47
chains is dominant. This finding means that finally, consistency between diffraction measurements and (text-book) explanation of this polymerisation (liquid-liquid) phase transition could be established. For l-P, the situation is somewhat more complicated: the lower pressure data can be described by P4 molecules and the higher pressure data cannot, but this does not necessarily mean that at higher pressure, a true polymeric network would be formed.
As a continuation of our systematic structural studies on molecular liquids, we have measured by neutron diffraction the total structure factor of liquid Si2Cl6, CBr3D and CD3I.
RMC modeling of these data confirmed our previous suggestion that reasonable structural models can be obtained on the basis of a single measurement if terminal atoms are relatively large and scattering from them dominates the diffraction pattern. In our cases, substitution of halide atoms by hydrogen/deuterium (in CBr3D and CD3I) led to increasingly unrealistic models.
0 5 10 15 20
0.0 0.5 1.0 1.5 2.0
S(Q)
Q(Å-1)
(b)
g(r)
r(Å)
0 2 4 6 8 10 12 14
-0.4 -0.2 0.0 0.2 0.4
(a)
Figure 2. (a) Experimental (markers) and RMC simulated (solid line) structure factors
for Si2Cl6. (b) Partial pair correlation functions calculated from the particle configurations. Solid line: gSiSi(r); dashed
line: gSiCl(r); dotted line: gClCl(r).
0 2 4 6 8 10 12
0.0 0.5 1.0 1.5 2.0
S(Q)
r(Å) Q(Å-1)
(b)
g(r)
0 2 4 6 8 10 12 14 16
-0.5 0.0 0.5 1.0
1.5 (a)
Figure 3. (a) Experimental (markers) and RMC simulated (solid line) structure
factors for CD3I. (b) Partial pair correlation functions calculated from the particle configurations. Solid line: gCD(r);
dashed line: gID(r); dotted line: gDD(r);
dash-dotted line: gCC(r).
By RMC modeling of neutron and X-ray diffraction data on molten ZnCl2 and MgCl2, we showed that although the structures are similar in terms of two-body correlations, there are important differences in the higher order correlations (e.g. bond angle distributions). It was therefore possible to demonstrate that there is a structural basis for the high viscosity and good glass-forming ability of molten ZnCl2, and why this is not the same for MgCl2. Internal stress studies. — Internal stresses play an important role in the lifetime of engineering materials. Binary alloys, where the two components have different linear thermal coefficients are under investigations by high resolution neutron diffraction. For Fe95Cu5 it was found, that after special heat treatment, Cu precipitates first on the grain boundaries of iron matrix and the remaining Cu — at lower temperature — precipitates inside the grains. The inside Cu suffers higher stresses than the ones on the grain boundaries.
49
E-Mail:
Pál Jóvári jovari@sunserv.kfki.hu László Kőszegi koszegi@szfki.hu György Mészáros meszaros@szfki.hu László Pusztai lp@szfki.hu
Zoltán Somogyvári zs@szfki.hu Erzsébet Sváb svab@szfki.hu
Grants and international cooperations
OTKA T 029402 Neutron diffraction study and modelling of partially ordered systems (E. Sváb, 1999-2002)
OTKA T 029433 Dynamic neutron-, gamma-, and x-ray radiography investigations and modelling of streaming processes (sub-contract E. Sváb, 1999-2002) OTKA T 32308 Neutron diffraction at the Budapest Research Reactor (L. Pusztai,
2000-2003)
EU HPRI-CT-1999-50013 Software for computer Aided Neutron Scattering (L. Pusztai, 2000-2002)
NWO N 31766 Polarised neutron investigations of nanocrystalline materials (L.
Pusztai, 2000-2002)
AKP 2000-92,4 Interpretation of diffraction data from molecular liquids (L. Pusztai, 2001-2002)
HAS-BAS (Hungarian-Bulgarian bilateral) Project N15: Structure study by neutron scattering (E. Sváb, 1999-)
HAS-SRA (Hungarian-Swedish bilateral): Neutron diffraction study of molecular liquids (L. Pusztai, 2001)
HAS-MMST (Hungarian-Mexican bilateral): Reverse Monte Carlo simulations (L. Pusztai, 2001-)
Long term visitor
Kiril Krezhov, Institute for Nuclear Research and Nuclear Energy, Bulgarian Academy of Sciences, April 3-May 15 and November 3-December 15, 2001 (Host: E. Sváb)
Publications
Articles
K.1. P. Jóvári, Gy. Mészáros, L. Pusztai, E. Sváb: The structure of liquid tetrachlorides CCl4, SiCl4, GeCl4, TiCl4, VCl4, and SnCl4. J. Chem. Phys. 114, 8082-8090 (2001).
