Hydrolysis properties of uranium monocarbide and dicarbide

JOURNAL

HYDROLYSIS

OF THE

PROPERTIES

LESS-COMMOS

MET.4LS

OF URANIUM

419

MONOCARBIDE

AND DICARBIDE

University

of Califoifornia,

Los

Alamos

Scientific

(Received

I;cbruarv

Labovatovy, roth,

Los

Alnmos,

X.M.

(lT.S..4

.)

1962)

The hydrolysis of commercial UC and IT& prepared by arc melting uranium metal and spectra grade graphite was investigated. X quantitative mass spectrographic study of the room temperature gaseous hydrolysis products showed UC to produce mainly methane and UC2 to produce mainly ethane and other alkanes. The UC gaseous hydrolysis products are very similar to those produced by ThC and PuC. The UC2 products are similar to those produced by ThCz in that both consist of about two-thirds even-numbered carbon atom hydrocarbons, about three-tenths hydrogen plus methane, and a small fraction of catenated odd-numbered carbon atom hydrocarbons. INTRODUCTION

The hydrolysis of uranium carbide (“U&,“) was first studied by MOISSAN’-“, who reported 14.27% Hz, 79.32% CH4, 5.9694 CzH4, and 0.45s/o &Hz were produced at room temperature.

All percentages

are expressed

in mole percent.

The hydrolysis

(temperature not stated) of two partially analyzed “uranium carbide” specimens was carried out by LEBEAU AND DA~~IEKS4. The first specimen contained 1.4751 graphite, whereas the second contained no graphite, 91.6% uranium (total U, free and combined), and 90.85% “uranium carbide.” The gas analysis results were 49.6zyl; and 28.91% Hz, 12.98% and 19.79% CH4, 24.160/‘, and 22.680/O CZHG, 2.74% and 5.55% Cd%, 0.76% and 4.73% C4H 10, 2.26% and 1.36;/, C2H4, 5.56% C3Hs and higher alkenes, and 1.92~/~ and 2.55% acetylenes, respectively.

and 14.437; (The results

from two runs on the first specimen are averaged.) A comprehensive investigation entitled “Uranium carbides - their preparation, study, and hydrolysis” was carried out by LITZ~ for his doctoral dissertation. The hydrolysis of UC was studied from 83 to 4oo”C, and it was found that the volume percent HZ increased from 12.4~/~ to 99% and the CH4 decreased from 81% to 0.5”5 over this temperature range. The Hz and CH4 concentrations changed very rapidly with temperature above 2oo°C. At 83°C the gaseous products found (in volume percent, which is nearly identical to mole percent) were 12.4% HZ, 81% CH4,3.90/6 higher paraffins, 1.6% olefins, 0.4% CO, and 0.3% COz. No acetylenes were detected. The reaction of UC2 with water and various aqueous solutions was studied at 81”C, and it was concluded that the gaseous hydrolysis products are essentially the same in pure water, acid or basic solutions or in an oxidizing medium (HCl acidulated FeC13 solution). The gaseous products resulting from the 81°C pure water hydrolysis were 17:~ Hz, 309/o methane, 30% ethane, 0.7:/o propane, 7.29: butane -+ pentane, 2.506 ethvlenc,

