Structure of crystals in dental enamel and synthetic hydroxyapatite

1983 ◽  
Vol 41 ◽  
pp. 44-45
Author(s):  
J. D. McLean ◽  
D. G. A. Nelson
Keyword(s):  
Chemical Composition ◽  
Dental Enamel ◽  
Atomic Resolution ◽  
Starting Point ◽  
High Resolution Images ◽  
Synthetic Hydroxyapatite ◽  
Electron Microscopes ◽  
Lattice Resolution ◽  
Hydroxy Groups ◽  
Hydroxyapatite Crystals

Biological apatites in dental enamel, dentine and bone closely resemble, in chemical composition, the mineral hydroxyapatite with the unit cell Ca10(PO4)6(OH)2. Substitutions occur frequently, e.g. fluoride in place of hydroxy groups, carbonate for phosphate, and with other elements such as magnesium, zinc, strontium, and lead instead of calcium. The substituents are known to influence the response of the material to attack by dilute organic acids and are, therefore, of importance in the process of dental caries.The sub-lattice resolution available with some modern electron microscopes makes it feasible to attempt detection of the effect of substituted groups on the structure of the hydroxyapatite crystals. As a starting point in such a venture we have obtained high-resolution images of apatite crystals and used computer image calculation techniques to interpret the micrographs at near-atomic resolution.

Effect of strain on ADF-STEM high-resolution images

1991 ◽  
Vol 49 ◽  
pp. 666-667
Author(s):  
M. Kelly ◽  
D.M. Bird
Keyword(s):  
High Resolution ◽  
Strong Influence ◽  
Intensity Variation ◽  
Dark Field ◽  
Atomic Resolution ◽  
Strain Fields ◽  
High Resolution Image ◽  
Annular Dark Field ◽  
High Resolution Images ◽  
Interesting Alternative

It is well known that strain fields can have a strong influence on the details of HREM images. This, for example, can cause problems in the analysis of edge-on interfaces between lattice mismatched materials. An interesting alternative to conventional HREM imaging has recently been advanced by Pennycook and co-workers where the intensity variation in the annular dark field (ADF) detector is monitored as a STEM probe is scanned across the specimen. It is believed that the observed atomic-resolution contrast is correlated with the intensity of the STEM probe at the atomic sites and the way in which this varies as the probe moves from cell to cell. As well as providing a directly interpretable high-resolution image, there are reasons for believing that ADF-STEM images may be less suseptible to strain than conventional HREM. This is because HREM images arise from the interference of several diffracted beams, each of which is governed by all the excited Bloch waves in the crystal.

Transmission electron microscope studies in special ceramics

1978 ◽  
Vol 36 (1) ◽  
pp. 268-269
Author(s):  
A. Zangvil ◽  
L.J. Gauckler ◽  
G. Schneider ◽  
M. Rühle
Keyword(s):  
Phase Diagrams ◽  
Crystal Structures ◽  
Thin Foil ◽  
Limited Extent ◽  
Complex Materials ◽  
X Ray Diffraction ◽  
X Ray ◽  
Transmission Electron ◽  
Electron Microscopes ◽  
Lattice Resolution

The use of high temperature special ceramics which are usually complex materials based on oxides, nitrides, carbides and borides of silicon and aluminum, is critically dependent on their thermomechanical and other physical properties. The investigations of the phase diagrams, crystal structures and microstructural features are essential for better understanding of the macro-properties. Phase diagrams and crystal structures have been studied mainly by X-ray diffraction (XRD). Transmission electron microscopy (TEM) has contributed to this field to a very limited extent; it has been used more extensively in the study of microstructure, phase transformations and lattice defects. Often only TEM can give solutions to numerous problems in the above fields, since the various phases exist in extremely fine grains and subgrain structures; single crystals of appreciable size are often not available. Examples with some of our experimental results from two multicomponent systems are presented here. The standard ion thinning technique was used for the preparation of thin foil samples, which were then investigated with JEOL 200A and Siemens ELMISKOP 102 (for the lattice resolution work) electron microscopes.

