it not be so large as to introduce uncertainty into the calculated value of the effective diffusion coefficient. Nomenclature
f = flux of a component, mole, (length)?(time) n = molecular densit). mole (length)3 7 = velocity, length time x = space coordinate, length 1 = mole fraction, diniensionlesr D = binarv diffusion coefficient, (length)* time G = mass velocitv, mass (length)*(time) L = length of diffusion path, length hl = molecular \\eight, mass/mole
Acknowledgment
I t is a pleasure to acknowledge the helpful criticisms and suggestions offered by Donald S. Scott. Cniversity of British Columbia, Vancouver, B. C., Canada. literature Cited
(1) Hirschfelder, J. O., Curtis, C. F.: Bird, R. B., "Molecular Theory of Gases and Liquids," p. 516: LYiley. New York, 1954. (2) Hoogschagen, Jan, I N D . ENG.CHEM. 47, 906 (1955). (3) Scott, D. S., Cox, K. E.. Can. J . Chem. Eng. 38, 201 (1960). (4) Weisz, P. B., Z.physik. Chem. (Frankfurt) [N.S.] 11, 1 (1957). (5) Wicke, E., Kallenbach, R., Kolloid-2. 97, 135 (1941). RECEIVED for review January 9, 1961 ACCEPTED August 15. 1961
PLUTONIUM HEXAFLUORIDE THERMAL DECOMPOSITION RATES J A C K F I S C H E R , L . E. T R E V O R R O W , G . J. Argonne National Laboratory, Argonne, Ill.
Uranium and plutonium may be recovered f r o m nuclear reactor irradiated oxide fuel elements by fluoride volatility Important to the process is the minimizing of loss when plutonium hexafluoride is transported through
processing.
heated zones where ihermal decomposition may take place. Thermal decomposition studies, both static and flow, have shown that the rate is dependent on the surface a r e a of the plutonium tetrafluoride produced i n the decomposition and the pressure of the hexafluoride.
The hexafluoride can be
efficiently recovered from the 500' C. zone of the fluorination reactor by rapid quenching of the effluent gas and can be transferred withoLt difficulty by distillation or by tronspiration in a fluorine or helium stream.
HE Direct Fluorination \.olatility Process is being developed Tat Argonne Xational Laboratory to recover uranium and plutonium from spent uranium dioxide power reactor fuels. After removal of the cladding: the fuel will be treated Xvith fluorine to convert the oxides to the respective fluorides. Uranium can be separated from plutonium by taking advantage of the difference in rates of fluorination of the tetrafluorides and the difference in chemical reactivities of the hexafluorides. Uranium and plutonium \rill be recovered separately and highly decontaminated from fission products. Uranium hexafluoride is relatively stable a t elevated temperatures. whereas plu-tonium hexafluoride undergoes thermal decomposition to plutonium tetrafluoride and fluorine. Knowledge of the equilibrium constant and rate of thermal decomposition of plutonium hexafluoride is of prime importance in many steps of the direct fluorination volatility process. Both the stoichiometry and the equilibria involved in the decomposition of plutonium hexafluoride have been investigated previously (5). T h e rate of thermal decomposition of plutonium hexafluoride vapor has been studied by a static method a t initial
V O G E L ,
A N D W . A. SHlNN
pressures of 17 to 98 cm. at a temperature of 161 C. T h e rate has also been studied by a flow method at lower partial pressures and at temperatures from 150" to 250' C. Laboratory work has been carried out on the fluorination of plutonium dioxide and tetrafluoride and also on the efficiency of transport of plutonium hexafluoride which illustrates the use of equilibriums and kinetic data and their importance to the process. T h e rate of decomposition is dependent both on the surface area of plutonium tetrafluoride and on the pressure of plutonium hexafluoride. Experimental results on the thermal decomposition have been fitted to a rate equation assuming concurrent first and zero orders rvith respect to plutonium hexafluoride pressure. Maximum recovery of plutonium hexafluoride from a fluorination reactor was obtained by cooling the effluent rapidly to a temperature belo\\ 150' C. Plutonium hexafluoride has been transferred \vith recoveries of greater than 99.3yc at temperatures of 25' to 70' C. T h e transfers were made by distillation and by transpiration in fluorine or helium. Experimental
Special apparatus and techniques must be employed because of physical and chemical properties of plutonium hexafluoride. T h e triple point of plutonium hexafluoride is 51.59" C.. 533.0 mm.: and the boiling point at one atmosphere is 02.16' C. ( 7 ) . Plutonium hexafluoride is a very strong fluorinating agent. and reacts vigorously Lvith many chemicals. I t must be handled in closed systems. preferably metal. under anhydrous conditions. T h e predominant isotope ivhich \vi11 be encountered in reactor fuel processing-and the one most available for experimentation-is plutonium-239. This has a high specific activity and a long biological half-life and is therefore extremely toxic. T h e maximum permissible body burden has been set at 10-7 gram. Glove boxes are used to prevent inhalation or ingestion of plutonium. T h e emitted highl>energetic alpha particles react with light nuclei, such as fluorine, to produce fast neutrons. This neutron hazard must also be considered by a n experimenter \\orking with 100-gram quantities of plutonium. VOL. 1
NO. 1
JANUARY 1962
47
i,u
DECOMPOSITION VESSEL (440 mU
'
BY PASS
CONDENSER (300mU
* VACUUM
50 grams Pu02
MANIFOLD AND ADDITIONAL COLD TRAPS NOT SHOWN
.
