RRFM 2009 Transactions - European Nuclear Society

The µ-XRD measurements were performed in reflection mode, on the ID22 beam line at the
ESRF (European Synchrotron Radiation Facility) in Grenoble (France). To fulfil safety
requirements, samples were conditioned under kapton tape. The photon energy was set to
17 keV and the beam size on the samples was of the order of 2x20 µm 2. The length of the
beam print was positioned parallel to the reaction front and the sample was moved µm per
µm, perpendicularly to this front, between each acquisition.
3. Results
3.1. SEM+EDS characterization of ILs
As previously shown by M. Cornen et al. [4-5], in the conditions used in this work for
performing interdiffusion annealings, the IL thickness decreases when the Si content in Al
increases, with a threlshold value of about 5 wt%, beyond which an increase of the Si
content doesn't lead to a significant additional decrease of the IL thickness. SEM+EDS
characterizations have shown that this critical value of about 5 wt% is also linked to a
significant change in the IL microstructure and composition. That's the reason why two cases
were more particularly taken into consideration in this study :
- U-Mo7/Al-Si2 couples (Si content : below the threshold value),
- U-Mo7/Al-Si7 and U-Mo7/Al-Si10 couples (Si content : above the threshold value).
The U-Mo7/Al-Si5 samples will also be shortly described.
The results given below are valid for those annealed at 450°C but also for those which
underwent a complementary heat treatment at 350°C. Indeed, no significant evolutions of the
ILs compositions occurred during this complementary annealing. The ILs thicknesses can
vary from one place to the other along the reaction interface, in the same sample or from one
sample to another (for the same type of couple and the same annealing). This is due to a
relatively high dispersion of the kinetics results, linked to the experimental procedure.
All the elementary compositions, determined by EDS, are given in at%. They are only semiquantitative
and, thus, must be considered caustiously especially when low concentrations
are measured (of the order of one to a few at%, the accuracy of the measurements being
estimated to about 1 at%).
Figures 2 and 3 summarise the results obtained on U-Mo7/Al-Si2 and U-Mo7/Al-Si7 diffusion
couples, as representative of the two main types of ILs that can be found in the studied
samples :
- Type 1 (Si content : from 2 to 5 wt%) : characterized by the absence of Si, close to the U-
Mo side, a slight and progressive Si enrichment, in the intermediate part of the IL and a Si
enrichment of the order of 13 at%, close to Al-Si.
Al-Si2
Third area
U 17 Mo 2 Al 69 Si 13 (at%)
R (Al+Si /U+Mo) ~ 4.4
Thickness : ~ 12.5% of total IL one
Second area
From U 17 Mo 2 Al 81 to U 17 Mo 2 Al 78 Si 3 (at%)
Thickness : ~ 75% of total IL one
First area
U 17 Mo 2 Al 81 (at%)
100 µm Thickness : ~ 12,5% of total IL one
Presence of periodic sub-layers
UMo7
Figure 2 : SEM+EDS typical results obtained on an U-Mo7/Al-Si2 diffusion couple.
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