Sulphuric acid has a tendency to form hydrates, small clusters containing a few water molecules, in the gas phase. Hydrate formation has a stabilising effect on the vapour as the pressure of sulphuric acid drops (relative to unhydrated vapor), decreasing the nucleation rate. In classical nucleation theories the hydration energies and the hydrate distribution are predicted assuming that hydrates can be described as liquid droplets having thermodynamic properties of bulk liquid. To obtain a better understanding of the structures and formation energies of the smallest clusters, we have performed ab initio density functional calculations of the mono-,di-, and trihydrates. The hydrogen bonds between the molecules are found to be strong. The more water molecules the hydrate contains, the clearer ring-like structure is formed. Comparison to classical values for the hydration enthalpies confirms that the properties of bulk liquid do not describe the properties of the smallest clusters too well. The energy barrier for proton transfer reaction H2SO4⋅H2O →HSO4−⋅H3O+ for mono- and dihydrate is high, and protonisation is unlikely to occur, but in trihydrate the protonisation has almost occurred and the barrier is very low. We also studied the singly protonised monohydrate, and found that while sulphuric acid forms H bonds with the OH parts, the hydrogen sulphate ion tends to bind with the O (S=O) part, and the second proton stays tightly in the ion.

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The aim of this study was the fabrication of three-dimensional, highly porous, bioactive scaffolds using a recently developed bioactive glass powder, denominated '0106', with nominal composition (in wt%): 50 SiO(2), 22.6 CaO, 5.9 Na(2)O, 4 P(2)O(5), 12 K(2)O, 5.3 MgO and 0.2 B(2)O(3). The optimum sintering conditions for the fabrication of scaffolds by the foam-replica method were identified (sintering temperature: 670 degrees C and dwell time: 5 h). Composite samples were also fabricated by applying a biopolymer coating of poly((D,L)-lactic acid) (PDLLA) using a dip coating process. The average compressive strength values were 0.4 MPa for uncoated and 0.6 MPa for coated scaffolds. In vitro bioactivity studies in simulated body fluid (SBF) showed that a carbonate hydroxyapatite (HCAp) layer was deposited on uncoated and coated scaffolds after only 4 days of immersion in SBF, demonstrating the high in vitro bioactivity of the scaffolds. It was also confirmed that the scaffold structure remained amorphous (no crystallization) after the specific heat treatment used, with scaffolds exhibiting mechanical properties and bioactivity suitable for use in bone tissue engineering applications.