The Freezing of Water and Benzene in Porous Vycor Glass

Hodgson, C.; McIntosh, R.

doi:10.1139/v60-134

Cited by 46 publications

(32 citation statements)

References 7 publications

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“…The sharp change of slope of the vapor pressure isosteres does not prove that the transition is sharp as has been pointed out (7). T h e existence of a freezing range is to be expected according to the n~olecular picture of phase changes in adsorbed layers.…”

Section: Xenon Vapor Pressure and Expansion Isosteresmentioning

confidence: 82%

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Phase Transitions of Water and Xenon Adsorbed in Porous Vycor Glass

Litvan¹,

McIntosh²

1963

Can. J. Chem.

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ABSTRACT1Ieasurements of the expansion of porous Vqcor glass containing fixed quantities of adsorbed water indicate that in every instance a phase transition starts belo\\ -50" C, with the main change occurring below -160" C. Two other anomalies of the length variation mere observed near -22" C and -7" C when the amount of adsorbed water exceeded the value equivalent to two monolayers. The length of the adsorbent after co~npletion of a temperature cycle was different from the initial length. This is thought to be due to damage suffered by the glass aiid t o the fact that the length of the adsorbent is different for adsorption and desorption although the quantity adsorbed may be the same.The phase transition of adsorbed xenon takes place below the normal triple point and is a function of surface concentration as shown by length variations and equilibrium pressures for fixed quantities adsorbed. All transitions are gradual aiid hysteresis is exhibited by the isosteres. The adsorption isotherms for xenon -I'ycor glass show a decreasing adsorptive capacity and a contraction of the hysteresis loop with lower temperature. The inadequacy of the capillary coildensation theory of adsorption in relation t o these results is discussed.The capillary condensation theory assumes that the free energy of the adsorbate is less than that of bulk material a t the same temperature because it is held under concave menisci in the pores of the adsorbent. The vapor pressure of the condensed substance is calculated by the relationship due to Kelvin. The theory implies that the adsorbent is inert, and only the shape and size of the pores play any role in determining the adsorptive characteristics. I t follo\vs also that the adsorbate has bulk properties except the lowered free energy arising from the presence of the concave meniscus.There is, however, ample experimental evidence to the contrary. The observed dimensional changes of the adsorbents (0.37, in the case of 17ycor glass -water system (1)) during the adsorption process indicate that the solid is perturbed by the presence of the adsorbate. Similarly, the infrared spectra of the adsorbate contain lines caused by forbidden transitions normally observable only in the Raman spectra (2,3) showing that the adsorbed liquid is in a state different from the bulk state. The crystal structure of the frozen adsorbate, too, has been found by X-ray diffraction methods to differ from the one of the bulk crystal (4). Accordingly, solidified adsorbates failed to nucleate undercooled bulk liquid of the same composition (5). These findings are to be expected in view of the fact that adsorption is the result of molecular interaction between adsorbate and adsorbent, and this interaction perturbs both.On applying the equation due to Kelvin the question arises: is it permissible to use the relationship even as an approximation when most of the quantities involved are not only unknown quantitatively but are meaningless on a molecular scale? Surface tension (or even the tern1 surface itself) of a liquid ...

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Section: Xenon Vapor Pressure and Expansion Isosteresmentioning

confidence: 82%

“…But even so, the number of experimental results not explicable by the theory is growing and it seems desirable to examine its applicability under various conditions. One means of testing the theory has been shown to be the study of phase transitions of adsorbates (6,7). The present work is a continuation of that investigation.…”

mentioning

confidence: 88%

Phase Transitions of Water and Xenon Adsorbed in Porous Vycor Glass

Litvan¹,

McIntosh²

1963

Can. J. Chem.

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“…Great care was taken to ensure that deposition did not occur on the wire holding the sample to the spiral, or on the outer surface of the sample; after each temperature change was effected, the sample was pumped slightly and was then allowed to return to equilibrium. A "cooling-warming" isostere was also measured, in the same nlanner as other workers (5)(6)(7)(8). This experiment served as a useful comparison especially since the samples used in this work had different surface areas and porosities to the samples of other workers.…”

Section: Methodsmentioning

confidence: 99%

“…Isosteres As stated previously, this experiment probably leaves a saturated porous system in an undefined state, but because of its practical importance (it is the kind of treatment a material will receive in nature) and because many measurements of this type have been made previously (2,(5)(6)(7)(8) and have been correlated with calorimetric measurements (9, 81, it was deemed necessary to perform this experiment to provide comparison with previous results and to compare present results with those of experiments of Sections (1-4). It is thought that a satisfactory explanation can now be provided for the "cooling-warming" isosteres.…”

Section: ( 5 ) "Cooling-warnzing" Length Clzangementioning

confidence: 97%

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Length change – adsorption relations for the water – porous glass system to −40 °C

Feldman¹

1970

Can. J. Chem.

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Adsorption of water has been studied extensively above 0 "C, but the problem of the phase transition of adsorbates in porous materials is presented at temperatures below 0 "C. Experiments that show how phase transitions modify length change -adsorption relationships are described.Adsorption -length change measurements froin -40 to -0.5 and isotherms at -20 and -0.5 "C were obtained. In another group of experiments different forms of isosteres were also obtained; the principle that water should be allowed to enter the sample at the low temperature was usually followed.Isothernls and length change -adsorption characteristics below 0 "C are qualitatively similar to those above 0 "C, but a decrease in adsorptive capacity and length change was observed. These results and those obtained from the isosteres lead to the conclusion that capillary condensation and menisci theories are operative and that a solid meniscus exists. It follows therefore that the saturated vapor pressure of frozen adsorbate is greater than that of bulk ice and that its voli~metric expansion on freezing is similar to the bulk phase transition. It is shown how these phenomena can predict migration of water and generation of pressure within the porous body when it is subjected to cooling and warming cycles.

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2016

Durability Design of Concrete Structures

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The Freezing of Water and Benzene in Porous Vycor Glass

Cited by 46 publications

References 7 publications

Phase Transitions of Water and Xenon Adsorbed in Porous Vycor Glass

Phase Transitions of Water and Xenon Adsorbed in Porous Vycor Glass

Length change – adsorption relations for the water – porous glass system to −40 °C

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