48 research outputs found
Kinetics of crystallization of FeB-based amorphous alloys studied by neutron thermo-diffractometry
Kinetics of crystallization of two amorphous alloys, Fe70Cr10B20 and
Fe80Zr10B10, have been followed up by neutron thermodiffractometry experiments
performed in the two axis diffractometer D20 (ILL, Grenoble). The structural
changes are directly correlated with the temperature dependence of the
magnetization. Fe70Cr10B20 crystallizes following a two-step process: an
eutectic crystallization of alfa-Fe (bcc) and the metastable tetragonal phase
(Fe0.8Cr0.2)3B followed by another eutectic transformation to the stable phase
(Fe0.75Cr0.25)2B and more segregation of alfa-Fe. These tetragonal phases are
magnetically anisotropic, giving rise to a large increase of the coercivity.
This behaviour is similar to that of Fe80B20 alloys, with Cr atoms replacing
the Fe positions in both crystalline phases. Fe80Zr10B10 shows also a two-step
process in which two polymorphic transformations take place.Comment: 3 pages. Proceedings International Workshop Non-Crystalline Solids
2006, Gijon (Spain
Temperature and time dependent structure of the molten Ni81P19 alloy by neutron diffraction
The temperature and time dependent structure of molten NiP alloy of eutectic composition has been studied by neutron diffraction. Ni particles were found to exist in the melt at temperatures at least up to about 150 degrees above liquidus. The amount varies reversibly as temperature increases but decays slowly with time. Remarkably, particles still exist even after that the melt has been kept more than 30 h at different temperatures in the molten state. The static structure factor and the pair distribution function obtained at 1050 °C are presented
Crystal structure of Cu-Sn-In alloys around the {\eta} phase field studied by neutron diffraction
The study of the Cu-Sn-In ternary system has become of great importance in
recent years, due to new environmental regulations forcing to eliminate the use
of Pb in bonding technologies for electronic devices. A key relevant issue
concerns the intermetallic phases which grow in the bonding zone and are
determining in their quality and performance. In this work, we focus in the
{\eta}-phase (Cu2In or Cu6Sn5) that exists in both end binaries and as a
ternary phase. We present a neutron diffraction study of the constitution and
crystallography of a series of alloys around the 60 at.% Cu composition, and
with In contents ranging from 0 to 25 at.%, quenched from 300\degreeC. The
alloys were characterized by scanning electron microscopy, probe microanalysis
and high-resolution neutron diffraction. The Rietveld refinement of neutron
diffraction data allowed to improve the currently available model for site
occupancies in the hexagonal {\eta}-phase in the binary Cu-Sn as well as in
ternary alloys. For the first time, structural data is reported in the ternary
Cu-Sn-In {\eta}-phase as a function of composition, information that is of
fundamental technological importance as well as valuable input data for ongoing
modelisations of the ternary phase diagram.Comment: 8 pages, 10 figure
Arsenite sorption and co-precipitation with calcite
Sorption of As(III) by calcite was investigated as a function of As(III)
concentration, time and pH. The sorption isotherm, i.e. the log As(III) vs. log
[As(OH)3 degrees / Assat] plot is S-shaped and has been modelled on an extended
version of the surface precipitation model. At low concentrations, As(OH)3
degrees is adsorbed by complexation to surface Ca surface sites, as previously
described by the X-ray standing wave technique. The inflexion point of the
isotherm, where As(OH)3 degrees is limited by the amount of surface sites (ST),
yields 6 sites nm-2 in good agreement with crystallographic data. Beyond this
value, the amount of sorbed arsenic increases linearly with solution
concentration, up to the saturation of arsenic with respect to the
precipitation of CaHAsO3(s). The solid solutions formed in this concentration
range were examined by X-ray and neutron diffraction. The doped calcite lattice
parameters increase with arsenic content while c/a ratio remains constant. Our