Figure 1 Boat reactor system for preparing plutonium hexafluoride; vessel and auxiliary equipment for flow method decomposition studies
Materials. Commercial high purity fluorine was used in preparing plutonium hexafluoride. The plutonium hexafluoride was prepared by reacting fluorine, at 500 ' to 550 ' C., with plutonium dioxide or plutonium tetrafluoride, obtained from AEC sources. Figure 1 is a diagram of the fluorination system. Fluorine a t about 1 atm. of pressure was preheated and circulated by means of a magnetic piston pump over the plutonium compound, in a nickel boat, within a tubular nickel reaction furnace. The volatile plutonium hexafluoride was collected in nickel traps, cooled with dry ice. Equipment and Procedure. All of the equipment used in the experimental work was constructed with nickel and Monel. Component parts of the apparatus were connected by manifold systems to a high vacuum system consisting of mechanical and oil diffusion pumps, to a helium supply, to a fluorine supply, and to pressure measuring devices such as Bourdon gages and diaphragm pressure transmitters. Nickel valves, flare fittings, and silver soldered and welded joints served to connect the various components of the apparatus All of the equipment was pretreated with fluorine before use. RATE OF DECOMPOSITION OF PLUTONIUM HEXAFLUORIDESTATICMETHOD. The stoichiometry and equilibrium constants of the reaction PuF&)
e PuFds)
+ Fdg)
(1 1
have been established ( 5 ) . Since there is no change in the number of gas molecules in the reaction, it is not possible to follow the rate of decomposition of the vapor by pressure measurements in a static system. The deposition of plutonium tetrafluoride would interfere with measurement of the partial pressure of plutonium hexafluoride by many of the common physical methods such as spectrophotometry, thermal conductivity, and density. Both static and flow methods were employed to obtain rates. I n the static experiments, rates were obtained from initial and final compositions after heating a sample of plutonium hexafluoride for a given period to obtain integral rates. 48
I & E C PROCESS D E S I G N A N D D E V E L O P M E N T
decomposition
Prior to each experiment the storage vessel containing the plutonium hexafluoride was evacuated at -196' C. to remove fluorine accumulated from radiation decomposition. The plutonium hexafluoride \vas then transferred by vacuum distillation to a supply vessel, was condensed, and any remaining fluorine was removed by evacuation at -196' C. The 50-ml. supply vessel was connected by a manifold to a 50-ml. decomposition vessel which had been jveighed previously. The supply vessel and associated lines were heated to aid the transfer of adequate quantities of plutonium hexafluoride to the decomposition vessel. The vessel was preheated to the experimental temperature in a thermostated, aluminum block wound with Nichrome wire. The temperature of the decomposition vessel was held constant to 1 0 . 2 ' C. A n experiment was initiated by opening the valve to the evacuated decomposition vessel and allowing the xvarm plutonium hexafluoride to expand into it. The amount of plutonium hexafluoride transferred to the reaction vessel could be controlled by P-V-T measurements. At the end of the experiment> the furnace was loTvered, and the decomposition vessel was quenched in liquid nitrogen to approximately 100' C. in 1 minute and to room temperature in 2 minutes. The error introduced by decomposition during the quenching period \vas therefore small. After quenching, the decomposition vessel was \varmed to room temperature and weighed to determine the starting amount of plutonium hexafluoride. The vessel was then evacuated at 25' C. to remove plutonium hexafluoride and the fluorine formed during the reaction. The vessel was weighed again to find the weight of plutonium tetrafluoride formed. Partial pressures of plutonium hexafluoride were calculated from the \$,eights using the ideal gas law. A single reaction vessel Lias used for several consecutive experiments. Therefore, each experiment was carried out in the vessel containing plutonium tetrafluoride which had accumulated from previous experiments-a small correction w i i s made to account for the change in volume. RATE OF DECOMPOSITION OF PLUTONIUM HEXAFLCORIDEFLOW METHOD. The equipment described for determining
