In a binary system of A and B the melting temperature of pure A is 1050°C and the melting temperature of pure B is 1900°C. At 1250°C, the α solid solution (containing 50% of B), the β solid solution (containing 80% of B) and liquid (containing 30% of B) are in three phase equilibrium. At room temperature, the maximum solubility of B in the α phase is 30% and the maximum solubility of A in the β phase is 10%. Sketch the phase diagram of A and B, showing the phases present in each area of the diagram. What is the reaction that takes place at 1250°C?