UNCLASSIFIED
EMI-912(DSL.) 1-5
Co no Act No, W-7«05-*n|-W
ELECTROPLATED METALS ON URANIUM
PKoto»K>» Prlco $ C ,30
M icrofilm Prico 5 3.00
Avollobl* trow *k*
J. G. Beach Offic# of TocKnicol Sorvictt W. C. Schickner Doportmtnt of Commorco C. R. Konecny WoiKiogfon 75, 0 . C . C. L. Faust
May 7, 1954
------UOAl NOIICI -----—
r»M !■>»' •• •* « " ■« * 11 — ■ • ****-
BATTELLE MEMORIAL INSTITUTE 505 King Avenue Columbus 1, Ohio
UNCLASSIFIED Cl 6
TABLE OF CONTENTS '
Page
A B S T R A C T ...... 7
INTRODUCTION ...... 7
SUM M ARY O F R E S U L T S ...... 9
Corrosion Protection of Uranium by Electroplated Metals . . 9 Aluminum Cladding Electroplated Metals on Uranium .... 14 Procedure for Plating and Diffusion Alloying of Metals on Uranium ...... * . , . IS Prodedure for Adherent Electrodeposition of Aluminum . , , 18
EXPERIMENTAL DETAILS AND DISCUSSION ...... 18
% P re p a ra tio n of Test S a m p le s ...... 18 Diffusion Alloying of Electroplated Nickel on Uranium , . . , 25 Bond S trength of E le c tro c la d M etals on U r a n iu m , ...... 25 Corrosion Resistance of Nickel-Electroclad Uranium .... 29 H e a t-T re a tin g E q u ip m e n t...... 36 Corrosion Equipment...... 36
REFERENCES 39
/■ » • > • K. 7
ELECTROPLATED METALS ON URANIUM
J. G. Beach, W. C. Schickncr, C. R. Konecny, and C. L. Faust
ElectroplaUng on o m m a ia Miftf studied •« count ction lA# of M slug-type fuel element foe tke Nonfood R e f tors and m aluminum-dmd, flat-plate foil element foe the Sanmnnak Rimer Reactor*. Tktat titetroplaung studies ufti concurrent metal lurgical timidity audita art integrated to etpeditt deielopment of on >r Eltcbodtpo tiled olnmm w , ekroauum, copper, aeon, mmgm meet, nickel, palladium, tin, and hoc a* tramum uere tnvetm otel, fo o t /actors mere fennd to influence tke eonoaton protection ei uranium by electroplated metola: omnium a off f t preparation, method of elecVo- depoutton, type end tkickneae of elecaroploted metal, and conditions o f knot treat tnf refuted to turff t alloy tke composite. Vacuum keat treatment of uranium plated uttk nickel or von form* on alloy coating. Tke allor-coated uranium reuate carrot to a is boiling motor for periods from IQO to 1000 itmea that of bore uraniom. Hot-mater a ttfk oftkia nlloycooted uranium n generally toe allied aa pit-type corrosion el arena o f do fee la originating in the uranium mttoL Thin ao-dcpoaited metola on uronaum offer little or no corrosion remit- once. Hoot treatment of aluminum, chromium, copper, manganese, tin, or sine-plated uranium did not provide corrosion re intone e. > ------4 INTRODUCTION The present Hanford slugs, jacketed with aluminum, and having aluminum filicide aa an Intermediate slug coating, have been used with outstanding success. However, there is still a possibility that the alumi num and aluminum silicide layers will be penetrated by water. Then, a uranium intcrfacial layer corrodes away rapidly. Corrosion over the entire uranium surface follows. The rapid accumulation of the corrosion product, uranium hydride!1), under the cladding can lead to rapid swelling and distortion of the slug - sometimes enough to jam and rupture the pile process tube. When a slug-cladding failure is monitored, the defective slug must be removed to avoid such operating difficulties. The safe period between (1) Reference! lined it end of the report. a. / ■■■ * monitoring such a slug And its removal is considered to be less than one hour. A cladding is desired that will resist this rapid interfacial corrosion of the uranium when the aluminum jacket is penetrated. In 1952, a program directed toward an improved, Hanford-type fuel element was initiated. Early in 1953, a program was started to develop a flat-plate fuel clement with a well-bonded aluminum cladding for the Savannah River Reactors. Application of the present Hanford canning techniques to such flat plates introduces problems not encountered with the canning of slugs. Most of the metals having properties needed in these two programs can be used only in limited amounts for cladding because of their thermal-neutron-capture cross section. Aluminum thicknesses up to 30 mils were specified as the upper limit for a slug-cladding design. The thicknesses of various other metals equivalent in cross section to 30 mils of aluminum are listed in Table l. TA&I 1. THICKNESSES O f VARIOUS METALS EQUIVALENT IN CROSS SECTION TO 30 MILS Of ALUMINUM Macro Ckom Section. Denilty, Cron Section, Thickneat, M m ! cra*/g * 104 g /c n r cm t 104 m ill tom tab 0*92 9.9 9 432 U sd ft U.S 67 144 Zirconium ll.f t 6.6 77 50.4 Aluminum a 2 .7 130 30 n s 33 7.3 205 19.9 Niobium I t 8.6 611 6 .4 Zinc 9t 7.1 694 5 .6 Germanium 195 6 .4 1,053 3 .7 Molybdenum 1S1 10.2 1,540 2 .5 boo 260 7.9 2.054 1 .9 Antimony 320 6.6 2,112 1.8 Chromium 330 7.2 2.376 1 .6 Copp.1 340 8.6 2.924 1 .3 Titanium 700 4 .5 3,150 1 .2 Nickel 460 8 .9 4,094 • 1 .0 Palladium 450 12.0 5.400 0 .7 Platinum 250 21.8 5,375 0 .7 Mangarwtc 1390 7.4 10.286 ,, 0 .4 Cobalt 3500 8 .9 31.150 , 0 .1 Silver 2400 le.ft 35.700 0 .1 Gold 2900 19.3 55.970 V <0.1 4 : f (M 9 1 Electrt deposition as a method of coating uranium offers several advantages. Many metals can be adherently plated on