Alteration of Uranium-Rich Microlite

2000 ◽  
Vol 663 ◽  
Author(s):  
R. Gieré ◽  
E. C. Buck ◽  
R. Guggenheim ◽  
D. Mathys ◽  
E. Reusser ◽  
...  
Keyword(s):  
Electron Diffraction ◽  
Low Temperature ◽  
Nuclear Waste ◽  
X Ray ◽  
Geologic Time ◽  
Pyrochlore Group ◽  
Tropical Conditions ◽  
Natural Analogues ◽  
Growth Zoning ◽  
Ray Patterns

ABSTRACTMicrolite, a Ta-rich member of the pyrochlore group, occurs in 440 Ma old lithium pegmatites in Mozambique and exhibits a pronounced growth zoning, with a U-free core surrounded by a U-rich rim (UO2≤ 17 wt%). Subsequent to the uplift of the host rock, microlite was subjected to intense low-temperature alteration during which Na, Ca and F were leached from the microlite crystals. This alteration, resulting from exposure to tropical conditions, also led to localized redistribution of radiogenic Pb (formation of plumbomicrolite) and to hydration of microlite, but U remained immobile. The low-temperature alteration effects are only observed in the U-rich rim, which is characterized by abundant microfractures. As demonstrated by electron diffraction images and powder X-ray patterns, the U-rich rim is largely metamict. Our investigation illustrates the importance of natural analogues in evaluating the durability of pyrochlore-based nuclear waste-form materials over geologic time.

The determination of composition and thermal history of plagioclase by the X-ray powder method

1955 ◽  
Vol 30 (229) ◽  
pp. 648-656 ◽  
Author(s):  
J. Goodyear ◽  
W. J. Duffin
Keyword(s):  
Chemical Composition ◽  
Low Temperature ◽  
Similar Composition ◽  
X Ray ◽  
Naturally Occurring ◽  
Cell Dimensions ◽  
History Of ◽  
Unit Cell Dimensions ◽  
Ray Patterns

In a recent paper (hereafter referred to as GD) Goodyear and Dufiln (1954) described X-ray powder data for a number of synthetic and chemically analysed plagioclases of composition An0Abl00-Anl00Ab0. Important aspects of this work were a correlation of the X-ray patterns with chemical composition, and a distinction between the pattern of a naturally occurring material of low-temperature origin and that of a synthetic of similar composition. The investigation showed quite clearly that the unit-cell dimensions of a synthetic plagioelase depend but little on composition from An0Abl00 to An70Ab30, whilst they differ from those of the low-temperature modification greatly for albite, to a lessening degree as the composition approaches An70Ab30, and practically not at all in the range An70Ab30-Anl00Ab0.

Crystallization of anorthite from CaO–Al2O3–SiO2glasses

1970 ◽  
Vol 37 (291) ◽  
pp. 780-789 ◽  
Author(s):  
M. S. Y. Bhatty ◽  
J. A. Gard ◽  
F. P. Glasser
Keyword(s):  
Electron Diffraction ◽  
Low Temperature ◽  
Diffraction Pattern ◽  
Powder Diffraction ◽  
Powder Pattern ◽  
Molar Ratio ◽  
Measurable Effect ◽  
Apparent Absence ◽  
X Ray ◽  
Unique Manner

SummaryThe X-ray powder diffraction pattern of synthetic anorthite crystallized from a CaO-Al2O3-SiO2glass having the anorthite (1:1:2) molar ratio is identical with that reported in the literature, and also with that of a natural Japanese anorthite specimen. Increasing the CaO or SiO2content of the parent glasses used for crystallization studies has no measurable effect on that portion of the powder pattern attributable to anorthite. However, glasses containing an excess of Al2O3ranging from 5 to 10 mol % gave, after crystallization at temperatures belowc.1150 °C distinctively different powder pattern. Several powder reflections that are normally strong, such as, etc., were found to be virtually absent. Moreover, the chemical excess of Al2O3did not appear as a separate alumina-bearing phase. Upon reheating these anorthites to temperatures above 1200–50 °C or upon crystallizing a fresh portion of alumina-rich glass above 1200-50 °C, only the normal anorthite powder X-ray pattern was obtained; the pattern also contained some reflections due to corundum (α-Al2O3). Examination of the anomalous low-temperature anorthite by electron diffraction shows that the apparent absence of some powder lines is caused by both albite and Carlsbad twinning, which occur on an intimate scale not exceeding a few unit cell repeats. From the unique manner of its occurrence, the twinning is believed to be associated with the inclusion of an excess of Al3+in the anorthite.