K.2. P. Jóvári, L. Pusztai: Structure of disordered forms of selenium close to the melting point. Phys. Rev. B 64, 014205/1-6 (2001).
K.3. L. Pusztai, R.L. McGreevy*: The structure of molten ZnCl2 and MgCl2. J. Phys.:
Condens. Matter 13, 7213-7222 (2001).
K.4. Z. Somogyvári, E. Sváb, Gy. Mészáros, K. Krezhov*, P. Konstantinov*, T. Ungár*, J.
Gubicza*: Magnetic cation distribution in nanocrystalline Fe3O4. Materials Science Forum 378- 381, 771-776 (2001).
K.5. M. Balaskó*, E. Sváb, J. Pálfalvy*: Neutron radiography with optimized beam formation and filtering unit. Nondestr. Test. Eval. 16, 111-120 (2001).
K.6. M. Balaskó*, E. Sváb, G. Endrőczi*, L. Komlód*, I. Szikra*: Dynamic neutron radiography combined with vibration diagnostics, acoustic emission and thermovision testing. Nondestr. Test. Eval. 16, 297-307 (2001).
K.7. F. Kőrösi*, M. Balaskó*, E. Sváb: Dynamic neutron radiography study of oil infiltration in sandstone. Nondestr. Test. Eval. 16, 309-319 (2001).
K.8. L. Kőszegi: New outlook of a strain scanner neutron diffractometer at the Budapest Research Reactor. Journal of Neutron Research, accepted for publication.
K.9. L. Kőszegi, Gy. Mészáros: Stresses on two sets of Cu precipitates in Fe95Cu5 alloy.
Appl. Phys. A, accepted for publication.
K.10. P. Jóvári, L. Pusztai: On the structure of red amorphous phosphorus. Appl. Phys. A, accepted for publication.
K.11. P. Jóvári, Gy. Mészáros, L. Pusztai, E. Sváb: Neutron diffraction studies of some simple molecular systems: Si2Cl6, CBr3D and CD3I. Appl. Phys. A, accepted for publication
K.12. Z. Somogyvári, E. Sváb, Gy. Mészáros, K. Krezhov*, I. Nedkov*, I. Sajó*, F. Bourée*: Vacancy ordering in nanosized maghemite from neutron and X-ray powder diffraction. Appl. Phys. A, accepted for publication.
K.13. K. Krezhov*, Z. Somogyvári, Gy. Mészáros, E. Sváb, I. Nedkov*, F. Bourée*: Neutron powder diffraction study of (Co-Ti) substituted fine particle Ba-hexaferrite. Appl.
Phys. A, accepted for publication.
K.14. E. Sváb, Gy. Mészáros, Z. Somogyvári, M. Balaskó*, F. Kőrösi*: Neutron imaging of Zr-1%Nb fuel cladding material containing hydrogen. Applied Radiation and Isotopes, accepted for publication.
Conference proceedings
K.15. F. Kőrösi*, M. Balaskó*, E. Sváb: Water uptake of seeds observed by dynamic neutron radiography. In: Proc. Int. Conf. IFAC Modelling and Control in Agriculture, Wageningen, The Netherlands, Eds. G. van Straten, K.J. Keesman, J. Bontsema, Elsevier Science Ltd., The Netherlands, 2000, pp. 279-284.
Books, book chapters
K.16. E. Sváb, M. Balaskó*: Non-destructive testing: neutron radiography. In: Application of physical methods. Encyclopedia of Life Support Systems (EOLSS), UNESCO Publisher, accepted for publication.
K.17. P. Jóvári, L. Pusztai: Structural changes across phase transitions in disordered systems: Liquid sulphur, liquid phosphorus and amorphous ice. In: NATO ARW Series
‘New kinds of phase transitions: Transformations in disordered substances’, Eds.:
H.E. Stanley and V. Ryzhov, Kluwer Academic Publishers, accepted for publication
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Others
K.18. M. Balaskó*, E. Sváb, F. Kőrösi*: Neutron radiography imaging of hydrogen containing materials. Final Report-IAEA/F1-RC-655.3 (2000).