the decomposition rate by the static method was useful v, hen the partial pressure of plutonium hexafluoride was higher than 100 mm. For process development, however, decomposition rates a t partial pressures of 0 to 25 mm. must be known. These were obtained by a flow method in which plutonium hexafluoride a t known partial pressures was circulated through a heated vessel. This work was carried out in larger facilities which permitted preparation and handling of quantities of plutonium hexafluoride weighing up to 100 grams in a single experiment. These facilities are contained in a glove box, 10 feet long. 3l/2 feet wide, and 5 feet tall. Filtered laboratory air is passed through the box a t a flow rate of 50 cubic feet per minute. T h e air is discharged from the box through two banks of filters and finally vented to the outside of the building. In one set of experiments the effluent gas mixture, plutonium hexafluoride and fluorine, obtained from the fluorination of plutonium tetrafluoride, was passed through the cylindrical, heated, Monel decomposition vessel. T h e vessel was 2 inches in diameter and 10 inches in length. The gas stream flowed from the decomposition vessel into a cold trap where the plutonium hexafluoride was condensed. Fluorine was recirculated through the fluorinaticn furnace. At the end of the experiment, the decompositicn vessel was weighed to determine the quantity of plutonium tetrafluoride deposited in the vessel. The quantity of plutonium hexafluoride collected in the trap was also determined by weight. This amount plus the quantity which had decomposed in the decomposition vessel was used together with the total quantity of fluorine, as measured by the thermal flow rreter, to calculate the average ratio of plutonium hexafluoride to fluorine in the gas mixture. I n a second series of experiments, the cold trap containing plutonium hexafluoride was cooled in an ice bath, thereby maintaining the partial pressure of plutonium hexafluoride in ' C. the system at 18 mm., rhe vapor pressure of the solid at 0 ( 7 ) . Plutonium hexafluoride vapor, initially free of fluorine, was circulated through the decomposition vessel. T h e preheater and fluorination system were bypassed as indicated in Figure 1. During the course of these experiments the pressure of fluorine increased as the decomposition proceeded as shown by Equation 1. T h e rate of reaction could thus be followed by measuring the total pressure in the system as a function of time. T h e weight of the plutonium tetrafluoride deposited in the decomposition vessel w a s used with the total reaction time to calculate integral decomposition rates.
Results and Discussion Rate of Decomposition of Plutonium Hexafluoride a t 161 C.-Static Method. The reaction rates observed were presumed to be due to the thermal decomposition of plutonium hexafluoride, any reaction with the prefluorinated nickel vessel being considered negligible This assumption is supported by previous work in which, a t temperatures a t least as high as 370 C., there \vas no change in the number of gaseous moles when the hexafluoride decomposed in a prefluorinated nickel vessel ( 5 ) . This indicated that the predominant reaction was PuFs(g) PuFi(s) f Fz(g) and that the extent of the reaction +
Ni(s)
+ PuFe(g)
-+
PuFd(s) f NiFp(s)
(1) (2)
was negligible. T h e rate of decomposition of plutonium hexafluoride was studied by the static method in two types of vessels a t 161 C. T h e volumes of the vessels \vere almost equal, but one vessel was packed with nickel wool to increase the specific area. For
-'
the nonpacked vessel, the surface to volume ratio was 1.8 cm. and the volume was 52 ml. For the packed vessel, the surface to volume ratio was 14 cm.-', and the volume was 51 ml. The first few experiments in both vessels yielded very low decomposilion rates. The rates increased rapidly in the first few experiments for the nonpacked vessel, and then remained almost constant in subsequent experiments. I n the packed vessel, the rates increased to a value much greater than those in the nonpacked vessel containing about the same amount of plutonium tetrafluoride. I n the packed vessel, the plutonium tetrafluoride probably was deposited over a greater area on the surface and in the interstices of the nickel tvool. T h e rate of decomposition of plutonium hexafluoride is dependent upon the surface area of plutonium tetrafluoride. One of the reaction vessels was cut open, and the plutonium tetrafluoride was found on the walls of the vessel and as pieces on the bottom of the vessel. The distribution of plutonium tetrafluoride was not uniform. After the deposition of about 1 gram of plutonium tetrafluoride, in the nonpacked vessel, the rate constants became independent of the quantity of plutonium tetrafluoride in the vessel. This suggests that the active surface area increases initially in a new vessel, but after a certain point. additional accumulation of solid does not significantly increase the active surface area. This leveling-off effect in the nonpacked vessel made it possible to obtain data from which the constants of the rate equation could be calculated even though the surface area was not known. The results of the rate experiments by the static method in the nonpacked vessel are shown in Table I. The rate is dependent on the pressure of plutonium hexafluoride. These results together with the dependence on surface area can be explained by assuming that the rate of decomposition is the result of concurrent first and zero order reactions -dfildt
ko
4-kip,
(3)
