12 Phase Studies in the ZirconiumHydrogen-Uranium System H. H. KRAUSE, H. E. BIGONY, and J . R. DOIG, Jr. Battelle Memorial Institute, Columbus,
1
Ohio
Hydrogen-absorption
isotherms were
measured
over the range 535° to 835° C. by Sievert's method for alloys of zirconium containing 1 and 25 weight % uranium.
High-temperature x-ray
diffraction studies were made over approximately the same temperature range for the zirconium-1, -25, and -50 weight % uranium alloys.
In gen-
eral, these studies support the interpretation that, as hydrogen is absorbed, the alloys break down into uranium and zirconium, and the latter absorbs the
hydrogen.
Heats of solution of hydrogen
were found to range from —25.9 to —47.9 kcal. per mole for the 1 weight % alloy, and from —30.7 to —50.6 kcal. per mole for the 25 weight %
alloy.
Proposed isothermal sections of the
ternary diagram at 6 2 7 ° , 6 7 5 ° , and 750° C. are included.
Jhis study has been concerned with the phase relationships in the ternary system zirconium-hydrogen-uranium in the temperature range 500° to 800° C. To examine the concept of a fueled moderator for nuclear reactors, the absorption of hydrogen by two zirconium-uranium alloy compositions was measured. There is adequate information in the literature on the three binary systems involved. Libowitz and colleagues (12) have shown that uranium forms the single hydride, U H , at temperatures below 450° C. The zirconium-hydrogen system includes several hydride phases; the delta hydride, having a composition in the range ZrH to Z r H at elevated temperatures, is of the greatest interest for moderator purposes. The zirconium-hydrogen system has been described (1-5, 7, 8, 10, 11,13,16, 18-21). The uranium-zirconium system has also been studied in detail (15). The earliest study of the ternary system was by Gulbransen and his associates (6, 17), who obtained data on the 50 weight % uranium alloy. Their chief concern was the possible weakening effects of hydrogen absorption by such alloys in a pressurized-water reactor. More recently, L a Grange et al. (9) examined 3
l i 5
1
1 > 7
Present address, Boeing Aircraft Co., Wichita, Kan. 131
132
ADVANCES IN CHEMISTRY SERIES
a series of hydrided zirconium-uranium alloys for fueled moderator reactor applications. In the present investigation, the hydrogen-absorption data have been supplemented b y high-temperature x-ray diffraction. B y this means the solidstate reactions indicated b y the hydrogen-solubility data could be identified. Furthermore, x-ray examination of the samples at the absorption-isotherm temperature is desirable i n the system where transformations can occur even on rapid cooling from elevated temperatures. T h e h i g h diffusivity of hydrogen makes this system particularly susceptible to such changes, so quenching of samples was avoided i n this work. Selected alloys w i t h hydrogen contents near the terminal phases and the eutectoid composition were examined. Experimental
Procedures
T h e hydrogen-absorption isotherms were measured over the temperature range 535° to 835° C . for both the 1 and 25 weight % uranium alloys. N i n e alloy compositions were selected for x-ray study: zirconium-base alloys containing 1, 25, and 50 weight % uranium, each w i t h 10, 30, and 50 atomic % hydrogen, based on the zirconium content. T h e 10 and 50 atomic % hydrogen contents correspond to positions near the terminal phases i n the zirconium-hydrogen system, a n d the 30 atomic % hydrogen addition approximates the eutectoid composition. Materials and F a b r i c a t i o n Techniques. T h e zirconium used i n this work was iodide metal and the uranium was center-cut from biscuit stock. B o t h 1 and 50 weight % uranium alloys were double-melted b y consumable-electrode arcmelting, as part of large batches prepared for other studies. T h e 25 weight % uranium alloy was prepared b y a tungsten-electrode arc-melting method. The alloys were hot-rolled at 1500° F . , cleaned, a n d cold-rolled to a final thickness of 0.125 inch. V a c u u m fusion analysis showed that these alloys contained from 300 to 450 p.p.m. of oxygen, and less than 30 p.p.m. of hydrogen or nitrogen. Pure hydrogen for the isotherm determinations, and also for h y d r i d i n g the alloys used i n the x-ray study, was obtained b y the thermal decomposition of uranium hydride. Table I gives the composition of the hydrides used i n this program, as obtained b y vacuum-fusion analysis. Table 1.
