Gases impure helium

Corrosion tests were performed in the CORALLINE facility, a specific device equipped with two test sections at ambient pressure. The exposures ran at 750°C and 950°C for up to about 800 h. Each test section is composed of a horizontal quartz tube heated by an electrical furnace and can house only four specimens at the same time, in order to avoid interference between coupons. Furthermore, in order to limit the depletion of the impurities, each specimen was placed in its own gas flow line. The impure helium is supplied from pre-mixed cylinders. At the test-section inlet and outlet, a mirror-type hygrometer monitors the helium moisture and a gas chromatograph (He-ionisation detector) analyses the permanent gases. We verified that no significant depletion of the impurities occurred during the tests. Table 26.3 summarises the experimental conditions. 

In these gas-flow proportional counters, the windows are exceedingly thin, fragile,. and unavoidably leaky. Such a window is satisfactory only if a steady flow of. the filling gas is maintained at minimum pressure differential against the helium atmosphere in the optical path. The purging of impurities from the counter is an incidental benefit derived from the gas flow. Hendee, Fine, and Brown20 look upon the gas-flow proportional counter as a steppingstone on the road toward a windowless counter. 

The checkers found that gas chromatographic analysis of one sample using a 305 cm. by 0.3 cm. column packed with 10% SF-96 on Chromosorb P operated at 70° with a 60 ml./minute helium carrier gas flow rate gave five minor impurity peaks, two at shorter retention times, and three at longer retention times. None of these impurities was present in greater than 1.1% total impurities wrere 3%. 

The purity of gases used should also be specified, as certain impurities can have a decisive effect on storage behavior, e. g. gas desorption from stoppers. Greiff and Rightsel [1.96] have shown that influenza viruses without CPAs keep their infectivity best when stored with 1.6 % RM in helium. In argon, the infectivity decreases approx. 10 times and in 02 20 times faster if the average of the storage temperatures is used. 

Gas chromatographic analysis of the product from three consecutive preparations showed less than 0.1% impurity. Similar results were obtained on 0.005-ml. samples in an F. and M. 202 Temperature Programed Gas Chromatograph using two columns a 12-foot column of 10% HiVac grease and 5% Marlex-50 on 100-140 mesh Gas Chrom A, at a constant temperature of 275°, with a helium flow rate of 120 ml. per minute and a 20-foot column of 20% GE-SE 30 on 100-140 mesh Gas Chrom A, programed at 3.3° per minute from 250° to 300°, with a helium flow rate of 120 ml. per minute. 

Another form of head space analysis uses a purge trapping device to trap volatile impurities. In this technique a gas, e.g. helium, is bubbled through the sample which is dissolved in suitable solvent (usually water) and the volatile impurities are thus stripped from the solution and passed in the stream of gas through a polymeric adsorbant where they become trapped and thus concentrated. The stream of gas is then switched so it passes in reverse direction through the polymeric trap, which is heated to desorb the trapped volatiles and the gas stream is then diverted into the GC. This type of procedure is used in environmental analysis to concentrate volatiles in water which are present at low levels. 

Mobile phases are generally inert gases such as helium, argon, or nitrogen. The choice of carrier gas is often dependent upon the type of detector used. Gas is obtained from a tank, or sometimes from an electrolysis cell, and is passed through a series of reductors, equalizing valves, and traps to ensure constancy of pressure or flow and elimination of impurities as well. 

Materials. Cyclohexene, obtained by dehydration of reagent grade cyclohexanol (3), was heated at reflux over sodium metal, fractionated on a 60-cm. Helix packed column, stored over sodium, and filtered just before use. No impurity was found by gas chromatography (column, TCP and Si-550 carrier gas, helium). Propylene (Neriki Research Grade) used showed no impurity by gas chromatography (column, active carbon and acetonylacetone). 

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