Séverine Brassamin

Levitation apparatus for neutron diffraction investigations on high temperature liquids

We describe a new high temperature environment based on aerodynamic levitation and laser heating designed for neutron scattering experiments up to 3000°C. The sample is heated to the desired temperature with three CO2 lasers from different directions in order to obtain a homogeneous temperature distribution. The apparent temperature of the sample is measured with an optical pyrometer, and two video cameras are employed to monitor the sample behavior during heating. The levitation setup is enclosed in a vacuum-tight chamber, enabling a high degree of gas purity and a reproducible sample environment for structural investigations on both oxide and metallic melts. High-quality neutron diffraction data have been obtained on liquid Y3Al5O12 and ZrNi alloy for relatively short counting times (1.5h).

The structure of liquid calcium aluminates as investigated using neutron and high energy x-ray diffraction in combination with molecular dynamics simulation methods

The structure of laser heated aerodynamically levitated (CaO)(x)(Al₂O₃)(1-x) high temperature liquids, with x = 0.33, 0.5, 0.75, was measured by using neutron and high energy x-ray diffraction. The partial structure factors for the liquids at 2500 K were also determined using molecular dynamics computer simulations. The simulation results are in excellent agreement with the diffraction measurements. The results show a predominant tetrahedral Al coordination with approximately 20% of fivefold coordinated Al at x = 0.33 which reduces with increasing CaO concentration. The Ca atoms occupy a broad range of coordination environments but with a predominance of sixfold distorted octahedra. The simulations confirm the presence of 13, 7 and 0.6% OAl₃ triclusters connecting AlO₄ tetrahedra in the structure of CA2 (x = 0.33), CA (x = 0.5) and C3A (x = 0.75) liquids, respectively.

Structure and dynamics of levitated liquid materials

Aerodynamic levitation is a simple way to suspend samples which can be heated with CO2 lasers. The advantages of this technique are the simplicity and compactness of the device, making it possible to integrate the device easily into different kinds of experiments. In addition, all types of sample can be used, including metals and oxides. The integration of this technique at synchrotron and neutron sources provides powerful tools to study molten materials.

Structural properties of molten dilute aluminium–transition metal alloys

The short-range order in liquid binary Al-rich alloys (Al-Fe, Al-Ti) was studied by x-ray diffraction. The measurements were performed using a novel containerless technique which combines aerodynamic levitation with inductive heating. The average structure factors, S(Q), have been determined for various temperatures and compositions in the stable liquid state. From S(Q), the pair correlation functions, g(r), have been calculated. The first interatomic distance is nearly temperature-independent, whereas the first-shell coordination number decreases with increasing temperature for all the alloys investigated. For the Al-Fe alloys, room-temperature scanning electron microscropy (SEM) studies show the formation of a microstructure, namely the existence of Al(13)Fe(4) inclusions in the Al matrix.

Effect of Slag Impregnation on Macroscopic Deformation of Bauxite‐Based Material

This work aims at studying the volume change of bauxite corroded by a molten slag. Cylindrical samples were prepared by mixing ground bauxite with slag. Optical measurement at high temperature (1450 °C) of deformation with a high-resolution camera has been developed. Image processing allowed for determining the change in diameter of the sample. We showed that the deformation was induced by the precipitation of new expansive crystallised phases observed by SEM-EDS analyses. Adding pellets of the same slag upon the samples allowed to emphasize the effect of the slag amount on the size change. The change in diameter significantly increased in the impregnated area.