Thermodynamic investigations and substantiation of the aluminothermic fabrication method of calcium

Аннотация

To search for ways to solve the problem of decreasing the production prime cost of metallic calcium, it is proposed to consider its aluminothermic production by the example of the CaO–Al system. The thermodynamic analysis implemented for this system showed that the aluminothermic reduction of calcium from its oxide is technically performable under a pressure of 5–10 Pa and temperature of 1200–1500°C. It is revealed that the implementation of reduction under the residual pressure lower than 1 atm (101.3 Pa) considerably lowers the thermodynamic temperatures of the onset of the reaction. It is established that only three reactions, in the course of which calcium aluminates 3CaO ⋅ Al₂O₃, 5CaO ⋅ 3Al₂O₃ (12CaO ⋅ 7Al₂O₃), and CaO ⋅ Al₂O₃ are formed, can be used for the practical purposes. It is proposed, depending on the final state, to separate the process into a “low-temperature” one (up to 1200°C, the calcium yield is no higher than 64.3%) and a “high-temperature” one (up to 1500°C, up to 75% Ca). It is planned tofurther confirm these data experimentally.