1,721,018 research outputs found
Role of the water matric potential (M) and of equilibrium water content (EWC) on the water self-diffusion coefficient and on the oxygen permeability in hydrogel contact lenses
No full textThis paper illustrates a new thermodynamic and kinetic model that describes the relationship between the water self-diffusion
coefficient, D* w/g; in hydrogel contact lenses, in terms of water matric potential ψM and equilibrium water content (EWC).
Experimental measurements on commercial contact lenses yield water thermodynamic activity values ranging between 0.996 and
0.999. The corresponding CM matric potential is, respectively, between -8 and -2 J/mol at temperature 35°C. Comparison between water self-diffusion coefficients derived in this paper and those suggested by other authors shows that our values are greater (25%–50%) than the previous ones. The impact of this model on the nature of the oxygen permeability, ∏; in the lenses has been evaluated and the changes of ∏ with ψM and EWC are predicted and compared with direct experimental measurements. For the contact lenses investigated, the oxygen permeability turns out to be only a quadratic function of equilibrium water content, despite the fact that the fraction of the ‘‘free’’ water molecules can be as high as 50%
Liquid-like H2O adsorption layers to catalyze the Ca(OH)2/CO2 solid–gas reaction and to form a non-protective solid product layer at 20°C
No full textRheological properties of silica and kaolin dispersions in mineral paraffinic oil: effect of water films adsorbed on the solid particles
No full textThe effect of alkaline cations on the operation of the kraft recovery and other kilns
No full textCalcium oxide obtained by Calcium Carbonate decomposition has a very large number of industrial uses both, as catalyst or CO 2 sorbent and, for example, as process material in the paper industry. Its properties depend largely on the microstructure developed during carbonate decompositions and successive sintering of the just formed CaO. Impurities and additives can have strong influence on both product microstructure and energy process consumption. This paper revisits the effect of sodium on limestone decarbonation. NaOH or Na 2CO 3 in particular, fastens the decarbonation reaction and lowers the energy consumption with positive impact on the operation control and the quality of the product
Aluminum hydroxide microstructural units in gelled media aged, or nonaged, with alcohol and water
No full textAluminum hydroxide gelled media dispersed and then aged in alcohol (ES) or in water (WS) were prepared with a solid phase concentration equal to 0.45% v/v. A model for microstructural units dispersed in the liquid phase has been derived. The beneficial action of alcohol in giving xerogel powders with higher specific surface area and higher porosity has been explained on the basis that alcohol produces changes in the corresponding dispersed microstructural units. The effect of the aging time in alcohol and in water was evaluated, and the evolution of all parameters was described
Nanoscopic water layers adsorbed onto mesoporous silica aggregates and their effect on the stability and the static yield stress of their dispersion in liquid paraffin
No full textSilica-paraffin and kaolin-paraffin dispersions: Use of rheological and calorimetric methods to investigate the nature of their dispersed microstructure units
No full textEnthalpy of wetting of silica–paraffin dispersions is function of volume fraction θ. ► Microstructure of silica–paraffin dispersion evolves according to branching mechanism. ► Stability of a silica–paraffin microstructure is greater than kaolin–paraffin one. ► Percolation thresholds determined by analysing τ0 versus θ and ΔH versus θ are fairly equal
Thermally activated step for densification and creep of high-porosity MgO compacts in the intermediate sintering stage
No full textInfluence of microstructures on the functional properties of tin oxide-based gas sensors
No full textCalcium carbonate binding mechanisms in the setting of calcium and calcium-magnesium putty-limes
No full textCalcium and calcium magnesium putty-limes (C-L and C-M-L) were characterized, through SEM, Porosimeter and Chemical Analysis, to obtain information on the microstructure of their solid-phases. Irregular agglomerates of portlandite grains and large acicular crystallites of brucite are differently interconnected to form a cellular solid matrix dispersed into the saturated aqueous solution of the hydroxides. The setting of these putty-limes was followed also in a thermobalance with a thermostatic chamber designed to keep the temperature in the range 15–30 °C. The tests were done at a constant humidity of 80%, under isothermal conditions, and a wet and carbonated N 2 flux with 1% of CO 2 was added. The microstructure of the final samples was characterized by the usual methods of investigation at micro–macro scale. Drying kinetics and the related shrinkage processes were discussed on the basis of a modified Kelvin equation, which predicts for the C-L lime putty a larger shrinkage (50.3%) than for C-M-L (35.5%). The binding mechanisms of the calcium carbonate in the strengthening of the putty-lime systems is due to the interconnected texture formed by the calcium carbonate fine crystallites formed during the precipitation process. The scientific reasons for this microstructure evolution have been discussed and explained on the basis of experimental data and theory, leading to a better understanding of the complex relationships between drying, shrinkage and the chemical processes occurring in the setting of putty-lime
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