uranium in thinnesses not generally attainable by other cladding methods, and recessed areas of moderate dej>th can be covered. Electroplating programs were set up with two broad objectives: to determine the hot-water corrosion resistance that uranium can receive from electroplated metals alone; and to aid other studies on bending of wrought aluminum to uranium. Methods for electroplating on uranium were reported^* in 1944 and 1945. The corrosion resistance of nickel- or iron-plated uranium, when alloyed by heat treating, had been indicated(^) in 1944. Electroplated metals on uranium have received only limited attention during the interim years. SUMMARY OF RESULTS Corrosion Protection of Uranium by Electroplated Metals Diffusion-alloyed nickel-plated uranium has withstood corrosion in boiling water for 75 to 240 hr. This is the number of hours before a test sample gained or lost about l mg/cm^ and corresponds to corrosion rates between 0. 013 and 0. 004 mg/(cm^)(hr). Under the same conditions, un protected uranium was corroded with a weight loss of about 3 mg/(cm^)(hr). Thin as-electroplated nickel on uranium offered negligible protection. Once the boiling water penetrated the nickel and reached the uranium, rapid cor rosion occurred at the interface, and undercutting of the nickel took place. In a few hours, the entire uranium surface was corroding. The best corrosion resistance of nickel-plated uranium was observed for samples alloyed by heat treatment at 1250 to 1350 F. This produces beta structure in the uranium. Usually, attack in boiling water is not apparent for 24 hr or longer. The first corrosion is by localized pitting. For a set of samples, 3 by 1 by 0.1 in., nickel plated and alloyed by beta treating, the average corrosion rate was 0.009 mg/(cm2)(hr) for the first 122 hr. Thereafter, the average rates increased to 0, 17 mg/(cm2)(hr) during the next 59 hr and then to 0. 5 mg/(cm^)(hr). Failure of uranium coated with diffusion-alloyed nickel plate is not sudden or rapid. Rapid interfacial corrosion of the uranium does not take place, The break-through of a faulty fuel-element cladding probably could be detected due to escape of corrosion products in the process water before dangerous corrosion of the uranium occurred. Therefore, catastrophic rupture of a fuel element could be avoided. 10 • The curves shown in Figure l correspond to the types of corrosion and the over-all corrosion rates for various thicknesses of nickel and various conditions of alloying heat treatment. The relationship of these variables is shown by the data of Table Z t TABU 2. EFFECT OF N IC K a THICKNESS AND DIFFUSION* ALLOYING CONDITIONS ON THE BOILING-WA TER CORROSION OF URANIUM ELECTROCLAD WU H NICKEL Alloy Heal- ______Corrosion Chatactetistic*______* Nickel Treating Conditions^ Rate lor Thickness, Temperature, Time, Curve Resistance^), Hours ar Left, mils F hr Type^l hr m g /( c m 2 XhO 0.0 • • • . H 1/3 -3.0 0.6 1300 2 A 240 -0.005 1.0 1350 . 6 to 8 A 180 -0.006 2.0 1 3 % 1/12 A 180 -0.006 0.3 1250 1 B 100 -0.011 0.6 ' 1250 4 B 120 -0.009 0.6 1250 1 C 75 -0.015 0.5 500 to I000 (a) In a vacuum of leu than 10/i. (b) Curves are shown in Figure 2. (c) Hours in boiling water before weight change of 1 mg/cm2 01 sample. (d) Samples outgasscd and then vacuum scaled In Vycor or Pyre* lubes for balance o( heat treating. The type of corrosion represented by Curves A, B, and C is con sidered desirable. The corrosion resistance shown by Curve A possibly is greater than that needed for fuel elements when jacketed with aluminum. For aluminum-jacketed fuei elements, interfacial corrosion resistance is of paramount importance once the jacket has been penetrated by water. The type of corrosion corresponding to Curve G results from an accumulation of corrosion products under the nickel electrocladding. The stress exerted by the accumulated corrosion products blisters the nickel. Ultimately, the nickel plate ruptures and a rapid release of corrosion products to the water occurs. Until blistering or rupture occurs, such samples appear excellent. /. Typicol Curm Cor ration resistance of nlckel-elec traded uranium depends on the Integrity of nttoy coaling, The Integrity of the Alloy coating In turn depend# on the omnium m«Ul, the method of surface finishing! the con- dllloein of electroplating, And the conditions of diffusion Alloying. Defect# In the ursntum ourfnet metal, such as pits, stringers, nod inclusions, <*«•* discontinuities In the tlsctroplAtsd meul. These Arens, Although bridgsd during diffusion Alloying, mmnln weak points in tbs Alloy costing, And provide starting points for corrosion. Scnnll, unplntsd arena of slsctrl ent contact ere nlso dsfscts bridged by Alloying, but they seldom are the first nrsss to corrodt. An sstrsm e csss of t uranium-metal defect and the bridging by elec* tropiated meUle is shown In Figure 2. This sample had been plated with 0, l mil of nickel, diffusion alloyed st 1300 F for l hr, activated and agai » plated *Uh 0 .1 mil of nickel, followed by a flash plate of copper. Such a defect would cause pit- type corrosion of ths uranium. t f OX As polished MUSIS FIGURE 2 . AREA OF DEFECT IN AN ELBCTROCLAD URANIUM SAMPLE