Solid thorium carbides

XLl Carbon compounds and complexes XI.1.1 Solid thorium carbides 

There have been two extensive reviews of the thermodynamies of the Th-C system by [1975RAN], [1984HOL/RAN], since which there has been little work on these com-ponnds. Onr treatment therefore lends fairly heavily on the latter review, with a few updates and corrections as appropriate. 

There is a large corpus of data on the phase relationships and stabihty of the thorium caibides. Unfortunately, much of this information is conflicting, and it is still not possible to give many precise values for the thermodynamic properties of the carbides. These discrepancies may be due in part to the great difficulty encountered in preventing oxygen contamination of these materials. 

There is little new information to add to the review of the somewhat conflicting information on the phase relationships given by [1984HOL/RAN], which gives the preferred phase diagram, the essential points of which are summarised below. 

Thorium monocarbide has the NaCl face-centred cnbic stmeture, space group Fm 3 m, isomorphous with most of the actinide MX componnds. The limits of composition are still not well-defined, but up to ca. 1300 K probably extend from ThCo67(cr) to ThCo97(cr), the lattice parameter at room temperatnre varying from (5.303 + 0.002) to (5.346 + 0.002) A, see [1984HOL/RAN]. As noted earher, at higher temperatures the 

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The dicatbide, either by itself, mixed with uranium dicarbide, or in solid solution with uranium dicarbide, is used as fuel material in some versions of high-temperature gas-cooled reactors. Like uranium carbides, the thorium carbides react rapidly with water or moist air and must be protected from moisture in storage and fuel fabrication. 

EXPLOSION and FIRE CONCERNS combustible solid NFPA rating (NA) reacts to form explosive products with metal amides contact with acids may cause formation of poisonous hydrogen selenide gas incompatible or reacts violently with barium carbide, bromine pen-tafluoride, chromic oxide, fluorine, lithium carbide, lithium silicon, metals, nickel, sodium, nitric acid, nitrogen trichloride, oxygen, potassium, potassium bromate, rubidium carbide, zinc, silver bromate, uranium, strontium carbide, and thorium carbide toxic gases and vapors may be released in a fire involving selenium, sodium selenite, sodium selenate, and selenium dioxide use water for firefighting purposes. 

Krupka et al. (1973) observed the occurrence of a solid solution of scandium in the cubic thorium carbide, Th2C3 (ST PU2C3). The lattice parameter changes within the homogeneity range of Th2 o.6Sco-i 4C3 from n = 8.556 to a = 8.563 A, the value for Thi 4Sco.6C3 is n = 8.530 A. 

All IR spectrometers have a source of infrared radiation which is usually some solid material heated to incandescence by an electric current. The Nemst Glower is a source composed mainly of oxides of rare earths such as zirconium, yttrium and thorium, and the Globar is a silicon carbide rod. Other materials have been used as well. All these sources are fairly efficient emitters of infrared radiation and approach the energy distribution of a theo-rectical black body. 

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