2 also makes the plutonium surface passive. After the plu- 3,377,257 tonium has been cleaned and made passive in a solution ELECTROLYTIC PROCESS FOR CLEANING containing n,itrzte ions, it is washed in water and acetone. PLUTONIUM METAL Morris Kolodney, New York, N.Y., assignor to the United In order to illustrate the method of this invention but States of America as represented by the United States not to limit its spirit or scope, the presently preferred em- Atomic Energy Commission bodiment of the invention is presented in the following ex- No Drawing. Filed Apr. 28, 1948, Ser. No’~23,861 ample. 4 Ctaims. (Cl. 204-1.5) Example I This invention relates to a method of preparing metals A piece of plutonium foil, 0,5 inch square and 0.1 inch wiph clean, lustrous surfaces and, more particularly, to thick and a platinum electrode are connected as anode a method for removing the impurities from the surfaces of and cathode respectively in a Pyrex cent.a iner at room tem- plutonium objects. perature containing approximately 100 cubic centimeters Plutonium with clean, bright, lustrous surfaces is de- of concentrated (85 percent) otihophosphoric acid and 100 sirable for use in fabricating plutonium objects whioh cubic centimeters of C.P. ethylene glycol. Potential is ap- must be prepared with the plutonium in pure form and piied and the anode current density is adjusted to 0.5 am- which may not contain surface impurities such as plu- pere psr square inch. The bath is operated at room tern-, tonium oxicks. Plutonium metal compositions with clean, perature. The surfaces of the plutonium object are usually bright, lustrous surfaces which are not readily converted thoroughly cleaned with high current efficiency in about to impurities swh as oxides are also useful in neutronic 5 minutes at this current density. When the surfaces are reactors, in scientfic instruments, and the like. cleaned the current is turned off and the plutonium metal It is, however, difficmft to obtain plutonium objects with is removed from the bath. The plutonium object is im- clean, lustrous surfaces because the plutonium metal, plLL- mersed for from 15 to 60 seconds in a solution containing tonium alloys, or plutonium metal compacts containing 600 grams of ammonium nitrate per liter of concentrated a major proportion by weight phrtonium are so active and orthophosphoric acid. This immersion removes any brown the reagents which remove the impurities also excessively stain formed during the previous electrolysis znd a!so attack the plutonium metal causing a loss of the valuable renders the plutonium surfaces passive. The object is then metal and yielding a pitted surface. Morecver, even if washed successively wihh water and acetone and is thor- clean plutonium surfaces are obtained in this manner, they oughly dried. The plutonium object is placed in a cool, oxidize rapidly in air cs.using the bright surfaces to tom dry atmosphere. Under these conditions it will retain its a dull color because of the formation of plutonium oxide. clean, passive, lustrous surface. The object of this invention is, therefore, to provide a The embodiment presented in Example I is preferred because a polyhydric ahmhof such as ethylene glycol re- ?’= rapid, efficient method for cleaning the surfaces of plu- tonium metal compositions. duces the ionization and thus reduces even more the very A further object of this invention is to provide a method small amount of plutonium which is dissolved when Iplu- for removing impurities from the surfaces of plutonium tonium is made anodic in a solution containing phosphate plutonium alloys or plutonium metal compacts contain- ions in other soivents. A polyhydric alcohol such as ethyl- ing a major proportion by weight plutonium which does ene glycol also has the advantage that it is not very vola- not at the same time remove an appreciable amount of tile, it reduces the loss of salts due to the creeping of the the pure plutonium metal. solution, and it may be conveniently used in a closed sys- A still further object of ~is invention is to provide a tem. The orthophosphoric aoid and ammonium nitrate method for preparing plutonmm metal compcxsitions wi[h composition used for cleaning and making the plutonium clean, lustrous surfaces which will not readily be converted passive may be conveniently used in a closed system. to the oxides. However, despite the advantages of the embodiment Other objects and advantages of this method will be ap presented in Example I, other embodiments are, of course, parent from the following description. possible and even desirable under different conditions. For The objects of this invention are achieved by the proc- example, other polyhydric organic materials such as glyc- ess of removing the impuritim from the surface by making erol, dietbylene glycol, erythritol, sorbitol and/or like the plutonium metal bodies anodic in an ofectrolyte con- like may be used. Solvents such as water may be used taining phosphate ions. along with/or in place of the polyhydric alcohols. Sources More specifically, a solution containing phosphate ions of the phosphate ion, other than orthophosphoric acid, is p!riced in a container which may be of any material such as sodium monohydro~en phosphate, sodium dihy- which is not attacked by the electrolyte and which does dmgen phosphate, or trisodmm phosphate may be used. not absorb the solution containing the radioactive pluto- After the electrolysis step the plutonium object may be nium. For example, Pyrex gfass may be used for small washed with water or immersed in solutions containing ni- scale production while stainless steel containers are more trate ions supplied by other sources than the ammonium satisfactory for larger scale production. The plutonium nitrate in orthophosphoric acid used in Example I. For object which is to be cleaned is made the anode and a