Uraniufo Nickel Plated (0.2 Mil). Diffusion Alloyed (1300 F foe 1 Hr), Activated. Nickel Plated (0,1 Mil), and Copper Plated 1) A aeries of 4-in. Hanford slugs was plated with nickel (0.8 mil) and diffusion alloyed in vacuum for 1 hr at 1300 F. These slugs were prepared for evaluation in the canning program at Hanford. Five representative slugs of this series were randomly selected and corrosion tested in boiling dis tilled water to confirm the postulated corrosion resistance. Because suf ficiently accurate weighing of these slugs would have been difficult the corrosion rates were calculated from the amount of uranium in the corro sion water after the test period. The average boiling-water corrosion rate was 0,003 mg/(cm^)(hr). As expected! corrosion was localised as pit-type attack in areas of defects in the uranium surface. These defects were con tinued into the electroplated metal. Since the number and site of these weak areas in the alloy coating varied from slug to slug, some differences between the individual corrosion rates would be expected. These rates are listed in Table 3. T A M 8. SOBLUJC-WATER CORROSION PJ31STANCI OP DIFFUSION-ALLOTTED NICKEL* PLAT ED HANFORD URANIUM SLUGS Corrosion-Test Period^), Corrosion Rats(c >, Slug Number^*) hr mg/(cm2)(hr) 4304*2*14 6ft 0,0048 4341*2*24^ 65 0.002ft 4298*3*30 88 0,0074 4137*1*24 136 0.0032 4173-2*0 130 0,0066 (s) Pout*Inch Hanford tlugs. lithe finished, nickel plated (0.8 mil), and diffusion tlloyed at 1300 P for 1 hi in vacuum ( Eiectrodeposited iron on uranium, when diffusion alloyed, also pro vided boiling-water corrosion resistance. However, iron rusts in boiling water and thereby complicates the evaluation of corrosion behavior on uranium , • Eiectrodeposited aluminum, chromium, chromium-iron alloy, copper, manganese, tin, and zinc on uranium were also studied. But, as deposited or heat treated, these metals offered Uttle or no promise of protecting uranium in boiling distilled water, on 14 Aluminum Cladding Electroplated Metals on Uranium Aluminum cant are used on gluts in production piles, Aluminum is used because of Its unique combination of good corrosion resistance, low thermal** neutron-capture cross section, good heat conductivity, and low cost. Since aluminum and uranium diffuse at relatively low temperatures and form weak, brittle alloys, an interfacial diffusion barrier is necessary. Electroplated metals on uranium are desirable as barrier coating because they can be easily deposited in thinnesses that are within the specified cross- section limitation. Any one of several elcctrodepositable metals appears able to serve effectively as a diffusion barrier, but nickel was emphasised in these studies. Copper was rejected because it was undercut rapidly in boiling water. The outer surface of chromium plate on uranium has not been bonded satisfactorily to aluminum. Iron plate bears further study because of its lower cross section and lower cost. As with nickel, iron on uranium can also be diffusion alloyed to provide boiling-water corrosion resistance. Zinc rapidly diffuses through aluminum. Wrought aluminum claddings are well bonded to nickel-plated uranium by roll cladding, extrusion cladding, srnd pressure bonding. Aluminum is easily pressure bonded to copper-plated uranium as well. Copper-plated aluminum is spider bonded to uranium plated with nickel plus copper. Re ported studies'^1 ^ at other sites have also shown promising results with aluminum bonded to nickel-plated uranium. Aluminum coatings have been electrodeposited from a low-temperature (300 F) fused-salt bath'*®) and two organic bathsU^* ^ ). Coherent electro deposits up to 30 mils thick are possible from the two organic baths, but only 1-mil coatings have been electrodeposited from the fused-salt bath. Formerly, aluminum electrodeposits from the organic baths were electroformed shells. Because of a recent technical achievement, alumi num can now be electrodeposited adherently on copper, iron, nickel, and steel, by use of an activation method developed in this workU*), The interfacial corrosion resistance of aluminum-clad uranium is important because of the rare instances in which the coolant water pene* trates the cladding layers. Screening corrosion tests of uranium were made in boiling water, the uranium being protected by various barrier or bonding metals under pressure-bonded aluminum. Holes were drilled through the aluminum and into the uranium to approximate cladding failures. After 24 hours, samples with beta-alloyed (l hr, 1300 F) nickel plate on the uranium showed no undercutting corrosion.. Samples with as-deposited 4 # U JO 15 nickel or aluminum silicide showed only slight undercutting corrosion. However, samples with copper showed extensive undercutting corrosion. Screening corrosion tests were made in boiling water to evaluate the corrosion resistance of various solders for bonding aluminum to uranium. As-deposited nickel on uranium undercut too rapidly to allow an evaluation of the solders. To permit evaluation of the solders in boiling water, the nickel-plated uranium samples were beta alloyed prior to copper plating and solder bonding. As a result of this precaution, evaluation of the solders was not prevented by rapid corrosion of the uranium interfacial layers. Uranium pieces were electroclad with a nickel-plus-copper barrier layer and an aluminum jacket. The resulting compacts after hot pressing at 950 F and 4. 