Etude structurale d'un hydrate 10 Å instable de kaolinite

2000 ◽  
Vol 33 (4) ◽  
pp. 1075-1081 ◽  
Author(s):  
S. Jemai ◽  
A. Ben Haj Amara ◽  
J. Ben Brahim ◽  
A. Plançon
Keyword(s):  
Dimethyl Sulfoxide ◽  
Structural Characteristics ◽  
Ammonium Fluoride ◽  
Water Molecules ◽  
X Ray Diffraction ◽  
X Ray ◽  
Basal Distance

The treatment of KGa-1 kaolinite with dimethyl sulfoxide and ammonium fluoride heated at 383 K provides an unstable hydrated phase characterized by a 10 Å basal distance. When air-dried, this hydrate gives a dehydrated phase at 7.15 Å. The aim of this work is to determine the structural characteristics of this hydrate. The method used to characterize this hydrate is based on the comparison between experimental and calculated X-ray diffraction profiles. This study is achieved in two steps: the study of 00lreflections enabled the determination of the number of intercalated water molecules, their positions and the stacking mode along the normal to the (a,b) plane; and the study of thehklreflections withhand/ork≠ 0 enabled the determination of the stacking mode and the positions of water molecules in the (a,b) plane. The unstable hydrate is characterized by two water molecules per Al2Si2O5(OH)4unit situated atz1=z2= 7.57 Å. Two adjacent layers are translated with respect to each other withTI= −0.155a+ 0.13b+ 10n.

Etude structurale par diffraction des RX et spectroscopie IR des hydrates 10 et 8.4 Å de kaolinite

1999 ◽  
Vol 32 (5) ◽  
pp. 968-976 ◽  
Author(s):  
S. Jemai ◽  
A. Ben Haj Amara ◽  
J. Ben Brahim ◽  
A. Plançon
Keyword(s):  
Water Molecule ◽  
Octahedral Site ◽  
Ammonium Fluoride ◽  
Water Molecules ◽  
X Ray Diffraction ◽  
Tetrahedral Sheet ◽  
X Ray ◽  
Octahedral Sites ◽  
Sheet Structure

Two hydrated kaolinites, characterized by 10 and 8.4 Å basal distances, were synthesized by treating the kaolinite KGa-1 with dimethyl sulfoxide (DMSO) and ammonium fluoride (NH4F). The X-ray diffraction study was based on a comparison between the experimental and calculated profiles. This study was conducted in two steps: firstly, the study of the 00lreflections enabled the determination of the stacking mode alongc*, the number of water molecules and their positions along the normal to the plane of the sheet structure; secondly, the study of thehkbands, withhand/ork≠ 0, enabled the determination of the stacking mode and the positions of the water molecules in the (a,b) plane. The 10 Å hydrated kaolinite is characterized by two water molecules per Al2Si2O5(OH)4unit, situated at 3 and 3.4 Å from the hydroxyl surface, over the octahedral sites. Two adjacent layers are translated with respect to each other, withT11= −0.38a− 0.37b+ 10n. The 8.4 Å hydrated kaolinite is characterized by one water molecule per Al2Si2O5(OH)4unit, situated at 2.4 Å from the hydroxyl surface and inserted between the vacant octahedral site and the ditrigonal cavity of the tetrahedral sheet. The corresponding interlayer shift isT11= −0.355a+ 0.35b+ 8.4n.

Étude par Diffraction X des Modes d'Empilement de la Nacrite Hydratée et Deshydratée

1998 ◽  
Vol 31 (5) ◽  
pp. 654-662 ◽  
Author(s):  
A. Ben Haj Amara ◽  
J. Ben Brahim ◽  
A. Plançon ◽  
H. Ben Rhaiem
Keyword(s):  
Water Molecule ◽  
Octahedral Site ◽  
Structural Characteristics ◽  
X Ray Diffraction ◽  
Natural Mineral ◽  
Tetrahedral Sheet ◽  
X Ray ◽  
Basal Distance ◽  
Interlamellar Space

X-ray diffraction based on the comparison of experimental and calculated powder profiles enabled the determination of the structural characteristics of hydrated and dehydrated Tunisian nacrite. Using the concept describing the structure of natural nacrite, the stacking mode of the layers in the hydrated and dehydrated nacrite has been determined. The hydrate is characterized by an 8.42 Å basal distance; one water molecule per Si2Al2O5(OH)4is intercalated in the interlamellar space, located above the vacant octahedral site of the layer atz= 6.5 Å and inserted inside the ditrigonal cavity of the tetrahedral sheet of the upper layer. The dehydrated nacrite obtained by heating of the hydrate at 423 K has the same interlayer shiftt= −0.35aas the natural nacrite. Coherence domain sizes alongc^{\ast} and in theabplane are the same as those in the hydrate but different from those of the natural mineral. After dehydration, 5% of the layers had an interlayer shift similar to that obtained from the hydrate.

