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. to 10 atmospheres' methane pressure (with or without It is also within the contemplation of this invention to inert diluent gas) to cause the surface to convert to the utilize in such proportions the metals of the last enu carbide TiC or mixed carbide of the base metal. Further merated group in the form of sulfides, borides, carbides, 25 titanium metal which has been coated with carbon black and nitrides. Thus, the mixtures produced according to this may be heated to carbide forming temperature to form invention include for example, titanium sulfide-ruthenium carbide on the surface thereof. sulfide, titanium sulfide-platinum sulfide, titanium carbide Boride surfaces may be obtained by heating the tita ruthenium carbide, titanium carbide-ruthenium sulfide, tan nium metal anode base in contact with diborane, and talum sulfide-platinum sulfide, tungsten carbide-ruthenium 30 nitride surfaces by heating the metal in an atmosphere of sulfide, titanium sulfide-ruthenium oxide, titanium sulfide nitrogen or ammonia at a nitrogen, ammonia or diborane palladium oxide, titanium sulfide-rhodium oxide and other pressure of 0.1 to 10 atmospheres with or without inert similar mixture of compounds of the group platinum, diluent gas. palladium, rhodium, iridium, ruthenium, osmium, silver, Tantalum, zirconium, hafnium and tungsten anodes may gold, iron, nickel, chromium, lead, copper and manganese 35 be coated in the same Way using these metals in lieu of the mixed with one or more of the borides, carbides, nitrides titanium metal substrate. and sulfides of aluminum, titanium, tantalum, tungsten, In a further embodiment, carbon or graphite may be hafnium, zirconium and bismuth. used as the anode substrate, and is coated with an electro In applying mixtures of the metals of the two groups conductive coating which is highly resistant or effectively disclosed herein in the form of nitrides, carbides, sulfides 40 inert to the corrosition and/or erosion which tends to and borides, water, toluene or other organic and inorganic occur when it is exposed as an anode in electrolysis of an liquid medium can be employed to slurry the desired par alkali chloride such as sodium or potassium chloride ticles and the particles can be painted on the electrode such as the mixtures described above. Metallic platinum, surface to be coated. Subsequent heating to temperatures palladium, ruthenium, rhodium or other platinum metal, of 250 to 600 C. to evaporate solution results in firm or the corresponding oxide thereof such as ruthenium adherence of the particles to the electroconductive base dioxide or palladium dioxide may be applied above or in used. To improve adhesion a small amount of binder such admixture with titanium dioxide, silicon dioxide, zirco as silicic acid solution, sodium silicate-titanium hydroxide nium dioxide or magnetite to the graphite or carbon base. or titanic acid in water may be added to the slurry before These coatings may be applied by metal spraying, paint its application to the base. Also resinates of titanium, sili 50 ing, chemical deposition or by electrodeposition proc con, boron, or platinum group metals may be added. As SSS a further metal a molten mixture of two of the metal For example, a metal coated graphite or carbon may members, e.g., titanium and ruthenium may be sprayed on be heated to 400 to 600 C. in steam to form the corre the anode substrate. Then the metal mixture may be sponding oxide thereof. Also the carbon or graphite may heated in sulfur vapor, HS, diborane, nitrogen, methane be thoroughly coated and surface impregnated with a or the like to convert the surface at least partly to sulfide, solution of a resinate of a platinum group resinate such as boride, carbide, nitride, etc. When platinum is so applied, ruthenium resinate and then heated in air at 300 to 500 it usually remains in metallic state with the titanium or C. The sulfides, nitrides, carbides and borides of the other similar member converting as herein contemplated. With metals employed in the novel coatings, that is aluminum, respect to these mixtures, heating is usually in the absence 60 titanium, tantalum, tungsten, hafnium, bismuth and zir of air, water or oxygen to inhibit breakdown of the com conium, may be applied in the spray solutions or as resin pounds into oxides and metals. ateS. Although the above description of anodes had primar As a general rule, graphite or carbon thus coated does ily referred to titanium metal as the base substrate, it is to not have the desired stability when used as an anode in be understood that other corrosion-resistant bases, such as 65 the electrolysis of alkali metal chloride because the thin tantalum, zirconium, tungsten or the like, may be substi coatings (rarely in excess of 0.0001 inch and often in the tuted for titanium metal and anodes provided according range of 0.00001 inch or below) flake off the anode dur to the above disclosure. Especially advantageous anodes ing electrolysis. may be obtained using