420

C. I'.KEMPTER

0.7% propylene, 8.7% higher olefines, 2.17" acetylenes, 0.9% CO, and0.2% COZ. The gas phase hydrolysis of UC2 was studied from IOO to 248°C and it was found that the volume percent HZ increased from 47% to 96% and the CH4 decreased from 10% to r.17~ over this temperature range in analogy withthe UC hydrolysis. The concentration of the higher paraffins and the olefins also decreased with increasing temperature. The UCz-Hz0 reaction proceeded at a much faster rate than the UC-Hz0 reaction, and in both cases the only detectable uranium product was UOs. MALLETT, GERD~ AND NELSON~state that U&a does not react appreciably with water even at 75°C. ALBRECHTANDI(OEHL~-8 studied the kinetics of the reaction of UC2 with water vapor at 29 & 3 mm of Hg from 50 to 2oo’C. The rate constant was expressed by the equation : k = I .88.104 exp (-8350/RI‘), where the pre-exponential frequency factor is in pg cm-%ec-1 and the activation energy is in caljmole. The linear rate constant varied from 0.044 pg cm-‘Jsec-1 at 50°C to 3.2 ,ugcm-%ec-r at 2oo’C. The only reaction product identified by X-ray diffraction was UOz. BOETTCHER AND SCHNEIDER~ studied the UC hydrolysis and stated “In a short-term test no detectable attack could be discerned with water at temperatures below 5o”C, while at 60°C attack was visible after one hour. At 65°C 600 mg/cmz/h of surface material was removed and at IOOOCviolent reaction occurred.“. In reporting their investigation of the UTh-C system, BRETT, LAW ANDLIVEY 10 stated that “uranium dicarbide as prepared does not decompose by reaction with water-vapour at room temperature. It is stable in air up to zoo°C but by 300°C has decomposed to form UaOs. In argon saturated with water-vapour, decomposition does not take place until above 300°C when UOs is formed in contrast to the formation of U308 as in air.“. These investigators used “UC2 + C” pellets. Reaction rate studies of thorium-uranium dicarbides in moist air have been recently reported by ENGLE, GOEDDEL ANDLUBXrii. For arc melted UC2 having a bulk particle surface area of 30 cm2jg they found an initial rate constant of 0.25 ,ug/cms/sec at 50°C assuming a linear rate law. For the 30 and50YZ hydrolysesof UC2, aqualitative analysis of the gases produced showed HZ, CHJ, C2H4, and &He to be present. A rate study of the UC-Hz0 vapor reaction was carried out by MURBACH~~. Two samples were reacted with water vapor at 20 mm of Hg. The first sample (1.74 g) gained 0.05 mg/min/g at 400°C and 0.44 mg/min/g at 460°C. The second sample (0.79 g) gained 1.81 mg/min/g at 600°C initially, but the rate rapidly decreased to 0.17 mg/ min/g. The most recent report of uranium carbide hydrolysis studies is that of BRADLEY ANDFERRISIS who investigated the reaction of uranium monocarbide with water at 80°C and 90°C and with 5.6 M HCl at 80°C. They found that in all three cases a brown U(W) compound and essentially the same gaseous products (approx. II vol.% Hz, 86 v01.~/~CH4, z vol.% &Ha, and 0.6 vol.% C3Hs at 80°C) were evolved. These results were compared to those obtained by OCKENDEN~~ in his 2o°C hydrolysis of UC who reported 8% Hz, 85% CH4, 5% C2H 6, and 1% C&s paraffins. The close agreement of the 80°C and 90°C hydrolysis product distribution is not in agreement with the findings of LITZ”. BRADLEY ANDFERRIS Ia also hydrolyzed some UC-U& mixtures at 80°C and found that as the UC2 concentration increased from o to about 63 wt.%, the methane decreased to 14 vol.%, and the hydrogen and ethane increased to 23 and 38 vol.%, respectively. Early articles discussing the theory of carbide hydrolysis have been written by J. Less-Commcm Metals, 4 (1962) 4Ig-q.5

HYDROLYSIS PROPERTIES OF UC APU‘D CCa SCHMAHL~~and by SCHMIDT~~~.More recent discussions ysis of the uranium carbides have been presented doctoral

involving

421 the theory of hydrol-

by LITZ~ and by PALENIK]~ in their

dissertations. EXPERIhlENTAL 31ETHODS

Uranium monocarbide “sponge” was obtained from the Davison Chemical Company (Erwin, Tennessee). Uranium dicarbide was prepared by arc melting (with a spectrographite

electrode)

weighed

quantities

of uranium

and spectra

grade graphite

in a

helium atmosphere. The experimental techniques used have been described in detail by KE~~PTER AWL) KRIKORIAN~X; the hydrolysis studies were carried out in a “Pyrex” reaction tube which could be directly attached to a mass spectrograph. The assembly was allowed to stand overnight at an ambient temperature of about 25°C before coupling to the mass spectrograph. All operations with the UC and UC2, except helium flushed dry box. Both materials

---I00 mesh powders. X-ray powder diffraction examination Cu I<.\ radiation. The lattice parameters and are not corrected

metallography,

were hydrolyzed

were carried out in a

in the form of freshly- ground

was carried out on a r\jorelco unit using were determined on an IBM 704 computer

for refraction. RESULTS AND DISCUSSION

The spectrographic

analysis

results for the UC and UC2 (in this article the notations

UC and UC2 will be understood to denote the UC and tetragonal not necessarily imply stoichiometry) are shown in Table I.

