Characterization of hydroxyapatite by electron microscopy.

The obtention of hydroxyapatite (HAp) is reported using brushite (CaHPO4.2H2O) and the skeleton of a starfish (Mellita eduardobarrosoi sp. nov.), primarily composed of magnesian calcite ((Ca,Mg)CO3) as precursors. Stoichiometric amounts of both were reacted under hydrothermal conditions: a pressure of 5.8 MPa and a temperature of 200 degrees C for 2, 4, 6, 8, 10, and 20 h of reaction times. The samples obtained were characterized by means of scanning electron microscopy, X-ray diffraction, infrared spectroscopy, and transmission electron microscopy. Two defined populations of HAp fibers were found: A bundle of fibers 75 mum in length and 1-13 mum in diameter, and a second bundle of fibers 5 mum in length and less than 0.5 mum in diameter. Furthermore, an increase in HAp formation and a Ca/P ratio as a function of reaction time were observed. The growth mechanism of HAp is also discussed.     

Characterization of palladium nanoparticles by using X-ray reflectivity, EXAFS, and electron microscopy

We compared the characteristics of dodecanethiolate palladium nanoparticles synthesized by two different techniques, a one-phase method and a two-phase method. From transmission electron microscopy (TEM), we determined that the particle sizes were 46 +/- 10 angstroms and 20 +/- 5 angstroms for the one- and two-phase particles, respectively. Electron diffraction confirmed that their structure was face-centered cubic (fcc). The lattice constant a0 was 3.98 +/- 0.01 angstroms and 3.90 +/- 0.01 angstroms for the one- and two-phase particles, respectively. High-resolution TEM (HRTEM) showed that the one-phase particles had an ordered core surrounded by a disordered shell structure, while the two-phase particles appeared to be crystalline throughout. The particles were also analyzed with extended X-ray absorption fine structure (EXAFS). A cuboctahedral fcc model was used to fit the data, which implied particle sizes of less than 10 angstroms for both the one- and two-phase particles. The discrepancy between the two techniques was attributed to the presence of a disordered phase, which we presumed was composed of Pd-S compounds. Compared with the bulk palladium, lattice expansion was observed in both one- and two-phase particles by electron diffraction, HRTEM, and EXAFS. At the air/water interface, a uniform film that produced surface pressure/area isotherms could only be obtained from the two-phase particles. The one-phase particles did not wet the water surface. X-ray reflectivity data indicated that the Langmuir monolayer of the two-phase particles was only 13 angstroms thick. TEM revealed the diameter of the particles in this layer to be 23 angstroms; hence the particles assumed an oblate structure after spreading. EXAFS examination of a stack of 750 Langmuir monolayers indicated far fewer Pd-S compounds, which may have dissolved in the water. The data were consistent with a model of a monolayer of truncated cuboctahedron Pd particles that were 7 angstroms thick and 19 angstroms in diameter.     

X-ray CT microtomography and mechanical response of foamed polysiloxane elastomers

3D X-ray computer microtomography (CT) experiments have been performed to assess the microstructure of scaled cellular polysiloxane elastomers and to predict how key morphological features alter as a function of compressive loading. In the work reported here, full scale (nominally 600 μm pore size) and half scale (nominally 300 μm pore size) polydimethylsiloxane foams (M97) were prepared using extractable urea particles, and tested. CT test methodology was developed to image foam microstructure at different levels of compression. 1D magnetic resonance imaging (MRI) experiments have also been performed on full scale foams for baseline characterisation. Material porosity, bulk density and dynamic mechanical analysis (DMA) stress/strain responses as a function of compression were recorded. Our results show that undesirable engineering stress responses are evident when the material microstructure (cell size and shape) is non-uniform and complex. This is particularly evident when non-spherical urea particles are used, leading to undesirable scaled foam microstructures with mechanical responses that do not match that shown by ‘full scale’ versions. Through the use of X-ray CT and MRI, our studies have provided insights into the link between manufacturing, polymer architecture (cell size/shape) and mechanical response of scaled M97 cellular materials. The data collected will support materials FEA (finite element model) code development activities, as well as help identify how the material architecture can be modified to achieve more controlled and uniform mechanical responses.     