Hydrogen Content of Hydrided Alloys Used in X-Ray Diffraction Study Uranium Concentration, Weight %
Hydrogen concn. per a t o m , at. %
7
25
50
10.4 31.7 49.3
10.8 31.6 48.4
10.0 34.1 48.4
Individual wire sections chosen for straightness and desirable cross-sectional shape were cut to desired length and etched i n a nitric acid-hydrofluoric a c i d water solution to remove the inevitable scale that occurs on closed heating. T h e bright sample was then rinsed i n 1 to 1 nitric acid to remove any green deposit that might have formed during etching. E a c h alloy was examined b y x-ray at temperature levels about 100° C . apart, starting at either 400° or 500° C , and extending to 800° C . T h e 400° or 500° C . level was preceeded b y room-temperature examination, and the sample was sometimes re-examined at room temperature after the elevated-temperature excursion. E a c h x-ray photogram was obtained b y a 2-hour exposure to unfiltered nickel radiation. The 800° C . examination was seldom considered useful because of apparent reaction w i t h the capillary w a l l . T h e diffraction photograms at that temperature
12 KRAUSE ET AL.
Zirconium-Hydrogen-Uranium
Systems
133
level indicated the presence of uranium dioxide, cristobalite from devitrification of the silica capillary, and an unknown corrosion product. These effects were sometimes noted to a m i l d degree at 700° C . also. I n most cases of the 800° C . examination, the silica capillary split open during exposure. Apparatus. T h e hydrogen-absorption system, a modified Sievert's apparatus, consisted of three self-contained units. T h e first unit provided a source of, and storage facilities for, pure hydrogen, w h i c h was obtained b y the thermal decom position of uranium hydride. T h e second unit provided precise metering of h y drogen at a known temperature, for delivery to the reaction system. T h e third unit was a constant-volume section i n w h i c h the reaction of hydrogen w i t h the zirconium-uranium alloy occurred at a controlled temperature ( ± 3 ° C ) . T h e equilibrium pressures of hydrogen were measured i n this section also. The x-ray studies were made w i t h a high-temperature x-ray diffraction camera of Hume-Rothery design. This camera h a d a 9-cm. diameter a n d employed the Straumanis film setting. A fine C h r o m e l - A l u m e l thermocouple within the furnace cavity a n d adjacent to the sample served to measure a n d control temperature. The sample temperature was calibrated against the thermocouple e.m.f. through a series of lattice-constant measurements on pure silver. Experimental Methods. T h e absorption of hydrogen b y the zirconiumuranium alloys was measured isothermally, using the constant-volume section of the system. A n Auto vac gage was used to measure pressures below 2 m m . , and a large-bore manometer was used for higher pressures. A cathetometer was e m ployed for the manometer readings. Possible contaminants such as mercury and stopcock grease were excluded from the reaction vessel b y means of a —78° C . trap. T h e alloy samples were placed i n a n Inconel container to prevent possible reaction w i t h the mullite tube i n w h i c h the hydriding was effected. A t each temperature successive additions of hydrogen were made and the equilibrium pressures measured. E q u i l i b r i u m was reached i n minutes at tem peratures above 700° C , but several hours were required at lower temperatures. Additions of hydrogen were continued u n t i l the amount of hydrogen absorbed per gram of zirconium approximated 60 atomic % . T h e volume of hydrogen taken u p by the sample was determined as the