5 tons per sq in. pressure for 5 minutes resisted corro sion in boiling water for an average of 250 hours. Other hot-pressed samples of electrodeposited aluminum on nickel, iron, or copper-plated uranium resisted corrosion for about 100 hours. These systems are being investigated further. How fast aluminum claddings on uranium are undercut by corrosion is being studied as a function of bonding procedures and barrier metals. Experimental tests are being prepared. Procedure for Plating and Diffusion Alloying of Metals on Uranium The procedure for nickel plating on uranium, as given below, is sim ilar to that reported earlier^) except for the composition of the nickel- plating bath. The conditions for heat treating are those that produce the alloy coating most resistant to corrosion with l/2 to 1-mil of nickel. 1. D escale A. Alternative methods 1. G rit b la st a. Grit, 50-mesh steel b. Air pressure, 80 psi 2. Vapor b la st a. Grit, 100-mesh Novacuiite (quartzose rock) in water b. Air pressure, 80 psi • 5. Lathe finish 4. Shaper finish 5. Machine grinding finish .11 16 II. Clean A. Chronological steps 1. Solvent degrease a. Solvent, trichloroethylene b. Contact, by wiping or vapor degreasing 2. Alkaline clean a. Bath, Anodex 75 g/l at 180 F b. Electrical current, 25 amp/ft^ cathodic c. Time, 2 min 3. Water rinse III. Activate A. Chronological steps 1. Chemical pickle a. Bath, nitric acid, 50 per cent by volume of 1. 42 sp gr acid b. T em p e ra tu re , 80 ± 10 F c. Time, 5 to 10 min 2. Warm-water rinse 3. Anodic etch a. Bath, phosphoric acid 50 per cent by volume of 1.69 sp gr acid plus hydrochloric acid 2 p e r cent by volume of 1.19 sp gr acid b. Temperature, 100 F c. Current density, 50am p/sqft d. Time, 10 min 4. Cold-water rinse 5. Chemical pickle, repeat I1LA1 6, Cold-water rinse- Electroplate A. Alternative plates 1. Nickel a. Bath composition N iS04-7H 20 « 145 g/l iter MgS04* 7H20 75 g /lite r NH4C1 15 g /lite r H3BO3 15 g/liter XXXD* 20 c c /lite r pH, 5. 5 ± 0.1 b. Temperature, 100 F c. Cathode current density (1) Strike, 30 amp/ft^ for \/Z min (2) Plate, lS'amp/ft^ d. Plating rate, 0.75mil/hr •proprietary vetting igcnt, The Harshav Chemical Company. 12 17 2. Iron a. Bath composition FeS04*7Hi0 300 g/iitcr FeClZ-4HzO 40 g/litcr (NH4)2S04 15 g /lite r H3BO3 30 g/liter Na OOCH (sodium formate) 15 g/liter Duponol ME* l g/Uter pH 4.1 to 4.2 b. Temperature, 140 F c. Cathode current density (1) Strike, 60 amp/ft2 for 30 sec (2) Plate, 30 amp/ft2 d. Plating rate, 2. 0 m ils/hr 3. Chromium a. Bath composition Cr03 400 g/liter HzSC>4 4.0 g/liter b. Temperature, 104 F c. Cathode current density (1) Strike, 600 amp/ft2 for 30 sec (2) Plate, 300 amp/ft^ d. Plating rate, 1.0 mil/hr 4. Copper a. Bath composition CuS04* 5H^O 210 g/liter H2SO4 82. 5 g/liter b. Temperature, 100 F c. Cathode current density (1) Strike, 50 amp/ft^ for 1 min (2) Plate, 25 amp/ft* d. Plating rate, 1.4 m ils/hr 5. Aluminum** a. Special precautioni (1) After activation the uranium is dried in air or alcohol and ether (2) Exclude moisture from bath (3) Use dry trap above bath (4) Bleed dry nitrogen into trap to minimine flammability of bath and moisture absorption b. Bath composition AIQ.3 332 g/liter LiH 6 g/liter Ethyl ether balance •Proprietary wetting agent. .E. 1. du Pont de Nemours & Company. Inc. **The activation using fatty acids or stearato chromic chloride is not necessary when plating on uranium itself. '*■ ■' 13 i r c. Temperature, 70 to 90 F d. Cathode current density, 10 amp/ft^ e. Plating rate, 0. 5 m il/h r V, Solid-state diffusion alloy of iron-uranium and nickel-uranium A. Conditions 1. Atmosphere in furnace, air at <10#i mercury absolute pressure Z, Time, 1 hr 3. Temperature, 1300 F Procedure for Adherent Electrodeposition of Aluminum I The electrodeposition of adherent aluminum on common metals re quires a special activation procedure for the metal being coated. Aluminum, copper, iron, nickel, steel* and stainless steel are activated as for aqueous plating and then dipped in ethyl alcohol to remove or displace rinse water; dipped in isopropyl alcohol solution of stearato chromic chloride*, drained for a few seconds; dipped In oleic acid; drained for a few seconds; immersed in the plating bath and allowed to rest for two minutes, before current is applied. EXPERIMENTAL DETAILS AND DISCUSSION Study of the corrosion resistance of electroclad uranium is an im portant part of this work. Significant effects were attributed to: the kind of electrocladding metal, the type of electroplating bath, the conditions of heat treatment to diffusion alloy the surface metals, and the homogeneity of the uranium. Preparation of Test Samples The uranium used in these studies was seldom "hand picked", but was that which was available. Generally, it deemed to be representative of present uranium metal. Samples, Z by 1 in. or 3 by 1 in., were cut from *Quilonf E. I. du Pont de Nemoun A Company, he. 1 A 19 sheet rolled to between 0,1 and 0. 