Properties of Carrier Gases for Gas

Properties of Carrier Gases for Gas Chromatography, 8-135 Properties of Cryogenic Fluids, 6-131 Properties of Fatty Acids and Their Methyl... 

The usual carrier gas used for the CVD processes is H2 because of its low density and viscosity for better flow behaviour. Moreover, the recirculation in the reactor chamber can obviously be reduced because of its high thermal conductivity. Under conditions of the same gas flow velocity and substrate temperature the temperature gradients in Ar and N2 are steeper than that in H2 within the boundary layer. In some cases H2 also plays the role of reaction agent. Sometimes Ar, N2 or 02 is used as carrier gas according to the processing requirements. The physical properties of some gases are listed in Table 3.2, including the density (p), viscosity ( i), thermal conductivity (a) and specific heat (Cp). 

There are several reports in the literature that measure binary adsorption equilibria using gas chromatography [4,S,6]. In GC techniques the adsorbent is equilibrated with a continuous flow of carrier gas (gas 1). Then a pulse of gas 2 is injected at the column inlet. A peak of the gas 2 is eluted at the exit of the column after some time. Net retention time (or volume) is calculated from the first moment of the peak after correcting for void volume (by measuring the retention time of a non-adsorbing species). If the carrier gas is inert (i.e. helium) the net retention time is related to the pure component Henry s constant. Typical binary measurements reported so r use a mixture of the two gases as carrier and introduce a small perturbation in composition. The net retention volume is related to the thermodynamic properties by [4]... 

It is normal practice to assume that the typical carrier gases used for gas chromatography are ideal. This allows volume corrections to be made using the ideal gas laws and for gas-solute interactions to be ignored in the interpretation of retention properties. For the most exact work, it may be necessary to allow for non-ideal behavior of the gas phase by applying a correction for solute-gas phase interactions [21,22]. For carrier gases that are insoluble in the stationary phase and at moderate column inlet pressures Eq. (1.5) is a reasonable approximation... 

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