Binary carbides

Binary carbides are formed when the metals are heated strongly with carbon. The most important carbide of the group IA and IIA metals is calcium carbide, CaC2. Ibis carbide is actually an acelylide because it contains the C/ ion and it reacts with water to produce acetylene. 

Figure 7.18 Enthalpy of formation of binary carbides and diborides [25, 26] as a function of the average number of valence electrons per atom.

Francium, binary carbide not reported, 11 210 Franck-Condon effect, 16 69 energy, 21 180, 188, 189 envelopes, 16 80, 89, 90 hot bands, 16 90 factors, 32 47 principle, 21 179, 181 vibronic replica, 35 370 frd redon, 38 412, 414 Freeze quench EPR spectroscopy (FQ-EPR), CODH/ACS, 47 318 Fremy s salt, 33 106 Friedel-Crafts reaction, 17 194 cyclophosphazene, 21 65, 66 Frontier molecular orbitals, heteronuclear gold cluster compounds, 39 378-381 Frozen solutions, MOssbauer spectra in studies of, 15 101-103... 

Germanes hydride, 2 76 reactivity of, 2 87 Germanium anionic cluster, 24 227 azides, preparation, 9 138 properties, 9 135-136, 139, 141 binary carbide not reported, 11 211 carbides, preparation of, 11 163 chalcogenide halides, 23 390 chlorides, mass spectra of, 18 248, 249 complexes, xenon fluoride reactions, 46 85 compounds, see also Organogermanium compounds... 

Pair-of-dimer effects, chromium, 43 287-289 Palladium alkoxides, 26 316 7t-allylic complexes of, 4 114-118 [9JaneS, complexes, 35 27-30 112-16]aneS4 complexes, 35 53-54 [l5]aneS, complexes, 35 59 (l8)aneS4 complexes, 35 66-68 associative ligand substitutions, 34 248 bimetallic tetrazadiene complexes, 30 57 binary carbide not reported, 11 209 bridging triazenide complex, structure, 30 10 carbonyl clusters, 30 133 carboxylates... 

Radiolaria, strontium and barium sulfate biomineralization, 36 169-170 Radiopharmaceuticals, design, 36 25-28 Radiosensitizers, 36 37 Radish white root ferredoxins, 38 231 Radium, binary carbide not reported, 11 210 Radon... 

TABLE 4 Selected Binary Carbides, Nitrides, and Borides with Transition Temperature. 

FIGURE 3.3 Calculated pore volumes for CDC from various metal carbides assuming conformal transformation. (From Dash, R.K., Nanoporous carbons derived from binary carbides and their optimization for hydrogen storage, PhD Thesis, Drexel University, Philadelphia, PA, 2006.)... 

Boron forms a binary carbide, often written B4C but actually non-stoichiometry, and compounds with most metals. The stoichiometries and structures of these solids mostly defy simple interpretation. Many types of chains, layers and polyhedra of boron atoms are found. Simple examples are CaB6 and UB12, containing linked octahedra and icosahedra, respectively. 

The crystal structures adopted by the binary carbides and nitrides are similar to those found in noble metals. The resemblance is not coincidental, and has been explained using Engel-Brewer valence bond theory [5]. Briefly, the main group elements C and N increase the metal s effective s-p electron count, so that structures and chemical properties of the early transition metals resemble those of the Group 8 metals. This idea was first introduced by Levy and Boudart [6] who noted that tungsten carbide had platinum-like properties. 

For Ti, Zr, and Hf carbonitrides, including also binary carbides and nitrides, the Young s, shear, and bulk modulus as well as the Poisson number have been measured by ultrasonic measurements as a function of the C/N ratio. The data are given in Figure 10. 

Although this process is an important method whereby very pure and well-crystallized binary carbides can be obtained, no successful attempts with multicomponent carbides have been reported so far. Apparently the conditions for the simultaneous deposition of more than one or two carbides are not easily adjusted. Likewise the simultaneous decomposition of carbonyl mixtures should be feasible, but so far no successful experiments have been reported. 

Other binary carbides. Boron and carbon form a series of boron carbide phases of which B4C appears to be the most ordered. There are several competing structural models for boron carbide which have been investigated by B and C... 

The representative binary carbide, nitride, and oxide systems displaying metallic properties are summarized in Figure 1, where they are arranged in conformity with the... 

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