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Journa l of Research of the National Bureau of Sta ndards Vol. 52, No.3, March 1954 Research Paper 2483
Silver-Uranium System 1 R. W. Buzzard, D. P. Fickle, and J. J. Park
The phase diagram of the system silver-uranium was constructed from data obtained by thermal analysis, metallographic examination, and X-ray diffraction. The system is characteri zed by a eutect ic having a composition of approximately 5 weight percent of uranium occurring at 9500 C, and a monotectic occ urring at 1,132 0 C, and 0.23 weight percen t of silver. The solid solubility of uranium in silver appeared t o be between 0.1 and 0.4 weight percent at the eutect ic temperature; no appreciable solubility of silver in uranium_wa s noted. The temperat ures of t he gamma-beta a nd t he beta-alpha transforma t ion of uranium apparently were unaffected by silver .
1. Introduction treating operation. Analyses of the silver-rich alloys were made only for uranium and, as uranium oxide The purpose of this investigation was to make a was included in the total uranium reported by this survey of the silvel'-uranium system and to develop method, there is a possibili ty that sufficient uranium the constitution diagram by correlation of th ermal, oxide was retained in th e low-uranium alloys « 0.5 X-ray, and microscopic studies. weight percent) to cause tho results of the chemical analyses for uranium to be higher th a.n the actual 2. Previous Work ura.nilIDl conten t of the alloys. In view of the change of composition of the a.llo~' s caused by these factors A survey of the literature showed that information during subsequen t thermal studi es, the reported com on the constitution of the silv er-uranium system was positions of the alloys (tables 1 and 2) wer e deter meager [lV It has bee n reported that silver and mined after examination rather tha n on the "as uranium separated into two distinct layers on melt cast" material. ing, with very li ttle evidence of alloying [2] and were mutually insoluble, A eutec tic was observed in the T A BT, E 1. Sum mary of ther/nul data obtained Jor silver silver layer, and consid erable loss of silv er by evap 1/1'aniu?n alloys orization \\'as noted [2]. 'r hcrmnl arrC's t Silver· 3. Preparation of Alloys {3->a
The bas e metals consisted of ,,-, 99.9 percen t of wt-% °C °C °C °C °C uranium (.l\fallinckrodt Biscui t) and 999-fine silver. 100 961 99. 99 959 958 The alloys wer e prepared in beryllia crucibl es in a 99. 98 959 99. 97 957 954 high-frequenc.v induction furnace under an atmos 99. 95 956 95'1 phere of purified argon [3]. 99. 85 9.\6 955 98. 30 959 9,.0 It was observed from sectioned ingots prepared in 95. 70 949 770 658 0. 23 I, J35 952 764 661 the composition range of 30 weight percen t of silver .04 1, J28 956 765 654 that silver and uranium separated into layers when . 035 1, 133 94 2 766 650 molten (fig. 1). Chemi cal analysis of a number of 0 1, J33 762 653 ingots revealed that the silver layer consisten tly • Composiiions show the ratio of (llC component metals and do not refl ect contained 4 to 5 weight percent of uranium. This the impllrities. factor was later used to advantage by taking the 4 to 5 weight percent of uranium alloy as a master T A B LE 2. SV1nmary of microsco pic data obtai ned for silv el' alloy; other alloys were made by direct alloying. lIraniwn alloys The m elting characteristics of the system required N um ber of phases observed- quenching temperatures, °C that the temperature of charges consisting of primary U r H.l li um a uranium and silver be raised above the melting point As cast 600 700 800 900 950 955 of ura.nium in order to obtain alloying. The molten silver had a high vapor pressure and, at the melting wt-% L ______temperature of uranium, a high loss of silver by 0. 01 1 1 1 1 L ______1 . 03 1 1 1 1 L ______1 vaporization was encountered. . 1 1 1 1 1 1 . 4 2 2 2 2 F usiol1 ____ Fusion . Uranium was an effective deoxidizer of silver so 1. 7 2 2 2 2 Do. 1.8 2 2 2 2 F usion __ __ Do. that, as uranium oxide was rejected from the m elt, __ _d o ______Do. 2. 1 2 2 2 2 ___ do ______this oxidation caused a loss of uranium from the 3. 0 2 2 2 2 ___ do ______Do. 4. 0 2 2 2 2 ___do ______Do. silver-rich alloys on each subsequent melting or heat- .5. 0 2 2 2 2 Do.
