STRUCTURE, PROPERTIES AND REACTIONS OF CAO IN BURNT LIME .1. DESIGN OF A NEW MODEL OF BURNT LIME

The work presented is, due to its complexity, for convenience divided in three parts: Part 1 - Design of a new model of burnt lime, Part 2 - Diffusion of carbon into solid lime, and Part 3 - Composite reactions of CaO and C in solid and liquid state. Part 1 is presented here. Specified doubts as regards the validity of the accepted thermodynamics of calcium oxide are experimentally supported by comparative calorimetric measurements of the heat of solution of CaO made from metal and carbonate, showing the latter to be more positive by 35-36 kJ mol-1 than the former. A crystallographic model of recrystallised burnt lime is developed on the assumption that the former calcite lattice governs the recrystallisation process. The model indicates that burnt lime contains crystalline CaO in two equal parts, characterised by length of valency bonds of 2.41 angstrom [CaO (c)] and 3.91 angstrom [CaO (n)]. The measured additional energy in CaO (n) of 70-72 kJ fits with the calculated potential electric energy of the expanded ionic bonds developed at the cost of the bond-strength of the oxide. The effect of the electric field in freshly burnt lime is absence of surface tension in the calcine itself and suspension of surface energy in contacting compounds. This causes ionic diffusion of water and carbon into the expanded lattice where the ions are coupled to the valency bonds in assumed interstate compounds available for later solid state reactions in the system. Application of the model to the CaO-SiO2-system indicates that the electric charge of burnt lime may be preserved and activated in the production of Portland cement. If so, it may also be the driving force in the sequence of reactions that convert the wet concrete-mix into solid rock.