Impure carbons

Pure carbon disulfide is a clear, colorless Hquid with a deHcate etherHke odor. A faint yellow color slowly develops upon exposure to sunlight. Low-grade commercial carbon disulfide may display some color and may have a strong, foul odor because of sulfurous impurities. Carbon disulfide is slightly miscible with water, but it is a good solvent for many organic compounds. Thermodynamic constants (1), vapor pressure (1,2), spectral transmission (3,4), and other properties (1,2,5—7) of carbon disulfide have been deterrnined. Principal properties are Hsted in Table 1. 

In Fig. 11 we show the Raman speetrum of earbo-naeeous soot eontaining l-2 nm diameter, singlewall nanotubes produeed from Co/Ni-eatalyzed carbon plasma[28). These samples were prepared at MER, Inc. The sharp line components in the spectrum are quite similar to that from the Co-catalyzed carbons. Sharp, first-order peaks at 1568 cm and 1594 cm , and second-order peaks at -2680 cm" and -3180 cm are observed, and identified with single-wall nanotubes. Superimposed on this spectrum is the contribution from disordered sp carbon. A narrowed, disorder-induced D-band and an increased intensity in the second-order features of this sample indicate that these impurity carbons have been partially graphitized (i.e., compare the spectrum of carbon black prepared at 850°C, Fig. Id, to that which has been heat treated at 2820°C, Fig. Ic). 

Bischoff JL, Fitzpatrick JA (1991) U-series dating of impure carbonates An isochron technique using total-sample dissolution. Geochim Cosmochim Acta 55 543-554 Broecker WS, Olson EA, Orr PC (1960) Radiocarbon measurements and annual rings in cave formations. Nature 185 93-94... 

Kaufman A (1993) An evaluation of several methods for determining h/U ages in impure carbonates. Geochim Cosmochim Acta 57 2303- 2317... 

Ku T-L, Liang ZC (1984) The dating of impure carbonates with decay series isotopes. Nucl Instr Meth 223 563-571... 

Tantalum obtained by carbothermic reduction at 2000 °C and 10-4 torr is more than 99.8% pure. The levels of the principal impurities, carbon and oxygen, are less than 0.1% each. 

Impure carbon and red phosphorus are oxidised violently, and silicon, promoted by traces of manganese dioxide, is oxidised with ignition. 

The fact that n-type crystals thus grown are semi-insulating cannot be explained from the viewpoint of the phase diagram. The semi-insulating phase is regarded as a pseudo-intrinsic semiconductor, i.e. the concentration of free carriers is very low, due to the carrier compensation in some sense. Holmers et al. have concluded from their data that the concentration of free carrier called EL2 , Nq, is compensated for by that of acceptors derived from impurity carbon, Ta et carried out a similar investigation independently and reached the same conclusion. 

Preparation.—Carbon disulphide is prepared by passing sulphur vapour over red hot charcoal. The preparation may be carried out on a small scale by heating pieces of charcoal in a combustion tube placed in a furnace slightly tilted, a Liebig potash bulb, immersed in ice, being attached to the lower end of the tube, and small pieces of sulphur introduced into the upper end of the tube which is then closed with a cork. Sulphur vapour passes over the red-hot charcoal and impure carbon disulphide containing sulphur in solution is gradually formed and collects in the cooled receiver. 

While all electrodes are subject to adsorption of reactants, products, or impurities, carbon has special properties in this regard. The wide use of activated carbon for adsorption of a wide range of materials, organic and inorganic, is evidence of the likelihood of adsorption to carbon electrodes. As will be noted later, adsorption to carbon depends on electrode history, and adsorption effects can be an important issue when choosing carbon electrodes for a given application. 