scholarly journals Calcioferrite with composition (Ca3.94Sr0.06)Mg1.01(Fe2.93Al1.07)(PO4)6(OH)4·12H2O

2014 ◽  
Vol 70 (3) ◽  
pp. i16-i17
Author(s):  
Barbara Lafuente ◽  
Robert T. Downs ◽  
Hexiong Yang ◽  
Robert A. Jenkins
Keyword(s):  
Single Crystal ◽  
Water Molecules ◽  
Site Symmetry ◽  
Natural Sample ◽  
X Ray Diffraction ◽  
X Ray ◽  
Hydrogen Bonding Interactions ◽  
Small Crystals ◽  
Hydrated Calcium

Calcioferrite, ideally Ca4MgFe3+4(PO4)6(OH)4·12H2O (tetracalcium magnesium tetrairon(III) hexakis-phosphate tetrahydroxide dodecahydrate), is a member of the calcioferrite group of hydrated calcium phosphate minerals with the general formula Ca4AB4(PO4)6(OH)4·12H2O, whereA= Mg, Fe2+, Mn2+andB= Al, Fe3+. Calcioferrite and the other three known members of the group, montgomeryite (A= Mg,B= Al), kingsmountite (A= Fe2+,B= Al), and zodacite (A= Mn2+,B= Fe3+), usually occur as very small crystals, making their structure refinements by conventional single-crystal X-ray diffraction challenging. This study presents the first structure determination of calcioferrite with composition (Ca3.94Sr0.06)Mg1.01(Fe2.93Al1.07)(PO4)6(OH)4·12H2O based on single-crystal X-ray diffraction data collected from a natural sample from the Moculta quarry in Angaston, Australia. Calcioferrite is isostructural with montgomeryite, the only member of the group with a reported structure. The calcioferrite structure is characterized by (Fe/Al)O6octahedra (site symmetries 2 and -1) sharing corners (OH) to form chains running parallel to [101]. These chains are linked together by PO4tetrahedra (site symmetries 2 and 1), forming [(Fe/Al)3(PO4)3(OH)2] layers stacking along [010], which are connected by (Ca/Sr)2+cations (site symmetry 2) and Mg2+cations (site symmetry 2; half-occupation). Hydrogen-bonding interactions involving the water molecules (one of which is equally disordered over two positions) and OH function are also present between these layers. The relatively weaker bonds between the layers account for the cleavage of the mineral parallel to (010).

scholarly journals DETERMINATION OF PIROCARBON MATRIX CHARACTERISTICS IN CARBON/CARBON COMPOSITES

2021 ◽  
Vol 64 (5) ◽  
pp. 44-49
Author(s):  
Maria V. Papkova ◽  
Sergei V. Tashchilov ◽  
Ilya V. Magnitsky ◽  
Alexander E. Dvoretsky
Keyword(s):  
Structural Characteristics ◽  
Three Dimensional ◽  
Carbon Composites ◽  
X Ray Diffraction ◽  
X Ray ◽  
Extinction Angle ◽  
Parallel Layer ◽  
The Matrix ◽  
Average Size

One of the methods of carbon/carbon composites (C/C composites) production is the deposition of a pyrocarbon (pyC) matrix in a porous preform. The investigation of the pyC matrix characteristics is based on the optical anisotropy with determination of the extinction angle Ae and X-ray diffraction determination of the interplanar spacing d002, crystallite size in the direction of stacking of graphite layers Lc and average size of graphite planes parallel layer in crystallites La. In this study, three previously produced by the thermal gradient method with different parameters specimens of C/C composites were investigated by optical microscopy and X-ray diffraction methods. The studied specimens have a different type of a texture and different structural characteristics of the pyC matrix. Extinction angle Ae for specimen 1, specimen 2 and 3 was 5°, 19° and 41°, respectively. The range of the extinction angle for the pyC matrix is wider than that presented in literature. And according to the classification of pyC the matrix of specimen 1, specimen 2 and 3 is dark laminar pyC, rough laminar pyC and highly textured pyC. For specimen 2 the largest d002 equal to 0.3476 nm was observed. The lowest degree of three-dimensional ordering relative other specimens was for the specimen 2 with rough laminar pyC matrix. The highest degree of three-dimensional ordering was for the specimen 3 with highly textured pyC matrix. However, there is no direct relationship between the textural and structural characteristics of the pyC matrix. Therefore, the study of the pyC matrix should be based on optical and X-ray diffraction methods.

scholarly journals X-RAY DIFFRACTION METHOD FOR DETERMINATION OF SIZES AND STRUCTURAL CHARACTERISTICS OF NANOGRAPHITES IN ACTIVATED CARBON MATERIALS

