Rapid synthesis of octosilicate, a layered alkali silicate, by heterogeneous nucleation at the solid–liquid interface

This paper describes a novel method for rapidly synthesizing the crystalline alkali silicates ilerite and octosilicate by heterogeneous nucleation at a solid–liquid interface. To form the solid–liquid interface in the starting sodium silicate solution, solid balls of different materials and sizes were dispersed in the solution. The ball-containing solutions were subjected to a static hydrothermal reaction. The presence of the balls promoted crystallization, leading to a considerable reduction in the time required to attain chemical equilibrium. The time reduction effect was noticeable when zirconia balls were used, which had a relatively high critical surface tension. The surface area of the balls also greatly affected the crystallization process, and the estimated total number of formed crystals was nearly proportional to the surface area of the balls (i.e., the solid–liquid interfacial area), suggesting that crystallization was promoted by the heterogeneous nucleation on the surface of the balls. The presence/absence of balls can serve to control both nucleation and crystal growth, which may facilitate size control of the products. This method yielded well-grown crystals with a lateral size almost twice that of a product synthesized by conventional synthesis. The use of the solid–liquid interface was useful in both reducing the crystallization time and controlling the size of the crystals.