Powder diffraction of sodalite in a multiphase ceramic used to immobilize radioactive waste

2005 ◽  
Vol 20 (3) ◽  
pp. 212-214 ◽  
Author(s):  
S. M. Frank ◽  
T. L. Barber ◽  
M. J. Lambregts
Keyword(s):  
Radioactive Waste ◽  
Powder Diffraction ◽  
Lattice Parameter ◽  
Magic Angle Spinning ◽  
High Level Waste ◽  
Resonance Spectroscopy ◽  
Magic Angle ◽  
X Ray ◽  
Angle Spinning ◽  
High Level

The title compound, ∣Na6Li1.6K0.4Cl2∣[Al6Si6O24]‐SOD, is similar to sodalite proper, but the introduction of Li and K into the structure creates a reduction in unit-cell volume and additional collapse of the framework tetrahedra. Refinement of an X-ray powder diffraction pattern of a multiphase material yielded for sodalite a lattice parameter of 0.88427 (2) nm, an Al–O–Si bond angle of 137.9(3°), and Al–O and Si–O bond lengths of 0.1730(5) nm and 0.1620(5) nm, respectively. The angle of the unique Al–O–Si bond corresponds well with the 138° obtained by 29Si solid-state magic-angle-spinning nuclear magnetic resonance spectroscopy. This characterization is important since the compound constitutes an essential part of a radioactive waste form intended for a high-level waste repository.

Sol-gel synthesis of a nanoparticulate aluminosilicate precursor for homogeneous mullite ceramics

2006 ◽  
Vol 21 (5) ◽  
pp. 1279-1285 ◽  
Author(s):  
Jarkko Leivo ◽  
Mika Lindén ◽  
Cilâine V. Teixeira ◽  
Janne Puputti ◽  
Jessica Rosenholm ◽  
...  
Keyword(s):  
Spinel Phase ◽  
Sol Gel ◽  
Magic Angle Spinning ◽  
Resonance Spectroscopy ◽  
Magic Angle ◽  
X Ray Diffraction ◽  
X Ray ◽  
Bond Density ◽  
Angle Spinning ◽  
Sol Gel Synthesis

An amorphous nanoparticulate aluminosilicate 3/2-mullite precursor has been synthesized and carefully characterized. The sol contained 2-nm particles of Q3(3Al) silica species together with six-coordinated alumina, which suggested an allophane-like structure of the nanoparticles. The sol remained stable for years, and formed an easily redispersible physical gel upon solvent evaporation. The gel crystallized to mullite at temperatures below 1000 °C, without going through any intermediate spinel phase. Thus, the nanoparticulate precursor is regarded as a homogeneous high-purity mullite precursor with a high Si–O–Al bond density, which is useful in the preparation of various nanostructured Al-rich aluminosilicate materials. The sols and gels were characterized by small-angle x-ray scattering, dynamic light scattering, x-ray diffraction, 27Al and 29Si magic-angle spinning (MAS) nuclear magnetic resonance spectroscopy, and differential thermal analysis.

Structure of compounds E(SnMe3)4 (E = Si, Ge) as seen by high-resolution X-ray powder diffraction and solid-state NMR

2001 ◽  
Vol 58 (1) ◽  
pp. 52-61 ◽  
Author(s):  
Robert E. Dinnebier ◽  
Piotr Bernatowicz ◽  
Xavier Helluy ◽  
Angelika Sebald ◽  
Markus Wunschel ◽  
...  
Keyword(s):  
High Temperature ◽  
High Resolution ◽  
Low Temperature ◽  
Powder Diffraction ◽  
Variable Temperature ◽  
Lattice Parameter ◽  
Magic Angle Spinning ◽  
Magic Angle ◽  
Space Group ◽  
X Ray