vrherep is the pressure of plutonium hexafluoride. The data in Table I were used to calculate values for the constants of E:quation 3 using its integrated form. The values are k~ == 1.09 X lo-' cm. min.-', and kl = 2.50 X cm. min-'. These constants were used with Equation 3 to calculate values of final plutonium hexafluoride pressure for each experimental value of initial plutonium hexafluoride pressure. T h e calculated final pressures are in agreement with the experimental data. T h e rates obtained in the packed vessel increased with increasing mass of plutonium tetrafluoride. T h e rate constant, k l , for the first order homogeneous reaction was assumed to
Tluble 1. Experimental Data Agree with That Predicted from Concurrent Zero and First Order Equation for Thermal Decomposition Rates
'
Temperature, 161 C.; static method1 initial volume of vessel, 52.0 ml. nonpacked reaction vessel; reaction time, 90 min.
Initial Pressure, Cm.
98.1 59.6 51.2 32.6 16.8
Calculated Final Pressure, Deuiatton, Cm . Cm . 69.2 -1.2 38.6 f0.7 31.9 f0.4 17.1 f0.6 4.5 -1.4 Average deviation + O . 9 cm.
Final Pressure, Cm 70.4 37.9 31.5 16.5 5.9
.
VOL.
1
NO. 1
JANUARY
1962
49
hold for the rates obtained in both vessels. T h e value of k l was then used together with the rates in the packed vessel and Equation 3 to calculate values of ko for the rates in the packed vessel. The values of ko thus calculated were not constant, but increased in order of the mass of plutonium tetrafluoride present during a decomposition. This is illustrated in Figure 2. T h e rate constant, ko, for the heterogeneous reaction, should be expressed as a value per unit surface area. I t has not been possible, however, to measure solid surface areas in the work carried out thus far. Since the rates were dependent on the mass of plutonium tetrafluoride in the packed vessel, the active surface area was assumed to be approximately proportional to the mass of plutonium tetrafluoride in the packed vessel. cm. min.? g. Based on this assumption, ko = 39 + 7 X PuF4-l. T h e uncertainty value shows a rather wide variance, but this is to be expected considering the probable wide variance of active surface area with the mass of plutonium tetrafluoride. The zero and first order dependence of the rate is similar to that reported for the decomposition of germanium tetrahydride ( 4 ) . T h e first order dependence can be attributed to unimolecular, homogeneous decomposition of plutonium hexafluoride in the gas phase, and the zero order dependence can be attributed to simultaneous, heterogeneous decomposition of plutonium hexafluoride on the surface of plutonium tetrafluoride saturated by chemically adsorbed gas. Rate of Decomposition of Plutonium Hexafluoride-Flow AT PARTIALPRESSURE OF 18 MM. Method, DECOMPOSITION In these experiments, plutonium hexafluoride a t a partial pressure of 18 mm. was pumped through a 440-ml. decomposition vessel a t a fixed temperature. I n the course of a single experiment, the gas in the cyclic system was re-circulated through the vessel containing solid plutonium hexafluoride a t 0' C. Since the decomposition rate is slow compared with the flow rate, about 200 ml. per minute, the partial pressure of pluto-
0
I .o
20
nium hexafluoride in the decomposition vessel was maintained at 18 mm., its vapor pressure a t 0" C. As the decomposition proceeded, the partial pressure of fluorine increased, and the change in total pressure with time was a measure of the reaction rate. The rate of change of total pressure was also indicative of the effect of added fluorine on the reaction. The reaction vessel was arranged in a vertical position in the furnace. Plutonium tetrafluoride deposited on the walls and bottom of the vessel. The reaction surface of plutonium tetrafluoride after the decomposition of a small quantity of plutonium hexafluoride should reach a constant value as was the case with the nonpacked vessel in the static rate experiments. The rates of plutonium hexafluoride decomposition are compared in Figure 3 for three different temperatures. The change of total pressures with the time depart slightly from a linear function. Thus the fluorine represses the rate of decomposition to a very small degree. Since this work was done only at a single pressure of plutonium hexafluoride, and since the rate Equation 3 contains two constants, it is not possible to use these data to calculate activation energies. T h e rates in terms of mass of plutonium hexafluoride decomposed per unit time can be correlated with the temperatures using a relation similar to the Arrhenius equation Rate = Ae-E'/RT
(4)
where E' is not an activation energy, but rather a temperature coefficient. The value of E' calculated from this work was 12 kcal. mole-'. DECOMPOSITION O F PLUTOXIUM HEXAFLUORIDE IN EFFLUENT FROM FLUORINATTON OF PLUTOSIUM TETRAFLUORIDE. I n the fluorination of plutonium oxide the volatile plutonium hexafluoride must be transported from the hot reactor to a condenser and in this transfer the rate of thermal decomposition of plutonium hexafluoride is of importance in process application.