UC2 phases, and do

The chemical analysis results for the UC and UC2 are shown in Table II. If one assumes o.zo~/~ and 0.25% oxygen by difference to be present as UOZ, the resultant empirical formulas are U00.94 and UC 1 B; however, if oxygen is present in J.

I~~SS-COWZVUIPI,Metals,

4 (IQ~Z)

.+IO 42.5

C. P. KEMPTER

422

solid solution the formulas are UC0.92800.031 and UC1.8700.04. The analytical methods used have been discussed by KRIEGE~~. Examination by X-ray powder diffraction showed the UC to consist mainly of face-centered cubic UC (a = 4.9603 f 0.0001 A) TABLE II CHEMICAL

ANALYSIS

RESULTS

ON

UC

AND

UC

94.84

4.96

0.52

IJCz

90.32

9.43

0.93

UC2

99.80 99.75

with very weak lines of UOZ present. The UC2 X-ray film showed only lines of bodycentered tetragonal UC2 (a = 3.5206 f 0.0003 A, c = 5.9823 5 0.0017 A). A metallographic examination of the UC2 by HOFFMAN of this Laboratory showed UC2 with some carbon needles present. The mass spectrographic results (gaseous hydrocarbons and hydrogen) are shown in Table III.

MASS

Ha

TABLE III RESULTS OF UC AND UC2 HYDROLYSIS

SPECTROGRAPHIC

CHa

UC.

5.9

79.7

UC2

14.1

‘7.3

&HI

0.8 5.3

CzHs

3.1 39.4

&HI

CaHe

CaHs

I.2

0.4

2.0

I.5

CaHx

4.2 9.5

CnHm

0.5 5.9

(mole

CrH,o

“/o)

C.H,.

CeH,n

1.6 2.0

2.6

The UC hydrolysis produced about 86% gaseous alkanes (&Hz,++,z), and is thus similar to the ThC hydrolysis reported by KEMPTER AND KRIKORIAN~~, which yielded about 89% gaseous alkanes, and to the PuC hydrolysis reported by DRUMMOND, MCDONALD, OCKENDEN AND WELCI@~, which produced mainly hydrogen and methane together with a small quantity of higher aliphatic hydrocarbons. The UC2 hydrolysis produced 64.6% alkanes, but only about 114as much methane as the UC hydrolysis. It would appear that MoIsSAN’S~-~ “U&3” consisted mainly of UC. The above results for UC compare fairly well with the 83°C results of LIZ+, the zo°C results of OCKENDENTS, and the 80°C and 9o°C results of BRADLEY AND FERRIS~~. It is difficult to compare the above results for UC2 with those of LEBEAU AND DAMIENS~ because of the wide spread of their data; however, their three hydrolyses produced 2 to 3 112times as much hydrogen as observed above. One possible source of hydrogen in their hydrolyses would be from the reaction of any free uranium with water. w~~~~21.22 has recently reviewed the corrosion behavior of uranium, including aqueous corrosion. If one subtracts the percentages of Hz produced, and then calculates the percentages of hydrocarbons based on total hydrocarbon summations for the two specimens of LEBEAU AND DAMIENS~ and for the UC2 specimen in Table III, one finds a semi-quantitative agreement between hydrocarbon species for the three sets of results. Moreover, if one makes the same comparison between the ThC2 hydrolysis results of LEBEAU AND DAMIENS~, who reported 59.6% Hz, and KEMPTER AND KRIKORIAN~~, who reported J. Less-Common Metals, 4 (1962) 419-425

HYIIROLYSIS

27.2%

Ha there

is a fair agreement

phase purity of the specimens can only

PROPERTIES

compare

results

OF UC

of hydrocarbon

hydrolyzed

by LEBEAU

on a speculative

basis.

ANI) UC2

423

species distribution. AND

DAMIENS~

Since

the

is unknown,

one

the 81°C

lJCa

If one compares

hydrolysis results of LIT@ with the UC2 results in Table III, the agreement is not good cvenif oneextrapolates hiscomposition tIersus temperature curve to room temperature. Unfortunately, LIZ+ did not present analytical or X-ray diffraction characterization of the specimens he hydrolyzed. Since UC is often found as a second phase in UC2 preparations, it is interesting to note that the hydrolysis products calculated for a 20 UC-80 UC2 molar mixture (using the data in Table hydrolysis results of LITZ. This is shown in Table IV.

