Formation mechanism of Mg(OH)2 prepared by hydration of magnesia clinker in magnesium salt solution: (Part 1)

Abstract

Mg(OH)2 particles of hexagonal plate and prism are prepared by hydration of magnesia clinker in magnesium salt solution. The hydration mechanism of magnesia was investigated by measuring reaction rates and SEM observations. The hydration rate was proportional to the surface area of MgO particles, suggesting that the reaction proceeds by the dissolution of MgO particles followed by the precipitation of Mg(OH)2 and that the dissolution was rate-controlling. In Mg(CH3COO)2 system, the reaction was divided roughly into two stages. The rate of the first stage was about half that of the second stage. MgO surface was covered with dense Mg(OH)2 layer during the first stage. At the second stage, however, Mg(OH)2 layer peeled off from MgO surface. These results suggested that the rate-controlling mechanism in the dissolution of MgO was diffusion through the product layer of Mg(OH)2 at the first stage, and surface reaction at the second stage. In MgCl2 system, the rate remained constant only in a short period and decreased gradually with reaction time. Mg(OH)2 films on MgO were observed as in Mg(CH3COO)2 system, though it did not peel off completely. Hence, this product layer prevented MgO from dissolution and limited the rate in MgCl2 system.