US 3372107 A
Description (OCR text may contain errors)
tutu-'1 3,372,107 ELECTRODE MATERIAL FOR ELECTROLYTIC PROCESSES Alfred Klein, 1265 47th St., Brooklyn, N.Y. 11219 No Drawing. Continuation-impart of application Ser. No.
278,421, May 6, 1963.. This application Jan. 17, 1964,
Ser. No. 338,327
" 'TCiaims. (Cl. 204-291) This invention relates to new and improved electrode material, more particularly it relates to new and .irnproved anode electrode materials for use in electrolytic processes possessing high electric conductivity coupled with mechanical strength, thermal stability, and resistance to chemical attack.
The present application constitutes a continuation-inpart of the application, Ser. No. 278,421, filed May 6, 1963, and now abandoned, by the present inventor, for "Electrically Conductive Metallic Ceramic Compositions and Method of Making Same."
In the electrolytic production of chlorine it has been the usual practice to employ graphite anodes. However,
the conventional graphite anode is subject to attack by aqueous salt solutions causing the surface of the anode to become extremely porous and soft. This action subsequently accelerates the disintegration of the graphite electrode. This deterioration decreases the power efficiency of the cell. Furthermore, the conventional treatment of graphite anodes by impregnating them with oils or resins have not displayed any substantial improvement over the conventional graphite anodes.
In the electrolytic production of perchlorates it has been the usual practice to employ platinum metal anodes. The economics of producing sodium perchlorate depends on the platinum metal lost in the cell. This loss occurs by two methods, chemical corrosion and erosion. In the commercial manufacture of ammonium perchlorate, sodium perchlorate is used as the starting material. Ammonium perchlorate is used for rocket propellants in solid boosters, for both space exploration and military missiles. Up to 75%, by weight of these boosters contain ammonium perchlorate.
Consequently, it is a primary obiect of this invention to provide ceramic compositions that display excellent resistance to attack by the electrolysis of aqueous salt solutions, and practical methods of making them.
There are a number of metallic materials that exhibit relatively high chemical inertness. But, nevertheless can not be used as anodes for electrolysis because they become passive to the passage of electric current. This is due to the formation of an oxide coating on the entire surface. This oxide coating allows the electrons to flow only in one direction, from the metal to the solution.
With the foregoing in mind, it is the principal object of the present invention to expound on a method of overcoming the passivity of these electrically conductive materials and still retain their chemical inertness and electrical conductivity to a high degree.
A further object of this invention is to provide an anodic composition that displays excellent resistance to attack by the electrolysis of salt solutions.
A still further object of the instant invention is to provide anodic compositions exhibiting low electrical resist ance which are most economical, efiicient and suitable for use as anodes in an electrolytic cell for the production of chlorine, hypochlorites, chlorite, chlorates, perchlorates and the electrolytic production of many organic as well as inorganic chemicals.
An additional object of this invention is to provide anodic compositions that will permit normal handling and use without cracking, chipping or breaking.
United States Patent 0 These and other objects and advantages of this invention will become apparent from the following description and claims.
This invention broadly consists of compositions of matter comprising in combination a conductive metal com= pound or metal, lead oxide (PhD) and an alkali metal silicate. These metal and conductive metal compounds are selected from the group of electrically conductive materials that exhibit relatively high chemical inertness but remain passive to electric current in a solution when used as an anode.
More specifically, a preferred composition comprised in combination an alkali metal silicate, lead monoxide, tantalum metal powder, tantalum nitride (TaN) and tantalum oxides (TaO Ta o titanium hydride, TiO- and asbestos.
It is preferred that the conductive components be a finely divided powder, although good results were obtained with mesh powder. The asbestos used is of finely divided short fibers.
Specific compositions of the anode material utilizin tantalum metal powder as the conductive component comprise mixtures within the following ranges in terms .of percentage, by weight.
Specific compositions of the anode material utilizing tungsten metal powder as the conductive component comprise mixtures within the following ranges in terms of percentage by weight.
Operable Preferred Proportions Proportions Tungsten Metal Powder 20-85 40-80 PbO Lead Monoxide 10-50 20-40 T10, Titanium Dioxide 0-10 0-5 Ashes 0-10 0-5 N agSit 5-25 5-20 TiH Titanium Hydride. 0-20 0-15 Specific compositions containing conductive metal compounds Ma-Xb (M=metal, X=non-metalH, Si, C, N, P, O, S, etc.) as the conductive component are as follows in percentage by weight.
Operable Preferred Proportions Proportions Ma.Xb (conductive metal compound powdered) 20-80 40-80 N iijsitot (water glass dry weight) 10-30 10-20 PbO (lead monoxide) 10-60 10-40 'IiO: (titanium dioxide) 0-10 0-5 Asbestos 0-10 0-5 The relationship of a to b, when b is at a maximum, is 1/2, (a='1, b=2). .When b is at a minimum it approaches zero. Therefore, if a is equal to one, b will vary from zero to two.
The foregoing materials are mixed to form a paste. It is then milled until a homogeneous mixture is obtained. Water may be added while mixing to obtain the desired consistency.
