such as a bimetallic strip or other known elements may be substituted for the unit shown in FIG. 9, and it is not considered necessary to illustrate all of these variations, because they are well-known to those skilled in the art.

In embodiment shown in FIG. 5, an accumulator 69 is laced in the supply line 61a downstream of the cell 11a to collect the scale sloughed off from the cathode in the cell. Although this accumulator is optional to the operation of the basic invention, it is considered advantageous because it assists in keeping the swimming pool water clean and in achieving the beneficial result of calcium removal which in turn provides softer swimming pool water.

As best seen in FIG. 5 this accumulator comprises a housing 96 having a baffle 97 therein and a settling section 98 equipped with a suitable valve 99 at the bottom thereof.

In this way, the bafile causes the scale to fall into the section 98 and the scale is removed by operation of valve 99. The opening of valve 99 allows a certain amount of water to pass out through the lower portion of the accumulator to flush out the scale accumulated therein.

In a typical operation, daily cycles are used with the on time being a period of say 12 hours and the off time a period of say 12 hours. Other operations have utilized a period of hours on time and 14 hours off time, and it is believed that a wide variation may be achieved with excellent results. It is also believed that intermittent operation of the heater may have certain advantages in that the clock timer may be utilized to have the heater on during only part of the time that the electrolytic action is on. In this way, the heater may be on and off several times during a single continuous on time for the electrolytic portion of the cell. This promotes temperature fluctuation and helps in the mechanical action described above.

From the foregoing description, it is seen that we have provided an improved electrolytic cell which is relatively simple and inexpensive in construction, rugged and durable in operation, and yet provides excellent economy of expensive platinum material.

We claim:

1. An electrolytic cell for making chlorine solutions by electrolysis, comprising a housing adapted for connection in a fluid conduit,

a cathode carried by the housing and formed to provide an active cathodic surface within said housing,

an anode carried within said housing and having an active anodic surface in substantially evenly spaced relation to said cathodic surface,

said cathode being formed at its active surface thereof with a metal between zinc and magnesium inclusive in the electromotive series,

said anode being formed with a metal at the active surface thereof selected from the platinum family of metals, and circuit means for intermittently impressing an electric potential between said anode and said cathode,

said circuit means adapted to provide a short circuit between said anode and cathode when the electric potential is turned off.

2. The electrolytic cell defined in claim 1, in which the metal used for the active cathodic surface is provided by coating said metal on the inner wall of the housing.

3. The electrolytic cell defined in claim 1, in which the housing is formed from the metal utilized to provide the active cathodic surface.

4. The electrolytic cell defined in claim 1, in which the cathode is carried as a separate member within the hous- 5. The electrolytic cell defined in claim 1, in which the active cathodic surface is formed from a metal selected from the class consisting of zinc, magnesium, and aluminum.

6. The electrolytic cell defined in claim 5, in which the metal is zinc.

7. The electrolytic cell defined in claim 5, in which the metal is magnesium.

8. The electrolytic cell defined in claim 5, in which the metal is aluminum.

9. The electrolytic cell defined in claim 1, in which the cathode is formed with its entire active cathodic surface in a curved shape and having a smooth configuration.

10. The electrolytic cell defined in claim 1, in which the short circuit portion of the circuit means contains a variable resistor.

11. An electrolytic cell for making chlorine from chloride solutions by electrolysis, comprising a metallic housing formed to serve as a cathode and containing a section having two substantially fiat walls in substantially parallel relation for providing active cathodic surfaces in face-to-face relation within the housing,

a flat anode plate mounted in substantially evenly spaced relation between the flat walls of the housing forming the cathode area thereof, and

circuit means for intermittently impressing an electric potential between said anode and said cathode,

said circuit means adapted to provide a short circuit when the electric potential is turned off,

said anode plate being contructed with active surfaces containing a material selected from the platinum family,

and said cathode being formed with the active cathodic surfaces thereof containing a metal between zinc and magnesium inclusive in the electromotive series.

12. The electrolytic cell defined in claim 11, in which the metal providing the active cathodic surfaces is selected from the class consisting of zinc, magnesium, and aluminum.

13. The electrolytic cell defined in claim 12, in which the cathodic metal is present on the inner walls of the housing at the active cathodic position in the form of a layer of metal afiixed firmly to the housing.

14. The electrolytic cell defined in claim 13, in which the metal is zinc.

15. The electrolytic cell defined in claim 12, in which the housing is substantially entirely formed of the metal serving to provide the active cathodic surface.

References Cited UNITED STATES PATENTS 2,864,750 12/1958 Hughes, IL, et al. 204-228X 3,222,269 12/1965 Stanton 204272X 3,282,823 11/1966 Richards 204-272 3,481,857 12/1969 Gray 204272 JOHN H. MACK, Primary Examiner D. R. VALENTINE, Assistant Examiner U.S. Cl. X.R. 204242, 292

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