Equilibria in a ZnCl2–H2O–NaOH System, According to Data from Potentiometric Titration, and Selecting Conditions for the Hydrochemical Synthesis of ZnS and ZnSe Films

Resumo

Equilibrium processes that occur in the ZnCl₂–H₂O–NaOH system are studied via the potentiometric titration of zinc chloride in the 0.00006–1.01 mol/L range of concentrations. Based on mathematical simulations, a number of polynuclear structures and soluble phases are identified in the system. Values of the instability constants of complex forms and the constants of the dynamic equilibria of weakly soluble zinc compounds are calculated, along with their stoichiometric compositions and areas of sustainable existence. Refined boundary conditions are determined, along with areas of the formation of ZnSe and ZnS when they are precipitated using sodium selenosulfate and thiourea, respectively. ZnSe and ZnS layers around 1000 and 200 nm thick are obtained via hydrochemical deposition on glass-ceramic substrates. Based on electron microscopy data, it is concluded that the layers consist of spherical aggregates with mean sizes of around 350–450 nm for ZnSe and 50–200 nm for ZnS, generated from primary particles with sizes of around 20–60 and 20–30 nm, respectively.