Kinetic of colloidal-chemical transformations during the decomposition of ammonia complexes of Zn(II) in alkaline solutions

Maria A. Maximova ; Evgeny V. Polyakov ; Ilya V. Volkov ; Aleksandr P. Tyutyunnik ; Alexey A. Ioshin

Nanosistemy: fizika, himiâ, matematika, Tome 15 (2024) no. 4, pp. 498-509.

Résumé

For the closed system $(\Sigma)$: Zn$^{2+}$–NH$_{3,aq}$–NH$_{3,gas}$, H$^+$–OH$^-$–N$_{2,gas}$, experimental data on the change in the concentration of in the composition of the ammonia complex Zn(NH$_3$)$^{2+}_4$ in solution, colloidal particles Zn(OH)$_2$/ZnO in solution and growing film on the reactor walls are presented depending on the synthesis time, zinc concentration and synthesis temperature Ts in the range of 50 – 99$^\circ$C. It has been established that up to 95$^\circ$C the ion-molecular growth of Zn(OH)$_2$/ZnO clusters in solution $(\Sigma)$ proceeds in a diffusion-controlled mode of homogeneous growth until reaching of their critical size. Further growth of ther critical clusters is followed by aggregation and coalescence of critical sized clusters into microcrystals with the formation of a film on a glass substrate of various morphologies. The solubility of such a film is determined by the size of critical clusters, which preserves in the growing polycrystal in the form of coherent scattering region $(CSR)$. With an increase in the synthesis temperature to 99$^\circ$C, the aggregation mechanism is replaced by a faster diffusion-controlled attachment of Zn (II) ammonia complex to the end surface of the growing microcrystals simultaneously in colloid solution and in the film.

Détail

Keywords: ammonia complex, Zn(OH)$_2$/ZnO, colloid, film, growth, mechanism.
Mots-clés : Zn(II)