Über Lithium‐ und Natriumuranate(V) und über strukturelle Beziehungen zwischen den Verbindungstypen Li₇AO₆ und Li₈AO₆

Abstract

Ockerfarbenes Li3UO4, zartgrünes Li7UO6 und hellbraunes Na3UO4 als offenbar basenreichste Verbindung im System Na2O—U2O5 wurden auf thermischem Wege nach verschiedenen Methoden dargestellt. Die Eigenschaften der Verbindungen werden beschrieben. Bei der Reduktion von Li2UO4 und Na2UO4 im H2‐Strom, ebenso bei der Umsetzung von UO2 mit Li2O bzw. Na2O wurden ebenfalls Uranate(V) erhalten. Alkaliuranate(IV) scheinen nicht stabil zu sein. Li7UO6 ist mit anderen Verbindungen des Formeltyps Li7AVO6 isotyp (A  Sb, Bi, Nb, Ta, Ru, Os); sein Pulverdiagramm zeigt eine überraschende, sehr weitgehende Ähnlichkeit mit Diagrammen des Verbindungstyps Li8AIVO6 (A  Sn, Pb, Zr, Hf, Ir, Pt).

Thermodynamic investigation of Na2U2O7 using Knudsen effusion mass spectrometry and high temperature X-ray diffraction

“…(U, Pu) O 2 mixed oxide fuel is currently the preferred option for SFRs, and as such, the structural [1,2], thermodynamic [3][4][5][6][7][8], magnetic [9][10][11], and spectroscopic [12][13][14][15][16][17][18][19] properties of the Na-U-O and Na-Pu-O ternary compounds have been investigated in the past. The potential products of interaction are numerous: (Na 3 UO 4 , NaUO 3 , Na 2 UO 4 , Na 4 UO 5 ,Na 2 U 2 O 7 , Na 6 U 7 O 24 ) [20][21][22][23]1,24,25], and (Na 2 PuO 3 , Na 3 PuO 4 , Na 6 PuO 5 , Na 4 Pu 2 O 5 , Na 4 PuO 5 , Na 5 PuO 6 ) [1,2,26] for the first and second systems, respectively, but not all well characterized.…”

Low temperature heat capacity of α-Na2NpO4

“…One condition for the applicability of this relation was an identical coordination of U in the uranate and in UO 3 . CaUO 4 was found outside of the general trend, mainly due to the 8-fold coordination of U in the compound, compared to the 6-fold coordination in UO 3 .…”

“…The structural [3][4][5][6][7][8][9][10][11][12] and thermodynamic [13,14] properties of Na-U-O ternary compounds are fairly well-known. By contrast, the data available on the Na-Np-O and Na-Pu-O systems are very limited [15][16][17]14].…”

A New Look at the Structural Properties of Trisodium Uranate Na3UO4

“…On the basis of the latter quantitative analysis, the formation of a metastable intermediate tetravalent uranate Na 4 UO 4 was described for temperatures below 848 K by direct reaction between UO 2 and Na 2 O, followed by a decomposition reaction above 873 K with progressive loss of sodium toward the Na 3+x UO 4 composition. The structure of this metastable intermediate Na 4 UO 4 phase was described as fcc, very close to the structure of Scholder and Glaser, 11 with a cell parameter of 4.78 Å, and the decomposition reaction to Na 3 UO 4 was shown to be irreversible. To the authors' knowledge, no other studies have been reported since the work of Pillon et al, 19 and the discrepancies have remained.…”