(570g) Sorel Cement Reactions and Their Kinetics

Mixing solid MgO with MgCl2 brine produces Sorel cement. Experimental cement formulations were developed using ratios of 0.898 to 1.318 kg of MgO per liter (7.5 to 11 pounds of MgO per gallon) of brine with brines that vary in MgCl2 concentration from 20% to 33%. X-ray analysis of the set cement after 24 hours indicates that the dominant setting reaction is:

5 MgO + 1 MgCl2 + 13 H2O → 5Mg(OH)2?MgCl2?8H2O (5-phase)

with a significant amount of material that is amorphous in addition to other minor cement components, e.g. Mg(OH)2. Cements formulated near the stoichiometric ratio of the 5-phase reaction, e.g. 0.8987 kg/L (7.5 lbs/gal) and 28.9±0.15% MgCl2 brine, are mechanically the strongest. Kinetic experiments observed that the 5-phase is formed quickly, but the kinetics are not complete for several days. The cement does not set by the 5-phase reaction when exposed to Cu K x-rays but gives a putty like form having MgCl2*6H2O crystals that do not set into a cement.