difference between that added and the volume remaining i n the reaction system at equilibrium. Corrections were made for the differences i n manifold temperatures encountered during the experiments. F o r the x-ray work, " w i r e " samples were prepared b y shearing 0.010-inch sheet of the desired uranium-zirconium alloy composition, keeping the w i d t h as close to the thickness as possible. A small batch of these wires was then hydrided at 600° C . to the desired hydrogen content along w i t h a small block of the same alloy to b r i n g the sample weight to a feasible value. T h e hydrided material of each composition was then sealed i n an evacuated V y c o r capsule and homogenized at 1000° C . Results and Discussion T h e absorption-isotherm method provides a very useful approach to the study of a gas-solid system. Inflection points i n the isotherms locate phase boundaries, and a plot of l o g Ρ vs. 1/T (Arrhenius plot) permits calculation of heats of solu tion and estimation of the eutectoid temperature. T h e shape of the isotherms de pends only on those phases w h i c h affect the hydrogen absorption, rather than a l l phases present. T h e actual phases present were identified b y high-temperature x-ray diffraction. T h e designation of the phases follows terminology commonly used i n U . S. Atomic E n e r g y Commission studies: = hexagonal close-packed zirconium = body-centered cubic form of zirconium δ = face-centered cubic zirconium hydride e = face-centered tetragonal zirconium hydride ot — orthorhombic uranium βν = tetragonal uranium
a β
Zr
Ζτ
v
ADVANCES IN CHEMISTRY SERIES
134
γ = body-centered cubic uranium y = uranium-rich series of solid solutions formed between y u and β y = zirconium-rich series of solid solutions formed between y and β 8 = solid solution of γ and α π
1
Ζτ
2
v
U Z r 2
Ζν
Ζτ
Ό
T h e phase diagrams of the uranium-zirconium and uranium-hydrogen systems employed i n this work were those given b y R o u g h and Bauer (15). T h e zirconiumhydrogen phase diagram used is a composite of data found i n the various references to that system, and is presented i n F i g u r e 1.
300r-
L
W
0
10
20
30
40
50
60
70
Hydrogen, atom per cent
Figure
1.
Phase
diagram of system
zirconium-hydrogen
Zirconium-1 W e i g h t % U r a n i u m A l l o y . Isotherms for the 1 weight % uranium alloy were r u n at six temperatures, covering the range 534° to 802° C . The x-ray diffraction studies on this alloy were made at room temperature and from 500° to 800° C . The general effect of the addition of the uranium is to shift the phase boundaries of the zirconium-hydrogen system to slightly lower hydro gen percentages. The eutectoid temperature is also lowered from 547° to 541° C . H Y D R O G E N - A B S O R P T I O N ISOTHERMS.
T h e isotherms determined for the z i r
conium-1 weight % uranium alloy are shown i n Figure 2. Solid solution of h y drogen i n the alloy is represented b y the initial portions of a l l the curves, w h i c h show a rapid change of pressure w i t h the volume of hydrogen absorbed. T h e inflection points of the curves represent phase boundaries, and the transition from α-zirconium to a multiphase region is indicated b y the first such point on each curve. T h e vertical portions of the curves, w h i c h indicate hydrogen uptake at constant pressure, show the extent of the multiphase regions. T h e isotherm at 534° C . has a very sharp inflection, followed b y an almost vertical portion, as the multiphase region is tranversed. T h e second inflection i n
12 KRAUSE ET AL.
0.5
Zirconium-Hydrogen-Uranium
1.0
1.5
20
2.5
30
3.5
4.0
Systems
4.5
5.0
135
5.5
Log Ρ , μ
Figure
2.
