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Crystal structure studies of cone snail shells by powder x-ray diffraction
Title
Crystal structure studies of cone snail shells by powder x-ray diffraction.
Creator
Khanal, Suraj P., Kathriarachchi, Vindu, Kyriacou, Andreas, Leventouri, Theodora, Graduate College
Date Issued
2011-04-08
PURL
http://purl.flvc.org/fcla/dt/3165805
Subject Headings
Snails, Shells, X-rays --Diffraction
Format
Document (PDF)
Rietveld analysis of powder diffraction data from a carbonate fluorapatite
Title
Rietveld analysis of powder diffraction data from a carbonate fluorapatite.
Creator
Moghaddam, Hadi Yazdani, Florida Atlantic University, Leventouri, Theodora
Abstract/Description
The mechanism of the carbonate substitution in the apatite structure is unraveled through analysis of Rietveld refinements of powder diffraction data from a single-phase natural carbonate fluorapatite (francolite). The refined values of the P-O bond lengths give a ~1.6% distortion of the phosphate tetrahedron caused by the carbonate substitution. The two bond lengths P-O1 and P-O2 and their corresponding angles on the mirror plane of the phosphate tetrahedron are mainly disturbed by this...
Show moreThe mechanism of the carbonate substitution in the apatite structure is unraveled through analysis of Rietveld refinements of powder diffraction data from a single-phase natural carbonate fluorapatite (francolite). The refined values of the P-O bond lengths give a ~1.6% distortion of the phosphate tetrahedron caused by the carbonate substitution. The two bond lengths P-O1 and P-O2 and their corresponding angles on the mirror plane of the phosphate tetrahedron are mainly disturbed by this substitution. A static positional disorder, mainly of the atoms at the tetrahedral sites, is revealed from the temperature dependence of the atomic anisotropic displacement parameters. A model for the mechanism of the carbonate entrance in the apatite structure is proposed.
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Date Issued
2000
PURL
http://purl.flvc.org/fcla/dt/12718
Subject Headings
Rietveld method, Apatite, X-rays--Diffraction
Format
Document (PDF)
X-ray and neutron diffraction studies of a silicon-substituted bioapatite
Title
X-ray and neutron diffraction studies of a silicon-substituted bioapatite.
Creator
Bunaciu, Camelia Emanuela., Florida Atlantic University, Leventouri, Theodora
Abstract/Description
The effect of silicon (Si) substitution on the structural properties of hydroxyapatite (HAp) is investigated with powder x-ray and neutron diffraction methods. For this purpose, a series of samples of pure hydroxyapatite and 0.4 wt % Si substituted hydroxyapatite were prepared following a precipitation method. Phase identification from x-ray powder diffraction measurements showed a single hydroxyapatite phase in all the samples. Powder neutron diffraction patterns from room temperature down...
Show moreThe effect of silicon (Si) substitution on the structural properties of hydroxyapatite (HAp) is investigated with powder x-ray and neutron diffraction methods. For this purpose, a series of samples of pure hydroxyapatite and 0.4 wt % Si substituted hydroxyapatite were prepared following a precipitation method. Phase identification from x-ray powder diffraction measurements showed a single hydroxyapatite phase in all the samples. Powder neutron diffraction patterns from room temperature down to 15 K are analyzed using the Rietveld method. The refined lattice constants, interatomic distances and isotropic atomic displacement parameters as a function of temperature for the pure and substituted hydroxyapatite are compared.
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Date Issued
2002
PURL
http://purl.flvc.org/fcla/dt/12879
Subject Headings
X-rays--Diffraction, Neutrons--Diffraction, Hydroxyapatite, Silicon
Format
Document (PDF)
X-ray and neutron powder diffraction studies of a biocompatible apatite
Title
X-ray and neutron powder diffraction studies of a biocompatible apatite.
Creator
Papanearchou, Nearchos I., Florida Atlantic University, Leventouri, Theodora
Abstract/Description
The problem of the carbonate substitution in bioapatites is studied via x-ray and neutron powder diffraction. A series of samples of low temperature carbonate hydroxyapatites with varying carbonate content was synthesized. The carbonate solubility in the hydroxyapatite system was studied with x-ray diffraction. The detailed crystal structure parameters of the synthetic carbonate hydroxyapatites were studied as a function of temperature and carbonate content from the analysis of Rietveld...
