The carbonation kinetics of calcium hydroxide nanoparticles: A Boundary Nucleation and Growth description

HYPOTHESIS

The reaction of Ca(OH)₂ with CO₂ to form CaCO₃ (carbonation process) is of high interest for construction materials, environmental applications and art preservation. Here, the "Boundary Nucleation and Growth" model (BNGM) was adopted for the first time to consider the effect of the surface area of Ca(OH)₂ nanoparticles on the carbonation kinetics.

EXPERIMENTS

The carbonation of commercial and laboratory-prepared particles' dispersions was monitored by Fourier Transform Infrared Spectroscopy, and the BNGM was used to analyze the data. The contributions of nucleation and growth of CaCO₃ were evaluated separately.

FINDINGS

During carbonation the boundary regions of the Ca(OH)₂ particles are densely populated with CaCO₃ nuclei, and transform early with subsequent thickening of slab-like regions centered on the original boundaries. A BNGM limiting case equation was thus used to fit the kinetics, where the transformation rate decreases exponentially with time. The carbonation rate constants, activation energies, and linear growth rate were calculated. Particles with larger size and lower surface area show a decrease of the rate at which the non-nucleated grains between the boundaries transform, and an increase of the ending time of Ca(OH)₂ transformation. The effect of temperature on the carbonation kinetics and on the CaCO₃ polymorphs formation was evaluated.

Modified α,α'-trehalose and d-glucose: green monomers for the synthesis of vinyl copolymers

Allyl saccharide/vinyl copolymers were synthesized using renewable feedstocks (α,α'-trehalose and d-glucose) to obtain 'green monomers'. Properly designed synthetic procedures were used to obtain copolymers with high purity and without protection/deprotection steps in agreement with the principles of green chemistry and industrial sustainability. The use of saccharide derivatives as monomers allowed products to be obtained that showed high affinity and compatibility for the cellulosic substrates, like paper or wood, and that were suitable for applications like adhesion or consolidation in the field of cultural heritage. All reaction products were characterized by FT-IR and NMR spectroscopies and SEC analyses, while thermal properties were evaluated by DSC analyses.

Structural characterization of magnesium silicate hydrate: towards the design of eco-sustainable cements

Magnesium-based cement is one of the most interesting eco-sustainable alternatives to standard cementitious binders. The reasons for the interest towards this material are twofold: (i) its production process, using magnesium silicates, brine or seawater, dramatically reduces CO2 emissions with respect to Portland cement production, and (ii) it is very well suited to applications in radioactive waste encapsulation. In spite of its potential, assessment of the structural properties of its binder phase (magnesium silicate hydrate or M-S-H) is far from complete, especially because of its amorphous character. In this work, a comprehensive structural characterization of M-S-H was obtained using a multi-technique approach, including a detailed solid-state NMR investigation and, in particular, for the first time, quantitative (29)Si solid-state NMR data. M-S-H was prepared through room-temperature hydration of highly reactive MgO and silica fume and was monitored for 28 days. The results clearly evidenced the presence in M-S-H of "chrysotile-like" and "talc-like" sub-nanometric domains, which are approximately in a 1 : 1 molar ratio after long-time hydration. Both these kinds of domains have a high degree of condensation, corresponding to the presence of a small amount of silanols in the tetrahedral sheets. The decisive improvement obtained in the knowledge of M-S-H structure paves the way for tailoring the macroscopic properties of eco-sustainable cements by means of a bottom-up approach.

[Influence of environmental temperature on absorption of xylose in fasting animals]

The A. have studied 28 pairs of rats; 17 pairs received 1,1 g of soya oil; 7 pairs were starved. The partners were kept; one at the environmental temperature of 6 degrees C, the other at 30 degrees C. After a night, all rats were tested for xylose absorption. Xylose intestinal absorption in the rats kept at the environmental temperature of 30 degrees C after soya oil decreased of 42,88 +/- 8,14 of the value found at 6 degrees C; it decreased of 15,59 +/- 3,20% after a night of fast. Both decreases were significant (P less 0.01).