Adsorption of Neopentane on Magnesium Oxide as Odserved in Thermodynamic Aspect

概要

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The absorption of neopentane on magnesium oxide has been investigated by a conventional static system in the temperature range between -50 to -10℃. With the increase in the pressure of the adsorbate, the amount of adsorption at each temperature rapidly increased in the initial stage of adsorption and then increased proportionally. The saturated amount of monolayer adsorption obtained by the extrapolation of adsorptionpressure relation increased with the rise in the pretreatment temperature of magnesium oxide. The molecular area of neopentane on the surface was calculated from the monolayer capacity and the surface area and was estimated to be 30Å^2. With the increase of the surface coverage, the isosteric heat of adsorption rapidly decreased in the initial stage and then reached a stationary value of 4.5 Kcal/mole. On the other hand, the differential molar entropy of adsorption rapidly increased and then gradually decreased with the increase of the coverage. Both the heat and the entropy of adsorption were independent of the pretreatment temperature of magnesium oxide. From these points of view, the thermal treatment does not change the adsorptive property of the surface but the number of the sites for neopentane adsorption. Furthermore, it might be considered that neopentane first chemisorbed and then adsorbed physically on the surface of magnesium oxide.
〔長崎大学教養部〕の論文