conductive metal oxides, such as This may be prevented or suppressed by impregnating lead dioxide, manganese dioxide or magnetite, either as a 70 the graphite or carbon or treating the surface thereof with base or as an undercoating on a metal base such as tita a hydrophobic sealant or an agent which renders the car nium, chromium, tantalum, lead, stainless steel or other bon, or graphite surface hydrophobic or water-repellant. metal base. This oxide base or undercoating may then be The graphite or carbon anode base may be of the same coated with ruthenium oxide or other conductive oxide of carbon which is now conventionally used an anodes in a platinum group metal or with platinum or other platinum 75 alkali chlorine cells. In its unimpregnated state, it is por 3,649,485 5 6 ous. As herein contemplated this porous anode is ren EXAMPLE I dered hydrophobic or water repellant before and/or after application of the electroconductive coating. Thus, the A coating composition is prepared by mixing toluene anode comprises a hydrophobic or non water wetting or solution of 3.75 grams of platinum resinate (7.5 percent water repellant base with the resistant electroconductive platinum by weight), 1 gram of titanium sulfide and 4 coatings discussed above disposed on the base. grams of toluene. The titanium sulfide is thoroughly mixed To impart hydrophobic properties to the carbon it may in the toluene-resinate mixture and the resulting mixture is be subjected to the action of methyl trichlorosilane, vinyl painted on a titanium strip which is prior to painting, trichlorosilane or other chlorosilane containing up to 6 pickled in HCl solution. The painted surface is heated in carbon atoms, usually in the vapor state and at tempera 0. air to 450° C. for a period of 1 hour. The procedure is tures up to 200° C. Also, the graphite or carbon may be repeated five times to provide a tightly bonded coating of impregnated with a liquid silicone resin, such as methyl titanium sulfide-platinum to the titanium base. polysiloxane. In addition, the electrode may be impreg EXAMPLE II nated with solid methyl or other alkyl polysiloxanes or sili A coating composition is prepared by mixing 0.5 gram cones, such as dimethyl silicone, phenylethyl silicone, cy 5 of ruthenium oxide and 2 grams of titanium sulfide clohexyl silicone resin, diphenyl silicone resin ethyl sili with 10 cm.3 of toluene. The composition is painted on cone resin or the like. Also, the electrode may be impreg the surface of a titanium metal strip. The strip is heated nated with solid polymers of fluoroethylenes, such as poly to a temperature of 350° C. in air. The strip is cooled, tetrafluoroethylene or polymers of vinylidene fluoride. recoated and then reheated. This procedure is followed The graphite or carbon electrodes may be impregnated 20 until five coats are applied and subjected to heat in air with solid hydrophobic or water-repellant resins by dipping at 350° C. The finished strip contains titanium sulfide the electrode into a solution or slurry of the resin, if de ruthenium oxide on the surface and is suitable for use as sired, under pressure, and then vaporizing off the solvent. an anode in the electrolysis of alkali metal chloride solu Alternatively, the solvent or liquid in which resin is dis tions. solved or suspended may itself be polymerizable. Typical 25 liquids of this type include linseed oil, methyl methacry EXAMPLE III late, methyl acrylate acrylamid, styrene, vinylidene fluo A coating composition is prepared by mixing 1 gram ride, tetrafluoroethylene or like compound containing a of ruthenium oxide, 1 gram of titanium carbide with 10 polymerizable -C=C- group. The hydrophobic or wa cm.8 of toluene. A titanium mesh strip is painted with ter-repellant resin and a polymerization catalyst are dis 30 this mixture and heat treated in air at a temperature of persed, dissolved or suspended in the liquid to produce a 350 C. for 1 hour. The process of painting and heating fluid mixture and the carbonaceous electrode is impreg is repeated five times. The electrode formed contains a nated by dipping it into the suspension, if desired, under a coating of titanium carbide and ruthenium oxide and is superatmospheric pressure. Thereafter, the impregnated suitable for use as an anode in the electrolysis of alkali electrode is heated to activate the catalyst and polymerize 35 metal chloride solutions to produce alkali metal hydroxide the solvent, and chlorine. Following impregnation as described above, the car EXAMPLE IV bonaceous electrode is coated with the novel coating mix A coating composition is prepared by mixing 1 gram tures described above. After the coating operation the of ruthenium oxide and 1 gram of tungsten carbide with anode may be impregnated with or dipped into a solution 40 10 cm.8 of toluene. A tantalum strip whose surface has of the water-repellant material in order to close pores in been previously cleaned by washing with a concentrated the coating. HCl is painted with the above mixture. The painted sur The