2018 ◽  
Vol 59 (9) ◽  
pp. 62
Author(s):  
Nikita S. Saenko ◽  
Albert M. Ziatdinov
Keyword(s):  
Activated Carbon ◽  
Carbon Fibers ◽  
Structural Characteristics ◽  
Diffraction Method ◽  
X Ray Diffraction ◽  
X Ray ◽  
X Ray Scattering ◽  
Nanocrystalline Graphite ◽  
Ray Scattering

The method for determination of sizes and structural characteristics of nanographites in activated carbon fibers (ACFs) by analyzing their experimental X-ray diffraction profiles has been developed in the paper. It uses the curves of X‑ray scattering calculated for the set of nanographites consisting of benzene- and phenalene-bazed nanographenes of various sizes, which interatomic and interlayer distances depend on the number of atoms in layer. The developed method can be also applied to analysis of the X-ray diffraction profiles of other nanocrystalline graphite structures. The data acquired by the method agree with results of Raman spectroscopy and small-angle X-ray scattering on ACFs structure motives.

Experimental determination of electrostatic properties of Na–X zeolite from high resolution X-ray diffraction

2014 ◽  
Vol 16 (24) ◽  
pp. 12228-12236 ◽  
Author(s):  
F. F. Porcher ◽  
M. Souhassou ◽  
C. E. P. Lecomte
Keyword(s):  
High Resolution ◽  
Water Molecules ◽  
X Ray Diffraction ◽  
Cation Site ◽  
X Ray ◽  
X Zeolite ◽  
Adsorption Of Water ◽  
Zeolite P ◽  
Resolution Single

High resolution single crystal X-ray diffraction is used to obtain the electron density and atomic charges in Na–X zeolite. The Coulomb potential and interaction energies are calculated for a given Na+ distribution and are discussed in connection with cation site affinities and adsorption of water molecules in the zeolite.

The structure determination of a binuclear copper(II) complex of aTetra-Schiff base macrocycle

1976 ◽  
Vol 29 (3) ◽  
pp. 515 ◽  
Author(s):  
BF Hoskins ◽  
NJ McLeod ◽  
HA Schaap
Keyword(s):  
Schiff Base ◽  
Least Squares Method ◽  
Condensation Product ◽  
Water Molecules ◽  
X Ray Diffraction ◽  
Binuclear Copper ◽  
Apical Position ◽  
X Ray ◽  
Space Groups

The structure of the complex Lcu2Cl2,6H2O (where LH2 is the tetra-Schiff base macrocycle formed as the condensation product of propane-1,3-diamine and 2-hydroxy-5-methylisophthal- aldehyde in the mole ratio 2: 2) was determined by single-crystal X-ray diffraction methods. The crystals are monoclinic, a 7.720(1), b 17.079(1), c 11.171(1) � and β 91.50(1)�, with two molecules per unit cell. It has proved difficult to resolve the ambiguity between the three possible space groups (C2, Cm, and C2/m) and the initial model has been refined in each using a full-matrix least-squares method. The space group C2/m seems the most likely and the structure is described in it; R 0.049 for the 1369 independent reflections measured using counter methods. The structure analysis has confirmed the anticipated cyclic structure of the ligand with the two copper atoms held together in a binuclear arrangement by the planar N4O2 donor set; the Cu.. .Cu distance is 3.133(1)�. Each copper atom has a distorted square-pyramidal environment with the apical position of each being occupied by a chlorine atom; the two chlorine atoms are on the opposite sides of the macrocycle. The water molecules are not coordinated, but form an extensive system of hydrogen bonding throughout the crystal with discrete binuclear molecules of the LCu2Cl2 complex.

X-ray diffraction studies on the arrangement of water molecules in a smectite. I.Homogeneous two-water-layer Na-beidellite

1983 ◽  
Vol 16 (2) ◽  
pp. 264-269 ◽  
Author(s):  
J. B. Brahim ◽  
N. Armagˇan ◽  
G. Besson ◽  
C. Tchoubar
Keyword(s):  
Size Distribution ◽  
Critical Analysis ◽  
Structural Characteristics ◽  
Water Layer ◽  
Water Molecules ◽  
X Ray Diffraction ◽  
X Ray ◽  
Water Layers ◽  
Diffraction Patterns ◽  
Indirect Analysis

A method of indirect analysis of X-ray diffraction patterns of homogeneous hydrated microcrystalline silicates is introduced. This method is applied to a sodium beidellite of Rupsroth, Bavaria, Germany, hydrated with two water layers to determine all its structural characteristics: namely, the average dimension and size distribution of coherent domains, stacking mode of the layers along the c* direction, levels and number per unit cell of water molecules. A critical analysis on the `concept of homogeneity' of hydrates and a discussion on the conditions of its application to lamellar microcrystalline silicates with a few numbers of layers are made.

