Comparison of Properties of Different Materials by Adsorptions N2 and Ar at Temperature –196 °C

The article is focused on comparing of the structural properties of different adsorption materials. The measurement of adsorption isotherms was carried out in nitrogen and argon at a temperature of –196 °C. The individual isotherms using selected samples were measured on an Autosorb ASiQ instrument. BET surfaces and total pore volumes of individual samples were calculated and compared from the resulting isotherms. The results show relatively high differences between the adsorption isotherm measured by using nitrogen and argon. For the Envisorb sample, which consists of up to 85% silicagel, the BET surface area calculated from the nitrogen adsorption isotherm was 45 % higher than when measuring the adsorption isotherm using argon as the adsorptive. For silicagel SGR 50 was the difference between BET surface area measurements with nitrogen and argon only 4 %. The opposite phenomenon was calculated for the material activated carbon SC 40, where the BET surface measured by argon was higher than BET surface measured by nitrogen. Of the adsorbents used, nitrogen appears to be more suitable; only for carbonbased microporous materials is it better to use argon as an adsorptive. The evaluation of the measured adsorption isotherms by the t-plot method showed a good usability of this method when it is applied similarly to the BET method for adsorption isotherms in the range of adsorptive rel. pressure ranged from 0.05 to 0.35. This method is a reliable tool for determining the proportion of the smallest pores (micropores) in the total surface area of a given adsorbent. However, in the case of adsorbents with a very low proportion of micropores, its accuracy is lower.