Inert gases, molecular compounds

The compounds dissolve in or are adsorbed by this stationary phase to a degree determined by their boiling points. Compounds that are not strongly retained by the column are rapidly pushed to the other end by the stream of inert gas. The compounds that are strongly retained by the column migrate at slower rates. Since the boiling point is inversely related to molecular weight, the smallest compounds tend to elute from the column first. 

In order for a soHd to bum it must be volatilized, because combustion is almost exclusively a gas-phase phenomenon. In the case of a polymer, this means that decomposition must occur. The decomposition begins in the soHd phase and may continue in the Hquid (melt) and gas phases. Decomposition produces low molecular weight chemical compounds that eventually enter the gas phase. Heat from combustion causes further decomposition and volatilization and, therefore, further combustion. Thus the burning of a soHd is like a chain reaction. For a compound to function as a flame retardant it must intermpt this cycle in some way. There are several mechanistic descriptions by which flame retardants modify flammabiUty. Each flame retardant actually functions by a combination of mechanisms. For example, metal hydroxides such as Al(OH)2 decompose endothermically (thermal quenching) to give water (inert gas dilution). In addition, in cases where up to 60 wt % of Al(OH)2 may be used, such as in polyolefins, the physical dilution effect cannot be ignored. 

The diatomic molecule of fluorine does not form higher compounds (such as F3, F4, - ) because each fluorine atom has only one partially filled valence orbital. Each nucleus in Fs is close to a number of electrons sufficient to fill the valence orbitals. Under these circumstances, the diatomic molecule behaves like an inert gas atom toward other such molecules. The forces that cause molecular fluorine to condense at 85°K are, then, the same as those that cause the inert gases to condense. These forces are named van der Waals forces, after the Dutch scientist who studied them. 

Various sample enrichment techniques are used to isolate volatile organic compounds from mammalian secretions and excretions. The dynamic headspace stripping of volatiles from collected material with purified inert gas and trapping of the volatile compounds on a porous polymer as described by Novotny [3], have been adapted by other workers to concentrate volatiles from various mammalian secretions [4-6]. It is risky to use activated charcoal as an adsorbent in the traps that are used in these methods because of the selective adsorption of compounds with different polarities and molecular sizes on different types of activated charcoal. Due to the high catalytic activity of activated charcoal, thermal conversion can occur if thermal desorption is used to recover the trapped material from such a trap. 

The hexafluoride decomposes on heating also decomposed by UV radiation to lower fluorides and reacts with the inert gas xenon, forming a solid product, Xe(PtFe). It reacts with molecular oxygen to produce 02+PtFe The compound attacks glass at ordinary temperatures. 

Solvents and eluents must not be stored in plastic bottles because plasticizers and other low-molecular compounds may diffuse into the liquid. Eluent reservoirs should always be capped, either gas-tight or not depending on whether the solvents are stored or in use. Figure 4.1 shows a solvent supply vessel with aU possible accessories heating (for thermostating), reflux condenser, magnetic stirrer, vacuum pump, inert gas line and excess temperature control. 

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