Monitoring the Crystallization Stages of Silicalite by Positron Lifetime Spectroscopy

2008 ◽  
Vol 607 ◽  
pp. 173-176 ◽  
Author(s):  
Z. Kajcsos ◽  
C. Kosanovic ◽  
S. Bosnar ◽  
B. Subotic ◽  
P. Major ◽  
...  
Keyword(s):  
Porous Media ◽  
Positron Annihilation ◽  
Free Volume ◽  
Positron Lifetime ◽  
Large Change ◽  
Zeolite Framework ◽  
Positron Lifetime Spectroscopy

In porous media, positron annihilation techniques (PAT) revealed the existence of annihilation modi with long lifetimes connected to structural and extrastructural free volumes acting as trapping centres for o-Ps. Our aim in this work was to study the influence of the synthesis applied for the production of the zeolite framework and the correlation between the trapping pattern and crystallization progress. PAT lifetime (LT) measurements were performed in silicalite-1 samples in various stages of crystallization and a large change was observed in the long components. The results are discussed in connection to the crystallization and the availability of free volume.

Preliminary Positron Lifetime Results on Free Volumes in Cyclodextrins

2010 ◽  
Vol 666 ◽  
pp. 99-102 ◽  
Author(s):  
Maria Fatima Ferreira Marques ◽  
A.M.G. Moreira Da Silva ◽  
P.M. Gordo ◽  
Z. Kajcsos
Keyword(s):  
Positron Annihilation ◽  
Free Volume ◽  
Positron Lifetime ◽  
Positron Annihilation Lifetime Spectroscopy ◽  
Positron Source ◽  
Lifetime Component ◽  
Positron Annihilation Lifetime ◽  
Long Lifetime

Positron annihilation lifetime spectroscopy was used to study the free-volume parameters in various pure -, - and -cyclodextrins samples and, in the case of β-cyclodextrin, with inclusion of S-carvone and thymoquinone. The results clearly indicate the presence of long lifetime components related to Ps-formation. The data show that the addition of S-carvone to β-cyclodextrin results in a decrease of o-Ps lifetime that we ascribe to a reduction of free volume holes from 81.8 to 63.7 Å3. The long lifetime component disappears when thymoquinone is added to -cyclodextrin, indicating this substance acts as an o-Ps quencher. For all samples studied, a decrease in the long lifetime component values was observed with increasing source in situ time, a result that might be attributed to the irradiation of the sample by the 22Na positron source.

Defects Distribution of Pr2Fe14B Hard Magnetic Magnet from Amorphous to Nanostructures Characterized by Positron Annihilation Spectroscopy

2005 ◽  
Vol 475-479 ◽  
pp. 2123-2126
Author(s):  
Yu Cheng Wu ◽  
W. Sprengel ◽  
K. Reimann ◽  
K.J. Reichle ◽  
D. Goll ◽  
...  
Keyword(s):  
Positron Annihilation ◽  
Grain Growth ◽  
Melt Spinning ◽  
Positron Lifetime ◽  
Positron Annihilation Spectroscopy ◽  
Amorphous Structure ◽  
Defect Distribution ◽  
Positron Lifetime Spectroscopy ◽  
Positron Lifetimes ◽  
Shape And Size

The defect distributions have been investigated using positron lifetime spectroscopy on amorphous and nanocrystalline Pr2Fe14B samples, produced by melt-spinning and nanocrystallization route. The main two components can be concluded that were ascribed to vacancy-like defects in the intergranular layers or the interfaces, and microvoids or large free volumes with size compared to several missing atoms at the interactions of the atomic aggregates or the crystallites. The remarkable changes in the positron lifetimes from the amorphous structure to the nanocrystalline with varied sizes can be interpreted, indicating that the structural transformation and the grain growth induce the defect distribution changes occurring at the interfaces with different shape and size.

Positron spectroscopy of bulk and near-surface defects in semiconductors

1989 ◽  
Vol 67 (8) ◽  
pp. 813-817
Author(s):  
P. Hautojārvi
Keyword(s):  
Positron Annihilation ◽  
Positron Lifetime ◽  
Surface Defects ◽  
Positron Beam ◽  
Near Surface ◽  
Slow Positron ◽  
Positron Spectroscopy ◽  
Positron Lifetime Spectroscopy ◽  
Defects In Semiconductors ◽  
Ion Implanted

The use of positron annihilation to study defects in semiconductors is discussed. Positron-lifetime spectroscopy reveals As vacancies in as-grown GaAs and gives information on ionization levels. The vacancy profiles in ion-implanted Si are investigated by slow positron beam.

scholarly journals POSITRON LIFETIME MEASUREMENTS IN NATURAL RUBBER WITH DIFFERENT FILLERS

2013 ◽  
Vol 22 ◽  
pp. 112-117 ◽  
Author(s):  
A. MANDAL ◽  
S. MUKHERJEE ◽  
S. PAN ◽  
A. SENGUPTA
Keyword(s):  
Natural Rubber ◽  
Positron Annihilation ◽  
Free Volume ◽  
Positron Lifetime ◽  
Amorphous Region ◽  
Filler Concentration ◽  
Lifetime Measurements ◽  
Positron Annihilation Lifetime

