Inert-gas effect

The example indicates that the inert gas effect would be difficult to measure at 1 atm, but becomes appreciable at very high pressures. 

If the SiH4/02 mixture is not sufficiently diluted with an inert gas, then gas phase nucleation typically occurs and Si02 particulates are formed. Generally, N2 is used as the diluent, but some work has been done with Ar, C02, and He. Depending on the reactor configuration, an inert gas effects the deposition rates in different ways. 

Interesting additional inert gas effects have been observed by Biron and Nalbandjan [17]. Using silica vessels they confirmed the above behaviour but in experiments under conditions analogous to those used by Semenova, already discussed, they found the critical explosion pressures to be unaffected by argon addition. Their results are given in Table 4. The conditions used by Semenova correspond with extremely low chain breaking efficiency at the vessel wall, and under these conditions the rates... 

Tipper and Williams studied the reaction over the temperature range 20-570 °C in the presence of nitrogen and sulphur dioxide, they reported an inert gas effect on the rate. Both the non-integral orders found by Treacy and Daniels, and the inert gas effect found by Tipper and Williams are in disagreement with the findings of Johnston and Slentz , Ashmore et and Thomas and... 

Several experiments were done in the unpacked and packed vessel in the presence of a large excess of He to test for inert gas effects. The [NH3] / [O3] 0 ratios varied from 1.5-23, and all the decay curves obeyed first-order kinetics. The relative gaseous product yields were essentially unaffected in the unpacked cell (products were not analyzed in the... 

The effect of added CO2 on the formation of CO was investigated by Calwell and Hoare - with about 10 quanta.l . sec absorbed intensities, and at temperatures of 50-200 °C. The value of co increased with increasing presstire at all temperatures investigated however, above 120 °C the pressure effect was less pronounced and was more complex in character. It has been suggested that, in the temperature range 120-200 °C, the inert gas effect is due to the acceleration of the decomposition of electronically excited acetone molecules. However, below 100 °C, the increase of co with increasing inert gas pressure is mainly related to the pressure dependence of the homogeneous decomposition of the acetyl radicals. 

Srinivasan favoured the concerted mechanism for reactions I-IV. His reasoning was based, above all, on the lack of any effect caused by O2. In support of his view he claimed that inert gases exert a different, in some cases even opposite, influence on the formation of the various products, which, thus, cannot all originate from the same biradical. However, as appears from the above discussion and from that which follows, the inert gas effects are, in fact, compatible with the biradical mechanism as well. 

Kinzl, M. et al., SAFT modeling of inert-gas effects on the cloud-point pressures in ethylene copolymerization systems poly(ethylene-co-vinyl acetate)- -vinyl acetate-i-ethylene and poly(ethylene-co-hexene-l)-thexene-l-tethylene with carbon dioxide, nitrogen or -butane, Ind. Eng. Ghent. Res., 39, 541-546, 2000. 

Kumar, R., and Sircar, S., Adiabatic sorption of bulk or dilute single adsorbate from an inert gas Effect of gas-solid mass and heat transfer coefficients, Chem. Eng. Commun., 26(4), 339-354 (1984). 

Inerts concentration. The reaction might be carried out in the presence of an inert material. This could be a solvent in a liquid-phase reaction or an inert gas in a gas-phase reaction. Figure 2.96 shows that if the reaction involves an increase in the number of moles, then adding inert material will increase equilibrium conversion. On the other hand, if the reaction involves a decrease in the number of moles, then inert concentration should be decreased (see Fig. 2.96). If there is no change in the number of moles during reaction, then inert material has no effect on equilibrium conversion. 

The action of this and other anti-bumping devices e.g., minute carborundum chips) is dependent upon the fact that the transformation of a superheated liquid into the vapour will take place immediately if a vapour phase e.g., any inert gas) is introduced. The effect may be compared with that produced by the introduction of a small quantity of a solid phaM into a supercooled liquid, e.g., of ice into supercooled water. 