2 in, thick. Fernald rolled uranium, machined to Hanford-slug dimensions, was also used. • Defects in the uranium, such as inclusions, stringers, and seams, varied from sample to sample. Since the defects could not be predicted, random selection of samples and random processing order were used when possible. This procedure helped to minimise the effect of metal variation on the conclusions. No effect of uranium metal, hot or cold rolled, or of method of surface finishing on the corrosion resistance of nickel-clad uranium could be isolated. The variation in corrosion results among samples presumably prepared in the same way was greater than that attributed to the above • variables. Surface Finishing Since thin electrodeposits cannot overcome defects in a metal surface, finishing and activation for electroplating should be designed to provide the best possible starting surface. An ideal starting surface for electro deposition would be smooth and homogeneous; free of porosity, worked metal, or other surface defects; and easily activated for adherent electroplating. The surface of the uranium metal used in these studies did not meet these specifications. As-rolled uranium has a surface scale that must be removed for uni form activation and electroplating. Mechanical, chemical, and electro chemical surface finishing have been explored. Mechanical surface finishing was preferred because it did not accentuate defects in the metal. Surface grinding, lathe turning, shaper finishing, vapor blasting, or dry grit blasting removed scale and provided uranium surfaces easily plated upon. The quality of the finish produced by any of these methods depended on the operator' a care. . Surface grinding provided the smoothest finish. The grinding tech niques are those also recommended for beryllium, thorium, titanium, and zirconium; i, e ., "soft wheel"*, low wheel-surface speeds (by use of small- diameter wheels), low table speeds, good coolant flow, and no "hogging" cuts. Improper grinding resulted in a burned, checked uranium surface difficult to cover uniformly with electroplated metal. Vapor blasting** and grit blasting*** also provided satisfactory sur faces for electroplating. Grit blasting is more economical. The presently •DeSano Alundum or Norton Crystloa. ••Novaculite 100 NV8, Vapor Blast Corporation. •"50-meih steel grit. i -15 20 used activation methods produce a surface roughness that is independent of the uranium surface finish whether vapor or grit blasted. Chemical and electrochemical finishing can be most effective only when the metal is homogeneous. Such finishing of uranium removed scale and worked metal, and produced smooth surfaces. Inclusions were selec tively attacked, however, resulting in accentuated surface defects that were difficult or impossible to bridge by a thin electroplated metal. Chemical descaling was accomplished in 50 volume per cent nitric J acid (1. 42 sp gr) at 150 F and chemical polishing in a solution of ammonium btfluoride (150 g/liter NH4 FHF) at 80 F. Electropolishing was done in a solution of 25 volume per cent sulfuric acid (1.84 sp gr) plus 25 volume per cent phosphoric acid (1.69 sp gr) at 80 F with 300 amp/ft^ anodic current density. These fluoride and phosphate treatments left passive films on the uranium. However, both types of films were easily removed by immersion in a 120 F water solution of sodium hydroxide containing hydrogen peroxide. Racking Generally, uranium samples were racked for activation-and plating with point contacts at two opposite ends of the sample. In some cases, additional point contacts were made to add mechanical stability. Stainless steel racks were protected with commercial rack-coating lacquers to mask a ll areas exposed to the processing solutions, except for the point contacts. 4 The unplated point-contact areas appear to have been adequately bridged by diffusion alloying, since these areas were seldom those of initial attack in boiling water. When these areas are the principal point of electrociadding weakness, racking and jigging can be designed to provide changing contact areas, and thereby avoid these unplated contact areas and provide over-all electroplating. Activation *^r Plating Several methods of activating uranium for plating were evaluated. The principal resulting differences were in amount of roughening of the uranium surface and the degree of adhesion of the electroplated metal. Activation of uranium for adherent electroplating-involves anodic etching in chloride solutions. This treatment leaves the uranium surface with a gelatinous salt film that is subsequently dissolved in a nitric acid 21 solution. The activated uranium surface then appears crystalline and sub sequent electroplates are well bonded. Three anodic etching solutions studied were: trichloroacetic acid, sodium chloride, and phosphoric acid with hydrochloric acid. They were equally effective. The phosphoric-hydrochloric acid solution, however, was selected for use because it is cheaper and less toxic than the trichloro acetic acid solution. The sodium chloride solution did not offer sufficient advantages to merit further development. Photomicrographs