Hydrogen-absorption isotherms for 1 weight % uranium alloy
zirconium-
the 534° C . isotherm indicates the transition to the single hydrogen-absorbing phase, δ-zirconium hydride. Because this isotherm lies below the eutectoid tem perature, only two phase boundaries are crossed. The four isotherms at 626°, 6 5 1 ° , 703°, and 755° C . have similar shapes, but the transition back to solid solution is not so sharply defined as the other transitions. The 802° C . isotherm differs slightly from the others, i n that the inflections at l o w hydrogen absorptions are not very pronounced. However, when the data are plotted on the phase diagram, a narrow multiphase region appears. Extrapola tion indicates that above 875° C . this multiphase region w o u l d not exist. T h e remainder of the isotherm is the same as the others. T h e phase boundaries w h i c h are indicated b y these isotherms represent slight shifts from those of the zirconium-hydrogen system, and show that no unexpected change results from small uranium additions. X - R A Y DIFFRACTION STUDY. T h e intensities of the phase patterns observed for the 1 weight % uranium alloy are presented i n Table II. T h e intensity is indicative of the quantity of a given phase that is present, b u t the amount present is not necessarily proportional to the intensity. These data show that a was present i n Zr
ADVANCES IN CHEMISTRY SERIES
136
all three alloys u p to 600° C , indicating either that at the 30 a n d 50 atom % hydrogen levels reaction was incomplete, or the sample was below the solvus surface on the a side of the ternary eutectoids. T h e lattice constant of the γ phase increased from 3.62 A . at 10 atom % hydrogen to 3.66 A . at 30 atom % and to 3.69 A . at 50 atom %. Zr
Table II.
Phases Detected by X-Ray Diffraction Examination of Hydrided Zirconium-1 Weight % Uranium Alloy
Hydrogen Content, At. % i
n
10
30
50
a
%
r
Temp.,°
C.
a-Zr
Intensities of Phase Patterns Observed" Unknown A d-ZrH y-UZr x
26 500 600 700 800
S S S
O O o M O
27 500 600 720 815
s vs MS
O O S VS
28 515 600 700 815
M M M O O
sο
Ο Ο
vs o o MF VS
s
S = strong, M = m e d i u m , F = faint, V = very, O =
W F - V F VVF-VF VVF-VF O O
O O O MF S
M MS F O O
O o o
MS S M O O
O O O O MF
o
MF
absent.
A n unidentifiable phase, designated as U n k n o w n A , was detected i n moderate intensity at 700° C . This material was observed i n several samples at 700° and 800° C , a n d is believed to be a surface contamination resulting from a reaction w i t h the silica container. This unknown phase remains when the sample is cooled to room temperature. Z i r c o n i u m - 2 5 W e i g h t % U r a n i u m A l l o y . Thirteen hydrogen-absorption iso therms covering the range 572° to 835° C . were r u n on the 25 weight % uranium alloy. The x-ray diffraction patterns were taken at room temperature and at 500°, 600°, 700°, and 800° C . T h e effect of the uranium on the zirconium-hydrogen system i n this case is appreciable below 40 atomic % hydrogen. T h e phase boundaries of the zirconium-hydrogen system w h i c h define the a-zirconium plus /J-zirconium hydride region are shifted to m u c h higher hydrogen contents. S i m i larly, the eutectoid shifts from 32 to 38 atomic % hydrogen, and its temperature boundary rises from 547° to 601° C . HYDROGEN-ABSORPTION ISOTHERMS.
T h e isotherms for the 25 weight %
uranium alloy constitute a family of curves closely resembling each other. Seven of the 13 isotherms w h i c h were measured are plotted i n F i g u r e 3. Isotherms inter mediate between each adjacent pair were omitted to reduce the complexity of the plot. T h e isotherms at 572° C . (not shown) a n d at 601° C . cross only two phase boundaries, because they are below the eutectic temperature. W h e n the isotherms for the 25 weight % uranium alloy are compared w i t h those for the 1 weight % alloy, significant differences are noted. T h e region of solid solution of hydrogen i n the alloy is m u c h broader i n the 25 weight % alloy, as a large amount of uranium is being precipitated from the alloy. T h e result is to shift the first two phase boundaries to compositions of greater hydrogen content. The third a n d fourth phase boundaries are practically unchanged, since they are i n a region i n w h i c h δ-zirconium hydride predominates, and precipitation of uranium is no longer occurring.