Straczekite, a new calcium barium potassium vanadate mineral from Wilson Springs, Arkansas

1984 ◽  
Vol 48 (347) ◽  
pp. 289-293 ◽  
Author(s):  
Howard T. Evans ◽  
Gordon Nord ◽  
John Marinenko ◽  
Charles Milton
Keyword(s):  
Electron Diffraction ◽  
Chemical Analysis ◽  
Single Crystal ◽  
General Formula ◽  
Secondary Mineral ◽  
Calculated Density ◽  
X Ray ◽  
Cell Parameters ◽  
Diffraction Patterns ◽  
Ray Patterns

AbstractStraczekite, a new calcium barium potassium vanadate from Wilson Springs (formerly Potash Sulfur Springs), Arkansas, occurs as a rare secondary mineral in fibrous seams in gangue. The dark greenish-black crystals are very soft, thin laths up to 0.5 mm in length, forming thick masses. No single-crystal X-ray patterns could be obtained, but good electron diffraction patterns yielded a monoclinic unit cell in space group C2/m, C2, or Cm. The cell parameters were refined by least squares analysis of Guinier-Hägg X-ray powder data: a 11.679(2), b 3.6608(4), c 10.636(2)Å, β = 100.53(4)° (strongest lines are: 003, 3.486, 100; 001, 10.449, 50; 020 1.8306, 50; 6̄01/510, 1.9437, 15; 111/2̄03, 3.255, 10; 311/3̄12, 2.492, 10; 021, 1.8030, 10). Chemical analysis yields the formula: (Ca0.39Ba0.31K0.33Na0.11)(V1.594+V6.315+Fe0.103+)O20.02(H2O)2.9. The calculated density is 3.21 g/cm3. The mineral conforms to a series of synthetic vanadium bronzes, typified by Ag1-xV2O5 of known structure. It represents a new series of layer vanadate minerals of general formula MxV8O20·yH2O, similar in properties but distinct from the hewettite series (MxV6O16·yH2O).

Natural Pyrochlores: Analogues For Actinide Host Phases in Radioactive Waste Forms

1984 ◽  
Vol 44 ◽  
Author(s):  
Gregory R. Lumpkin ◽  
Rodney C. Ewing
Keyword(s):  
Electron Diffraction ◽  
Radioactive Waste ◽  
Nuclear Waste ◽  
Pyrochlore Structure ◽  
Structure Type ◽  
Saturation Level ◽  
Waste Forms ◽  
Natural Analogues ◽  
Alteration Processes ◽  
Nuclear Waste Forms

AbstractSignificant amounts of the pyrochlore structure type, and derivative structures like zirconolite, have been reported to occur in crystalline, polyphase, nuclear waste forms [1,2,3,4]. Pyrochlore has abundant and chemically diverse natural analogues. Many of these contain U and Th and have been transformed to the electron-diffraction amorphous, “metamict” state by alpha-recoil nuclei. A variety of geochemical alteration processes may occur before, during, and after reaching the final saturation level for alpha-recoil damage (∼1026 alpha-events/m3 ). The purpose of this paper is to examine these alteration effects in radiation-damaged natural pyrochlores.

scholarly journals Hydrogen disorder in kaatialaite Fe[AsO2(OH)2]5H2O from Jáchymov, Czech Republic: determination from low-temperature 3D electron diffraction

IUCrJ ◽  
2021 ◽  
Vol 8 (1) ◽  
pp. 116-123
Author(s):  
Gwladys Steciuk ◽  
Juraj Majzlan ◽  
Jakub Plášil
Keyword(s):  
Hydrogen Bonding ◽  
Czech Republic ◽  
Electron Diffraction ◽  
Low Temperature ◽  
X Ray Diffraction ◽  
Hydrogen Atoms ◽  
X Ray ◽  
Heavy Atoms ◽  
Recent Developments ◽  
3D Electron

Kaatialaite mineral Fe[AsO2(OH)2]5H2O from Jáchymov, Czech Republic forms white aggregates of needle-shaped crystals with micrometric size. Its structure at ambient temperature has already been reported but hydrogen atoms could not be identified from single-crystal X-ray diffraction. An analysis using 3D electron diffraction at low temperature brings to light the hydrogen positions and the existence of hydrogen disorder. At 100 K, kaatialaite is described in a monoclinic unit cell of a = 15.46, b = 19.996, c = 4.808 Å, β = 91.64° and V = 1485.64 Å3 with space group P21/n. The hydrogen sites were revealed after refinements both considering the dynamical effects and ignoring them. The possibility to access most of the hydrogen positions, including partially occupied ones among heavy atoms, from the kinematical refinement is due to the recent developments in the analysis of 3D electron data. The hydrogen bonding observed in kaatialaite provides examples of H2O configurations that have not been observed before in the structures of oxysalts with the presence of unusual inverse transformer H2O groups.

The structure of chloromethyl thiocyanate, CH2ClSCN, in gas and crystalline phases

2015 ◽  
Vol 17 (24) ◽  
pp. 15805-15812 ◽  
Author(s):  
Y. Berrueta Martínez ◽  
L. S. Rodríguez Pirani ◽  
M. F. Erben ◽  
C. G. Reuter ◽  
Y. V. Vishnevskiy ◽  
...  
Keyword(s):  
Electron Diffraction ◽  
Low Temperature ◽  
Single Crystal ◽  
Gas Phase ◽  
Solid Phase ◽  
Gas Electron Diffraction ◽  
X Ray Diffraction ◽  
X Ray ◽  
Conformational Properties

The structural and conformational properties of chloromethyl thiocyanate, CH2ClSCN, were studied in the solid phase and in the gas phase usingin situlow-temperature single-crystal X-ray diffraction experiments (XRD) and gas electron diffraction (GED), respectively.

scholarly journals Präparative und spektroskopische Untersuchungen zur Dimorphie von CsNiF3.

