Thermochemistry and Structure of Model Waste Glass Compositions

1989 ◽  
Vol 176 ◽  
Author(s):  
Adam J. G. Ellison ◽  
Alexandra Navrotsky
Keyword(s):  
Enthalpies Of Solution ◽  
Charge Balance ◽  
Coordination Polyhedra ◽  
Waste Containment ◽  
Enthalpies Of Mixing ◽  
Heats Of Mixing ◽  
Major Oxide ◽  
Mechanical Mixtures ◽  
End Members ◽  
Glass Compositions

ABSTRACTEnthalpies of mixing of major oxide and waste components of proposed DWPF glasses are estimated. Several proposed glass compositions have very similar molar proportions of major structure-related components. Heats of mixing of major components are predicted to be small (glassy reference states), but may be endothermic or exothermic. Lanthanides are likely to form regions in the glasses rich in R-O-Si bonds but relatively depleted in Si-O-Si bonds. Measured enthalpies of solution of simple lanthanide-bearing glasses resemble those of mechanical mixtures of these end-members, with near-zero enthalpies of mixing for fairly large variations in lanthanide concentrations. DWPF glasses have alkalis in excess of those needed to charge-balance all T3+ cations in tetrahedral coordination. Electropositive +4, +5, and +6 cations are expected to use these excess alkalis to stabilize their own coordination polyhedra, forming complexes with effectively constant macroscopic stoichiometric ratios which contribute to enthalpies of solution in direct proportion to their concentration. Therefore, variations in the concentrations of high-valence cations in DWPF waste containment glasses are also predicted to result in near-zero enthalpies of mixing.

Transuranium Element Incorporation into the β-U3O8 Uranyl Sheet

1996 ◽  
Vol 465 ◽  
Author(s):  
M. L. Miller ◽  
P. C. Burns ◽  
R. J. Finch ◽  
R. C. Ewing
Keyword(s):  
Crystal Structure ◽  
Spent Nuclear Fuel ◽  
Chemical Characteristics ◽  
Transuranium Element ◽  
Limited Data ◽  
Charge Balance ◽  
Coordination Polyhedra ◽  
Structural Details ◽  
Structure Determinations ◽  
Shared Edge

ABSTRACTSpent nuclear fuel (SNF) is unstable under oxidizing conditions. Although recent studies have determined the paragenetic sequence for uranium phases that result from the corrosion of SNF, there are only limited data on the potential of alteration phases for the incorporation of transuranium elements. The crystal chemical characteristics of transuranic elements (TUE) are to a certain extent similar to uranium; thus TUE incorporation into the sheets of uranyl oxide hydrate structures can be assessed by examination of the structural details of the β-U3O8 sheet type.The sheets of uranyl polyhedra observed in the crystal structure of β-U3O8 also occur in the mineral billietite (Ba[(UO2)3O2(OH)3]2(H2O)4), where they alternate with α-U3O8 type sheets. Preliminary crystal structure determinations for the minerals ianthinite, ([U24+(HO2)4O6(HO)4(H2O)4](H2O)5), and “wyartite II” (mineral name not approved by IMA committee on mineral names), {CaCo3}[U4+(UO2)2O3(OH)2](H2O)4, indicate that these phases also contain β-U3O8 type sheets. The β-U3O8sheet anion topology contains triangular, rhombic, and pentagonal sites in the proportions 2: 1:2. In all structures containing β-U3O8 type sheets, the triangular sites are vacant. The pentagonal sites are filled with U6+O2 forming pentagonal bipyramids. The rhombic dipyramids filling the rhombic sites contain U6+O2 in billietite, U4+O2 in β-U3O8U4+(H2O)2 in ianthinite, and U4+O3 in “wyartite-II” (in which one apical anion is replaced by two O atoms forming a shared edge with a carbonate triangle of the interlayer). Interlayer species include: H2O (billietite, “wyartite II”, and ianthinite), Ba2+ (billietite) Ca2+ (”wyartite II”), and CO3−2 (”wyartite II”); there is no interlayer in β-U3O8. The similarity of known TUE coordination polyhedra with those of U suggests that the β-U3O8 sheet will accommodate TUE substitution coupled with variations in apical anion configuration and interlayer population providing the required charge balance.