12 KRAUSE ET AL.
Zirconium-Hydrogen-Uranium
5.5
6.0
3. Hydrogen-absorption isotherms for conium-25 weight % uranium alloy
zir
2.0
2.5
3.0
3.5
Log Figure
4.0
4.5
137
Systems
5.0
Ρ, μ
T h e vertical portions of the isotherms for the 25 weight % alloy, repre senting hydrogen uptake at constant pressure, show no variation of pressure w i t h composition, indicating that i n this slower hydrogen absorption, equilibrium of three solid phases has been reached. X - R A Y D I F F R A C T I O N STUDY. T h e x-ray diffraction data for the 25 weight % uranium alloy are presented i n T a b l e III. F o r the most part, the phases de tected i n the material containing 10 atom % hydrogen were what w o u l d be expected from the uranium-zirconium phase diagram. However, i n addition there was found a phase w h i c h was either 8 u z r omega-type phase w i t h the same structure. T h e latter phase is difficult to differentiate from the 8uzr2> d in uranium-zirconium alloys it decomposes into α and 8uzr2 upon annealing. W i t h 30 atom % hydrogen present, ctjj a n d δ-zirconium hydride appeared as expected. However, at 720° and 815° C , the gamma phase was split into two portions having the lattice constants 3.68 and 3.64 Α., respectively. A n e w phase, w h i c h has been designated as U n k n o w n B , also appeared at 720° C . These re sults were verified i n three different samples at 700° C . level. It is suspected that the two different gamma phases were of h i g h hydrogen and l o w hydrogen contents, respectively. T h e high-hydrogen phase is probably the enlargement of the gamma field of the zirconium-hydrogen eutectoid, and the phase of l o w hydrogen con tent is probably a similar effect at the zirconium-uranium eutectoid. U n k n o w n Β may be a complex uranium-zirconium hydride. 2
OT
a
n
a
Ζτ
n
ADVANCES IN CHEMISTRY SERIES
138 Table III.
Phases Detected by X-Ray Diffraction Examination Intensities
Hydrogen Content, At. % in Zr
a
b
c d
Temp., ° C.
ω or d-UZr
a-Zr
a-U
10
26 500 600 700 815
Ο VF MS VF Ο
O O VF O Q
S S O O O
30
26 515 620 720
S S MS Ο
F F M F
O O
30
815
Ο
O
50
26 515 600 700
Ο Ο Ο Ο
F F MF Yd
S = strong, M = m e d i u m , F = faint, D u p l e x g a m m a p h ase observed. Unknown B. β-uranium rather t h a n α-uranium.
Table IV.
V =
2
o o o
very, Ο
o o o o
= absent.
Phases Detected by X-Ray Diffraction Examination Intensities
Hydrogen Content, At. % in Zr
Temp., ° C.
10 10 10 10 30 30 30 30 30 50 50 50 50 50
28 500 600 700 28 515 620 720 815 28 515 620 720 800
a-Zr Ο M M M Ο Ο O O O O O O O O
F
to V F to V F t o V F
a-U
ô-UZr
Ο MF MS VF MS M M O O MF M M MF' O
VS S
° S = strong, M = m e d i u m , F = faint, V = very, Ο = F a i n t patterns for b o t h U O a n d U 0 were obtained. /3-uranium. b
2
o o o o o o o o o o o o absent.
2
c
In the alloy having 50 atom % hydrogen, β patterns appeared at 700° C , and the unidentified pattern previously designated as U n k n o w n A was found at 815° C . Some faint U 0 patterns were also observed, probably resulting from slight surface contamination w i t h oxygen. Z i r c o n i u m - 5 0 W e i g h t % U r a n i u m A l l o y . This system was examined by Gulbransen and his associates (6, 17), but their x-ray studies were made on quenched samples, so there has been uncertainty as to the exact nature of the phases present at the higher temperatures. Consequently, x-ray diffraction pat terns of the 50 weight % uranium alloy were taken over the range 500° to 800° C . (Table I V ) . A 50 weight % uranium alloy, free of interstitial impurities such as hydrogen, would consist of the intermetallic compound U Z r , designated as the delta phase. ν
