Determination of Adsorption Layers on Silicon Sorption Artifacts using the Gravimetric Method

Abstract

The adsorption layers on the surface of silicon artifacts were determined experimentally as a function of relative air humidity in the range of 0.07 \ h \ 0.73 using the gravimetric method. 1 kg silicon sorption artifacts were fabricated with the same surface finish and material properties, but they had a very different surface area of 507.8 cm 2 . In this experiment, an ultra-precision mass comparator and special humidity control unit were used. We found that the sorption behavior of the silicon surface was type II by BET classification with the parameters l m = 0.017 lg/cm 2 , and c B = 9.3 from the adsorption isotherm of water vapor on the surface of silicon with R z \ 26.6 nm. The coefficient of water vapor adsorption in moist air was estimated as dl/dh = 65.3 ng cm -2 in a limited humidity range of 0.3 \ h \ 0.6.

Design of sorption and buoyancy artefacts made of silicon

“…However, their design and handling conditions must be determined carefully in order to provide an expected standard deviation for mass in the range of 2 × 10 -8 . So far, only a few transfer standards made of natural silicon with nominal mass of 1 kg, that are comparable to silicon spheres, are manufactured and investigated [5].…”