Carbon in molybdenum

A typical analytical procedure, such as that for carbon in molybdenum, can be summarized as follows. 

Vandecasteele et al. (53)(55)(56) describe the determination of carbon in molybdenum and tungsten. The irradiation conditions are given in Table V-6. 

The choice of the incident energy is not critical for the determination of carbon in tungsten. It is however very important for the instrumental determination of carbon in molybdenum. Fig. V-1 gives relative thick target yields for the Mo(d,n) " Tc and Mo(d,p) Mo reactions as a function of the energy (55). These were determined by irradiation of a stack of molybdenum foils with 5 MeV deuterons. For comparison, the thick... 

The equipment for the chemical separation of described in Chapter II, section 3.8.1. was developed to determine carbon in molybdenum and tungsten (79). The samples (1 to 2 g) were irradiated for 40 minutes. To preclude the effects of competing nuclear reactions, the maximum energy of the photon beam was limited to 25 MeV. 

Baker et al. (80) and Lutz and Masters (81) also used combustion in oxygen to determine carbon in molybdenum by photon activation analysis. The former ignited the samples directly, without any additions. The latter used lead to prevent the distillation of molybdenum trioxide (MoO ). 

The determination of carbon in molybdenum and tungsten is already since 1969 the subject of studies in the frame of the working group "Sonder-und RefraktSrmetalle" of the Chemistry Committee of GDMB (Gesellschaft Deutscher MetalIhutten- und Bergleute). In the case of molybdenum (91) combustion methods carried out in 8 laboratories yielded the results... 

Table V-10 Results of a GDMB round robin on the determination of carbon in molybdenum by combustion (91)...

More recently BCR organized a round robin for carbon in molybdenum on BCR-RM 23, which confirmed the suitability of activation analytical methods and the low concentration level of carbon in molybdenum (94) (Table V-13). 

The extraction of titanium is still relatively costly first the dioxide Ti02 is converted to the tetrachloride TiCl4 by heating with carbon in a stream of chlorine the tetrachloride is a volatile liquid which can be rendered pure by fractional distillation. The next stage is costly the reduction of the tetrachloride to the metal, with magnesium. must be carried out in a molybdenum-coated iron crucible in an atmospheric of argon at about 1100 K ... 

Chromium is the most effective addition to improve the resistance of steels to corrosion and oxidation at elevated temperatures, and the chromium—molybdenum steels are an important class of alloys for use in steam (qv) power plants, petroleum (qv) refineries, and chemical-process equipment. The chromium content in these steels varies from 0.5 to 10%. As a group, the low carbon chromium—molybdenum steels have similar creep—mpture strengths, regardless of the chromium content, but corrosion and oxidation resistance increase progressively with chromium content. 

Nitrogen and carbon are the most potent solutes to obtain high strength in refractory metals (55). Particulady effective ate carbides and carbonitrides of hafnium in tungsten, niobium, and tantalum alloys, and carbides of titanium and zirconium in molybdenum alloys. 

Hydrogen at elevated temperatures can also attack the carbon in steel, forming methane bubbles that can link to form cracks. Alloying materials such as molybdenum and chromium combine with the carbon in steel to prevent decarburization by hydrogen (132). 

NOTE Steel consists of ferrite and pearlite phases. Ferrite is a solid solution of carbon in iron, whereas pearlite is a mixture of ferrite and laminar cementite. Cementite is a carbide, such as ferric carbide (Fe3C), although part of the iron content may be replaced by other metals including molybdenum. 

In a noteworthy series of studies, Herndon has shown that cyclopropylcarbenes can be used as four-carbon components in molybdenum- and tungsten-mediated [4 + 2 + l]-reactions with alkynes and carbon monoxide (CO). These reactions give cycloheptadienones in moderate yields and with moderate selectivity (Equations (26)—(28)). The mechanism of this reaction is proposed to proceed through a series of steps involving metathesis, GO insertion, ketene formation, cyclopropane cleavage, and finally reductive elimination (Scheme 43).133... 

Sulphides. MoS2 was prepared by electrolysis at 1000°C of a melt consisting of sodium tetraborate, sodium fluoride, sodium carbonate in which molybdenum (VI) oxide and sulphur were dissolved. The electrolysis was carried out at 1000°C with the melt contained in a graphite crucible also acting as anode. After electrolysis, the excess electrolyte was dissolved in water to obtain crystalline MoS2, containing however up to 2% carbon. A similar method was used for WS2 carbon was the principal impurity in the sulphides. 

In addition to these classical aromatic ring hydroxylations, many nitrogen heterocycles are substrates for molybdenum-containing enzymes, such as xanthine oxidase and aldehyde oxidase, which are present in the hepatic cytosolic fractions from various animal species. The molybdenum hydroxylases (B-75MI10902) catalyze the oxidation of electron-deficient carbons in aromatic nitrogen heterocycles. The reactions catalyzed by these enzymes are generally represented by equations (2) and (3). 

Tantalum Carbide, TaC, has been prepared by heating a mixture of tantalum pentoxide and carbon in a molybdenum boat at 1260° C. in a stream of hydrogen,2 or by the action of hydrogen and carbon monoxide on tantalum pentachloride. It is a dark grey or black substance which is insoluble in all acids, and bums to the pentoxide when powdered and heated in air. Density—13 96. It melts with decomposition at 4100° abs., which is probably the highest melting-point yet recorded for a chemical compound. Its hardness coefficient fees between 9 and 10. It is a good conductor of electricity.4 For its crystal structure see reference cited.5... 

C-H functionalization, 10, 121 C-H intermolecular functionalization, 10, 122 C-H intramolecular functionalization, 10, 130 olefin functionalization, 10, 155 /)3-Carbon atoms, C-H bond functionalization activated alkyl groups intermolecularly, 10, 111 activated alkyl groups intramolecularly, 10, 114 alkanes and alkyl units, 10, 102 Carbon-based ligands, alkali metal chemistry, 2, 3 Carbon-based 77-ligands, in molybdenum carbonyls alkenes, 5, 433 alkynes, 5, 435 allenes, 5, 433... 

Carbon-based 7]4-ligands, in molybdenum carbonyls, 5, 448 Carbon-based 7]5-ligands, in molybdenum carbonyls, 5, 453 Carbon-based 7]6-ligands, with molybdenum carbonyls arenes, 5, 478 cycloheptatrienes, 5, 480... 

Carbon-based 7]7-ligands, in molybdenum carbonyls, 5, 483 Carbon-boron bond formation... 

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