Positron annihilation lifetime spectra (PLAS) have been measured for natural rubber polymer with different fillers (Titenium dioxide, Nanosilica and Nanoclay) as a function of filler concentration to investigate how these fillers affect the microstructure of free volume of natural rubber. The lifetime spectra is analyzed by using LT9.0 and the longest lived component(τo-Ps) is attributed to the pick- off annihilation of o-Ps in free volume sites, available mostly in the amorphous region of polymer. On the basis of the τo-Ps values the radii of the free volume holes (Rh) are calculated. The PALS results show that o-Ps lifetime as well as the size of free volume decreases with the increase of filler concentration.

A STUDY OF RECOVERY STAGES IN SOME PLASTICALLY DEFORMED ALUMINUM ALLOYS BY POSITRON LIFETIME SPECTROSCOPY

2005 ◽  
Vol 12 (02) ◽  
pp. 203-207 ◽  
Author(s):  
M. A. ABDEL-RAHMAN ◽  
M. S. ABDALLAH ◽  
EMAD A. BADAWI
Keyword(s):  
Aluminum Alloys ◽  
Positron Annihilation ◽  
Room Temperature ◽  
Positron Lifetime ◽  
Isochronal Annealing ◽  
Temperature Range ◽  
Positron Lifetime Spectroscopy

Positron annihilation was performed to study the isochronal annealing of wrought (2024, 7075) and casting ( AlSi 11.35 Mg 0.23, AlSi 10.9 Mg 0.17 Sr 0.06) aluminum alloys in the temperature range from room temperature to 773 K after they had been deformed at room temperature with 25% deformation. Two annealing stages of microstructures were distinguished which were attributed to recovery in 2024, and AlSi 11.35 Mg 0.23, AlSi 10.9 Mg 0.17 Sr 0.06 due to point and dislocations respectively, and only one due to dislocations in 7075.

Temperature and time dependence of free volume in bisphenol A polycarbonate studied by positron lifetime spectroscopy

1992 ◽  
Vol 25 (19) ◽  
pp. 5089-5093 ◽  
Author(s):  
J. E. Kluin ◽  
Z. Yu ◽  
S. Vleeshouwers ◽  
J. D. McGervey ◽  
A. M. Jamieson ◽  
...  
Keyword(s):  
Bisphenol A ◽  
Time Dependence ◽  
Free Volume ◽  
Positron Lifetime ◽  
Bisphenol A Polycarbonate ◽  
Positron Lifetime Spectroscopy

Effect of Water on the Size Distribution of Free-Volume Holes in Nafion Membrane

2012 ◽  
Vol 733 ◽  
pp. 49-52 ◽  
Author(s):  
Jakub Čížek ◽  
Zuzana Barnovská ◽  
Michal Šourek ◽  
Ivan Procházka
Keyword(s):  
Size Distribution ◽  
Free Volume ◽  
Water Uptake ◽  
Positron Lifetime ◽  
Ionic Clusters ◽  
Mean Size ◽  
Positron Lifetime Spectroscopy ◽  
The Mean ◽  
Kinetics Of

Positron lifetime spectroscopy was employed for investigation of the size distribution of free volume holes in Nafion N-1110 membrane. Size distribution of free volume holes was determined in the as-received and dried membrane and in the membrane immersed in water at various temperatures. It was found that absorbed water causes reduction of the mean size of free volume holes and increase of their dispersion and concentration. This indicates that free volumes are split by swollen ionic clusters absorbing water. The kinetics of water uptake and the amount of absorbed solvent was determined by in-situ measurement of the weight increase.

scholarly journals Free-Volume Studies in Polycaprolactone/Poly(propylene oxide) Urethane/Urea Membranes by Positron Lifetime Spectroscopy

2008 ◽  
Vol 113 (5) ◽  
pp. 1359-1364 ◽  
Author(s):  
M.F. Ferreira Marques ◽  
P.M. Gordo ◽  
A.P. de Lima ◽  
D.P. Queiroz ◽  
M. Norberta de Pinho ◽  
...  
Keyword(s):  
Free Volume ◽  
Propylene Oxide ◽  
Positron Lifetime ◽  
Positron Lifetime Spectroscopy ◽  
Poly Propylene

scholarly journals Temperature dependence of free volume distributions in polymers studied by positron lifetime spectroscopy

1993 ◽  
Vol 03 (C4) ◽  
pp. 265-270 ◽  
Author(s):  
J. KRIŠTIAK ◽  
K. KRIŠTIAKOVÁ ◽  
O. ŠAUŠA ◽  
P. BANDŽUCH ◽  
J. BARTOŠ
Keyword(s):  
Temperature Dependence ◽  
Free Volume ◽  
Positron Lifetime ◽  
Positron Lifetime Spectroscopy
Sign in / Sign up

Export Citation Format

Share Document