Study of Uranium Incorporation Into Zircon: Solubility Limits and Durability of Fixation

1997 ◽  
Vol 506 ◽  
Author(s):  
S.V. Ioudintsev ◽  
B.I. Omelianenko ◽  
M.I. Lapina
Keyword(s):  
Radioactive Decay ◽  
Temperature Treatment ◽  
Hot Water ◽  
High Temperature Treatment ◽  
Hydrothermal Conditions ◽  
Cell Dimensions ◽  
Oxygen Buffer ◽  
Unit Cell Dimensions ◽  
Strong Depletion ◽  
Made In

ABSTRACTResearch on synthetic zircons fabricated in system ZrO2-UO2-SiO2 at T = 400 - 750° C, PH20 = 100-200 MPa, and Ni-NiO oxygen buffer was made in order to estimate the limits of uranium incorporation into the phase's structure. It was shown that up to 27 wt.% of uranium may locally enter into the synthetic zircons. SEM/EDS study of the samples has showed that the element is uniformly distributed within the zircon crystals. Incorporation of U into zircon increases its unit-cell dimensions up to α = 6.70 A and c = 6.00 A relative to 6.60 and 5.98 A for a pure phase without impurities.After thermal high temperature treatment of the samples under 1400° C, in air, for 6 hours inhomogeneous distribution of uranium within the zircon grains was revealed. Very small uranium rich spots probably corresponding to a newly formed phase were observed in the zircon crystals. Contents of the element throughout the grains decreased to about 10 wt.%. It is probably caused by destruction of zircon-coffinite solid solution formed at hydrothermal conditions in the course of its re-heating.Study of interaction of natural zircons with alkaline carbonate solution at 100° C shows that U release from the phase can reach up to 6 % of total uranium in the samples even under relatively short term interaction. Loss of uranium rises with the element content (or amorphisation degree) and run duration, as well as with grain size reduction. Research on uranium distribution in natural zircons picked up from altered and weathered rocks is characterised by strong depletion of U at grain margins relative to the centre of the crystals. These results indicate that zircon may lose some uranium and, probably, the other actinides with time due to its lattice destruction under radioactive decay followed by hot water attack.

Electrophilic cleavage of cyclopropanes. IV. The reaction of 2-nitrobenzenesulphenyl chloride with tetracyclo[3.2.0.02,7.04,6]heptane in methanol and acetic acid: the crystal structure of exo-3-(2′-nitrophenylthio)-exo-5-methoxytricyclo[2.2.1.02,6]heptane, C14H15NO3S

1983 ◽  
Vol 61 (6) ◽  
pp. 1176-1184 ◽  
Author(s):  
Dennis G. Garratt ◽  
Maria Przybylska ◽  
Miroslaw Cygler
Keyword(s):  
Crystal Structure ◽  
Acetic Acid ◽  
Ring Opening ◽  
Sulphur Atom ◽  
X Ray ◽  
Cell Dimensions ◽  
Unit Cell Dimensions ◽  
Unambiguous Assignment ◽  
Made In ◽  
C Nmr

The electrophilic cleavage of a cyclopropane single bond in tetracyclo[3.2.0.02,7.04,6]heptane by 2-nitrobenzenesulphenyl chloride in methanol and acetic acid has been studied using both nmr and single crystal X-ray structural determination techniques. The orientation of ring opening has been shown to be inversion as a result of electrophilic corner attack. The crystal structure of one adduct allowed the unambiguous assignment of exo-3-(2′-nitrophenylthio)-exo-5-methoxytricyclo [2.2.1.02,6]-heptane, C14H15NO3S. This species crystallizes in space group P21/a with unit cell dimensions a = 10.633(1), b = 13.637(1), c = 9.938(1) Å, β = 115.36(1)°, Z = 4. The structure was solved by MULTAN 78. The parameters were refined by block-diagonal least squares to a final R = 0.039 for 2445 observed reflections. Of particular interest is an interaction between the sulphur atom and the oxygen atom of the nitro group with an [Formula: see text] distance of 2.694(2) Å and [Formula: see text]. The data presented in this paper show errors in previous assignments based on 13C nmr spectroscopy made in this laboratory and indicate the danger of basing assignments of configuration in nortricyclenes entirely upon this technique.

