Tungsten carbon

Protonation of 12 yields a compound best described as a face-protonated methylidyne complex, the tungsten-carbon bond length lying in the range observed for a triple bond (28). Protonation of the osmium compound 13 yields a true carbene complex, which for R = Ph has been characterized by X-ray crystallography (see Sections IV and VI). 

A. A. Holscher and W. M. H. Sachtler, Chemisorption and surface corrosion in the tungsten + carbon monoxide system, as smdied by field emission and field on microscopy, Dis. Faraday Soc. 41, 29 (1966). 

The tungsten-carbon single, double, and triple bond lengths in this compound are 225.8, 194.2. and 178.5 pm, respectively, and the accompanying W—C—C bond angles are 124°. 150°. and 175 , all of which is quite consistent with tungsten-carbon bond orders of 1,2. and 3. 

The first successful X-ray study involved frans-(iodo)tetracarbonyl-(phenylcarbyne) tungsten(0) (87, 88) (Fig. 9). It confirmed in essence our concepts, and yielded an extremely short tungsten-carbon distance of... 

AP rifle bullets usually have a bullet tip filler (usually lead) which is designed to cushion the effect of the impact on the AP core, which is very hard and brittle and can break on impact without a cushioning effect. The AP core is also frequently surrounded with a thin sheath of lead between the core and the bullet jacket. The AP core is usually hardened steel such as tungsten/carbon, tungsten/chromium, manganese/molybdenum, chro-mium/vanadium, or chromium/molybdenum. 

The more frequently used forms of electrical heating, such as resistance and induction, have limited use above 3000°K. (Ml, Dl, C2, FI, F4, B3). Tungsten, carbon, and some of the carbides are the only solid materials capable of use as resistors or susceptors above that temperature. Conducting liquids, although potentially capable of reaching higher temperatures than these solids as electrical resistance elements, suffer from problems of containment and have not been used above 3000°K. except in levitation melting (01, W6). 

Li et al °° examined the properties of two organometallic tungsten-carbon complexes, tungsten pentacarbonyl pyridine (TPCP) and tungsten pentacarbonyl fraw -l,2-bis(4-pyridyl)-thylene (TPCB), that also had been studied experimentally. They considered the isolated monomers as well as dimers and studied the systems in solutions. They used density-functional methods in order to calculate the linear and nonlinear responses to electric fields, and the solvents were treated with a... 

Table 43 The static dipole moment, the average polarizability, and the average first hyperpolarizability for different tungsten-carbon complexes. The second entry gives the conditions, and the third gives the method. All results are from ref. 100... 

Two tungsten-carbon compounds exist in the tungsten-carbon system W2C and WC as well as low melting point eutectica in the systems W/W2C and W2CAVC. Monotungsten carbide is by far the most important metal carbide in cemented carbide metallurgy (see Section 5.6.5.4). 

In a study of reductive McMurry-type coupling of carbonyl compounds with (OR)3WsW(OR)3 (R = 2,2-dimethylpropyl), a dinuclear cyclopropylmethylidene complex 14 was isolated and structurally characterized by X-ray.The cyclopropyl group remained intact (also in subsequent coupling reactions with other carbonyl compounds) thus, no long-lived carbene intermediate (or cation or anion) is involved and the tungsten carbon bond must have considerable covalent [Pg.1893]

The Atmosphere. Industrial carburization of tungsten powder is commonly carried out in hydrogen or hydrogen-containing gas mixtures. Hydrogen reacts with the solid carbon in the W -H C mixture to form methane (at temperatures <1600°C) or acetylene (>1600°C), which transport the carbon in tungsten-carbon black mixes over larger... 

Figure 3.21 shows the change of the product composition with carburization time in hydrogen for a tungsten-carbon black mixture at 1119°C. After only 10 minutes at this temperature most of the metal was transformed to W2C, which was ffien only slowly converted to WC. This result is characteristic for the temperature range of 1050 to 1850 °C and W particle sizes of 1.3 to 20 pm [3.71]. It is remarkable that W2C forms during carburization even at 900 °C, which is well below its eutectoid decomposition teniperature of 1250°C. 

The binary tungsten-carbon system (Fig. 4.1) [4.13-4.15] is of high technical importance. It contains three intermediate compounds W2C(P), WCi ((y), and WC(5), the latter being the main constituent in most of the commercial cemented carbides (hardmetals see Chapter 9). Besides, ternary and even more complex compoimds exist which are of interest in alloyed steels and cemented carbides. Tungsten hexacarbonyl is an important precursor for organic synthesis. 

Figure 5.11 Measured reflectivity versus photon energy of a tungsten-carbon LSM d= 5k., 0=51.7mrad, AT=260 layers, d=67A, d=8.3 A. The fundamental has a peak reflectivity of 19% and a bandpass dEtE of 0.6%. From Bilderback et al (1983) with permission.

Both complexes result from the insertion of butyne into one of the tungsten-carbon bonds of the bridging alkylidene ligand. However, in XVII the two double bonds are... 

The cathodes can be of the hot type such as tungsten, carbon or molybdenum, cathodes which obviously must be used in a non oxidizing atmosphere. Under certain conditions of oxidizing atmosphere one can use zirconium or hafnium cathodes. The so-called cold cathodes are generally made of copper is -i - ). Heat losses at the cathode are generally quite low (less than 15% of power input to the arc). For a tungsten cathode tip, erosion with current is of g/Clb... 

The rare-earth-metal-(chromium, molybdenum, tungsten)-carbon... 

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