The story of steel begins when iron ore is fed into a blast furnace (Fig. 16.45). The furnace, which is approximately 40 m in height, is continuously filled at the top with a mixture of ore, coke (impure carbon obtained by heating coal in the absence of air), and limestone. Each kilogram of iron produced requires about 1.75 kg of ore, 0.75 kg of coke, and 0.25 kg of limestone. The limestone, which is primarily calcium carbonate, undergoes thermal decomposition to calcium oxide (lime) and carbon dioxide. The calcium oxide, which contains the Lewis base 02, helps to remove the acidic (nonmetal oxide) and amphoteric impurities from the ore ... 

This consists of more or less impure carbon mixed with ferruginous sand or with clay and other silicates. It is lead grey or blackish, shining, and greasy to the touch. 

The yellow color of commercial carbon disulfide is due to the presence of small amounts of dissolved sulfur. The rather disagreeable odor of this material is also due to the presence of impurities. Carbon disulfide is a highly flammable liquid which is very poisonous and which is only very slightly soluble in water. 

The gas is then cooled to 30-50 °C and the carbon dioxide is removed by amine absorption or other processes. The remaining impurities - carbon monoxide, methane, nitrogen, argon - are removed in a final pressure-swing adsorption (PSA) step to yield >99.5% pure hydrogen. One of the main problems with this process is that the carbon dioxide is removed by the amine unit as a low-pressure gas. This gas must be compressed to 80 bar to be pipelined for sequestration. This compression step alone requires massive compressors and uses 4—5% of the total power output of the plant. The amine treatment step itself uses even more energy, so the total energy consumption is 15% of the power produced by the plant. 

The elements can be obtained by reduction of oxides or halides. Highly divide carbon black is used as a catalyst and black pigment, and impure carbon (coke) for reducing some metal oxides (e.g., in the manufacture of iron). Pure silicon prepared by reduction of SiCl4 with Mg is used in electronics (silicon chips) although much larger quantities of impure Si are used in steels. 

Of course, oxygen is not the only impurity that will react with beryllium. Another material that is important in forming mixed-material layers with beryllium is carbon. The saturated value of retention that has been found in beryllium surfaces exposed to a large deuterium ion fluence could easily be overshadowed if a carbon rich layer forms on the beryllium surface due to impurity carbon ions in the incident plasma flux. The hydrogen retention properties of plasma deposited carbon films has been shown to dominate the total retention in beryllium samples exposed to the plasma at lower temperature. Once the sample temperature during exposure approaches 500°C there is little difference between the retention in Be/C mixed-material layers compared to clean beryllium samples [48]. The temperature dependence of the retention of carbon containing mixed material layers, as well as that of clean beryllium surfaces is shown in Fig. 14.10. There are two possible explanations for the reduced retention in the mixed-material layers formed at elevated temperature. The first is that beryllium carbide forms more readily at elevated temperature and less retention is expected in beryllium carbide [11]. The second is that carbon films deposited at elevated temperature also tend to retain less hydrogen isotopes [49]. 

Use and exposure Pure carbon disulfide is a colorless liquid with a sweet odor similar to that of chloroform, while impure carbon disulfide is a yellowish liquid with an unpleasant odor like that of rotting radishes. Exposure to carbon disulhde occurs in industrial workplaces. Industries associated with coal gasihcation plants release carbon disulfide, carbonyl sulfide, and hydrogen sulhde. Carbon disulhde is used in large quantities as an industrial chemical for the production of viscose rayon hbers. In fact, the major... 

Iron ore is reduced to iron with coke (impure carbon). Calculate the mass of Fe that can be produced from Fc203 with 15.00 kg of carbon. The reaction may be represented as follows ... 

The following equilibrium is used to convert water and coal (impure carbon) to a (more convenient) gaseous fuel, called water gas. ... 

Hydrogen is prepared by the water gas reaction, which results from the passage of steam over white-hot coke (impure carbon, a nonmetal) at 1500°C. The mixture of products commonly called water gas is used industrially as a fuel. Both components, CO and H2, undergo combustion. 

Zinci carbonas impurus. Zinci carbonas impurus. Impure carbonate of zinc. 

---