Sept. 24; 1946. A, VQN |-||PPEL 2,408,116,. SELENIUN comma ELEMENTS AND METHOD or‘ MAKING THE! _ ‘ Filed July 12, 1941 sag/W0” a 2 Jé'LE/V/DE 1744/ . IN VENTOR ATTORNEY PalentedWMlHB' 2,408,116 UNITED STATES PATENT OFFICE 2,408,116 SELENIUM COATED ELEMENTS AND METHOD OF MAKING THEM Arthur von Hippel, Weston, Mass., assignor to Federal Telephone & Radio Corporation, a cor poration of Delaware Application July 12, 1941, Serial No. 402,103 10 Claims. (Cl. 148-6) ' 2 1 In the single ?gure of the drawing is shown. by way of example, a disc, partly broken away, This invention relates to processes of treating metal surfaces and products thereof, and it com prises processes wherein metal surfaces are sub iect to the action of selenidingagents to form a film including a form of selenium, presumably a metal selenium compound on the surface; it fur ther comprises processes wherein such coated sur faces are thereafter further coated with sele nium, and it further comprises the products of which may be considered as a selenium recti?er disc or a photo-sensitive element made in ac cordance with my invention. The dimensions of the disc are exaggerated in order to more clearly illustrate the component parts. This comprises a metal disc I coated with a ?lm 2 of a metal selenium compound of the 10 metal. On the upper surface of the disc is shown such processes. a selenium layer 3. The application of selenium to metals, such as Thus my invention in part can be looked upon - iron, nickel. and others, for the purpose of ' pre as the formation of a metal-selenium ?lm on the paring photoelectric cells, recti?ers, and the‘ like, metal prior to the application of metallic sele has hitherto presented many problems. Selenium metal is customarily applied by spreading the 15 nium thereto with the metal "selenide” acting as a bonding agent for bonding the metal to the molten selenium on the metal surface or other overlying selenium coating. This film also im wise producing a smooth coating on one surface. ' proves the surface tension relationship so that Selenimn, however, has a very high tension and the metallic selenium more readily spreads it is di?lcult to “wet” the metal surface with the molten selenium. As a consequence the selenium 20 smoothly over the disc. Electronic diffraction diagrams of metal surfaces “selenided” under dif layer is not uniformly spread on the disc and ferent conditions reveal different types of crys does not adhere ?rmly thereto. The problem in talline structures produced by compounds of the volves at least two factors. The ?rst is that of selenium and the metal plates. so changing surface tension relationships be Thin ?lms of metal-selenium compound can ~ tween molten selenium and the metal to be coated 25 be formed upon the metal surface in many di?er that the selenium will spread evenly over the , ent ways. One of the most convenient is that of metal. This can be realized by thoroughly clean- . ing the metal surface prior to applying the sele nium. The second factor has to do with estab dipping the metal, or otherwise treating its sur face, with aqueous solutions of selenious acid or lishing a ?rm bond of adhesion between the sele 30 a. selenate, to which in some cases nitric acid has nium and the metal. The adherence of the ?lm to the metal is of great importance in plates’ or been added. It has been previously found that an improved bond could be obtained by roughing the surface of - nitric acid. For example, one suitable solution > (for convenience called bath 1) consists of an aqueous nitric acid solution containing, in each discs to be used as recti?ers or light sensitive liter, about 252 grams of nitric acid and about cells, and hithertothere has been no satisfactory way of improving the "bond" between the metal 35 105 grams of selenious acid expressed as $802. Such a solution is approximately 4 normal in and the selenium ?lm. The metal surface on which a ?lm of the selenide is to be formed is dipped or other wise contacted with such a solution. The time discs before applying selenium thereto. However, even this rougheni'n'g does not secure a su?lciently 40 of dipping is not important, from two to ten minutes is adequate. In such a solution the metal close or ?rm bond. Moreover. it cannot be satis of the surface undergoing treatment reacts with factorily applied to base metal discs such as iron or aluminum discs which have been plated with another metal, such as nickel'or zinc, because the roughening treatment will cut through the plat ing exposing the plated metalto corrosion. selenium ions to form a metal-selenium com pound. 45 Theoretically, the reactions occurring are prob matings on metal surfaces can be made to adhere . ably as follows, using nickel as an example. When the nickel, for example, a strip or disc thereof, is immersed in the solution, the surface dling, abrasion, and the like, so that the selenium plates are not readily damaged in use. My invention is based upon the discovery that amount of nitrous oxide (NO) is also liberated and the nitrous oxide reduces selenious acid present to liberate divalent selenium ions. These selenium metal adheres much more strongly to - negative ions react with the positive nickel I have now discovered ways by which selenium of the nickel is attacked by the acid in the solu tenaciously thereto and thus I am able to prepare . selenium-coated metals which resist ro'ugh han 50 tion and nickel ions are formed. A certain metal surfaces which have ?rst been “selenided.” 