Show moreThe problem of the carbonate substitution in bioapatites is studied via x-ray and neutron powder diffraction. A series of samples of low temperature carbonate hydroxyapatites with varying carbonate content was synthesized. The carbonate solubility in the hydroxyapatite system was studied with x-ray diffraction. The detailed crystal structure parameters of the synthetic carbonate hydroxyapatites were studied as a function of temperature and carbonate content from the analysis of Rietveld refinements of neutron powder diffraction data. The phosphate tetrahedron is distorted by the carbonate substitution. The tetrahedral bond lengths P-O1 and P-O2 decrease by 2--3%. The atomic displacement parameters (ADPs) of the tetrahedral P, O1, O2, and O3 sites reveal a static disorder in the carbonate hydroxyapatite specimens. The results of the present comparison are consistent with the mechanism of carbonate substitution on the mirror plane of the phosphate tetrahedron.
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Date Issued
2000
PURL
http://purl.flvc.org/fcla/dt/12719
Subject Headings
Apatite, X-rays--Diffraction, Neutrons--Diffraction
Format
Document (PDF)
Simultaneous x-ray and neutron diffraction Rietveld refinements of nanophase Fe substituted hydroxyapatite
Title
Simultaneous x-ray and neutron diffraction Rietveld refinements of nanophase Fe substituted hydroxyapatite.
Creator
Kyriacou, Andreas, Charles E. Schmidt College of Science, Department of Physics
Abstract/Description
The effect of Fe substitution on the crystal structure of hydroxyapatite (HAp) is studied by applying simultaneous Rietveld refinements of powder x-ray and neutron diffraction patterns. Fe is one of the trace elements replacing Ca in HAp, which is the major mineral phase in bones and teeth. The morphology and magnetic properties of the Fe-HAp system are also studied by transmission electron microscopy and magnetization measurements. Samples of Ca(5-x)Fex(PO4)3OH with 0
Show moreThe effect of Fe substitution on the crystal structure of hydroxyapatite (HAp) is studied by applying simultaneous Rietveld refinements of powder x-ray and neutron diffraction patterns. Fe is one of the trace elements replacing Ca in HAp, which is the major mineral phase in bones and teeth. The morphology and magnetic properties of the Fe-HAp system are also studied by transmission electron microscopy and magnetization measurements. Samples of Ca(5-x)Fex(PO4)3OH with 0< x < 0.3 were prepared. Single phase HAp was identified in x-ray diffraction patterns (XRD) of samples with x < 0.1 inferring that the solubility limits are less than 0.1. Hematite ((Sa(B-Fe2O3) is identified as a secondary phase for higher Fe content. The refined parameters show that Fe is incorporated in the HAp structure by replacing Ca in the two crystallographic sites with a preference at the Ca2 site. This preference explains the small effect of the Fe substitution on the lattice constants of HAp. The overall decrease of the lattice constants is explained by the ionic vi size difference of Ca and Fe. The increasing trend of the a-lattice constant with x in the Fe substituted samples is attributed to a lattice relaxation caused by the substitution of the 4- and 6-fold Fe at the 7- and 9-fold Ca1 and Ca2 sites. This Ca local geometry reduction is indicated by a slight increase of the Ca1-O3 and Ca2-O1 bond lengths. Above the solubility limit x = 0.05, the Fe is partitioned in and out of the HAp structure with increasing nominal Fe content x. The excess Fe is oxidized to hematite. The TEM analysis and magnetic measurements support the results of the simultaneous Rietveld refinements. The TEM images show no significant effect on the morphology and size of the HAp particles upon Fe incorporation. The particles are either spheres or short rods of dimensions 20-60 nm. Hematite particles are imaged in the samples with x exceeding the solubility limit. These particles
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Date Issued
Florida Atlantic University
PURL
http://purl.flvc.org/FAU/3342204
Subject Headings
X-rays, Diffraction, Rietveld method, Nanostructured materials, Biomedical materials
Format
Document (PDF)