Low temperature self-agglomeration of metallic Ag nanoparticles on silica sol–gel thin films
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A facile sol–gel synthesis for self-agglomeration of metallic silver nanoparticles, with fcc crystalline structure, on the silica surface in a low annealing temperature has been introduced. X-ray photoelectron spectroscopy (XPS) revealed initial agglomeration (∼30 times greater than the nominal concentration of Ag) of the nanoparticles on the surface of the dried film (100 °C) and also their oxidation as well as easy diffusion (with 0.08 eV required activation energy) into the porous silica thin films, by increasing the annealing temperature (200–400 °C). By raising the Ag concentration from 0.2 to 1.6 mol% in the sol, the average size of the Ag nanoparticles increased from ∼5 to 37 nm corresponding to a redshift of the optical plasmon resonance absorption peak from 404 to 467 nm. The high concentration of Ag (1.6 mol%) in the sol resulted in a rough surface containing compact nanoparticles. Using power spectral density analysis of the atomic force microscopy images, we have found that the highest contributions in the surface roughness of the dried silica films were caused by the particles ranging from ∼62 to 159 nm. The particles smaller than ∼39 nm did not show any detectable contributions in the surface roughness of the dried silica film. Based on the XPS analysis, a mechanism has also been proposed for the self-agglomeration of the Ag nanoparticles on the surface of the aqueous sol–gel silica thin films.In 2O 3 thin film is prepared by sol gel technology. We analyzed the relation between the prepared conditions and the resistance of the thin film. The thin film was researched by XPS,XRD, so we got the structure and composition of the thin film, and direct heat gas sensor was fabricated with this thin film. It has good sensitivity to C 2H 2OH.
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Abstract Agglomeration of bed material is a major operational problem in fluidized bed combustion, especially when using biofuels. The main mechanism of agglomeration involves the formation of low melting point compounds, which results in increased particle stickiness and formation of agglomerates. The presence of alkali components from the biofuels leads to reactions with silica from the bed material, forming alkali silicates that have a melting point below the typical operating temperatures of about 850 °C. In addition, hydrodynamics and particle interaction mechanisms will play a role. If no counteraction is taken, severe agglomeration can eventually result in defluidization of the bed and subsequent shut‐down of the installation. Therefore, an early warning system to reliably detect agglomeration is of high importance. Such a system typically consists of the measurement of operating variables such as pressure coupled with analysis of these data. Different methods proposed in the literature are reviewed in this chapter. As soon as agglomeration has been detected, appropriate counteractions should be taken, such as changing the operating conditions or using additives. Alternatively, different bed materials can be used or the fluidized bed design may be adapted to become less susceptible to agglomeration.
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Fluidized bed combustion
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In many industries, the food industry among them, agglomeration has been for a long time a proven method of improving certain properties of particulate solids. By agglomeration, fine particles are transformed into larger aggregates, which have well-defined properties and are easier to handle in bulk. Agglomeration processes are applied whenever the finely dispersed state of a particulate solid – caused by its production history or necessary for its later use – shall be temporarily suspended.
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Economies of scope
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We investigate the effects of a reduction in trade costs on industrial location and welfare in an economy with external economies of scale. We propose a Chamberlinian agglomeration model with footloose capital, which is analytically-solvable. With respect to industrial location, we demonstrate that a reduction in trade cost is likely to lead to agglomeration. With respect to welfare, we show that agglomeration makes a country with agglomeration better off, and the country without agglomeration better or worse off, depending on the degree of external economies of scale. We also prove that agglomeration makes the overall economy better off.
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Preparation of nano-scale powders and application of nanomaterial are persecuted by agglomeration of nano-scale powders. In this paper, the mechanism and influencing factors of nano-scale powder agglomeration are analysed, and technology for solving the problem of nano-scale powder agglomeration and obtaining good dispersiion of nano-scale powders is presented.
Nanomaterials
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In the paper,the preparation of nanosized Al2O3 powders by pyrolysis of NH4AlO(OH)HCO3 is introduced.Based on the preparation process,we elaborat the mechanism of agglomeration,and the anti-agglomeration mechanism is discussed.In the end,some methods of anti-agglomeration are showed.
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Anodic particle coloumetry is used to size silver nanoparticles impacting a carbon microelectrode in a potassium chloride/citrate solution. Besides their size, their agglomeration state in solution is also investigated solely by electrochemical means and subsequent data analysis. Validation of this new approach to nanoparticle agglomeration studies is performed by comparison with the results of a commercially available nanoparticle tracking analysis system, which shows excellent agreement. Moreover, it is demonstrated that the electrochemical technique has the advantage of directly yielding the number of atoms per impacting nanoparticle irrespective of its shape. This is not true for the optical nanoparticle tracking system, which requires a correction for the nonspherical shape of agglomerated nanoparticles to derive reasonable information on the agglomeration state.
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Transport investments can induce positive productivity benefits via agglomeration economies by increasing the scale and efficiency of spatial economic interactions. In assessing the ‘agglomeration benefits’ of transport investments we need to understand the spatial scale over which these externalities are distributed. This report is concerned with the effect of urban agglomeration on productivity and with how agglomeration externalities diminish with distance from source.
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