"Helium Adsorption measurements of the Surface Area and the Van der Waals constant for 0.10 micron Nuclepore Filters"
This semester I will be doing a low temperature physics project under the supervision of Dr. Peter Sheldon who acquired his Ph.D. in this field. We will be measuring the binding strength of Helium to Nuclepore filters as well as their total surface area, all at 4 Kelvin. Nuclepore filters are plastic and used mainly in the Biological field. However, we will be using them for their specific surface properties. The apparatus pictured below will allow us to admit a known number of Helium atoms into a system where the pressure meter will determine the warm pressure of the system. We will have to apply several corrections to this data before we will be able to find the surface area of the 1490 filters in the sample cell. Ultimately, we are trying to define the relationship between the pressure of the sample cell and the number of atoms adsorbed to filters under those conditions. Therefore, two problems exist with this data: The total number of Helium atoms in the sample cell does not represent the number of atoms bound to the nuclepore filters, and the warm pressure read by the pressure meter isn't the pressure that necessarily occurs in the sample cell. Thus, we will need to define a functional relationship between the cold pressure inside the sample cell and the warm pressure outside. To do so, we will apply a Thermo Molecular Correction (TMC) to our data. This correction will adjust for the differences in pressure in and outside the sample cell. Next, we will need to find the relationship between the adjusted temperatures of the TMC to the number of atoms not adsorbed to filters. From this data, and the known number of atoms in the system, we will have determined a function for the number of atoms adsorbed to filters versus the cold pressure of the sample cell. From these adjustments of our intial data, the surface area of the filters and their specific Van der Waals constant may be calculated with the 3-parameter BET and Franckel-Halsey-Hill (FHH) equations.
Here is the apparatus to be used:
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