electrodes described above may be of any conveni face is heat treated to a temperature of 350° C. for one ent construction, such as in the form of screens, grids, ex hour in air. The process of painting with the above mix panded metal sheets or rods of any geometric cross-sec 45 ture and heat treating the painted surface is repeated tion. until five coats have been applied and heat treated. The Rod-like electrodes are advantageous in some cases be electrode formed contains a titanium base with a coating cause they have two or more sides and can readily be of tungsten carbide and ruthenium oxide on the surface. coated on all sides. Inevitably some loss of the surface The finished electrode is suitable for use as an anode noble metal or oxide or sulfide or other coating takes 50 in the electrolysis of an alkali metal chloride solution to place as for example an alkali metal chlorine cell is op produce alkali metal hydroxide and elemental chlorine. erated. This causes a gradual depletion of the coating which will be observed by increase in voltage between EXAMPLE V anode and cathode. When the voltage rise becomes appre 55 A coating mixture is prepared by mixing 1 gram of ciable to make reduction in power consumption desirable, platinum sulfide (PtS2) with 2.5 grams of titanium sulfide the rod electrodes may be rotated to present a fresh Sur in 10 cm. of hydropropyl alcohol. The mixture is painted face of the coating and this may be continued until the on a titanium metal strip and the coated metal strip is coating on all sides of the rod has been consumed. By this then heated at 500° C. for 20 minutes. The strip is then means the life of the electrode is longer and interruption 60 cooled, recoated with said mixture and reheated to the of cell operation for anode change avoided. Same temperature for the same period of time. This pro As explained above, the anodes hereindescribed have cedure is repeated five times. The finished electrode has the advantage that they are dimensionally stable and re a strong, cohesive coating of platinum sulfide and tita main unaffected over a long period of time, e.g., one to nium sulfide bonded to the titanium base metal. three or more years, when used in the electrolysis of so 65 EXAMPLE VI dium or potassium chloride in a mercury cathode cell or A coating composition is prepared by mixing 1 gram in a diaphragm cell. Since they are of long life, they may of tungsten boride with 0.5 gram of ruthenium oxide in 10 be maintained at a close but essentially constant spacing cm. of toluene. The mixture so prepared is painted on from the cell cathode, with consequent power savings, 70 the surface of a titanium strip which is then subjected to decrease in plugging of diaphragms or contamination of the application of heat at a temperature of 350° C. for mercury amalgam. a period of one hour. The titanium strip is cooled, coated The following examples are illustrative of methods suit with another layer of said mixture and reheated under able for preparing the novel electrodes hereinabove dis the same conditions. This procedure is repeated five times. closed. 75 The finished electrode contains a strong, cohesive coating 3,649,485 7 8 of tungsten boride and ruthenium oxide firmly bonded graphite which has been impregnated with a toluene solu to the titanium base. tion of a polymerizable polyester of propylene glycol and a hexachloro cyclopentadiene-maleic acid adduct or 1, 4, EXAMPLE VII 5, 7 tetra chloro, 6, 7 difluoro bicyclo-(2,2,1)-5 heptene A graphite slab is impregnated with chlorinated par dicarboxylic acid such as shown in U.S. Pat. 2,783,215. affin containing 55 percent by weight of combined chlo Such solution should contain 0.5 percent by weight of rine. This slab is subjected to the action of gaseous an benzoyl peroxide based on the polyester and the impreg hydrous hydrogen fluoride to replace chlorine atoms nated graphite is then heated at a temperature of 60 to thereof and to fluorinate the surface of the graphite. The 120° C. to polymerize it to its final state of cure. Such Surface of this graphite electrode is painted with a mix O product may then be exposed to anhydrous H.F. to re ture comprising 10 grams of platinum resinate containing place chlorine atoms thereof. 7.5 percent platinum by weight in 30 cm.8 of toluene. The The electrodes produced in the manner described here electrode is then subjected to the application of heat in in in the description and above examples may be utilized an inert atmosphere (nitrogen, argon or the like) at a as the cell anodes in both mercury and diaphgram cells temperature of 250° C. for one hour. The electrode 15 used for the electrolysis of alkali metal chlorides. These is then recoated and again heat treated. This procedure electrodes are also useful as anodes for the production of is repeated five times, the final heating being at 500° C. Sodium chlorate by electrolysis of alkali metal chlorides. The resulting graphite electrode has a thin coating of Typical cells in which these electrodes may be used are metallic