I Investigation sponsored by the Atomic Energy Commission at the National B ureau of Sta ndards. a Compositions show the ratio of the compon ent metals nnd do not refle ct 2 Figll res in brackets ind icate the literature references at the end of tllis paper. the impurities. 149
------4.2. Microscopic Analysis The specimens for microscopic examination were mounted in Bakelite, ground on a series of si1icon carbide papers, with the finishing paper of 000 grit, and finished either on a levigated alumina lap or electrolytically, using 70 v at l 7f amp, 3 to 6 immer sions of 10-sec duration in an electrolyte of the follow · ing composition: 20 g of chromic acid; 30 ml of ,vater, and 100 ml of glacial acetic acid. In general, the structures of the silver-rich alloys were developed by swabbing with a modified chromic sulfuric-acid solution [5] composed of 1 part of a concentrated stock solution (IOO-mi saturated solu tion of potassium dichroIPate in water, 2-ml satu rated solution of sodium chloride in water, and lO-ml of concentrated sulfuric acid) in 9 parts of water. The silver-rich alloys developed a grayish coating and required a light polish on a alumina finishing lap after etching. The structures of the uranium alloys were developed electrolytically in a lO-peI'cent chromic-acid solution, using 0.5 amp and 4 v at 25° C. Specimens to be quenched '''ere sealed under argon in high-silica glass tubes of 7-mm bore, homo genized for 8 days at 925° C, and furnace-cooled. The alloys were quenched in ice water, using the nickel-block technique, in the manner described for the titanium-uranium alloys [3].
4.3. X-ray Analysis The specimens used for the mit;roscopic studies were subsequently placed in an X -ray spectrometer and a chart obtained of the (Cu-Ka) X -ray diffrac tion lines at room temperature. By this method it was possible to identify the phases present in the alloys and correlate the X -ray and microscopic data. 5. Results 5.1 . Thermal Data
FIGURE 1. Ingot contQ1:ning 30 weight percent of silver showing The results of thermal analysis (table 1) were the uranium (dark) and silver (light) layers . were obtained from the two terminal-alloy series (0 to 0.23 weight percent of silver and 0 to .5 weight pcrcent of uranium). The alloys in the composition 4 . Experimental Procedures range 0.23 to 95 weight percent of silver separated into two layers during the thermal-analysis cycle, 4 .1. Thermal Analysis each layer having an analysis within the respective terminal-alloy composition range, as indicated above. The thermal arrests were determined by time Thermal-analysis data of the silver-rich alloys temperature analysis, using a molybdenum-wound (1 to 5 weight percent of uranium) showed consistent resistance furnace. The accessory apparatus in arrests in the vicinity of 950° C. Similar arrests cluded a program controller to maintain uniform were observed for the uranium-rich alloys; in these heating and cooling rates and an electronic recorder alloys a second arrest was observed at approximately to reproduce automatically the heating and cooling 1,132° C. The uranium transformations were noted curves [4]. Tne thermal curves were obtained from in all alloys and were apparently unaffected by specimens of approximately 50 g, which were heated silver. and cooled at a controlled rate of 2° C/min with the Two alloys (30 weight percent and 50 weight furnace operating under an atmosphere of purified percent of silver) in the composition range of the argon. The thermal arrests were derived from the liquid miscibility gap were prepared, and time cooling curves. temperature cooling curves were determined on the
150 whole ingot. Arrests identical to those previously A eutectic-like structure WitS observed in both Lhc recorded for the uranium-rich terminal alloys were uranium-rich (fig. 2A) and the s ilver-rich (fig. 2B) observlx l. Tho l'C' sultant ingots showed a sharp alloys. R es ults of the micr oscopic analyses showed line of demal'ca Lion between a silver-rich and an the eutectic composition Lo be a pproximaLely 5 uranium-rich layer. The layers were parted and weight percen t of urani urn and the monoLecLic reexamined by thermal analysis. E ach layer de composition to be approximately 0.23 weigh t pC'l' veloped arrests characteristic of the r espective cen t of silver . In the composition range 0.4 to 5.0 terminal-alloy series. The miscibility gap extended weigh t per cent of uranium, some evidence of fu sion over the greater portion of the system. It was not was observed at the edges of the specim ens quenched possible to obtain liquidus determinations for com from 950° C and complete fu sion was observed at positions in excess of 5 weigh t percent of manium 955° C. This confirmed the eutectic temperatm e bccause the allo ys separated into two layers during of 950° C as observed by th ermal analysis. thermal analysis. This indicated tha t the liquidus rose sharply from the eutectic to th e monotectic 5 .3. X-ray Identification temperat ul'C. On the basis of these observations, it was concluded that th e composition range of the X-ray diffraction charts were obtained, uSing the miscibility gap was determined to be a pproximately same surfaces of the spccimcns as were examined 0.23 to 94.5 weigllt percen t of silver at the mono microscopically; the results of the X-ray and mi cro tectic temperatures. The vapor pressure of silver scopic examination were then con·elated. Only greatly influenced the determination of the thermal uranium and silver lines wcre observed for the alloys arrests in th e Lll'anium-ri ch alloys. It was evident examined in this system . that sil ver had Ii ttle effect on the thermal arrests of the uranium-rich alloys, and the temperatures used in the construction of the diagram wer e b ased 6. Proposed Diagram on ,the values obtained for m anium. The thermal arrests, derived from the cooling 5.2. Microstructures of the Alloys curves, wcre obtained from "as-cast" alloys tha t were r apidly cool cd from the liquid condiLion. In the study of the microstructures of these alloys Chemical analysis showed these lngoLs Lo be homo (table 2), using the number of iden tifia ble phases geneous from top to bottom. Since both sil ver and presen t as the criterion, it was revealed Lhat Lhe uranium wcrc lost during th c thermal analysi cyclc, solubility of m anium in silver lies between 0.1 and the repor ted alloy compositions arc those deLermined 0.4 weigh t percen t at room t mperatul'e, and li ttle from the chemical analysis of sam pI es cut from Lhe change in this value was obse rved betwecm 25° C and ingot (at the thermoco uple tip) aftcr Lh ermal 950 0 :C. analysis.
