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Metal Oxide/CNT/Graphene Nanostructures for Chemiresistive Gas Sensors
Published in Vidya Nand Singh, Chemical Methods for Processing Nanomaterials, 2021
Sanju Rani, Manoj Kumar, Yogesh Singh, Rahul Kumar, V.N. Singh
In the process of crystal formation, there are mainly three steps: Nucleation: For a specific solvent, a substance has a certain solubility, and when it’s supersaturated, the solute is precipitated, which in turn forms crystal nuclei.Growth: After the nuclei is formed, they adhere to each other and the rate of super-saturation becomes less so that nuclei is formed again and an equilibrium is obtained. If the nucleation time is short, it will lead to a more uniform grain size.Ripening: In this process, which is typically called Ostwald ripening, larger particles are grown over a period of time, and on the other hand, small particles become more small and finally dissolve.
Liquid-Phase Sintering
Published in M. N. Rahaman, Ceramic Processing and Sintering, 2017
where S is the solubility of a particle with a radius a in the liquid, S0 is the equilibrium solubility of the solid in the liquid at a planar interface, γsl is the specific energy of the solid–liquid interface, Ω is the atomic volume, k is the Boltzmann constant, and T is the absolute temperature. According Eq. (10.6), the solubility increases with decreasing particle radius, so matter transport will occur from small particles to large particles, leading to Ostwald ripening. In addition, asperities have a small radius of curvature and they tend to dissolve. Pits, crevices, and necks between the particles have negative radii of curvature, so solubility is diminished and precipitation is enhanced in those regions.
“Soft” Chemical Synthesis and Manipulation of Semiconductor Nanocrystals
Published in Victor I. Klimov, Nanocrystal Quantum Dots, 2017
Jennifer A. Hollingsworth, Victor I. Klimov
Size and size dispersion can be controlled during the reaction, as well as postpreparatively. In general, time is a key variable; longer reaction times yield larger average particle size. Nucleation and growth temperatures play contrasting roles. Lower nucleation temperatures support lower monomer concentrations and can yield larger-size nuclei. Whereas, higher growth temperatures can generate larger particles as the rate of monomer addition to existing particles is enhanced. Also, Ostwald ripening occurs more readily at higher temperatures. Precursor concentration can influence both the nucleation and the growth process, and its effect is dependent on the surfactant/precursor-concentration ratio and the identity of the surfactants (i.e., the strength of interaction between the surfactant and the NQD or between the surfactant and the monomer species). All else being equal, higher precursor concentrations promote the formation of fewer, larger nuclei and, thus, larger NQD particle size. Similarly, low stabilizer:precursor ratios yield larger particles. Also, weak stabilizer-NQD binding supports growth of large particles and, if too weakly coordinating, agglomeration of particles into insoluble aggregates.10 Stabilizer–monomer interactions may influence growth processes, as well. Ligands that bind strongly to monomer species may permit unusually high monomer concentrations that are required for very fast growth (see Section 1.3),17 or they may promote reductive elimination of the metal species (see later).18
Complex selection of a demulsifier: laboratory studies, numerical simulation and field tests
Published in Geosystem Engineering, 2023
Ilyushin Pavel Yurievich, Vyatkin Kirill Andreevich, Kozlov Anton Vadimovich
The processes of creaming and sedimentation are caused primarily by the difference in density between oil and water. The direction of phase movement in these processes depends on the type of emulsion (Pensini et al., 2014; Roques-Carmes et al., 2014). The flocculation process is characteristic of W/O emulsions, in which water particles stick together, forming aggregates. The rate of this process depends on the water content in the emulsion, temperature, and the properties of water and oil (Kang et al., 2018). Ostwald ripening is a process of droplet growth due to the achievement of the final solubility of the dispersed phase, which leads to the movement of droplets towards each other (Takahashi et al., 2016; Zwicker et al., 2015). Coalescence is the final and most important stage of oil demulsification. In this process, particles combine to form large drops, resulting in gravitational phase separation (Eow & Ghadiri, 2002; Mhatre et al., 2018; Mousavi et al., 2014).
Modelling of non-metallic inclusions in steel
Published in Mineral Processing and Extractive Metallurgy, 2020
Lifeng Zhang, Qiang Ren, Haojian Duan, Ying Ren, Wei Chen, Gong Cheng, Wen Yang, Seetharaman Sridhar
In 2002, the current author described the mechanisms controlling the evolution of inclusions (Zhang and Pluschkell 2003), as shown in Figure 3 (Zhang 2013). After adding and dissolving the deoxidiser alloy, oxide particles nucleate, precipitate, and quickly grow. This stage is mainly controlled by the diffusion of deoxidiser elements and oxygen. ‘Ostwald-ripening’ causes larger particles to grow and smaller particles to shrink. Brownian motion of small particles contributes to the growth of <2 μm inclusions by random collision. After particles grow large enough, collisions in turbulent fluid flow become effective in the further growing of the inclusions. Buoyancy rising, bubble attachment, and fluid transport remove large inclusions from the bulk melt and transfer them to the top slag or to the refractory walls of the vessel. Small inclusions and some big inclusions remain in the liquid steel and are passed downstream to the next processing step. This general progression of inclusions is also disturbed by the oxygen absorption from the surroundings and by the slag emulsification.
Formulation of roselle extract water-in-oil nanoemulsion for controlled pulmonary delivery
Published in Journal of Dispersion Science and Technology, 2023
Adil Omer Baba Shekh, Roswanira Abdul Wahab, Nur Azzanizawaty Yahya
Ostwald ripening is when small droplet particles diffuse together to form larger droplet particles. The dispersed phase then absorbs energy from the surrounding, increasing the kinetic energy and promoting higher probabilities of effective collisions in the dispersed phase.[72] However, this phenomenon is preventable using sufficient ripening inhibitor, i.e., oil, to formulate a w/o NE to retard the growth of the roselle extract droplets.[76] The Ostwald ripening rate was observed by this study by plotting the r3 versus the storage time graph (Figure 2b). As can be seen, the Ostwald ripening effect in the w/o NE was influenced differently by storage temperatures and ingredient composition. Samples stored at 4 °C and 25 °C were stable, with no increase in MDS at the lowest Ostwald ripening rate. However, storage at 35 °C showed the highest Ostwald ripening rate, corroborating a similar observation by a similar study.[42] They reported that particles in the NE absorbed energy from their surroundings as the temperature increased, elevating the system's kinetic movements. The same changes were expected of the roselle extract droplets in the w/o NE, with increased diffusion among the particles.[77] Overall, the w/o roselle extract NE samples stored at 4 °C and 25 °C were markedly more stable than ones stored at 35 °C. Presumably, the low-temperature storage of the latter retarded the Ostwald ripening effect following the substantially reduced kinetic energy, which diminished droplets' mobility.[78]