Analysis Technique - Micromeritics TriStar II 3020 Service Manual

Analysis Sequence
The valves in the schematic are described below.

Analysis Technique

The TriStar II 3020 Analyzer uses physical adsorption and capillary condensation principles to
obtain information about the surface area and porosity of a solid material. The analytical
technique is simple: a sample contained in an evacuated sample tube is cooled (typically) to
cryogenic temperature, then is exposed to analysis gas at a series of precisely controlled
pressures. With each incremental pressure increase, the number of gas molecules adsorbed on
the surface increases. The equilibrated pressure (P) is compared to the saturation pressure (Po)
and their relative pressure ratio (P/Po) is recorded along with the quantity of gas adsorbed by
the sample at each equilibrated pressure.
As adsorption proceeds, the thickness of the adsorbed film increases. Any micropores in the
surface are filled first, then the free surface becomes completely covered, and finally the larger
pores are filled by capillary condensation. The process may continue to the point of bulk
condensation of the analysis gas. Then, the desorption process may begin in which pressure
systematically is reduced resulting in liberation of the adsorbed molecules. As with the
adsorption process, the changing quantity of gas on the solid surface at each decreasing
equilibrium pressure is quantified. These two sets of data describe the adsorption and
desorption isotherms. Analysis of the shape of the isotherms yields information about the
surface and internal pore characteristics of the material.
3-2
Valve(s)
1 through 3 Sample ports
4 Po port
5 Isolation valve
6 Isolation valve
7 Helium port
8 and 9 Analysis gas ports
10 Vacuum
11 through 13 Unrestricted vacuum for sample ports
14 Analysis gas port
15 10-mmHg isolation valve (displays
only if the Krypton option is installed).
Unmarked Servo
TriStar II 3020 Service
Description
Jul 09