EXPERIMENTÁLNÍ STUDIUM A MODELOVÁNÍ PRAVIDELNÝCH PÁSKŮ V KŘEMIČITÝCH HYDRATOVANÝCH GELECH

Periodic structures can be seen practically everywhere in the world. In order to understand them deeply it is crucial to find a model, which can describe these structures to show their genesis and to predict their behavior while changing various input parameters. This paper deals with the experimental study on Liesegang ring formation made of copper chromate ions with copper sulphate used as an outer electrolyte and potassium chromate as an inner electrolyte. An aqueous solution of sodium silicate has been used as gel medium. The experiments were carried out in beakers as testing samples to find suitable sample weights of electrolyte compounds, then glass columns were used. The reaction process was periodically measured and photographed. Few few hours aft er start of the experiment, the first ring of precipitated copper chromate appeared. In the end, when all ions were consumed, the column was cut through, and the ion concentration was estimated by atomic absorption spectrophotometry and calculated theoretically using equation based on first and second Fick´s law of diffusion. The final calculation of diffusion coefficient was determined by least squares of deviations between measured and theoretical values of concentrations depending on the parameters D and C2 which gave us real values of diffusion coefficients and concentrations of ions in our system.

Synthesis and characterization of (NH4)1.5Cu2Cr2O8(OH)1.5⋅H2O

A new single-phase copper chromate compound was successfully synthesized by a hydrothermal method and characterized by XRD, SEM, TGA, and XRF analysis. The experimental XRD pattern was analyzed by automatic indexing and the compound was found to be monoclinic with space group P21/a and unit-cell parameters of a=10.1829(11) Å, b=4.9516(6) Å, c=7.2899(7) Å, and β=103.64(1)°. The chemical formula of the copper chromate compound determined by XRF and TGA was determined to be (NH4)1.5Cu2Cr2O8(OH)1.5⋅H2O. XRD results also showed that the synthesized compound decomposed into CuCr2O4 and CuO after being calcined at 600 °C.