Study of the structural evolution of the 10 Å unstable hydrate of kaolinite during dehydration by XRD and SAXS

2003 ◽  
Vol 36 (3) ◽  
pp. 898-905 ◽  
Author(s):  
S. Naamen ◽  
S. Jemai ◽  
H. Ben Rhaiem ◽  
A. Ben Haj Amara
Keyword(s):  
Structural Evolution ◽  
Second Phase ◽  
X Ray Diffraction ◽  
X Ray ◽  
X Ray Scattering ◽  
Number Of Layers ◽  
Before And After ◽  
Basal Distance ◽  
Clay Layers

This work deals with understanding the structural evolution of the dehydration of the 10 Å unstable hydrate of kaolinite. The method used to characterize this hydrate is based on a comparison between the experimental and the calculated X-ray diffraction profiles. The study was achieved in two steps: (i) the quantitative interpretation of 00lreflections enabled the determination of the number of intercalated water molecules, their positions and the stacking mode of the clay layers along the normal to the (a,b) plane; and (ii) the study of thehklreflections withhand/ork≠ 0 enabled the characterization of the structural evolution in the (a,b) plane of the hydrated kaolinite during dehydration. The hydrate is made up of two demixed phases. The first phase is homogenous and corresponds to a 10 Å hydrated kaolinite, characterized by two H2O molecules per Si2Al2O5(OH)4situated atZ= 7.1 Å from the surface oxygen. Two adjacent layers are translated with respect to each other, withT1= −0.155a+ 0.13b+ 10n. The abundance of this phase decreases during dehydration. The second phase is made up of 10 Å hydrated layers, 8.4 Å hydrated layers and 7.2 Å dehydrated kaolinite layers, randomly interstratified. The abundance of this second phase increases during dehydration. The corresponding interlayer shifts are respectivelyT21= −0.155a+ 0.13b+ 10nfor the 10 Å hydrated layer,T22= −0.355a+ 0.35b+ 8.4nfor the 8.4 Å hydrate andT23= −0.36a− 0.024b+ 7.2nfor the natural kaolinite. In addition to these interlayer shifts, some translation defects are introduced, such as −b/3, which exists in the initial kaolinite. The interpretation of the small-angle X-ray scattering (SAXS) patterns showed that the particle thickness remained the same before and after the hydration treatments, whereas X-ray diffraction (XRD) results indicated that the hydration of kaolinite caused a decrease of the mean number of layers \bar m per crystallite from 40 to 20 layers. This decrease is related to the presence of H2O molecules situated within the micropores in the kaolinite particles that leave their interlayer space after heating at 573 K. The resulting dehydrated compound is characterized by the same basal distance and mean number of layers \bar m per crystallite as for the natural kaolinite, while the proportion of the defects, such as the −b/3 translation, increases in the completely dehydrated compound (45%) compared with the natural kaolinite (10%).

scholarly journals Evaluation of models determined by neutron diffraction and proposed improvements to their validation and deposition

2018 ◽  
Vol 74 (8) ◽  
pp. 800-813 ◽  
Author(s):  
Dorothee Liebschner ◽  
Pavel V. Afonine ◽  
Nigel W. Moriarty ◽  
Paul Langan ◽  
Paul D. Adams
Keyword(s):  
Neutron Diffraction ◽  
Current Model ◽  
Data Bank ◽  
Water Molecules ◽  
Macromolecular Crystallography ◽  
X Ray Diffraction ◽  
X Ray ◽  
Manual Intervention ◽  
Data Files

The Protein Data Bank (PDB) contains a growing number of models that have been determined using neutron diffraction or a hybrid method that combines X-ray and neutron diffraction. The advantage of neutron diffraction experiments is that the positions of all atoms can be determined, including H atoms, which are hardly detectable by X-ray diffraction. This allows the determination of protonation states and the assignment of H atoms to water molecules. Because neutrons are scattered differently by hydrogen and its isotope deuterium, neutron diffraction in combination with H/D exchange can provide information on accessibility, dynamics and chemical lability. In this study, the deposited data, models and model-to-data fit for all PDB entries that used neutron diffraction as the source of experimental data have been analysed. In many cases, the reported R work and R free values were not reproducible. In such cases, the model and data files were analysed to identify the reasons for this mismatch. The issues responsible for the discrepancies are summarized and explained. The analysis unveiled limitations to the annotation, deposition and validation of models and data, and a lack of community-wide accepted standards for the description of neutron models and data, as well as deficiencies in current model refinement tools. Most of the issues identified concern the handling of H atoms. Since the primary use of neutron macromolecular crystallography is to locate and directly visualize H atoms, it is important to address these issues, so that the deposited neutron models allow the retrieval of the maximum amount of information with the smallest effort of manual intervention. A path forward to improving the annotation, validation and deposition of neutron models and hybrid X-ray and neutron models is suggested.

Sign in / Sign up

Export Citation Format

Share Document