Physical properties of synthetic and natural pyroxenes in the system diopside–hedenbergite–acmite

1969 ◽  
Vol 37 (286) ◽  
pp. 216-229 ◽  
Author(s):  
J. Nolan
Keyword(s):  
Unit Cell ◽  
Refractive Indices ◽  
Linear Change ◽  
Cell Parameters ◽  
Complete Solid Solution ◽  
Cell Dimensions ◽  
Oxygen Buffer ◽  
The Many ◽  
Unit Cell Dimensions ◽  
End Members

SummaryUnit cell dimensions and refractive indices have been determined for synthetic pyroxenes in the system CaMgSi2O6-CaFeSi2O6-NaFeSi2O6, which have been crystallized and annealed on the nickel-bunsenite (Ni-NiO) oxygen buffer curve at 700 °C and a total pressure of 2 kb. The data presented confirms the many postulates that a complete solid solution series does exist in the subsolidus region of the ‘ternary’ system. The unit cell dimensions show an almost linear change with composition between the end members. The determined cell parameters for a series of analysed natural alkali pyroxenes have been compared with the data for the synthetic pyroxenes and close agreement was found between both sets of data. The variation of the unit cell dimensions and refractive indices has been examined in relation to the possible ionic substitutions taking place in the pyroxenes.

scholarly journals A comparative anatomy of protein crystals: lessons from the automatic processing of 56 000 samples

IUCrJ ◽  
2019 ◽  
Vol 6 (5) ◽  
pp. 822-831 ◽  
Author(s):  
Olof Svensson ◽  
Maciej Gilski ◽  
Didier Nurizzo ◽  
Matthew W. Bowler
Keyword(s):  
Molecular Weight ◽  
Data Collection ◽  
Comparative Anatomy ◽  
Automatic Processing ◽  
X Ray Crystallography ◽  
Cell Dimensions ◽  
Unit Cell Dimensions ◽  
Crystal Volume ◽  
Made In

The fully automatic processing of crystals of macromolecules has presented a unique opportunity to gather information on the samples that is not usually recorded. This has proved invaluable in improving sample-location, characterization and data-collection algorithms. After operating for four years, MASSIF-1 has now processed over 56 000 samples, gathering information at each stage, from the volume of the crystal to the unit-cell dimensions, the space group, the quality of the data collected and the reasoning behind the decisions made in data collection. This provides an unprecedented opportunity to analyse these data together, providing a detailed landscape of macromolecular crystals, intimate details of their contents and, importantly, how the two are related. The data show that mosaic spread is unrelated to the size or shape of crystals and demonstrate experimentally that diffraction intensities scale in proportion to crystal volume and molecular weight. It is also shown that crystal volume scales inversely with molecular weight. The results set the scene for the development of X-ray crystallography in a changing environment for structural biology.

The External Shape of Human γ GI Immunoglobulin from Crystal Sections

1971 ◽  
Vol 29 ◽  
pp. 428-429
Author(s):  
L. W. Labaw
Keyword(s):  
Molecular Weight ◽  
Sodium Phosphate ◽  
Osmium Tetroxide ◽  
Unit Cell ◽  
Monoclinic Space Group ◽  
X Ray ◽  
Large Molecular Weight ◽  
Cell Dimensions ◽  
Unit Cell Dimensions ◽  
Crystallographic Axes

Crystals of a human γGl immunoglobulin have the external morphology of diamond shaped prisms. X-ray studies have shown them to be monoclinic, space group C2, with 2 molecules per unit cell. The unit cell dimensions are a = 194.1, b = 91.7, c = 51.6Å, 8 = 102°. The relatively large molecular weight of 151,000 and these unit cell dimensions made this a promising crystal to study in the EM.Crystals similar to those used in the x-ray studies were fixed at 5°C for three weeks in a solution of mother liquor containing 5 x 10-5M sodium phosphate, pH 7.0, and 0.03% glutaraldehyde. They were postfixed with 1% osmium tetroxide for 15 min. and embedded in Maraglas the usual way. Sections were cut perpendicular to the three crystallographic axes. Such a section cut with its plane perpendicular to the z direction is shown in Fig. 1.This projection of the crystal in the z direction shows periodicities in at least four different directions but these are only seen clearly by sighting obliquely along the micrograph.