Electron crystallographic determination of the 3-D structure of staurolite at atomic resolution

1991 ◽  
Vol 49 ◽  
pp. 540-541
Author(s):  
Kenneth H. Downing ◽  
Hu Meisheng ◽  
Hans-Rudolf Went ◽  
Michael A. O'Keefe
Keyword(s):  
High Resolution ◽  
Three Dimensional ◽  
High Resolution Electron Microscopy ◽  
Atomic Resolution ◽  
Dimensional Structure ◽  
Structure Information ◽  
Resolution Electron ◽  
Scattering Effects ◽  
High Resolution Images ◽  
Effects Of Radiation

With current advances in electron microscope design, high resolution electron microscopy has become routine, and point resolutions of better than 2Å have been obtained in images of many inorganic crystals. Although this resolution is sufficient to resolve interatomic spacings, interpretation generally requires comparison of experimental images with calculations. Since the images are two-dimensional representations of projections of the full three-dimensional structure, information is invariably lost in the overlapping images of atoms at various heights. The technique of electron crystallography, in which information from several views of a crystal is combined, has been developed to obtain three-dimensional information on proteins. The resolution in images of proteins is severely limited by effects of radiation damage. In principle, atomic-resolution, 3D reconstructions should be obtainable from specimens that are resistant to damage. The most serious problem would appear to be in obtaining high-resolution images from areas that are thin enough that dynamical scattering effects can be ignored.

Distortion in lattice-resolution scanned-probe microscope images

1993 ◽  
Vol 51 ◽  
pp. 522-523
Author(s):  
L. Fei
Keyword(s):  
Film Studies ◽  
Lattice Structure ◽  
Substrate Material ◽  
Repulsive Force ◽  
Instrument Calibration ◽  
Microscope Images ◽  
Probe Microscope ◽  
Electron Microscopes ◽  
Diffraction Patterns ◽  
Lattice Resolution

Scanned probe microscopes (SPM) have been widely used for studying the structure of a variety material surfaces and thin films. Interpretation of SPM images, however, remains a debatable subject at best. Unlike electron microscopes (EMs) where diffraction patterns and images regularly provide data on lattice spacings and angles within 1-2% and ∽1° accuracy, our experience indicates that lattice distances and angles in raw SPM images can be off by as much as 10% and ∽6°, respectively. Because SPM images can be affected by processes like the coupling between fast and slow scan direction, hysteresis of piezoelectric scanner, thermal drift, anisotropic tip and sample interaction, etc., the causes for such a large discrepancy maybe complex even though manufacturers suggest that the correction can be done through only instrument calibration.We show here that scanning repulsive force microscope (SFM or AFM) images of freshly cleaved mica, a substrate material used for thin film studies as well as for SFM instrument calibration, are distorted compared with the lattice structure expected for mica.

scholarly journals Traditional Applications of Tannin Rich Extracts Supported by Scientific Data: Chemical Composition, Bioavailability and Bioaccessibility

Foods ◽  
2021 ◽  
Vol 10 (2) ◽  
pp. 251
Author(s):  
Maria Fraga-Corral ◽  
Paz Otero ◽  
Lucia Cassani ◽  
Javier Echave ◽  
Paula Garcia-Oliveira ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Chemical Nature ◽  
Scientific Evidence ◽  
Scientific Data ◽  
Attractive Alternative ◽  
Chemical Profile ◽  
Traditional Use ◽  
Starting Point ◽  
Scientific Approach ◽  
Food Applications

