Atomization dicarbides

Thallous Azidodithiocarbonate A637-L Thallous-Thallic Azide A623-R Thermonuclear or Fusion Bomb. See under Atomic Bomb A499-L Thorium Dicarbide A82-R Tin Azide A624-L Titanium Carbide A82-R Titanous Chloride Method for Determination of Nitrobenzene in Aniline A415-R TNT Recovery from Scrap Amatol A161-L Toluidine. See under Aminotoluenes A265-R... 

The dicarbide is also formed if hexachloroethane is used as a source of carbide atoms 254). 

Bigger clusters have been formed, for instance, by the expansion of laser evaporated material in a gas still under vacuum. For metal-carbon cluster systems (including M C + of Ti, Zr and V), their formation and the origin of delayed atomic ions were studied in a laser vaporization source coupled to a time-of-flight mass spectrometer. The mass spectrum of metal-carbon cluster ions (TiC2 and Zr C j+ cluster ions) obtained by using a titanium-zirconium (50 50) mixed alloy rod produced in a laser vaporization source (Nd YAG, X = 532 nm) and subsequently ionized by a XeCl excimer laser (308 nm) is shown in Figure 9.61. For cluster formation, methane ( 15% seeded in helium) is pulsed over the rod and the produced clusters are supersonically expanded in the vacuum. The mass spectrum shows the production of many zirconium-carbon clusters. Under these conditions only the titanium monomer, titanium dioxide and titanium dicarbide ions are formed. 

A. The peripheral dicarbide cluster Co6(C2)(CO)14(S) (435) contains a boat array of Co atoms, of which the four basal ones form an essentially regular square. The two apical Co atoms are connected through a Co-C-C-Co link the C-C separation is 1.37(2) A. These two carbon atoms are also bonded to the four basal Co atoms. The core geometry of the cluster is illustrated in Fig. 40. 

Lonsdale, H. K., Graves, J. N., Vaporization of the dicarbides of uranium, thorium, and protactinium, Thermodynamics of nuclear materials, Proc. Int. Symp., pp.60I-623, International Atomic Energy Agency, Vienna, Austria, (1963). Cited oupage 343. 

Other clusters containing twelve rhodium atoms are all based on dicarbide derivatives in which the carbide occupies a Rhg trigonal prismatic site. Fig. 22 shows... 

Carbides.— The crystal chemistry of ternary and more complex carbides has been reviewed. The dissociation energies of gaseous metal dicarbides have also been reviewed and compared with those of the corresponding chal-cogenide systems for which information is available. The results of two mass-spectrometric investigations of the atomization energies ( atom,o) dissociation energies (Z)S), and enthalpies of formation (A/ff°... 

According to the data in table 1, the eutectic temperature increases with increasing atomic number of the light rare earth in the dicarbide, and reaches a maximum at... 

Rare earth dicarbides are commonly formed in the rare-earth (except for europium)-carbon systems. Many investigators, in particular Atoji, have made a great contribution to the determination of the structure of RC2. The neutron diffraction investigations on the structure of the rare earth dicarbide, first by Atoji and Medrud (1959) showed that for the lanthanum dicarbide the atomic coordinates in the unit cell are (000, ) + (OOz) for carbon atoms and z = 0 for lanthanum atoms, and the carbon positional parameter z(A) is 0.403 + 0.002, corresponding to a well-defined minimum at a C-C distance of 1.28 0.03 A. LaC2 can probably be described approximately in terms of ions, with the extra electron in a conduction... 

Other interatomic distances in the rare earth dicarbides show unusual features. Pauling s bond number (Pauling 1960) for the C-R and R-R bonds in these dicarbides increases roughly with the atomic number of the rare earth atom 0.5 (C-La) to 0.9 (C Lu) (Atoji 1961) for the nearest C-R distance 0.2 to 0.35 for the next nearest C-4R distances 0.1 to 0.2 for the nearest R-R distances which are equal to the lattice parameters 3 to 5 and 3.5 to 4.5, respectively, for the total bond numbers of the carbon and rare earth atoms. The bond numbers for YC2 fall between Ho and Lu, indicating that Y in YC2 behaves as a heavy lanthanide (Atoji 1961, 1962). 

The shortest R-R distances in the rare earth sesquicarbides, Rq-3Ri, are nearly 10% shorter than the shortest R R distances in the dicarbides, which are equal to their lattice parameters. Other R0-2R2 and R0-6R3 distances are also shorter than this value, indicating that there are stronger R-R interactions in the sesquicarbides than in the dicarbides. The interatomic distances in Ce2C3, particularly the Ce-Ce distances are markedly smaller than the expected values for CcjCj with the pure trivalent Ce atoms. This is in accordance with the result obtained from the paramagnetic scattering analysis (Atoji and Williams 1967). 

As described above, in the dicarbides and the sesquicarbides of the rare earth elements there are pairs of carbon atoms, while in the hypocarbides, either the cubic structure or the trigonal one, the carbon atoms are isolated and no longer appear as pairs. In the intermediate carbides, R15C19, the tetragonal structure is made up of distorted metal octahedra, carbon pairs and also single carbon atoms. 

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