LlTZ5

t;(‘e

2" rc/80 t:C‘a _

The 80°C hydrolysis

'7 13.r

30 29.8

2.5 4.1

30 3L.L

III)

2.1 1.5

agree well with the81”C

7.9 0.9

results of BRADLEY AND FERRIs~~ on a UC-UC2

9.4 IL.1

mixture

are

consistent with the results in Table III withrespecttothechangesinhydrocarbonconcentrations; however, the increase in hydrogen concentration observed by these investigators

is much larger than

one would predict

from the Table

III

data.

Since

metallographic examination of their 63 wt.% UC2 mixture showed “a third unidentified phase” and the reaction was carried out at a higher temperature, it is difficult to make rigid comparisons. Although the hydrolysis results for the isomorphous carbides, ThC and UC, agree very well as pointed out above, such is not the case for the homotypic carbides ThCT and UC*. As previously shown by KE~IPTER AND KRIKoRIAN~*, the ThC2 hydrolysis produces about twice as much hydrogen, about one seventh as much methane, and about ten times as many alkynes. In both ThCz and UC2 ,the carbon atoms occur in pairs with bond distances of about 1.4h-I.59 A and 1.340 A, respectively. It is interesting to note that if one sums the even-numbered carbon atom hydrolysis products for ThCz and CCa, the results are 67.4% and 64.2;;, respectively. Thus they constitute the major hydrocarbon percentage and are nearly the same. Moreover, the sums of the catenated odd-numbered carbon atom hydrolysis products are 3.00/;, and 4.4%, respectively. Thus they constitute the minor hydrocarbon species and are nearly the same. Finally, if one sums the Ha and CHJ (the only non-catenated hydrocarbon spetics), the results are nearly the same -- 29.6% and 31.4~/~, respectively. X distinction is made between CH4 and the catenated hydrocarbon species because in lattices such as ThC and UC where the minimum C-C distances (3.78 A and 3.51 A, rc,spectively) are appreciably greater than aliphatic C-C bond distances (1.20~1.54 a), one would intuitively expect CH4 as the major aliphatic species; however, in lattices such as ThC2 and UC2 where the carbon atoms occur in pairs, one would then expect catenated hydrocarbons as the major species. The C-C bond distance in ThCz is similar to the C-C alkane bond distance of 1.54 A, and 35.1:/o catenated alkanes are produced as

C. P. KEMPTER

424

the major hydrocarbon species; however, the C-C bond distance in UC2 is similar to the C= Calkenebond distance of I.334 A, but 47.3% catenated alkanes are evolved as the major hydrocarbon ally as the predominant

species. Of course it is possible that alkenes are formed initihydrocarbon species in the UC2 hydrolysis, but are rapidly re-

duced in part to alkanes. In the above discussion, it must be remembered that themass spectrographic method gives only those species having sufficient vapor pressure to be detected. It seems likely

that

both

UC and UC2 become

coated

during hydrolysis

with hydrocarbons

which inhibit further hydrolysis. One possible support of such inhibition by coating was found in the X-ray diffraction examination of the hydrolysis products after they had been standing under water for a number of days at room temperature. Each of the two mixtures was washed on a Buchner filtering assembly first with distilled water, then with ethanol to remove water, and finally with trichloroethylene to remove ethanol and hydrocarbons. The solid residue was then transferred to a dry box for X-ray specimen preparation. The X-ray film of the UC residue showed both UOZ and unreacted UC, whereas the UC2 film showed both UOZ and unreacted UC2. In the case of ThC and ThCs hydrolysis, however, KEMPTER AND KRIKORIAN~~ found only ThOz. In view of this difference,