55 ions to form nickel selenide, NiSe. However, the reactions actually occurring may be somewhat Thatis to say, it adheres more tenaciously to sur more complicated than this simple explanation faces which have been provided with a thin ?lm > would indicate. In any event, the nickel selenium formed from a bath containing selenium, pre sumably forming a metal selenium compound of compound is deposited on the surfaces of the the metal prior to applying the selenium metal 60 nickel strip or disc exposed to the solution. Then coating the treated metal is withdrawn from the aqueous 2,408,110 solution. washed and dried. It can thereafter be coated with molten selenium and the selenium layer thus provided on the metal is uniform throughout and adheres firmly to the base metal. The temperature during the “selenidin8" oper ation is not critical although I ?nd it advan tageous to use moderately elevated temperatures of about 50° C. to 60° C. when using the nitric 4 was generally preferable that selenates also are applicable. I do not wish, however, to be limited to the particular "seleniding” baths described above. All of them will preferably contain selenium as an acid or salt in solution, together with other ‘ constituents which will react with the metal to form metal ions thereof so that these positive ions can react with divalent negative selenium the solution at 57° C. treatment must continue 10 ions to form a metal selenium compound. Cop for a minimum time of about 10 minutes to pro per, nickel, iron, zinc, tin, magnesium-aluminum duce the desired result. If the treatment is con alloys, steels of various kinds, and other metals tinued too long, a pitting of the base metal re can be selenided as described above. sults. Before “seleniding” the surface of the metal If the above selenious acid solution is made up 15 it is advantageous to ?rst thoroughly clean it to with 5 normal nitric acid (bath 2) instead of 4 free it of any solid particles, grease, rust, and the normal then the temperature, for "seleniding” like. While this canbe accomplished in any way, nickel, can be reduced to about 45° C. for the I find it advantageous to first wipe the metal same time of treatment. with a cloth to free it of any solid particles, dust, These solutions are somewhat unstable due to 20 etc., then degrease the metal with any suitable the formation of nitrous acid. This can be over solvent for oils and fats, such as trichlorethylene, come by the addition of sodium nitrite, in an ethylene dichloride, and the like, then subject amount of about 30 grams per liter, to the solu the metal to an -electro-cleaning operation in tion to form (bath 3). At the same time the ways known to the art. Finally the thus treated temperature during the seleniding operation can metal can be washed in hot and cold water and be reduced to about 29° C. for the ten minutes of pickled in hydrochloric acid solutions, for ex treatment. ample, to remove any rust and oxidation prod If instead of 30 grams 60 grams of sodium ni ucts. Metal surfaces so treated and ?nally trite is added to the 4 normal HNOa solution washed free of acid are quite readily wetted by (bath 3A) two minutes treatment at about 29° C. 30 selenium so that homogeneous ?lms of metallic is su?lcient for producing a ?lm to which the selenium can be applied thereto but the selenium selenium will ?rmly adhere. does not adhere very strongly. But by selenium acid-selenious acid solution just described. With In the foregoing example I have illustrated treating the surface of the metal prior to the ways of practicing my invention for "selenidin8” application of the selenium, as described above, nickel prior to the application of metallic sele 35 I am able to obtain selenium-coated surfaces nium coatings thereto. The same process is used wherein the selenium metal has greatly improved when iron is to be pretreated prior to coating adherences. with selenium. Iron surfaces ordinarily require Having thus described my invention, what I a shorter dipping time than do nickel surfaces. claim is: As examples, it was found that iron when treated 40 1. In the coating of metal surfaces for the pro with (bath 1) required only two minutes at 29° duction of selenium coated plates the steps which C. and with (bath 2) only three minutes at 22° C. comprise treating the metal surface with a solu Many other metals can be provided with a tion containing a form of selenium to form a coating of a metal-selenium compound in ex metal-selenium compound thereon and there actly the same way. For example, magnesium 45 after coating the treated surface with selenium. aluminum alloys, such as that known as Dow 2. The process as in claim 1 wherein the surface Metal, can be dipped in aqueous solutions con to be coated is nickel. taining selenious acid, thereafter washed and dried, and ?nally coated with metallic selenium 3. The process as in claim 1 wherein the surface to be coated is zinc. in any convenient way. With this alloy a se 60 4. The process as in claim 1 wherein the surface lenium compound having a gray color is formed to be treated is a magnesium-aluminum alloy. but the actual chemical composition of such com 5. The process of coating metal surfaces with pound is not clearly understood. Dow-Metal is destroyed by acids so for this metal the nitric selenium which comprises the steps of treating types of solution to give satisfactory ?lms are lenium compound of the metal formed by sub Jecting the surface of metal to an aqueous solu the surface with an aqueous solution containing acid is omitted. In tests it was found that a 55 nitric and selenious acid to form a metal selenium 60% S802 solution produced a satisfactory ?lm compound on the surface and thereafter coating with a two minute treatment at 21° C. and a the treated surface with selenium. 10% S802 solution produced a satisfactory coat 6. The process as in claim 5 wherein the surface ing in three minutes at 21° C. to be coated 1s nickel. Tests alsoéindicate that the same bene?cial 60 7. The process as in claim 5 wherein the surface effects can be obtained with other metals, for to be coated is zinc. example, the results of treating zinc with three 8. A selenium-coated metal plate having a se Bath I Metal Tempera Time mm 140 Minutes ,tion of selenious acid underlying the selenium coating. s '’ C’. mseori-"i norm ‘HNOQ ......... - . Zn 1 21 %%8e0|+2 norm BNO; .......... .. Zn 5 21 1—1%NaSe04+2 norm BN0. ....... . . Zn 2 21 9. Selenium-coated nickel having a nickel-se lenium compound formed by subjecting the sur face of the nickel to an aqueous solution of se 70 lenious acid underlying the selenium coating. 10. A process of treating galvanized iron sur faces with selenious acid to form a zinc selenium compound thereon. It was found that while selenious acid (SeOa) ARTHUR VON I-IIPPEL.