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2 Nukleonika

2 2013

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Ortho-positronium migration in mesopores of MCM-41, MSF and SBA-3

Zaleski R., Błażewicz A., Kierys A.

Nukleonika

2013

Vol. 58, No. 1

235-240

Three materials: MCM-41, MSF and SBA-3 with a very similar pore diameter but different lengths of cylindrical pores were investigated using the nitrogen sorption method and positron annihilation lifetime spectroscopy. The size of primary pores and interparticle spaces obtained by both methods is similar. However, volume ratios between the discussed kinds of pores found by the above-mentioned methods differ significantly. Such discrepancy is the result of both ortho-positronium migration and the inaccessibility of the pores for nitrogen. Comparing the results of nitrogen sorption and positron annihilation lifetime spectroscopy allows us to estimate that connectivity between the primary pores and the interparticle spaces is the highest in MCM-41 and lowest in SBA-3.

Gas filling of SBA - 15 silica micropores probed by positron annihilation lifetime spectroscopy (PALS)

Gorgol M., Zaleski R., Kierys A.

Nukleonika

2013

Vol. 58, No. 1

229-233

Positron annihilation lifetime measurements were conducted in situ while two gasses (nitrogen and oxygen, respectively) were introduced into the SBA-15 porous silica sample. Slow changes in lifetime spectra were observed during a long lasting gas interaction with the sample. Introduced gases slowly filled the free volumes, starting from the smallest ones, especially small micropores. In the presence of a gas, the rate of change of ortho-positronium (o-Ps) and unbound positron intensity was larger than the rate of change of lifetime. This suggests the existence of an additional process, which reduces the number of ortho-positronium atoms due to the interaction with the gas. Moreover, the process of filling pores with gas was slower than the process of emptying them while the gas was pumped out.