The Rate of Adsorption Option allows you to measure how quickly (or slowly) a sample adsorbs each dose of gas -- new data you can use to evaluate surface structure.
The basic concept behind the Rate of Adsorption (ROA) option for the ASAP 2010 analyzer is deceptively simple. It doses the sample, records pressure change per dose vs. time, and creates graphs of the data. Yet, the Rate of Adsorption option is more than simply measuring the time it takes a dose of gas to adsorb. It lets you set the gas dose volume, select a target pressure, and decide how long to measure the change in pressure during adsorption (seconds, minutes, etc.)
In other words, you can now selectively evaluate rate of adsorption (or equilibration, for that matter) as a means of understanding surface structure as well as pore structure.
For example, suppose you have measured both the surface area and the pore volume (per gram of sample) of two activated charcoals. Both charcoals are found to exhibit equal values. Further measurements on each of the rate of adsorption reveal, however, that one material takes twice as long to adsorb a given amount of gas as the other. This indicates a differing pore structure. The faster adsorbing charcoal may have relatively large external pore openings which progressively branch into smaller channels toward the interior. The slower adsorbing material may have only a network of small pores which cannot as readily transport gas between the surface and the interior.
Sets Up In About One Minute
Unlike the other ASAP 2020 dosing routines, the ROA routine applies identical doses of adsorptive to the sample and records the pressure change versus time for each dose. To set up the ROA routine, you select three parameters:
- a fixed dose amount
- a target pressure
- a time interval for the dose to adsorb
The ASAP 2020 then converts this pressure history to actual amounts adsorbed. Data are presented as cumulative and incremental curves and tables. Up to four sample curves can be overlaid in one graph making it easy to compare differences in ROA.