it is interesting

to examine

the higher molecular

weight

distribution of the ThC versus UC and the ThCz versus UC2 gaseous hydrolysis products and to compare the percentage of hydrocarbon species where the C subscript is greater than 4. For ThC and UC these are 0.0% and 1.6%, and for ThCz and UC2,2.0% and 4.6%. However, the analogy does not hold for comparison of MC versus MC2 lattices since the 2.0% for ThCz is greater than the 1.6% for UC, and yet the ThCs hydrolysis but not the UC hydrolysis appeared to go to completion. With respect to reaction rates, it was observed that the UC2 hydrolyzed much faster than the UC, in agreement with LITZ~. ENGLE, GOEDDEL AND L~;BY’~ found that ThCz reacts about ten times faster than UC2 and that the carbon-deficient materials had somewhat lower rates. They found that hydrolysis curves of percent weight gain versus time for ThC2, UC2, and ThCz-UC2 solid solutions showed rapid initial weight gains followed by a long plateau with a slight positive slope. In the foregoing discussions, one must of course consider all of the possible variables that might influence both the reaction rate and the distribution of hydrolysis products

such as temperature,

pressure,

water purity,

metal

carbide

purity,

and C/M

molar ratio. ACKNOWLEDGEMENTS The author wishes to thank K. V. DAVIDSON for the UC2 preparation, Dr. E. D. LOUGHRAN for mass spectrographic analyses, G. C. HEASLEV for chemical analyses, JUANITA V. PENA for spectrographic analyses, JOSEPHINE E. POWERS for the IBM 704 fits, and L. A. WAHMAN for X-ray film reading and general assistance. REFERENCES 1 H. 2 H. 3 4 5 6

MOISSAN, Bull. sot. chim. Pavis, ‘7 (1897) 14. MOISSAN, Compt. rend., 127 (1898) 911. H. MOISSAN, The Electric Furnace, 2nd edn., (English translation), Easton, Pa., U.S.A., 1920. P. LEBEAU AND ,4. DAMIENS, Conzpf. rend., 156 (1913) 1987. L. M. LITZ, Ph.D. Dissevtation, Ohio State University, 1948. M. W. MALLETT, A. F. GERDS AND H. R. NELSON, J. Electrochem.

TheChemical

J. Less-Conzmon

Sm.,

Publishing

99 (1952)

iWet&-,

Co.,

197.

4 (1962)

419-425

HYI>ROLYSIS PROPISRTIES OF UC ASI) i \I\'. %I. ALBRECHT

AND B. G. KOEHL,

PYOC. 2nd U..V. Inierf7. Coxf.

IJC2 Prnce_ful

4~5 IYses ,~?tov~ic Enevgyl

Vol. 6, LT. N. Publ. Geneva, Switzerland, 1958. 8 \\‘. 91. ,-ZLBRECHT AND B. G. KOEHL, Battellr Mem. lxst. REpt. .Vo. B,Z(IZ-1313, January ~7, rcp,g. 3 A. BOETTCHER A~YD G. SCHXEIDER, Proc. 2nd (7.X. Z&rwz. Conf. P~acefztl ~_~ses~~fowzic Enwg~~, Vol. 6, U. N. F’ubl., Geneva, Switzerland, Ig,jX.

AEC R. and D. Rrpt., LA’;JA-.YK-633~, July 1.5, 1901. 1:Xhf. 1. I~RADLRVAND I,. MM.FERRIS, Oak Ridge A’atl. Lab. Refit. OKSL-3101, August 31, 1901 11 I). iv. OC.KE~DEK, personal communication to BR,xDLE~ .kxI)I'ISRRIS,I>cccmbcr 14, I95<)_ ‘j s. (;. SCHMAHL, %. Elrctsochem., $0 (lg34) 68. 113J. SCHMIDT, %. Elpctrochenz., 40 (1934) 170. 17 G. J. I'ALENI~C.Ph.D. dissertation,lTni\-ersit]; of Southern C‘alif., 1960.

l2 R. 1%'.MURHACH,

Ix (‘. I'. [(EMPTER AND N. H. KRII~ORIAX, /. &'S~-~U??MM1~2lkf&k, I!)0 Ii. KRIE~E, I.os.-l/umosSci. Lab. Refit. L.4-2306, (1939).

_t (I@)

24-t.

2’) J_ IA. I)R~-MMoN~, B. J. ~ICDONALI), Fl. yl. OCKEZIDEN AR‘13 G. .\. \$‘EIXH, ,/. C‘hPm. .%I . . (‘957) 47%. “1 J. 1‘. \vAHER, IAS .Ilamos Sri. Lab. Rept. LA?-2035 (1958). 2s J. T. \VAI+F.R,I7.S. .4fomic Energy Comm. h’rpt. TZD-7587, (1900).