example, the nitrate ions may be furnished ,by nitric acid. metal such as platinum or stainless steel is made tbe Some of these modifications are illustrated in the follow- cathode. Potential is applied to the electrodes in the bath ing Example II which is also not intended to be limiting for a predetermined period of time. After electrolysis. all on the spirit or scope of the invention. the surface impurities such as plutonium oxide are re- Example II moved without the loss of an appreciable amount of phL- tonium but the plutonium object is usua~ly covered with A piece of plutonium foil 0.5 inch square and 0.1 inch a th,in brown film which is probably a complex compound. thick and a platinum electrode are connected as anode Most of this film may be removed by washing the pluto- and cathode respectively in a Pyrex dish containing 15 nium object in a stream of water. However, the film may grams of trisodium phosphate in 100 cubic centimeters of be conveniently and completely removed by dipping the aqueous solution. Potential is applied and the anede cur- object in a solution containing nitrate ions, as pointed out rent density is adjusted to 1 ampere per square inch. The in copending application SN. 23,864, filed Apr. 28, 1948, plutonium foil is rapidly cleaned at a high current effi- by the same inventor, now Patent 2,915,387, issued Dec. ciency. The current density gradually falls to a very low 1, 1959. This dipping in a solution containing nitrate ions value as the oxide is removed so that at the end of the 3,377,257 ,. - .. 3 h.. ,. 4 cleaning period the voltage may !be increased to 12 volts What is c!aimed is: or more without an appreciable flow of current. After 1. A proc.ass for cleaning plutonium metal composi- cleaning, the plutonium metal is immersed in concen- tions which comprises making a plutonium metal compo- ,- trated nitric acid. It is lhen washed with water, then ace- sition anodic in an electrolyte consisting essentially of tone, and dried. The metal thus treated retains its bright, 5 from 15 to 75 percent by volume concentrated oithophos- lustrous surface and does not dull when stored in a cool, phoric acid and from 85 to 25 percent by volume ethylene dry atmosphere. The method is very efficient and may be glycol. carried out without any appreciable 10SSof the valuable 2. A process for cleaning phrtonium metal composi- plutonium. tions which comprises making a plutonium metal compo- In other embodiments of the method of the invention 10 sition a.rmdic in an electrolyte consisting essentially of it is possible to use other equivalent aqueous phosphate equal parb by VOIUme concentrated orthophosphoric acid salts in which the sodium is replaced by another mono- and ethylene glycol. valent cation. The cation may be, for example, the am- 3. A process for cleaning plutonium metal composi- monium radical or alkali metals such as lithium and po- tions which comprises making a plutonium metal compo- tassium. When an electrolyte consisting of an aqueous 15 sition anodic in an electrolyte consisting essentially of solution Containing 120 grams per liter of potassium equal parb by volume concentrated orthophosphoric acid monohydrogen phosphate is substituted for the trisodium and ethylene glycol, and immersing the plutonium metal phosphate solution used in Example 11, an anode current composition for at least 15 seconds in an oxidizing solu- density of 0.8 ampere per square inch gives rapid clean- tion of the class consisting of nitric acid and a mixture of ing with high current efficiency of the plutonium metal 20 ammonium niwate in orthcphosphoric acid. object. The object can then be used or made passive by 4. A process for cleaning plutonium metal composi- the methods mentioned in Example I or II. tions which comprises making a plutonium metal compo- The time necessary for removing tie impurities pres- sition anodic in an electrolyte consisting essentially of ent on the surface of the plutonium varies with the equal parts by volume concentrated orthophosphonc acid sample. The current densities used in the examples may, 25 and ethylene glycol, and immersing the plutonium metal of course, be varied. An anode current density of from composition for about one minute in concentrated nitric 0.2 to 1.0 ampere per square inch will satisfactorily acid. clean in from 3 to 10 minutes most plutonium surfaces on References Cited which the only impurity present is plutonium oxide. UNITED STATES PATENTTS The various embodiments of the method of this inven- 30 tion have the advantage that although the impurities such 1,658,222 2/1928 Burns ------204—141.5 as oxides are removed, there is no appreciable removaf of 1,824,932 9/1931 Schermer ------252—142X the plutonium metal since the electrolytes do not appreci- 2,315,695 4/1943 Faust ------204—141.5 ably attach plutonium. 2j428,464 10/1947 Lumel al. It is to be understood that when plutonium metal com- 35 FOREIGN PATENTS positions are mentioned in the specification or in the 558,925 1/1944 Great Britain. claims, pure plutonium, or plutonium alloys, or plutonium metal compacts containing a major proportion by weight OTHER REFERENCES plutonium are meant. Metal Cleaning and Finishing (October 1931) pp. 785- Tine method also has the advantage that the rate of 40 789. cleaning can be controlled within wide limits through The Transuranium Elements, IV-14B, . National Nu- simple current adjmtments. clear Energy Series, Scaborg, Katz, Manning, McGraw- Although the conditions have been stated very specifi- Hill Book Co., New York (1949), lsted., pp. 133, 139. cally hereinbefore, because there are many possible em- REUBEN EPSTEIN, Prinrary Examiner. bodiments of the method of the invention, it is not in- 45 tended to limit its spirit or scope except as indicated in JOHN R. SPECK, WILLIAM G. WILES, Examiners. the following claims. S. F. GLASS, Assktcmt Examiner.