of Figure 3 show 1-mil nickel plates on uranium surfaces. The microroughness of activated uranium surfaces and the excellent microthrowing of nickel into the roughened surface are apparent. , Activation of uranium for adherent electroplating without the dis advantage of gross roughening is being explored. For a specified weight of an electroplated metal, that applied to a smooth surface should be more effective than that applied over a rough surface. The amount of uranium dissolved during activation is of interest because this metal m ust be salvaged and reprocessed. The present activation dissolves about 60 mg/cm^ of surface activated. An activation that dissolved less uranium would be an advantage in production plating of fuel elements. Electroplating The baths for. electroplating on uranium are similar to those for plating on other chemically active metals; e. g., beryllium, manganese, thorium, and zinc. Low pH baths (lower than pH 4.0) containing chlorides must be avoided. Several baths are suitable for plating nickel, iron, copper, or aluminum on uranium. Baths of good microthrowing power to cover uni" formly the roughened uranium surface are favored. Nickel was deposited adherently on uranium from three different baths. The plating bath* containing MgSC>4** was generally used in this work. Nickel of any reasonable thickness could be deposited from this bath and be expected to provide best corrosion resistance when alloyed with the uranium. A strike plating bath containing sodium sulfate** was also in vestigated. The thickness of electroplated nickel from this bath is limited to thin strike deposits. A Watts-type bath chemically attacked uranium. However, if the higher plating speed of a Watts-type bath is desired, it can be used after the uranium is covered by nickel deposited from one of the other baths. 'See section on Procedure for Plating and Diffusion Alloying of Metals on Uranium. •Salt used to suppreu ionization of nickel. / Nickel electroplate Intetfacla! turface Uranium metal 50OX Ai poliihed N117I I. Uranium Starling Surface: Suifiut Ground Nickel electroplate Intiriaclal surface Uranium metal COOX Ai polished NU79 b. Uranium Starting Surface: Grit Milted After Surface Grinding FIGURE 3 . ONE-MIL NICKEL ELECTROPLATES ON URANIUM A C T IV A T E D ^ PHOSPHORIC* HYDROCHLORIC ACID SOLUTION V 1 s *1 Adherent nickel directly on uranium was also deposited tram a fluo bo rate-type bath*. However, such deposits did not protect the uranium •van when they were diffusion alloyed. The use of wetting agents to prevent pitting of the nlckal during electrodeposition is desirable. No deleterious effects of any occluded organics were observed. The use of boric acid in the nickel-plating bath was questioned because of possible boron contamination* However, an electrodeposited nickel foil from the high-pH nickel bath containing MgSOq was analysed and showed less than l ppm boron, A roiled *'LM nickel foil analysed 5 ppm boron. Two baths for depositing .ron are suitable for plating on uranium, One containing ferrous ammonium sulfate at high pH, however, did not produce satisfactory iron deposits consistently. The bath uaed in this work** produced uniform, sound iron deposits, Doth acid sulfate and alkaline cyanide bathv were uaed to electro- deposit sdherent copper on uranium. However, the acid sulfate bath** was preferred because of its excellent microthrowing power. Two organic baths for electrodepositing aluminum were recently reportedO^i The bath based on ethyl ether and LiH was used in thla work. It yields sound deposits reproducibly and is cheaper to prepare and operate than the ethyl pyridinium bromide bath. The bath contains aluminum chloride and lithium hydride dissolved in absolute ethyl ether. Water in the bath will prevent plating of aluminum. Baths of 2-l/2-liter volume were prepared In 3-neck, 3-llter flasks pro vided with stirrer, thermometer, and inlet and outlet for a slow stream of dry nitrogen gas. A rubber Gooch tube, connected from one neck of the flask to the bottle of AICI3 or LiH, was used for material transfer. The reacting mixture was kept below minus 10 C to avoid ether evaporation, A dry ice-acetone bath around the flask removed the heat of reaction. The plating cell was a 3-liter cylindrical glass jar. A dry box made of 2S aluminum with two sets of stainless steel doors to give access to the bsth rested on top of the cell. Dry nitrogen gas wa« slowly bled into the dry box. Figure 4 shows this aluminum-plating setup. Anodes oi 99.994 per cent pure aluminum welded to ZS aluminum rods were used. The anode rods passing through holes in the dry box were in sulated by polyethylene tubing. To suppress ether evaporation, glass bulbs were floated on the bath surface. Synthetaslne*** was used as a plating rack coating in this bath. ^General Chemical Company. **Sce section on Procedure for Plating and Diffusion Alloying of Metals on Uranium. ••Synthetaslne Protective Coatings, Inc,, New York. f'l 24 pip W g m m m k m W&KL | i a «- 8 !