Annual Report 2009/2010 - JUWEL - Forschungszentrum Jülich
Annual Report 2009/2010 - JUWEL - Forschungszentrum Jülich
Annual Report 2009/2010 - JUWEL - Forschungszentrum Jülich
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TG /%<br />
100<br />
98<br />
96<br />
94<br />
92<br />
90<br />
88<br />
86<br />
84<br />
82<br />
0 50 100 150 200 250 300 350<br />
Zeit /min<br />
DSC /(mW/mg)<br />
Temperatur /°C<br />
Exo [1]<br />
800<br />
[1]<br />
0.05<br />
0<br />
-0.05<br />
200<br />
-0.10<br />
[1]<br />
-0.15<br />
700<br />
600<br />
500<br />
400<br />
300<br />
100<br />
100.00<br />
99.50<br />
99.00<br />
98.50<br />
98.00<br />
97.50<br />
97.00<br />
96.50<br />
96.00<br />
TG /%<br />
0 20 40 60 80 100 120 140<br />
Zeit /min<br />
DSC /(mW/mg)<br />
Temperatur /°C<br />
Exo [1]<br />
900<br />
[1]<br />
0<br />
0.6<br />
0.4<br />
0.2<br />
-0.2<br />
[1]<br />
800<br />
700<br />
600<br />
500<br />
400<br />
300<br />
200<br />
100<br />
Tab. 17: Composition of precursor solution for gelation<br />
Number R(Urea) R(HMTA)<br />
1 2 1,875<br />
2 2 1,65<br />
3 2 1,35<br />
4 1,8 1,88<br />
5 1,8 1,65<br />
Thermal treatment of the uranium / neodymium gels<br />
Previous research showed that, although it is possible to achieve crack free gels, the thermal<br />
treatment leads with high certainties to crack formation in the spheres. This is due to<br />
decomposition of rests of the gelation chemicals urea and HMTA during the treatment, as<br />
well as to multiples phase changes until the final UO 2 fluorite-lattice is achieved. [3, 5, 6] As<br />
these effects put significant stress on the structure of the microspheres, efforts have to be<br />
taken to understand mechanisms and to improve the program of thermal treatment in a way<br />
that the formerly mentioned factors are counteracted.<br />
Using the available literature as orientation [7], a modified calcination profile was developed.<br />
The temperature programme with the corresponding TG-DSC is illustrated in Fig. 53. Also<br />
the sintering was altered by letting it completely take place in reductive atmosphere (forming<br />
gas). The TG-DSC is illustrated in Fig. 53.<br />
SEM investigations of the microspheres after sintering showed a high integrity with barely<br />
visible crack formation Fig. 54.<br />
These parameters were applied in an oven for a thermal treatment of spheres with different<br />
gel formulations. After sintering, most of the spheres were macroscopically intact but showed<br />
cracks under an optical microscope. Nevertheless, XRD investigations of theses spheres<br />
revealed them to have a UO 2 fluorite-lattice without any other (Fig. 55). With the old<br />
calcination and sintering programmes this could not be achieved.<br />
Fig. 53:<br />
TG-DSCs of new calcination (left) and sintering (right) programme.<br />
80
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