Hollandite crystal structure

Figure 7. Crystal structures of (a) hollandite, (b) romanechite (psilomelane), and (c) todorokite. The structures arc shown as three-dimensional arrangements of the MnO() octahedra (the tunnel-tilling cations and water molecules, respectively, are not shown in these plots) and as projections along the short axis. Small, medium, and large circles represenl the manganese atoms, oxygen atoms, and the foreign cations or water molecules, respectively. Open circles, height z. = 0 fdled circles, height z = Vi.

Phase X has been observed in a number of studies on hydrous potassium-bearing systems (Trpnnes, 1990, 2002 Inoue et al., 1998a Luth, 1997). Its stability relations have been studied by Konzett and Fei (2000), who found that it breaks down between 20 GPa and 23 GPa at 1,500-1,700 °C. Its breakdown products were reported by Konzett and Fei (2000) to be K-hollandite, y-Mg2Si04, majorite, Ca-perovskite, and fluid. Hence, phase X is not succeeded by another hydrous potassic solid phase, and is therefore the hydrous potassic (solid) phase with the highest-pressure stability. The crystal structures of phase X and some related phases were determined by Yang et al. (2001). 

Figure 7.19 Polyhedral presentation of crystal structures viewed along the short axes of 2.88-3.01 A. (1) hollandite [168-173] ...

A second-generation immobilization material, synroc, is in development. This synthetic rock, based on mixed titanate phases such as zirconolite, hollandite, or perovskite, incorporates the HLW elements into its crystal structure, yielding excellent chemical stability. Synroc features leach rates more than an order of magnitude lower than borosilicate glass. 

Figure 3.7 Crystal structures of (a) hollandite, (b) romanechite (psilomelane), and (c) todorokite. The structures are shown as three-dimensional arrangements of the MnOe octahedra (the tunnel-filling cations and water molecules, respectively, are not...

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