105 research outputs found
Computational Modeling of Silicate Glasses: A Quantitative Structure-Property Relationship Perspective
This article reviews the present state of Quantitative Structure-Property
Relationships (QSPR) in glass design and gives an outlook into future developments.
First an overview is given of the statistical methodology, with particular emphasis
to the integration of QSPR with molecular dynamics simulations to derive informative
structural descriptors. Then, the potentiality of this approach as a tool for
interpretative and predictive purposes is highlighted by a number of recent inspiring
applications
Spin, charge and orbital ordering in ferrimagnetic insulator YBaMnO
The oxygen-deficient (double) perovskite YBaMnO, containing
corner-linked MnO square pyramids, is found to exhibit ferrimagnetic
ordering in its ground state. In the present work we report
generalized-gradient-corrected, relativistic first-principles full-potential
density-functional calculations performed on YBaMnO in the nonmagnetic,
ferromagnetic and ferrimagnetic states. The charge, orbital and spin orderings
are explained with site-, angular momentum- and orbital-projected density of
states, charge-density plots, electronic structure and total energy studies.
YBaMnO is found to stabilize in a G-type ferrimagnetic state in
accordance with experimental results. The experimentally observed insulating
behavior appears only when we include ferrimagnetic ordering in our
calculation. We observed significant optical anisotropy in this material
originating from the combined effect of ferrimagnetic ordering and crystal
field splitting. In order to gain knowledge about the presence of different
valence states for Mn in YBaMnO we have calculated -edge x-ray
absorption near-edge spectra for the Mn and O atoms. The presence of the
different valence states for Mn is clearly established from the x-ray
absorption near-edge spectra, hyperfine field parameters and the magnetic
properties study. Among the experimentally proposed structures, the recently
reported description based on 4/ is found to represent the stable
structure
Diffraction techniques and vibrational spectroscopy opportunities to characterise bones
From a histological point of view, bones that allow body mobility and protection of internal organs consist not only of different organic and inorganic tissues but include vascular and nervous elements as well. Moreover, due to its ability to host different ions and cations, its mineral part represents an important reservoir, playing a key role in the metabolic activity of the organism. From a structural point of view, bones can be considered as a composite material displaying a hierarchical structure at different scales. At the nanometre scale, an organic part, i.e. collagen fibrils and an inorganic part, i.e. calcium phosphate nanocrystals are intimately mixed to assure particular mechanical properties
Multitechnique approach to V-ZrSiO4 pigment characterization and synthesis optimization
The synthesis of blue-turquoise V-ZrSiO4 Pigment from an aqueous solution of Na2O center dot 2.5SiO(2)center dot 5H(2)O (soluble glass) and the citrate complexes of zirconium and vanadium was investigated as a function of V2O5 contents, mineralizers (NaF and/or LiNO3) addition and thermal cycle. Blue V-ZrSiO4 was obtained without mineralizers addition for the (ZrO2)(SiO2)(V2O5)(0.09) composition; QPA analysis shows that a thermal cycle 3 h long, T-max = 800 degrees C, can lead to a 78.0 wt.% of ZrSiO4. The addition of mineralizers gave rise to 73.0 wt.% of ZrSiO4 for the (ZrO2)(SiO2)(NaF)(0.16)(V2O5)(0.09)(LiNO3)(0.09) composition and a thermal cycle 2 h long, T-max = 800 degrees C. LiN03 can favour both ZrSiO4 formation and a fairly blue colour, up to LiNO3 = 0.09 moles; NaF seems effective on ZrSiO4 formation only when mixed with LiNO3 through the formation of LiF HT-XRD analysis of this composition agrees with QPA results at the corresponding temperature; ZrSiO4 was present (64.0 wt.%) at 730 degrees C and good colour parameters were obtained. (c) 2006 Elsevier Ltd. All rights reserved
Structural and spectroscopic characterization of anorthite synthesized from secondary raw materials
5noreservedRecycling of secondary raw materials is a priority of waste handling in the countries of the
European community. A virtual secondary raw material of great importance is the product of
the thermal transformation of cement – asbestos. This work illustrates the study of calcination
products obtained starting from the product of the thermal transformation of cement-asbestos
at 1200 °C, added to primary raw materials (kaolin, aluminum hydroxide) and boric acid as
mineralizing agent. The calcination has been conducted at 1200 °C for 1 hour. The
crystallization kinetics has been monitored using in situ high temperature X-ray powder
diffraction. The microscopic characterization of the final product of calcination has been
conducted with SEM and TEM imaging supported by X-ray microanalysis. The structure
refinement was conducted on the powder sample using the Rietveld method. The results are
compared with the spectroscopic characterization including Mössbauer and UV-Vis
spectroscopies. The final product of the calcination is essentially anorthite (about 89 wt%)
with minor spinel (11 wt%). All experimental data converge to support the hypothesis that
the anorthite is stoichiometric, and the small amounts of iron detected (1.32 wt%) is Fe3+
hosted in the structure of spinel.mixedGUALTIERI A.F; ANDREOZZI G.B; GIACOBBE C; LUSVARDI C; C. VITIGUALTIERI A., F; ANDREOZZI G., B; Giacobbe, C; Lusvardi, C; Viti, Cecili
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