2
2
12 KRAUSE ET AL.
Zirconium-Hydrogen-Uranium
139
Systems
of Hydrided Zirconium-25 Weight % Uranium Alloy of Phase Patterns Observed"
L
Unknown y-UZr
ZrH
A
Other
MS Ο S S S ο F MF S and
O VF O O o M M MS VVF
O O O o M O O O VF
VVF VVF VF VVF MF O VVF F M'
U0 VVF O O O O O O O O
O
VS
O
O
S S MS MF
o o o o
VVF O VVF VVF
O VF WF VF
x
M
2
and
M*
O O M S
U
k
e
P
a
r
a
m
e
t
e
r
3.56 3.631* 3.639 3.615 3.68 3.68 a n d 3.64 3.68 a n d 3.64
b
S
a
of Cubic Gamma Phase, A.
3.68 ' 3.712
of Hydrided Zirconium-50 Weight % Uranium Alloy of Phase Patterns Observed"
Lattice Parameter Unknown
y-UZr
Ο Ο MF S Ο Ο Ο MS M Ο Ο Ο Ο Ο
ZrH
x
Ο VF Ο Ο M M MS F Ο MS S S S S
A
Other
O O O M O O O VF MS O O O VF S
VVF WF VVF WF VVF WF VF VF VF VF O O VF VF
f Cubic. Gamma
n
U0 O O O O O F F F* S O VF VVF VF F
Phase, A.
2
3*61 3.608
3.696 3.710
This was also found to be the case for the alloy w i t h 10 atomic % hydrogen at room temperature. However, at 500° C . medium-faint patterns of a a n d ajj appeared, although a large amount of the delta U Z r remained. A t 600° C , the delta phase disappeared completely, and the α and otjj phases were correspond ingly increased i n intensity. Despite the difficulty i n distinguishing between small amounts of gamma and delta phase (the! delta pattern resembles merely a superlattice pattern of the gamma), a minor amount of gamma phase was detected. A t 700° C , the gamma phase predominated, b u t a considerable quantity of a was also present, w i t h possibly a trace of ajj. T h e results for this alloy show that hydrogen at a concentration of 10 atomic % (based on the zirconium present) reduces the stability of the delta compound. A t the higher hydrogen concen trations the delta phase was not observed at a l l . These facts are a verification Zv
2
Ζτ
Z r
ADVANCES IN
140
CHEMISTRY SERIES
of similar results obtained b y Gulbransen and associates (17). T h e effect of hydrogen on the stability of the delta phase is therefore comparable to the effect of oxygen and nitrogen on the uranium-zirconium system (14). T h e delta phase is possibly a nonequilibrium structure produced by the transformation of the gamma phase. A t 30 and 50 atomic % hydrogen the alloy consisted essentially of α and the face-centered cubic zirconium hydride. β replaced at 720° C . for the 50 atom % hydrogen alloy. The unidentified phase previously designated as U n known A appeared above 700° C . at a l l hydrogen levels i n this alloy. Heats of Solution. T h e heat of solution of hydrogen i n these zirconiumuranium systems was determined from the Arrhenius plots of the isotherm data (log Ρ vs. l/T). T h e average Δ Η values, calculated from the slopes of the isochors, increase w i t h the hydrogen content until the system has been completely converted to δ-zirconium hydride and uranium, after w h i c h the value drops slightly. These results, presented i n Table V , indicate that the hydrogen is held more strongly as it passes through the solid-solution stage into compound forma tion. T h e uranium-zirconium alloy is broken down i n the process and the hydrogen reacts w i t h the zirconium. T h e heat of solution i n uranium is about + 1 kcal. per mole as compared to —35 kcal. per mole for pure zirconium, indicative of the m u c h greater stability of the zirconium hydride. π
ν
Figure 4.
Proposed Zr-H-U 627° C. section
phase diagram
12. KRAUSE ET AL.
Zirconium-Hydrogen-Uranium
s+r
Figure 5.
8
2
Proposed Zr-H-U
Systems
8+H
141
2
phase diagram
675° C. section Table V.
