3,649,485 United States Patent Office Patented Mar. 14, 1972 2 3,649,485 one member of the group of elements silver, gold, iron, ELECTROLYSIS OF BRINE USING COATED nickel, chromium, palladium, platinum, rhodium, iridium, CARBONANODES ruthenium, osmium, lead, copper and manganese. These Raymond S. Chisholm, Pittsburgh, Pa., assignor to elements may be in the form of the metallic element itself, PPG industries, Inc., Pittsburgh, Pa. or its oxide, nitride, carbide, boride or sulfide. No Drawing. Filed Oct. 2, 1968, Ser. No. 764,618 The coatings of the instant invention may be applied in Int. C. C01b 11/26, B01k 3/06 various ways to provide the desired mixed coating. Thus, U.S. C. 204-95 4 Claims for example, titanium sulfide particles may be mixed with a commercial metal resinate, such as platinum resinate or 10 iridium resinate, which are manufactured by Englehard ABSTRACT OF THE DISCLOSURE Industries, Inc., and the mixture applied to the titanium Novel electrodes are described having an electrocon anode base and heated to temperatures of 400 to 600 C., ductive base and a coating applied to the base. The coat with consequent breakdown of the platinum or iridium ing consists of the sulfides, nitrides, borides and carbides resinate to the corresponding metal. In such a case the of the elements aluminum, tantalum, titanium, bismuth, amount of platinum or iridium resinate is enough to tungsten, zirconium and hafnium mixed with the metals, provide titanium sulfide in the range of 5 to 95 mole per oxides, sulfides, nitrides, borides and carbides of the ele cent, preferably 25 to 75 mole percent of the sum of the ments gold, silver, platinum, palladium, ruthenium, platinum metal plus the titanium sulfide on a molecular rhodium, iridium, osmium, nickel, chromium, lead, basis in the coating and the heating is usually conducted copper and manganese. The use of the novel electrodes under vacuum or in a gas which is inert to titanium sulfide in alkali metal chlorine cells, both diaphragm and or at least does not substantially decompose the sulfide. mercury type, alkali metal chlorate cells and other similar Suitable temperatures for this purpose are 300 to 550° C. electrolytic applications is disclosed. In like manner, sulfides of other metals, including bismuth sulfide (BiS), tantalum sulfide (TaaS), alumi num sulfide (Al2S), tungsten disulfides (WS), tungsten BACKGROUND OF THE INVENTION trisulfide (WS), zirconium disulfide (ZrS) and hafnium In recent years much research activity has centered sulfide (HtS) may be applied to metal base such as a around the acquisition of improved electrodes for elec titanium base with the above platinum type resinates in trolytic cell operation. This activity has been spurred on the same way as titanium sulfide is applied and in the by the desire to produce electrodes having long life and 30 same molecular proportions. low voltage characteristics in order to achieve substantial Coatings of metal oxide-metal sulfide and/or metal power savings in electrolytic cell operations and reduced Sulfide mixtures, such as mixtures of ruthenium dioxide, electrode and maintenance costs. The evidence of this rhodium oxide or palladium dioxide or other correspond activity is amply demonstrated by the numerous patents ing conductive oxides of a platinum group metal, or lead issued in the United States and abroad on new electrodes. dioxide or manganese dioxide, may be applied to a titani Electrodes having platinum group metals on their sur um metal base, for example, by mixing the desired metal sulfide with a solution of a resinate of these platinum faces and a base of metal such as titanium have been group metals and heating a coating of the resulting mix reported (U.S. Pat. 3,242,050). Electrodes of a titanium ture at 300 to 600 C. The oxide or metal, which forms base with material such as ruthenium oxide as a coating 40 as the resinate breaks down, forms the oxide and tends to have also been described. While electrodes of these types bond the sulfide to the titanium base and/or to provide achieve lower voltage characteristics in operation than a the base with a conductive coating suitable for the pur conventional graphite electrode in an alkali chlorine cell poses herein contemplated. for example, they are subject to some drawbacks. Loss of Where a resinate of a metal which forms electrocon coating in the case of platinum metal coating when a ductive oxides or corrosion-resistant metal is employed, the short circuit occurs is sometimes encountered. Contami amount of such resinate may be at any convenient level. nation by the contents of an electrolytic cell can lead to However, since titanium sulfide, zirconium sulfide and loss of coating surface. Poor adherence of coatings to the the like are electroconductive, the presence of both a metallic base employed is also encountered during a pro noble metal, or noble metal oxide on the one