| Popis: |
Four independent parameters: solvent (ROH, R = CH3, C2H5, C3H7, n-C4H9); NH3 and H2O concentrations and temperature have been varied and consequently the final diameter of silica particles determined. The bigger the solvent, the larger the particles (210 nm : CH3OH-550 nm : butanol). Increasing H2O and NH3 contents lead to an increase of the diameter. Following both the particle size (MET) and the weight evolution of silica as time enables to prove that Ostwald ripening does not occur, since the number of particles does not decrease during the growing. Measurements at 20, 30, 40°C give an Arrhenius law relating the speed rate and the temperature, the activation energy being 3.5 Kcal/mole. Raising temperature increases the kinetics as well as the nuclei generation, so that smaller homodisperse particles can be obtained (o ∼ 120 nm at 20°C to 70 nm at 40°C in C2H5OH). |
