Residual gas impurity

Interference by signals from residual gas impurities, e.g., with... 

Natural gas is usually produced from the well and transported to the gas processing plant at high pressure, in the range 500-1500 psi. To minimize recompression costs, the membrane process must remove impurities from the gas into the permeate stream, leaving the methane, ethane, and other hydrocarbons in the high-pressure residue gas. This requirement determines the type of membranes that can be used for this separation. Figure 8.30 is a graphical representation of the factors of molecular size and condensability that affect selection of membranes for natural gas separations. 

It should be noted that the materials are synthesized under non-equilibrium conditions as the experiments are performed in a dynamic vacuum, and the local vapour pressure of the alkali metal is unknown. The rate and extent of reaction will depend on the nature of the alkali metal, the temperature of the film and the presence of residual ambient gas impurities, which are not controlled in these preliminary experiments. At present, the effect of these variables on the conductivities cannot be assessed. Synthesis in a closed system will be required to determine the relevant thermodynamic parameters. 

The positions of the vague maxima were not reproducible. In our opinion this type of behaviour is due to small amounts of Si and/or B subsurface impurities, which were not detectable in our AES analysis. Small amounts of these elements are known to form stable oxides at the surface (15-19). Type I and type II, however, were fully reproducible. Type I (fig.3d) is a Pt-like behaviour comparable to those of pure Pt (fig.3a) and the Pt-rich alloy (fig.3b). Type II (fig.3e), which shows a maximum for the oxygen intensity likewise at 800 K, is a Rh-like behaviour (compare fig.3c). The maximum relative intensity is lower than that observed for pure Rh. The figures also show that for the Rh-rich alloy the dashed line is much lower relative to the solid line than for pure Rh. This might indicate that the surface oxygen is more easily removed by the residual gas on the alloy than on the pure Rh. It was shown earlier that on a Pt-Rh alloy surface oxygen preferentially occupies the Rh sites leaving the Pt sites initially free (10). If many free Pt sites are present at the surface... 

LEED experiments are usually performed in a UHV chamber that is maintained at pressures below 10 mbar ( 10 Pa). The maintenance of a sufficiently low pressure is important to avoid residual gas adsorption and thus to keep the surface free of impurity during the measurement. In fact, a surface can be contaminated by a monolayer of gas in 1 s with a sticking coefficient of 1 with an ambient pressure of 10 mbar. Thus, the timescale of the experiment may be estimated to be 1000 s before the surface is contaminated with one monolayer of the residual gas. 

According to Pumera (2009), there is also a problem connected with the features of CNTs synthesis. CNTs are typically grown from carbon-containing gas with the use of metallic catalytic nanoparticles. It is well documented that such nanoparticles remain in the CNTs even after extensive purification procedures, leading to two very significant problems (Pumera et al. 2007). It has been shown that such residual metallic impurities are electrochemically active even when intercalated within the CNTs and... 

After volumetric flow measurement (FT) the crude helium gas is fed to the station. Atthe outlet of each individual adsorber G1-G4 the pressure is measured (PT) and maintained in the pure helium flow (PC). The desorption of impurities from the adsorbent respectively the regeneration of the loaded adsorber is controlled via purging steps with pure helium and via flow respectively pressure control of the residual gas (FC). Pressure or flow fluctuations of the residual gas are dampened by a buffer tank (b). 

Molecular ions are observed in spectra from rare earth metals with ion intensities similar to non-rare earth samples. Table 37C.2 lists typical intensity relationships observed in rare earth metal spectra for oxygen, fluorine, and carbon impurities and their associated matrix cluster ion intensities. Although the source of these ions relative to the solid sample has been studied by Muheim (1972, 1973), certain facets of their character remain clouded. Their intensities tend to be erratic and depend upon many parameters such as non-metallic impurity content, residual gas level in the spectrometer ion source chamber, contaminants on the surface of the metal sample, chemical environment, etc. The analytical usefulness of these cluster ion signals has not been established. 

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