Tannins are polyphenolic compounds historically utilized in textile and adhesive industries, but also in traditional human and animal medicines or foodstuffs. Since 20th-century, advances in analytical chemistry have allowed disclosure of the chemical nature of these molecules. The chemical profile of extracts obtained from previously selected species was investigated to try to establish a bridge between traditional background and scientific data. The study of the chemical composition of these extracts has permitted us to correlate the presence of tannins and other related molecules with the effectiveness of their apparent uses. The revision of traditional knowledge paired with scientific evidence may provide a supporting background on their use and the basis for developing innovative pharmacology and food applications based on formulations using natural sources of tannins. This traditional-scientific approach can result useful due to the raising consumers’ demand for natural products in markets, to which tannin-rich extracts may pose an attractive alternative. Therefore, it is of interest to back traditional applications with accurate data while meeting consumer’s acceptance. In this review, several species known to contain high amounts of tannins have been selected as a starting point to establish a correlation between their alleged traditional use, tannins content and composition and potential bioaccessibility.

scholarly journals Data Processing for Atomic Resolution Electron Energy Loss Spectroscopy

2012 ◽  
Vol 18 (4) ◽  
pp. 667-675 ◽  
Author(s):  
Paul Cueva ◽  
Robert Hovden ◽  
Julia A. Mundy ◽  
Huolin L. Xin ◽  
David A. Muller
Keyword(s):  
Energy Loss ◽  
Electron Energy ◽  
Electron Energy Loss Spectroscopy ◽  
Principal Component ◽  
Power Laws ◽  
Atomic Resolution ◽  
Background Error ◽  
Background Estimation ◽  
Electron Microscopes ◽  
Electron Energy Loss

AbstractThe high beam current and subangstrom resolution of aberration-corrected scanning transmission electron microscopes has enabled electron energy loss spectroscopy (EELS) mapping with atomic resolution. These spectral maps are often dose limited and spatially oversampled, leading to low counts/channel and are thus highly sensitive to errors in background estimation. However, by taking advantage of redundancy in the dataset map, one can improve background estimation and increase chemical sensitivity. We consider two such approaches—linear combination of power laws and local background averaging—that reduce background error and improve signal extraction. Principal component analysis (PCA) can also be used to analyze spectrum images, but the poor peak-to-background ratio in EELS can lead to serious artifacts if raw EELS data are PCA filtered. We identify common artifacts and discuss alternative approaches. These algorithms are implemented within the Cornell Spectrum Imager, an open source software package for spectroscopic analysis.

Research on causes of hot-tearing of AA3003 aluminum billet during DC casting process

2021 ◽  
Vol 95 ◽  
pp. 29-37
Author(s):  
Bach Dao Hong ◽  
◽  
Trung Trinh Van
Keyword(s):  
Chemical Composition ◽  
Casting Process ◽  
Direct Chill ◽  
Hot Tearing ◽  
Cast Aluminum ◽  
Allowable Limit ◽  
Chemical Composition Distribution ◽  
Electron Microscopes ◽  
Scanning Electron Microscopes ◽  
Direct Chill Casting Process

AA3003 aluminum alloy made from raw scrap materials that have the advantage of economical use, but hottearing often occurs in the product billets of the direct chill casting process. This study used ANOVA analysis method for determination of chemical composition of AA3003 aluminum billet products to show influence of chemical composition on hot-tearing ability. The evaluation of the microstructure and chemical composition distribution of the elements by optical and scanning electron microscopes combined with energy dispersive spectroscopy showed the existence of impurities such as Cu, Zn, Fe, Pb exceeding the allowable limit in aluminum billets, especially at grain boundary, which can be the main reason for the hot-tearing of cast aluminum billets.

STUDIES ON THE CHEMICAL COMPOSITION OF DENTAL ENAMEL DURING PROFESSIONAL BLEACHING WITH CARBAMIDE PEROXIDE COMPLEX

2021 ◽  
Vol 17 (75) ◽  
pp. 157
Author(s):  
I. M. Tkachenko ◽  
A. V. Lemeshko ◽  
N. N. Brailko ◽  
V. V. Kovalenko ◽  
M. A. Shundryk
Keyword(s):  
Chemical Composition ◽  
Dental Enamel ◽  
Carbamide Peroxide
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