Analysis Technique - Micromeritics 3Flex Service Manual

Analysis Sequence
The valves in the schematic are described below.
1 through 3
4
5
6
7
8
10
11
12
13 thru 16
Unmarked

Analysis Technique

The 3Flex 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)
Sample ports
Po port
Servo valve
Manifold vacuum
Isolation
Vacuum
Reference volume (Service mode only)
Analysis gas port (Nitrogen)
Helium port
Additional analysis gas ports
Servo
Description
3Flex Service Manual
Aug 2013