scholarly journals The solid solutions of rebulite and jankovićite in the phase system Tl2S-As2S3-Sb2S3

2015 ◽  
Vol 34 (1) ◽  
pp. 125
Author(s):  
Tonci Balic-Zunic ◽  
Yves Moëlo ◽  
Ljiljana Karanović ◽  
Peter Berlepsch
Keyword(s):  
Crystal Structure ◽  
Solid Solution ◽  
Solid Solutions ◽  
Unit Cell ◽  
Phase System ◽  
Structural Topology ◽  
Coordination Polyhedra ◽  
Ideal Composition ◽  
End Members ◽  
Compositional Line

Syntheses along the Tl<sub>5</sub>(As,Sb)<sub>13</sub>S<sub>22</sub> compositional line in the Tl<sub>2</sub>S-As<sub>2</sub>S<sub>3</sub>-Sb<sub>2</sub>S<sub>3</sub> phase system showed that the compositional range of rebulite extends from  Tl<sub>5</sub>As<sub>9.5</sub>Sb<sub>3.5</sub>S<sub>22</sub> to Tl<sub>5</sub>As<sub>7.75</sub>Sb<sub>5.25</sub>S<sub>22</sub>. The Sb-rich end-member is in equilibrium with jankovićite of ideal composition Tl<sub>5</sub>Sb<sub>7.5</sub>As<sub>5.5</sub>S<sub>22</sub>. It is considered to be the As-rich end-member of the jankovićite solid solution. The crystal structure analyses of crystals from the As and Sb end-members of rebulite show that the Sb/As substitution is present in Sb3, Sb4, Sb5, As1 and As2 structural sites. Of them, Sb3 is always Sb dominated whereas other four vary from As- to Sb-dominated over the range of the solid solution. The change of the structural topology from jankovićite to rebulite, the closely related but not identical structures, is explained through necessity to accommodate the smaller volumes of the As coordination polyhedra and is accomplished through unit-cell twinning over the periodic (001)<sub>reb</sub> twin boundaries. The As end-member of the rebulite solid solution is in equilibrium with the phase of Tl<sub>2.4</sub>Sb<sub>0.68</sub>As<sub>7.18</sub>S<sub>13</sub> ideal composition, interpreted as imhofite.

Differential Enthalpies of Solution of Components in Binary Systems 2 CaO . Al2O3 . SiO2-CaO . Al2O3 . 2 SiO2, CaO . SiO2-CaO . Al2O3 . 2 SiO2 and CaO . SiO2-2 CaO . Al2O3 . SiO2

1993 ◽  
Vol 58 (9) ◽  
pp. 1989-1996 ◽  
Author(s):  
Ladislav Kosa ◽  
Ivan Nerád ◽  
Jozef Strečko ◽  
Ivo Proks ◽  
Katarína Adamkovičová
Keyword(s):  
Binary Systems ◽  
The Other ◽  
Enthalpies Of Solution ◽  
Heat Of Solution ◽  
Differential Heat ◽  
Temperature Range ◽  
Enthalpies Of Mixing ◽  
Other Hand ◽  
Temperature Dependences

Differential enthalpies of solution of components in binary systems 2 CaO . Al2O3 . SiO2-CaO . Al2O3 . 2 SiO2, CaO . SiO2-CaO . Al2O3 . 2 SiO2 and CaO . SiO2-2 CaO . Al2O3 . SiO2 as the function of composition and temperature were determined on the base of isothermal composition dependences of enthalpies of mixing and temperature dependences of heats of fusion of their pure components. From the values of the first differential heat of solution of CaO . Al2O3 . 2 SiO2 and 2 CaO . Al2O3 . SiO2 in CaO . SiO2 over temperature range considered we can conclude that the reactions were closed chains of SiO4 tetrahedra in CaO . SiO2 melt break, are exothermic. On the other hand positive values of this quantity for CaO . SiO2 in CaO . Al2O3 . 2 SiO2 and 2 CaO . Al2O3 . SiO2 led us to the conclusion that the progressive breaking originally closed chains in CaO . SiO2 melt has endothermic character.