The compounds tetrakis(trimethylstannyl)germane, Ge(SnMe3)4 (1), and tetrakis(trimethylstannyl)silane, Si(SnMe3)4 (2), have crystal structures with the quasispherical molecules in a closed-packed stacking. At room temperature both structures have the space group P\bar 1 (Z = 2) with a = 9.94457 (5), b = 14.52927 (8), c = 9.16021 (5) Å, α = 90.53390 (30), β = 111.73080 (30), γ = 90.0049 (4)°, and V = 1229.414 (12) Å3 for (1) and a = 9.92009 (7), b = 14.51029 (11), c = 9.13585 (7) Å, α = 90.4769 (4), β = 111.6724 (4), γ = 89.9877 (6)°, and V = 1222.037 (16) Å3 for (2). The molecules are found to be ordered as a result of steric interactions between neighboring molecules, as shown by analyzing the distances between the atoms. Upon heating, both compounds undergo a first-order phase transition at temperatures Tc = 348 ± 5 K, as characterized by a relative jump of the lattice parameter of ∼16%. At 353 K, both structures have the space group P\bar 1 (Z = 4), with a = 14.2037 (2) Å, and V = 2865.52 (7) Å3 for (1) and a = 14.1346 (2) Å, and V = 2823.90 (7) Å3 for (2). Rietveld refinements were performed for the low-temperature phases measured at T = 295 K [R wp = 0.0844 for (1), R wp = 0.0940 for (2)] and for the high-temperature phases measured at T = 353 K [R wp = 0.0891 for (1), R wp = 0.0542 for (2)]. The combination of high-resolution X-ray powder diffraction measurements and variable-temperature magic-angle-spinning 13C, 29Si and 119Sn NMR experiments demonstrates low crystallographic and molecular (C 1) symmetries for the low-temperature phases of (1) and (2) at temperatures T < 348 ± 5 K and high crystallographic symmetry due to rotational disorder for the high-temperature phases at temperatures T > 348 ± 5 K.

Analytical chemical applications of high-resolution nuclear magnetic resonance spectroscopy of solids

1982 ◽  
Vol 305 (1491) ◽  
pp. 591-607 ◽  
Keyword(s):  
Solid State ◽  
High Resolution ◽  
Structural Data ◽  
Magic Angle Spinning ◽  
Resonance Spectroscopy ◽  
Magic Angle ◽  
General Applicability ◽  
Phenolic Resins ◽  
X Ray ◽  
Angle Spinning

The basis of the combined cross-polarization-magic-angle spinning (c.p.-m.a.s.) experiment, which yields high-resolution n.m.r. spectra of solid materials, is described and the general applicability of the technique, including its quantitative reliability, discussed. Solid-state n.m.r. is in many ways complementary to X-ray diffraction, as shown by its application to amorphous systems in which diffraction methods cannot be used (for example resins, coals, glasses and surface-immobilized catalysts) and also by its application to crystalline materials where X-ray structural data are available but where, for various reasons, a fuller description of the structure may be obtained by n.m.r. Examples include zeolites and chemically exchanging solid systems. The technique also provides a bridge between the solid-state structures of conformationally mobile and charged species as determined by diffraction techniques and the structures of these species in solution. Quantitative reliability of the c.p.-m.a.s. technique has been evaluated for phenolic resins and coals.

scholarly journals Spectroscopic evaluation of UVI–cement mineral interactions: ettringite and hydrotalcite

2022 ◽  
Vol 29 (1) ◽  
Author(s):  
Antonia S. Yorkshire ◽  
Martin C. Stennett ◽  
Brant Walkley ◽  
Sarah E. O'Sullivan ◽  
Lucy M. Mottram ◽  
...  
Keyword(s):  
Radioactive Waste ◽  
Secondary Phase ◽  
Cementitious Materials ◽  
Magic Angle Spinning ◽  
Supplementary Cementitious Materials ◽  
Magic Angle ◽  
Coordination Environment ◽  
X Ray ◽  
Uranyl Carbonate ◽  
Angle Spinning

Portland cement based grouts used for radioactive waste immobilization contain high replacement levels of supplementary cementitious materials, including blast-furnace slag and fly ash. The minerals formed upon hydration of these cements may have capacity for binding actinide elements present in radioactive waste. In this work, the minerals ettringite (Ca6Al2(SO4)3(OH)12·26H2O) and hydrotalcite (Mg6Al2(OH)16CO3·4H2O) were selected to investigate the importance of minor cement hydrate phases in sequestering and immobilizing UVI from radioactive waste streams. U L III-edge X-ray absorption spectroscopy (XAS) was used to probe the UVI coordination environment in contact with these minerals. For the first time, solid-state 27Al magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy was applied to probe the Al coordination environment in these UVI-contacted minerals and make inferences on the UVI coordination, in conjunction with the X-ray spectroscopy analyses. The U L III-edge XAS analysis of the UVI-contacted ettringite phases found them to be similar (>∼70%) to the uranyl oxyhydroxides present in a mixed becquerelite/metaschoepite mineral. Fitting of the EXAFS region, in combination with 27Al NMR analysis, indicated that a disordered Ca- or Al-bearing UVI secondary phase also formed. For the UVI-contacted hydrotalcite phases, the XAS and 27Al NMR data were interpreted as being similar to uranyl carbonate, that was likely Mg-containing.

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