IL35237A - Metal oxide electrodes - Google Patents

Description

Metal electrodes SHAMROCK 33413 OXIDE ELECTRODES ABSTRACT OF THE DISCLOSURE electrode comprises a itanium substrate at least partially coated with a solid solution titanium dioxide and at least one oxide from of tungsten and The electrodes are particularly useful as anodes for the is of alkali halide BACKGROUND OP THE INVENTION A wide variety of materials have been known over the years for use as particularly in electrolytic Because of its low cost and electrical graphite has seen particularly especially as an anode material in cells for the electrolysis of alkali metal halide most particularly fo the production of chlorine and is not without its the most important of which is its relatively poor resistance to the corrosive conditions existing within most electrolytic notably mercury and c For this reason a number of other materials have been proposed for use as In one group may be considered such materials as lead dioxide and platinum While these materials exhibit generally favorable electrical and electrolytic they are not sufficiently resistant to the corrosive actio of most cells and for this reason are not of great commercial particularly for the electrolysis of alkali metal halide another group are the more recently proposed dimensionally stable anodes which consist of an electrolytic lly active precious precious o precious metal oxide coating o a valve notably These electrodes effective in that they exhibit favorable overvoltage have a low electrical resistivity and for the most part are resistant to the conditions o these stable anodes have the rather serious drawback that they require substantial amounts of precious as their name are extremely expensive and in limited the ultimate commercial success of these precious dimensionally stable despite their favorable may be limited owing to the economic considerations involved in using such a rare commodity as a basic Hot only is there the consideration of capital investment in the materials for forming the anode but it must also be taken into account despite their even these anodes have a finite wear rate which means that the anodes must eventually be thereby requiring further investment in precious metals STATEMENT OF Therefore it an object of the present invention to provide an electrode of good dimensional stability and having favorable electrical electrolytic which electrode is constructed of relatively inexpensive This and other objects of the present invention will become apparent to those skilled in the art from the description and claims which electrolytically active coating in the form of a solution of dioxide and at least one oxide selected from the group consisting of tungsten and vanadium Such an electrode is characterized by its good stability as evidenced by its resistance to the corrosive effects of an alkali metal its excellent electrical conductivity as evidenced by its low resistance to the passage of current and its good electrolytic activity as evidenced by its ability to discharge chlorine from an aqueous alkali metal It is further and importantly characterized by a relatively wide spread in the potentials at which chlorine and for are thereby indicating an ability to operate at improved chlorine DESCRIPTION OP PREFERRED EMBODIMENTS The term when used throughout the speci and claims to refer to the material of construction or of the electrode intended to include both titanium and titanium alloys as well as titanium and titanium alloys having a core of a more electrically conductive such as copper or Any conventional form of structure may be solid or flat or slotted or The novelty of the present invention relates primarily to the nature and identity of the electrolytically active coating applied to at least a portion of the surface of the titanium This coating should contain at least a portion of a solid solution of titanium dioxide and at least one oxide selected from the group consisting of tungsten titanium dioxide crystal lattice and substituted with molecule of one of the foregoing metal Mixtures of oxides are also It found that of the group set forth hereinabove fit particularly easily effectively into the titanium crystal owing to their similar crystal structure and other The solid should have a titanium d other oxide atomic ratio of from 10 si preferably owing to the properties of the titanium it is only necessary that a portion of the surface of the be coated with the electrolytically active in practice it is easier and often more effective if the entire useful surface of the electrode is Typicall th s coating should applied at rate of from 10 per of anode surface on a basis Such a rate of application gives an optiisum and useful li fo an anode to be used in electrolysis of alkali metal halide it will be appreciated that other processes may require a heavier or lighter coating to obtain optimum While a number of methods may be used for applying the solid coating to the titanium it will be appreciated that these methods must be carefully chosen in order to insure that a solid solution is in fact Anodes forme entirely from mere physical mixtures of as opposed to solid solutions will not have lasting electrolytic activity and will wear illustrative and preferred method of applying the coatings of the present invention is by painting a solution of salts of the respective metals onto the surface of the titanium the salts to the proper solid solution of The temperature to which the painted titanium substrate is heated will determine the degree of formation of the solid solution and this temperature will vary somewhat for each metal the exact determination of this factor being well within the skills of those in the It is not required that conversion of the salts to a solid solution be effective since even a limited degree of solid solution formation is quite The degree of conversion to the solid solution will however have a bearing on the useful life of the It been found that it is desirable for the solid solution coating to be formed in a number of steps than one thick Use of a coating technique in which the coating is built up to its final thickness through the application of a number of thin results in a coating containing the largest percentage of the desirable solid solution form of the It appears that formation of this solid solution is by the proximity of the titanium metal the presence of rutile titanium For this reason slow application of a number of coats insures that each successively applied coating will be formed in proximity to the required titanium or rutile hence resulting in optimum coating As discussed and in addition to all the inherent advantages of a dimensionally stable electrode such as reduced capacity for operation at higher minimum of attention in reduced contamination of electrolyte and product the electrodes of the present invention are good electrical conductors the chlorine that the potential at which chlorine is alkali chloride is at least as low and often lower that of conventional graphite A further advantage of the present as compared to conventional dimensionally stable is the wider difference between the potentials at which chlorine and oxygen are That is to the voltage spread between the potential at chlorine is discharged and potential at which oxygen is discharged at an electrode of the present when employed as an anode in an alkali chloride is greater than the spread obtained using a titanium metal dimensionally stable The significance of this factor is obvious in tha less current will be wasted producing oxygen in the cell thereby resulting in greater chlorine efficiency and reduced contamination of the chlorine with In order that those skilled in the art may readily understand the present invention and certain preferred embodiments by which it may be carried into the following specific examples are 1 A titanium disc is prepared for coatin by degreasing in etching in hydrochloric acid at and finally rinsing with water and The titanium disc is then given a thin by of a composition containing one part parts by HG1 aqueous parts parts anol and parts Following application of this the disc is heated to for 7 minutes after which the above painting and heating cycles are repeated until a total of six coats of the soli when employed as an anode in a saturated aqueous sodium chloride solution at discharges chlorine at a as compared to a saturated calomel of at a current density of A comparable potential obtained with graphite is volts While the invention has been described by reference to certain specific embodiments it is not to be so limited since certain changes and alterations may be made which are the full and intended scope of the appended insufficientOCRQuality

Claims (2)

1. CLAIMS 1, An electrode vjhich comprises a t tanium substrate bearing on at least a portion of the surface thereof an electrolytically active coating in the form of a solid solution of titanium dioxide and at least one oxide selected from the group consisting of molybdenum, tin, tungsten and vanadium oxides,

2. A method for conducting an electrolytic process which comprises using as at least one of the electrodes in said process a titanium substrate having on at least a portion of the surface thereof an electrolytically active coating in the form of a solid solution of titanium dioxide and at least one oxide selected from the group consisting of molybdenum, tin, tungsten and vanadium oxides, 3· An electrolytic process for the production of chlorine and caustic by passing a direct current between an anode and a cathode immersed in an aqueous sodium chloride solution, characterized in that the anode comprises a titanium metal substrate having a coating on at least a portion of the surface thereof, which coating comprises a solid solution of titanium dioxide and at least one oxide selected from the group consisting of molybdenum, tin, tungsten and vanadium oxides.