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Cahill, David G. Weisensee, Patricia 2012-02-01T00:47:05Z 2014-02-01T11:00:28Z 2011-12 2012-02-01T00:47:05Z 2011-12 This thesis presents experimental results on thermal conductivity measurements on both irradiated and unirradiated uranium oxides between 90 K and 658 K. The irradiation doses range from 5x10^13 argon ions/cm² to 2x10^16 Ar+/cm² at 2 MeV and room temperature. The main focus lies on 360 – 500 nm single crystal UO2 and U3O8 thin films grown on YSZ substrates. The U3O8 samples are formed by heating the UO2 in air for 2.5 hours at 600°C and slow cooling. From a comparison between data measured by an optical pump-probe technique – time-domain thermoreflectance (TDTR) – and a heat transport model the thermal conductivity of the sample under study can be determined. For UO2, the thermal conductivity is found to be 10.2 W/m.K at 323 K and with increasing temperatures its behavior is inversely proportional to the temperature. At 648 K the thermal conductivity is 4.9 W/m.K. The thermal conductivity peaks between 200 and 250 K and decreases for decreasing temperatures. Upon irradiation the thermal conductivity at 323 K decreases to 8.6 W/m.K for a dose of 5x10^13 Ar+/cm² and to 4 W/m.K for 7x10^14 Ar+/cm² and 1x10^16 Ar+/cm². At 648 K the corresponding values are 5.2 W/m.K, 4.2 W/m.K and 2.5 W/m.K for the mentioned doses. A modified model by Klemens is used to predict the irradiation effect on the thermal conductivity for low and medium doses. For high doses non-linearities during the irradiation limit the further decrease in thermal conductivity and cannot be captured by the model. Due to self-annealing during the experiments, irradiated samples do not show a 1/T behavior. U3O8 is studied with irradiation doses of 0 Ar+/cm², 7x10^14 Ar+/cm², 2x10^15 Ar+/cm² and 2x10^16 Ar+/cm². Their thermal conductivities at 333 K are 1.67 W/m.K, 0.96 W/m.K, 1.2 W/m.K and 1.97 W/m.K, respectively. The self-annealing is found to be stronger than in UO2 so that the thermal conductivities at 658 K are 1.3 W/m.K, 1.18 W/m.K, 1.36 W/m.K and 1.86 W/m.K, respectively, for the above mentioned doses. For lower doses the thermal conductivity decreases with increasing dose but then starts increasing again for higher doses. This is probably caused by re-crystallization and the formation of a second phase of UO2+x in U3O8. In general, it is found that oxidation of UO2 has a stronger influence on the thermal conductivity than irradiation with argon ions. Item withdrawn by Mark Zulauf (zulauf@illinois.edu) on 2011-12-05T21:56:45Z Item was in collections: University of Illinois Theses & Dissertations (ID: 1) No. of bitstreams: 2 Weisensee_Patricia.doc: 6940672 bytes, checksum: a5c0957a5b794fd21390031cfa52c7e0 (MD5) Weisensee_Patricia.pdf: 3804373 bytes, checksum: 5572e2c8cee49ecb61aa28209a92f4b2 (MD5) Made available in DSpace on 2012-02-01T00:47:05Z (GMT). No. of bitstreams: 3 Weisensee_Patricia.pdf: 3804339 bytes, checksum: c03908907f30968aa877a9e653a9b3e9 (MD5) Weisensee_Patricia.doc: 6940672 bytes, checksum: a5c0957a5b794fd21390031cfa52c7e0 (MD5) license.txt: 4068 bytes, checksum: f9bed2a7608febce57d5cace1e59fde3 (MD5) Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by William Ingram (wingram2@illinois.edu) on 2012-02-01T00:50:35Z Item is restricted until 2014-02-01T00:50:07Z Item reinstated by Sarah Shreeves (sshreeve@illinois.edu) on 2014-02-01T11:00:28Z Item was in collections: Graduate Theses and Dissertations at Illinois (ID: 204) Dissertations and Theses - Materials Science and Engineering (ID: 649) No. of bitstreams: 4 Weisensee_Patricia.pdf.txt: 122766 bytes, checksum: babcf15bcb27168550b853c6ea268968 (MD5) Weisensee_Patricia.pdf: 3804339 bytes, checksum: c03908907f30968aa877a9e653a9b3e9 (MD5) Weisensee_Patricia.doc: 6940672 bytes, checksum: a5c0957a5b794fd21390031cfa52c7e0 (MD5) license.txt: 4068 bytes, checksum: f9bed2a7608febce57d5cace1e59fde3 (MD5) Item released from any restrictions by Sarah Shreeves (sshreeve@illinois.edu) on 2014-02-01T11:00:28Z http://hdl.handle.net/2142/29456 en © 2011 Patricia B. Weisensee Thermal Conductivity Uranium Dioxide UO2 U3O8 Ion (Ar) Irradiation Damage Thin Film Thermal conductivity of UO2 and U3O8 epitaxial layers damaged by ion irradiation Dissertation / Thesis text Materials Science & Engineerng 1919 Materials Science & Engr 0130 University of Illinois at Urbana-Champaign Thesis M.S. MS:Materials Sci & Engr -UIUC 10KS0130MS