HEATSOF IMM:ERSION IN THE THORIUM OXIDE-WATER SYSTEM large crystal into smaller ones is largely an increment of enthalpy. For the above reasons, it seems quite possible that someone may find a method of producing a more macroscopic form of PbOz, giving a lower and more fundamental potential than the one commonly found for the lead storage cell. However, there would appear to be doubtful practical advantage in trying to accomplish this. If ithe typical lead cell is able to store a small additional amount of energy, owing to the higher free
573
energy of microscopic lead dioxide, there is no obvious reason to discourage any such serendipity. In this sense the values for Ezes.legiven in Table VI may also have considerable permanence. Acknowledgment. We thank R. H. Lamoreaux and P. R. Siemens for assisting with the low-temperature measurements on PbOz, D. H. Templeton for numerous X-ray diffraction patterns and their analysis, and A. Pabst for supplying a mineral sample of PbOz for analysis.
Heats of Immersion in the Thorium Oxide-Water System,
111. Variation
with Specific Surface Area and Outgassing Temperature112 by E. L. Fuller, Jr., H. F. Holmes, C. H. Secoy, and J. E. Stuckey Reactor chemistry Division, Oak Ridge National LabOTdOTy, Oak Ridge, Tennessee 97860 (Received July 17, 1067)
The heats of immersion of thorium oxide samples in water show that there are three modes of interaction of water with the surface and further elucidate the temperature realms of stability for these surface species. Considerable evidence is shown that high-temperature calcination produces material that is nearly devoid of the high-energy surface heterogeneities present in the original high surface area material. These conclusions are based on data for 25-500' outgassing of thoria samples with specific surface areas ranging from 1 to 35 m2/g. Samples with high specific surface areas liberated a portion of their immersional heat via two kinetically controlled processes, in addition to the instantaneous portion.
Introduction
oxalate. The physical properties of this series are given in Table I. Table I1 gives the impurity analyses of In the continuing investigation of the nature of the the initial 650' calcined material. The loss-of-ignition interaction of water with the surface of thorium dioxide, (LOI) data are questionable, owing to the strong contria second series of heats of immersion has been measured of environmental conditions. butions to be compared to previous ~ o r k . ~The t ~ variation of heats of immersion with respect to specific surface area Results and outgassing; temperature is recognized as a useful The low-fired, high surface area samples F, G, and H, tool for evaluation of the water-oxide i n t e r a ~ t i o n . ~ - ~ We hope that this work may help to elucidate the (1) Reaearch sponsored by the U. S. Atomic Energy Commission under contract with the Union Carbide Corporation. water-thorium oxide interaction, as well as oxide-water (2) Presented in part a t the 163rd National Meeting of the American systems in general.
Experimental Section The equipment and techniques employed for this study have been described in detail in an earlier report. Following the technique used earlier, samples of thoria were calcined from an initial batch to produce samples of lesser specific surface area. Both series were prepared by a 650' decomposition of thorium
Chemical Society, Miami Beach, Fla., April 1967. (3) H. F. Holmes and C. H. Secoy, J . Phys. Chem., 69, 161 (1966). (4) H. F. Holmes, E. L. Fuller, Jr., and C. H. Secoy, {bid., 70, 436
(1966). (6) J. A. G. Taylor, J. A. Hockey, and B. A. Pethica, Proc. Brit. Ceram. SOC.,5 , 133 (1966). (6) J. A. G. Taylor and J. A. Hockey, J . Phys. Chem., 70, 2169 (1966). (7) A. C. Zettlemoyer, R. D. Iyengar, and P. Scheidt, J . Colloid Interface Sci., 22, 172 (1966).
Volume 76, Number 6 February 1968
FULLER, HOLMES, SECOY, AND STUCKEY
574
~
_
_
_
Table I: Properties of ThOg Samples (ORNL Lot D T 102W) Code
Calcining temp," "C Specific surface area: m* g-1 Mean particle diameter,'
F
G
H
I
J
650 35.5
800 14.5
1000 6.60
1200 2.96
1400 1.55
1600 0.948
1.73
1.86
1.77
1.54
1.60
158
98.5
235
655
1485
2542
>2500
K
CL
Crystallite size,d A a
At temperature for 4 hr in air.
Nitrogen adsorption a t 77°K.
Sedimentation analyses.
X-Ray diffraction line broadening,
500
Table 11: Impurity Analyses of Thorium Dioxide ORNL Lot D T 102W" Cl