* 25 The aluminum deposits were ductile. A mat surface appearance was due to a columnar-type structure. A surface showed flat or angular pentagonal patterns. Figure 5a illustrates one of these. Figure 5b illus trates the cross section of an aluminum deposit with flat and angular surfaces on steel. The columnar structure was not appreciably changed by varying several conditions of electrodeposition, Electrodeposition at 10 amp/ft* was best. Electrodeposition at 20 amp/ft* resulted in cracked aluminum at the edges of flat samples. Use of periodic-reverse-current plating produced a less dense structure. Diffusion Alloying of Electroplated Nickel on Uranium Most of the heat treating to diffusion alloy the samples was done in vacuum, under pressure of less than 10ji, so as to avoid oxidation of the uranium. Figure 6 shows photomicrographs of diffusion illoyed nickel on uranium. Alloying occurred during heat treating at 1300 F for 1 hr, and the alloys appeared similar regardless of the uranium surface preparation. The sections of uranium-nickel interface shown in Figure 6 and Figure 3 may be compared since they are views of the same specimens before and after diffusion treatment. Nickel appears to have diffused Into the uranium rather than uranium into the nickel. Figure 7 shows the effect of the temperature of heat treating on the alloying of nickel-plated uranium. No gross difference is apparent for alloys formed in 1 hr at temperatures between 1250 and 1340 F, However, the flow of uranium-nickel eutectic alloy is apparent for the composite that had been heat treated for 1 hr at 1380 F. Control of alloying above 1360 F was difficult. Bond Strength of Electroclad Metals on Uranium The as-deposited adhesion of nickel on uranium was greater than 18,000 psi, as indicated by modulus of rupture^). After heat treatment, the strength of the diffusion alloys defined the bond strength. This varied for different metals or different combinations of metals on uranium. Electroplated nickel on uranium showed good adhesion after heat treatment at 750 F for 96 hr. After heat treatment at 1000 F for 24 hr, the bond strength was about 10, 000 psi. After heat treating in the beta region, it was about 7000 psi. 4 *) 60OX H ottch N6438 ft. Pentagonal Structure on Surfaot of Aluminum Rati (Not* Edge of Cuba Projecting Up at lower Right.) WX 1/2 per cent HP N4495 b . Cron Section of Aluminum Plate Showing Plain and Angular Surface* FIGURES. STRUCTURES IN AIUMINUM ELECTROPLATES K. I •f Unalloyed nickel electroplate Nickel •uranium alloy layers Unalloyed uranium 60 OX As polUhed N1I99 a. Uranium Starting Surface: Surface Ground; Phosphoric-Hydrochloric Add Activation for Plating Unalloyed nickel electroplate Nickel-uranium alloy layers Unalloyed uranium 6O0X At polished N1690 b. Uranium Starting Surface: Grit Blasted After Surface Grinding; Phosphoric-Hydrochloric Acid Activation for Plating FIGURES. NICKEL-PLATED URANIUM AFTER HEAT TREATMENT AT 1300 F FOR l HR 28 Ifoalloyad nickel Alloy Uycn Uranium 280X 1340 F 99074 Alloy Uytrt Uranium ■ 1380 F 99078 FIGURE 7. EFPBCT OF TEMPERATURE ON THE ALLOYING OF NICKEL-PLATED URANIUM IN 1 HR 29 On nickel-plated uranium, wrought aluminum hat been bonded with strengths greater than 30,000 psi. At this stress the aluminum or aluminum-nickel alloy ruptured, without breaking the uranium-nickel bond. The as-deposited adhesion of copper on uranium was about 5000 psi, but increased to about 7000 psi after heat treatment at 500 or 750 F. After heat treatment at 1000 F for 48 or 9b h r, the bond was about 4000 psi. Between uranium and electrodeposited aluminum, the adhesion was good. The bond resisted digging and prying with a knife blade, coarse filing of an edge, and bending a sample to fracture. However, peening and hammering the aluminum deposit resulted in bond failure. Diffusion alloy ing of electrodeposited aluminum on uranium was detected after heating at 392 F for 24 hr. This alloying and that occurring at 482 F and 572 F are shown in Figure 8. Rapid alloying and formation of brittle intermetallics preclude any heat treatment of aluminum directly on uranium. Corrosion Resistance of Nickel-Electroclad Uranium To guide the programming of this work, screening corrosion tests were made. These were used to determine how the boiling-water corrosion resistance of electrociad uranium was affected by differing protection. The weighed samples were tested for periods of 20 to 24 hr, reweighed, and photographed when gross changes were apparent. Loose corrosion products were brushed off before drying and weighing. To determine the ultimate corrosion trend, samples were tested usually until a weight loss of 10 to 20 mg/cm^ occurred. Distilled water (300,000 to 810, OOO-ohm-cm specific resistance) was used as corrodent. The water was changed after each test period. Figures 9a, 9b, and 9c arc progressive photographs of beta-alloyed nickel electroplates on uranium. Figure 9a shows them before corrosion testing. The derk areas are visual effects of uranium-nickel alloying, Figures 9b and 9c show the same samples after 101 and 163 hr in boiling distilled water. On some of these samples, a semicircular marking can be seen. This is an outline of the quartz tube in which the samples were racked in the corrosion cell. Some corrosion rates for these specimens are given in Figure 1 and Table 2. Figures 10a and 10b show five representative diffusion-alloyed, nickel-pUted Hanford slugs, before and after corrosion testing. Tvyo slugs, tested In boiling water for 65 hr, illustrate seam or stringer-type corrosion. One slug, tested for 85 hr, illustrates pit-type corrosion. The two slugs, 30 Aluminum electroplate Diffuiion sene Uranium N1238 Aluminum electroplate Aluminum-uranium alloy layer Uranium N1239 b. 84 Hr at 480 F Aluminum electroplate Void ■ Aluminum - uranium alloy layer Uranium 500X No etch N1840 c . 