High-Temperature, High-Pressure Hydrothermal Synthesis and Characterization of a Salt-Inclusion Mixed-Valence Uranium(V,VI) Silicate: [Na9F2][(UVO2)(UVIO2)2(Si2O7)2]

2013 ◽  
Vol 52 (12) ◽  
pp. 7230-7235 ◽  
Author(s):  
Yu-Chih Chang ◽  
Wen-Jung Chang ◽  
Sophie Boudin ◽  
Kwang-Hwa Lii
Keyword(s):  
High Pressure ◽  
High Temperature ◽  
Hydrothermal Synthesis ◽  
Mixed Valence ◽  
Synthesis And Characterization ◽  
High Temperature High Pressure

scholarly journals High-T, High-P Hydrothermal Synthesis of Uranium Silicates and Germanates

2014 ◽  
Vol 70 (a1) ◽  
pp. C759-C759
Author(s):  
Kwang-Hwa Lii
Keyword(s):  
High Pressure ◽  
High Temperature ◽  
Hydrothermal Synthesis ◽  
Alkali Metals ◽  
Spent Nuclear Fuel ◽  
Mixed Valence ◽  
Oxidation States ◽  
Uranyl Silicates ◽  
High Pressure Reaction ◽  
High Temperature High Pressure

Most uranium minerals can be classified as oxidized species in which U is fully oxidized to U(VI), and reduced species, in which U occurs primarily as U(IV). Uranyl silicates are an important group of uranium(VI) minerals in the altered zones of many uranium deposits [1]. Uranyl silicates have also received attention because they form when spent nuclear fuel interacts with water containing silicon under oxidizing conditions. One naturally occurring uranium(IV) silicate exists, namely coffinite (USiO4), which is the most important ore mineral for uranium after uraninite. Numerous synthetic uranium(VI) silicates and germanates containing organic amines or alkali metals as countercations have also been reported [2]. In contrast to the uranium(VI) compounds, the chemistry of materials containing uranium(V) is considerably less developed owing to the tendency of U(V) to either oxidize to U(VI) or disproportionate to U(IV) and U(VI). We have synthesized a pentavalent-uranium silicate and a germanate by a high-temperature, high-pressure hydrothermal method in gold ampoules contained in a high-pressure reaction vessel at ca. 600 °C and 170 MPa [3a,b]. Following the synthesis of the U(V) compounds, a number of mixed-valence uranium silicates and germanates have been synthesized, for example, a mixed-valence uranium(IV,V) silicate, Cs2K(UO)2Si4O12 [3c], a uranium(IV,VI) germanate, Cs8U(UO2)3(Ge3O9)3·3H2O [3d], uranium(V,VI) silicates and germanates, A3(U2O4)Ge2O7 (A = Rb, Cs) and [Na9F2][(UO2)3(Si2O7)2] [3e,f], and a uranium(IV,V,VI) silicate, Na7UO2(UO)2(UO2)2Si4O16 [3g] in which three oxidation states of uranium co-exist in one compound. In addition, tetravalent-uranium compounds, Cs2USi6O15 and Cs4UGe8O20 [3h,i], were also synthesized. All members in the family of uranium silicates and germanates with the oxidation states of uranium from +4 to +6 have been observed. In this presentation the high-temperature, high-pressure hydrothermal synthesis, crystal structures, and XPS spectroscopy of these interesting compounds will be reported.

scholarly journals Multianvil High-Pressure/High-Temperature Synthesis and Characterization of multiferroic HP-Co3TeO6

2021 ◽  
Author(s):  
Gunter Heymann ◽  
Elisabeth Selb ◽  
Toni Buttlar ◽  
Oliver Janka ◽  
Martina Tribus ◽  
...  
Keyword(s):  
High Pressure ◽  
High Temperature ◽  
Type Structure ◽  
Synthesis And Characterization ◽  
Temperature Synthesis ◽  
Space Group ◽  
Crystal System ◽  
High Temperature Synthesis ◽  
High Pressure High Temperature

By high-pressure/high-temperature multianvil synthesis a new high-pressure (HP) phase of Co3TeO6 was obtained. The compound crystallizes in the acentric trigonal crystal system of the Ni3TeO6-type structure with space group R3...

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