hand and a longed electrolytic operation. Since these coatings tend 50 conductive sulfide on the other, offers certain advantages. to be composed of costly materials, any loss of coating The noble metals or noble metal oxides have high con must be considered undesirable. ductivity and chemical resistance but are expensive, and In accordance with this invention novel mixtures of the combination of a less expensive metal such as titani materials are employed to provide low voltage electrolytic um sulfide permits reduction in chemical cost while re surfaces for use as electrodes in electrolytic cell opera taining the advantageous conductivity and chemical resist tions which are resistant to contamination by cell electro ance. Films containing 5 to 95 percent, preferably 25 to lytes and products and which may be firmly bonded to a 75 percent, of the titanium or other metal sulfide on the base metal with little or no tendency to lose that bond one hand, and 95 to 5 percent, preferably 75 to 25 per during electrolysis. Furthermore electrodes constructed cent on a molar basis, of a noble metal or noble metal in accordance with this invention exhibit satisfactory over 60 oxide on the other hand, may be provided. voltage characteristics and an inertness to conditions of Additionally, it is to be understood that any other electrolysis that insure long life. organic solution of noble metal or platinum group metal, In accordance with this invention an electrode is pre which compound or solution decomposes to metal or oxide pared for use in an eletctrolytic cell, particularly for use on heating, can be used in lieu of the corresponding res in alkali metal chlorine and chlorate cells by coating a 65 inate thereof. This includes the application of the afore base metal with a mixture of compounds and/or elements. said sulfides with water or organic solutions of palladium The mixture of materials affixed to the base metal is com di-n-butylamino nitrile, iridium chloride, ruthenium nitro posed of at least one member of the group of the elements Sobromide, chloroplatinic acid, etc. Typical of such solu tantalum, titanium, aluminum, hafnium, zirconium, tions is a mixture in the proportion of 20 cubic centimeters bismuth and tungsten. This member is provided in the 70 of isopropyl alcohol, 1 gram of ruthenium tetrachloride, mixture on the base metal in the form of a boride, carbide, and 20 cubic centimeters of linalool having dispersed nitride or sulfide. The novel mixture also contains at least therein any of the aforesaid sulfides. 3,649,485 3 4. In the above discussion particular emphasis has been group metal and a sulfide, boride, nitride or carbide of the placed upon the use of sulfides of the metals aluminum, group titanium, tantalum, zirconium, hafnium, aluminum, zirconium, bismuth, tantalum, titanium, hafnium and tung bismuth and tungsten to provide a low cost anode for sten, and in particular titanium sulfide. While any of the alkali metal chloride electrolysis in mercury or diaphragm sulfides of these metals may be utilized, it is also contem cells. Such anodes are light in weight, sturdy, and have a plated that carbides, nitrides and borides of these metals low chlorine overvoltage. may also be employed in preparing the novel coating mix Other anodes which may be used for the electrolysis of tures of this invention. Thus, titanium carbide particles aqueous alkali metal chloride solution to produce chlo can be incorporated in a resinate solution of a platinum rine and alkali metal hydroxide or alkali metal amalgam group metal and the solution applied to an appropriate O are those which provide an anode surface which is exposed electrically conductive base. After the base is coated with to the solution composed of silicides, borides, nitrides, the titanium carbide containing resinate, for example, a carbonitrides, and carbides of titanium, zirconium, tanta platinum resinate (7.5 percent platinum), the electrode sur lum, hafnium or tungsten. The anode may be composed face is heated to 300 to 600° C. in air to produce a coating entirely of one or more of these compounds or the sub of titanium carbide-platinum on the metal base. A similar 15 strate may be metal and the surface carbide, nitride, car procedure can be followed to provide mixtures (in the pro bonitride, silicide or boride. portions specified above for sulfide and oxide) of the car As a typical illustration, freshly cleaned titanium metal bides, nitrides, borides and sulfides of tantalum, tungsten, or titanium metal alloy containing 0.5 to 5 percent by zirconium, hafnium, aluminum and bismuth with the weight of aluminum, magnesium, molybdenum, tin, chro metals palladium, platinum, rhodium, iridium, ruthenium, 20 mium or iron, may be heated at 800 to 1000 C, in an osmium, silver, gold, iron, nickel, chromium, lead, copper atmosphere of methane which may be at a pressure of 0.5 and manganese.