Uranium oxides are known as nonstoichiometric compounds whose composition changes according to external conditions such as temperature and oxygen partial pressure. The change of composition caused by the formation of defect structure results in a change of their properties. In this paper, the compositional changes of UO2 and doped UO2 [(U, M)O2; M=La, Ti, Pu, Th, Nb, Cr, etc.] and also those of other uranium oxides (U4O9, U3O8) are shown against oxygen partial pressure. From the results of doped UO2, it is concluded that the valence control rule holds to a first approximation. The defect structures are estimated both from log x vs. log Po2 (x: deviation from the stoichiometric composition and Po2: oxygen partial pressure) and log vs. log Po2 (: electrical conductivity) relations. The defect structures of UO2 and doped UO2 are derived based on the Willis model for UO2+x. The detect structure of U4O9 phase is similar to that of UO2+x, but the defect structures of U3O8 phase are complicated due to the existence of many higher-order phase transitions. The thermodynamic data such as the partial molar enthalpy and entropy and the heat capacity are important to characterize the defect structure. The high temperature heat capacities of UO2 doped with Gd show pronounced increases at high temperatures the onset temperature decreases as the dopant content increases. The increase of heat capacity is interpreted to be due to the formation of lattice defects. The heat capacity measurements on U4O9 and U3O8 clucidate the presence of the phase transition. The mechanisms of these phase transitions are discussed.
Authors:Viorel Chihaia, Karl Sohlberg, Teodora Todorova, Valentin Alexiev and Thomas Weber
respect to the bulk. The surface atoms typically undergo relaxation and reconstruction processes to adopt to the new equilibrium conditions. For catalysis, point defects, adatoms, dopants, vacancies or topological defects (dislocations) on the geometrical
. Prichard 1987 A surgical and suturing method: three case reports J. Periodontol. 12 819 – 826 .
. R. Pontoriero S. Nyman J. Lindhe 1987 Guided tissue regeneration in the treatment of furcation defects in man J. Clin
Authors:István Hartyánszky, Sándor Varga, Kálmán Havasi, Barna Babik, Márta Katona and Gábor Bogáts
., Király, L., et al.: Surgical management of congenital heart defects in adolescent and adult patients, between years 2001–2008. [Tapasztalataink a fiatal- és felnőttkori veleszületett szívhibák sebészi kezelésében 2001–2008.] Orv. Hetil., 2009, 150 (37
Authors:István Hartyánszky, László Székely, László Szudi, Sándor Mihályi, Krisztina Kádár, András Temesvári, Hajnalka Bálint, András Szatmári and Attila Tóth
Hartyánszky, I., Székely, A., Király, L., et al.: Surgical management of congenital heart defects in adolescent and adult patients, between years 2001–2008. [Tapasztalataink a fiatal- és felnőttkori veleszületett szívhibák sebészi kezelésében 2001–2008.] Orv