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Wyświetlanie 1-3 z 3
Tytuł:
Fractal Structure of C-S-H and Tobermorite Phases
Autorzy:
Janik, J. A.
Kurdowski, W.
Podsiadły, R.
Samseth, J.
Powiązania:
https://bibliotekanauki.pl/articles/2028897.pdf
Data publikacji:
2001-10
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
61.12.Ex
82.70.Gg
Opis:
The C-S-H I phase is the main component of the cement paste, which is a near-amorphous, highly porous gel. Due to high porosity of the sample in this phase we can observe a fractal nature of the volume pores distribution, similar to that observed for silica aerogels. The C-S-H I phase is thermodynamically unstable and crystallize to a tobermorite phase, forming crystal aggregates on the surface of the amorphous paste. The mixture of these two phases, formed in this way, have irregular volume and surface structures, both of which may exhibit the fractal nature. To study the fractal nature of the matter the small angle neutron scattering method is frequently used. We present here the results of small angle neutron scattering studies supported by the X-ray diffraction and scanning electron microscope observations of several samples with the common molar C/S ratio equal to 1. Some of the samples were autoclaved during various time periods to accelerate transformation of the C-S-H I phase to tobermorite. We observed the fractal properties of the volume structure of all samples under study. Moreover, we observed also the fractal behaviors of the surfaces of the samples which were autoclaved.
Źródło:
Acta Physica Polonica A; 2001, 100, 4; 529-537
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Studies of Fractal Aspects of Cement
Autorzy:
Janik, J. A.
Kurdowski, W.
Podsiadły, R.
Samseth, J.
Powiązania:
https://bibliotekanauki.pl/articles/1952755.pdf
Data publikacji:
1996-12
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
61.12.Ex
82.70.Gg
Opis:
Small angle neutron scattering can be used to reveal the fractal nature of matter. The problems of fractal aspects of the structure of cement are related to those of fractal aspects of silica aerogels. Natural cement, when mixed with water, transforms after a series of chemical reactions (in a large part) into an amorphous phase called C-S-H. It is believed that the cationic sublattice composed of CaO$\text{}_{6}$ octahedrons constitutes the C-S-H structural basis, to which the SiO$\text{}_{4}$ tetrahedral chains are attached. It is a layer structure in which the cation sublattice determines the way of SiO$\text{}_{4}$ condensation. It is natural to expect that in this way one may obtain a really amorphous substance, since some tetrahedrons may be lacking, which leads to defects. We present here the results of a small angle neutron scattering and X-ray diffraction study of several samples with the pure C-S-H phase for which during the process of chemical synthesis various ratios of molar contents of CaO and SiO$\text{}_{2}$ were used (various C/S ratios). We obtained a gradual change of fractal characteristics with the change of C/S ratio.
Źródło:
Acta Physica Polonica A; 1996, 90, 6; 1179-1184
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Spin Wave Dynamics of 2D and 3D Heisenberg Antiferromagnets
Autorzy:
Cowley, R.
Tennant, D.
Coldea, R.
Powiązania:
https://bibliotekanauki.pl/articles/1810280.pdf
Data publikacji:
2009-01
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.40.Gb
75.50.Ee
61.12.Ex
Opis:
The excitations of the 2D Heisenberg antiferromagnet, $Rb_2MnF_4$, were studied using neutron scattering techniques with the MAPS spectrometer at the ISIS facility of Rutherford Appleton Laboratory. Measurements were made of the magnetic excitations over the whole 2D Brillouin zone at 6 temperatures below the ordering temperature of 38 K and 6 temperatures above. It was found that the excitations were well defined if their wave vectors were larger than the inverse correlation length and were overdamped if the wave vectors of the excitations were smaller than the inverse correlation length. In more detail we have compared our experimental results with the results of classical simulations and the results gave a very adequate description of the experimental results except at the lowest temperature where the form of the dispersion relation was correct but the energies of the excitations were in error. Nevertheless, classical simulations do provide an efficient and easily implemented methodology for modelling the excitations in the Heisenberg magnets. The damping of the excitations was experimentally found to follow a $T^2$ behaviour over all wave vector and energy scales. This is in agreement with the classical simulations but inconsistent with analytic theories of the damping for the 2D Heisenberg model and in particular does not agree with hydrodynamic behaviour or dynamic scaling. The result is similar to that found in 3D Heisenberg systems and suggests that more analytic theory is needed to explain the experimental results for both 2D and 3D Heisenberg magnets.
Źródło:
Acta Physica Polonica A; 2009, 115, 1; 19-24
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
    Wyświetlanie 1-3 z 3

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