Characterization of Langmuir-Blodgett organoclay films using X-ray reflectivity and atomic force microscopy

Monolayers of organoclay platelets were formed at the air/water interface using the Langmuir technique and were then investigated either by in situ or lifted onto Si wafers and studied ex situ, using X-ray reflectivity (XR) methods. The XR data showed that the surfactant molecules on the clay platelets formed a dense, self-assembled monolayer where the molecules were tilted at an angle of 35 degrees +/-6 degrees from the normal to the dry clay surface. The surfactant layers only covered a fraction of the clay platelet surface area, where the fractional surface coverage for the three clays studied (C6A, C15A, and C20A) was found to be 0.90, 0.86, and 0.73, respectively. These values were significantly higher than those estimated from the cation exchange capacity (CEC) values. Rather than being uniformly distributed, the surfactant was clustered in patchy regions, indicating that the surface of the clay platelets had both polar and non-polar segments. This heterogeneity confirmed the hypothesis which was previously invoked to explain the distribution of the clay platelets in melt mixed homopolymer and polymer blend nanocomposites.     

Identification of organic compounds by microscopy and X-ray diffractometry

Summary Primary and secondary crystallographic constants can be utilized conveniently for identifications of crystalline organic and inorganic materials by microscopy and X-ray diffractometry. Several specific properties can be measured under the petrographical microscope, including optic axial angle, character, dispersion, and in addition, refractive index directions can be established. The d spacings and their intensities as determined with the X-ray diffractometer serve to identify crystalline materials. The two instruments should be considered as supplementary tools for identifying crystals.Both instruments supply a means for identification and semiquantitative analysis of mixed crystal systems. Data are presented for the systems: acetic-propionic p-bromoanilides and acet-propion-2.4-dinitro-phenylhydrazones.

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Zusammenfassung Primäre und sekundäre kristallographische Konstanten können zur Identifizierung kristallisierter organischer und anorganischer Stoffe auf mikroskopischem Wege und durch Röntgendiffraktometrie gut herangezogen werden. Einzelne spezifische Eigenschaften können unter dem petrographischen Mikroskop gemessen werden, so der optische Achsenwinkel, der Charakter, die Dispersion. Außerdem kann man Angaben über den Brechungsindex erhalten. Die mit dem Röntgendiffraktometer bestimmten Netzebenenabstände d und deren Intensitäten dienen zur Identifizierung kristallisierter Stoffe. Die beiden Instrumente sind als Hilfsmittel zur Erkennung von Kristallen anzusehen.Sie bieten die Möglichkeit zur Identifizierung und halbquantitativen Analyse von Mischkristallsystemen. Daten für die Systeme Essigsäure-Propionsäure-p-Bromanilid und Acetaldehyd-Propionaldehyd-2,4-Dinitrophenylhydrazon werden mitgeteilt.

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Résumé Les constantes cristallographiques primaires et secondaires sont utilisables pour l'identification de composés cristallins organiques et minéraux par microscopie et diffractométrie de rayons X. Il est possible de mesurer diverses propriétés spécifiques sous le microscope pétrographique, savoir: l'angle des axes optiques, le caractère et la dispersion optiques. Il est en outre possible de déterminer les directions des indices de réfraction primaires. Les espacements «d» et leurs intensités déterminés par le diffractomètre à rayons X permettent d'identifier les substances cristallines. Les deux instruments doivent être considérés comme complémentaires pour l'identification de cristaux. Chacun d'entre eux fournit un moyen d'identification et d'analyse semi quantitative des systèmes de cristaux mixtes. On rend compte de résultats obtenus pour les systèmes: p-bromoanilides acétique et propionique ainsi que 2, 4-dinitro phénylhydrazones de l'acétaldéhyde et du propionaldéhyde.

     

Quantitative characterization of bamboo cortex structure based on X-ray microtomography

Cellulose - Bamboo is a natural fiber composite with layered structure. Millions of years of evolution have endowed bamboo with the most effective structure in nature. The ingenious microstructure...     

Characterization and discrimination of pollen by Raman microscopy

The chemical characterization and discrimination of allergy-relevant pollen (common ragweed (Ambrosia artemisiifolia), white birch (Betula pendula), English oak (Quercus robur), and European linden (Tilia cordata)) has been studied by Raman microscopy. Spectra were obtained at different excitation wavelengths (514, 633, and 780 nm) and various methods were examined to minimize the strong fluorescence background. The use of a He–Ne laser (633 nm) for excitation yields high-quality single pollen Raman spectra, which contain multiple bands due to pollen components such as carotenoids, proteins, nucleic acids, carbohydrates, and lipids. Multivariate classification, i.e. principal component analysis (PCA) and hierarchical cluster analysis, demonstrated the validity of the approach for discrimination between different pollen species.     

