Thorium structure

The Arbeitsgemeinschaft Versuchsreaktor (AVR) and Thorium High-Temperature Reactor (THTR-300) were both helium-cooled reactors of the pebble-bed design [29,42,43]. The major design parameters of the AVR and THTR are shown in Table 10. Construction started on the AVR in 1961 and full power operation at 15MW(e) commenced in May 1967. The core of the AVR consisted of approximately 100,000 spherical pebble type fuel elements (see Section 5). The pebble bed was surrounded by a cylindrical graphite reflector and structural carbon... 

Compounds with Sc, Y, lanthanoids and actinoids are of three types. Those with composition ME have the (6-coordinated) NaCl structure, whereas M3E4 (and sometimes M4E3) adopt the body-centred thorium phosphide structure (Th3P4) with 8-coordinated M, and ME2 are like ThAsi in which each Th has 9 As neighbours. Most of these compounds are metallic and those of uranium are magnetically ordered. Full details of the structures and properties of the several hundred other transition metal-Group 15 element compounds fall outside the scope of this treatment, but three particularly important structure types should be mentioned because of their widespread occurrence and relation to other structure types, namely C0AS3,... 

Thorium, (dimethylformamide)tetrakis(tropolone)-structure, 1, 98 Thorium, hexanitrato-structure, 1,101 Thorium, pentacarbonato-stereochcmistry, I, 99 Thorium, tetrachlorobis(octamethylpyro-phosphoramide)-structure, 1, 89... 

Thorium, tetrakis(4,4,4-trifluoro-l-thienyl-l, 3-butanedione)(trioctylphosphine oxide)-structure, 1, 98 Thorium, triaquatetranitrato-structure, 1, 99... 

The deposition of pyrolytic graphite in a fluidized bed is used in the production of biomedical components such as heart valves, ] and in the coating of uranium- and thorium-carbides nuclear-fuel particles for high temperature gas-cooled reactors, for the purpose of containing the products of nuclear fission.fl" The carbon is obtained from the decomposition of propane (CgHg) or propylene (CgHg) at 1350°C, or of methane (CH4) at 1800°C. Its structure is usually isotropic (see Ch. 4). 

The structural chemistry of the actinides is often similar to that of lighter transition metals, such as Zr and Hf, and to that of the lanthanides however, the diffuse nature of the 5/ orbitals leads to some differences and specifically to interesting magnetic and electrical properties. The actinide sulfides are generally isostructural with the selenides, but not with the analogous tellurides. The binary chalcogenides of uranium and thorium have been discussed in detail [66], but the structural... 

Coprecipitation is a partitioning process whereby toxic heavy metals precipitate from the aqueous phase even if the equilibrium solubility has not been exceeded. This process occurs when heavy metals are incorporated into the structure of silicon, aluminum, and iron oxides when these latter compounds precipitate out of solution. Iron hydroxide collects more toxic heavy metals (chromium, nickel, arsenic, selenium, cadmium, and thorium) during precipitation than aluminum hydroxide.38 Coprecipitation is considered to effectively remove trace amounts of lead and chromium from solution in injected wastes at New Johnsonville, Tennessee.39 Coprecipitation with carbonate minerals may be an important mechanism for dealing with cobalt, lead, zinc, and cadmium. 

Application of this picture to the present thorium acyl system (J,) suggests that a hydrogen atom migration to the electron deficient carbenoid p orbital must occur from a conformation (J) other than that found in the crystal structure (H) (Figure 1) to yield the cis product. These relationships are illustrated in eqs.(7) and (8) ... 

Although not the central subject of this review, several thorium dihaptocarbamoyl complexes ( 4) Th(n2-CONR2)/ were also examined with respect to thorium hydride-catalyzed reduction. Under 0.75 atm H2 and over the course of several days at temperatures as high as 100°C, no hydrogenation was observed. These results are in accord with other spectral, structural, and chemical data (14) indicating the importance of carbamoyl resonance hybrids O and P, and that the carbene-like reactivity is significantly reduced in comparison to the acyls (14) ... 

This article reviews recent results on the chemical, spectral and structural properties of bis(pentamethylcyclopentadienyl) thorium and uranium dihaptoacyl complexes produced by migratory insertion of carbon monoxide into actinide-carbon sigma bonds. 

Nuclear dating has been most helpful in establishing the history of the earth and of the moon and of the meteorites. The fact is, there is no other way of measuring their ages. Prior to the discovery of natural radioactivity in the late 19th century, indirect methods were used to estimate the age of the earth, but there were no real answers until the radioactivity of thorium, uranium, and potassium were discovered and we began to understand atomic structure and to realize that nuclear transformation was essentially independent of the chemical form. 

Although not part of soil, lichens, by virtue of their solubilising action on rocks, contribute to the elemental enrichment of soil. Several studies have identified lichen acids as complexing agents for the iron and aluminium of rocks (95, 96). An examination of the various structures indicates that the basic structure responsible for the chelation is the carboxylic acid group with an orthophenolic group. Grodzinskii (97) has found lichens to be intense accumulators of elements in the uranium-radium, actinouranium and thorium orders. 

Following the characterization of U(COT)2, the analogous thorium complex was synthesized 12). Its physical and chemical properties were so different from those of the uranium compound that initially there was question as to whether the complex had the same -sandwich structure. The X-ray structure anal5 is however showed it to be isostructural with U(COT)2 11). Subsequently, Pu(COT)2 13), Np(COT) 13), and Pa(COT)2 14, 15) have been prepared and their X-ray powder patterns show them all to be isostructural with U(COT)2. 

Crucial in determining the progress (or lack of it) of this type of reaction is the location and structure of the solid product in relation to the solid reagent. Thus, whilst a solid block of copper or a solid block of thorium will remain stable in the atmosphere at room temperature with only some surface oxidation, a solid block of certain intermetallic... 

AII information obtained from HSDB 1990 except where noted Structures are based on tetra valency of thorium unless otherwise stated CAS 1990 RTECS 1989 SANSS 1988... 

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