The crystal and molecular structure of tris(pentamethylenedithiocarbamate) chromium(III)-chloroform (1 : 2)

1981 ◽  
Vol 46 (1) ◽  
pp. 6-19 ◽  
Author(s):  
Viktor Kettman ◽  
Ján Garaj ◽  
Jaroslav Majer
Keyword(s):  
Molecular Structure ◽  
Structural Analysis ◽  
Crystal And Molecular Structure ◽  
Analysis Method ◽  
Complex Molecules ◽  
Coordination Polyhedra ◽  
X Ray ◽  
Cell Dimensions ◽  
Crustal Density ◽  
Unit Cell Dimensions

The crystal and molecular structure of [Cr(S2CN(CH2)5)3].2 CHCl3 was found by the X-ray structural analysis method. The value R 0.090 was found for 1 131 observed independent reflections. The substance crystallizes in a space group of symmetry P212121 with the following unit cell dimensions: a = 0.8675 (6), b = 1.815(2), c = 2.155(3) nm. The experimentally observed crustal density was 1.48 Mgm-3 and the value calculated for Z = 4 was 1.51 Mgm-3. The CrS6 coordination polyhedron has the shape of a trigonally distorted octahedron, where the D3 symmetry is a approximately retained. The degree of trigonal distortion expressed as the projection of the chelate S-Cr-S angle onto the plane perpendicular to the C3 pseudo axis is Φ = 41.7° (Φ = 60° for an octahedron). The skeleton of the structure formed by the complex molecules contains channels filled with chloroform molecules. The specific type of complex-chloroform interaction consists of the formation of hydrogen bonds of the chloroform protons with the fully occupied pπ-orbitals of the sulphur atoms in the coordination polyhedra. The low stability and crystal decomposition can be explained by loss of chloroform from the channels.

Water Molecule Dispositions in the Cesium Sulfate α- and β-Alums: Single-Crystal Neutron Diffraction Studies of CsM(SO4)2.12H2O (M=V, Rh)

1993 ◽  
Vol 46 (9) ◽  
pp. 1337 ◽  
Author(s):  
JK Beattie ◽  
SP Best ◽  
FH Moore ◽  
BW Skelton ◽  
AH White
Keyword(s):  
Neutron Diffraction ◽  
Water Molecule ◽  
Single Crystal ◽  
Tilt Angle ◽  
Room Temperature ◽  
Bond Angle ◽  
Sulfate Salt ◽  
Cell Dimensions ◽  
Coordinated Water ◽  
Unit Cell Dimensions

Room-temperature single-crystal neutron diffraction studies are recorded for two alums, Cs( Rh /V)(SO4)2.12H2O [cubic, Pa3, a 12.357(5) ( Rh ), 12.434(1)Ǻ (V)], residuals 0.037 and 0.068 for 328 and 164 'observed' reflections, with the intention of defining water molecule hydrogen atom orientations. Whereas the two tervalent hexaaqua cations are similar in size [ rM -O = 2.010(6)Ǻ (M = V) and 2.006(2)Ǻ (M = Rh )] the vanadium salt adopts the β alum modification while rhodium gives an α alum. Significantly, the water coordination geometry is different in the two cases with the tilt angle between the plane of the water molecule and the M-O bond vector being 1° (M = V) and 35° (M = Rh ). The tilt angle for water coordinated to rhodium in CsRh (SeO4)2.12H2O is inferred from the unit cell dimensions to be similar to that of the corresponding sulfate salt and not that which generally pertains for caesium selenate alums. Significant differences in the H-O-H bond angle are found for trigonal planar and trigonal pyramidal water coordination, suggesting that differences in the metal(III)-water interaction are a determinant of the geometry of the coordinated water molecule in the caesium sulfate/ selenate alum lattices.

Sign in / Sign up

Export Citation Format

Share Document