Characterization of sugarcane bagasse by autofluorescence microscopy

The spatial distribution of chemical compounds in sugarcane bagasse is an important issue in its use as a raw material for second generation ethanol production from cellulose hydrolysis. Lignocellulosic materials including whole bagasse, fiber, pith, and respective samples obtained after chemical bleaching were investigated using confocal fluorescence microscopy and spectroscopy with one and two-photon excitation. Autofluorescence from unbleached samples revealed that emission from fiber walls containing the lignin fraction was longitudinally oriented. After bleaching treatment, the oriented emission was partially disrupted. Autofluorescence from bleached samples with a residual lignin content of about 1 % was ascribed to improved dispersion of remaining fluorophores throughout the samples inducing a concomitant reduction of fluorescence self-quenching in the samples. The combination of autofluorescence images with spectral emission and lifetime measurements provides a tool for microscopic characterization of natural bagasse samples. Moreover, the technique allows monitoring bleaching processes related to lignin removal.     

Quantitative comparison of X-ray fluorescence microtomography setups: Standard and confocal collimator apparatus

Recently, there has been a renewed interest for fluorescence spectroscopy, as provided by modern setups which allow 2D and 3D imaging of elemental distributions. Two directions are currently under development: the SR-based fluorescence tomography in polar scanning geometry, provided by the new generation of X-ray microprobes and the confocal scanning geometry, which can be fielded in both SR and laboratory environments. The new probes bring forth a new age in fluorescence spectrometry: high resolution, high intensity and high sensitivity which allow 3D elemental mapping of volumes. The major task now is the development of these complex tools into fully quantitative probes, reproducible and straightforward for general use. In this work we analyze two X-ray fluorescence microtomography techniques: an apparatus tomography using a confocal collimator for the data collection and a standard first generation Computed Tomography (CT) in the parallel scanning scheme. We calculate the deposited dose (amount of energy deposited and distributed in the sample during the data collection time) and find the conditions for the choice of the tomography scheme.     

X-ray microtomography studies of nascent polyolefin particles polymerized over magnesium chloride-supported catalysts

Drastic changes occur during the initial stages of the α-olefin polymerization over heterogeneous catalysts. Fragmentation of the support takes place as polymer is formed at the active sites within the voids of the support/catalyst. Magnesium chloride-supported titanium catalyst/polymer particles have been analyzed employing high-resolution computed microtomography (CMT) using synchrotron radiation at Brookhaven National Laboratory. The changes in morphology, the spatial distribution of the support/catalyst fragments, porosity, and polymer distribution in single growing polypropylene and polyethylene particles have been studied. These studies documented considerable macroporosity ( > 2 μm in size) within the growing catalyst/support/polymer particles. The largest pores may be due to agglomeration of smaller subparticles. Our results confirm that the initial fragmentation of the support proceeds readily and uniformly to yield a multi-grain growth of subparticle agglomerates. The support/catalyst fragments appear to be distributed relatively uniformly within the growing polymer particle. The surface of the subparticle agglomerates is accessible through the void-space between growing catalyst/particle grains. This may facilitate monomer transport to the activate sites through the polymer/catalyst particles. © 1993 John Wiley & Sons, Inc.     

Characterization of nanomaterials in food by electron microscopy

Engineered nanomaterials (ENMs) are increasingly being used in the food industry. In order to assess the efficacy and the risks of these materials, it is essential to have access to methods that not only detect the nanomaterials, but also provide information on the characteristics of the materials (e.g., size and shape).This review presents an overview of electron microscopy (EM)-based methods that have been, or have the potential to be, applied to imaging ENMs in foodstuffs. We provide an overview of approaches to sample preparation, including drying, chemical treatment, fixation and cryogenic methods. We then describe standard and non-standard EM-based approaches that are available for imaging prepared samples. Finally, we present a strategy for selecting the most appropriate method for a particular foodstuff.     

Interaction of human plasma fibrinogen with commercially pure titanium as studied with atomic force microscopy and X-ray photoelectron spectroscopy

The surface of a biomaterial interacts with the body fluid upon implantation in the human body. The biocompatibility of a material is strongly influenced by the adsorption of proteins onto the surface. Titanium is frequently used as a biomaterial for implants in orthopedics and cardiovascular devices. Understanding the biocompatibility is very important to improve implants. The surface chemistry of an implant material and its influence on the interaction with body fluid is crucial in that perspective. The main goal of this study was to investigate the conformation of human plasma fibrinogen (HPF) adsorbed on commercially pure titanium (CP Ti) on a molecular level by means of ex situ atomic force microscopy (AFM). With X-ray photoelectron spectroscopy combined with argon ion beam depth profiling, it was shown that the oxide layer present at the surface was mainly composed of TiO2, with a small percentage of Ti2O3. Ex situ AFM imaging showed the conformation of HPF on CP Ti. Single molecules and aggregates of fibrinogen were observed. The trinodular structure of single HPF molecules (two spherical D domains at the distal ends of the extended molecule and the central spherical E domain) adsorbed onto CP Ti was visualized. Aggregate formation through the connection of the D domains of the HPF molecules was observed on CP Ti. The alphaC domains of HPF were not visible on CP Ti. The ex situ AFM images indicated conformational changes of HPF upon adsorption onto CP Ti. The conformation of the adsorbed HPF molecules was different on mica and titanium. The difference in wettability between both substrates caused a larger spread of the protein on the CP Ti surface and thus resulted in a larger perturbation to the native structure of HPF as compared to mica.     