84 Hr at 670 P FIGURE 8. NEAT TREATMENT OF ALUMINUM-PLATED URANIUM : n \ 31 ______Plffuiiflo ■Alloying Tim e______, 1 Hr______4 Hr Nldwl Thlckneu Nickel Thickncn 0.1 Mil 0.6 Ml 1.0 MU 0.3 MU 0,6 MU 1.0 MU 3 /3 X 98143 FIGURE 0*. DIFFUSION-ALLOYED NICKEL-PLATED URANIUM BEFORE CORROSION TESTING Dtffinioo-All crying Time ______i r t ______4Jto______Nickel ThlckneM______Nickel Thicknea 0,3 1411 0.6 MU 1.0 MU 0.3 MU 0.6 MU 1.0 MU 3/3X 96406 FIGURE 9b. SUFFUSION-ALLOYED NICKEL-PLATED URANIUM AFT® 101 HR IN BOILING WATER 33 ______Plffurioo-Alloying Time______1 Hr______4 Hi Nickel Thlcknes Nickel Thickne* 0,3 MU 0.6 MU 1.0 MU 0.3 MU 0.6 Mil i.O MU 2/3X 99515 S FIGURE 9c . DIFFUSION-ALLOYED NICKEL-PLATED URANIUM " AFTER 163 HR IN BOILING WATER t Dr*-"--'. About1/M m IMfc lUt 1* DTSN JIT)HKLPA* LG AT *. Ot HR1NftOUWG WATS * 1 Oft . DUTUSON* * AJLIOTS) HCKHLHPLAT*) , 10*. SLUGSFlCUftl U ATTS ia Ui . ;V . i U • . > £ & ( ' V . I . V V W ^ m si Mbi b lM NM31 \ 36 tested for 136 hr, illustrate the more extensive pit-type corrosion. These slugs lost between 10 and 136 mg per slug* with an average corrosion rate of about 0.005 mg/(cm*)(hr). Heat-Treating Equipment The vacuum heat-treating equipment used in this work is shown in Figure il. Samples were heat treated in a Vycor tube mounted horizontally and connected to the vacuum system by a ground-glass ball joint. Temperature control of the furnace was actuated by either of two thermocouples, one at the furnace-tube wall for rough control and the other inside the Vycor sample tube. This latter thermocouple was horiaontally centered with the samples and about \/l in. above them. Rapid heating and cooling were accomplished by sliding the furnace on or off the furnace tube. Heating times varied from 8 min for 100 or 200 g of metal to 15 min for 500 or 600 g. Cooling to below 300 F was generally accomplished in about 12 min. Corrosion Equipment A corrosion setup is shown in Figure 12. Battery jars (10 liters) with condenser cover plates were used. Samples were racked in slotted quarts tubes to avoid metal coupling and the slotted quarts tubes were supported on nickel racks. Heat was supplied by infrared bulbs or an Inconel immersion heater. Corrosion testing of nickel-elcctroclad slugs was done in individual 1-litcr corrosion cells so as to isolate the corrosion products. Slugs rested on the bottom of the cells and heat was supplied by infrared bulbs. Aluminum condenser plates were used to minimise evaporation of the water. The corrosion weight loss was determined by analysis of the uranium in the corroding water. 4 m & > m ■ 1 I 1 J: , gaSSil||p;i>sS':ip« tlfg^ •:: «.* i§fe Stellfeg^^ ■ ■ . «§ • :«*§? ;■•■•. - ' : m v i ■ '■." 3sS f :.• ' v .../ ...... - ' -' '• s.-.-.'.;.'..-- .•.-.•/V .v ,'w •:•.'• “ .fe : : § s £ .; '°W * 'il i > |Bj ' ' ;gB,!S,-.■ ,U-, ••&. ■ -,vU;-v, i;igmBx,l!{Sp,?-.. # i v c ^ • ^ ^ ; u>, :i ,v > ,u ;;c ...... fmm Mk m i l l ItO U M II. VACUUM tMAT-TWATINO m 39 REFERENCES (1) Waber, J. T ., “An Analyala of Pile Process Data on the Corrosion of Uranium in Various Media”, LA 1381 (I)etcmbcr 22, 1948) isausd March 6, 1952. (2) Cray, A. G., “The Electroplating of Tuballoy-Handbook”, CT 2116 (February 6, 1945), (3) Wchrman, R., “Electroplating • Final Report", CT 2443 (December 1, 1944). (4) Hoglund, V. F ., “ Development of Electroplated Metallic Coatings on Tuballoy - Final Report”, A 3422 (January 31, 1943). (5) Borgmier, B. J., "Coating Canning and Testing Methods for Natural Uranium Fuel Elements • a Bibliography in Three Parts", HW 25368 (August 18, 1952). (6) Andelin, H. L ., "Nickel Plating of Uranium”, HW 30243 (December 9, 1953). (7) Sprowl, J. D., ct al., " Preparation and Characteristics of Hot-Press, Canned, Aluminum-Silicon Coated, Fuel Elements", HW 29916 (October 1, 1953), (8) Storchheim, S,, and Zambrow, J. L ., “ Preliminary Report on Canning of Electroplated Uranium Slugs", SEP 115 (May 30, 1953). (9) Storchheim, S., Zambrow, J. L., and Hausner, H. W., "Solid State Bonding of Aluminum and Nickel", SEP 132 (August 8, 1953). (10) Collins, F. R ., “Aluminum Plating from Fused Salts", Iron Age, 169 (3), 100 (1952). (11) Couch, D ., and Brenner, A., “A Hydride Bath for the Electrodeposition of Aluminum", J. Electrochem. Soc., 99, 234-244 (1952). (12) Safranek, W. H., Schickner, W. C., and Faust, C. L., “Electro forming Aluminum Waveguides Using Organo-Aluminum Plating Batha", J. Electrochem. Soc., 99, 53-59 (1952). i (13) Schickner, W. C., “Aluminum Electrodeposits Made Adherent", Steel (November 2, 1953). - 035 (14) Schickncr, W. C ., Beach, J. G ,, and Fault, C. L. , "Electroplating on Zirconium", BMl 707 (November IS, 1951), 4nn )3ti