Degassing techniques

Helium Sparging—A solvent degassing technique in which helium gas is bubbled through solvents to displace dissolved gases before solvent mixing, compression, and pumping. 

Figure 2.9. Kinetics of hydrogen removal from the melt (an aluminium aiioy) with different degassing techniques (1) universai fiux, (2) uitrasonic treatment, (3) vacuum treatment and (4) ultrasonic treatment in vacuo. (Reproduced with permission of Elsevier...

Table 8. Comparison of Industrial Degassing Techniques for an AL4 Alloy3...

Undoubtedly, the degassing technique used in [325] did not result in complete removal of the adsorbed oxygen (this fact was pointed out by the authors). The presence of oxygen on the carbon surface caused a significant decrease in the energy of the C-Cl adsorption bond. On the other hand, it is obvious that the coverage by oxygen in the Keyes-Marshall experiments was considerably lower than in samples subjected to air- or anodic oxidation. Therefore, in our experiments a lower heat of chlorine adsorption could be expected ... 

Bromo-2-methylpropane [507-19-7] M 137.0, b 71-73 , d 1.218, n 1.429. Neutralised with K2CO3, distd, and dehydrated using molecular sieves (5A), then vacuum distd and degassed by ireeze-pump-thaw technique. Sealed under vacuum. 

One other highly useful chronometer is measurement of °Po- b disequilibria. °Po has a half-life of 138.4 days making the chronometer active for 2 yrs. °Po- °Pb fractionation is based on Po but not Pb partitioning into volatiles during degassing (Gill et al. 1985). Ey repeat analysis of °Po, Rubin et al. (1994) constrained the time of eruption of several samples from 9°N EPR to windows of-100 days. These dates are consistent with eruption windows based on submersible observation. Thus, this technique can provide critical age constraints for other U-series parent-daughter pairs but requires that samples be collected and analyzed as soon as possible after eruption. 

The photodegradation of PVCa solutions has been studied to determine a mechanism for the photodegradation process and identify the excited states involved. The polymer was secondary grade (Aldrich Chemical Company) that was further purified by reprecipitation three times from methylene chloride solution by the dropwise addition into methly alcohol. Solutions in methylene chloride were found to yellow rapidly in air upon exposure to 360 nm light, whereas solutions degassed by the freeze-pump-thaw technique showed little yellowing. 

The densities of polymers can be determined by the pyknometer technique or by the flotation method. In the pyknometer technique the liquid volume displaced by the polymer sample is determined by weighing. Most polymers have a density larger than that of water, which can, therefore, be used as the liquid. Polymers in the form of powders or pressed discs tend to adsorb or occlude air bubbles, which can lead to serious errors. This can be largely prevented by careful degassing of the pyknometer and polymer sample under vacuum before filling with liquid, and/or by addition of a small amount (0.1%) of commercial detergent to lower the surface tension of the water. 

The following operations are all carried out under oxygen-free nitrogen using standard Schlenk techniques.9,10 Solvents and liquid reagents are degassed before use. 

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