platinum which has some porosity. Despite its cells such as described in U.S. Pats. 3,337,443; 3,203,882 porosity, it is suitable for use in an alkali chlorine cell 20 and 3,308,047. The electrodes are also useful in the elec of the diaphragm or flowing mercury cathode type and troplating art where they are typically employed as celi has an unusually long life much longer than that of anodes. The above are typical of processes where the novel ordinary graphite. It may also be utilized as an anode of electrodes herein desclosed may be employed but it will an alkali metal chlorate cell. be obvious that they may be employed in any electrolytic 25 operation where high chemical resistance of electrodes Various other embodiments are possible. For example, is desired. Example VII may be practiced using a graphite anode While the invention has been described with reference impregnated with polymeric tetrafluoroethylene in lieu to certain specific examples and illustrative embodiments, of the chlorinated paraffin in which case the contact with it is not intended that the invention be limited thereby hydrogen fluoride may be dispensed with. 30 except insofar as appears in the accompanying claims. Further, an oxide coating may be provided in lieu of I claim: platinum metal by applying ruthenium resinate or rho 1. In the method of electrolyzing an aqueous solution dium resinate or palladium resinate in place of platinum of alkali metal chloride, the improvement which com resinate to either the fluoro paraffin or polytetrafluoro prises imposing an electromotive force between an anode ethylene. In Such a case the heating may be conducted 35 and a cathode, the anode comprising a porous electro in steam, air or air diluted with nitrogen since the fluoro conductive carbon base, the pores of said electroconduc ethylene polymer protects the graphite or carbon base tive carbon base having disposed therein an inert, hydro from danger of oxidation. phobic sealant, an electroconductive exterior surface in All of the above impregnated carbon bases may be direct electrical contact with said porous electroconductive used as such as anodes for electrolysis of alkali metal 40 carbon base and in contact with the aqueous alkali metal chloride brine. However, best results (low overvoltage, chloride to be electrolyzed, the said exterior surface com etc.) may be obtained when the above electroconductive prising at least one member of a first group consisting of coatings are applied. In either case the graphite surface aluminum, tantalum, titanium, hafnium, zirconium, bis must be sufficiently exposed to be electroconductive and muth and tungsten, the member of said first group being where the impregnant is present as a film on the surface 45 present as a sulfide, nitride, boride or carbide, and at least it should be ground off or otherwise exposed so that elec one member of a second group consisting of palladium, troconductive coating is in electrical contact with the platinum, rhodium, iridium, ruthenium, osmium, silver, graphite and can conduct current therefrom. gold, iron, nickel, chlorium, lead, copper and manganese, Also it will be understood that a mixture of toluene the member of said second group being present as a metal, Solution of ruthenium resinate containing 4 percent by 50 oxide, boride, nitride, sulfide or carbide. Weight of ruthenium with enough sodium metasilicate or 2. The process of claim wherein the hydrophobic ma cobalt ammonium silicate or other soluble colloidal metal terial is a silicone. Soluble in aqueous medium dissolved in water to provide 3. The process of claim wherein the hydrophobic ma about 5 to 25 percent silicate based on the ruthenium. terial is a polymer of an ethylenic fluoro hydrocarbon. This mixture may be applied to the graphite base, care 55 being taken to prevent segregation of the aqueous and 4. The process of claim 1 wherein the hydrophobic ma organic phases following the process of Example I. terial is a fluoro carbon. As stated above the carbon may be treated with a siloxane silicone, oils or waxy solids or alkyl chlorosilane References Cited to render it hydrophobic prior to coating. Good results 60 UNITED STATES PATENTS may be obtained using a phenyl silicone. In order to 3,276,911 10/1966 Schoeneweis ------204-290 X minimize attack of the silane treated surface or the 3,480,538 11/1969 Stuorm ------204-290 siloxane or silicone thereon it is most advantageous to ob 3,493,478 2/1970 Udupa et al. ------204-95 X tain carbon impregnated with the chloro or fluoro deriva tives of such silicones or silanes. This may be done by 65 FOREIGN PATENTS dipping the silane or silicone impregnated base into liquid chlorine to chlorinate the impregnant and if desired the 679,339 9/1952 Great Britains. surface may be fluorinated by then exposing the chlori FREDERICK C. EDMUNDSON, Primary Examiner nated base to anhydrous H2F2 in liquid or vapor state to replace the attached chlorine atoms with fluorine. 70 U.S. Cl. X.R. Also Example VII may be practiced with carbon or 204-290