The role of ζ-(zeta)potential of mineral grains in the initial deposition kinetics of colloidal particles in geochemically heterogeneous porous media is investigated. Colloid deposition experiments with colloidal silica particles flowing through columns packed with chemically heterogeneous sand were carried out. Patchwise chemical heterogeneity was introduced to the granular porous medium by modifying the surface chemistry of a fraction of the quartz sand grains via reaction with aminosilane. Experimental initial colloid deposition rates and resulting collision efficiencies were compared to theoretical predictions based on the measured average ζ-potential of the chemically heterogeneous sand. It is shown that colloid deposition kinetics are controlled by the degree of patchwise chemical heterogeneity and that use of the measured ζ-potential of the granular porous medium in theoretical predictions leads to erroneous results.

A study was conducted on the control of the chemical reactivity of sodium utilizing the atomic interaction between sodium and nanoparticles. The authors reported in a previous paper that the atomic interaction between sodium and nanoparticles increases and has the potential to suppress chemical reactivity. In this paper, the authors examined the released reaction heat and reaction behavior. As a result, it was confirmed that the released reaction heat and reaction rate decreased. From the results of experimental studies, it is clear that the suppression of chemical reactivity is caused by changes in sodium evaporation rate and fundamental physical properties such as surface tension, which originate from the change in the atomic interaction between sodium and nanoparticle atoms. The suppression of chemical reactivity applied to an FBR coolant was estimated for the cases of sodium combustion and sodium-water reaction. It was confirmed that the concept of suspending nanoparticles into sodium has a high potential for the suppression of chemical reactivity. The applicability as coolant to the FBR was investigated, including not only the chemical reaction properties but also the aspects of heat transfer and operation.

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