Papers by Author: Šárka Hošková

Abstract: Nanofibers are very promising new type of material with a broad range of possible applications. The new NANOSPIDER technology opens a possibility to produce nanofabrics in an amount large enough for them to start being interesting as a construction material. There are many so-called passive applications of nanotextiles (including different types of filters and protective layers), and active applications, when the active chemical agent is incorporated in their structure. In the present paper, however, the new possible application of nanofabrics is proposed: as a base material on which technically interesting nanoclusters are heterogeneously nucleated. The basic thermodynamics of heterogeneous nucleation on nanofibers is considered. The extreme curvature of nanofibers manifests itself in an energetic barrier of nucleation, which is quite different from a case of nucleation on a flat surface. The expression for Gibbs energy of cluster formation is derived, taking into account the elastic strain resulting from a volume (or shape) changes during nucleation.

Abstract: A novel method that allows determining instantaneous concentration of calcium ions, Ca2+, in hydrated cement paste (HCP) is suggested. EDTA solution (belonging to a group of carboxylic acids/carboxylates and borates) seems to be very effective retarder altering nucleation and subsequent growth of newly forming clusters of calcium minerals. Concentrations of Ca2+ have been determined for various water to cement ratios, at different times and for given temperature.

Abstract: A very early stage of cement paste hydration is studied at microscopic level of description. Within context of nucleation theory the critical (and, thus, growable) size of clusters of calcium hydroxide (so-called portlandite) is estimated for chosen water to cement ratios at given temperature. Furthermore, also the barrier of portlandite nulceation is determined. It is shown that these static characteristics of process are practically unchanged contrary to number density of portlandite critical clusters formed in unit volume of mixture per unit time.