The process of activated sintering of magnesium oxide obtained from sea water (by precipitation with 80 % and 120 % of the stoichiometric quantity of the dolomite lime) was examined with addition of 1, 2 and 5 wt.-% TiO2, at temperatures of 1600 degrees C and 1700 degrees C with soaking at the maximum temperature of 1, 3 and 5 hours, respectively. The product density and porosity were examined and the dependencies obtained were described by appropriate analytical expressions. The compatibility relationships between the addition of TiO2 and the B2O3 content in the sintered magnesium oxide samples were determined, based on an important theorem due to Onsanger. The phenomenological cofficients were calculated for two irreversible processes, namely, those of formation of Ca2B2O5 and CaTiO3, respectively.