1976 ◽  
Vol 31 (1) ◽  
pp. 60-65 ◽  
Author(s):  
R. Haegele ◽  
D. Babel ◽  
D. Reinen
Keyword(s):  
Low Temperature ◽  
Perovskite Structure ◽  
Spectral Band ◽  
Ligand Field ◽  
X Ray ◽  
Bond Angles ◽  
Green Colour ◽  
Ligand Field Spectra ◽  
Ray Patterns

While the stable modification of CsNiF3 is of green colour, a yellow phase is obtained by fluorination of CsNiCl3 and decomposition of the product “CsNiF4”, which contains Ni4+ and Ni3+ besides Ni2+. The two modifications have the 2L- and 9L-perovskite-structure, respectively, and are characterized by their X-ray patterns and low-temperature ligand field spectra. The differences in colours and spectral band positions are discussed with respect to the Ni-F-Ni bond angles

X-Ray Studies of Low-Temperature Polybutadiene and Butadiene-Styrene Copolymers

1949 ◽  
Vol 22 (2) ◽  
pp. 356-369 ◽  
Author(s):  
Karl E. Beu ◽  
W. B. Reynolds ◽  
C. F. Fryling ◽  
H. L. McMurry
Keyword(s):  
Molecular Weight ◽  
Low Temperature ◽  
Polymer Chains ◽  
Polymerization Temperature ◽  
X Ray ◽  
Styrene Copolymers ◽  
Emulsion Polymerizations ◽  
Diffraction Patterns ◽  
Ray Patterns ◽  
Butadiene Styrene

Abstract Although it is now generally recognized that the temperature of polymerization affects profoundly the properties of emulsion elastomers, there is very little evidence available pertaining to the cause of the variations of properties. It is felt by some that the improved properties of low-temperature elastomers can be related to variations in molecular weight and molecular-weight distribution. In this laboratory, however, the opinion has prevailed that the lower emulsion polymerization temperatures appreciably alter the fine structure of the molecules with an increase in the regularity of the polymer chains. If there were actually less branching and cross-linking in low-temperature polymers, and less 1,2-addition to monomer components, the increased order should be evident from x-ray diffraction patterns. To provide information on the above questions, x-ray studies were made with four purposes in view: (1) to determine the effect of polymerization temperature on the crystallization properties of unstretched and stretched polybutadienes; (2) to determine the influence of styrene content on the crystallization of butadiene-styrene copolymers; (3) to study some effects of compounding and vulcanization on crystallizable polybutadiene; and (4) to use the preferred orientation patterns obtained from some of these polymers for structural evaluations. To accomplish these objectives, x-ray patterns were obtained at several temperatures of some unstretched and stretched polybutadiene polymers, butadiene-styrene copolymers, and a vulcanized and compounded polybutadiene. The polybutadienes were prepared by emulsion polymerizations at 55°, 40°, 30°, 20°, 5°, −10° and −20° C. Since the −20° C polybutadiene showed the most marked crystallization patterns, the effects of compounding and of styrene addition were studied, using polymers prepared at this temperature for comparison. Three butadiene-styrene copolymers containing, respectively, 10, 20, and 30 per cent styrene in the monomer charge and one vulcanized polybutadiene compounded with Wyex carbon black were studied.

Microtubule nucleation sequence studied by time-resolved x-ray scattering and electron microscopy

1983 ◽  
Vol 41 ◽  
pp. 766-767
Author(s):  
Eva-Maria Mandelkow ◽  
Eckhard Mandelkow ◽  
Joan Bordas
Keyword(s):  
Electron Microscopy ◽  
Dynamic Equilibrium ◽  
Time Resolved ◽  
X Ray ◽  
Additional Information ◽  
X Ray Scattering ◽  
Low Concentrations ◽  
Microtubule Growth ◽  
Ray Patterns ◽  
Ray Scattering

When a solution of microtubule protein is changed from non-polymerising to polymerising conditions (e.g. by temperature jump or mixing with GTP) there is a series of structural transitions preceding microtubule growth. These have been detected by time-resolved X-ray scattering using synchrotron radiation, and they may be classified into pre-nucleation and nucleation events. X-ray patterns are good indicators for the average behavior of the particles in solution, but they are difficult to interpret unless additional information on their structure is available. We therefore studied the assembly process by electron microscopy under conditions approaching those of the X-ray experiment. There are two difficulties in the EM approach: One is that the particles important for assembly are usually small and not very regular and therefore tend to be overlooked. Secondly EM specimens require low concentrations which favor disassembly of the particles one wants to observe since there is a dynamic equilibrium between polymers and subunits.

Sign in / Sign up

Export Citation Format

Share Document