Characterization of elastomeric blends by atomic force microscopy

The bulk mechanical properties of a blend of elastomers are found to depend on the micro and nano scale morphology of the phases of the materials in the blend. In this study, we examine the phase morphology of blends of incompatible elastomers using Atomic Force Microscopy (AFM). Specifically, nanoindentation and Tapping Mode AFM (TMAFM) imaging techniques are used as experimental tools for mapping the composition of unfilled elastomeric blends. Depending on the composition of the blend, either co‐continuous or discontinuous domain/matrix morphology is observed. To identify the different components in bromobutyl (BIIR)/natural rubber (NR) blends, nanoscale indentation measurements were made on the observed phase‐separated regions. Results from force mode AFM and mechanical measurements of bulk NR and BIIR are used to assist in the interpretation of the TMAFM results for the BIIR/NR blends. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 492–503, 2006     

X-ray fluorescence analysis of titanium alloys

An X-ray solution method is proposed for determining major amounts of Mo, Sn and Zr in Ti alloys. The method utilizes adjacent elements in the periodic table as internal standards and has been successfully applied to levels of 3-10% Sn, 11-40% Mo and 6-20% Zr. The procedure involves three steps: dissolving the sample with a suitable acid mixture; adding the suitable internal standard at the concentration levels experimentally found to give optimum accuracy and precision; analysing the resulting solution mixture by X-ray fluorescence. Antimony was found to be a suitable internal standard for its adjacent element tin at a concentration ratio of 3:1 Sb:Sn. Niobium was successfully used for both its adjacent elements, molybdenum and zirconium, at 2:1 concentration ratios, Nb:Mo and Nb:Zr. A number of elements non-adjacent to tin, molybdenum and zirconium (i.e., copper, bromine, titanium, bismuth and tantalum) were experimentally found unsuitable as internal standards. Concentration factors of the internal standard and the adjacent elements sought were found to affect significantly the precision of analysis.     

Characterization of particulate matter from the Metropolitan Zone of the Valley of Mexico by scanning electron microscopy and energy dispersive X-ray analysis

Samples of total suspended particles (TSP) and PM10 respirable particles from five monitoring stations from the network system of the Metropolitan Zone of the Valley of Mexico (MZVM) were analyzed by scanning electron microscopy (SEM) and energy-dispersive X-ray microanalysis (EDX). Morphology and chemical composition allowed to identify six groups. The analysis shows that the most abundant groups are Al-Si-O, Fe, and metals, the first one in the TSP fraction. Trace metal, commonly associated to PM10 at a receptor location, will depend on the relative influences of local anthropogenic sources. Metal group was observed in all samples, mainly in Tlalnepantla and CES zones (28–46%).     

Characterization of small particles by micro X-ray fluorescence

Micro X-ray fluorescence was used to study both homogeneous and heterogeneous particle systems. Specifically, homogeneous glass microspheres and heterogeneous soil particle samples were prepared by both bulk and single particle sample preparation methods for evaluation by micro X-ray fluorescence. Single particle sample preparation methods allow for single particles from a collected sample to be isolated and individually presented to the micro X-ray fluorescence instrument for analysis. Various particle dispersion methods, including immobilization onto Tacky Dot™ slides, mounting onto double-sided sticky tape affixed to polypropylene film, or attachment to polypropylene film using 3M Artist's Adhesive, were used to separate the sample particles for single particle analysis. These methods were then compared and evaluated for their ability to disperse the particles into an array of single separated particles for optimal micro X-ray fluorescence characterization with minimal background contribution from the particle mounting surface. Bulk methods of particle sample preparation, which included pellet preparation and aerosol impaction, used a large quantity of collected single particles to make a single homogeneous specimen for presentation to the instrument for analysis. It was found that single particle elemental analysis by micro X-ray fluorescence can be performed if the particles are well separated (minimum separation distance = excitation source beam diameter) down to a particle mass of ∼ 0.04 ng and a mean particle diameter of ∼ 0.06 μm. Homogeneous particulates can be adequately characterized by micro X-ray fluorescence using either bulk or single particle analysis methods, with no loss of analytical information. Heterogeneous samples are much harder to characterize, and both single particle as well as bulk analyses must be performed on the sample to insure full elemental characterization by micro X-ray fluorescence.