Carbon, impurity

Basic oxygen furnaces (BOFs) have largely replaced open hearth furnaces for steelmaking. A water-cooled oxygen lance is used to blow high-purity oxygen into the molten metal bath. This causes violent agitation and rapid oxidation of the carbon, impurities, and some of the iron. The reaction is exothermic, and an entire heat cycle requires only 30-50 min. The atmospheric emissions from the BOF process are listed in Table 30-16. 

Once one layer has formed (the primary nanotube core), further secondary layers appear to deposit with various degrees of epitaxial coherence. When inhomogeneous deposition occurs in PCNTs, the thickening has a characteristic spindle shape, which may be a consequence of non-carbon impurities which impede graphitization (see below) —this is not the case for ACNTs were growth takes place in an essentially allcarbon atmosphere, except, of course, for the rare gas. These spindles probably include the appropriate num-... 

Silica, Si02, is a hard, rigid network solid that is insoluble in water. It occurs naturally as quartz and as sand, which consists of small fragments of quartz, usually colored golden brown by iron oxide impurities. Some precious and semiprecious stones are impure silica (Fig. 14.36). Flint is silica colored black by carbon impurities. 

The T dependence of the solubility of CsH in Cs differs significantly from those for solutions of the hydrides in the other alkali metals. Distillation leaves behind involatile impurity salts, but oxygen transport from distilland to receiver has been observed. Oxygen can be carried over with the distillate in the form of COj or CO, the former being produced by decomposition of carbonate and the latter by reduction of oxides with a carbon impurity under dry conditions near the end of distillation. The identification of CO among the noncondensable gases during the distillation of Cs lends support to this. ... 

Out of three phases reported for Ca3N2 [12], to date only the cubic (a) nitride phase is confirmed, crystallizing in the anti-bixbyite type structure. In addition, the carbodiimide nitride Ca4(CN2)N2 [13] may hold for another unconfirmed calcium nitride phase, and Can(CN2)2N6 stands for the ill-defined CauNg [14]. Here we note again that carbon impurities may produce significant difficulties in reactions. 

For organic ligands used in the synthesis, carbon impurities of 5-10% are present in the materials. C-CP/MAS NMR spectra demonstrate that these impurities are present in the form of pyrogenic carbon (Fig. 19.5). 

Figure 4.28. STM image of a PtRh(lOO) surface. Although the bulk contains equal amounts of each element, the surface consists of 69% of platinum (dark) and 31 % of rhodium (bright), in agreement with the expected surface segregation of platinum on clean Pt-Rh alloys in ultrahigh vacuum. The black spots are due to carbon impurities. It is seen that platinum and rhodium have a tendency to cluster in small groups of the same elements.

A colorless gel formed which was isolated by vacuum evaporation of the volatiles. The resulting colorless glassy solid was pyrolyzed in vacuo at 900°C for 24 hours in a quartz tube and the evolved volatiles identified as NH3 and NH4CI. The remaining solid was briefly (2 hours) heated in air at 1200°C in order to remove minor carbon impurities and to improve crystallinity. This solid was then treated at room temperature with 40% aqueous HF to remove boric acid and silica formed in small quantities. The solid obtained at 900°C was identified as boron nitride however, the majority of the material was amorphous. After treatment at 1200°C, white crystalline boron-nitride was obtained in about 55% yield. 

There can be no doubt that even with a noble metal such as platinum, the surface can be heavily contaminated with carbon when the latter is used as a supporting material (51). This may be ameliorated by cautious treatment with oxygen which oxidizes this carbon impurity to carbon dioxide. Nevertheless, it is extremely doubtful if any platinum surface in platinum/carbon can be prepared without an appreciable, and perhaps substantial, amount of impurity. 

The acid reflux procedure was first described by Rinzler el al. [28], in which raw nanotube materials are refluxed in nitric acid to oxidize the metals and carbon impurities. Acid-treated CNTs are considered to have carboxylic acid groups at the tube ends and, possibly, at defects on the side walls. The functionalized SWNTs have considerably different properties from those of the pristine tubes. 

In many cases the measured enthalpies must be corrected for impurities present in the original sample, often in an ill-defined state. A carbon impurity present in an Si3N4 sample may reasonably be assumed to be present as SiC [53], The carbon-containing species in VSi2, for example, is more uncertain it may be SiC, but it... 

Carbonate impurity in pharmaceutical chemicals usually arise from contamination with atmospheric... 

This process is very simple and requires low temperatures. However, the MWCNTs predominantly contain a large number of structural defects as well as amorphous carbon impurities. Furthermore, a significant part of the salt remains encapsulated within the CNTs. 

Fig. 16.5 (a) Supercell models for bulk anatase (96 atoms) and (b) partial geometry model for three carbon impurities in the anatase supercell. The yellow spheres represent 0 atoms, the small brown spheres represent Ti atoms, and the black spheres represent the carbon impurities. Adapted from Pacchioni etal. [76] with kind permission from the American Chemical Society (2005). 

Aqueous sulfuric acid (HtSOJ H to-ao Tuofstex carbide, platfmaa metals, carbon Impure hydrogen Air Long life demonstrated In laboratory cells. 

However, for the alloys discussed in this paper it is always found that e2 - e j > 2 a. Hence, at equilibrium no reversal in surface enrichment can occur as a function of alloy concentration. Such an inversion, as reported by Takasu and Shimizu (57) for Ni-Cu alloys, has to be related to the particular conditions under which their experiment was performed. It is possible that their results were influenced by the presence of oxygen or carbon impurities in their alloy samples, which would cause enrichment in nickel. 

Depth profiles are usually presented as atomic concentrations versus sputter time, assuming we know the rate at which the sample sputters. A typical depth profile is shown in Figure 25. It is interesting to see that at the surface there is carbon, silicon dioxide and some molybdenum. As soon as the surface layer is sputtered off (300 A), the oxygen and carbon impurities drop to constant and small values. For this CVD film, the molybdenum silicide came out to be very silicon rich. We can also see that the stoichiometry of the silicide changed with position (depth) in the film. 

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