Adsorption and desorption of water

The stoppers for vials contain a certain amount of water, which depends on the composition of the stoppers. De Grazio and Flynn [1.86] showed, that the selection of the polymer, the additives for the vulcanization, and the filler influence the adsorption and desorption of water. However even the best possible mixture increases the RM in 215 mg sucrose from 1.95 % to 2.65 % during 3 months storage time at room temperature. Other stopper mixtures show an increase up to 1.7 %. Pikal and Shah [1.87] demonstrated, that the desorption of water from the stopper and the absorption of water by the product depends, in the equilibrium state, on the mass and water content of the stopper and the water content and sorption behavior of the dry product. 

The moisture content of the paper has a strong effect on the folding endurance test. The swelling and shrinkage which accompany adsorption and desorption of water vapor cause shifting and rearrangement of... 

Differential thermal analysis. The phenomena of adsorption and desorption of water and the loss of physically bound water have been investigated by differential thermal analysis (112,151a). In this method, a small amount of the sample to be examined and a sample of inert material (e.g., calcined alumina) are placed in separate wells in a nickel block. A thermocouple junction is placed in each of the samples and the thermocouple leads are connected in series but with opposing e.m.f. s. The nickel... 

Koretsky et al. calculated site densities for particular low index faces of six oxides and six silicate minerals and average site densities for cleavage and growth faces, and showed that these methods lead to very different results. Full documentation of depth, length of broken bond and Brown bond strengths of broken bonds for particular types of sites is presented. The ranges of TVs calculated by Koretsky et al. [7] and in their literature data collection (tritium exchange, acid-base titrations, NMR, adsorption and desorption of water at various conditions, and saturation experiments with different adsorbates in solution) for six oxides are listed in Table 5.1. 

Alumina film sensors have been used in various industries such as medicine and foodstuffs. Figure 20-4 (a) shows a schematic view of an alumina film sensor which is formed by the anodic oxidation of an aluminum plate in an acid solution and then the deposition of a Au film as an electrode. The equivalent circuit of this sensor element is shown in Figure 20-4 (b). The resistance and capacitance are changed by the adsorption and desorption of water. This alumina film sensor has fast response times, and even a few ppm of water in the atmosphere can be detected. However, the use of this element is restricted to dry atmospheres because of the hysteresis and the change of sensor characteristics which occur during operation [11]. 

Porous silicas are usually mesoporous materials and they can be made with a variety of pore dimensions. In particular, silica glasses can be made with well-defined pore diameters, typically in the range 30-250 A, using sol-gel methods. Such a system provides a good model for testing the models of relaxation behaviour of fluids in porous solids. It is normally found that the two-site fast-exchange model for relaxation described above for macroporous systems is still valid. For instance, H and relaxation times have been measured during both adsorption and desorption of water in a porous silica. Despite hysteresis in the observed adsorption isotherms, it was found that the relaxation times depended solely on water content.For deuterated water in some porous silicas, multicomponent relaxation behaviour for T2 and Tip has been observed, and this has been attributed to the fractal nature of the pore structure. 

Chung, D.S. and Pfost, H.B., Adsorption and desorption of water vapor by cereal grains and their products, Trans. ASAE, 10(4) 552-575, 1967. 

The phenomena occurring during the adsorption and desorption of water vapour in the paste were discussed in the previous chapter. 

FIGURE 1.13 Isotherms of water adsorption at 293 K on silicas shown in Table 1.4 in (a, c) mmol/g and (b) mmol/m, (c) adsorption and desorption of water is shown, and (d) distribution functions of free energy of water adsorption onto silicas. (Adapted from J. Colloid Interface Sci., 242, Gun ko, V.M., Mironyuk, I.F., Zarko, V.I. et al.. Fumed silicas possessing different morphology and hydrophilicity, 90-103,2001d. Copyright 2001, with permission from Elsevier.)... 

Berend I, Cases JM, Francois M, Uriot JP, Michot L, Masion A, Thomas F (1995) Mechanism of adsorption and desorption of water vapor by homoionic montmorillonites 2. The Li, Na K, Rb and Cs -exchanged forms. Clays Clay Miner 43 324-336... 

Stimiman Ml, Hrrang C, Srrrith RS, Joyce SA, Kay BD (1996) The adsorption and desorption of water on single crystal MgO(lOO) The role of strrface defects. J Chem Phys 105 1295-1298 Sterling TL, Salmon J, Becker DJ, Savarese DF (1999) How to Brrild a Beowrrlf A Grride to the Implemerrtation arrd Application of PC Clrrsters, MTT Press, Cambridge, Massachusetts. 

Fu MH, Zhang ZZ, Low PF (1990) Changes in the properties of a montmorillonite-water system during the adsorption and desorption of water hysteresis. Clays Qay Miner 38 485 92 Fujii K, Nakano M (1984) Chemical potential of water adsorbed to bentonite. Trans Japanese Soc Irrigation Drainage Rural Eng 112 43-53 (in Japanese)... 

Montagne, X., Lynch, J., Freund, E., et al. (1987). A study of the adsorption sites on thoria by STEM and FTIR spectroscopy. Adsorption and desorption of water and methanol. J. Chem. Soc. Faraday Trans. /, 83, pp. 1417-1425. 

Alas, adsorption is more complex than VLE or than the simple picture show above. Figure 11.27 shows experimental data for the adsorption and desorption of water on silica gel [31]. 

The interaction of water with many materials can have a significant impact on the material properties, for example plasticisation of the glass transition temperature and stabihty. TGA measurements under controlled humidity are useful in studying the adsorption and desorption of water and for distinguishing bound and unbound water. Dynamic vapour sorption (DVS) is a similar technique and has its own class of dedicated instrumentation. A full description of this is outside the scope of this book. 

Jurinak, J. J., 1961. The effect of pretreatment on the adsorption and desorption of water vapor by lithium and calcium kaolinite. J, Phys, Chem, 65 62-64. 

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