Heats of Solution of Hydrogen in Zirconium-Uranium Alloys
Zirconium-Hydrogen
Phases
—AH, Kcal. per Mole 1 wt. % uranium
a + H solid solution «zr + βζι-H two-phase region 0zrH + H solid solution βζτΉ. + 5zrH two-phase region 5zrH + H solid solution Zr
25.9 29.5 33.4 47.9 41.2
2
2
2
25 wt. % uraniuh. 30.7 35.2 39.1 50.6 47.2
F o r the 1 weight % uranium alloy, the values of the heat of solution range from —25.9 to —47.9 kcal. per mole, whereas the values i n corresponding parts of the system are higher for the 25 weight % alloy. T h e range is —30.7 to —50.6 kcal. per mole, indicating that the rejection of a larger amount of uranium has only a small effect on the energy requirements for hydriding. Ternary Diagrams. Proposed isothermal sections of the zirconium-hydrogenuranium ternary diagram at 627°, 675°, and 750° C . are shown i n Figures 4, 5, and 6. T h e isotherm and x-ray diffraction data from this study, when combined w i t h those of previous investigators and the known binary diagrams, permit de duction of these sections. T h e exact extent of some of the very narrow regions is i n doubt, because of the difficulty i n pinpointing these small areas. The single-phase fields of α-zirconium, the y uranium-zirconium solid solu tion, a n d δ-zirconium hydride have well-defined phase boundaries. However, the exact limits of the single-phase fields of the y uranium-zirconium solid solution, α-uranium, and β-uranium are not as certain. 2
1
ADVANCES IN CHEMISTRY SERIES
142
r~A
+ H
2
\+\\\
n\\ \?° 5 0
A
8+)9 + H ^ 0
/
u
\
\ /
/
30yf
/
y , +
2
/ 2
\
A
I
20/ ΙΟ/
60
0
JV80 \
A ^ W 90
sj 80
W 70
V/
10
60
8
Figure 6.
Proposed Zr-H-U
8 + H,
phase diagram
750° C. section T h e rather narrow two-phase fields such as the delta hydride + a - u r a n i u m i n the 627° section, and the corresponding delta hydride +/?-uranium i n the 675° and 750° sections have somewhat uncertain limits. Other two-phase fields are w e l l defined. Similarly, the limits of the broader areas having three solid phases are fairly certain, whereas those of extremely narrow regions such as the γι + 72 + oturanium i n the 675° C . section and the delta hydride + γι + β-uranium i n the 675° a n d 750° C . sections are subject to question. A d d i t i o n a l x-ray data w o u l d be helpful i n defining these phase fields.
Literature Cited (1) Edwards, R. K., Levesque, P., Cubiciotti, D., J. Am. Chem. Soc. 77, 1307 (1955). (2) Ells, C. E., McQuillan, A. D., J. Inst. Metals 85, 89 (1956-57). (3) Espagno, L., Azon, P., Bastien, P., Compt. Rend. 248, 2003-5 (1959). (4) Gulbransen, Ε. Α., Andrew, K. F., J. Electrochem. Soc. 101, 474 (1954). (5) Gulbransen, Ε. Α., Andrew, K. F., Trans. AIME 203, 136 (1955). (6) Gulbransen, Ε. Α., Andrew, K. F., Ruka, R. J., "Solubility of Hydrogen in the 50 w/o Uranium-Zirconium Alloy," Westinghouse Research Laboratories Rept. 100 FF1010-P1 (Oct. 16, 1956). (7) Hagg, G., Z. physik. Chem. (Leipzig) 11B, 433 (1930-31). (8) Hall, M . N., Martin, S. L., Rees, A. L., Trans, Faraday Soc. 41, 306 (1945). (9) La Grange, L . D., Dykstra, L . J., Dixon, J. M . , Merten, U., J. Phys, Chem. 63, 2035 (1959). (10) Libowitz, G. G., J. Nucl. Mater. 2, 1-22 (1960). (11) Libowitz, G. G., U. S. At. Energy Comm. Rept. NAA-SR-5015 (June 30, 1960).
12. KRAUSE ET AL.
Zirconium-Hydrogen-Uranium Systems
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