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Home , Lead dioxide

United States Patent Office 2,749,489

Patented June 5, 1956

LEAD, DIOXIDE COUNTERELECTRODE

A. C. D.C. 2,749,489. Wolts Wolts Current, applied output nafen. DRY CONTACT RECTIFIERS 5 Simon Ernst Mayer and Ronald Alfred Hill, London, 40 25 O 35 20 25 England, assignors to International Standard Electric 30 10 40 Corporation, New York, N.Y. 20 4. 50. No Drawing. Application December 4, 1950, O THALLICOXIDE COUNTER. Serial No. 199,138. ELECTRODE 20 Claims. C. 317-238) 3.7 3.4 2.3, This invention relates to alternating current rectifiers of 5 the dry contact type and to methods of making them. It is known that the of some metals behave as in making the above tests the rectifiers were arranged in semi-conductors, that is to say, the electrical conductivity full wave bridge connections. of the increases with increase of temperature and It is to be understood that, although a rectifier having that the oxides of some other metals behave in the same 20 a semi-conductor layer comprising a single oxide of metal Way as a metal, that is to say, the electrical conductivity and a counter-electrode layer having a single oxide of of the oxide decreases with increase of temperature. Ox metal, has been described, the invention includes rectifiers ides of metals in the semi-conductor class include such ox having a semi-conductor layer comprising two or more ides as dioxide, oxide and oxide and semi-conducting oxides of metals and/or a counter-elec Oxides of metals in the metallically conducting class in trode comprising two or more conducting oxides of metals. clude Such oxides as dioxide, ferroso-ferric-oxide, While the principles of the invention have been de dioxide and thallic oxide. scribed above in connection with specific embodiments, Oxides of metals in the metallically conducting class and particular modifications thereof, it is to be clearly un may be further distinguished as comprising oxides which derstood that this description is made only by way of ex go to the in electrolysis. 30 ample and not as a limitation on the scope of the invention. According to the invention an alternating current recti What we claim is: fier of the dry contact type comprises a disc or plate con 1. A dry contact rectifier consisting solely of two layers: sisting of consolidated semi-conducting metal oxide in in a base plate consisting of a consolidated powder of one or timate contact with a metallically conducting oxide. more semi-conducting metallic oxides, and a layer of one A semi-conducting metal oxide may be consolidated by 35 or more conducting metallic oxides in intimate mechanical pressing or pressing and sintering the oxide in powdered and electrical contact with one surface of said plate. form, with or without suitable admixtures and/or tem 2. Rectifier according to claim 1, in which the semi porary binding agents. conducting metallic oxide is nickel oxide. Other methods of consolidating the semi-conducting 3. Rectifier according to claim 1, in which the semi metal oxide may, however, be employed. 40 conducting metallic oxide is . In one form of construction of rectifiers according to 4. Rectifier according to claim 1, in which the semi the invention, we have employed as the semi-conductor conducting metallic oxide is . layer, thin flat discs of sintered titanium dioxide to one 5. Rectifier according to claim 1, in which the semi side of which a flat disc of lead dioxide or thallic oxide conducting metallic oxide is nickel oxide in combination is applied and retained in position by clamping. Elec with approximately 10% lead borate added thereto. trical contact with the outer surfaces of the two discs of 6. Rectifier according to claim 1, in which the semi each rectifier was made by means of colloidal , conducting metallic oxide is zinc oxide in combination deposited thereon in known manner. As will be obvious it with approximately 10% lead borate added thereto. was necessary to take simple precautions to prevent the 7. Rectifier according to claim 1, in which the semi rectifiers being short circuited by the clamps. 5) conducting metallic oxide is titanium dioxide in combina In order to form a disc of titanium dioxide, titanium tion with approximately 10% lead borate added thereto. dioxide is powdered and mixed if desired with about 10% 8. Rectifier according to claim 1, in which said conduct of lead borate. The powder, either dry or formed into a ing metallic oxide layer is in the form of a disc of com paste for instance with water, is then pressed into the form pressed conducting metallic oxide powder, in combina of a disc and, after drying if paste is used, is fired in a 55 tion with means clamping said disc to said plate. neutral atmosphere such as at about 1300° C. 9. Rectifier according to claim 8, in which the conduct for one hour. It has been found advantageous to re ing metallic oxide is lead dioxide. oxidise the surface of the titanium dioxide disc by heating 10. Rectifier according to ciaim 8, in which the conduct in-air for a few minutes at 500° C. ing metallic oxide is thallic oxide. The disc of lead dioxide or thallic oxide was formed by 60 11. Rectifier according to claim 8, in which the conduct pressing lead dioxide or thallic oxide in powdered form ing metallic oxide is a mixture of lead dioxide and thalic in a mould. oxide. In another form of construction of rectifiers according 12. Rectifier according to claim 1, in which the con to the invention, the counter-electrode layer was applied ducting metallic oxide is lead dioxide. to the surface of the sintered titanium oxide disc through 65 13. Rectifier according to claim 1, in which the con a volatile carrier medium in which lead dioxide or thallic ducting metallic oxide is thallic oxide. oxide in powdered form was mixed in suspension. In 14. Rectifier according to claim 1, in which the con one case the carrier medium comprised lacquer which, ducting metallic oxide is a mixture of lead dioxide and after drying, retained the counter-electrode in position thallic oxide. without the need for clamping means. O 15. The method of making a dry contact rectifier con The electrical properties of a rectifier made as described sisting of only two layers which comprises forming a base above can be summarised as follows: plate by consolidating one or more powdered semi-con 2,749,489 3 4. ducting oxides, and applying solely one additional layer plate is formed by adding water to the semi-conducting consisting of one or more conducting metallic oxides in metallic oxides in such amount as to form a paste, press intimate electrical and mechanical contact with one sur ing said paste into the desired shape of the plate, drying face of said plate. the shaped plate, and firing the same in a neutral atmos 16. Method according to claim 15, in which said base phere for approximately one hour at approximately 1300 plate is formed by adding water to the semi-conducting me C., and in which said layer of conducting metallic oxides is tallic oxides in such amount as to form a paste, pressing applied by mixing the conducting metallic oxides in a vola said paste into the desired shape of the plate, drying the tile carrier, applying the carrier mixture to one surface of shaped plate, and firing the same in a neutral atmosphere the base plate, and then drying the rectifier. for apploximately one hour at approximately 1300 C. 0. 17. Method according to claim 16, which includes the References Cited in the file of this patent further step of re-oxidizing the surface of the plate by UNITED STATES PATENTS heating the same in air for several minutes at approxi mately 500 C. 929,582 Garretson ------July 27, 1909 18. Method according to claim 15, which includes the 15 1,741,291 Friederich et al. ------Dec. 31, 1929 steps of forming said layer of conducting metallic oxides 1,748,012 Dooley------Feb. 18, 1930 as a separate body by pressing powdered conducting metal 1,776,217 Dooley ------Sept. 16, 1930 lic oxides in a mold, and then clamping said separate body 1,796,372 Jamison ------Mar. 17, 1931 to said base plate. 1,985,118 Van Geel et al. ------Dec. 18, 1934 19. Method according to claim 15, in which said layer 20 2,267,954 Schumacher ------Dec. 30, 1941 of conducting metallic oxides is applied by mixing the con 2,462,906 Sauerborn ------Mar. 1, 1949 ducting metallic oxides in a volatile carrier, applying the 2,465,768 Van Geel et al. ------Mar. 29, 1949 carrier mixture to one surface of the base plate, and then drying the rectifier. FOREIGN PATENTS 20. A method according to claim 15, in which said base 25 247,861 Switzerland ------Jan. 3, 1948