1,720,997 research outputs found
Synthesis and Characterization of Hydroxapatite, Fluoride-Substituted Hydroxyapatite and Fluorapatite
No full textA study of structural memory effects in synthetic hydrotalcites using environmental SEM
No full textThe ‘memory’ effect in synthetic hydrotalcite was demonstrated using d(001) and d(002) peaks in XRD patterns. These peaks were present in the hydrotalcite before it was calcined, and after it was reformed, but not in the thermally activated hydrotalcite. SEM images were taken of the hydrotalcite, to show the layering and size of the crystals. Environmental SEM (ESEM) images were taken of the thermally activated hydrotalcite, and then manipulation of temperature and pressure allowed water to condense on the sample. The ESEM images show that the layered structure is reforming following exposure to water
Development of porous metal oxide thin films by co-evaporation
No full textThis paper focuses on the development of mixed metal oxide thin films and physical characterization of the films. The films were produced by co-evaporation of titanium oxide and tungsten oxide powders. This allowed the development of titanium oxide-tungsten oxide films as analyzed using XPS. Examination in the SEM and AFM showed that the films were nano-porous with the pore size and pore orientation varying as a function of the deposition angle. UV-Vis spectra of the films show an increase of transmittance with increasing deposition angle which is attributed to the structure and porosity of the films. Raman analysis indicated that the as-deposited films have broad and weak Raman characteristics, attributed to the nanocrystal nature of the films and the presence of defects, and the peak broadening deceases after annealing the film, as expected
Modification of Wyoming montmorillonite surfaces using a cationic surfactant
No full textSurfaces of Wyoming SWy-2-Na-montmorillonite were modified using ultrasonic and hydrothermal methods through the intercalation and adsorption of the cationic surfactant octadecyltrimethylammonium bromide (ODTMA). Changes in the surfaces and structure were characterized using X-Ray diffraction (XRD), thermal analysis (TG), and electron microscopy. The ultrasonic preparation method results in higher surfactant concentration within the montmorillonite interlayer when compared with the hydrothermal method. Three different molecular environments for surfactants within the surface modified montmorillonite are proposed based upon their different decomposition temperatures. Both XRD patterns and TEM images demonstrate that SWy-2-Na-montmorillonite contains superlayers. TEM images of organoclays prepared at high surfactant concentrations, show alternate basal spacings between neighbouring layers. SEM images show that modification with surfactant reduces the clay particle size and aggregation. Organoclays prepared at low surfactant concentration display curved flakes whereas they become flat with increasing intercalated surfactant. Novel surfactant modified montmorillonite results in the formation of new nanophases with the potential for the removal of organic impurities from aqueous media
The Distribution Of Ga in Ga-Pillared Montmorillonites: A Transmission Electron Microscopy And Microanalysis Study
No full textThe distribution of Ga in the interlayer of montmorillonite pillared with a Ga polyoxocation complex has been studied by transmission electron microscopy, energy-dispersive X-ray microanalysis (EDX), X-ray mapping and powder X-ray diffraction in combination with N adsorption- desorption. To view the clay layers by TEM, the pillared clay was embedded in Spurrs resin in a preferred orientation, and sectioned with an ultramicrotome perpendicular to the layers. Montmorillonites pillared with Al and AlGa complexes were also prepared for microanalysis in the TEM. The Ga X-ray peaks could be easily distinguished in the EDX spectra, allowing concentrations relative to other elements to be determined. Elemental X-ray maps for Ga, Si and Al in the Ga-pillared clay cross-sections demonstrated that the Ga was homogeneously distributed throughout the crystal thickness. Comparison of the analytical data with that from the Al and AlGa-pillared clays and the starting material suggested that an approximately constant amount of the intercalated species per amount of Si in the clay became incorporated into the structure in each case. Calculation of the formula for the Ga-pillared montmorillonite showed that 0.89 Ga is present per formula unit containing 8 (Si + Al), which is equivalent to 20 silicate rings, each consisting of 6 tetrahedra, for every Ga pillar. The actual dimension of the pillar, based results from the elemental analyses and XRD is 8.7 Å and the mean distance between the pillars is 44.3 Å, which is in good agreement with the average pore size of 39 Å obtained by N adsorption-desorption measurements. This study shows a new approach for obtaining more detailed information on the pillars in pillared clay by combining analytical data from X-ray microanalysis with measurements by XRD and N adsorption-desorption
Microstructure study of early in situ reaction of fly ash geopolymer observed by Environmental Scanning Electron Microscopy (ESEM)
No full textGoing Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Supramolecular selection in molecular alloys
No full textComplexes of the type \[M(phen)3](PF6)2 (M = Ni(II), Fe(II), Ru(II) and phen = 1,10-phenanthroline) were found to co-crystallize to form molecular alloys (solid solutions of molecules) with general formula \[MAxMB1–x(phen)3](PF6)2·0.5H2O in which the relative concentrations of the metal complexes in the crystals closely match those in the crystallizing solution. Consequently, the composition of the co-crystals can be accurately predicted and controlled by modulating the relative concentrations of the metal complexes in the crystallizing solution. Although they are chemically and structurally similar, complexes of the type \[M(bipy)3](PF6)2 (M = Ni(II), Fe(II), Ru(II) and bipy = 2,2′-bipyridine) display markedly different behavior upon co-crystallization. In this case, the resulting co-crystals of general formula \[MAxMB1–x(bipy)3](PF6)2 have relative concentrations of the constituent complexes that are markedly different from the relative concentrations of the complexes initially present in the crystallizing solution. For example, when the nickel and iron complexes are co-crystallized from a solution containing a 50:50 ratio of each, the result is the formation of some crystals with a higher proportion of iron and others with a higher proportion of nickel. The relative concentrations of the metal complexes in the crystals can vary from those in the crystallizing solutions by as much as 15%. This result was observed for a range of combinations of metal complexes (Ni/Fe, Ni/Ru, and Fe/Ru) and a range of starting concentrations in the crystallizing solutions (90:10 through to 10:90 in 10% increments). To explain this remarkable result, we introduce the concept of “supramolecular selection”, which is a process driven by molecular recognition that leads to the partially selective aggregation of like molecules during crystallization
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