Thorium oxide systems

The thorium oxide system is dominated by Th02. The dioxide can be synthesized by burning a number of thorium compounds, including hydroxides, oxalates, carbonates, and so on. The Th02 crystalhzes in the cubic fluorite structure. Th02 is very heat resistant as are all of the actinide oxides and melts at 3390 °C, which is the highest for any known metal oxide. 

Parallel ketonization of acetic acid and propionic acid was one of the transformations of this type studied in our Laboratory. Ryba6ek and Setinek (94) investigated the kinetics of these reactions in the gaseous phase at 316°C using thorium oxide on activated carbon (p. 27) as the catalyst. This model system allowed the study of each reaction separately as well as of the simultaneous conversion of both acids. 

Ternary soap-water-salt system, phase behavior of, 22 727-728 Ternary thorium oxides, 24 762 Teme steel, 14 778 Terodiline, 5 122... 

Aside from the recently described Cu/Th02 catalysts, copper on chromia and copper on silica have been reported to catalyze methanol synthesis at low temperatures and pressures in various communications that are neither patents nor refereed publications. It is not feasible to critically review statements unsupported by published data or verifiable examples. However, physical and chemical interactions similar to those documented in the copper-zinc oxide catalysts are possible in several copper-metal oxide systems and the active form of copper may be stabilized by oxides of zinc, thorium, chromium, silicon, and many other elements. At the same time it is doubtful that more active and selective binary copper-based catalysts than... 

In Figure 8 we have plotted the lanthanum oxide, cerium oxide, and thorium oxide concentrations for sherds excavated in the Dominican Republic and Venezuela and sherds from the Metro excavations using a computer system developed for this purpose at Brookhaven National Laboratory (8). On the basis of these three oxides there is a distinct separation between the sherds from the Dominican Republic and Venezuela and those from Mexico City. Unlike the sherds from the Dominican Republic and Venezuela, the sherds from Mexico City appear not to have originated in Spain, at least at that specific source. There is further evidence of this distinction between the two sets of sherds. X-ray diffraction analysis of the samples from Jerez and from the New World showed that the sherds from Jerez, the Dominican Republic, and Venezuela had intense quartz peaks whereas the sherds from Mexico City did not. This constitutes additional evidence that the majolica from Mexico City came from a different source than the majolica from the Caribbean sites. 

In addition, the particle size of the solid phase must be sufficiently large to allow the separation of the sohd and aqueous phases and this is, in practice, difficult for small particles. This is probably the main reasons for the widely different solubihty that is reported for Th(IV) hydrous oxide phases. The attainment of solubihty equilibrium is often a slow process, in particular for ciystahine thorium oxides [2001HUB/BAR], [2003NEC/ALT] and care must be taken to ensure that true equihbrium has been attained in the system. The solubility of hydrous thorium oxide is low at pH > 5, but sorption of thorium on the container walls is no problem as the thorium buffer capacity of the system is determined by the solid phase the situation is different in liquid-liquid extraction where the thorium buffer capacity is low. 

Introduction. Experiments have been carried out at the Oak Ridge National I.aboratory as part of a continuing program to determine the effect of radiation on the physical properties of aqueous suspensions of thorium oxide. Since changes in particle size, surface properties, and viscosity of the suspension might have a deleterious effect on the operability of a homogeneous-reactor slurry system, thc.se properties were examined in detail. 

The preliminary catalyst evaluation was carried out with slurries of thorium oxide fired at 900°C. Subsequent experience with molybdenum oxide has indicated that it is inactive with low-fired oxides, and its activity at least at low concentrations is decreased by the presence of uranium oxide (see the following discussion). Hence in slurry systems using low-fired thorium oxide or thorium-uranium oxides, silver, palladium, and platinum, which are active in these slurries, may prove to be useful [154]. 

R. N. Lyon, The Choice in Thorium Oxide Slurries for the Prevention of Caking in Circulating Systems, USAEC Report CF-57-4-77, Oak Ridge National Laboratory, 1957. 

D. G. Thomas, Atmospheric Pressure System for Determining Resuspension Velocity of Thorium Oxide Slurries in Round Horizontal Pipes, USAEC Report (- F-56-10-136, Oak Rids e National Laboratory, 1956. 

In the feed preparation step, uranyl sulfate solution from the reactor core and thorium oxide from the blanket system, freed of D2O and suspended in ordinary water, are fed into the dissolver tank. The di.s.solvent is 13 N nitric acid to which has been added catalytic amounts (0.04 N) of sodium fluoride. When short-cooled thorium is being processed, potassium iodide is added continuously to the dissolver to provide for isotopic dilution of the large amount of fission-produced which is present. The dissolver solution is continuously sparged with air, and the volatilized iodine is removed from the off-gases in a caustic scrubber. 

Similar gas- and li( uid-recireulating systems are used to remove heat from ih( blanket, which consists of a thorium-oxide slurry in D2O containing 500 to 1000 g Tli/litcr. The slurry is recirculated by means of a 12.4()0-gpm canned-motor pump through a gas. separator and through a loO-.Mw heat exchanger. 

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