Patent ES-365482-A1 (ES)
Title: Electrode and coating therefor
IPC: C02F1/461
Filed: 1969-03-31
Abstract: An electrode for use in electrolytic processes comprises a base of a conductive material and a coating on at least part of the surface of the base consisting of a mixed-crystal material comprising the oxide(s) of one or more film-forming metals in a proportion higher than 50% by weight and one or more non-film-forming conductors, the base, the oxide(s) and the said conductors being chemically resistant to the electrolyte and to products of the electrolytic process. The term "film-forming metals" is defined as meaning metals which when connected as an anode in an electrolyte form an oxide coating on their surface which seals off the subjacent metal so as to bar the passage of current after a period of 3-5 minutes. The film-forming metal may be aluminium, tantalum, titanium, zirconium, niobium, bismuth and tungsten. The term "non-film-forming conductors" is defined as meaning conductors which when connected as an anode in an electrolyte do not hinder the passage of current, apart from internal resistance into or out of the electrolyte practically without losses. The non-film-forming conductors may be a mixture of a metal and the oxide of the metal, or a mixture of two metals, - or of a mixture of a metal and an oxide of a different metal. The conductor may be gold, silver, platinum, palladium, iridium, ruthenium, osmium, rhodium, iron, nickel, chromium, copper, lead, manganese, and the oxide thereof, graphite, nitrides, carbides, and sulphides. The base may be aluminium, tantalum, titanium, zirconium, bismuth, tungsten, niobium, iron, nickel, lead, alloys thereof and graphite. The mixed-crystal material may be formed by coprecipitation of an oxide of a film-forming metal with the other material of the mixture constituting the coating, the coprecipitation being effected chemically, thermally, electrically or by combination of these methods, e.g. by evaporating the solvent from a solution applied to the surface of the electrode, adjusting the acidity of the solution to form a suspension and immersing the electrode in the suspension and effecting electro-phoresis to precipitate the materials on to the electrode, preferably followed by sintering by vacuum sputtering, the base being the cathode with at least one anode of a film-forming metal and at least one anode of a non-film-forming conductor by immersing the electrode in an electrolyte consisting of a solution of salts or other compounds of one or more film-forming metals, and a soluble compound of a non-forming metal or metals or an oxide or oxides of such metals and effecting electrolysis. This electrolysis can be effected using A. C. or D. C. with the electrode as anode. Under anodic conditions hydroxides of the metals may be deposited. Such hydroxides can be subsequently sealed by boiling in water or by heating. Examples of processes in which the electrode may be used are the electrolysis of brine in mercury cells or diaphragm cells for the production of chlorine and alkali metal, the electrolytic production of chlorates, hydrochlorites, persulphates, perborates, the electrolytic oxidation of organic compounds such as liquid or gaseous hydrocarbons e.g. propylene or ethylene, the electrolytic deposition of metals, desalination of water, sterilization of water, and fuel cells. The electrode is suitable for use as an anode in cathode protection systems and as a cathode in bi-polar cells. A coating may cover at least 2% of that surface of the electrode intended to be placed in the electrolyte. The base may be pre-treated in order to clean the surface before the coating is applied e.g. de-greasing, roughening, ultrasonic vibration. The mixed-crystal material may be prepared by coprecipitation and then applied to the base e.g. by means of hammering, or by a plasma burner. The soluble compounds of the filmforming metals may be organic titanates, tantalates, niobates, zirconates. Many examples of electrodes, processes for making electrodes and applications of the electrodes are described.