3.0
WEIGHT PuF4, grams
A Figure 2. Zero order rate constant varies with amount of plutonium tetrafluoride decomposition product in packed reaction vessel
Figure 3. Plutonium hexafluoride decomposition rate drops rapidly with temperature 50
I & E C PROCESS D E S I G N AND DEVELOPMENT
b
0
5
IO
15 TIME, hours
20
25
Table II. Plutonium Hexafluoride in the Hot Fluorine Effluent Gas of the Fluorination Reactor Can Be Recovered with Minimum Decomposition Loss if the Gas I s Quenched Rapidly to Approximately 150' C. Total decomposition time in each experiment, 24 hours. Pressure of fluorine entering the decomposition vessel, 600 to 670 mm.
Rate of Mole Ratio Decomposition Decompoi;tion, PuFe/Fz Entering Temp., O C. G. PuFs Hr.-l Decomp. Vessel 0.00309 7 . 8 X 10-3 144 =k 25 206 & 2 0.104 7 . 9 x 10-3 8 . 0 X 10-3 244 & 30 0.248
Equlib. Const. (1, 5 ) PuF~Fz at Temp. of Decomp. Vessel 0.35 X 0.88 x 10-3 1.6 X
The equilibrium constant at the fluorination temperature (550' C.) is 13 x 10-3 ( I , 5).
T h e fluorination of plutonium dioxide proceeds with a n initial rapid conversion to plutonium tetrafluoride ( 3 ) . Therefore, the maximum ratio of plutonium hexafluoride to fluorine in the effluent from the fluorination reactor can be estimated from the equilibrium constant for the reaction, in Equation 1. The plutonium hexafluoride to fluorine ratio in the effluent stream will he equal to or lesc; than the equilibrium constant a t the fluorination temperature. The equilibrium constant, however, decreases with te.mperature. Therefore, the plutonium hexafluoride to fluorine ratio in the effluent stream will be greater than the equilibrium constant a t all temperatures below some value in the process line between the fluorination reactor and condenser. This will provide a driving force for the decomposition reaction. Since the rate of decomposition also decreases with temperature, the amount of decomposition can be minimized by cooling the effluent gas stream rapidly to a temperature a t which the rate of decomposition is slow. Laboratory prepara.:ion of plutonium hexafluoride with high yields is proof in itrielf that the compound can be efficiently recovered from a fluorination reactor under certain conditions. T h e fluorination of p1.utonium dioxide on the plant scale, however, is to be done in a fluid bed under conditions that are quite different from those used in the laboratory. Plant conditions which will permit the maximum recovery of plutonium hexafluoride from the fluorination reactor effluent must be chosen. T o aid in the choice of these conditions a series of three experiments was carried out to study the decomposition of plutonium hexafluori.de in the effluent gas from a laboratory fluorination of plutonium tetrafluoride. The temperatures of the decomposition vessel through which the effluent passed in these three experiments was 145', 206', and 244' C. The vessel was the same a s that used in the flow experiments described previously. Table 11 shows the data on decomposition of plutonium hexafluoride in the fluorination effluent. I n all three experiments, the ratio of plutonium hexafluoride to fluorine was greater than the equili.brium constant a t the temperature of the decomposition vessel. T h e rate of decomposition in the effluent stream will vary with the plutonium tetrafluoride surface area to volume: ratio in the process line. Therefore, the rates in Table I1 cannot be directly extrapolated to process conditions. T h e results indicate, however, that decomposition of significant amounts clf plutonium hexafluoride in the effluent from the fluorination reactor will be limited to the section of the line which is a t a temperature between 550" and 150" C. TRANSFER O F PLUTOSIUM HEXAFLUORIDE. The rate of decomposition of plutonium hexafluoride a t temperatures below 140" C. is slow enough that gram quantities of the
Table 111.