F I GUR E 2. As-cast alloys, showing characteristic eutecticlike stntctutes f ound in both the uranium-rich and the silver-rich terminal alloys. A, 4.5 weight percent of uranium, cb romic-sulfuric etch. D, 0.07 weight percent of Silver, electrolytic etch , 10-p ercent ch romic acid. Magn ifi cation, X IOO .
151 ATOMIC PERCENT SILVE.R ATOM IC PER CEN T SILV ER 97.2 98.2 99.1 I 0 10 20 30 40 50 60 70 BO 90 100 Y+ L:I' , L. 14 00 1000 , , 1800 1300 2400 , 8+ ,. • ,' e - - 0-' t=. I LI+ Lz IL2 0 950 C 99.6 to ~ 8 1200 I'- \ 2200 000 1132°C I /100 2000 · :' 1600 I y + 8 Y+ L. I ;' ... :; 1000 L>. 0 950°C I 1800 w w 961·C . w cr 800 I
FIGURE 3. S ilver-uranium system, 94 to 100 weight percent FIGURE 4. Silver-uranium system . of silver. M icroscopic data: 0 , ooe pl.ase; V , two phase; e, fosion. 7. Summary Thermal arrests were observed at about 950°, The silver-uranium system (fig. 4) was constructed 762°, and 653° C in both the uranium and silver-rich from data obtained by thermal, microscopic and alloys, and in the vicinity of 1,132° C in the uranium X-ray analyses. rich aUoys. Microscopic studies revealed a eutectic The important features of the system include: (a) like structure in both series of alloys. It was indi A monotectic at 0.23 weight percent of silver and cated that a monotectic occurred in the system at 1,132° C with a liquid miscibility gap extending approximately 0.23 weight percent of silver and at from 0.23 weight percent to approximately 94.5 the melting point of uranium; it was not possible to weight percent of silver. (b) A eutectic at approxi differentiate between the melting point of uranium mately 5 weight percent of uranium and 950° C. and the monotectic temperature. In the silver-rich (c) The solubility of uranium in silver appeared to terminal alloys, fusion was noted at about 950° C in be between 0.1 and 0.4 weight percent at the eutectic the composition range 0.4 to 5.0 weight percent of temperature while no appreciable solubility of silver uranium (table 2), indicating a eutectic occurring at in uranium was noted. (d) The gamma-beta and 950° C and approximately 6 weight percent of ura the beta-alpha transformations of uranium were nium. The microscopic studies of the quenched apparently unaffected by silver. alloys used in the determination of the silver-ura niunl solvus were made on specimens that were heat The authors express their appreciation to M al'tha treated prior to chemical analysis. It was well S. Richmond for the chemical analysis. established that the solubility of uranium in silver is less than 0.4 weight percent at the eutectic temper 8. References ature of 950° C (fig. 3) . In evaluating the studies of the alloys in the composition range of less than [1] R. W . Buzzard and H . E. Cleaves, J . Met. and Ceram. 0.4 weight percent of uranium, it must be borne in (TID65) 1, 43 (1948). [2] Battelle Memorial lnst., Report CT 2483 (Dec. 1, 1944). mind that the uranium-oxide content of the alloy [3] R. W . Buzzard, R. B. Liss, amI D . P. Fickle, J. Research appears as uranium in the chemical analysis, and It NBS 50, 209- 214 (1953) RP2412. is quite possible that the solubility may be even lower [4] R. W . Buzzard, J . Research NBS 50, 63- 67 (1953) than reported. No intermediate phases or inter RP2389. metallic compounds were observed in the system [5] Am. Soc. Metals Handbook, p . 1110 (1948) . as a result of X-ray, thermal, or microscopic analysis. WASHINGTON, November 4, 1953.
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