results made on bulk calcite on the atomic displacement of As atoms along
[0001] direction extend those published by Cheng et al., (1999) on calcite
surface. This study provides a molecular-level explanation for why As(III) is
trapped by calcite in industrial treatments.Comment: 9 page
Structural investigation of glasses along the MgSiO3–CaSiO3 join: Diffraction studies
International audienceThe structure of glasses along the MgSiO3-CaSiO3 join has been investigated by X-ray and neutron diffraction measurements. Structure models were constructed by fitting the experimental data using the Reverse Monte Carlo method (RMC). The structural data indicate a random mixing between MgSiO3 and CaSiO3 glasses, in accordance with their melt properties. Though important disordering is observed, the structure evolves continuously along the join. The Ca environment is essentially similar for all compositions, with an average of 6 to 7-coordinated sites. The Mg environment tends to have higher coordinated sites as the MgO content decreases. There is a continuous mixing of Ca-Mg pairs with a non-random distribution emphasized by the distinct cation-cation distances. Changes were observed in the topology of the silicate network. The proportion of non-bridging oxygens decreases, the number of free-oxygens increases and the ring size distribution is shifted to high-membered rings in the Mg-rich glasses. These structural investigations indicate important differences with the crystalline pyroxene structure
Structural study of Ca–Mg and K–Mg mixing in silicate glasses by neutron diffraction
International audienceNeutron diffraction has been used to study the structure in two series of xCaO.(2−x)MgO.2SiO2 and xK2O.(2−x) MgO.4SiO2 glasses and the effect of Ca–Mg and K–Mg mixing, showing a different chemical dependence of the structure of these mixed glasses. The data are consistent with a random mixing of CaSiO3 andMgSiO3 structures for the Ca/Mg substitution. The coordination of Ca and Mg remains constant in Ca–Mg silicate glasses but a decrease of Mg coordination is observed in the K–Mg silicate glasses with the addition of K2O. In these latter glasses, the medium range order is also significantly affected by the K/Mg substitution, due to the distinct structural role played by K and Mg in these glasses
Neutron powder diffraction study at high temperature of the Ruddlesden-Popper phase Sr3Fe2O6 + δ
The crystal and oxygen defect structure of the n = 2 Ruddlesden-Popper phase Sr3Fe2O6 + δ have been studied by in situ high temperature neutron powder diffraction in the temperature range 20 ≤ T ≤ 900 °C in air. The analysis of the neutron diffraction data revealed the presence of structural oxygen vacancies on both the O(1) sites linking the octahedra along the c axis and the O(3) sites in the FeO2 planes of the perovskite layers. The oxygen vacancies on the O(3) site increase with temperature up to ∼ 0.25 per formula unit at T = 900 °C. This result supports previously proposed oxygen ion diffusion mechanism in Sr3Fe2O6 + δ that involves the migration of vacancies from an O(3) site to an adjacent O(1) site. The total linear expansion along the c axis αc = 17.7(5) · 10- 6 K- 1 mainly affects the perovskite block while the width of the rock salt layers remains stable with temperature. The total volumetric expansion αV / 3 = 20(1) · 10- 6 K- 1 is around the average of the TEC values (14.8-27.1 K- 1) reported for the perovskite system La1 - xSrxCo1 - yFeyO3 - δ.Fil: Prado, Fernando Daniel. Comisión Nacional de EnergÃa Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - BahÃa Blanca. Instituto de FÃsica del Sur. Universidad Nacional del Sur. Departamento de FÃsica. Instituto de FÃsica del Sur; ArgentinaFil: Mogni, Liliana Verónica. Consejo Nacional de Investigaciones CientÃficas y Técnicas; Argentina. Comisión Nacional de EnergÃa Atómica. Centro Atómico Bariloche; ArgentinaFil: Cuello, G.J.. Institut Laue Langevin; FranciaFil: Caneiro, Alberto. Consejo Nacional de Investigaciones CientÃficas y Técnicas; Argentina. Comisión Nacional de EnergÃa Atómica. Centro Atómico Bariloche; Argentin