The introduction of additional alkyl groups mostly involves the formation of a bond between a carbanion and a carbon attached to a suitable leaving group. S,.,2-reactions prevail, although radical mechanisms are also possible, especially if organometallic compounds are involved. Since many carbanions and radicals are easily oxidized by oxygen, working under inert gas is advised, until it has been shown for each specific reaction that air has no harmful effect on yields. 

Increasing or decreasing the partial pressure of a gas is the same as increasing or decreasing its concentration. The effect on a reaction s equilibrium position can be analyzed as described in the preceding example for aqueous solutes. Since the concentration of a gas depends on its partial pressure, and not on the total pressure of the system, adding or removing an inert gas has no effect on the equilibrium position of a gas-phase reaction. 

Collision of an ion with an inert gas molecule leads to some deflection in the ion trajectory. After several collisions, the ion could have been deflected so much that it no longer reaches the detector. This effect attenuates the ion beam as it passes through the gas cell, leading to loss of instrumental sensitivity. An attenuation of 50 to 70% is acceptable and is not unusual in practice. 

The ethylene glycol liberated by reaction (5.L) is removed by lowering the pressure or purging with an inert gas. Because the ethylene glycol produced by reaction (5.L) is removed, proper stoichiometry is assured by proceeding via the intermediate, bis(2-hydroxyethyl) terephthalate otherwise the excess glycol used initially would have a deleterious effect on the degree of polymerization. Poly(ethylene terephthalate) is more familiar by some of its trade names Mylar as a film and Dacron, Kodel, or Terylene as fibers it is also known by the acronym PET. 

Discussion of the concepts and procedures involved in designing packed gas absorption systems shall first be confined to simple gas absorption processes without compHcations isothermal absorption of a solute from a mixture containing an inert gas into a nonvolatile solvent without chemical reaction. Gas and Hquid are assumed to move through the packing in a plug-flow fashion. Deviations such as nonisotherma1 operation, multicomponent mass transfer effects, and departure from plug flow are treated in later sections. 

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. 

Materials of Construction. In choosing the proper materials of constmction for storing and using hydrazine, it is necessary to consider both the effects of the material on the stabiUty and quaUty of the hydrazine as well as the effect of the hydrazine on the material of constmction. Hydrazine is thermally stable, storable for years without adverse effects either to the product or the storage container provided the recommended materials are used, all systems are clean, and an inert gas, ie, nitrogen, is maintained over the system at all times. Table 10 is a brief listing of materials compatibiUty (125). 

Recombination reactions are highly exothermic and are inefficient at low pressures because the molecule, as initially formed, contains all of the vibrational energy required for redissociation. Addition of an inert gas increases chemiluminescence by removing excess vibrational energy by coUision (192,193). Thus in the nitrogen afterglow chemiluminescence efficiency increases proportionally with nitrogen pressure at low pressures up to about 33 Pa (0.25 torr) (194). However, inert gas also quenches the excited product and above about 66 Pa (0.5 torr) the two effects offset each other, so that chemiluminescence intensity becomes independent of pressure (192,195). 

Ozone can be analyzed by titrimetry, direct and colorimetric spectrometry, amperometry, oxidation—reduction potential (ORP), chemiluminescence, calorimetry, thermal conductivity, and isothermal pressure change on decomposition. The last three methods ate not frequently employed. Proper measurement of ozone in water requites an awareness of its reactivity, instabiUty, volatility, and the potential effect of interfering substances. To eliminate interferences, ozone sometimes is sparged out of solution by using an inert gas for analysis in the gas phase or on reabsorption in a clean solution. Historically, the most common analytical procedure has been the iodometric method in which gaseous ozone is absorbed by aqueous KI. 

Inert gas flush packing in plastic-laminated pouches, although less effective than vacuum packing, can remove or displace 80—90% of the oxygen in the package. These packages offer satisfactory shelf life and are sold primarily to institutions. 

---