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Wyświetlanie 1-8 z 8
Tytuł:
Positron Porosimetry Studies of Template Removal from As-Synthesized MCM-41 Silica
Autorzy:
Zaleski, R.
Wawryszczuk, J.
Powiązania:
https://bibliotekanauki.pl/articles/1812554.pdf
Data publikacji:
2008-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
36.10.Dr
61.43.Gt
81.07.-b
Opis:
The course of template removal from MCM-41 pores was investigated by positron annihilation lifetime spectroscopy. Two methods of removal were the object of interest: a decarbonisation after standard calcination procedure and a novel procedure - pyrolysis in vacuum. The shapes of positron lifetime spectra of decarbonised sample are determined by positronium quenching caused by presence of carbon deposit on the surface. Positron annihilation lifetime spectroscopy allows also monitoring the evolution of empty space inside pores. During pyrolysis no conductive carbon is produced, so consecutive stages of template material transformation are easy to observe. In the case of pyrolysis the effect of pore emptying is obtained at temperature 500 K, lower comparing to calcination and decarbonisation (820 K).
Źródło:
Acta Physica Polonica A; 2008, 113, 5; 1543-1550
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Vapour Absorption in Melamine-Formaldehyde Resin
Autorzy:
Wawryszczuk, J.
Ciesielski, K.
Goworek, J.
Powiązania:
https://bibliotekanauki.pl/articles/2025738.pdf
Data publikacji:
2001
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
36.10.Dr
61.41.+e
66.30.-h
Opis:
The effects of vapour absorption on positron annihilation in cross-linked polymer were investigated. Contrary to linear polymers, absorption of vapour in cross-linked resin leads to the shortening of o-Ps lifetime. In vacuum absorbed molecules diffuse out. At room temperature desorption of hexane and hexanol is not complete; full elimination of absorbed molecules requires sample temperature increase.
Źródło:
Acta Physica Polonica A; 2001, 99, 3-4; 523-528
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Influence of Temperature and Pressure on the Free Volume in Thermo-Shrunken Polyethylene by Positron Annihilation
Autorzy:
Danch, A.
Osoba, W.
Wawryszczuk, J.
Powiązania:
https://bibliotekanauki.pl/articles/1812484.pdf
Data publikacji:
2008-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.60.+z
78.70.Bj
Opis:
Positron lifetime measurements were performed as a function of temperature and pressure for thermo-shrunken polyethylene. Mean volume of free volume cavities in the investigated polymer was estimated from the results of the measurements. This mean volume turned out to be the smooth function of temperature (from room temperature to 8.5 K) and high pressure (from 0.1 MPa to about 500 MPa). The effect of trapping of the free electrons produced during positron irradiation was observed at low temperature.
Źródło:
Acta Physica Polonica A; 2008, 113, 5; 1307-1313
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Positronium Formation in Solid Long-Chain Alkanes
Autorzy:
Zaleski, R.
Wawryszczuk, J.
Goworek, T.
Powiązania:
https://bibliotekanauki.pl/articles/2042188.pdf
Data publikacji:
2005-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
36.10.Dr
78.70.Bj
Opis:
This paper represents a fragment of systematic studies on positron annihilation in solid saturated hydrocarbons (alkanes, paraffins) from C$\text{}_{17}$H$\text{}_{36}$ to C$\text{}_{30}$H$\text{}_{62}$. The Tao-Eldrup model and its extensions allow to identify the places in the crystalline structure where positronium is trapped, and estimate respective trap sizes. In the rigid phase I positronium locates mainly in two-dimensional empty spaces between the lamellae of crystal structure. Additional free volumes exist in high temperature phases due to appearance of n-alkane conformers representing a non-planar molecule distortion. The rise of ortho-positronium intensity with the sample irradiation dose, which was seen earlier in polymers, is observed also in n-alkanes. One can find similarities between the ortho-positronium annihilation in crystalline alkanes and polymers, like exponential character of that rise, and the trap bleaching by illumination. It confirms the same origin of the intensity growth, i.e. the accumulation of trapped electrons. Two kinds of electron traps were found. The time constant of electron accumulation in the traps depends on the carbon chain length and varies with temperature in different way for even- and odd-numbered alkanes.
Źródło:
Acta Physica Polonica A; 2005, 107, 4; 635-641
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Three-Quantum Annihilation in Porous Vycor Glass
Autorzy:
Jasińska, B.
Wawryszczuk, J.
Zaleski, R.
Powiązania:
https://bibliotekanauki.pl/articles/2043332.pdf
Data publikacji:
2005-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
36.10.Dr
78.70.Bj
Opis:
Three methods of determination of 3γ o-Ps decay intensity are compared. The estimate of 3γ fraction obtained from classical lifetime measurements can be distorted due to a higher absorption of theγ quanta from the continuous spectrum of three-quantum decay, compared to two-quantum one.
Źródło:
Acta Physica Polonica A; 2005, 107, 5; 821-825
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Pressure Effects in ortho-Positronium Annihilation
Autorzy:
Goworek, T.
Wawryszczuk, J.
Zaleski, R.
Powiązania:
https://bibliotekanauki.pl/articles/2042179.pdf
Data publikacji:
2005-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
36.10.Dr
78.70.Bj
Opis:
A short review of experiments concerning the influence of high pressure on positron annihilation in molecular solids is given. To this kind of experiments belong e.g. pressure inhibition of positronium formation, pressure induced phase transitions, and free volume swelling in the media intercalated by high pressure gas.
Źródło:
Acta Physica Polonica A; 2005, 107, 4; 608-614
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Ortho-Positronium in Some n-Alkanes; Influence of Temperature and Pressure
Autorzy:
Zgardzińska, B.
Pietrow, M.
Goworek, T.
Wawryszczuk, J.
Powiązania:
https://bibliotekanauki.pl/articles/2047166.pdf
Data publikacji:
2006-11
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
36.10.Dr
61.80.Fe
71.60.+z
78.70.Bj
Opis:
Positron lifetime spectra were measured for a series of odd-numbered n-alkanes from C$\text{}_{11}$H$\text{}_{24}$ to C$\text{}_{19}$H$\text{}_{40}$ as a function of temperature and pressure. The ortho-Ps lifetimes in the rotator phase and the increase in intensity at the transition to that phase can be explained by location of Ps in the vicinity of kink-type conformers. The relation between o-Ps lifetime and molecule length can be described in the framework of extended Tao-Eldrup model. One can eliminate the effect of intensity rise in time by sample illumination or by application of high pressure. A decrease in temperature by 1 K is equivalent to an increase in pressure by about 4 MPa.
Źródło:
Acta Physica Polonica A; 2006, 110, 5; 747-753
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Testing the Extended Tao-Eldrup Model. Silica Gels Produced with Polymer Template
Autorzy:
Śniegocka, M.
Jasińska, B.
Wawryszczuk, J.
Zaleski, R.
Deryło-Marczewska, A.
Skrzypek, I.
Powiązania:
https://bibliotekanauki.pl/articles/2043364.pdf
Data publikacji:
2005-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
61.43.Gt
Opis:
The temperature dependence of o-Ps lifetime in the pores calculated from extended Tao-Eldrup model was compared to the experimental data, collected for a set of silica gels synthesized using the polymer template technique. For the sample with average pore radii 2.0 nm rather good agreement between the model and experiment was found. For the sample with narrow pores (near 1.0 nm) the lifetime spectrum was complex. Except the range of highest temperatures the lifetimes are far from model calculations.
Źródło:
Acta Physica Polonica A; 2005, 107, 5; 868-873
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
    Wyświetlanie 1-8 z 8

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