R Camerini1, G Poggi1, D Chelazzi1, F Ridi1, R Giorgi1, P Baglioni2. 1. Department of Chemistry "Ugo Schiff" and CSGI, University of Florence, Via della Lastruccia 3, 50019 Sesto Fiorentino (FI), Italy. 2. Department of Chemistry "Ugo Schiff" and CSGI, University of Florence, Via della Lastruccia 3, 50019 Sesto Fiorentino (FI), Italy. Electronic address: baglioni@csgi.unifi.it.
Abstract
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.
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.