Understanding the mechanism of nucleation and growth of magnesium hydroxide prepared by electrochemical deposition

The mechanism of nucleation and growth is crucial for the controllable synthesis and processing of materials. In this study, we systematically investigated the crystallization kinetics of magnesium hydroxide (Mg(OH)₂) synthesized via electrochemical deposition, with a focus on elucidating the effects of current density, temperature, and Mg^{2 +} concentration on nucleation and growth dynamics. The approach constituted an innovative revelation of the regulatory mechanism of the nucleation-growth process in Mg(OH)₂ crystallization in the electrochemical deposition process. The nucleation rate was closely related to the degree of supersaturation and also to the specific surface Gibbs free energy. As the nucleation rate increases, the growth rate increases simultaneously, but the increase in growth rate decreases slightly when the current density reaches 0.05 A/cm², and the nucleation rate was larger than the growth rate when the current density reaches 0.1 A/cm². This was related to the “competition” in growth and nucleation. Through real-time monitoring of interfacial supersaturation and morphological evolution, we obtained empirical equations for the nucleation rate constant and growth rate constant, respectively. At the nucleation stage, the nucleation rate constant was modelled as a segmented function. At current densities of 0.0125–0.5 A/cm², the nucleation rate constants were on the order of 0.48 ± 0.07 for Mg²⁺ concentration and 0.32 ± 0.03 for current density. At current densities of 0.1 A/cm², the nucleation rate constants were on the order of 0.10 ± 0.02 for Mg²⁺ concentration and 0.03 ± 0.01 for current density. During the growth stage, the growth rate constants were on the order of 0.09 ± 0.01 for Mg²⁺ concentration and 0.15 ± 0.01 for current density. The kinetic framework establishes predictive relationships between process parameters and crystal formation mechanism, providing theoretical guidance for tailoring Mg(OH)₂ architectures in flame-retardant and wastewater treatment applications.