Corkite from Aggeneys, Bushmanland, South Africa

1990 ◽  
Vol 54 (377) ◽  
pp. 603-608 ◽  
Author(s):  
H. de Bruiyn ◽  
W. A. Van Der Westhuizen ◽  
G. J. Beukes ◽  
T. Q. Meyer
Keyword(s):  
Solid Solution ◽  
General Formula ◽  
Regional Distribution ◽  
The Other ◽  
Iron Formation ◽  
Charge Balance ◽  
X Ray Diffraction ◽  
Broken Hill ◽  
Complete Solid Solution ◽  
End Members

AbstractCorkite associated with plumbojarosite and goethite occurs in gossan and iron-formation at Black Mountain and Broken Hill, Aggeneys. Electron microprobe analyses indicate that there are two groups of corkite present in the area; one with high Cu and low (PO4)3− and the other with low Cu and high (PO and the other with low Cu and high (PO4)3− contents. This can be explained in terms of the general formula contents. This can be explained in terms of the general formula AB2(XO4)2(OH)6, where the incorporation of divalent ions in the B site is accompanied by the exchange of trivalent anions by divalent ones to retain charge balance. Complete solid-solution is inferred between (SO4)2−and (PO4)3− end members, indicating that the jarosite and beudantite groups form part of the same solid-solution series. The distribution of Zn in corkite also reflects the regional distribution of zinc grades in the area, becoming more zinc-rich from west to east. New X-ray diffraction parameters are also presented which update existing data.

scholarly journals Polysomatic apatites

2010 ◽  
Vol 66 (1) ◽  
pp. 1-16 ◽  
Author(s):  
Tom Baikie ◽  
Stevin S. Pramana ◽  
Cristiano Ferraris ◽  
Yizhong Huang ◽  
Emma Kendrick ◽  
...  
Keyword(s):  
State Of The Art ◽  
Functional Materials ◽  
Abundant Species ◽  
Complex Structures ◽  
Charge Balance ◽  
Principal Characteristics ◽  
X Ray ◽  
Structure Building ◽  
End Members ◽  
Stacking Disorder

Certain complex structures are logically regarded as intergrowths of chemically or topologically discrete modules. When the proportions of these components vary systematically a polysomatic series is created, whose construction provides a basis for understanding defects, symmetry alternation and trends in physical properties. Here, we describe the polysomatic family A 5N B 3N O9N + 6 X Nδ (2 ≤ N ≤ ∞) that is built by condensing N apatite modules (A 5 B 3O18 X δ) in configurations to create B n O3n + 1 (1 ≤ n ≤ ∞) tetrahedral chains. Hydroxyapatite [Ca10(PO4)6(OH)2] typifies a widely studied polysome where N = 2 and the tetrahedra are isolated in A 10(BO4)6 X 2 compounds, but N = 3 A 15(B 2O7)3(BO4)3 X 3 (ganomalite) and N = 4 A 20(B 2O7)6 X 4 (nasonite) are also known, with the X site untenanted or partially occupied as required for charge balance. The apatite modules, while topologically identical, are often compositionally or symmetrically distinct, and an infinite number of polysomes is feasible, generally with the restriction being that an A:B = 5:3 cation ratio be maintained. The end-members are the N = 2 polysome with all tetrahedra separated, and N = ∞, in which the hypothetical compound A 5 B 3O9 X contains infinite, corner-connected tetrahedral strings. The principal characteristics of a polysome are summarized using the nomenclature apatite-(A B X)-NS, where A/B/X are the most abundant species in these sites, N is the number of modules in the crystallographic repeat, and S is the symmetry symbol (usually H, T, M or A). This article examines the state-of-the-art in polysomatic apatite synthesis and crystallochemical design. It also presents X-ray and neutron powder diffraction investigations for several polysome chemical series and examines the prevalence of stacking disorder by electron microscopy. These insights into the structure-building principles of apatite polysomes will guide their development as functional materials.

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