Water vapour, influence

It is also established that water is able to enter a vitreous phase and, acting as a glass network modifier , enhance ionic mobilities. There is no doubt that the nature of the grain boundary phase, coupled with the presence of water vapour, influences the diffusion of silver from electrodes and terminations in multilayer capacitors leading to eventual inter-electrode shorting and component failure [9]. 

Harrison, H.S., 1970 Stratospheric Ozone with Added Water Vapour Influence of High Altitude Aircraft , in Science, 170 734. 

In more recent work embrittlement in water vapour-saturated air and in various aqueous solutions has been systematically examined together with the influence of strain rate, alloy composition and loading mode, all in conjunction with various metallographic techniques. The general conclusion is that stress-corrosion crack propagation in aluminium alloys under open circuit conditions is mainly caused by hydrogen embrittlement, but that there is a component of the fracture process that is caused by dissolution. The relative importance of these two processes may well vary between alloys of different composition or even between specimens of an alloy that have been heat treated differently. 

The kinetics and mechanisms of dehydration of crystalline hydrates are considered in Chaps. 4 and 5. It is, however, relevant to mention here that the conditions during dehydration can influence the reactivity of the anhydrous salt (or lower hydrate) formed. Thus, anhydrous solids produced under high vacuum are often amorphous, while those prepared in the presence of appreciable amounts of water vapour may be crystalline [281-283,374],... 

Rate parameters [(da/df), A, E measured for dehydroxylations are frequently sensitive to the availability of water vapour in the vicinity of the reactant and this accounts for the apparent variations in kinetic data sometimes found between different reports concerned with the same reaction. Water adsorbed on product adjoining the reaction interface could be expected to participate in the reversible proton transfer step, the precursor to water elimination. Despite this influence of PH2o on reaction rate, we are aware of no reported instance of S—T behaviour in dehydroxylations. 

The influence of other active components, such as 1, OH, H on a semiconductor sensor, with other conditions being the same, is comparable with the influence of atomic oxygen [50]. Contribution of N and OH is proportional to their relative contents (compared to that of atomic oxygen) in the atmosphere and may become essential at altitudes lower than 60 - 70 km. The use of selective detectors excludes the influence of atomic hydrogen. Studies of adsorption of water vapours on ZnO films [50] show that their influence is negligibly small at the film temperatures below 100°C. Variations of electric conductivity of the films under the influence of water vapours and of an atomic oxygen are comparable at the ratio of their concentrations [H20]/[0] = 10" . 

Apart from molecular vibrations, also rotational states bear a significant influence on the appearance of vibrational spectra. Similar to electronic transitions that are influenced by the vibrational states of the molecules (e.g. fluorescence, Figure 3-f), vibrational transitions involve the rotational state of a molecule. In the gas phase the rotational states may superimpose a rotational fine structure on the (mid-)IR bands, like the multitude of narrow water vapour absorption bands. In condensed phases, intermolecular interactions blur the rotational states, resulting in band broadening and band shifting effects rather than isolated bands. 

Willemer, H. Water vapour pressure, its influence on the freeze-drying process and its control. 40th Annnual Congress of the International Association for Pharmaceutical Technology, Abstracts 1-67, Medpharm GmbH, Scientific Publishers, Stuttgart, Marz 1994... 

J. Kappler, N. Barsan, U. Weimar, and W. Gopel. Influence of water vapour on nanocrystalline Sn02 to monitor CO and CH4 , Proc. Eurosensors XI, Warschau, Poland (1997), 1177-1180. 

The oxygen isotope ratio of ice cores is mostly controlled by a different influence, however the temperature of the clouds from which the snow fell. When water vapour condenses to water or ice, isotope sifting occurs just as it does during evaporation - but in reverse the lighter isotope stays behind. The last precipitation to leave a cloud - the snow that falls over the poles - is therefore enriched in O. The amount of enrichment turns out to depend on how cold it is over the ice sheet. So ice-core isotope records show us how atmospheric temperatures have changed over time. 

In localities where there is much sunshine, the proportion NH3 HN03 is less than in localities where there is less sunshine owing to the favourable influence of light on the oxidation of ammonia to the nitrate. The ammonium nitrate is formed in at least three ways (i) The putrefaction of organic matter followed by the oxidation of the ammonia (ii) the action of electric discharges on ammonia and water vapour and (iii) the action of nitrifying bacteria on ammoniacal compounds. 

Wilson and Miles [12] have measured the absorption of nitric acid by treating with it nitrocotton of 13.8% N. Under a pressure of 4 mm Hg as much as 15% of HN03, was absorbed by this nitrocotton. Nitric acid is absorbed better by a lowernitrated substance, just as the absorption of water vapour is easier in the case of lower-nitrated nitrocellulose. The maximum absorption has been established with nitrocellulose of 7% N. The amount of nitric acid absorbed by cellulose depends on its type. For native cellulose it amounts to about 25% by weight of the cellulose, and approaches 50% for mercerized cellulose. Such differences in the behaviour of different kinds of nitrocellulose indicates that swelling has an appreciable influence on absorption. Mercerized cotton which is more liable to swell simultaneously shows stronger absorption. 

XI. Very complete desiccation prevents the combination of hydrogen and chlorine under the influence of light of the visible region. Coehn and Jung found that there was no combination in systems where the pressure of water vapour was estimated to be 10-7 mm. Hg, but that the reaction took place rapidly when the pressure was 10-5 mm. Bodenstein and Dux had found that variation of the pressure of water vapour between 10 mm. and 10 3 mm. had no effect on the combination. 

The union of hydrogen and chlorine under the influence of visible fight is analogous to the extent that when the partial pressure of water vapour is 10-7 mm. the reaction is said to be inhibited, while at all higher pressures it proceeds normally. 

The influence of hydrothermal treatment on the concentration of Bransted sites, which are directly related to tetrahedrally framework aluminum, has been studied by FTIR spectroscopy in dependence on the Al content. A previously calcined and dehydrated H,A1-MCM-41, containing only ca. 20% of the initial Bransted acid sites, was in situ treated with water vapour at 80°C in the IR cell. After subsequent removal of loosely bound water by evacuation, which was controlled by the disappearance of the deformation mode of water at 1640 cm 1, ammonia was loaded to determine the change of the Bransted acidity. Based on the intensity of the BS band at 1450 cm 1, a distinct increase of the Bransted site content is found (Fig. 2). In comparison with the ammonium exchanged MCM-41, the amount of Bransted sites rises to 53% of the initial value observed with the ammonium exchanged MCM-41. 

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