Patented Jan. 21, 1947. 2,414,438 UNITED STATES PATENT of FICE 2,414,438 ELECTRoDEPoSITION OF SELENIUM Mortimer C. Bloom, Newton Highlands, Mass, as signor, by mesne assignments, to Federal Tele phone and Radio Corporation, New York, N.Y., a corporation of Delaware No Drawing. Application December 1, 1942, Serial No. 467,562 4. Claims. (C. 204-56) 2 This invention relates to the electro-deposition Another way of preparing the solution is to of Selenium and has for its object to provide a, dissolve powdered selenium in a solution of SO method of depositing metallic selenium evenly in dium hydroxide. This will form the desired so a pure form and without the use of corrosive SO dium selenide (Na2Se2). It will form, in addi lutionS. tion, sodium selenite (Na2Set4O3) which is use Another object is to attain an even and fine less for the purpose of anodic plating as the --4 grained selenium deposit on a base element which ions will pass to the cathode rather than the will be useful for a rectifier or photocell. anode. Consequently, it is preferred to use a so Selenium has heretofore been electro-deposited lution containing only the desired selenide and cathodically by the use of solutions producing O not the selenite; and the selenide free from the quadrivalent selenium cations (Se). Such a selenite can be had by the method of treating Condition is had in a selenious acid solution Con with the gas H2Se, taining an excess of acid as disclosed and claimed For the anode almost any conducting plate or in copending application Ser. No. 420,906, filed element may be used, for example, platinum and November 29, 1941, of which I am a joint inventor. 15 nickel. Deposits on carbon are even more ad In the use of that method the Set ions carry the herent. For the cathode almost any conductor Selenium to the cathode, depositing it there in can be used although one should be selected which metallic form. Unless the proper plating condi is non-reactive with the solution. Cathodes of tions are maintained, the base plate or element platinum and carbon have been found satisfac on which selenium is deposited by the cathodic 20 tory; and a mixture of carbon and Selenium is method may sometimes become corroded by the even better as the selenium in it will tend to re acid of the Solution, and sometimes the selenium plenish the solution. deposit is pitted by hydrogen released at the cath The current density through the solution is not Ode from the acid. very critical; and in general, the higher the cur In accordance with my present invention, I 25 rent the shorter is the time needed for a deposit. electro-deposit metallic selenium on an anode in It is preferable however not to use excessive cur a non-acid Solution having anions containing rents, in order to avoid the evolution of oxygen. Selenium in the negative valence, thereby avoid A current density of 10 amperes per Square foot ing the tendency toward corrosion and pitting of anode surface has been found satisfactory and Sometimes encountered in an acid solution. My 30 a good deposit will be obtained in about twenty invention is practiced by immersing a conductive minutes at this density. element as an anode in such a solution. The cath The selenium deposits thus obtained can be Ode preferably contains selenium which can pass made fine-grained and will be free from all in into the Solution to replenish that used up in the purities which do not deposit anodically, and also electro-deposition on the anode. 35 from impurities which do deposit anodically but l I have found that the selenides meet the re only at different voltage and current levels from quirements for the solution. The selenides of so that being used. As the selenide solutions are dium, potassium or ammonia, and also of the less non-acid they will not tend to corrode ordinary common alkali elements, such as lithium, rubid base elements used as the anode; and there will ium and caesium may be used, as Well as alkaline 40 be an absence of pitting of the selenium deposit. selenides formed from the alkaline earth group. The selenium thus obtained may be scraped off Sodium selenide (Na2Se) is easily and cheaply and used for purposes requiring a pure selenium. obtainable for the purpose. This can be prepared On the other hand, the deposit is uniform and by passing the gas H2Se through a Sodium hy fine-grained so that it can be used as deposited on droxide (NaOH) solution. The Sodium hydroxide 45 the anode in a selenium rectifier or photocell. A solution may be of practically any strength. A counterelectrode may be applied to the selenium concentration of 100 grams of sodium hydroxide as by spraying the surface with Wood's metal in per liter of solution has been found satisfactory; a well-known manner. and both double this concentration and half this What is claimed is: concentration have also been found satisfactory. 50 1. In a process for forming an adherent fine These concentrations are not - critical. The grained coating of metallic selenium upon an elec amount of gas passed through is not critical but tro-conductor surface, the step that comprises preferably there should be used enough gas to sat electro-depositing the metallic selenium upon said urate or nearly saturate the solution with the electro-conductor as the anode of a pair of elec g2S. 55 trodes in an aqueous alkaline solution that com 3 2,414488 prises essentially a selenide selected from the electro-depositing the metallic selenium upon sai class consisting of ammonium, alkali metal, and electro-conductor as the anode of a pair of elec alkaline earth metal selenides. trodes in an aqueous alkaline solution compris 2. In a process for forming an adherent fine ing essentially potassium selenide. grained coating of metallic selenium upon an elec 4. In a process for forming an adherent fine tro-conductor surface, the step that comprises grained coating of metallic selenium upon an elec electro-depositing the metallic selenium upon tro-conductor Surface, the step that comprise said eelctro-conductor as the anode of a pair of electro-depositing the metallic selenium upon electrodes in an aqueous alkaline solution com said electro-conductor as the anode of a pair of prising essentially sodium selenide. 10 electrodes in an aqueous alkaline solution com 3. In a process for forming an adherent fine prising essentially ammonium selenide. grained coating of metallic selenium upon an elec tro-conductor surface, the step that comprises MORTIMER C.BLOOM. .