High Efficiencies Were Obtained in Transferring Plutonium Hexafluoride in the Vapor Phase Temperature o f transfer path
70' C.
PuF.
PuF~ Vaporized, G. 28.43 (0.04)o 28.49(0.04) 23.38 ( 0 051
Recove;ed Transfer in Condenser, G. Recovery, % Gas 28.40 (0.05)0 99.98 He 28.35(0.01) 99.51 He 23.37 10.08) 99.96 He 48.53 (o.ooj 99.41 He 48.82 (0.05j 45.83 ( 0 . 0 1 ) 99.48 He 46.07 (0.0'2) 40.21 (0.01) 99.31 He 40.49 (0.03) 14.90(0.08) 14.93(0.43) 100.20 FZ 44.80 (0.06) 44.81 ( 0 . 0 0 ) 100.02 (Vacuum) a Small corrections were made for loss of fluorine by alpha radiation decomposition. The correction, in grams, is shown in parentheses.
compound can be handled without decomposition of a significant fraction of the material. This is illustrated by the results of the efficiency of transfer of plutonium hexafluoride by bacuum distillation and by transpiration in a stream of fluorine or helium gas. The transfer was made between two vessels, each of about a 300-ml. volume. T h e flow path a t 70' C . included about 2 feet of 5,le-inch I.D. tubing and several Hoke diaphragm valves. The results of the transfers are listed in Table 111. Multigram quantities of plutonium hexafluoride can be transferred by these means with recoveries of greater than 9 9,370. Uranium hexafluoride is conveniently transferred by gravity flow in the liquid state. The same technique for the transfer of plutonium hexafluoride might prove convenient in process application. T o demonstrate that the plutonium hexafluoride decomposition rate a t a temperature slightly above its triple point was not prohibitively high, a 38-gram sample of plutonium hexafluoride was maintained at a temperature of 60" C. for 24 hours. During that time, 0.66 gram of the sample decomposed to plutonium tetrafluoride. Several experimenters have reported values for the rate of decomposition of plutonium hexafluoride by the alpha radiation of plutonium-239 ( 7 , 2, 6). A calculation, using a value of Zyodecomposition per day in the condensed phase and 0.35y0 per day for the vapor phase ( 6 ) , showed that 0.70 gram of the plutonium hexafluoride sample in this experiment should have decomposed from the alpha radiation alone. This experiment shows that the total rate of decomposition of liquid plutonium hexafluoride a t 60" C. is comparable to the rate of radiation decomposition. literature Cited (1) Florin, A. E., Tannenbaum, I. R., Lemons, J. F., J . Inorg. & Nuclear Chem. 2, 368 (1956). 12) Mandleberg, C. J., Rae, H. K., Hurst, R., Long, G., Davies, D., Francis, K. E., Zbid., 2, 358 (1956). 13) Steindler. M. J.. Steidl. D. V.. Steunenberrz. R. K., 'Vuclear Sci. and Eng. 6 , 333 (1959j. (4) Tamaru, K., Boudart, M., Taylor, H., J . Phvz. Chem. 59, 801 ,
I
"l
(1 9551. \--/.
(5) Trevorrow, L. E., Steunenberg, R. K., Shinn. W. .4.,Ibid., 65, 398 (1961). (6) Weinstock, B., Malm, J. G., J. Inorg. &? Kuclear Chem. 2, 380 (1956). (7) Weinstock, B., Weaver, E. E., Malm, J. G., Ibid., 11, 104 (19 59).
RECEIVED for review February 16: 1961 ACCEPTED July 24, 1961 Work performed under the auspices of the U. S. Atomic Energy Commission. Division of Industrial and Engineering Chemistry, 139th Meeting, ACS, St. Louis, Mo., March 1961. VOL. 1
NO. 1
JANUARY
1962
51