After blending, the foregoing mixtures 'are dried and heat-pressed to form a desired shape, by any of the wellknown pressure molding methods. The pressure used in fabricating the shape should be above 1000 pounds per square inch.
The mixtures are dried and heated at about 800 degrees centigrate to 1000 degrees centigrade, for about two to fifteen minutes, while maintaining 'a substantial constant pressure within the mold. The molds are com pletely wrapped in a metal foil (as aluminum foil) before heat pressing. This practice prevents excessive oxidation of the conductive component. Lower temperature or pressure produces a lower density highly porous body, thus increasing the specific electrical resistance.
After heat-pressing the mixture, the mold is allowed to cool to approximately 100 degrees centigrade before removal from the pressure mold.
The foregoing ceramic materials have been found to have relatively low electric resistances. The specific resistance ranges from 0.01 ohm-cm. and higher.
An important advantage of some of these compositions is its ability to be applied to and fired on conductive materials suitable for anodic use, i.e., graphite, titanium sheets, etc., thus forming a layer of highly chemical resistant anode material on the surface of these electrodes.
To illustrate more specifically the preparation of these compositions, the following is given.
An aqueous solution of 1.5 grams of sodium tetra silicate dissolved in 10 cc. of water was mixed with 10 grams of tantalum powder, 2.5 grams of PbO and 0.05 Til-l. This mixture was ground into a paste and then dried in an oven to form a dark gray powder. This powder was heat-pressed in a mold /2" by ,4, by at 900 degrees centigrade and 1500 pounds per square inch. After cooling to about 100 degrees centigrade the pressure was removed from the mold and this ceramic mold was used 'as an anode in a saturated salt solution at 92 degrees centigrade at a pH of 2.5 with a current density of 2 amp/in. at 3 volts. Tungsten powder can be used as a replacement for tantalum.
0.3 gram of water glass dissolved in one cubic centi meter of water was mixed with 2 grams of tantalum metal powder (350 mesh), 0.5 gram PbO (lead monoxide), 0.05 gram of titanium hydride.
This mixture was ground to a uniform paste which was then applied while wet onto the surface of a titanium stick ,4 x 1" x 6". The paste was applied to only one side of the titanium stick on an area of 1" x 1". After troweling the paste evenly on this area, this coating is dried in an oven for preliminary drying. The titanium stick is covered with aluminum foil and placed in a hot-press. This mold was heated to 800 degrees centigrade and pressed to about 1500 pounds per square inch for approximately 2 minutes. The mold was then allowed to cool The titanium stick was then removed from the mold and the aluminum foil that was cemented on the surface of the 1" x. 1" ceramic application was removed by anodic etching in 5% NaClO.
To illustrate the resistance to chemical attack of these ceramic anode compositions, the sample 1" x l" x ,5 ceramic composition pressed upon the titanium. stick was used as an anode in 100 cc. of water containing 84 grams of NaCl0 0.5 gram CaClfor a period of about 20 hours. A current density of 3 amps per square inch and 6.2 volts was used. This current density and voltage was maintained throughout the 20 hours and a temperature of 45 degrees centigrade was maintained. This solution was then tested for perchlorates and was found to contain over 90% by weight sodium perchlorate.
Graphite electrodes were coated with this conductive ceramic material in a, manner similar to the method used in coating titanium.
When tested as an anode for chlorine production from NaCl solutions, an overvoltage from 0.2-0.3 volt was observed 'at 20 degrees centigrade.
This patch of test material on the titanium and graphite anodes remained unaltered and the surface hard.
It is to be understood that although the compositions and processes have been described with specific reference to particular embodiments thereof, this is' not intended by way of limitation since changes and alterations therein may be made which are within the full intended scope of this invention, and that the use of the products is not limited to any specific application.
What I claim is:
1. A composition of matter for use as an anode in electrolysis, comprising a mixture of 20% to 80% by weight of electrically conductive components, said coriductive components being reactive metals and characterized by their possessing high chemical inertness to anodic oxidation and becoming passive when they are made anodic in salt solutions, from 10% to 40% by weight of 'an alkali metal silicate and from 10% to by weight of lead monoxide.
2. The composition of claim 1 wherein the alkali metal silicate is sodium tetrasilicate.
3. The composition of claim 1 wherein said conductive component is finely divided tantalum metal powder.
4. The composition of claim 1 wherein said conductive component is finely divided titanium metal powder.
5. The composition of claim 1 which further contains a small amount of a reactive metal compound being characterized by its possessing high chemical inertness to anodic oxidation and becoming passive when it is made anodic in salt solutions.
6. The composition of claim 5 wherein the alkali metal silicate is sodium tetrasilicate.
7. The composition of claim 5 wherein said conductive component is titanium hydride.
8. The composition of claim 5 wherein said conductive component is tantalum hydride.
References Cited UNITED STATES PATENTS 2,467,114 4/ 1949 Deyrup 106-49 2,642,364 6/1953 Beatty et al. 106-49 2,915,442 12/1959 Lewis 204-291 HOWARD S. WILLIAMS, Primary Examiner.
JOHN H. MACK, Examiner.
D. R. JORDAN, Assistant Examiner.