Search results for "Nucleation"
showing 10 items of 364 documents
Deactivation of ice nuclei due to atmospherically relevant surface coatings
2009
The ice nucleation characteristics of Arizona test dust (ATD) and illite clay, surrogates for atmospheric ice nuclei, have been determined at the Aerosol Interactions and Dynamics in the Atmosphere (AIDA) chamber located at the Research Center Karlsruhe in Germany. The objective of this research was to determine the effect of sulfuric acid and ammonium sulfate coatings on the ability of these mineral dust surrogates to nucleate ice in an environment where particles realistically compete for water vapor. Coated ATD particles required higher saturations at all temperatures considered, from −20 to −45 ◦ C, than did identical uncoated particles. Freezing of coated particles often required satur…
Crystal structure and microstructure of synthetic hexagonal magnesium–cobalt cordierite solid solutions (Mg2−2xCo2xAl4Si5O18)
2013
Co2+-containing cordierite glasses, of nominal compositions (Mg1−xCox)2Al4Si5O18(withx= 0, 0.2, 0.4, 0.6, 0.8 and 1), were prepared by melting colloidal gel precursors. After isothermal heating at 1273 K for around 28 h, a single-phase α-cordierite (high-temperature hexagonal polymorph) was synthesized. All materials were investigated using X-ray powder diffraction and field-emission scanning electron microscopy. The crystal structure and microstructure were determined from X-ray diffraction patterns. Rietveld refinement confirmed the formation of magnesium–cobalt cordierite solid solutions. The unit-cell volume increased with the increase of cobalt content in the starting glass. The crysta…
Competition between heterogeneous and homogeneous nucleation near a flat wall
2009
We studied the competition between heterogeneous and homogeneous nucleation of an aqueous suspension of charged colloidal spheres close to the container walls. Samples of equilibrium crystalline structure were shear-melted and the metastable melt left to solidify after the cessation of shear. The crystallization kinetics was monitored using time-resolved scattering techniques: at low particle number densities n we applied an improved static light scattering method while at large particle concentrations ultra-small-angle x-ray scattering was applied for the first time. Our results show some unexpected behavior: the heterogeneous nucleation at the container walls is delayed in comparison to t…
A novel colorimetric experimental technique for the characterisation of metal hydroxides reactive crystallization phenomena
2021
The reactive crystallization of metal hydroxides constitutes a field of raising interest driven by the importance of metals recovery and the wide industrial applications of their hydroxides. A popular example is related to the case of magnesium hydroxide (Mg(OH)2), which is widely employed in the fields of water treatment, desulphurization of fuel gases, pharmaceutical industry, refractory field and flame retardants
Heterogeneous nucleation of colloidal melts under the influence of shearing fields
2004
Large, oriented single crystals may be obtained from shear melts of colloidal particles after nucleation at the container walls. We are here interested in the processes occurring during the initial phase of their formation. Using different microscopic and scattering techniques we here studied highly charged suspensions of spherical particles, dispersed in low salt or deionized water, in single and double wall confinement, during and after cessation of shear. While the equilibrium phase of our colloidal solids is body centred cubic, the shear induced precursors of heterogeneous nuclei consist of wall based, oriented, registered or freely sliding layers with in plane hexagonal symmetry. Cessa…
Structure and diffusion of oxygen and silicon interstitials in silicon
1999
Abstract Ab initio quantum chemical simulation of silicon interstitials and oxygen-related defects Oi, V–O2, and V–O4 in oxygen-containing silicon was performed using the embedded molecular cluster model. The defect geometry and electronic structure were studied. The migration activation energy for Oi defect was estimated as 2.73 eV at the atmospheric pressure, and 2.70, 2.68, and 1.92 eV for the lattice compressed by 0.25, 0.37, or 5.0 per cent, respectively. The activation energy of silicon interstitial is not changing with pressure. The molecular cluster used to simulate V–O4 defect with C2v symmetry was shown to have only slight deviation from D2d at atmospheric pressure, a strong devia…
Float glass colouring by ion exchange
2008
Abstract Back in the Middle Ages, glass artists used to produce yellowish colorations in soda-lime glasses using mixtures that contained silver salts, clay composites and natural oils. The resulting colour was a characteristic pale yellow known as silver-stain. This coloration is mainly caused by the extinction – absorption and, to a lesser extent, scattering – of light occasioned by silver nanoparticles formed inside the glass. This colouring technique comprises a heat treatment divided in two stages: in the first one, an ion exchange between the silver ions in the mixture and the alkali ions in the glass takes place. This process is called nucleation of silver nanoparticles. The second st…
Supercritical hydrothermal synthesis of ZnO nanopowders beyond the critical point : understanding of nucleation and growth steps
2014
The supercritical hydrothermal synthesis of nanopowders (especially metal oxide) has been widely studied. To the best of our knowledge, no nanoparticle formation mechanism has been published yet. In this prospect, this study is dedicated to the understanding of metal oxide nanoparticle nucleation and growth mechanisms. For this purpose, zinc oxide is used as a model material. First, the influence of synthesis operating conditions such as pressure, temperature, pH, precursor concentrations and solution flow rates on particle morphological properties (size, particle size distribution or morphologies) has been investigated. Hence, two approaches have simultaneously been carried out. The first …
Lysozyme crystallization rates controlled by anomalous fluctuations
2005
Abstract Nucleation of protein aggregates and crystals is a process activated by statistical fluctuations of concentration. Nucleation rates may change by several orders of magnitude upon apparently minor changes in the multidimensional space of parameters (temperature, pH, protein concentration, salt type and concentrations, additives). We use available data on hen egg lysozyme crystal induction times in different solution conditions. We measure by static and dynamic light scattering the amplitudes and lifetimes of anomalously ample and long-lived fluctuations occurring in proximity of the liquid–liquid demixing region of the given lysozyme solutions. This allows determining the related sp…
Effect of T-R conformational change on sickle-cell hemoglobin interactions and aggregation
2004
We compare the role of a conformational switch and that of a point mutation in the thermodynamic stability of a protein solution and in the consequent propensity toward aggregation. We study sickle-cell hemoglobin (HbS), the beta6 Glu-Val point mutant of adult human hemoglobin (HbA), in its R (CO-liganded) conformation, and compare its aggregation properties to those of both HbS and HbA in their T (unliganded) conformation. Static and dynamic light scattering measurements performed for various hemoglobin concentrations showed critical divergences with mean field exponents as temperature was increased. This allowed determining spinodal data points T(S)(c) by extrapolation. These points were …