Effect of Mechanical Pressure on the Recrystallization of Zinc Oxide in a Water Fluid Medium under Cold Sintering

The effect of mechanical pressure on the change in the crystal size distribution (CSD) during the treatment of zinc oxide in a water medium in the presence of an activating additive, such as zinc acetate or ammonium chloride, is studied by analyzing the images taken on a scanning electron microscope (SEM). The results of ZnO treatment at temperatures of 220–296°C in ceramic cold sintering processes and under similar conditions without mechanical pressure in an autoclave are compared. It is concluded that the additives to the reaction medium have an effect of the rate of exchange by water molecules between the water medium and the water bonded in the ZnO structure and activate the solid-phase mobility and redistribution of mass between crystals. Mechanical pressure intensifies the solid-phase mobility activation effect and leads to an increase in the probability of crystal coalescence and the size of a ceramic grain under cold sintering. Surface spreading is predominant in the process of treatment in water fluid medium without mechanical pressure. A mechanism is proposed for the effect of a water medium on mass transfer and the change of dispersion composition during the recrystallization of ZnO powder with the formation of new finely dispersed crystals, which differ from initial powder crystals in their properties.