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Recent Advances and Future Perspectives in Heterophase Polymerization
Published in Hugo Hernandez, Klaus Tauer, Heterophase Polymerization, 2021
Another assumption recently questioned by Tauer et al. [99] is the effect of oxygen and other gases on the kinetics of heterophase free-radical polymerization. Oxygen, on one hand, may accelerate or decelerate the polymerization depending on the polymerization conditions and on the phase where radicals are generated. Furthermore, oxygen as well as any other gas present in the system may dissolve in the continuous phase affecting mass transfer phenomena. A very special influence of air dissolved in the aqueous phase was observed during particle nucleation experiments. The reproducibility ofthe experimental data could be drastically improved when the aqueous phase was degassed prior to the experiments [100]. A similar effect was observed when styrene quiescently was placed on top of water and the equilibration of styrene in water was followed with multi-angle laser light scattering [101]. During the equilibration period, the scattering intensity increased for degassed water much stronger than for water saturated with air. The increase in the scattering intensity goes along with the formation of styrene drops (cf. Section III). The origin of both effects is not clear yet. At the moment, the most plausible explanation is the influence, in the sense of heterogeneous nucleation, of tiny associates of air molecules (nanobubbles) on the formation of particles and droplets in the first and second examples, respectively.
Soil behaviour during artificial freezing — Part 1 : Frost heaving 3D tests
Published in Jean-François Thimus, Ground Freezing 2000 - Frost Action in Soils, 2020
H. Côté, J.F. Thimus, R. Rijkers, M. Naaktgeboren
The water used during all test steps is demineralized and degassed water. No saturation is required for clay samples, but the sand samples need to be saturated before further operations. The consolidation is made in two phases: a normal pressure consolidation, a temperature acclimatisation to +3°C and axial load addition for anisotropic test. After the stabilisation of volume (water expulsions) and axial deformation, the temperature is slowly downed to +3°C to avoid thermal shock. For clay, the consolidation at this temperature takes three days and for sand a few hours. Before the test, axial load is gradually added on the piston via an oedometric bench if required. After stabilisation of the axial deformation, the test can begin. The pressures submitted during the consolidation steps and the test are the same (except for the drainage: consolidation step is always drained). In table 1, the pressures for different sand tests are presented, each item is done for two different intern temperatures: −15°C and −30°C. The pressures for tests with clay are in table 2.
Surface Forces in Nanostructures
Published in Victor M. Starov, Nanoscience, 2010
It is reasonable to assume that proper hydrophobic attraction exists only in degassed water, that is, in the absence of gas bubbles. It allows one to treat the nature of structural forces from a uniform standpoint, through its relation to modification of the boundary layer structure: namely water density growth and normal orientation of water dipoles in the case of hydrophilic repulsion forces, or water density decrease and tangential orientation of water dipoles in the case of hydrophobic attraction forces. In any case, the values of λ are close for hydrophilic and hydrophobic forces and are within 1-2 nm, which corresponds to the length of correlation in bulk water. It allows inclusion of short-range structural forces of both types into the total disjoining pressure isotherm.
Effect of dissolved air on the flotation behaviour of coal-kaolinite binary mixtures
Published in International Journal of Coal Preparation and Utilization, 2021
Chenwei Li, Yaowen Xing, Kunkun Zhen, Haijun Zhang
In this paper, natural and degassed deionized water were used. The degassed water was prepared by boiling deionized water at 100°C for 90 min, and the water was then cooled and stored in a sealed bottle for use. This method removed most of the pre-existing gas nuclei in water and has been described elsewhere (Dai, Fornasiero, and Ralston 1998; Zhou et al. 2010). The flotation performance using degassed water was compared to standard conditions where no gas had been dissolved in the water to explore the effect of dissolved air on coal flotation in the presence of kaolinite clay.